ELE1911
Electrical & Electronic practice A
Practice book
Semester 2 2015
Student name: __________________________________________________________________
Student number: _________________________________________________________________
Program: _______________________________________________________________________
Published by
University of Southern Queensland
Toowoomba Queensland 4350
Australia
http://www.usq.edu.au
© University of Southern Queensland, 2015.2.
Copyrighted materials reproduced herein are used under the provisions of the Copyright Act 1968 as amended, or as a
result of application to the copyright owner.
No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means
electronic, mechanical, photocopying, recording or otherwise without prior permission.
Table of Contents
Practice courses for electrical, electronic & computer engineering programmes . 1
Introduction ....................................................................................................................... 1
External students ............................................................................................................. 3
Claiming exemption ......................................................................................................... 4
Course content and pre-requisite knowledge .............................................................. 4
External students ...................................................................................................................................... 4
Day students.............................................................................................................................................. 5
Staff associated with this practice course .................................................................... 5
Requisite materials........................................................................................................... 5
Assessment....................................................................................................................... 6
Lab completion log – record of competency ................................................................ 7
Digital lab ......................................................................................................................... 10
Revision (part 1): Introduction to Micro-Cap digital simulation ............................... 10
2. Introduction .......................................................................................................................................... 13
3. Action of lamps and switches ............................................................................................................. 13
4. Inverters............................................................................................................................................... 13
Revision (part 2) – AND, OR, NAND and NOR gates .................................................. 15
1. NAND gates......................................................................................................................................... 15
2. AND gates ........................................................................................................................................... 16
3. OR gates.............................................................................................................................................. 16
4. NOR gates ........................................................................................................................................... 16
5. Questions ............................................................................................................................................ 18
Activity 1: XOR, equivalence, half adder & comparator ............................................ 20
1.1 The exclusive OR circuit ................................................................................................................... 20
1.2 Simple comparator ............................................................................................................................ 21
1.3 An exclusive OR gate using four NAND gates ................................................................................ 22
1.4 The half adder ................................................................................................................................... 22
1.5 A simple logic block .......................................................................................................................... 23
1.6 Questions .......................................................................................................................................... 24
Activity 2: Flip-flops ....................................................................................................... 27
2.1 Two cross coupled NAND gates; the simple latch .......................................................................... 27
2.2 The simple clocked RS flip-flop ........................................................................................................ 28
2.3 Application – simple data memory or type ‘D’ flip-flop .................................................................... 30
2.4 The principle of the master slave ‘JK’ flip-flop ................................................................................. 30
Activity 3: Serial counter ............................................................................................... 33
3.1 A four-bit serial counter using J-K flip-flops ..................................................................................... 33
3.2 Altering the natural count sequence ................................................................................................ 34
Activity 4: Team project, part A – PRBS generator design ....................................... 36
Revision ................................................................................................................................................... 37
Activity 5: Part 1 – Introduction to the THRSim11 software...................................... 43
Procedure ................................................................................................................................................ 43
Simulation ................................................................................................................................................ 45
Target 68HC11 microprocessor board................................................................................................... 47
Activity 5: Part 2 – Introduction to programming the 68HC11 .................................. 48
Procedure ................................................................................................................................................ 50
Activity 5.6: Use of a clock to program a delay .......................................................... 54
Procedure ................................................................................................................................................ 55
Activity 5.7: Seven segment display ............................................................................ 55
Procedure ................................................................................................................................................ 56
Activity 5.8: PRBS generator design – part B ........................................................................................ 58
Revision ................................................................................................................................................... 59
Activity 9: Introduction to PLCs ................................................................................... 62
Activity 10: PLC application .......................................................................................... 62
Electronics lab ................................................................................................................ 63
Activity 1: Familiarisation with test equipment .......................................................... 63
Activity 2: Introduction to breadboarding ................................................................... 64
Activity 3: Electronics project construction ............................................................... 64
Activity 4: Electronics project testing ......................................................................... 65
Electrical technology activities .................................................................................... 66
Electrical safety – rules ................................................................................................. 66
Electricity supply and accidents ............................................................................................................. 66
Factors affecting electric shock .............................................................................................................. 66
Human body as conductor...................................................................................................................... 67
Effect of magnitude of current ................................................................................................................ 68
Main effects on the body ........................................................................................................................ 68
Resuscitation ........................................................................................................................................... 69
University of Southern Queensland ............................................................................. 70
Energy systems laboratory: safety rules................................................................................................ 70
Safety instructions: please read and observe ....................................................................................... 71
Using instruments in electrical laboratories ........................................................................................... 72
Using A.C. measuring instruments .............................................................................. 72
Activity A1: Kirchhoff’s laws......................................................................................... 75
Aims ......................................................................................................................................................... 75
Theory...................................................................................................................................................... 75
Activity A2: Resistance measurement of DC machine windings ............................ 77
Activity A3: D.C. shunt motor performance ................................................................ 78
Activity A3: D.C. shunt motor performance pre-determination ............................... 88
Experiment A3: D.C. shunt motor performance pre-determination ...................................................... 89
Activity B1: Transformer tests...................................................................................... 91
Activity B2: Three-phase transformer connections................................................. 103
Activity C1: Power factor improvement .................................................................... 107
Activity C2: Series resonance..................................................................................... 112
Activity C3: Capacitor-start single phase induction motor: load test ................... 116
Activity D1: Three-phase circuits: star and delta connected loads ...................... 121
Activity D2: Three-phase induction motor – DC generator tests........................... 123
Appendix A: Reading analog multimeter scales ...................................................... 135
Reading analog multimeter scales............................................................................. 135
1 ELE1911 Electrical and electronic practice A
Practice courses for electrical, electronic & computer
engineering programmes
Introduction
The purpose of the system of practice courses is to develop practical skills, the ability to
function effectively as part of a team, and in the case of Bachelor of Engineering students,
an understanding of the responsibilities of a professional engineer.
Practice courses are zero unit, zero tuition cost courses which are assessed on a pass/fail basis
i.e. no other grades are possible. Their nominal duration is 40 hours, of which 35 hours will
be laboratory work, group projects or other structured activities. The remainder is set aside
for assimilation, report writing and assessment.
For day mode students, practice activities will usually be synchronised with relevant
academic units, and distributed over one semester. Day students will normally complete two
practice courses a year.
For external students, the practice courses are available as intensive on-campus residential
schools, normally of one week duration. Students will usually complete one residential school
per year. However, the timing of these has been arranged such that the more critical courses
can be completed in pairs over a two week period, in order to minimise visits to campus.
The practice courses which apply to Electrical and Electronic engineering programmes are
shown in table 1, and those for Computer Systems Engineering (including BEng/BIT),
Instrumentation and Control Engineering and Software Engineering are shown in table 2.
Table 1: Practice courses for electrical and electronic majors
Practice course
Number
Name
Residential school for
external students
Usage
ADEE
BEng
Tech
(EE)
BEng
(EE)
Year
Month and week
ENG1901
Engineering practice 1
✓
✓
✓
1
Feb, wk 13 (note 5)
ELE1911
Elec. & electr. prac. A
✓
✓
✓
2
Feb, wk 13 (note 1)
ELE2912
Elec. & electr. prac. B
✓
✓
✓
3
Feb, wk 14
ELE2913
Elec. & electr. prac. C
✓
✓
✓
4
Sept, wk 9 (note 2)
ELE3914
Elec. & electr. prac. D
✓
✓
5
Sept, wk 10 (note 3)
ELE3915
Elec. & electr. prac. E
✓
6
Sept, wk 10 (note 4)
ENG3902
Professional practice 1
✓
7
Sept, wk 9
ENG4903
Professional practice 2
✓
8
Sept, wk 9
2 ELE1911 Electrical and electronic practice A
Table 2: Computer systems, instrumentation and control, and software engineering majors
Practice course
Residential school for
external students
Usage
Number
Name
AD
CS
BET
(CS)
BEng BEng/ BEng BEng
(CS)
BIT
(IC) (SW)
ENG1901
Engineering practice 1
✓
✓
✓
✓
✓
✓
1
S3, week 13 (5)
ELE1911
Elec. & electr. prac. A
✓
✓
✓
✓
✓
✓
2
S3, week 13 (1)
ELE2912
Elec. & electr. prac. B
✓
✓
✓
✓
✓
✓
3
S3, wk 14
ELE3913
Comp. sys. eng. prac.
✓
✓
✓
✓
4/5
Sept, 9 (2)
ELE3914
Elec. & electr. prac. D
✓
5
Sept, 10 (3)
ELE3915
Elec. & electr. prac. E
6/7
Sept, 10 (4)
ELE3916
SWEng. team practice
6
Sept, 10 (4)
ENG3905
Mechatronic practice
6
Sept, 10
ENG3902
Professional practice 1
✓
✓
✓
✓
7
Sept, 9
ENG4903
Professional practice 2
✓
✓
✓
✓
8
Sept, 9
✓
✓
✓
✓
✓
Yr
Month, week
●
Numbers in parentheses refer to notes below.
●
As far as possible, students should follow the recommended enrolment pattern for their
programme, as shown in the University handbook.
Notes on tables regarding residential schools for external students
1. ELE1911 may be delayed for one year and completed together with ELE2912 over a
two-week period.
2. ELE2913 (or ELE3913) may be delayed for one year and completed together with
ELE3914 over a two-week period.
3. ELE3914 can be delayed and completed together with ENG3902 over a two-week period.
4. ELE3915 (or ELE3916) can be delayed and completed together with ENG4903 over a
two-week period.
5. ENG1901 is also available in the September recess, in week 9.
6. Information regarding year in which residential schools should be undertaken does not
apply to the BEng/BIT in external mode. This may only be undertaken by students who
are eligible for at least two years advanced standing. Hence the year in which practice
courses are undertaken will depend very much on individual enrolment patterns.
3 ELE1911 Electrical and electronic practice A
External students
Students studying in external mode will complete each practice course by attending a one
week intensive residential school, and submitting written reports as required. The practice
courses should not be completed until all pre-requisite courses have been completed. Students
should either have completed the co-requisite courses, or be currently enrolled in them.
Students are normally expected to attend for the full duration of the nominated residential
school period. This should be the whole of the week, i.e. 8 am Monday to 5 pm Friday,
except where alternative arrangements have been made because a Public Holiday falls within
the week.
Students planning to attend should check the USQ web site for the final timetable 2 or
3 weeks before the residential school.
Prior to attendance at residential schools, students should refresh their knowledge of any
courses listed as pre- or co-requisites. It is advisable to bring to the residential school the
study books for these courses, as you will probably wish to refer to them during the week.
During the on-campus Orientation programme at the start of the residential school, students
will be given details of:
●
any changes to the timetable
●
what groups they might be in
●
any other relevant information.
Because of space constraints in the USQ Handbook it has not been possible to describe the
pre- and co-requisite requirements in great detail. These are described more fully in the
practice books provided to you when you enrol in these courses, and you should check these
carefully. Each practice course should be completed at the stage in your programme where
you will gain maximum benefit from attendance. This will be made easier if students follow
the recommended Enrolment pattern for their programme.
External students will not normally complete more than one practice course per year.
However, the completion of some practice courses can be delayed by one year, to allow two
residential schools to be completed end to end over a two-week period. This feature is
designed to assist external students who travel to USQ from remote locations or from
overseas.
External students in the Electrical and Electronic Engineering, Power and Instrumentation
and Control majors should note that there are two practice courses in their fourth year, one in
February and one in September. In the case of Associate Diploma students following the
recommended enrolment pattern, this will correspond to their final year.
Day students
Day students will normally complete practical activities in association with related academic
courses, and these will be credited to the relevant practice courses. However, there may be a
few activities which do not occur in parallel with a related academic course e.g. printed
circuit board activities for Bachelor of Engineering students.
4 ELE1911 Electrical and electronic practice A
Claiming exemption
As is the case with any other course, you may apply for exemption from a practice course, on
the basis of previous equivalent study, training or work experience. When making any
application for exemption it is your responsibility to provide:
●
proof of completion
●
details of what you have completed previously, with regard to subject matter and also
contact hours or workload.
In some cases this may take the form of a letter from your employer on company letterhead,
verifying that you have had relevant experience or training. It is recommended that you draw
up a table of all the activities within the practice course, and then summarise beside each your
relevant experience or training. This should then be attached to the letter of verification from
your employer.
Do not submit original certificates. Copies should be verified as true copies by a Justice of
the Peace (or an official of equivalent standing in the case of an overseas application).
If you are granted an exemption from a course, then this will appear on your academic record,
and you will not have to enrol in the course.
If you have already been granted exemption from practice courses, as part of a block of
exemptions in recognition of previous study, then further claims for exemption from
subsequent practice courses will not normally be considered. This is because the awarding of
a block of exemptions involves a trade-off between work the student has completed but has
not been given credit for, and work the student has not completed but has been given credit
for. The awarding of further exemptions will upset this balance.
Course content and pre-requisite knowledge
This practice course contains activities relevant to the following academic courses, which are
specified as co-requisites:
●
ELE1301 Computer engineering
●
ELE1502 Electronic circuits
●
ELE1801 Electrical technology.
External students
The residential school for this course is in the week of February. External students following
a standard enrolment pattern should complete this residential school at the end of their second
year of enrolment, after completion of all of the courses specified as above as co-requisites.
It is advisable to bring to the residential school the study books and texts for the co-requisite
courses listed above.
5 ELE1911 Electrical and electronic practice A
It is permissible to delay the residential school for one year so that it can be completed in
conjunction with the residential school for ELE2912 Electrical and electronic practice B over
a two-week period.
Day students
Day students following one of the standard enrolment patterns shown in the USQ Handbook
or Faculty Guide to Programmes should enrol in practice courses as indicated in the
enrolment pattern.
Staff associated with this practice course
Examiner:
Mr Mark Norman
Phone: (07) 4631 2912
Fax:
(07) 4631 2526
Email: <Mark.Norman@usq.edu.au>
Moderator: Dr Hong Zhou
Other staff closely associated with this practice course will be the examiners of the academic
courses which are supported by these practical activities. These are:
ELE1301 Mr Glenn Harris
ELE1502 Mr Mark Norman
ELE1801 Mr Ron Sharma and Mr Gordon Hampson
Many other full time and part time staff will assist with the running of laboratory sessions for
day students, and with residential schools for external students.
Requisite materials
●
A cheap scientific calculator (which need not be programmable or have graphics)
●
A cheap protractor; scale ruler; dividers and drawing compass; HB pencil and eraser
●
A pad of A4 graph paper with 2 mm squares.
6 ELE1911 Electrical and electronic practice A
Assessment
No separate formal laboratory reports are required for this practice course. All that is required
is that you complete the practical work to the satisfaction of the laboratory supervisor. Some
of the activities require you to fill in data or answer questions on the activity sheets.
At the conclusion of each practical session you must present this practice book to your
supervisor for his signature, which certifies that you have completed the activity. If you
wander out of the laboratory without checking with the supervisor, there may be no record
that you have completed the activity, and you may have to repeat the activities.
This course is assessed on a Pass/Fail basis.
To obtain a Pass you must have completed at least 80% of the activity hours associated with
the course, which will be interpreted as 80% of each group of activities. This flexibility is
intended to allow for sickness and unforeseen accidents or emergencies. It is not acceptable
to omit a complete group of activities. In normal circumstances it is expected that students
should complete all of the activities.
You will be required to produce the Lab Completion Log from this practice book to verify
that you have completed (or been exempted from) all of the activities required to achieve a
pass in this course.
7 ELE1911 Electrical and electronic practice A
Lab completion log – record of competency
Student name: ________________________________________
Student number: _____________________
Program: ______________________________________________________________________________________
Approx.
duration
Activity title
Digital Lab
Supervisor’s name/s:
Activity 1: XOR, equivalence, half adder & comparator
2
Activity 2: Flip-flops
2
Activity 3: Serial counter
2
Activity 4: PRBS generator logic design, part A
2
Activity 5: Introduction to THRSim11
2
Activity 6: Using a clock to program a delay
2
Activity 7: Seven segment display
2
Activity 8: PRBS generator software design, part B
2
Activity 9: Introduction to PLCs
2
Activity 10: PLC application
2
Electronics lab
Supervisor’s name/s:
Activity 1: Introduction to test equipment
2
Activity 2: Introduction to bread-boarding
2
Activity 3: Electronic project construction
4
Activity 4: Electronic project testing
2
Electrical technology lab
Supervisor’s name/s:
Activity A1: Kirchhoff’s laws
0.5
Activity A2: DC shunt motor performance
1.5
Activity B1: Transformer tests
B1.1 Preliminary tests
B1.2 No-load test
B1.3 Short-circuit test
Activity B2: Three-phase transformer connections
Activity C1: Power factor improvement
Activity C2: Series resonance
Activity C3: Capacitor-start single-phase – Induction motor: load test
2
0.5
1
1.5
1
Activity D1: Three-phase circuits: star and delta-connected loads
0.5
Activity D2: Three-phase induction motor – DC generator tests
1.5
Competency demonstrated
(Supervisor to sign)
Date
8 ELE1911 Electrical and electronic practice A
University of Southern Queensland
Faculty of Engineering and Surveying
Safety briefing
To comply with the Workplace Health and Safety Act, the Faculty Safety Officer requests that all
students are given a safety briefing during the first week. A record is kept of those present at the safety
briefing as proof that an attempt has been made to meet the Workplace Health and Safety obligations.
1. Z-Block building evacuation plan and emergency procedures
University buildings are to be evacuated when the building evacuation siren sounds. In Z Block, this
alarm consists of two separate tones. The first tone is a warning tone indicating that the building may
be about to be evacuated. The second tone is more urgent in sound and has a voice-over telling
occupants to evacuate the building. On hearing an alarm or the call ‘evacuate’, all occupants should:
●
Cease all activities without delay.
●
Leave the building immediately by the designated fire or emergency exits to be used by all
students and staff on that floor. Do not use lifts. Leave personal possessions behind.
●
Proceed to the designated assembly area, western side of Z Block, well away from the building.
●
Keep clear of entry/exit ways. Give assistance, if required, to persons who use a walking aid.
●
Comply with the directions of Emergency Squad members, who wear orange hard hats.
2. Emergency telephone numbers and how to summon help
For all emergencies, telephone:
Work hours (8.30am – 5pm) (on campus) 2222
After hours
(on campus) 2222
The phone number of the University Nurse is listed on the emergency phones.
To call for emergency assistance or raise a fire alarm, yell for help; e.g. – ‘Help!’ or ‘Fire!’
First-aid and emergency-trained personnel are rostered to be available in the vicinity.
3. Location of first aid kits
First Aid kits may be found in the following locations:
Z Block First floor
Z109 (not accessible after hours)
Z Block Second floor Foyer
Z Block Third floor
Foyer
Z Block Fourth floor
Z475 – Sick Room – (not accessible after hours)
4. Personal protection
Fully covered shoes must be worn in laboratories; no loose, long hair; no loose clothing or loose
jewellery.
DECLARATION: I have read and understood the above safety instructions.
STUDENT NAME (Please Print): STUDENT NUMBER:
........................................
SIGNATURE:
DATE:
................................ ................................ ......../......../........
9 ELE1911 Electrical and electronic practice A
Faculty of Engineering
and Surveying
THE ENERGY SYSTEMS ELECTRICAL LABORATORIES CONTAIN SAFETY
HAZARDS WHICH MUST BE TREATED WITH DUE CAUTION AT ALL TIMES.
YOUR SAFETY, WHILE YOU ARE AT USQ, IS PARAMOUNT TO THE UNIVERSITY.
USQ also has obligations under the Workplace Health and Safety Act. You can assist the University to
meet its obligations under the Act, and to ensure that your health and your safety are protected.
Please complete the form below, so that the University can put in place protective measures to ensure
your health and safety whilst you use the facilities in the Energy Systems Laboratory.
To assist your supervisor to ensure your safety, please complete the following questionnaire. Any
information disclosed will be held in confidence.
Do you suffer from any of the following disabilities:
YES
NO
1. Colour-blindness or any visual disability.
2. Hearing problems.
3. Dexterity problems.
4. Inability to stand comfortably during practical classes.
Are you currently taking any medication or drugs, prescribed or otherwise,
which may impair your ability to concentrate, to follow instructions, or to
operate the laboratory equipment safely?
Do you have any other condition that may affect your ability to work safely
during practical classes?
If ‘YES’, please give details: ___________________________________________________
__________________________________________________________________________
__________________________________________________________________________
Contact information: _________________________________________________________
These matters may be discussed with you confidentially in relation to your work in the laboratories.
I understand that I should inform USQ of any medical condition during my course to assist in ensuring
my safety. I can inform the Head of Discipline confidentially, in writing, to that effect.
Student name (please print): _______________ Signature: ____________ Date:
Student number: ____________________________
/
/
Safety form 001/03
10 ELE1911 Electrical and electronic practice A
Digital lab
Note: Write down all workings as these will be checked in order for activities to be marked as
completed.
Revision (part 1): Introduction to Micro-Cap digital simulation
Aim

To familiarise students with digital circuit simulation using Micro-Cap simulation
software
To introduce digital concepts associated switching circuits and logic elements.

Objectives
Upon successful completion of this activity, students should:


have demonstrated the operation of simple circuit consisting of switches and lamps
be familiar with the use of simulation software to perform basic digital functions.
1. Getting started
To start Micro-Cap double-click the desktop icon or click the Windows ‘Start’ button to select MicroCap from the programs menu. This will bring up the following program window, in which you build
your circuit.
Micro-Cap is supplied with a large number of circuit components, both digital and analogue. To learn
how to build and simulate digital circuits using these components it is best to start with a small
project. To begin, familiarise yourself with the menus and toolbars.
11 ELE1911 Electrical and electronic practice A
The pull down menus are used primarily to:



load and save files
access circuit components
select circuit analysis (simulation) tools.
The toolbars enable quick access to the more frequently used features.
You will now build a simple circuit consisting of a battery, a switch and a lamp. For the switch and
the lamp you will use animated components. This will allow you to operate the switch to light the
lamp.
Figure 1: Analogue LED circuit
To place an animated switch on the drawing, select the Component > Animation > Animated SPST
Switch menu option. Once the component is selected from the menu the component symbol will
replace the cursor. You can then place as many of that component onto the drawing as required. Each
copy will have its own unique identifier.
You only need one switch, so move the component to the desired position (near the center of the
workspace). Click and hold the left-mouse button, while still holding the left mouse button down click
the right mouse button one or more times to rotate the component in 90 degree steps. Once the desired
rotation is obtained release both buttons. The switch is now positioned on the drawing.
The cursor will remain in the component mode, ready to place another switch. Select the Component
> Animation > Animated Analog LED menu option and place a LED on the drawing about 2cm to
the right of the switch. At this point the LED’s component properties dialogue box will open. This
dialogue box allows you to set various component attributes. Click OK to exit the box.
12 ELE1911 Electrical and electronic practice A
Now click the Battery button on the components toolbar. Place the battery to the left of the switch,
with the correct orientation, as shown in figure 1. When this component is placed the component
properties dialogue box will open. Enter 9v in the Value box then click OK.
Now click the Ground button on the components toolbar. Place this component on the negative end of
the battery.
The final task is to wire the components together. To do this you need to enter the wire mode. Click
the Wire mode button.
Once again the cursor will change indicating that you are in the wire mode. Move the cursor to the
positive end of the battery, click and hold the left mouse button. Move to the left side of the switch
and release the mouse button. A wire should now exist between the two points. Note that this wiring
mode allows you to place one or two segments of wire at 90 degrees to each other. If you place a small
right angle segment by mistake it is easily removed.
To remove a component or wire segment, first enter the select mode by clicking the Select mode
button then click the left mouse button on a blank area of the diagram to ensure no components or
wires are highlighted. Next, using the left mouse button click the component or wire segment to be
removed. The object should now be highlighted. Press the Delete button on the keyboard.
Return to the wire mode and continue to wire the circuit as shown in figure 1. To exit the wire mode
click the Select mode button.
The circuit can now be analysed using one or more of the circuit analysis tools. For this circuit you
will carryout a Dynamic DC analysis. This analysis tool allows you to change parts of the circuit and
to observe the effect of that change. In particular, you are able to close the switch and observe the
change of state of the LED. In other words, turn the LED on.
Ensure that you are in the Select mode. Now select Analysis > Dynamic DC menu option. When the
Dynamic DC dialogue box appears, press OK. If node voltages appear turn them off by clicking the
Node Voltages button.
The LED can now be turned on by double-clicking the switch. Point the cursor near the switch lever
then double-click the left mouse button. The LED will change colour indicating the ON state. Doubleclick the switch again to turn the LED off. You must be in the select mode to do this.
Micro-cap is a powerful circuit simulator and for this course you will barely touch on its full
capabilities. However, the few features you do use will provide an invaluable learning tool for this
course. Each home activity for the digital logic part of this course will be based on Micro-Cap. If you
have any difficulty using the software or would like to learn more about its features select Help from
the main menu to find the answer.
13 ELE1911 Electrical and electronic practice A
You will now build on figure 1 for the first logic activity.
2. Introduction
In Boolean Algebra – the algebra of logic – each variable can have either of two possible values ‘0’
and ‘1’. These two values represent two contrary states. The value ‘1’ can be used to mean ‘TRUE’
and then the value ‘0’ will mean not true or ‘FALSE’. Similarly ‘1’ can mean ‘HIGH’ and ‘0’ will
mean ‘LOW’ as shown in the table below:
‘1’
TRUE
YES
ON
HIGH
OUTPUT
HOT
WET
‘0’
FALSE
NO
OFF
LOW
NO OUTPUT
COLD
DRY
In this activity you will produce these logic levels using a switch and test the logic levels with a lamp
(LEDs). The output of a switch will be ‘0’ or ‘1’ according to the switch position and if you connect a
lamp to the switch, it will light (change colour) if the output is ‘1’ and not light if the output is a ‘0’.
3. Action of lamps and switches
Using the circuit of figure 1 you were able to check the function of the switch and the lamp (LED).
When the switch is open it will produce a logic ‘0’ at its output. This logic ‘0’ is indicated by the lamp
being OFF (white or no colour). When the switch is closed it will produce a logic ‘1’ at its output.
This logic ‘1’ is indicated by the lamp being ON (yellow in colour).
To be able to perform this and future activities using digital logic components you need to change the
circuit of figure 1 to the following. Delete the Animated Analogue LED and replace it with an
Animated Digital LED. Remove the wire link to ground.
Figure 2: Digital LED circuit
When this circuit is analysed, using Dynamic DC analysis, opening the switch results in a logic ‘0’
being applied to the LED causing it to be OFF (black). Closing the switch results in a logic ‘1’ being
applied to the LED causing it to be ON (red).
4. Inverters
An inverter is a device that has one input and one output but the output logic level is always the
opposite of the input logic level.
Connect an inverter and another digital LED to the right of the current digital LED as shown in the
following diagram. To do this, select the inverter from the component toolbar and position it to the
right of the LED. When the component properties dialogue box appears select the DO_GATE timing
14 ELE1911 Electrical and electronic practice A
model then click OK. Select an animated digital LED from the Components menu and place it to the
right of the inverter. Insert a wire between the current LED and the inverter input and between the
inverter output and the new LED.
Ensure the cursor is in the select mode then run the Dynamic DC analysis and observe the effect of
opening and closing the switch. Note the logic level at the output of the inverter is opposite to the
logic level at the input.
Figure 3: Inverter circuit
Figure 3 can be further simplified by replacing the battery and switch with a digital switch as shown in
figure 4. The animated digital switch can be found under the Component > Animation menu option.
Figure 4: Modified inverter circuit
15 ELE1911 Electrical and electronic practice A
Revision (part 2) – AND, OR, NAND and NOR gates
Equipment required


1 large digital circuit board
1 power supply
Logic blocks
A logic block is a unit which combines and manipulates the binary inputs to perform some logic
function and produce one or more outputs. Each output will be a ‘0’ or ‘1’ depending on the
combination of input values.
Fundamental logic blocks
There are four fundamental logic blocks, AND, OR, NAND, NOR and their properties are summarised
in the table below:
The NAND gate is the logic gate most readily available in integrated circuit form but the other three
basic gates may be constructed from NAND gates and inverters.
1. NAND gates
Connect the three input NAND gate to switches and lamps as shown in figure 1 (over next page).
(a) Check through the truth table of a NAND gate
(b) Disconnect one input to the NAND gate. Complete a truth table for the remaining two inputs.
Does a NAND gate respond to an unconnected input as if it were connected to logic ‘1’ or logic ‘0’?
Answer
.
16 ELE1911 Electrical and electronic practice A
2. AND gates
The NAND function is Z  A  B ; if the output of a NAND gate is inverted we get
W  Z  A B  A B
With the same layout as in item 1, use a second NAND gate module as an inverter as shown dotted in
figure 1. Confirm the truth table of an AND gate.
3. OR gates
By inverting the inputs to a NAND gate the system becomes an OR gate. By De Morgan’s theorem
A B  A B
Connect the logic circuit shown in figure 2. Check the circuit truth table against that of an OR gate.
4. NOR gates
If the output of an OR gate is connected to an inverter the circuit becomes a NOR gate. Use another
inverter (or NAND) gate to change the circuit of item 3 into a NOR gate and check its truth table.
A
B
A B
0
0
1
0
1
1
1
0
1
0
0
0
Z (= output of your
circuit for item 4)
17 ELE1911 Electrical and electronic practice A
Figure 2
Figure 1
18 ELE1911 Electrical and electronic practice A
5. Questions
(a) Complete this truth table
A
0
B
0
0
1
1
0
1
1
A B
A B
(b) Consider the following logic block. The inputs to the AND gate are A and B.
The output Z is therefore A  B
The logic block is represented by the function
Z=A  B
Circle the answer that represents the function of the following logic block.
Answer: (a) Z = A  B , (b) Z = A  B , (c) Z = A  B , (d) Z = A  B
19 ELE1911 Electrical and electronic practice A
(c) Complete this truth table
A
0
B
0
0
1
1
0
1
1
A+B
A+B
(d) Circle the answer that represents the function of the following logic block.
Answer: (a) Z = A  B , (b) Z = A  B , (c) Z = A  B , (d) Z = A  B
20 ELE1911 Electrical and electronic practice A
Activity 1: XOR, equivalence, half adder & comparator
Equipment required


1 large digital circuit board
1 power supply
Simple combinational logic
1.1 The exclusive OR circuit
The Exclusive OR circuit is a logic block with two inputs and the output is true if either (but
not both) of the inputs is true. The truth table is:
A
0
0
B
0
1
Z
0
1
1
1
0
1
1
0
Z = ‘1’ if A = ‘1’ OR B = ‘1’ but not both
i.e. Z  AB  AB
Consider the logic circuit figure 1.1.
Figure 1.1
Connect this circuit on the patchboard, check that the circuit performs according to the truth
table given above.
21 ELE1911 Electrical and electronic practice A
1.2 Simple comparator
A minor modification to the circuit of item 1.1 will enable it to compare two binary digits and
produce an output ‘1’ where they are the same and ‘0’ when different. Writing this in truth
table form gives:
A
0
0
B
0
1
Z
1
0
1
1
0
1
0
1
i.e. Z = ‘1’ if A = B
i.e. Z  AB  AB
Consider the logic circuit of figure 1.2.
Figure 1.2
Connect this circuit on the patchboard and check that the circuit performs according to the
truth table given above.
22 ELE1911 Electrical and electronic practice A
1.3 An exclusive OR gate using four NAND gates
Figure 1.3
The logic circuit shown in figure 1.3 also acts as an Exclusive OR circuit. Wire the circuit on
the patchboard, check the truth table to show that this is so. Also theoretically derive Z as a
function of A and B and simplify to Z  AB  AB .
Solution
Z  A  AB B  AB
 A A  B   B  A  B 
 AB  AB
1.4 The half adder
A half adder is a logic block which accepts two binary digits as inputs and produces two
outputs. One output is the sum of the two digits and the other is a carry digit.
The truth table will be:
A
B
Sum 
Carry (Co )
0
0
0
1
0
1
0
0
1
0
1
0
The first output column follows the same sequence as the Exclusive OR circuit (item 1.1)
while the second column has the same output as that of an AND circuit (item 1.2).
A half adder can be constructed from an exclusive OR circuit together with an AND circuit.
The logic circuit is shown in figure 1.4. Connect the circuit on the patchboard and check its
performance against the truth table.
23 ELE1911 Electrical and electronic practice A
Figure 1.4
1.5 A simple logic block
Determine the truth table and Boolean expressions for the outputs of this circuit, and check
that they are consistent.
Figure 1.5
24 ELE1911 Electrical and electronic practice A
1.6 Questions
(a) Refer to the following diagram
What are the Boolean expressions for Y and Z?
Y=
Z=
If A = 0, B = 0 and C=1, then
Y=
Z=
(b) Refer to the following diagram
What is the Boolean expression for Z in terms of A, B & C?
Z=
Complete the truth table for this logic diagram.
25 ELE1911 Electrical and electronic practice A
A
0
0
B
0
0
C
0
1
X = AB
1
1
1
1
0
0
0
0
1
1
0
1
1
1
1
0
0
1
1
1
0
0
0
1
1
1
1
1
0
1
Y = BC
Z = XY
(c) Simplify the following expressions using De Morgan’s Theorems.
i.
Z  ABC
ii.
Z  (A  B)  C
iii.
Z  ABC
(d) Determine whether or not the output of the following logic diagram is the same as
Z  (A  B)CD
26 ELE1911 Electrical and electronic practice A
To solve this problem determine, from the logic diagram above, an expression for Z. Simplify
the expression using De Morgans Theorems.
27 ELE1911 Electrical and electronic practice A
Activity 2: Flip-flops
Scope
Types of flip-flop; simple latch
set – reset, clocked set – reset
D-type, master-slave JK.
Equipment required

1 digital circuit board for items 1, 2, 3

1 power supply or

2 digital circuit boards for item 4

1 power supply
Flip-flops
2.1 Two cross coupled NAND gates; the simple latch
Two cross coupled NAND gates form a simple latch or flip-flop. Connect two NAND gates
as shown in figure 2.1a.
Figure 2.1a
Check and complete the truth table of the system.
28 ELE1911 Electrical and electronic practice A
With a logic ‘1’ input on A and B simultaneously, the outputs at QA and QB may be ‘0’ and
‘1’ or ‘1’ and ‘0’ respectively. This can be easily verified by putting ‘1’ on A and ‘1’ on B
and reducing A or B to ‘0’ alternately. This circuit is sometimes referred to as an SR flip-flop
(set – reset flip-flop), where a logic ‘0’ on input A will set the output QA to logic ‘1’ and a
logic ‘0’ on input B will reset the output QA to logic’0’.
2.1.1 Application
This simple latching circuit forms the basic anti-bounce circuit figure 2.1b, used to prevent
the train of pulses formed by bouncing switch contacts, from being applied to a sequential
logic system where it is likely to give rise to a malfunctioning of that system.
Figure 2.1b
With the switch in position A the logic levels are as shown in the diagram. When the switch
lever breaks away from A, an input of the upper NAND gate changes to ‘1’ but the output
remains unchanged. The lever may bounce on contact A many times without affecting the
logic level at Q. When the switch lever changes to B, the output will reverse at the first
contact and will remain unchanged if the contacts bounce at B.
2.2 The simple clocked RS flip-flop
Adding two gates on the input side of the cross coupled NAND gates prevents the inputs on
the R and S terminals from being applied to the latching circuit unless the clock is in the high
or ‘1’ state. The circuit is unable to respond to the RS input until a clock pulse is applied.
The clock pulse may be generated by a change over switch (followed by an anti-bounce
circuit), or just a simple switch.
Connect the circuit shown in figure 2.2. Note: the additional NAND gates invert the SR
inputs.
29 ELE1911 Electrical and electronic practice A
Figure 2.2
Check and complete the truth table.
Note:
Qn is the state of Q before a clock pulse is applied. (i.e. Now)
Qn+1 is the state of Q after a clock pulse is applied. (i.e. After clock pulse)
When R = S = ‘1’, Qn+1 can be ‘0’ or ‘1’ depending on the speed of the individual gates.
The truth table can be summarised in a shorter form as shown below:
30 ELE1911 Electrical and electronic practice A
The first row in the truth table states that there will be NO CHANGE in the logic state of the
output when logic ‘0’ is applied to both R and S inputs.
2.3 Application – simple data memory or type ‘D’ flip-flop
This is a modified RS flip-flop with only a single D input, the second input to the RS flipflop being obtained via an inverter.
The truth table will be:
Construct this flip-flop from the logic circuit diagram figure 2.3. Check the truth table.
Figure 2.3
2.4 The principle of the master slave ‘JK’ flip-flop
The truth table of an RS flip-flop is:
31 ELE1911 Electrical and electronic practice A
Note: for an RS flip-flop ‘Qn+1’ occurs on the rising edge of the clock pulse.
This flip-flop suffers from the severe restriction in that an input R = ‘1’, S = ‘1’ is not
permitted as the resultant output is indeterminate.
The way this is overcome can be verified on the logic board.
Figure 2.4
Note:
If you do not have enough spare gates to complete this diagram, remember that
other gates can be transformed as necessary.
i.e.
3 input NAND
2 input NOR + 2 NOTs
2 input NAND
2 input NAND
(refer to the study book for ELE1301 or confirm through application of
DeMorgan’s Theorems)
Connect two clocked RS flip-flops to form a JK flip-flop as shown in figure 2.4 then check
and complete the following truth table:
32 ELE1911 Electrical and electronic practice A
Check carefully that this is equivalent to:
By using an anti-bounce circuit for the CLOCK input, the internal states of the ‘master’ flipflop can be studied while the CLOCK is held high and this will illustrate more clearly the
master-slave action and show that the ‘slave’ flip-flop takes up its new state as the CLOCK
goes down again. That is, Qn+1 will occur on the falling edge of the clock pulse. Connect a
lamp to the CLOCK line to indicate its state at any time.
33 ELE1911 Electrical and electronic practice A
Activity 3: Serial counter
1. The study of a four-bit serial counter.
2. Methods to alter the natural count sequence.
3.1 A four-bit serial counter using J-K flip-flops
Notes
1. JK flip-flops wired serially in a toggle mode will naturally count in binary.
2. The output frequency of the second FF is half the frequency of the first FF, etc.
7. The total number of natural states that a serial counter has is 2n where n is the number of
FFs in the counter.
(a) Referring to the diagram shown in figure 6.1 for a four-bit serial counter:
1. complete the truth table (B)
8. complete the timing table (C)
9. configure the four J-K flip-flops as shown in diagram (A). Connect test lamps to
the outputs A, B, C and D and verify that with an appropriate clock input, the
counter outputs change as predicted.
34 ELE1911 Electrical and electronic practice A
(A) JK flip-flops wired to work as a four-bit serial counter; (B) truth table of the four-bit serial
counter; (C) timing diagram for the four-bit serial counter.
Figure 3.1
3.2 Altering the natural count sequence
The natural counting sequence of a serial counter can be changed. For example, the 3-bit
counter in figure 3.2 naturally counts through eight states. If some application demands a
counter say with seven states, one of the natural states can be skipped. The circuit of figure
3.2 shows how this can be done. The circuit in figure3.2 is wired to skip a state, the state with
outputs A, B and C all HIGH (equivalent to decimal 7). That is, the use of the NAND gate
does not permit all outputs to stay HIGH between clock pulses. Thus the modified 3-bit
counter arrives at the state that is equivalent to decimal 7, outputs A, B, and C do go HIGH
but only for an instant. At this instant three HIGHS are applied to the input of the NAND
gate, causing its output, the RESET signal, to go LOW> The ACTIVE LOW RESET
signal output from the NAND resets all the FFs, causing their outputs A through C to go
LOW and stay that way until the next clock pulse. Thus, as shown in the timing diagram for
this circuit, outputs A, B and C are all HIGH only momentarily, long enough to cause a LOW
going RESET pulse to each FFs CD (direct clear) input. Therefore, immediately after the
seventh pulse, but before the eighth, outputs A through C are all LOW.
35 ELE1911 Electrical and electronic practice A
Figure 3.2
36 ELE1911 Electrical and electronic practice A
Activity 4: Team project, part A – PRBS generator design
Equipment required
Equipment required:
MicroCap8 demo software
Logic board
Flip-flop board
Plug pack
Power supply
Task
1. To design from first principles a pseudo-random binary sequence generator (PRBS)
based on parallel counter design techniques. Your supervisor will provide the
required binary sequence.
The generator should:

Use J-K flip-flops.

Be clocked by a single switch.
2. Use the count sequence provided by your supervisor and the form attached to this
activity to generate your design.
3. Simulate the design using MicroCap8 (transient analysis).
4. Implement the design on the hardware boards.
5. Demonstrate the design to your supervisor.
6. Retain the design for part B of the project.
In part B of this project the pseudo-random binary sequence generator will be interfaced with
the 68HC11 microprocessor to provide a visual indication of the binary sequence.
Attachments
1. Revision material, including a design example.
2. Blank karnaugh maps to use for your design.
37 ELE1911 Electrical and electronic practice A
Revision
Designing a PRBS generator
A pseudo-random binary sequence, (PRBS) generator is simply a parallel counter that
generates a sequence of binary digits that appear to be random or have no pattern. Strictly
speaking the sequence is not truly random as it repeats itself over and over again. These
PRBS signals are often used to test a data transmission system for errors in the transmitted
signal.
Several methods have been evolved, some analytical, some using map techniques. The main
advantage of a map technique is its simplicity and ease of understanding. This activity is
designed to illustrate this technique. Before commencing the activity you may find it helpful
to review the following example.
Example: PRBS generator design using J-K flip flops
Table 1: PRBS generator code sequence table
It is important to note that for parallel counters all flip flops change state simultaneously, so
the input to each flip flop must be prepared in advance for the clock.
Consider the Q output change of a clocked JK flip flop under various input conditions.
38 ELE1911 Electrical and electronic practice A
Table 2: JK flip-flop change table
X = Don’t care
The PRBS generator being described in this example requires 4 flip flops (one for each
binary digit, ABCD) to construct. In this case the four are marked FFA, FFB, FFC and FFD.
If we first consider the operation of FFA we see from the code sequence table that its output
is zero for all counts up to decimal 5. That is, the change from step 5 to 6 is 0 to 0. From step
6 to 7 the change is from 0 to 1, at 7 it returns back to 0, at 8 back to 1 and at 9 returns back
to 0 again (ie. loops back to the start). These observations can now be marked on another map
called a code change map for flip flop A corresponding to the steps shown in map 1 above.
Map 2: Code change map for FFA
Counts 0 to 5, FFA = 0, show as 0 → 0 on code change map.
After count 6, FFA → 1, show as 0 → 1 on code change map.
After count 7, FFA → 0, show as 1 → 0 on code change map.
After count 8, FFA → 1, show as 0 → 1 on code change map.
After count 9, FFA → 0, show as 1 → 0 on code change map.
The code change above is now used to determine what the J and K inputs will be for FFA.
This is normally done by marking the characteristics of a JK flip-flop onto two karnaugh
maps, one for the J input and one for the K input. These are called JK input logic maps.
Referring to both the JK change table and the code change map for FFA place the
corresponding values for J & K in the corresponding karnaugh map positions.
That is, wherever 0 → 0 appears in the code change map for FFA, place a ‘0’ in the J-map
and an ‘X’ in the K-map (the values for J & K are taken from the JK change table for 0 → 0).
Then wherever 0 → 1 appears in the code change map, place a ‘1’ in the J-map and an ‘X’ in
the K-map. Finally, wherever 1 → 0 appears in the code change map, place a ‘X’ in the J-map
and an ‘1’ in the K-map. Fill the remaining squares with ‘X’s.
Now loop the ‘1’s. Include ‘X’s where possible to obtain the largest loop.
39 ELE1911 Electrical and electronic practice A
Map 3: JK input
maps
The input signals for FFA have now been determined. A similar procedure is now followed to
obtain the input signals for FFB, FFC and FFD.
The results should be:
Table 3: JK input
logic
JA = B C D + B C D
KA = l
JB = C
KB = C
JC = B + D
KC = 1
JD = B C + A B C
KD = A + B C
Implementation:
40 ELE1911 Electrical and electronic practice A
The PRBS circuit above may look complex, but if you analyse each input separately the input
logic should correspond to table 3 above.
Transient analysis
Now run a transient analysis. Set up the transient analysis limits page as follows.
41 ELE1911 Electrical and electronic practice A
Click the run button. If your design is correct you should see the waveforms for each output,
the stimulus generator and the hexadecimal value for each time interval. These hex values
should correspond to the designed code sequence, beginning at 0.
42 ELE1911 Electrical and electronic practice A
The following activities will combine a number of computer processes to illustrate
microprocessor software design techniques. Combining a personal computer (having at least
one serial port) with the EZ-MICRO CPU-11 microprocessor development board, the user is
able to prototype hardware, develop, execute, and debug software using the Motorola
MC68HC11D0 microcomputer chip (which is the heart of the MICRO CPU-11).
The main components of the EZ-MICRO CPU-11 package that we will make use of are:

EZ-MICRO CPU-11 (based on the MC68HC11D0 CPU)

THRSim11 Simulator software for the PC.
43 ELE1911 Electrical and electronic practice A
Activity 5: Part 1 – Introduction to the THRSim11 software
The first activity will involve exercises to become familiar with the THRSim11 simulator
software, edit and assemble sample code, and download, execute and debug the code.
The most important outcome of this activity is that an appreciation of the overall process is
attained, even if an in-depth understanding of the procedures is not achieved.
Procedure
1. To provide power to the EZ-MICRO CPU-11 microprocessor board, connect the 9-Volt
AC wall transformer that is provided into a power-point and connect the 9-Volt plug
into the EZ-MICRO CPU-11 power jack connector.
2. Connect one end of the serial cable that is provided to the COM port (or serial port) of the
PC. Connect the other end of the cable to the serial port (9-pin make ‘DB’ connector) of
the EZ-MICRO CPU-11 microprocessor board.
3. Boot up the PC, and run the THRSim11 Simulator software. The THRSim11
program allows you to accomplish several tasks. It allows the serial
communication between the EZ-MICRO CPU-11 microprocessor board (target)
and the PC. It allows you to assemble 68HC11 assembly code, download the
assembled code to EZ-MICRO CPU-11 microprocessor board and execute/debug
the code. The following snapshot shows the start up screen for the THRSim11
Simulator.
The THRSim11 Simulator software establishes serial communications with the
EZ- MICRO CPU-11 microprocessor board and sends initial data to the CPU.
In order to create the assembly source code file ‘XXXLAB1.ASM’ for this activity,
you must select the New command from the File menu and the simulator will create a
new edit window. A 68HC11 assembler program can be written in this edit window. It
is also possible to cut and paste to/from this window from/to other text documents.
44 ELE1911 Electrical and electronic practice A
Note: Your initials will replace XXX when you save the program. Enter the
following source code:
After you have finished entering the above assembly language source code use the Save
As command from the File menu to save the information you have just entered.
4. The next step is to assemble your source code using the THRSim11 Simulator software.
With the Assemble command from the File menu or the related toolbar button the
contents of the edit window can be assembled into machine language. A list window
will be opened and the machine code will be loaded in the simulated memory.
The green line shows you where the PC register is pointing to.
Any errors encountered during assembly will be highlighted. Such errors are
probably due to typographical mistakes. Correct any errors in the XXXLAB1.ASM
file and re- assemble until there are no errors.
45 ELE1911 Electrical and electronic practice A
The program can be now simulated within the THRSim11 Simulator software or
downloaded to a target 68HC11 microprocessor board. Both methods will be used in
the following steps.
Simulation
5. Before running the assembled program within the THRSim11 Simulator open two
memory list boxes using the Memory List command from the View > Memory menu
options. For the first list box set the starting address to $0000 (data), and for the second
list set the starting address to $E000 (program).
Arrange the windows so that the assembled program and the memory list boxes are
visible, as shown below.
Note, the memory locations starting at $0000 should contain the initial value $ff and
those starting at $E000 should contain the machine code program, ready to run.
46 ELE1911 Electrical and electronic practice A
6. Run the program using the Run button or F9.
Note, the ARRAY memory locations $0000 to $0009 now contain the values $00 to $09.
If these values do not appear, there must be an error in the program.
The THRSim11 Simulator will execute the program and continuously loop on the last
instruction ‘LOOP2
JMP LOOP2’ until the STOP button on the toolbar is
pressed. Once the program has stopped the simulated 68HC11 should be reset. To do
this, press the RESET button on the toolbar.
7. Modify the ARRAY memory locations so that they contain $ff again.
To do this you first have to select the line where you want to enter the new value. Once
the line is highlighted, type in the new value. Press return after entering the value or click
the next line to be changed. The down arrow on the keyboard can also be used to enter
the new value and move to the next line.
8. The program could be executed again, however the program flow is not very clear. The
THRSim11 Simulator offers several features that can aid in the following program flow.
These features work together to support tracing program flow, monitoring register and
memory contents, and setting up breakpoints. The following exercise will use the CPU
Registers box and Step commands to step through the program one instruction at a time.
The CPU Registers box can be used to display and modify the contents of the A, B, X, Y,
C (condition code), S (stack pointer), and PC (program counter) registers. Registers are
memory locations that are closely bound to the core microprocessor. Registers have a
variety of special functions that regular memory locations do not share. The registers that
are used by this program are B, X, C, and PC.
The B register is a general purposed 8-bit wide register that is used to hold the variable
that controls the loop count, index into the ARRAY and the data that is stored in the
ARRAY.
The X register is a 16-bit register that is used to address or point to the array element that
will be changed.
The C register, often called the flags register, has bits that are set or reset depending on
various conditions that result from program execution. For this activity the Z (zero) flag
is used (bit 2 in the C register). The Z flag is set to 1 (true) when the execution of certain
instructions results in zero, otherwise it is reset to 0 (false).
Consider the effects of the ‘CMPB #10’ instruction. This instruction compares the
contents of the B register to the decimal value 10. If they are equal, the Z flag is set. If
not, the Z flag is reset. This flag setting is used in the following instruction ‘BNE
LOOP1’ to determine if the loop should be executed again or if it has finished.
The PC register contains the address of the next instruction that will be fetched. The PC
register is initialised to the program’s start address when the program is assembled.
It is now a simple matter to step though the program. To do this, press the STEP button
on the toolbar.
Stepping through the program one instruction at a time is a powerful way to analyse the
program flow. However, it can be noted that stepping through a code section that loops
many times could become very tedious. The THRSim11 Simulator offers another
command called Set Breakpoint that allows the program to run until it reaches the
instruction where the breakpoint has been established. You will learn how to use
breakpoints in the next activity.
47 ELE1911 Electrical and electronic practice A
Target 68HC11 microprocessor board
9. To run the program on the target microprocessor board, a few changes must be made to
the program. The changes are required to ensure that the program and data memory
locations coincide with the microprocessor board’s memory map.
10. Make the following changes to the XXXLAB1.ASM program:



Remove the last two lines of code, as the reset vector of the target microprocessor
is already set.
Change the ORG $0000 statement to ORG $1100
Change the ORG $E000 statement to ORG $1120
Save the program under a different name using the Save As command.
11. Assemble the program, then click the Download to target button on the toolbar (light
blue down arrow). The THRSim11 Simulator will download the machine code only to the
target microprocessor board.
12. Open two list boxes using the Target Memory List command from the Target >
Target Memory menu options. Set the start address of the first box to $1100 and the
second to $1120. The first box will display the data and the second will contain the
program code. Open the Target CPU Registers box as well, as shown below.
48 ELE1911 Electrical and electronic practice A
13. Run the program using the Target Go button (light blue forward arrow) or Ctrl+F9.
Note, the ARRAY memory locations $1100 to $1109 now contain the values $00 to $09.
The THRSim11 Simulator will execute the program and continuously loop on the last
instruction ‘LOOP2
JMP LOOP2’ until the RESET button on the
target microprocessor board is pressed.
14. Modify the ARRAY memory locations so that they contain $00.
To do this you first have to select the line where you want to enter the new value. Once
the line is highlighted, type in the new value. Press return after entering the value or click
the next line to be changed. The down arrow on the keyboard can also be used to enter
the new value and move to the next line.
15. Execute the program again. Press the RESET button on the target microprocessor board
to stop the program. If the ARRAY memory locations do not change, click in the memory
list box to force the update. It may be necessary to click on each line to update its value.
16. To shut down the system, unplug the 9-Volt AC power supply, and disconnect the serial
cable from the EZ-MICRO CPU-11.
Activity 5: Part 2 – Introduction to programming the 68HC11
The following activity is designed for gaining familiarity with the THRSim11 Simulator
debugging tools.
The program adds five decimal numbers using accumulator A and stores the final result in a
particular memory location.
49 ELE1911 Electrical and electronic practice A
The five decimal numbers to be added 1, 2, 3, 4, and 5 are to be stored in locations $0000 to
$0004 respectively and the answer is to be stored at location $0005.
A flow chart describing the program is shown below.
The program listing is as follows:
50 ELE1911 Electrical and electronic practice A
The program as listed contains a faults that will be used to demonstrate the editing facilities
available with the THRSim11 Simulator.
Procedure
A detailed procedure for entering (programming) and fault finding (debugging) follows:
1. Start Up and enter the program
A. Start the THRSim11 Simulator software.
B. In order to create the assembly source code file ‘XXXLAB2.ASM’ for this activity,
select the New command from the File menu.
C. Enter the assembly language source code as shown above then save the file, using
Save As from the File menu. Note: Your initials will replace XXX.
2. Assemble the source code
A. To do this, select the Assemble from the File menu or press the Assemble button on
the toolbar. The assembled program listing will appear in a new dialogue box. Look
at the assembled listing file. Two errors should have been generated. Correct the first
error in the XXXLAB2.ASM file and re-assemble. The second error should
disappear as it was caused by the first.
B. Open two memory list boxes using Memory List from the View > Memory menu.
For the first list box set the starting address at $0000 (data), and for the second list
set the starting address to $E000 (program).
Arrange the windows so that the assembled program and the memory list boxes are
visible, as shown below.
51 ELE1911 Electrical and electronic practice A
Figure 5.2.2: Memory lists
Note that memory locations starting at $0000 contain the initial values $01 to $05 and those
starting at $E000 contain the machine code program, ready to run.
3. Run the program
A. Run the program using the Run button or F9.
The THRSim11 Simulator will execute the program and continuously loop on the last
instruction ‘LOOP2
JMP LOOP2’ until the STOP button on the toolbar is
pressed. Once the program has stopped the simulated 68HC11 should be reset. To do
this, press the RESET button on the toolbar.
B. Note, the memory location labelled ANS ($0005) now contain the value $0A
(decimal 10). The correct answer is $0F or decimal 15; therefore there is a problem in
the program as originally defined. The following steps should help isolate the
problem and correct it.
4. Breakpoint and register display
A. It might be useful to see what the program was doing each time it went through the loop.
Therefore, set a breakpoint at the beginning of the loop, location $E009. To do this, use
the Set command from the Breakpoint menu. Enter $E009 as the breakpoint value.
52 ELE1911 Electrical and electronic practice A
B. Note, a yellow bar appears to indicate a break point has been set.
C. Run the program again. The program will run to the breakpoint and then pause. At
this point the program is suspended, and on detecting this breakpoint, the contents of
the registers may be viewed.
The registers should contain the following values:
D. To resume the execution of the program, select the Run button. Since the
breakpoint at location $E006 is in a loop it will again be the next breakpoint and
the program will pause. At this point the registers will contain:
Note that Accumulator A contains the partial sum and Accumulator B has been
decremented. The X Register has been incremented since the last breakpoint.
53 ELE1911 Electrical and electronic practice A
E. Select Run, and once again the registers may be examined:
F. Select Run, and once again the registers may be examined:
G. Select Run, and the program has now successfully completed the loop four times and
Accumulator A contains the incorrect sum.
5. Correcting the program
A. From above it is evident that although the program was supposed to add five
numbers, the loop was executed only four times. Therefore the LDAB#4 instruction
at locations $E001 – $E002 should have been initialised to five (5).
B. To remove the breakpoint, select Remove from the Breakpoint menu. Highlight the
breakpoint to be removed and click OK.
C. Edit the XXXLAB2.ASM file and update the value of the operand for the LDAB
D. mnemonic. Save the assembly language program. Re-assemble the program and run
it. D. The following should now be displayed, indicating the correct value stored in
location $0005.
54 ELE1911 Electrical and electronic practice A
Activity 5.6: Use of a clock to program a delay
Counting is a good way to create a programmable delay in your program. The 68HC11 in the
EZ-MICRO architecture is running at 2 MHz and yet our application may be required to blink
a light once every 5 seconds.
In any given microprocessor each instruction in each addressing mode takes a precise and
deterministic amount of time to execute. This means we can calculate how long it takes to
make a certain number of passes through a loop. By looking at each instruction’s information
sheet, we can identify the ‘execution time’, a value given in terms of cycles. The cycle time
of the 68HC11 on-board the EZ-MICRO Board running from an 8 MHz crystal is 500ns. The
LDAA instruction requires 2 cycles to execute in the immediate addressing mode. This means
that is takes 1 usecs for LDAA #5 to execute on the EZ-MICRO system. Execution times of a
few common looping instructions are provided:
LDAA
DECA
BNE
NOP
LDX
DEX
(imm)
2 cycles
2 cycles
3 cycles
2 cycles
3 cycles
3 cycles
(imm)
Consider the following code segment that executes a loop five times. The code segment has
two NOP instructions inside the loop, and these are used to provide additional delay.
LDAA
DECA
NOP
NOP
BNE
COUNT
#6
COUNT
The initialisation of the loop only occurs once. The LDAA instruction requires 1 usec. The
time for 6 passes through the interactive part of the loop can be computed as
6 passes × 4.5 usec/pass = 27 usec. So the total time required for one execution of the loop is
28 usecs.
The largest loop counter that we can create with a single byte of memory or a single byte
register is 256. However if we use a 16-bit register as a loop counter we can count up to (or
down from) 65 535. For a loop that requires 10 cycles per iteration, the total time required for
one execution of the loop is now 327 675 usec plus 1 usec to initialise the loop. Notice that as
the time required for all the iterations grows large the time required to initialise the loop
becomes less and less significant.
The index register is a 16-bit register that is very well suited for a loop counter. The
instructions LDX, INX, and DEX make it easy. For example, consider the following code
segment that creates a delay of almost exactly 0.25 seconds.
COUNT
LDX
DEX
NOP
BNE
#62 500
*3 cycles
*3 cycles
*2 cycles
COUNT
*2 cycles
55 ELE1911 Electrical and electronic practice A
Procedure
Write a program that creates a delay of approximately 1 second and then increments the
contents of Accumulator A and delays again. This delay-then-increment process should
continue indefinitely (when simulated only). While developing your program, use the
following guidelines.
1. Choose $E000 as the origin of your program code segment.
2. Create a nested loop; use index register X as the inner loop counter and ACCB as
the outer.
Note: The simulator runs much slower than the EZ-MICRO board. It is also not practical
to calculate the delay based on the number of machine cycles. Determine the value to be
placed in the index register by trial and error. A typical starting value for a 0.2 second
delay may be $0100 in the index register.
3. Run the program for 10 seconds then stop it. The value in accumulator A should be $0A.
4. Modify your program to run on the target board. Change the starting address to $1000.
Estimate the value to be placed in the index register based on the number of machine
cycles within the loops and a cycle time of 500nsec.
5. Test the value of accumulator A in your program so that the program can be stopped
when accumulator A reaches the count of 10. To stop the program, insert a ‘NOP’
instruction just before the end of the program. This will allow a target breakpoint to
be set.
6. Download the code to the 68HC11 microprocessor board. Set the target breakpoint,
then measure the time the program takes to run, it should be close to 10 seconds.
7. Examine the target CPU registers. You should see a value of $0A in Accumulator A.
Activity 5.7: Seven segment display
The aim of this activity is to illustrate two interfacing techniques that may be used to drive a
seven segment display.
1. The first technique utilises the peripheral interface adapters B and C of the 68HC11
microprocessor. The segments of the display are connected to the output pins of
peripheral register B. In this way, the character displayed will depend on the bit pattern
stored in peripheral register B. The illumination of the display is controlled by one output
pin of peripheral register C. This ensures that the display is not illuminated until valid
data appears in peripheral register B.
This technique will be simulated using the THRSim11 Simulator software.
5. The second technique utilises a BCD to 7 segment display decoder circuit built into the
EZ-MICRO Board. This technique is easier to program, but requires more circuitry than
the first. The character to be displayed is simply stored to a specified memory address
that represents the BCD to 7 segment decoder. So placing the required character on the
data bus will cause the appropriate segments to light when the address of the decoder
appears on the address bus.
Since the address bus provides the display enable signal, illumination of the display will
only occur while the specified address is on the bus. For this reason the display decoder
must be continually written to. In this way our brain ‘sees’ the display as being
continuously lit.
56 ELE1911 Electrical and electronic practice A
This technique will be illustrated using the EZ-MICRO board.
Procedure
1. To illustrate the first technique, enter the following program into the THRSim11
Simulator.
The program will display the number 3 on a 7 segment display. However, before simulating
the operation of the program it is necessary to connect the display to the simulated 68HC11
output ports.
To do this, select 7-Segments display from the Connect > 7-Segments Displays menu
options. A 7 segment display box will appear in the workspace. Move the display to avoid
obscuring other open dialogue boxes. To connect the display, right click within the display.
Select the Connect option to display the Connect dialogue box, as shown below.
Connect the 68HC11 pins to the component (display) pins by highlighting the two nodes to
be connected then click the Connect button. When all pins are connected, as shown above,
click OK.
Save the program file as XXXLAB6a.ASM. Assemble and run the program. If there are no
errors, the number 3 should appear in the display box.
57 ELE1911 Electrical and electronic practice A
2. Modify the program to display the number 5 for a few seconds then turn the display off.
Confirm the program works as expected then stop it. Close all open dialogue boxes.
3. Create a new program using New from the File menu.
4. To illustrate the second technique, enter the following program.
5. Assemble the program then download it to the target EZ-MICRO board using the
Download to Target Board button on the toolbar. Run the program on the target using
the Target Go button on the toolbar. Confirm that the number 3 is displayed for about
1 second.
6. Modify the program to display the number 5 for 5 seconds.
58 ELE1911 Electrical and electronic practice A
Activity 5.8: PRBS generator design – part B
Equipment required

68HC11 development board

Logic board

Flip-flop board

Plug packs

Power supply
Task
1. To interface the pseudo-random binary sequence generator designed in part A with
the 68HC11 microprocessor development board and to provide a visual indication
of the binary sequence on the development board.
The generator should:


use J-K flip-flops
be clocked by a single switch (on the logic board).
Procedure
1. Construct the generator designed in part A.
2. Connect the generator to the 68HC11 uP development board.
3. Write a program that will, when interrupted, read the output of the generator.
4. Download the program to the 68HC11 uP development board (target board).
5. Run the program on the target board.
7. Clock the generator with the switch and observe the target display.
Attachments
1. Revision – Interrupts.
2. Initial code.
Reference

ELE1301 study book, module 11 – MC68HC11 instruction set (In particular, tables
11.1, 11.3 & 11.4).
59 ELE1911 Electrical and electronic practice A
Revision
1. Interrupts
A major difference exists between most peripherals when they are connected to a CPU and
that is ‘speed of operation’. In general most peripherals are very slow compared with a CPU.
Signals between the CPU and the peripheral indicating when each other is ready to transfer
data, are known as ‘Interrupts’.
An interrupt can also be a signal to a CPU to halt its normal operations and do something
more important. These signals are used for alarm inputs, external control of processes or
debugging aids in software development. Generally interrupts fall into three categories:

internal

external

software.
For this activity we need to use an external interrupt.
External interrupts are generated by signals from peripheral devices. They may be requesting
data transfers or indicating a failure has occurred. A good example of this is a machine error.
In this case the interrupt may be used to initiate a special routine to quickly store and display
an error code in the few milliseconds before the machine shuts down.
When an interrupt is received by the CPU it:

Completes the current instruction in its program

Stores all of its registers contents in memory

Executes a special program called the Interrupt Service Routine (ISR)

Returns to the point where it left the original program.
Various methods are used to transfer control to the ISR.
On interrupt, the 68HC11 obtains a 16-bit interrupt vector from 2 fixed memory locations
($FFF2 and $FFF3). This interrupt vector ($01EE for the ìP development board) is then
loaded into the program counter as the address of where the first instruction of the ISR
resides.
For this activity the program will go to the vector address $01EE for the first instruction of
the interrupt service routine, which is actually a jump to another location in the program area
of memory. To do this the following code may be included at the end of a program.
ORG
$01EE
JMP
IRQISR
An interrupt from the PRBS generator will cause CPU to suspend its current execution and
perform a special ISR and when finished return to the main program.
After executing the ISR, how does MPU know where to return to?
As outlined previously, this is taken care of automatically by the CPU as it temporarily stores
the current address of the PC on the stack before it branches to the ISR.
Actually it stores PC, Index Reg, AccA, AccB and CCR in that order, on the stack.
When the RTI is executed it restores these values to their respective sources in the reverse
order as the stack is a Last In First Off (LIFO) device.
The following flowcharts may be used as a guide for this activity.
60 ELE1911 Electrical and electronic practice A
Note: ‘loop’ is designed to continually refresh the display while waiting for an IRQ. So, no
instructions are associated with the ‘wait for interrupt’ block.
61 ELE1911 Electrical and electronic practice A
2. Initial code
62 ELE1911 Electrical and electronic practice A
Activity 9: Introduction to PLCs
Equipment required
To be advised by the instructor.
Activity 10: PLC application
Equipment required
To be advised by the instructor.
63 ELE1911 Electrical and electronic practice A
Electronics lab
Please bring your electronic construction breadboard to residential school. You can use it to
build your circuit on and avoid the need to construct your circuits more than once on the
shared breadboards here.
Activity 1: Familiarisation with test equipment
Spend the first hour or so of your time here getting used to the test equipment on the bench.
Use the following activities to ensure that you know the basic capabilities and limitations of
the equipment:
Power supply and multimeter:
Measure the following voltages with the digital multimeter set on a d.c. volts range.
●
Voltage between +5V terminal and common
●
Voltage between +5V terminal and the common on the other side of the supply
●
Voltage between +5V terminal and ground
●
Voltage between +Variable terminal and common.
●
Ensure that you know how to adjust the voltage.
Oscilloscope and function generator:
●
Set up the function generator output to be a sine wave at about 1kHz, with no d.c. offset.
●
Connect the output to channel 1 of the oscilloscope.
●
Trigger the display to achieve a stable trace. You may need to get help with this – be sure
you know how to do it properly.
●
Measure the period of the signal with the oscilloscope and compare it to the nominal
period of the function generator signed.
●
Measure the voltage of the signal with both the oscilloscope and the meter set on a.c.
volts. Make sure that both give similar values.
●
Vary the settings of the function generator, frequency, level, wave form, and d.c. offset,
and observe the oscilloscope trace. Ensure that you can measure the d.c. offset value by
selectivity d.c. coupling.
64 ELE1911 Electrical and electronic practice A
Activity 2: Introduction to breadboarding
To be advised by the instructor.
Activity 3: Electronics project construction
3.1 Build the circuit comprising the comparators (LM339), logic circuit IC2a and IC2b
(74LS00) and the LED. Vary the input voltage and ensure that the circuit works to
indicate when the input voltage is within a fixed range.
Measure the following:
●
The voltages defining the voltage range.
●
The voltage range of the input at which in-range/out-of-range indication occurs.
●
The voltages of the logic levels at all three pins of the IC. Estimate the current in the
LED. Is this acceptable?
3.2 Build the lower frequency oscillator based on the 555 timer and ensure that it works.
Sketch approximately to scale and in correct time relationship, the waveforms at the
threshold and output pins of the 555. Compare the period of the output signal with that
obtained by calculation.
3.3 Build the higher frequency 555 oscillator. Repeat the procedure of 3.2. Pin RES will
have to be high for oscillation.
3.4 Add the logic circuity comprising IC6a and IC6 b (74LS00) to the oscillators. When will
there be a signal at the output of IC6b? Sketch this output waveform.
3.5 Build the amplifier based on the LM741 op amp. You may choose to adjust some values
here. Adjust the potentiometer to achieve an output voltage which swings both positive
and negative. Record your final output waveform with the previous circuit connected.
Measure the voltage gain and compare it to theory.
3.6 Build the circuit driving the 8 ohm load or speaker. Connect the amplifier. Sketch the
waveform across the speaker. Check that the transistors are capable of supplying the
current and that the 741 can supply the required base current.
3.7 Ensure that the whole circuit operates to detect a certain voltage range and indicate it
with a sound output.
65 ELE1911 Electrical and electronic practice A
Activity 4: Electronics project testing
To be advised by the instructor.
ELE1911 – Electronic circuit
66 ELE1911 Electrical and electronic practice A
Electrical technology activities
Electrical safety – rules
Electricity supply and accidents
The use of electricity is of immense importance and benefit to the industry, the home, and the
welfare of the community generally. However, the possibility of electric shock, which can
cause injury and death, is always there.
An analysis of electrical accidents indicates that in most cases the victims contacted the
normal supply of 240 volts. There were also some accidents involving contact with high
voltage transmission lines and aerial distribution conductors with a line voltage of 415 volts.
Death from electric shock has occurred from contact with the electrodes of leads of electric
welders, in which the voltage was less than 100 volts.
The question that may be asked then is, why supply at 240 V and not a lower value
(e.g. 32 V)? The reason is that if the ordinary supply were 32 volts, it certainly would be
safer, but the cost of electricity supply would be much greater due to the heavier and more
expensive cables and other equipment required by both the supply authority and the
householder.
Electrical accidents are often the result of misadventures of careless persons undertaking
make-shift repairs (to domestic appliances and workshop equipment which become faulty
due to misuse and lack of proper care and maintenance). They can be avoided by a commonsense approach in observing the rules of personal safety. Strict adherence to the safety
regulations and recommended working procedures in using adequate safety devices (such as
protective clothing, gloves, goggles, face-masks, helmets), warning notices, safety-barriers,
security locks, rescue-observer, insulated tools etc., is recommended.
Domestic electrical installations and equipment rated at 240 V are quite safe if installed and
used in accordance with the various methods, procedures and regulations which have been
adopted by the Electricity Boards and the State Electricity Commission.
Lower voltages, particularly 32 volts, are used in industry for such applications as inspection
lead-lights. The supply for these is obtained from 240/32 V transformers.
Factors affecting electric shock
To receive a shock a person must contact two points between which there is a difference of
potential, for example between the active conductor and the earthed metal frame of an electric
iron. The resulting current flow through the body causes the damage. Investigations have
shown that the following electrical and physiological factors, determine the severity of the
shock.
67 ELE1911 Electrical and electronic practice A
Table 1: Factors affecting electric shock
Electrical
Duration of current
Frequency of current
Physiological
General physical condition of victim
e.g. Weak heart
Wave shape of current
Body resistance
Magnitude of current
Skin resistance
Voltage applied initially
Path of current
Phase of heart cycle
Table 2: Body current and physiological effect
Current (50 Hz)
Physiological phenomena
<1 mA
None
1 mA
Perception threshold
Feeling or lethal incidence
Imperceptible
1–3 mA
Mild sensation
3–10 mA
Painful sensation
10 mA
Paralysis threshold of arms
Cannot release hand grip, if no
grip, victim may be thrown clear
30 mA
Respiratory paralysis
Stoppage of breathing (frequently
fatal)
75 mA
Fibrillation threshold 0.5%
Heart action discoordinated
(probably fatal)
250 mA
Fibrillation threshold 99.5%
(>5 s exposure)
4A
Heart paralysis threshold
(no fibrillation)
Heart stops for duration of current
passage. For short shocks, may
restart on interruption of current
(usually not fatal from heart misfunction)
>5A
Tissue burning
Not fatal unless vital organs are
burnt
Human body as conductor
Alternating voltage at 50 Hz reaches maximum value at intervals of 0.01 second. When such
a voltage is applied to the human body, the nerve-muscle system is still attempting to recover
68 ELE1911 Electrical and electronic practice A
from one peak when it is subjected to the next. Consequently with an a.c. current of sufficient
magnitude the muscles remain in spasm and the victim remains locked to the a.c. supply.
Direct current causes momentary locking (at make or break) but not continuous spasm.
If the frequency is raised, the body is able to tolerate more current. The shock effect is
detectable up to about 50 kHz. Above this frequency, only heating is experienced, and this
effect is used in diathermy where 1 MHz or more is used.
The electric resistance of the human body varies with the condition of the skin, which is
responsible for most of the resistance, and the situation of the body. Obviously when a person
is perspiring his resistance is lowered. Also, if part of the body is immersed in water,
resistance is lowered. Once the skin is punctured, body resistance decreases greatly.
Consequently, prolonged time of application of current, by causing sweating and blistering
and finally destruction of the skin, is more dangerous than a brushing contact.
The average resistance of the body, from hand to hand, with intact dry healthy skin is
approximately 3000 ohms. This figure can be reduced to about 500 ohms by soaking the
hands in water. Body resistance is also reduced when the contact area and the contact
pressure with a conductor is increased.
Effect of magnitude of current
Current of 1 to 3 milliampere magnitude can be felt by the person without shock condition.
The ‘let-go’ voltage at which an individual can release himself from contact varies in
individuals from 15 to 19 volts a.c. and the ‘let-go current’ is in the range of 8 to
14 milliamperes and leads to micro-shock conditions.
Alternating currents from ‘let-go’ values and up to 25 milliamperes cause muscular cramps
and may lead to exhaustion, loss of consciousness and ability to breathe. Muscular
convulsions will cease when the current is removed, but the inability to breathe may persist,
requiring artificial resuscitation (macro-shock condition).
If the body current exceeds 25 milliamperes, the severity of the shock situation is intensified
to ventricular fibrillations. It is a condition where the heart loses its rhythm and the heart
muscles quiver in an uncoordinated manner, diminishing the possibility of reviving the
victim. The heart is vulnerable because currents, whether from hand to hand, or hand to foot,
travel principally in the blood vessels and so reach and traverse the heart. Artificial
respiration in itself, does nothing to restore heart rhythm. The time of contact for fibrillation
to occur is related to the cardiac cycle and the current for fibrillation:
I  60 / t
Main effects on the body
Current through the body may cause one or more of the following effects:
a. Paralytic injury to the brain.
b. Injury to the heart and hence circulatory failure.
c. Damage to tissue and organs by severe burns.
d. Respiratory failure.
e. Muscular convulsions.
69 ELE1911 Electrical and electronic practice A
Resuscitation
Attempts to revive victims of electric shock are often successful if a person with a knowledge
of resuscitation methods is available to immediately apply them. Prompt action by a rescuer
is essential as the chances of death increase with each minute of delay in commencing
resuscitation.
Course of action
A quick appraisal of the situation should be made by a rescuer when approaching a victim. If
the victim is still in contact with a live conductor, then the supply should be immediately
switched off, or the flexible cord pulled out of the socket of the wall outlet. In some
situations, such as a fallen conductor in the street, the means of switching off supply are not
readily accessible. The rescuer, in this case, must move the victim from the conductor
without himself becoming the second victim. Dry wood, dry clothing, rope, blankets, rubber
mats and rubber gloves provide sufficient insulation for 240 volts. The rescuer must decide
on the spot how to effectively use these materials to shift the electric conductors.
If an unconscious person has to be moved before artificial respiration is commenced, he may
be carried, rolled or dragged. The uppermost thought in a rescuer’s mind should be to
commence resuscitation with minimum delay.
Medical assistance should be fetched as soon as possible, but commencement of artificial
respiration should not be delayed for this purpose.
Methods of resuscitation
Obtain Safety and Resuscitation Publications. Thoroughly study and learn the most effective
and normally-preferred resuscitation methods.
70 ELE1911 Electrical and electronic practice A
University of Southern Queensland
Faculty of Engineering and Surveying
Energy systems laboratory: safety rules
8. Before proceeding to conduct any Energy Systems Laboratory work, as directed, students
must firstly provide written notification to the instructor if they:
● have a physical disability
● have a history of physical illness
● have a current medical condition
or
● are on medication that may cause impairment of judgement or slow reaction time, so
that appropriate safety procedures and precautions can be arranged and implemented.
Students who are presently unwell (i.e. feel faint or dizzy, etc.) must notify the instructor
(in private) before proceeding with any Energy Systems Laboratory work.
All information given is confidential and is disclosed only to the instructor and
Laboratory Technician in Charge as necessary to ensure personal safety in the Laboratory
at all times.
9. Do not proceed to set up an activity unless you have prepared proper circuit diagrams
with a detailed equipment listing and these have been approved by the instructor.
10. Connect according to the approved circuit diagrams, using colour-coded cables for easy
identification. If any changes are made to the connections, these must be recorded in the
report. If major changes were made, then draw revised circuit diagrams.
11. Never switch on the power supply unless:
● you have thoroughly checked the connections, starting settings of controls, instrument
ranges and supply details
● you have carefully studied the safety requirements and precautionary measures,
starting and stopping procedures and operational sequences
● you have consulted the instructor and clarified all your doubts
● the instructor has checked and approved your connections and set up.
12. Use appropriate protective measures (fuses, switches, and circuit breakers). Protect
measuring instruments from surge currents. If anything appears to be wrong switch off
the supply at the circuit breaker or switch.
13. In case of emergency, promptly inform the instructor and proceed to follow his/her
instructions in a calm and orderly manner.
14. Lay out the equipment on the test bench in a safe and easily accessible manner. Do not
crowd the test bench. Remove all unwanted items, spare cables and your own possessions
to another unused bench.
15. Since you will be working on exposed live parts at 240 V and 415 V, think before you do
anything. Prevent electrical accidents to persons and equipment by carefully observing
safety instructions.
71 ELE1911 Electrical and electronic practice A
Safety instructions: please read and observe
When connecting leads
1. Avoid using test-leads and connecting cables with damaged insulation or loose
terminations.
2. Avoid connecting more than two leads to any terminal.
3. Avoid spreading cables over rotating or hot parts.
4. Avoid over-tightening terminals, screws and nuts (finger-tightness is sufficient).
5. Avoid joining (or piggy-backing) connecting leads to obtain extended connection. (Use a
single cable of adequate length).
6. Avoid overloading cables by applying excessive currents. (Use thicker cables for currents
in excess of 7 A, thin cables for currents up to 7 A and thinner cables for currents less
than 1 A).
7. Avoid plugging and unplugging connector cables when the supply is switched on.
When working in the laboratory
1. Do not work in thongs, sandals or bare-feet.
2. Do not leave your energised circuit unattended.
3. Do not wear hanging chains and bracelets.
4. Do not hold metallic rulers and pens near live circuits.
5. Do not touch any bare conductors, terminals or rotating parts.
6. Do not pull or twist power cables.
7. Do not touch or shift hot lamps and resistors.
8. Do not meddle with equipment and notices.
9. Do not play tricks on other students.
10. Do not kick objects or push buttons with your foot.
11. Do not tap, shake, drag or drop instruments.
12. Do not rest your feet or arms on equipment.
13. Do not place paper pads over ventilating screens.
14. Do not lean over panels, trolleys or persons.
15. Do not place equipment on the floor or standing space.
Be safety conscious. Know what to do in case of emergency.
__________________________________________________
Neatly remove this section and hand to the laboratory supervisor.
I shall abide by the energy systems laboratory safety rules and instructions which I have read
and understood.
Name:
Signature:
Date:
72 ELE1911 Electrical and electronic practice A
Using instruments in electrical laboratories
Please read and observe
1. Inspect the instruments. Do not use if faulty or damaged.
2. Handle all instruments with gentleness and care.
Do not jar or drag meters on bench tops.
Do not pull wires connected to meters.
Do not tap the meter or subject it to vibration.
Do not write on the meter or use ball-point pen on the glass.
3. Before using any instrument consult its instruction manual.
Double-check meter usage and the correct method of connections.
Ascertain and observe the polarity markings of terminals.
Use d.c. meters in d.c. circuits and a.c. meters in a.c. circuits.
4. Check zero errors before using the instruments. If the mechanical zero requires resetting,
ask the instructor to do it for you. Do not use coins, blunt screw drivers, etc. on Set-Zero
screw.
5. Check accuracy class of the instrument, scale multiplying factors and subdivisions of
scale graduations for the range connected.
6. Check the correct positioning of the instrument.
Most laboratory instruments are positioned flat on the table.
Meters marked with  must be placed vertically on the table.
7. Do not place meters close to the edge of the table or on the floor.
Arrange meters in the front, so that their scales can be correctly read with ease.
8. Do not use meter terminals as junction posts.
Do not over-tighten terminals but check for loose connections.
9. Double-check the selected Range Setting for voltages and currents.
Read the meter indication on the correct scale.
First select the range higher than the value being measured.
If the reading is very low, then lower the scale range.
10. Current coils of ammeters, wattmeters, power factor meters and energy meters are likely
to be easily damaged. When switching-in circuits which may draw surge currents, shortcircuit the current coils using shorting switches. Do not exceed the rated current.
If you notice the instrument to be faulty or damaged before you use it, or if any wrong
connection or accident occurs, report to the Supervisor without delay.
Do not use multimeter with test prongs on energised circuits in CURRENT and OHMS
settings.
Do not switch on power without checking range setting of meters and controls.
Using A.C. measuring instruments
1. A.C. voltmeters
A.C. voltmeters are calibrated to indicate the effective (r.m.s.) value of sine-wave voltages.
The selected range of a multi-range instrument must be always higher than the expected
voltage in the test circuit and the setting may be changed to the next lower range if the
reading is too low on the selected range. Always check the range before using the meter.
73 ELE1911 Electrical and electronic practice A
Always connect the voltmeter in parallel with the circuit element, the voltage across which
is being measured. Where a single multi-range voltmeter is used to read the voltages across a
number of terminals, insulated leads with prongs or touch-clips are used and the meter need
not be permanently connected. Most laboratory instruments are placed horizontally on the
table (
).
2. A.C. ammeters
A.C. ammeters are calibrated to indicate the effective (r.m.s.) values of sinusoidal currents.
Always connect the ammeter in series with the circuit element, the current through which is
being measured. Choose a range setting higher than the expected circuit current. NEVER
connect an ammeter in parallel with a circuit element or across a supply source, as the meter
will be permanently damaged. DO NOT USE TEST-PRONG LEADS.
Polarity of connection to the ammeter terminals has no effect on the indication of the meter.
If using a multi-range instrument, always set it on the higher range and change the range to a
lower one if necessary.
3. A.C. wattmeters
A.C. wattmeters are calibrated to indicate the average real or active power supplied to a
circuit element. A wattmeter has one set of current terminals, (usually marked M or ±, and L
for the current range), and one set of voltage terminals (usually marked V+, and the voltage
range).
Connect the current terminals in series with the circuit element, M to the mains side and
L to the load side. Check the meter cover and select the correct current range setting so
that the meter range value is higher than the expected load current; one of the voltage
terminals (V+) is usually connected to M (or L).
Always record the multiplying factor corresponding to the selected voltage and current
ranges. Always check the current/voltage ranges connected before switching the power on.
Use the shorting switch to protect the current coil from surge currents.
Correct polarity connections must be observed, otherwise the pointer may be kicking
below zero. If the pointer is below zero when the circuit is switched off, then there is a zero
error. Ask the instructor to correct this zero error. If the meter is connected correctly and the
pointer reads below zero, then use the reversing switch and record the reading as negative in
sign.
For highly inductive or capacitive loads, the power factor is less than 0.2 and a low-powerfactor (l.p.f.) wattmeter is to be used. If the load power factor is 0.5 or more, use a wattmeter
calibrated at unity power factor (u.p.f.).
4. Power factor meter
74 ELE1911 Electrical and electronic practice A
A power factor meter indicates the cosine of the angle between a voltage and the current. It is
connected in the same way as a wattmeter. Since it has no spring control, the pointer may
drift when the supply is off. Note that the scale is not uniform. Always indicate whether
the p.f. value is lead or lag. If the voltage-coil or current-coil connections are reversed, the
pointer may deflect outside the scale range.
5. Energy meter (kilowatt-hour meter)
An energy meter is an integrating type instrument. It has a rotating disc the speed of which is
a measure of the energy supplied to the load. The meter has a constant (K revolutions per
kWh). Energy metered = (no. of revolutions of the disc) / K.
The meter is connected in the same way as a wattmeter. It is mounted in a vertical position.
6. Cathode ray oscilloscope
A cathode ray oscilloscope (CRO) is used to observe the time variations or waveforms of
voltages and to measure their properties. To observe the waveform of a current, the current is
passed through a resistor of known value and the voltage drop across the resistor is measured
using the CRO.
Note: An isolation transformer should be used to supply the 240-V power to the CRO in tests
where a circuit voltage is floating and common earth connection is not permissible.
75 ELE1911 Electrical and electronic practice A
Activity A1: Kirchhoff’s laws
Aims
1. To apply Ohm’s law and Kirchhoff’s current and voltage laws.
2. To verify the calculations by test measurements.
Theory
Refer to study book 1, chapter 4.
For the circuit is shown in figure 1:
I1, I2 and I3 are branch currents;
b and d are the only nodes;
a and c are merely terminations;
abda and bcdb are the closed loops.
Figure 1: Circuit
Node and terminal voltages
Using double subscript notation, the voltage differences between terminals can be written.
Applying Ohm’s law to the branches, using d as the common reference point:
Vad = E1
Vab = Vad – Vbd = R1.I1
Vad = E2
Vcb = Vcd – Vbd = R2.I2
Vbd = V3 = R3 ⋅ I3
From the equations above, the branch currents are:
I1 = Vab / R1 = (Vad – Vbd ) / R1 = (E1 – V3) / R1
I2 = Vcb / R2 = (Vcd – Vbd ) / R2 = (E2 – V3) / R2
I3 = Vbd / R3 = V3 / R3
Applying KCL at node b: I1 + I2 = I3
  ( E1  V3 ) / R1    ( E2  V3 ) / R2   (V2 / V3 )
 1
1
1
 ( E1 / R1 )  ( E2 / R2 )  V3 

 
 R1 R2 R3 
The branch conductances are: G1 = 1 / R1;
G2 = 1 / R2;
G3 = 1 / R3
1
1
1
V3  [( E1 / R1 )  ( E2 / R2 )] /  
 
 R1 R2 R3 
or V3 = [G1.E1 + G2.E2] / [G1 + G2 + G3] – Millman’s Parallel Generators Theorem
76 ELE1911 Electrical and electronic practice A
Parallel generators theorem analysis
77 ELE1911 Electrical and electronic practice A
Activity A2: Resistance measurement of DC machine windings
Aims
To conduct tests on a d.c. machine to determine:
1. The armature circuit resistance.
2. The shunt-field winding resistance.
Circuit diagrams and apparatus
Figure 1: Armature circuit
Figure 2: Shunt-field winding
Table 1: Measurement of resistances in a D.C. machine
Detail
Detail
M
D.C. machine, 230 V, 21.75 A,
1 500 r/min, MacFarlane Eng. Co.
S
Supply fuse switch 220 V,
30 A, d.c.
RL
Variable resistance, 250 Ω, 240 V,
20 A, GK Electrical
Rf
Variable resistance, 324 Ω,
British Electric Resistance Co.,
1.3 A
Va
Voltmeter, AVO 8 Mk III, 0–25 V
d.c., 2% F.S.D., 20 kΩ /V
Vf
Voltmeter, AVO 8 Mk III, 0–100 V
d.c., 2% F.S.D., 20 kΩ /V
Aa
Ammeter, 30–0–30 A d.c.
A.J. William Elec. Inst.,
Type P.C. 6, Class 1M
A
Ammeter, AVO 8 Mk III, 0–1 A
d.c., 1% F.S.D.
Instructions
1. Armature circuit resistance (Ra)
Note that armature circuit includes interpole winding and brush contacts.
Connect the circuit as in figure 1.
Set RL to limit the current to the rated value. Close S.
Adjust RL so that the rated current flows through the armature circuit.
78 ELE1911 Electrical and electronic practice A
If the armature starts to rotate, hold it still.
Note the voltage drops and currents for three positions of the armature. Record the
readings in table 2.
Calculate the mean value of Ra1 at θ1 = 20°C and then the value of Ra at θ2 = 75°C.
Ra  Ra1av 1  1  75  1 
1.  0.004 / K
1  20C
 temperature coefficient
of resistance at 1
 ambient temperature
2. Shunt-field resistance (Rf)
Connect the circuit as in figure 2.
Since the resistance of the winding is high, make sure the current If does not include the
current taken by the voltmeter. Take three readings. Record readings in table 2.
Calculate the mean value of Rf1 at θ1.
Determine the Rf value at 75°C.
Calculations
Table 2: Test data: resistances in a D.C. machine
Armature circuit
Field circuit
Va
V
Vf
V
Ia
A
If
A
Ra1
Ω
----
----
Rf1
Ω
----
----
Ra1av
Ω
----
average value
at temp. 20°C
Rflav
Ω
----
average value
at temp. 20°C
Ra
Ω
----
at temp. 75°C
Rf
Ω
----
at temp. 75°C
----
Activity A3: D.C. shunt motor performance
Aims
1. To run the d.c. shunt motor at the rated voltage and rated speed on no-load.
2. To predetermine the load characteristics of the motor from no-load test.
----
79 ELE1911 Electrical and electronic practice A
Circuit diagram and apparatus
Figure 1: D.C. shunt motor: no-load run test
Table 1: No-load run test: D.C. shunt motor list of apparatus
Detail
Detail
M
D.C. motor: 5 kW
230 V, 21.75 A, 1 500 r/min
N
Tachometer 0–2 000 r/min
R1
Variable resistance
50 Ω, 5 A, wire-wound
Rf
Variable resistance
330 Ω, 1.1 A
Va
Voltmeter, D.C.
0–300 V
Vt
Voltmeter, D.C.
0–300 V
A1
Ammeter, D.C.
0–5 A
A2
Ammeter, D.C.
0–3 A
F1
Fuse, 30 A, 250 V D.C.
F2
Fuse, 5 A, 250 V D.C.
Instructions
Shunt Motor
No-Load Run Test
Decouple the motor from the shaft load.
Connect the motor for no-load run as in figure 1.
Use a variable resistance R1 for starting.
Keep R1 at maximum and Rf at minimum resistance.
Close S after ensuring the starting and stopping procedures.
Check the meters for polarity and range.
Check the direction of rotation of the motor.
Note the direction marked on the end-frame.
(If the direction is wrong, open S.
Interchange the wires connected to Z and ZZ.
Close S. The motor should run in the correct direction.)
Adjust R1 gradually until Va = Vt .
80 ELE1911 Electrical and electronic practice A
Adjust Rf to obtain the rated speed.
Record the readings in table 3.
Reduce speed. Stop the motor. Open S.
Analysis
Calculations (refer to the practice example which follows this activity)
Calculate the rotational and fixed losses (table 3).
Assume a value of line current IL = x.ILr where x = load factor.
x is a variable: x = (0.25, 0.5, 0.75, 1 and 1.25) and the rated line
current = ILr. See sample calculations.
Complete the calculations for each IL in table 4.
Graphs
1. Plot the predetermined characteristics: efficiency (η), speed (N),
torque (T) and line current (IL) vs power output (Pout) on the same graph.
2. Plot torque (T) vs line current (IL) and torque (T) vs speed (N).
3. Draw the power flow diagram (to scale) at full load.
Table 2: D.C. shunt motor
Rated details of
motor
Vt:
V Ilr:
A N:
r/min Pout:
kW
Ω
Armature resistance Ra =
Table 3: No-load light running test: data and calculations
Supply voltage
Vt
=
V
No-load armature loss = Ra.Iao2
W
Field current
If
=
A
No-load armature input = (Va.Iao)
W
Armature voltage
Va
=
V
Iron, friction and windage losses
(rotational) Pr = Vt.Iao – Ra.Iao2 =
W
No-load armature current
Iao
=
Field circuit loss = Vt.If =
W
Speed
No
=
A
r/min Fixed losses PF = Pr + Vt.If =
W
81 ELE1911 Electrical and electronic practice A
Table 4: D.C. shunt motor: efficiency calculation by summation of losses
x
Load factor
No-load
Vt
Supply voltage
V
IL
Line current
x.ILr
A
If
Field current
A
Ia
Armature current
(IL – If)
A
Ia2Ra Armature losses
W
PF
Fixed losses
W
PL
Total losses
PF + Ia2Ra
W
Pin
Power input
VtIL
W
Pout
Power output
(Pin – PL)
W
η
Efficiency
(Pout/Pin) × 100
%
Ebo
No-load back e.m.f.
Va – Ra.Iao
V
Eb
Back e.m.f.
Va – Ra.Ia
V
N
Speed =
Eb.(No/Ebo)
r/min
T
Torque =
Pout/(2πN/60)
N.m
* At no-load, IL = Iao + If
*
0.25
0.5
0.75
1
1.25
82 ELE1911 Electrical and electronic practice A
D.C. shunt motor performance characteristics
SAMPLE CALCULATIONS
(At load factor x = 1):
Ra =
Ω
Ia
=
A
W
PF =
W
=
W
PL =
W
Pout
=
W
η
=
%
Eb
=
V
N
=
r/min
T
=
N.m
Vt
=
V
x
=
IL
=
A
If
=
I2aRa
=
Pin
A
Discussion
1. Efficiency vs Power Output _________________________________________________
_______________________________________________________________________
_______________________________________________________________________
2. Speed vs Power Output ____________________________________________________
_______________________________________________________________________
_______________________________________________________________________
3. Torque vs Power Output and Torque vs Speed __________________________________
_______________________________________________________________________
_______________________________________________________________________
4. Line Current vs Power Output _______________________________________________
_______________________________________________________________________
_______________________________________________________________________
5. Power Flow Diagram (Scale: 10 mm ≡ 2 kW) (See page 118)
83 ELE1911 Electrical and electronic practice A
D.C. shunt motor performance characteristics
84 ELE1911 Electrical and electronic practice A
Conclusions
1. Full-load performance
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
2. What would happen to a d.c. shunt motor if the d.c. supply is switched on:
(a) with no series resistance in the armature circuit?
(b) with a high resistance in series with the shunt field?
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
3. Limitations of the test method — Assumptions
(a) _____________________________________________________________________
(b) _____________________________________________________________________
(c) _____________________________________________________________________
(d) _____________________________________________________________________
4. Advantages of the test and predetermination
(a) _____________________________________________________________________
(b) _____________________________________________________________________
(c) _____________________________________________________________________
(d) _____________________________________________________________________
References (Harvard format)
1.
_______________________________________________________________________
_______________________________________________________________________
2.
_______________________________________________________________________
_______________________________________________________________________
85 ELE1911 Electrical and electronic practice A
Practice example: D.C. shunt motor performance
A d.c. shunt motor is rated at 5 kW, 1 500 r/min, and line current of 24 A at 200 V. The
armature circuit resistance is 0.8 W. It is run from a 200-V supply at 1 500 r/min. There is no
load on the shaft. The armature current is 1.5 A. The shunt field current is 1.0 A.
1. Assuming fixed supply and field settings, determine:
(a)
No-load armature power loss: Ra.Iao2
= 0.8 × (1.5)2
= 1.8 W
(b)
No-load armature power input: Vt.Iao
= 200 × 1.5
= 300.0 W
(c)
Rotational power losses: Pr
= 300 – 1.8
= 298.2 W
(d)
Shunt field circuit power loss: Vt.If
= 200 × 1.0
= 200 W
(e)
Fixed losses: PF = Pr + VtIf
= 298.2 + 200
= 498.2 W
(f)
No-load line current: ILo = Iao + If
= 1.5 + 1.0
= 2.5 A
(g)
Full-load armature current: Ia = ILr – If
= 24 – 1
= 23 A
2. Predetermine the following items at half-load (i.e. load factor x = 0.5):
(a)
Line current:
IL
= x.ILr
= 0.5 × 24
= 12 A
(b)
Armature current:
Ia
= IL – If
= 12 – 1
= 11 A
(c)
Armature power loss:
Pa
= Ra.Ia2
= 0.8 × 112
= 96.8 W
(d)
Total power losses:
PL
= PF+ Pa
= 498.2 + 96.8
= 595.0 W
(e)
Electrical power input:
Pin
= Vt.IL
= 200 × 12
= 2 400 W
(f)
Mechanical power output Pout
:
= Pin – PL
= 2 400 – 595
= 1 805 W
(g)
Efficiency:
(h)
η
= Pout / Pin
= 1 805 / 2 400
= 0.752
No-load back e.m.f Ebo
.
= Vt – Ra.Iao
= 200 – 0.8 × 1.5
= 198.8 V
(i)
Back e.m.f.:
Eb
= Vt – Ra.Ia
= 200 – 0.8 × 11
= 191.2 V
(j)
Speed:
N
= (No/Ebo).Eb = (1 500/198.8) × 191.2
= 1 443 r/min
(k)
Angular velocity: ω
= (2π/60).N
= (2π/60) × 1 443
= 151.07 rad/s
(l)
Torque output:
= Pout/ω
= 1 805 / 151.07
= 11.95 N.m
T
86 ELE1911 Electrical and electronic practice A
Power flow diagram for a D.C. shunt motor
87 ELE1911 Electrical and electronic practice A
88 ELE1911 Electrical and electronic practice A
Activity A3: D.C. shunt motor performance pre-determination
Table 3: No-Load light running test: data and calculations
Table 4: D.C. shunt motor: efficiency calculation by summation of losses
89 ELE1911 Electrical and electronic practice A
Experiment A3: D.C. shunt motor performance pre-determination
90 ELE1911 Electrical and electronic practice A
ELE1801 Electrical Technology appendix parts of a D.C. machine
Carefully examine the d.c. machine provided. Identify the parts listed and study the following table:
Note: The d.c. machine can be either a MOTOR (converts electrical energy into mechanical energy)
or a GENERATOR (converts mechanical energy into electrical energy).
Part
Constructional details
Function
Remarks
1.
stator frame
Cast iron, hollow, square/
cylindrical.
Stationary.
Supports pole pieces, end shields, and terminal
box.
Provides part of the path for the working
magnetic field.
Size varies according to machine rating. Often
finned to assist machine cooling.
2.
pole piece
Laminated steel bolted or
dove-tailed to stator core.
Supports the field coils.
Provides part of the path for the working
magnetic field.
Air-gap between pole piece and armature core
kept to a minimum.
3.
field coil
Insulated copper wire.
Carries field current that provides the working
magnetic field for the d.c. machine.
Can be connected in series of parallel.
4.
armature core
< 1 mm thin laminations
containing slots, keyway.
Supports armature coils: slots accommodate the Air-gap between armature teeth and pole piece
windings.
kept to a minimum. Central keyed hole
Provides part of the path for the working
accommodates shaft.
magnetic field.
5.
armature wind An assembly of coils made Carries armature current which provides a field Coil active parts reside in slots: non-active
ing
of insulated copper wire.
that interacts with the working magnetic field to parts form end windings. Skewed slots
give torque.
minimize cogging.
6.
commutator
Copper segments insulated Provides electrical connection between
by mica strips: form band. stationary and moving conductors. Fastened to
but insulated from shaft.
Allows current direction in armature
conductors to change as coils pass from N to S
poles and v.v.
7.
brushes
Carbon: a good conductor;
soft to prevent scoring.
Low brush pressure causes arcing. Carbon
particles attack insulation, causing shorting of
comm. segments.
8.
brush yoke
Steel assembly that holds
Fixed to stator core.
the brushes under pressure. Contains the spring that is used to adjust brush
pressure.
Motor: adjusting brush angle adjusts speed.
Generator: adjusting brush angle adjusts
voltage.
9.
shaft
Made of strong, relatively
low-permeability steel.
Supports the armature and the bearings.
Provides a means of connection to mechanical
load.
Provides a means of mechanical coupling.
Not part of the path for the working magnetic
field.
10. bearings
Ball-type (roller/taper
depending on application).
Reduces mechanical friction between stationary Replaced as part of routine maintenance, or as
and moving parts.
required (approximately every three years).
11. end shields
Made of cast iron. Support
the bearings.
Supports bearings and shaft. Houses the
bearings.
Gives protection for windings against
mechanical damage.
Electrical connection between stationary and
moving conductors. Excessive pressure adds
friction and causes commutator scoring.
In totally-enclosed machines, given protection
for windings against the environment.
91 ELE1911 Electrical and electronic practice A
Activity B1: Transformer tests
B.1.1 Preliminary tests
Aims
1. To be familiar with the constructional features of shell-type and core-type small power
transformers.
2. To test the continuity of windings.
3. To test the insulation resistance of windings.
Instructions
1. Inspection
Draw neat sketches to illustrate the constructional features of core-type and shell-type
transformers. Refer to ELE1801 study book, section 10.1. Note how leakage inductive
reactance of windings can be minimised by sandwich windings.
2. Continuity test
Using an ohmmeter, identify the terminals belonging to the same winding. If the winding
is open-circuited or not connected, the resistance between two terminals would be very
high (infinity). If a winding has a short-circuit, the resistance between its terminals would
be very low (close to zero). Record the results in table 1.
3. Insulation resistance test
Learn to use the Megger insulation tester. Refer to ELE1801 study book, chapter 9,
section 2, for Megger details. Connect the two primary terminals together to one test lead
and the other test lead to the core (or shield) terminal of the transformer. Rotate the
handle and record the readings in table 2 as values >2 MΩ or <2 MΩ.
Repeat the test on each of the windings and the core, and between the windings as well.
Record the results in table 2. If any value is greater than 2 MW, then the insulation is
‘safe’. If any value is less than 2 MW, then the insulation is ‘not safe’. (Note in table 2.)
Analysis
1. State the purposes of the transformer preliminary test.
2. Briefly comment on the results with respect to the minimum ‘safe’ level of insulation.
3. Neatly sketch constructional features of shell-type and core-type small power
transformers on the graph paper provided.
92 ELE1911 Electrical and electronic practice A
Table 1: Continuity test
Winding
Resistance (Ω)
Ω ≡ Ohmmeter
Secondary-1
Secondary-2
Primary
Figure 1
Table 2: Insultation resistance test (Megger test)
Tested between
Value
(MΩ)
Note
M ≡ Megger
G and A1 & A2 together
G and 21 & 22 together
G and 22 & 23 together
A1 & A2 and 21 & 22
A1 & A2 and 22 & 23
A1 and G
Figure 2
22 and G
Discussion of results/conclusions
1. State the purposes of the transformer preliminary tests: to test:
(a) ____________________________________________________________________
(b) ____________________________________________________________________
2. Briefly explain the term ‘minimum SAFE level of insulation’; comment on the results
obtained:
_______________________________________________________________________
_______________________________________________________________________
3. Indicate how leakage inductive reactance of windings can be minimised:
_______________________________________________________________________
_______________________________________________________________________
93 ELE1911 Electrical and electronic practice A
Reference (Harvard format)
1. _______________________________________________________________________
_______________________________________________________________________
94 ELE1911 Electrical and electronic practice A
95 ELE1911 Electrical and electronic practice A
B.1.2 No-load test
Aims
1. To conduct a no-load test on a single-phase transformer.
2. To determine: the iron-loss and magnetising components of no-load current; the voltage
transformation ratio; and the no-load equivalent circuit parameters.
3. To measure the e.m.f. per turn, and hence estimate the number of turns in the primary and
the secondary windings.
Instructions
1. Record the rating-plate details of the test transformer in table 1. Note: the low voltage
(L.V) winding is used as the primary.
Connect the test set-up as in figure 1. Check instrument ranges and scale factors.
Close S1. Open the wattmeter current-coil shorting switch (if not already open).
Adjust VAT to apply the rated supply voltage to the low-voltage (240-V) winding.
Record all the readings in table 2.
2. The tertiary test winding (search coil) has Nt =10 turns. See figure 3.
Connect a voltmeter across the test winding terminals.
Record the voltage (Vt) induced across the test winding in table 3.
3. Reduce the voltage to zero. Switch off S1.
Analysis
1. Calculate the transformation ratio, the components of no-load current and the no-load
equivalent circuit parameters (table 2). Refer to study book.
2. Calculate the voltage per turn, and the number of turns in the primary and the secondary
windings, using
Voltage per turn
Et = (Vt / Nt);
N1 (V1 / Et);
and N2 = (V2 / Et).
3. Draw below the transformer no-load phasor diagram showing voltages V1 and V2 and
currents Io, Ic and Im using the flux Φ as the reference. Indicate the no-load power-factor
angle ɸo. Use the scales: 10 mm ≡ 150 V; 10 mm ≡ 25 mA.
Transformer no-load phasor diagram
96 ELE1911 Electrical and electronic practice A
Table 1: List of apparatus
T
kVA
Test Transformer
S=
VA;
L.V. primary
V1
A.C. Voltmeter 0–300 V
f = 50 Hz
V2
A.C. Voltmeter 0–600 V
H.V. secondary
Ao
A.C. Ammeter 0–1–3 A
Wo
Wattmeter 0.5 A, 250 V, 0.2 p.f.
Nt
Test winding of 10 turns
VAT
Variable auto-transformer
Voltage
V1 =
V
V2 =
V
Current
I1 =
A
I2 =
A
Table 2: No-load test data
Figure 1: No-load test circuit
Table 3: E.M.F. per turn test
Figure 2: E.M.F. per turn test
Figure 3: Simple equivalent circuit diagram for transformer on no load
97 ELE1911 Electrical and electronic practice A
Discussion
1. State the purposes of the transformer no-load test:
(a) ____________________________________________________________________
(b) ____________________________________________________________________
(c) ____________________________________________________________________
(d) ____________________________________________________________________
2. Indicate the following key equations:
The apparent power balance: ________________________________________________
The m.m.f. balance: _______________________________________________________
The voltage, current and turns ratios: _________________________________________
3. Draw the no-load equivalent circuit diagram showing measured and calculated values.
Transformer no-load equivalent circuit diagram
4. Briefly explain what Ro and Xo represent.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Conclusions
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Reference (Harvard format)
1. _______________________________________________________________________
_______________________________________________________________________
98 ELE1911 Electrical and electronic practice A
B.1.3 Short-circuit test
Aims
1. To conduct a short-circuit test on a single-phase transformer and determine the rated-load
copper loss.
2. To determine the equivalent circuit parameters.
3. To pre-determine the efficiency.
Instructions
1. Study the circuit shown in figure 1. Check the connections. Set the auto-transformer for
minimum output voltage. Close switch S1.
Very carefully adjust the auto-transformer output (about 8–10 V only) to circulate the
rated current in the short-circuited high voltage (H.V) secondary winding.
Record the readings (table 1).
2. Reduce the voltage to zero. Switch off S1.
Analysis
1. Calculate the short-circuit power factor; the equivalent impedance, resistance and
reactance of the transformer (table 1). All values are referred to the low-voltage side, in
the equivalent circuit (figure 2 in table 2).
2. From both the NO-LOAD and SHORT-CIRCUIT TESTS, complete table 2 and 3 to
predetermine the transformer efficiency for load factors between 0.25 and 1.25.
3. Plot graphs of efficiency versus output power, for power factors of unity and 0.8 lagging.
4. Draw the transformer equivalent circuit below, showing all symbols and all measured
and calculated values at rated voltage and current, i.e. at rated load.
5. Draw the rated-load phasor diagram to scale (10 mm ≡ 500 mA) on the graph paper
supplied.
Transformer equivalent circuit diagram (show test data at rated load)
99 ELE1911 Electrical and electronic practice A
Determination of transformer equivalent circuit
Figure 1: Short-circuit test circuit diagram
Table 1: Short-circuit test data
Vs
I1
(Pc)
VAT Variable auto transformer
240 V/0–260 V, 5 A
12
 s  cos  s
Ws
(V)
(A)
(W)
Ze 
Ws
Vs I1

Vs
I1
(Ω)
Ws
Wattmeter 0–
25 V, 5 A, UPF
(A)
Vs
A.C. voltmeter; 0–30 V
As
A.C. ammeter, 0–5 A
ɸs =
cos–1(λs)
= cos–1(
A2
A.C. ammeter, 0–5 A
Re =
Ze . cos ɸs
=
×
=
Ω
T
Test transformer
Xe =
Ze . sin ɸs
=
×
=
Ω
lagging
= °
)
Table 2: Transformer equivalent circuit (transfer data from the no-load test)
Refer all values to the 240-volt side
I '2 = I2(N2/N1) :
V '2 = V2(N1/N2)
V1 =
V N1/N2
=
V2 =
V
=
n
R0 =
kΩ P0
=
W
X0 =
kΩ cos ɸs
=
lagging
Re =
Ω Pc
=
W
Xe =
Ω cos ɸs
=
lagging
Ze =
Ω Xe/Re
=
Figure 2: Transformer equivalent circuit
xm =
P0 / Pc =
100 ELE1911 Electrical and electronic practice A
Sample calculations (show working)
(a) Load factor x = .....
Power factor λ = 0.8 lagging
S
= Rated VA (from No-load test)
= VA
Pc
= Rated-load copper loss
= W
Iron loss
Po = W
Copper loss at load factor x
x2.Pc
=
= W
Total loss
PL
= P + x2.P
o
c
=
= W
Output power
Pout
= x.S.λ
=
= W
Input power
Pin
= Pout + PL
=
= W
Efficiency (%)
η
= Pout / Pin
=
= %
(b) Maximum efficiency condition
xm2.Pc = Po
λ = 1:
=
xm  Po / Pc
∴
Pout
= xm.S.λ
=
=
W
PL
= 2Po
=
=
W
Pin
= Pout + PL
=
=
W
∴ ηmax
= Pout / Pin
=
=
or
%
Table 3: Predetermination of efficiency
λ = cos ɸ = 1
Po
x
(W)
0.25
0.5
0.75
1.0
1.25
2
x Pc
xS
(W)
(VA)
λ = cos ɸ = 0.8 lagging
Pout
Pin
η
Pout
Pin
η
(W)
(W)
(%)
(W)
(W)
(%)
101 ELE1911 Electrical and electronic practice A
Discussion
1. State the purposes of the transformer short-circuit test: to determine:
(a) ____________________________________________________________________
(b) ____________________________________________________________________
(c) ____________________________________________________________________
(d) ____________________________________________________________________
Primary
Secondary
Load
_______________________________________________________________________
2. Briefly explain what Re and Xe represent.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
3. Briefly indicate any precautions and safety measures taken.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
4. Briefly explain the condition for maximum efficiency.
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Conclusions
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Reference (Harvard format)
1. _______________________________________________________________________
_______________________________________________________________________
102 ELE1911 Electrical and electronic practice A
103 ELE1911 Electrical and electronic practice A
Activity B2: Three-phase transformer connections
Aims
1. To check the correct and the incorrect star and delta connections of windings; and
2. To verify the relationships between line/phase voltages and line/phase currents for deltawye connection.
Instructions
1. For each of the three identical single-phase transformers, ensure that terminals are marked
with correct polarities.
2. The transformers are connected as in figure 3. Check that the connections and the voltage
ratings are correct.
Open the load switch S2.
Close the supply switch S1.
Ensure the voltmeter range setting is 600 V.
Record the phase and the line voltages (table 2).
Close S2.
Record the line and the phase currents (table 2).
Analysis
1. For each three-phase connection, verify the relationships:
(a) VL  Vp , and IL  3.I p for  -connection
(b) VL  3.Vp , and I L  I p for Y -connection
2. Draw the phasor diagram to scale showing all the phasors (optional).
3. Complete the three-phase transformer exercise.
Discussion
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
__________________________________________________________________________
104 ELE1911 Electrical and electronic practice A
Exercise: Three-phase transformers
Three identical single-phase transformers, arranged in a Δ–Y configuration, take power from
a three-phase supply at a line voltage of 415 V and deliver it to a three-phase load at a line
voltage of 120 V. The total load draws 15 kVA. Sketch a circuit diagram of the transformer
and load and determine the following values (show working):
Circuit diagram
1. The primary phase voltage.
2. The primary line current.
3. The primary phase current.
4. The secondary line voltage.
5. The secondary phase voltage.
6. The secondary line current.
7. The secondary phase current.
8. The transformation ratio of each transformer.
9. The kVA supplied by each transformer.
105 ELE1911 Electrical and electronic practice A
Table 1: Lists of apparatus
T
Single-phase power transformer
A
Digital ammeter or clip-on ammeter
V
Multi-range voltmeter
R
Loading resistor bank, 3-phase, ______ A
S1
Three-phase,
V,
/
V,
_______/______ A
50 Hz, _______ A supply
Voltmeter reads twice the phase voltage.
Figure 1: Wrong delta connection
Figure 3: Three-phase transformer ΔY connection
Voltmeter reads low (≈ 0 V)
Figure 2: Correct delta connection
106 ELE1911 Electrical and electronic practice A
Table 2: Delta-wye connected transformer
Primary Δ
Y Secondary
Verification
Voltages
VL1
VL2
VL2 = ____ VP2
VP1
VP2
VP1
n
VP 2
IL1
IL2
I L1  3.I P1
IP1
IP2
Line
Phase
Currents
Line
Phase
107 ELE1911 Electrical and electronic practice A
Activity C1: Power factor improvement
Aim
To calculate the power factor for the mercury vapour lamp circuit, and draw the phasor and
power diagrams.
Figure 1: Mercury vapour lamp circuit: power factor improvement
Theory
Refer to study book topic on power factor improvement.
Precautions
When the lamp is first switched on, its resistance is relatively low and a large current tends to
flow in the circuit.
Close S2 to switch in 25 μF in parallel with the lamp. This will limit the inrush current
thereby avoiding any overload of the instrument current coils. After the lamp has reached its
operating temperature, the current will stabilise at a lower value.
Once the lamp attains its operating conditions, do not switch off the supply. Switching on the
supply will not restart the lamp until the hot vapour has cooled to room temperature.
Table 1: List of apparatus
V
A.C. voltmeter, _______V
S2
Capacitor switch
A1
A.C. ammeter, _______A
C
Capacitor box
A2
A.C. ammeter, _______A
W
Wattmeter
______μF to _______μF, _______V
R
______A,_____V____
S1
Supply
_______V,_______A
Mercury vapour lamp
_______V,_______A,_______W
Switch,
L
Ballast inductor
108 ELE1911 Electrical and electronic practice A
Instructions
1. Check the circuit set up. Record details of apparatus used in table 1.
2. Switch in the capacitors as indicated in table 2 and record meter values.
Note 1:
When S2 is open, IL = I.
Note 2:
When operating conditions have stabilised, IL will remain constant since V, R, and
XL are constant.
Table 2: Power factor improvement
Measured values
C
(μF)
V
(V)
I
(A)
IC
(A)
IL
(A)
Calculated values
P
(W)
Q
(var)
S
(VA)
cos  
P
VI

0
.......
lagging ...........
20
.......
............ _____
55
.......
............ _____
Note: Record measured and calculated values to three (3) significant figures.
Analysis
1. Complete the calculations in table 2.
2. Draw to scale (20 V and 500 mA to 10 mm), on graph paper, a phasor diagram for V, I,
IC and IL values in table 2, with V as reference, and showing I = IL + IC for each of the
three capacitance values. (see page 113)
3. Draw to scale, (10 mm ≡ 100 W) on graph paper, power diagrams for P, Q and S values
from table 2, at C = 20 μF and 55 μF.
4. Calculate the value of capacitance required for unity power factor in the circuit. State
this value on the phasor diagram.
109 ELE1911 Electrical and electronic practice A
Sample calculations
For C = ....μF
Apparent power
S
=
V.I
=
×
Power factor
λ
=
cos ɸ
=
P / (V.I) =
Reactive power
Q
=
S. sin ɸ
=
×
=
S 2  P2
=
VA
/(
×
=
var
=

)
Figure 1: Phasor diagram for power factor improvement applied to an inductive-resistive load
(a mercury-vapour lamp and its associated iron-cored ballast)
=
=
var
110 ELE1911 Electrical and electronic practice A
Steps
1. Using a protractor, draw Io = IL to scale, lagging V by angle ɸo (calculate from p.f.).
2. Draw IC20, ...IC55 to scale, leading reference V by 90°, from the origin 0.
3. Complete the parallelograms on 0A ... 0B.
4. By phasor addition, IL + Icn = In: draw in phasors I20 ... I55 and estimate the value of C
needed for operation at unity p.f.
Discussion (itemise)
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Conclusions
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Reference (Harvard format)
1.
_______________________________________________________________________
_______________________________________________________________________
2.
_______________________________________________________________________
_______________________________________________________________________
111 ELE1911 Electrical and electronic practice A
112 ELE1911 Electrical and electronic practice A
Activity C2: Series resonance
Aim
To determine the current-frequency curve of a series R-L-C circuit theoretically and
experimentally.
Preparation
1. Study the theory and examples in the relevant study paper. Use the nominal values given
in figure 1 to complete the exercise in table 1 on the following page.
2. Calculate the resonance frequency (fr), using the values of R, L and C in figure 1.
3. For the seven (7) values of frequency f in table 1 calculate and plot the values of I versus f
in graph 1. Label this response ‘Theoretical’.
Instructions
1. Using the digital L-C-R meter provided, measure the values of required inductance,
capacitance and resistance. Measure the d.c. resistance Rdc of the inductor.
R=
Ω L=
mH
C=
nF
Rdc =
Ω
Figure 1: Series resonance circuit
2. Connect the circuit as shown in figure 1. Short leads are essential.
3. Adjust the sine wave output of the signal generator to exactly 16 volt peak-to-peak as
measured on Channel 1 of the CRO. Vary the signal generator frequency in 5-kHz steps
from 40 kHz to 15 kHz. Set the frequency accurately using the CRO timebase. At each
frequency, measure the peak-to-peak amplitudes of V1 and V0 on the CRO.
V1 may change, so adjust the amplitude to ensure that it remains constant.
Record f, V1 and V0 in the table. Calculate I0 = V0 / ( 2 2.R ).
Plot I versus f, as you take readings, superimposing on the theoretical graph. Label this
response ‘Measured’.
113 ELE1911 Electrical and electronic practice A
Resonance curves: preparatory work
Date:
Given: R = 600 Ω
L = 10 mH;
C = 4.7 nF;
V1 = 16.0 Vpp
(a) For the R-L-C series circuit, complete the table below. Note: ω = 2πf
(b) Plot R, |XC|, XL, X, Z and I versus f, on the graph paper supplied, in graphs 1 and 2.
(c) Verify: I  V / R ;
r
0
I1 
X Lr  X Cr  L / C
V1
2 2.Z
I0 
V0
2 2.R
Table 1: Series resonance: calculation of current from theoretical values and measured values
114 ELE1911 Electrical and electronic practice A
115 ELE1911 Electrical and electronic practice A
116 ELE1911 Electrical and electronic practice A
Activity C3: Capacitor-start single phase induction motor: load
test
Aims
1. To conduct a load test on a capacitor-start single-phase induction motor.
2. To determine its performance characteristics: Current I, Input Power Pi, Power factor p.f,
Speed N, Slip S, Torque T and Efficiency η versus Power Output Po.
Circuit diagram
Figure 1: Circuit diagram for the capacitor-start single-phase induction motor load test
Table 1: List of apparatus
F.H.P. Brake Motor Test Set –
(Jay Jay Instruments type FH1/4)
consisting of –
V

A.C. voltmeter 0–250 V, AVO 8
A

A.C. ammeter 0–2.5–10 A, AVO 8
M
Induction motor, single-phase,
capacitor-start, 240-V, 50-Hz,
1/8-h.p., 1 425-r/min, 1.4-A
coupled to –
W
Wattmeter, 250 V, 2.5 A, u.p.f.,
0–625 W, overcurrent protection,
50 Hz, class 1.0, A.J. William
B
Eddy-current brake with variable
torque and
dynamometer calibrated 0–2 N.m
PT
Photo-tachometer, 0–2 000 r/min
digital type
C
Capacitor, 16μF, 350 V a.c.
117 ELE1911 Electrical and electronic practice A
Procedure
1. Inspect the circuit: check the wiring using the diagram provided. Check the motor
rating-plate details. Check the list of apparatus used (table 1).
2. Precautions to be observed before starting the motor:
Set the dynamometer scale to zero using the knurled thumb screw behind the scale.
Protect the meters from overcurrent on start. Use 16-μF capacitor only.
Set the torque control rheostat to OFF for the ‘no-load’ condition.
3. Switch on the a.c. supply at the main switch S1.
Set the motor spring-loaded start/off/mn switch S2 to the START position then, once the
motor is running, smartly set switch S2 to the RUN position.
4. Reset meter scales. Release overcurrent protection on the current coils.
5. Record the voltage V, current I, input power Pi, speed N and torque T at ‘no load’
(table 2).
6. Increase the load on the motor by adjusting the torque control so that the dynamometer
indicates 0.2 N.m. Record the readings in table 2.
7. Repeat for torques of 0.4, 0.6, 0.8 and 1.0 N.m. Record the readings.
Do not operate the motor for load torques above 1.1 N.m.
Release the load.
8. Switch off the motor run/off/start switch and the a.c. supply.
Calculations
Determine the power output Po, efficiency η, power factor p.f and slip S, for each load torque
T and neatly record in table 2.
Full-load output power
Po
=
Rated brake horse power (B.H.P.) × 746
Rotational velocity
ω
=
2π.N/60
Full-load torque
T
=
Po / (2π.N/60)
Graph
On the same graph, plot current I, power factor p.f., torque T, speed N, percent slip S(%) and
percent efficiency η(%) versus power output Po.
118 ELE1911 Electrical and electronic practice A
Capacitor-start single-phase induction motor performance characteristics
Sample calculations
V = _____ V;
I = _____ A;
Pi = _____ W;
f = _____ Hz;
p = _____ poles
T = _____ N.m;
N = _____ r/min
Power factor p.f.
= Pi / (V.I)
= ___________
= _________ lagging
Rotational velocity ω
= 2π.N / 60
=
___________
= _________ rad/s
Output power Po
= T.ω
=
___________
= _________ W
Efficiency η (%)
= 100.(Po /Pi )
=
___________
= _________ %
Synchronous speed Ns
= 120.f / p
=
___________
= _________ r/min
Slip S (%)
= 100.(Ns – N) / Ns
=
___________
= _________ %
Table 2: Load test data and calculations
Test observations
T
V
I
Pi
(N.m)
(V)
(A)
(W)
Calculations
N
ω
Po
η
p.f.
S
(W)
(%)
(p.u.)
(%)
No.
1
2
3
4
5
6
Note: ‘p.u.’ stands for ‘per unit’.
(r/min) (rad/s)
119 ELE1911 Electrical and electronic practice A
120 ELE1911 Electrical and electronic practice A
Graph 1 – Capacitor-start single-phase induction motor: performance characteristics
121 ELE1911 Electrical and electronic practice A
Activity D1: Three-phase circuits: star and delta connected loads
Aims
●
●
To connect a balanced, 3-phase load consisting of three resistors in (a) star, and (b) delta
To measure line and phase values of current and voltage, and verify that:
I L  3.I p for delta:
●
and
VL  3.Vp for star and
To measure the total power in each case, using a three-phase wattmeter and to compare these values:
PC  3.I pVp ;
and
PC  3.I LVL
Instructions
1.
Connect the three resistors in star.
Measure and record ‘IL’ VL and Vp and PM.
IL,IP
VL
Vp
PM
PC
(A)
(V)
(V)
(W)
(W)
Does VL =
3.Vp ? _________________
Calculate PC and compare with PM.
_________________________________
2.
Connect the three resistors in delta
including an ammeter to measure IP.
Measure and record IL, PM and VL.
IL
IP
VL, Vp
PM
PC
(A)
(A)
(V)
(W)
(W)
Does IL =
3.I p ? _________________
Calculate PC and compare with PM.
_________________________________
122 ELE1911 Electrical and electronic practice A
3.
Compare the power used in star and delta.
______________________________________________________________________
______________________________________________________________________
123 ELE1911 Electrical and electronic practice A
Activity D2: Three-phase induction motor – DC generator tests
Aims
●
To inspect the constructional features of an induction motor, a d.c. shunt generator and an
auto-transformer
●
To conduct a load test on a three-phase induction motor-generator set
●
To determine the induction motor performance characteristics and
●
To verify three-phase voltage, current and power relationships.
Apparatus
Figure 1: Three-phase induction motor – D.C. generator load test circuit
Table 1: Apparatus: Three-phase induction motor – D.C. generator tests
Detail
M
Detail
Induction motor, three phase, Δ, 4.0 kW, G
415 V, 8.1 A, 1 420 r/min, 50 Hz
W1 Wattmeters, single-phase, 600 V, 10 A, RL
W2 0–1.5 kW, scale × 4, 50 Hz, Type P.W.6,
A.J. William Elec.
Variable resistance load, 3-f, 230 V,
5 kW in 0.5 kW switched increments,
Creswell England.
Vg
Voltmeter, D.C. AVO 8, Mk V, 0–300 V
VP Voltmeter

A
Ammeter, D.C., 30–0–30 A, class 1.0,
Type P.C.6, A.J. William Elec.
A1 Ammeter, A.C., AVO 8, Mk V, 0–10 A

N
Tachometer, 0–2 000 r/min, digital
EMTEK, auto-range
A2 Ammeter

AT Auto-transformer (Variac), 50 Hz, 240 V,
8 A, model type W20H
Warburton Franki
VL

Voltmeter, A.C., AVO 8, Mk III,
0–1 000 V
D.C. shunt generator, 5.0 kW, 230 V,
21.8 A, 1 500 r/min
124 ELE1911 Electrical and electronic practice A
Instructions
1. Check the circuit connections. Check the meter ranges and scale factors.
Prepare a list of apparatus used (table 1).
Record the rating plate details.
Adjust the two spring balances so that the machine frame has even clearance from its
bed.
2. Couple the motor with the d.c. shunt generator.
Note the marked direction of rotation on the machine frame.
Set the auto-transformer for minimum voltage.
Set field regulator RF at maximum resistance (i.e. for minimum current).
Switch off load resistor RL.
Ensure that the ammeters and wattmeters are set correctly.
Confirm what to do to reverse the direction of rotation.
3. Close switches S1 and S.
Carefully adjust the auto-transformer to start the motor.
Check the phase sequence and direction of rotation.
If the direction is wrong, switch off S1 and S.
Interchange any two of the supply connections at the auto-transformer.
Close switches S1 and S. Restart. Do not exceed 10 A line current on starting.
Check that the direction of rotation is now correct.
Check the d.c. meters for correct polarity.
Gradually adjust the auto-transformer output to the rated voltage of the motor.
4. Using RF, adjust the d.c. generator output voltage Vg to 230 V.
Switch in RL in steps, adjusting RF to maintain Vg at about 230 V so that the motor draws
the rated line current.
Adjust the spring balances so that the machine frame does not touch the bed.
Take the readings (line voltage, line current, power input, speed and spring balances) at
full-load and record them in table 2.
Measure the motor line current and the phase current and record them in table 3.
Measure the line and the phase voltages at the auto-transformer and record them in
table 3.
5. Reduce the load in steps and take four evenly-spaced sets of readings between full-load
and no-load (as indicated in table 2) resetting RF as necessary to keep Vg at 230 V.
6. Finally, switch out RL, adjusting RF to reduce Vg to a minimum.
Reduce the a.c. voltage to a minimum. Switch off and stop the motor.
Decouple the motor from the generator using the wingnuts on the bed.
Restart the motor and run it at the rated voltage on no-load.
Record the no-load readings (line voltage, line current, power input and speed) in table 2.
Three-phase induction motor performance characteristics
Sample calculations (at line current setting ≈ 3.8A)
125 ELE1911 Electrical and electronic practice A
1. Calculate the power input, power factor, torque, power output, efficiency and slip for the
motor for each load setting and tabulate the values (table 2).
Power input:
Pi
= (W1 + W2)
Power factor:
λ
= Pi / ( 3 VL .I L )
=
cos ɸ
=
W
=
lagging
Synchronous speed N
s
:
= 120 f / p
=
r/min
Slip:
S
= 100 × (Ns – N) / Ns
=
%
Torque:
T
= (F1 – F2) × 0.305
=
N.m
Power output:
Po
= 2πNT / 60
=
W
Efficiency:
η
= (Po / Pi) × 100
=
%
2. Calculate the capacitance rating (μF, VA and V) of the capacitor bank required to
improve the no-load motor supply power factor to a value of unity.
3. Verify that in star connection: line voltage =
3 × phase voltage.
4. Verify that the two wattmeter readings are given by:
W = VLIL cos (30° ± ɸ)
Graphs
1. Plot the induction motor characteristics: efficiency (η), speed (N), slip (S),
line current (IL), power factor (λ), and torque (T) versus output power (Po), on the same
graph.
2. Plot torque against slip on a separate graph sheet (see page 134).
3. Draw a phasor diagram to scale, headed as shown, for the induction motor at no load.
(see study book 2, p. 11.25, Summary: Three-phase A.C. system, delta connection)
Title: Phasor diagram for a delta-connected induction motor at no load
Scale Voltage – 10 mm
s:
≡ 75 V
Sequence: a-b-c
Current – 10 mm
≡ 2.0 A
p.f. = cos ɸ0 = ............ lagging
126 ELE1911 Electrical and electronic practice A
Table 2: Three-phase induction motor load test data
Observations and results
Test readings
IL
Approx. line current setting (A)
Unit
Line current
A
VL Line voltage
V
W1 Wattmeter-1
W
W2 Wattmeter-2
W
F1 Spring balance-1
N
F2 Spring balance-2
N
N
Speed
≈ 8.3
≈ 7.4
≈ 6.5
≈ 5.6
≈ 4.7
≈ 3.8
r/min
Observations and results
Approx. line current setting (A)
Pi
Power input
W
λ
Power factor (p.f.)
s
Slip
T
Torque
N.m
0
Po Power output
W
0
η
%
0
lagging
%
Efficiency
Table 3: Star and delta circuits verification (use rated-load values)
Circuit
Star
Auto-transformer
Delta
Induction motor
Line value
Phase value
Vab = VL =
Vas = VP =
Vbc = VL =
Vbs = VP =
Vca = VL =
Vcs = VP =
Ia = IL =
Iab = IP =
Ib = IL =
Ibc = IP =
Ic = IL =
Ica = IP =
Verification
VL  3. Vp
VL/VP = ...........
I L  3. I p
IL/IP = ...........
127 ELE1911 Electrical and electronic practice A
Three-phase induction motor performance characteristics
Three-phase, ..... V, ..... kW, ..... r/min induction motor
128 ELE1911 Electrical and electronic practice A
Discussion (itemise)
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Conclusions
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Reference (Harvard format)
1.
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continued
129 ELE1911 Electrical and electronic practice A
Appendix A: Example investigation: three-phase induction motor
1. A 5-kW, 415-V, 50-Hz,
Calculate
1 440-r/min, delta-connected,
cage-rotor motor has a full-load (a) Power input
current of 8.75 A at 0.866
(b) Power output
lagging p.f.
2. Determine the full-load
polar expressions of all the
phase and the line voltages
and currents. Write them
in matrix form.
=
=
=
=
(c) Efficiency
=
=
(d) Torque
=
=
(e) Synchronous speed
=
=
(f) Slip
=
=
Line voltages
= Phase voltages
V ab 


V bc  
V ca 





 V


Reference: Vab
Sequence: a-b-c
Line currents
I a 
 
Ib  
 I c 




Phase currents
 I ab 
 
 I bc  
 I ca 

 A






3. The no-load test-data for the motor are given:
VL = 4.15 V; ILo = 1.72 A
Pio = 340 W
(a) cos o  Pin / ( 3.VL .I L )
(b)
I o  I Lo / 3
Determine and indicate the equivalent circuit
paramters for the no-load condition.
(c)

Ro  VL / ( I o .cos o )

(Note: The induction motor equivalent circuit
per phase at no-load is similar to the
(d)
single-phase transformer equivalent circuit at
no-load.)
Xo

 VL / ( I o .sin o )


 A


130 ELE1911 Electrical and electronic practice A
4. Draw all the phasors in (2) in a neat diagram and identify them with correct letter
symbols.
Title:
Phasor diagram for a delta-connected induction motor at full load
Scales: Voltage – 10 mm ≡
V
Sequence:
Current – 10 mm ≡
A
p.f. = cos ɸ =
5. The power supplied to the 5-kW deltaconnected induction motor is measured
using two wattmeters.
Determine the indications of the two
wattmeters, at full-load.
|Vab | = |Vcb | = VL =
|Ia | = |Ic| = IL =
cos ɸ =
ɸ=
Two-wattmeter method: circuit
Wattmeter indications
W1  Vab .1a.cos 
Vab
Ia
 VL .I L cos (_ _ _ _)

W2  Vcb .1c.cos 

Vcb
Ic
 VL .I L cos (_ _ _ _)

Total active power: P = W1 + W2
P  3(VL .I L cos )

P  W1  W 2
 3(VL .I L cos (_ _ _ _))

131 ELE1911 Electrical and electronic practice A
Appendix B: Parts of an induction machine
Carefully inspect the induction motor provided. Identify the parts listed and complete the following table.
Part
Constructional details
Function
1. stator frame
Cast iron, hollow,
square/cylindrical. Stationary.
Supports motor parts.
2. stator core
Laminated sheet set.
Holds stator winding in position.
Remarks
Plays an important role with the
cooling/ventilation.
3. stator windings Three identical, insulated copper
coils, mounted on the stator pole
pieces.
Windings terminated in Y or Δ
in terminal box.
4. rotor core
Laminated sheet steel circular
Holds rotor windings in
disks, each insulated and pinned position.
into a cylinder.
Must be well insulated to
prevent short circuit and leakage
currents.
5. rotor windings
Wound rotor has an assembly of Carries the current that creates
coils made of insulated copper the torque which causes rotation.
wire.
6. slip-rings
(if any)
Wound rotor has phosphor
bronze copper alloy rings,
concentric with the shaft, and
terminating rotor windings.
To enable current to be correctly
distributed.
7. cooling system
Fan mounted on shaft inside
housing. Fins on outside of
motor casing.
Blows air past windings and
over case fins.
Fins of impeller fan are easily
broken if malfunction or roughly
handled.
8. terminal box
Insulated (plastic or other
material) to house connections
securely.
Provides connection to stator
windings and, as applicable,
wound rotor brushgear.
Important to keep well insulated.
9. shaft
Made of strong, relatively lowpermeability solid steel.
Supports rotor. Enables drive
rotation.
Shaft to bearing fit to be at close
tolerance.
10. bearings
Ball-type (roller/taper depending To enable easy shaft and rotor
on application) white metal.
rotation.
11. end-shields
Made of cast iron. Support the
bearings.
Must be kept in good condition;
lubricated; no wear; correct use
of loads.
Shaft bearings mounted in them. Bearing position concentric with
shaft.
132 ELE1911 Electrical and electronic practice A
133 ELE1911 Electrical and electronic practice A
Three-phase induction motor performance characteristics
Three-phase, 415 V, 4 kW, 1500 r/min induction motor
134 ELE1911 Electrical and electronic practice A
135 ELE1911 Electrical and electronic practice A
Appendix A: Reading analog multimeter scales
Reading analog multimeter scales
When DC voltage measurements are made on an analog multimeter, it is important to look at
the correlation between the range selector switch position and meter scale indication. For
example, when the range switch is in the 2.5-V position, the 0 to 250 scale is used, but the
scale value must be divided by 100. For example, 1.75 volts DC would be indicated as
shown in figure A.1.
Figure A.1: Reading 1.75 volts DC on the multimeter scale
When the range switch is in the AC 10-V position, the AC 0 to 10 scale is used. For example,
4.8 volts AC would be indicated as shown in figure A.2.
Figure A.2: Reading 4.80 volts AC on the multimeter scale
136 ELE1911 Electrical and electronic practice A
When the range switch is in the DC 250-V position, the 0 to 250 scale is used. For example,
160 volts DC would be indicated as shown in figure A.3.
Figure A.3: Reading 160 volts DC on the multimeter scale
When the range switch is in the DC 50-V position, the 0 to 50 scale is used. For example,
34.0 volts DC would be indicated as shown in figure A4.
Figure A.4: Reading 34.0 volts DC on the multimeter scale
137 ELE1911 Electrical and electronic practice A
When the range switch is in the DC 500-V position, the 0 to 50 scale is used, but the scale
value must be multiplied by 10. For example, 350 volts DC would be indicated as shown in
figure A.5.
Figure A.5: Reading 350 volts DC on the multimeter scale
In all of the examples given above, the pointer indicated exactly a particular scale division.
When the pointer rests between two scale divisions, an estimate as close as possible to the
true reading must be made. For example, a reading of 128 volts DC would be indicated as
shown in figure A.6.
Figure A.6: Reading 128 volts DC on the multimeter scale
138 ELE1911 Electrical and electronic practice A
In the previous multimeter examples, the top scale indicates resistance readings.
Note figure A.7.
Figure A.7: Multimeter ohms (resistance) scale
When the range switch is in the R × 1 position, the resistance reading is referenced to the
scale numbers. When the range switch is in the R × 100 position, the scale numbers must be
mentally multiplied by 100. When the range switch is in the R × 1 000 position, the scale
numbers must be mentally multiplied by 1 000 etc.
Before any resistance readings are taken, a calibration procedure must be followed. The
ohmmeter section of the multimeter applies a test voltage (from 1.5 to 22 volts) across a
component whose resistance is to be measured. The meter then indicates the test current that
is drawn in terms of ohms units.
Since the multimeter’s battery voltage decreases with use and time, the zero-adjust control
must be adjusted to bring the needle to the zero point on the ohms scale when the test leads
are shorted together. This calibration procedure must be done when first using the multimeter
for resistance measurements and whenever the resistance range position is changed, i.e. R × 1
range would be calibrated separately from the R × 100 range etc.
When the zero-adjust control is turned to its maximum position and the needle will not reach
zero on the ohms scale, the internal battery should be replaced.
Volume (decibel) level measurements are made from the bottom scale of the meter and
readings are usually in dBm; i.e. dB reference is 1 mW into 600 ohm. The multimeter A.C.
ranges are used in conjunction with a decibel conversion graph or table supplied by the
manufacturer to enable its use over an extended range of impedances.