Electric Circuits
TECH 101
Lab. Assignments
Winter 2014
Print Full Name………………………………
Prepared by David Lloyd (Rev. Nov. 2013)
Stop
Read and heed the Lab Safety precautions and rules listed below!
Caution
Must be used at all times in the Lab!
Go
Ahead and complete the Lab exercises after you have read the rules!
1. No food or drink allowed in the Lab.
2. No horse-play or practical jokes.
3. No running.
4. Report all accidents to the person in charge of the Lab and seek medical
assistance if required. The emergency telephone extension number is 4000,
or dial 911 to get the local emergency services.
5. Note the location of the power bar off switches. These switches will remove
electrical power from the benches. Lab lighting will not be affected.
6. If you observe someone in the process of receiving an electrical shock:
•
Do NOT touch them.
•
Immediately turn off the bench power at the power bar.
• Determine if the victim is conscious. If unconscious, determine if the victim
is breathing and/or has a pulse.
• If the victim is not breathing and/or has no pulse, immediately summon help.
If qualified, begin Artificial Respiration/CPR procedures.
7. Be aware of additional hazards/precautions relating to specific processes or
equipment. Read and comply with, all warning labels or notices.
2
Electric Circuits - TECH 101
General Information
Note: Attendance in the lab at the timetabled period is mandatory. Completion deadlines
are 1 week from the lab’s scheduled date. Any lab not completed in the scheduled time
or missed for legitimate reasons may be made up within that one week in one of the
many ‘Open Labs’. Most of the Open Labs have all the required electronic equipment
plus the necessary software installed on the computers. A verifying signature from a
teacher is required. This is a concession and cannot be used as an excuse not to attend
the regularly scheduled lab classes. After the one week grace period, any missed labs
will not be accepted. Under no circumstances is it permissible to hand in all labs for
grading during the final two weeks of the semester.
It is very important that you do not treat the EWB labs as exercises in keyboarding. Each
exercise is an experiment in electronics and as such you are expected to understand the
concepts behind it. Merely inserting and moving objects on a monitor screen or blindly
entering numbers into a spreadsheet is not a valid learning experiences. Do not expect
your work to be signed off as complete unless you have answered the questions, can
explain the answers in electronic terms and comprehend the objectives and conclusions
of each lab.
All labs are an integral part of the Introductory Analog Electronics course and completing
each lab, by the deadline, is a requirement for passing the laboratory portion of the
course. Failure to complete labs can result in a failing grade for that portion of the
course.
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Lab Exercise No.1
Introduction to the Lab
Part 1 HCNET login
Using the computer at your workstation, verify that you can login to Humber College’s
HCNET computer system.
If this is your first login to HCNET follow these instructions: Your username is your 8
character student user id on your timetable and your initial password is your 9 digit
Humber College student number. For the first login you must place a p- before the 9
digit Humber College student number.
You will be required to change your password the first time you login.
Part 2 Lab Handouts
Do you have copies of both lab handouts?
Yes/No
Is your name on the cover of both copies of the lab materials?
Yes/No
Is the name of your instructor on the cover page ?
Yes/No
Part 3 Electronic Lab Introduction
On the bench in front of you there are four pieces of standard lab equipment. Locate
and identify them.
DC Power Supply
Located? Yes/No
Digital Multimeter
Located? Yes/No
Function Generator
Located? Yes/No
Oscilloscope
Located? Yes/No
Part 4 Keeping lab Results
Recorded Data must have units
Most of the observations that you will make and record during this semester will be
numerical data as a result of measurements and calculations.
When recording numerical data, appropriate units for that data must be recorded also.
Failure to comply with this requirement, will likely result in your having to redo the
material or a loss of marks when the work is graded.
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Lab Exercise No. 2
Resistors and Resistance Measurement
Objective:
To identify commercial resistor values using the resistor colour code and to verify those
values by measurements with multi-meters.
Introduction:
The Resistor Color Code
The nominal value of a resistor can be read with
the help of the following colour band code table.
Your instructor will explain how to interpret the
table.
Colour Digit Value
Black
0
Brown
1
Red
2
Orange
3
Yellow
4
Green
5
Blue
6
Violet
7
Gray
8
White
9
Gold
Silver
No Colour
-
Multiplier
Tolerance
Reliability
1
10
+/- 1%
1%
100
+/- 2%
0.1%
1000
0.01%
10,000
0.001%
100,000
+/- 0.5%
1,000,000
+/- 0.25%
10,000,000
+/- 0.1%
+/- 0.05%
0.1
+/- 5%
0.01
+/- 10%
+/- 20%
Helpful Web site:
http://www.samengstrom.com/nxl/3660/4_band_resistor_color_code_page.en.html
Four Band Code
The first and second bands represent the significant digits, the third band the "Multiplier"
or number of zeros. The fourth band is the "Tolerance" in percent. The fifth band is
“Reliability”, representing an anticipated failure rate over a given number of hours (say
1,000) of operation. (Manufacturers may use their own colours for the reliability band).
Five or Six Band Code
Some resistors have an extra band to determine the significant digits. In this case the
first 3 bands are the significant digit bands, the 4th band is the multiplier or number of
zeros, the 5th band is the tolerance band, and the 6th band would be the "Reliability"
band.
Six band example: A 1 MΩ resistor with a tolerance of ±2% and a reliability of 1 %
would be:
Brown, Black, Black, Yellow, Red, Brown
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Measurement of Resistance
Three instrument types are available for measuring resistance. The two most common
ones are the Analog (VOM) and Digital (DMM or DVM) multi-meters. The analog is
usually less precise and requires slightly more work to use than the digital version but is
able to perform simple continuity checks or monitoring changes. We will focus on using
the DMM.
Digital Multimeter (DMM or DVM)
This is a multi-function meter. Digital meters can be purchased for as little as $20 or as
much as hundreds of dollars.
Press the power button on and the kΩ selector button. Plug a red lead into the meter’s
red ‘V/Ohm’ socket and black lead into the black ‘Com’ socket. Connect the leads one to
each end of a resistor. Some digital meters are auto-ranging, so it is just a matter of
taking the reading. Other digital meters require that an appropriate scale be chosen. If
the resistor value can not be guessed at, start at the highest scale and reduce scales
until you have the lowest scale without the display indicating the scale is too low. Each
lower scale will give you more significant figures (greater precision) in your
measurement. An open circuit or out of range ‘error’ value is usually indicated by a " 1 "
or flashing “0’s”.
Lab Instructions
Equipment:
1. Digital Multimeter, Battery Leads, Resistors from Parts Kit plus a 100 kΩ ±1%
resistor.
Procedure: Measurement of Resistance
1. After consulting the colour code above, record in the ‘Results - Table 1’ the colour
codes for the resistors shown.
2. Find these resistors in your lab kit. These resistors will likely be a ±5% tolerance.
Also obtain a 100 kΩ ±1% resistor from the parts-crib.
3. For all the resistors above, including the 1% 100 kΩ, complete the "Tolerance" and
"Resistor Range" columns in Table 1 using the example for the 180 Ω resistor.
Results: Table 1
Resistor
180 Ω
56 Ω
330 Ω
Colour Code
(Example) Brown Grey Brown Gold
1000 Ω
4.7 kΩ
68 kΩ
100 kΩ
100 kΩ
Tol %
+/- 5%
±1 %
8
Tol +/+/- 9 Ω
Range Ω
171 – 189 Ω
Note: The Tol +/-Ω figure will be calculated as the tolerance % of the nominal resistance.
e.g.
5% of 180 Ω is 9 Ω. The Range Ω figure is the nominal resistance minus and plus 9 Ω. e.g. 180 9 = 171 and 180 + 9 =189 therefore the range is 171 Ω to 189 Ω.
4. Measure the resistance value of each of the selected resistors using the digital multimeter (DVM) and record the values. Record the measured values in the Table 2.
Table 2
Resistor
180 Ω
56 Ω
330 Ω
DVM Measurement
(Example) 181 Ω
1000 Ω
4.7 kΩ
68 kΩ
100 kΩ
100 kΩ ± 1%
Procedure: Measurement of Open and Short Circuits
1. Plug a Red and Black leads into the V-Ω and COM terminals on the DVM. Make
sure that these 2 leads are not joined at the other end. This simulates an Open
circuit that might occur if the wires were broken or not connected.
What does the meter show in its display? ________________
What equivalent resistance (0 Ω or infinite Ω) is represented by the disconnected wires?
Pick One
Does this resistance represent an Open Circuit of a Short Circuit? Pick One
If the wires represented a switch, would the switch be Open or Closed? ___________
2.
Connect the ends of the wires together.
What does the meter display now? ________________
What equivalent resistance (0Ω or infinite Ω) is represented by the connected wires?
Pick One
Does this resistance represent an Open Circuit of a Short Circuit? Pick One
If the wires represented a switch, would the switch be Open or Closed? ___________
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QUESTIONS
1. Give the colour codes for each of the following (3 band system):
1.5 MΩ ±5%
………………………………………
6.8 kΩ ±10%
………………………………………
470 kΩ ±5%
………………………………………
2. Identify the resistors whose color codes are:
Brown Red Black Silver,
………………………..
Brown Red Yellow Gold,
……………………….
3. A technician measures the resistance of an electrical fuse and the meter reads 0Ω.
Is the fuse Good or Bad?
4. A technician measures the resistance of long length of wire and the meter gives an
Open circuit indication. Is the wire Continuous or Broken?
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
10
Date …………………………..
Lab Exercise No. 3
Measuring Voltage and Current
Objective:
To verify Ohm's Law for resistive circuits.
To gain experience in the measurement of Voltage and Current.
Equipment:
1. Analog Multi-meter
2. Digital Multi-meter and Bench Power Supply
3. Meter/Power Leads and Resistors from Student Lab Kit
Preliminary Information – How to Measure Voltage and Current
To measure a voltage drop across a component the component must be connected to a
power supply and the voltmeter must be connected in parallel or across the component
as shown in fig 1.
+Terminal
Break the circuit at this
Connect the meter
across the
component.
+
DC
Power
Supply
point and insert meter
across the break.
+Terminal
Red
Lead
V
A
Black
Lead
-
DC
Power
Supply
- Black
Lead
-Terminal
Red
Lead
+
fig 1.
-Terminal
fig. 2
Measuring current is more dangerous (to the
meter) than measuring voltage because the meter is acting as a short circuit with
basically zero resistance. If the meter is set to measure current and you accidentally
connect the meter as if to measure voltage (even momentarily), you will blow an internal
fuse in the meter and possibly destroy one of the meter’s internal resistors.
To measure current the component must be connected to a power supply and then the
circuit must be broken (open circuited) and the ammeter connected to each end of the
break (in series with the rest of the circuit) as shown in fig 2.
Lab Procedure – Starts here
1. In this lab we will be measuring voltage and current simultaneously using both the
analog meter (to measure voltage) and the digital meter (to measure current). From
your lab kit select a 1 kΩ resistor and mount it on a breadboard. Ensuring the power
supply is OFF and using the appropriate leads connect the DC power supply, resistor
and meters as shown in fig 3 on the following page.
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2. Be sure that the ‘voltage’ control
-
+
knob is turned to zero (fully
Black
Red
Com
2A
counter-clockwise),
and
the
terminal
terminal
‘current’ control knob is 1/3 of a
+Terminal
turn from the fully counter-clock
A
wise. This knob controls the
DC
Digital meter
amount of current the power
Power
set to mA / 20
supply allows before turning off the
Supply
range
voltage - a safety feature designed
to protect the power supply and
any
components
or
device
connected to it. If a circuit contains
-Terminal
fig 3.
a ‘short circuit’ the limiting circuitry
in the power supply shuts off the
voltage to prevent the current from increasing and burning out the supply or items
connected to it. Set the analog voltmeter to the DCV 10 range and the digital meter
to the mA /20 range. (Be sure the connection is to the Red 2A socket and not to the
top Red V/ Ω s ocke t
3. Turn the DC power supply ON and adjust voltage control until the analog voltmeter
reads 2 Volts (do not use the small meter on the power supply, it is not accurate).
The digital current meter should now be reading the circuit current in mA
(approximately 2mA). Record this value as IMEASURED in the 2V row of the 1000 Ω
result table below.
4. Next, we are going to continue the measurements and see if a normal resistor is a
"linear" component. Measure the voltage drop across, and the current through the
resistor for each power supply setting of 4, 6, 8 and 10V. Record all of these
measurements in the appropriate rows of the 1000 Ω results table below.
5. Re-arrange the expression for Ohm's Law (V = I*R) and calculate the theoretical
circuit current (I) in each case. Record these values as ICALC in the same result table.
6. Turn the power OFF. Remove the 1kΩ resistor and repeat steps 3 to 5 above with a
390 Ω resistor connected.
RESULTS Table 1
VR
0V
2V
4V
6V
8V
7.
10V
1000 Ω
IMEASURED
ICALC
VR
0V
2V
4V
6V
8V
10V
12
390 Ω
IMEASURED
ICALC
+
Red
terminal
V
Analog
meter
DCV 10
range
Black
Com
terminal
8. Plot graphs of I (measured resistor current) versus V (resistor voltage). Plot the
results for both resistors on the same graph. Scale the current axis to the maximum
value seen as Table 1
Graph of Current vs Voltage
I (ma)
2
4
6
8
10
V(volts)
Now we are going to keep the voltage constant and change the resistance.
9. Check that the supply voltage is still set to 10 Volts and measure the current through
the 1000 Ω resistor one more time. Switch the supply off and replace the resistor
with a 820 Ω value. Turn the supply back on and measure the current as before.
Record this value as IMEASURED in Table 2 below. Calculate the current values using
Ohms’ law.
10. Repeat step 9 for R = 680 Ω, 470 Ω and 270 Ω ohms without changing the power
supply voltage and record these values in the same table below.
11. Plot a second graph of I versus R for the fixed 10 Volts results above.
Results Table 2
Resistor
1000 Ω
820 Ω
680 Ω
470 Ω
270 Ω
IMEASURED
ICALCULATED
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Graph of Current vs Resistance
I (ma)
200
400
600
800
1000 Resistance (Ω)
QUESTIONS
1. Did the resistors that you used in parts 1 to 7 above obey Ohm's Law?
Why?
2. In your own words describe the relationship between circuit current and resistance
when voltage is constant.
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
14
Date …………………………..
Lab Exercise No. 4
Series Resistive Circuits
Objective:
To study the voltages and currents in series and parallel circuits and to gain skills in their
measurement.
To verify Ohms Law, Kirchoff's Voltage law and the laws of series circuits.
Equipment:
1. D.C. Power Supply and Digital Multi-meter
2. Resistors from Student Lab Kit
Procedure Part 1: Series Circuits
1. Construct the circuit shown below on a breadboard and adjust the power supply
voltage (Vsupply) to be as close to 10 volts as possible as measured by the DVM.
2. Calculate each voltage drop (V1,V2 & V3) and record the values below. Hint: Find RT,
IT and then use Ohm’s Law to find each voltage drop.
3. Measure the voltage drop (V1,V2 & V3) across each of the resistors.
Do the
measurements agree with the calculations?
4. Add the voltages (V1 + V2 + V3). Kirchhoff's Voltage Law (KVL) says that this sum
should equal the applied voltage, (VSUPPLY). Do the measured and calculated values
compare.
Calculated
R1
R2
R3
8.2K
3.3K
1.5K
Measured
V1 =
V1 =
V2 =
V2 =
V3 =
V3 =
VTOTAL =
VTOTAL =
VSUPPLY =
VSUPPLY =
Variable
DC Power Supply
Set to 10V
5. Use the same technique to measure the circuit current as used in previous labs.
First, turn off the power. Break the circuit at any point. Set the meter to a high current
range and insert it at the break point. Check that the lead polarity and the meter
ranges are correct and then switch the power back on. Reduce the meter range as
necessary and read the current. Record this value as IT.measurment below.
IT,measurement =
Now we will measure current in a different way - indirectly. Put all the wiring back to the
way it was, i.e. close any circuit wiring breaks.
15
6. We can now measure the current using the “Indirect method”. From the previous
table of measured voltages, determine the measured values of current using Ohm’s
Law. This is found by dividing the measured voltage drop for one of the resistors by
the value of the resistor (Ohm’s Law says I = V/R). Record the results in the Table
Vmeasured (recopy from previous table)
I measured
VR1 =
IR1 =
VR2 =
IR2 =
VR3 =
IR3 =
The currents you have measured in this manner should agree very closely with the
current measured in step 5. Comment as to the accuracy of this comparison.
7. This "indirect" measurement technique is very convenient if components are soldered
into a printed circuit board and the circuit cannot easily be broken. Use it for all future
current measurements unless told otherwise.
8. Find RTotal using the total of the actual values of the three resistors (R1 + R2 + R3).
RTotal ________________
9. Using Ohm’s law, calculate the theoretical value of the total current (ICalc = VSupply/RTotal).
Record this as ICALC. Compare this to your measured values and comment on the
comparison.
ICALC = ___________________
Now find the total resistance RTOTAL in 2 additional ways.
1. From Ohm’s Law
RTotal = 10V/ITotal, meas
2. Disconnect the leads from your circuit going to the power supply and plug them
directly into DVM set to Ohms scale and measure RTotal .
Enter the three values in the table
RTotal,Calc Calculated
RTotal,Meas
Ohms Law
RTotal,Meas
Ohmmeter
Questions
1. Which resistor had the largest voltage across it - the largest or the smallest?
2. Which resistor had the largest amount of current flow through it - the largest or the
smallest?
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Procedure Part 2: Introduction to Electronic Work Bench
Note: All work done in EWB is done individually not in groups
Objective:
To become familiar with the electronics simulation package EWB (Electronic Work
Bench), its menus, parts bins, functions and applications.
1. On a computer with EWB installed, open the application by clicking on the icon (if
present on the desktop), or using the Start, Programs, EWB functions.
2. You screen should have the following menu bar and function buttons (or very similar)
above a large blank work area.
3. The Menu Bar. The File menu offers the usual new, open, close, save, and print options.
The Edit menu the cut, copy, paste, delete options. The Circuit menu allows
manipulation of the circuit and components by rotating, flipping, zooming and setting
oions and restrictions. This menu will be used later in the lab.
4. Function Buttons. Below the menu bar are the function buttons that provide many of the
options contained within the menus. Slowly passing the mouse pointer over each one in
turn will display their function. The first 7 (starting from the left) are the familiar New,
Open, Save, Print, Cut, Copy and Paste found in most applications today. The next three
with the shaded triangles are Rotate, Flip Horizontal and Flip Vertical from the Circuit
menu.
5. The bottom row of buttons are the ‘Parts Bins’ containing all the components and
equipment required to simulate a complete electronic circuit or device.
Put the mouse pointer on each one in turn to see the name of each ‘Bin’,
and click on the button to open the bin and display the contents. Close
any bin that is open.
6. To create a circuit, parts from the bins must be dragged to the work area one at a time.
A simple circuit will be assembled as
follows:
a)
b)
c)
Click on the Sources bin
From the sources bin click, hold and drag to the work
area, one each of the Ground and Battery symbols.
Open the Basic bin.
d) Drag 3 Resistors on to the work area.
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e) Finally open the Indicators bin and drag a Voltmeter on to the work area.
The work area should now look like the diagram at below right.
7. Try highlighting any of the
components in the work area
by clicking on them. Notice that
the cursor changes to a hand
as you near the item and when
selected the item changes to
red. Clicking outside an object
will deselect it. When you click,
hold and drag the item, it
moves.
8. Click on the far right Resistor and while it is highlighted, click on the Rotate button in the
upper Function Button row. The resistor should rotate 90° to the vertical position.
9. Double click on the same resistor (which should now be vertical) and a Properties box,
with several Tabs opens. Click on the Label tab and in the upper box type R3. Click on
the Value tab and in the value box change the 1 to 1.5. (This is actually 1.5 k Ohms or
1500 Ohms). Click on OK and see the results of the changes. Repeat this process and
change the other 2 resistors to 3.3Ωk and 8.2 kΩ to match the values in the Part 1
circuit. Change the battery voltage to 10 V.
10. The components are now ready to be connected to each other, but first move the
Voltmeter out of the way by dragging it down and to the right. To connect the ground to
the battery proceed as follows:
• First click on the ground symbol to highlight it, then click, hold and drag the
symbol until it is directly beneath but not too close to the battery symbol.
• Move the mouse pointer to the very top of the symbol until a round black dot
appears.
• Click on the black dot and drag it towards the bottom of
the battery symbol.
• When a round black dot appears at the bottom of the
battery, release the mouse button and a line should now
remain, connecting the two together, as shown at right.
• Continue, connecting the top of the battery to the first
resistor, first resistor to the second resistor and the second resistor to the third
resistor to the middle of the line connecting the ground to the battery.
Your circuit should now look like this.
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11. Finally, move the Voltmeter to the right of R3 and connect it’s upper terminal to the
junction of the two resistors, and it’s lower terminal to the bottom of R3.
12. Click on the “1” of the main On/Off switch in the top right hand corner of the screen.
13. The reading on the meter will settle at a steady value. Record this value V3 =
…………… Volts. Click on the “0” of the On/Off switch in the top right corner.
14. Get another Voltmeter from the parts bin and connect it across the R2 resistor (top
meter terminal to left of resistor, bottom to the right). Switch the circuit on and record
this 2ND reading as V2 = ………..…… Volts. Click on the “0” of the On/Off switch.
15. Get a 3rd meter so that you can measure the voltage across R1.
16. Record the EWB measurements in the table. Are they similar to those made with
actual lab equipment in Part 1?
V1
V2
V3
17. Insert a current meter to measure the total
circuit current.
ITotal,measurement,EWB =
______________
How does this measurement compare with the
values measured in Part 1 of the lab.
18. Before continuing with the lab, you should save 1.
the circuit above to a USB memory stick, or to
your own H drive. Save the circuit as TECH101Lab4.ewb. Create a folder for all
files for this course.
Electronic Work Bench is a good vehicle for producing circuit diagrams for use in
technical documents such as lab reports. It is possible to copy/paste the circuit diagram
into word processing software.
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
19
Date …………………………..
20
Lab Exercise No. 5
Parallel Resistive Circuits
Procedure Part 1:
Parallel Circuits
1. Assemble the circuit at right, and set VSUPPLY
to 6 Volts as measured with the DVM.
Vsupply +
2. Using the DVM, measure the voltage across
R1, R2 and R3 and record the results below
right.
Is VR1 = VR2 = VR3
6V
'A'
-
R1
47k
R2
4.7k
Resistor
VR1
VR2
VR3
Voltage
YES/NO
What Law does this confirm?
3. Turn off the power, break the circuit at point ‘A’ and insert the DVM
set to measure current. Turn on the power and record the current
reading as ITOTAL
ITOTAL, meas = ……………………..
4. Break the circuit for each resistor and measure the individual branch currents.
Calculate IR1 (VR1/ R1) IR2 and IR3. Enter the results in the table on the following page.
Sum the two columns and enter this value as ISUM in the same table.
Measured
Calculated
IR1
IR2
IR3
ISUM
Does ISUM agree with ITOTAL from step 3 ?
…………
Should it agree? ………………..
What law does this
confirm?…………………….….……………
5. A measurement of RTOTAL1 is found as VTOTAL/ ITOTAL (use ITOTAL from step 3. above
and VTOTAL from step 2. above).
RTOTAL, meas 1 = ………………….
6. Disconnect the leads from the circuit at the power supply and plug them into the
DVM set to measure Resistance. Measure RTotal.
RTOTAL, meas 2 = ………………….
7. Calculate RTOTAL, Calc use your knowledge of calculating resistors in parallel
RTOTAL, Calc = ………………….
Do RTOTAL, meas 1 , RTOTAL, meas 2 and RTOTAL, Calc agree? ……………
21
R3
470
Questions:
1. Which resistor had the largest current flow through it? ……….………………………
2. Which resistor had the largest voltage across it? …………...….………………………
3. What are the resistance ratios for R1:R2…….…R2:R3…….… and R1:R3…….……
4. Are the current ratios IR2: IR1, IR3: IR2 and IR3: IR1 the same as the ratios of the
resistances? …………………….
5. Which is less RTOTAL or R3? …………….. Why? ……………………………….
Procedure Part 2: Parallel Circuits in Electronic Work Bench
Note: All work done in EWB is done individually not in groups
1. Using EWB, build the circuit from Part1 as shown in the diagram. Save the circuit as
TECH101Lab5.ewb.
2. Meter 1 is configured to measure the total circuit current (ITOTAL) and Meter 2
measures the current through R1. Activate the EWB circuit and measure and record
these currents. Move Meter 2 so that you can measure the current through R2 and then
move it again to measure the current through R3. Record the current values in the table
below.
ITOTAL
IR1
IR2
IR3
ISum
3. How do the results compare to those in Part 1? ………………………………………..
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
22
Date …………………………..
Lab Exercise No. 6
Series/Parallel Circuits
Objective:
To study resistance, voltages and currents in a complex series/parallel circuit and to gain
skill in measurements, calculations and fault analysis.
Equipment:
1. D.C. Power Supply and Digital Multi-meter
2. Resistors from Student Lab Kit
Procedure Part 1:
Calculation/measurement
1. Construct the circuit shown at right and
R1
adjust the power supply voltage (Vsupply) to
exactly 10 volts as measured on the DVM.
2. Using the DVM, measure the voltage drop
across each of the resistors R1 to R6 and
record them in the table below right.
100
R2
270
Vsup.
10V
3. Using the voltage across R6 determine a
R3
330
R4
560
R5
5.6k
1k
measurement of the total current (indirect
current measurement technique)
R6
ITOTAL,1 = ……………….
V1
4. Calculate
RTOTAL
from
V2
V3
V4
V5
circuit
theory
RTOTAL = ………………………
5. Using this value of VSUPPLY and RTOTAL determine a second measurement of total
current
ITOTAL, 2 = ……………………….. Compare this value with the value in 3 above.
Do they agree? ……………………..… Should they agree? ………………………
6. Add V2 and V3
V2+3 = ……………. Compare this value with V4 and V5 from
the table above. Is they the same? …………… Should they be the same? ………….
What law of parallel circuits does this confirm?
23
V6
7. Using the voltage across R4 or R5 as if they were a supply voltage VSUPPLY for R2 and
R3 calculate the theoretical voltage across R2 and R3 using the Voltage Divider
Formula.
Calculated V2 = ……………..………
Calculated V3 = ……..…….……………..
Compare these values with the measured values in the table.
Measured V2 = ……….….……..…..
Measured V3 = ……………..…….……..…
Are they the same? ……………….
Is this correct? ……………………….……..
Part 2: Fault Diagnosis – Open Circuits.
1. If R2 went ‘open circuit’ (lift one end of R2) predict whether ITOTAL would go UP or
DOWN? (Circle one).
2. Measure the voltage across R6.
V6 = ……………...
What is ITOTAL now? (Use Ohms Law)
ITOTAL = …………………..
Is this value higher or lower than the original ITOTAL? …………….
3. Measure the voltage drop across R1
V1 = ………… Using this voltage and the voltage across R6 in step 2 calculate the
voltage across R4 and R5
V4, Calc = …………….…. V5, Calc = …………….…...
4. Measure the voltage across R4 and R5
V4, Meas = …….
V5, Meas = ……….. Do these values agree with the calculations? ..
What series circuit law have you just confirmed?
5. Re-connect R2
6. If R1 went ‘open circuit’ would ITOTAL go UP or DOWN? (Circle one).
7. Disconnect R1, measure the voltage across R6
What is ITOTAL now?
V6 = ……….…..
ITOTAL = …………………..
Is this value higher or lower than ITOTAL1?…………….
Explain:
8. Reconnect R1.
24
Part 3: Fault Diagnosis – Short Circuits.
1. If R4 became a ‘short circuit’ (connect a wire from end of R4 to the other) predict
whether ITOTAL would go UP or DOWN? (Circle one).
2. Place a short circuit across R4 and measure the voltage across R6.
V6 = …………….. What is ITOTAL now ?
ITOTAL = …………...
Is this value higher or lower than the original ITOTAL?…………….
Predict the voltage across R2, R3 and R5 while R4 is shorted:
Predicted V2 = ……….
Predicted V3 = …………
Predicted V5 = …………
3. Measure V2, V3 and V5
Measured V2 = ……….. Measured V3 = ……..……
Measured V5 = ……….…
Do the predicted and measured values agree? ……………………………
Explain:
4. Remove the short circuit from R4
Part 4: Measuring RTotal
5. Disconnect the red and black leads from the power supply and connect them directly
to the DVM and measure the total resistance of the circuit. Compare this value with
the calculated value on the first page of this lab.
Measured RTOTAL = ……………. Calculated RTOTAL = …………….
Do the two values agree? ……………….
6. Calculate the percentage difference between the measured and calculated values.
% Difference = ………………………………..
What is the likely cause of this difference?
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
25
Date …………………………..
26
Lab Exercise No. 7
Voltage Divider and Meter Loading
Procedure Part 1:
Voltage Divider
1. Build the voltage divider circuit as shown. Calculate (using voltage
divider) and measure the voltage at Vx with respect to ground with a
DVM.
Show your calculation work here.
Vx, calc = ……………
Do the calculated
…………………
Vx, meas = …………
and
measured
values
agree?
2. For the circuit shown at right, calculate and measure
the voltages shown in the table.
Calculated
Measured
VAB
VBC
VBD
Do the calculated and measured values agree?
…………………
3. Design a two resistor voltage divider using resistors from your kit to give
a + 5V output voltage (within a ± 5% error) from a 9V power source.
Build the circuit and verify that it works.
What is the ± 5% range of acceptable voltages for VX?
……………V to …………… V
What are your values for R1 ……..….. R2 …………….. ?
What is your actual measured value of VX? …………………
Describe a useful purpose for this circuit.
27
Procedure Part 2:
Voltmeter Loading Errors
1. Build the circuit shown at right.
2. What is the expected voltage
VA,exp?
V A ,exp ___________
3. Measure the voltage VA with a
DVM
V A,meas ____________
Meter Resistance
The meter resistance of a DVM is a constant 10 MΩ on all scales.
4. Using voltage divider, calculate the voltage V taking into account that the Digital
meter with a meter resistance of 10 MΩ i s connected to the circuit. Hint: the 10 kΩ
resistor is in parallel with the 10 MΩ meter resistance.
5. V A calc,
____________
6. Change both of the 10 Ωk resistors to 2.2
calculation.
7. V A meas __________
MΩ.
Repeat the measurement and
V A calc ___________
Question
1. Calculate the percent error in VA caused by the DVM in each case.
10 kΩ circuit Percent error = _______________________
2.2 MΩ circuit Percent error = _______________________
% error = (V A exp - V A meas ) / V A exp x 100%
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
28
Date …………………………..
Lab Exercise No. 8
Variable Resistors and Power
Objective:
To study the characteristics of linear and log (tapered) variable resistors.
To apply voltage divider rules to variable and fixed resistors.
Equipment:
1. 10 kΩ linear pot, 10 kΩ Log (tapered) pot.
2. Digital Multi-meter, Electronic parts kit.
Procedure
Part 1: Linear Potentiometer
1. Obtain a 10 kΩ linear variable resistor (potentiometer, or just “pot”) and compare it to
the diagrams shown below. Be sure you understand the orientation and directions of
rotation. The "wiper" moves when the shaft is rotated.
2. With the shaft pointing toward you, turn the shaft to the full CW (clock-wise) position
and make a mark on the body of the variable resistor to indicate this point (as shown
below). Repeat this procedure by turning the shaft fully CCW (counter-clock-wise).
Mark the remaining area between CW and CCW as shown in the diagram below.
3. Using a DVM measure the three resistance values for each position (Resistance
from terminal 1 to 2, from terminal 2 to 3 & from terminal 1 to 3). Do not adjust the
’pot’ to the next setting until you have done all 3 measurements.
Linear Pot
Shaft
Position
R
1 to 2
R
2 to 3
R
1 to 3
Full CCW
1/4 turn
1/2 turn
3/4 turn
Full CW
4. Plot a graph of both the R1 to 2 and R2 to 3 values versus potentiometer setting.
Label each graph. Comment on the shape of the graph.
5. Repeat the steps above for the 10 kΩ Log (tapered) variable resistor. Enter the
results on the following page. (This type of resistor is common for audio system
volume controls).
29
Resistance (R1-2, and R2-3)
% Turn
Part 2: Log (Tapered) Pot.
Shaft
Position
R
1 to 2
R
2 to 3
R
1 to 3
Full CCW
1/4 turn
1/2 turn
3/4 turn
Full CW
Graphs of Resistance vs Turns (Log Pot). R1-2 and R2-3. Label each graph.
Resistance
30
Part 3: Voltage Divider Law
1. Connect the 10 kΩ linear variable resistor as shown. Connect the DVM to measure
the voltage from terminal 2 (wiper) to terminal 1 (ground). Be sure not to connect
terminal 2 (wiper) to ground or the +10V.
2. Gently turn the potentiometer from fully CCW to fully CW and observe the results on
the DVM.
What is the maximum voltage observed ?
VMAX = …………..
What is the minimum voltage observed ?
VMIN = …………..
3. Set the variable resistor to the 1/2 turn position and record the
voltage on the DVM in the table below.
4. Use the voltage divider formula to calculate the voltage from
terminal 2 to 1 based on the resistance values from the Linear
Pot table on the previous page. e.g. V at 1/2 turn = [10V/(R1
to 2 + R2 to 3)] * R1 to 2 . Record the value in the table below.
5. Record the measured and calculated voltages.
VMEAS
VCALC
V1/2 turn setting
6. Do the calculated and measured values compare? Yes /No
Part 4: Power in Resistors
1. From your kit find two resistors: a 100 Ω, ¼ watt and a 100 Ω 5 W. One at a time,
connect the resistors to +10 V DC using your bench power supply. Monitor carefully
the temperature of each resistor with your finger. Disconnect the 100 Ω, ¼ watt
resistor if it becomes too hot. Find the current from Ohms Law (I=V/R) and the
power (P=V I) dissipated in each resistor. Complete the following table.
R value
100Ω 1/4 W
100Ω 5 W
Voltage
Current
Part 5: Maximum Power Transfer in
Resistive Circuits
1. Build the circuit as shown. Use the DVM
to measure the voltage across RL.
31
Actual Power
Hot/ Warm/Cool?
2. Measure the voltage across RL and find the current through RL using Ohm’s law
(I=V/R).
3. Change RL to 2.2 kΩ and repeat the measurements. Repeat these measurements
for all of the values in the table shown.
4. Complete the table by calculating the power dissipated in RL (P=V x I) for each set of
measurements.
RL Value
4.7 kΩ
2.2 kΩ
1.0 kΩ
470 Ω
270 Ω
VL
IL (mA) – use Ohm’s law
PLoad (mW) (Power in RL)
5. Plot a graph of Load Power, PLoad (Y axis) versus RL value (X axis). Comment on the
shape of the graph.
PLoad
1k
2k
3k
4k
5k
Is there a value for RL where the load power in RL is a maximum? ……………….
What is this value for RL? ………………………..
Question
1. In your own words state the Maximum Power Transfer Theorem.
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
32
Date …………………………..
RL
Lab Exercise No. 9
Voltage Sources and Superposition
Objective: To investigate the characteristics of Ideal and Real voltage sources and the
principle of the Superposition Theorem.
Procedure: Part 1 – Ideal Voltage Source
1. Set the lab power supply on your bench to as close to 10 V as possible using the
DVM. Be sure that the current adjust knob on the power supply is set to mid-range.
Record this voltage as the open-circuit voltage VOC = …………………..
What is the source resistance for an ideal voltage source? RS = …………………..
What is the value of load resistor for an open circuit? RL =……………
2. Connect a 1 kΩ load resistor to the terminals of the power supply and measure the
voltage across the load resistor (called the loaded voltage) VLoad. Repeat this
measurement for all the resistor values in the table.
3. Caution: Do not use the 100Ω 1/8 or ¼ watt resistor in your kit.
Why? …………………………………………..
4. For each voltage determine the current in the resistor by Ohm’s Law.
5. Record the values in the table.
RLoad
1 kΩ
470 Ω
100 Ω, 5 Watt
50 Ω, 5 Watt
VLoad
ILoad
2. Comment on the results. What would the shape of a graph of VLoad vs ILoad look like?
4. With the 50 Ω resistor still connected, read the current value from the meter on the
DC power supply. Does it agree with the value from the table above? Turn the current
limiting knob slowly counterclockwise. What happens to the current and voltage values
of the power supply’s meters? What happened to the red LED indicator light?
Red LED indicator light turns
ON/OFF
The current adjusting knob …………….. the current value. (add the correct word).
33
Procedure: Part 2 – Real Voltage Source
1. Get a DC power adapter from the tool crib.
2. Record the output voltage and current ratings on the device
Output Voltage rating ________________
Output Current rating _______________
3. Plug the adapter in and measure the open-circuit voltage (no load attached) of the
DC adapter?
VLoad,OC = __________________
Does this measurement agree with the rated voltage for the adapter?
Yes/No
If Not why not?
4. Connect a 100 Ω 5 W resistor across the ends of the power adapter and measure
the loaded voltage. Calculate the current being drawn from the power adapter.
Repeat the measurement and calculation for a 50 Ω 5 W resistor. Record all the values
in the table.
Load value
Open circuit - ∞Ω
100 Ω 5 W
50 Ω 5 W
Load Voltage
Load Current
Plot a graph of Load Voltage vs Load Current.
Load voltage (V)
15
10
5
100
200
300
Load current (mA)
From the graph determine the load voltage at a load current of 300 mA.
34
Load Voltage = ______________
Procedure: Part 3 – Superposition Theorem
1. Connect the circuit shown using the dual source power supply on the lab bench. Be
sure that both buttons in the middle-center of the power supply are in the “out” position.
2. Measure the voltage across R3 and then determine the total current through R3 from
Ohm’s law.
VR3,Total = ……………………..
IR3, Total = …………………………
3. Remove the leads connecting DC Source 2 to the DC Power supply and join these
leads together – this is equivalent to replacing DC Source 2 with a short circuit.
4. Measure the voltage across R3 again and then determine the current through R3.
VR3 (due to DC Source 1) = ……………
IR3 (due to DC Source 1) = ………………
5. Reconnect DC Source 2 as it was before and now remove the leads connecting DC
Source 1 to the DC Power supply and join these leads together – this is equivalent to
replacing DC Source 1 with a short circuit.
6. Measure the voltage across R3 again and then determine the current through R3.
VR3 (due to DC Source 2) = ……………
IR3 (due to DC Source 2)= ………………
7. The total current in R3 (ISum) can be found by adding the contributions from DC
Source 1 and DC Source 2.
ISum = I (from DC Source 1) + I (from DC Source 2) = ……………………….
This value, ISum, should be the same as IR3, Total in step 2 above – is it?
35
Procedure: Part 4 - Reverse the DC Source 2 Polarity
1. Reconnect the leads for DC Source 1 to the power supply. Reverse the polarity of
DC Source 2 at the DC Power supply so that it is now -10 V.
2. Repeat the steps of Part 3. Some of the voltages current readings may be negative
values now.
VR3, Total = ……………………..
IR3, Total = …………………………
VR3 (due to DC Source 1) = ……………
IR3 (due to DC Source 1) = ………………
VR3 (due to DC Source 2) = …………
IR3 (due to DC Source 2)= …………
ISum = I (from DC Source 1) + I (from DC Source 2) = …………………………
Does this value of ISUM agree with the total current IR3, Total? ………………….
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
36
Date …………………………..
Lab Exercise No. 10
Thevenin’s Theorem
Objective: To use the concept of Thevenin’s Theorem to simplify a circuit and solve for
unknown voltages.
Introduction
A complex resistive series-parallel circuit can be difficult to analyze so the use of a
Thevenin Equivalent circuit can be helpful.
Procedure
1. Build the circuit shown at right. With the 1 kΩ load resistor connected measure the
loaded voltage between points A and B.
VLoad = ……………..
2. Disconnect the load resistor from the circuit as shown and measure the open-circuit
voltage, Vopen-cir, from point A to B.
Vopen-cir =
…………………
3. This open-circuit voltage, Vopen-cir, is also the Thevenin voltage, VTH, for the Thevenin
Equivalent Circuit shown.
VTH = ……………………
37
4. Calculate, from first principles, the Thevenin voltage, VTH, for the Thevenin
Equivalent Circuit. Show your work below.
VTH = ……………………
5. Disconnect the power leads to the circuit from the DC power supply and connect
them together. This simulates an Rsource = 0. Measure the total resistance of the
circuit by connecting an ohmmeter (DVM set to measure resistance) to points A and
B. This is the Thevenin resistance, RTH, for the Thevenin Equivalent Circuit.
RTH = ……………………….
6. Calculate, from first principles, the Thevenin resistance, RTH, for the Thevenin
Equivalent Circuit. Show your work below.
RTH = ……………………….
7. Build the Thevenin Equivalent Circuit. Use the nearest standard value in your kit for
RTH. Connect the load resistor and measure the loaded voltage between points A
and B.
Nearest standard value = …………
VLoad = ……………..
8. How does this value compare to what was measured in step 1? What is the percent
difference in the 2 measurements?
Percent difference = …………………………
9.
Now build the original and Thevenin Equivalent circuits in Electronic Workbench.
Verify that the load voltage is the same for each circuit.
VLoad, Original Cct = ……………..
VLoad, Thevenin Cct = ……………..
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
38
Date …………………………..
Lab Exercise No. 11
Oscilloscope and AC Waveforms
Objective:
To become familiar with the operation of the oscilloscope and function generator.
Equipment:
1. General Purpose Oscilloscope, Function Generator, Variable DC Power Supply
Initial Adjustment of Oscilloscope
Turn on the scope and wait for a trace. Press the CH1 (Channel 1) Menu button. On
the right side of the screen are the options for the CH1 menu display. By pressing the
appropriate button to the right of the screen set the following: Coupling to DC, Invert to
Off, BW Limit to Off, Voltage to 1X. Repeat these adjustments for Channel 2 if needed.
Repeated pressing of the CH1 or CH 2 menu buttons turns the CH1 or CH2 display On
and Off.
Part 1: DC Measurements using the Oscilloscope
1. On the CH 1 menu display, now set the CH1 Coupling mode to GND.
2. Turn the CH1 Vertical Position control knob until the scope trace appears in the
exact center of the screen. Now set the Coupling mode to DC. This sets the mid
screen position as the 0 V reference point used for determining if voltages are
positive or negative.
3. Adjust the CH1 vertical Volts/Div knob to 2 VOLTS/DIV. The setting is visible in the
bottom left corner of the screen.
4. Connect a Scope lead (coaxial cable) from the scope CH1 input to the + 5 V source
of the DC Power Supply as shown.
5. The scope face is ruled with vertical and
horizontal “hatched’ lines called Divisions.
There are 8 divisions vertically and 10
horizontally. Measure in divisions the
distance the trace moved UP on the
scope face from its original mid-screen
position. Multiply the number of divisions
by the Vertical Volts/Div setting (2 volts/div in this case).
6. Record this value below:
..............divisions times ...........Volts/division = ....................Volts.
7. Sketch the Voltage versus time display on the oscilloscope screen on the next page.
Record the VOLTS/DIV and SEC/DIV ‘scope settings in the box.
8. Reverse the red and black scope leads at the power supply and repeat the
measurement and drawing of the voltage waveform. Now the scope will display a
negative voltage relative to the 0 V reference of the scope and the trace on the
scope display will move DOWN.
39
9. Record the calculated voltage as negative.
.................divisions times ................Volts/division = ....................Volts.
+5 Volt sketch
-5 Volt sketch
Show the voltage levels – zero volts included – on the sketches.
Scope Settings
Chnl 1 (vertical) = ……….V/Div.
Horiz. Sweep Speed = ……..…Sec/Div
NOTE: In one of the steps above you connected the black ground lead of the scope to the positive
terminal of the power supply. This was safe, in this case, because the power supply's ground
terminal is an “isolated” or "floating ground" not a true "earth ground". In other cases (some
television sets, for example) it could be extremely dangerous to make this type of connection. If
another power supply uses an earth ground through the green lead of the power cord you could
generate a lot of current and smoke. Always be safe, check first.
Part 2: Waveform Measurements/ Function Generator SYNC or TTL Output
1. Return the oscilloscope to the starting point set of adjustments that you used above.
2. Connect the Function Generator SYNC or TTL output to the Scope CH1 input. Set
the function generator frequency to 1 kHz. Set CH1 Coupling input selector to DC.
NOTE: To get a ‘starting point’ waveform on the scope after changing the input
conditions, press the ‘AUTOSET’ button and wait a few seconds.
3. Adjust the Volts per division (V/div) to produce the largest vertical display without the
trace disappearing off the top or bottom of the screen (Not less than 2V/Div). Adjust
the Horizontal Timebase Control (Sec/div) to display about 2 complete cycles of the
signal waveform. Record both these settings in the appropriate box below.
40
4. Sketch the displayed square wave. Mark the following values on the sketch:
•
Max. positive voltage.
•
Minimum voltage.
•
One full cycle of waveform
•
0 V reference point.
Chnl 1 (vertical) = ……….V/Div.
Horiz. Sweep Speed = ……..…Sec/Div
Part 3: Function Generator Main Output
1. Set CH 1 of the scope to 1 volt/div and connect it to the main output (not TTL) of the
function generator. Set the function generator to give a 5 kHz Sine wave. Be sure the
scope is set to DC coupling. Adjust the amplitude until it fills about ¾ of the screen.
Adjust the frequency and observe its affect on the ‘scope. Return it to 5 kHz.
Repeat this for a triangular and square wave. Reset the amplitude back to fill approx
¾ of the screen each time.
2. Draw a representative sketch of each type of wave showing ‘scope settings, voltage
levels and the time for 1 cycle of the waveform. Mark the 0 volt point.
3. Measure the period T and frequency F.
Period time = …………..
Sine wave
F = ……………....
Triangular wave
Square wave
Chnl 1 (vertical) = ……….V/Div.
Horiz. Sweep Speed = ……..…Sec/Div
Part 4: DC Offset (Average Level)
Consult your teacher for an explanation of DC offset or average DC level.
1. Set the Ch 1 volts per division control to 1 volt/div and select GND for the input
coupling. Put the zero volt reference in the center of the screen and set the input
coupling back to DC. Connect a sine wave to Ch 1 at 5 kHz. Adjust the amplitude to
give a 2 V peak to peak sine wave (1Div up and 1Div down from the center of the
41
screen). Adjust the DC Offset of the waveform until it has a DC level of +1 volt (1
Div). Sketch this below.
2. Re-adjust the DC Offset control to give an overall DC level of -1 volt for the sine
wave. Make a sketch, label both sketches and include the scope settings.
Mark on the sketches the + 2 and -2 V voltage levels, and the 0 V point.
3. While the –1v DC offset is still present, change the coupling to AC, what happened?
CH 1 = ……….….. V/Div
Horizontal = ……….Sec/Div
Questions:
1. What is normally measured by the vertical deflection on the 'scope?
2. What is normally measured by the horizontal deflection?
3. What is the maximum CH 1 Volts/Div setting? _____________
4. From your answer to Q 3, what is the maximum voltage that the scope can display?
______________
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
42
Date …………………………..
Lab Exercise No. 12
A. C. Waveforms and Function Generator
Objective:
To gain a basic understanding of quantities used to describe AC waveforms.
Equipment:
1. Function Generator, Oscilloscope, DVM
2. Parts kit
3. 2 Scope leads, 2 x 100 Ω Resistors, 1 set Meter Leads
Procedure:
1. Using a scope lead connect the function generator Main output to channel 1 of the
oscilloscope as shown in the diagram below. Turn on the scope and adjust the
settings as follows:
•
•
•
•
Select Channel 1 (Press CH1 Menu button).
Set input coupling to DC
Set time base (Horiz - Sec/Div) to 0.1 mSec/div (100µSec/Div).
Set Channel 1 amplitude (Vert - Volts/Div) to 1 volt/div (Ensure Probe is set to X1).
2. Press CH 1 Menu button and set the input-coupling mode to GND. Move the trace to
the centre of the screen with the Vertical Position Control. Set to DC coupling mode.
The centre of the scope screen is now the 0 Volt reference point.
3. Turn on the function generator and adjust it as follows:
• Wave form type - select Sine wave
• Frequency - set to 2 kHz
• Adjust generator output/amplitude to give exactly 6 divisions on the scope so that the
voltage is 6 VPk-Pk
4. On the following page, sketch the waveform, record the scope settings and measure
VPk and VPk-Pk.
VPk-Pk = ____ divs * _____ V per Div. =
43
_____ Volts
VPk = _____ divs * _____ V per Div. =
_______ Volts
Calculate the RMS Voltage as:
VRMS = VPK /√2 = ……………………
5. Connect a Digital Voltmeter, set to AC volts, to
measure the function generator output voltage record the reading. This will be the RMS output
voltage. Do not adjust the function generator in any
manner.
Chnl 1 (vertical) = ……….V/Div.
Horiz. Sweep Speed = ……..…Sec/Div
VRMS = …………..
Compare this measured value with that calculated above in step 4
Calculate the % difference between these two readings =.............................%
6. Set the DVM to DC volts and repeat the measurement. You are measuring the
average value (DC voltage) of the sine wave.
What is the measured DC voltage?
What value should you get?
VDC AVG = ……………..
…………
8. Set the DC Offset control so that the DC voltmeter reads exactly +1V. Change the DVM
to AC volts and measure the RMS value of the waveform: VRMS = .……………..
Did this DC offset affect the RMS voltage of the sine wave?...................... (compare to
step 6).
9. Set the function generator DC Offset control until the DC offset level is back to 0 volts.
Connect the Red leads of the function generator and the scope to one end of a 100Ω
resistor and the two Black leads to the other end of the resistor. The resistor is now
acting as a 100 Ω “load” drawing “load current” from the function generator. Do not
adjust the amplitude or frequency of the function generator.
10. Re-measure the Pk-Pk, and Pk voltages on the scope and re-calculate the RMS
voltage.
VPk- Pk =………………
VPK =…………
VRMS =……………
The measurements in step 10 above are the "loaded" output voltages of the function
generator with “load current” flowing. The voltages you measured in step 4 above were
"open circuit", no “load”, no current flow readings. Which case, "loaded" or "open circuit",
gives the least output voltage? ………………..…………………
11. A measurement of circuit current (indirect measurement) can be made by taking the
loaded VRMS of step 10 and dividing by the value of the load resistor (Ohms Law). Do
this and express your result in mA RMS.
IRMS =…………………………..
44
12. Add another 100 Ω resistor in parallel with the first one and repeat the measurements
of step 10.
Total load resistance is now ……..…Ω. Will the current go up or down? ………..
VP- P = ………...
VPK =…….……
VRMS = ……….…
IRMS = ……...…
Using the scope measure the period of the sine wave and from this value determine the
frequency. Compare this measurement to the setting of the function generator.
Period Time T = _______divs * _________secs/div = ____________secs.
Freq = 1/T = ___________Hz.
Func.Gen setting = __________Hz
Questions:
1. Does the function generator behave as an Ideal or Real voltage source?
2. Convert the following to RMS units
a) 35 mA Pk = _______
b) 125 VP- P = _________
3. Convert the following to Pk units
a) 175 µA RMS = __________
b) 4.25 V P-P = ___________
4. Convert the following to Pk-Pk units
a) 175 µA RMS = _________
b) 1.33 mV RMS = ________
5. The function generator can be modelled as a voltage source in series with an internal
source resistance. Using the values you connected in steps 10 and 11 calculate the
value of this source resistance and draw the equivalent circuit. Show your work.
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
45
Date …………………………..
46
Lab Exercise 13
Capacitors in Electronic Circuits
Objective:
To gain a basic understanding of capacitors in electronic circuits and to
verify that they block DC, pass AC and take time to charge and discharge.
Equipment:
1. Function Generator, Oscilloscope, Parts Kit
Procedure Part 1: Coupling/Blocking Capacitor
1. Set up the circuit at right. Calculate the expected voltages at Points
A and B with respect to ground.
VA CALC = …….……..… VB CALC = ………..….….
Measure these voltages (with respect to ground).
VA,MEAS = ……………
VB,MEAS = …………….
2. Connect Point A to B with a piece of wire. Calculate and measure
VA and VB again.
VA CALC = ………. VB CALC = ………….
VA,MEAS = ……………
VB,MEAS = …………….
Waveform
at Point A
3. Remove the wire and connect a 1µF capacitor
between Points A and B. Be sure to connect the
capacitor with the correct polarity. (positive lead of C to
most positive voltage).
4. Re-measure VA and VB Comment on the differences
5. between these readings and the readings of step 2.
VA,MEAS = ……………
VB,MEAS = …………….
5. Connect a function generator set to about 2 VP-P sine
wave at 1 kHz to Point A. Use AC coupling on the
scope. Connect the scope to point A. Draw the
voltage waveform at Point A. Now move the scope to
Point B and draw the waveform.
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Waveform
at Point B
Answer the questions on the following page:
a) Did directly connecting points A and B with a piece of wire change the DC voltages VA
or VB from the values measured in step 1?
Yes/No
b) Did connecting Points A and B with a capacitor change the DC voltages VA and VB from
the values in step 1?
Yes/No
c) Did the capacitor allow the AC signal connected to Point A to pass to Point B?
Yes/No
Complete the following sentence:
A capacitor ……………. DC but …………….. AC current between points in a circuit.
Part 2: Bypass Capacitor (De-coupling)
1. Connect the circuit at right.
Set the function
generator to 2 VP- P at 2 kHz using the scope with DC
coupling. Be sure that the function generator
waveform has a +1 volt DC offset. Do not connect
the C1 capacitor at this time.
2. Using the scope observe and draw the waveform at
Point A. (Since it is a 2 equal resistor voltage
divider, both AC and DC should be ½ of function
generator settings). Be sure to use DC coupling on
the scope.
3. Is there a DC component at Point A?……….… How much?…..…....V.
Is there an AC component at Point A?……..…..
How much……….…VP-P.
4. Connect a 1µF capacitor across R2 the 10 KΩ resistor as shown. Repeat step 2.
Show voltage levels on diagrams
Without the
capacitor
With the capacitor
5. What is the capacitor doing to the AC component of the signal at Point A? ………...
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Part 3: Charging a Capacitor
1. Set up the circuit shown below right. Calculate the charging time constant for the circuit
(τ = RC). Connect a DVM set to DC volts to measure the capacitor voltage. Using a
watch or clock measure the time that the capacitor takes to charge. Close the switch to
position 1 at time zero and time from that point. You may need to repeat this
procedure several times to get it right. The charging rate will slow considerably
between 9 and 10V. Stop timing at approximately 9.8 V. To discharge the
capacitor quickly momentarily short one end of C to the other with a piece of
wire.
Charge Time = ……………………..
2. Compare your measured time to the calculated time (5 Time Constants - 5Τ).
1 Τ = R x C = ……………….…..
1
5 Τ = 5 x R x C = …………………………
R1
56k
+10V
R2
82k
How closely do they agree?
What do you think would create any discrepancy?
3. Move the switch to position 2 and measure the time for
the capacitor to discharge. Stop timing at
approximately 0.1 V. Calculate the capacitor discharge
time constant (TC) and compare 5 TCs to your
measured time.
Discharge Time = …………………..
TC = R x C = ……………………….
5 x R x C = …………………………….…
How closely do they agree?
In your own words explain why the charge and discharge times are different?
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
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Date …………………………..
WIRE
SWITCH
2
C1
100
uF
+
-
50
Lab Exercise 14
Oscilloscope and AC Waveforms in EWB
Objective:
To display and make measurements of various waveforms using
the Oscilloscope function of Electronics Workbench.
Procedure - Part A
1. On a computer with EWB installed, open the program and
create the circuit at right. The instrument on the left is a
Function Generator, and on the right is an Oscilloscope or
scope. Both can be found in the Instruments bin.
2. Double click on the Function Generator and in the window that
appears, set the controls as in those at below right and then
close the window. (Clicking on the up and down arrows for
each box adjusts the settings).
3. Double click on the Scope and set the controls as they
appear below. Do not close the window.
4. Click the ‘On’ switch, allow the circuit to run for a few
seconds then click it off. Don’t be concerned if nothing is
displayed on the scope. Save the circuit as
TECH101Lab13A.ewb
5.
6. Click
the Expand
button of the scope
and
move
the
horizontal scroll bar to
display at least two
complete cycles. (The
X Position up and
down
arrows
will
move the trace left or
right to line up the
start of a waveform
with a graticule line on
the scope display. This allows for more accurate time measurements).
7. Count the number of divisions for one complete cycle of the sine wave and multiply this
number by the horizontal speed setting (called Timebase on this scope). e.g. 3 Div *
.2mSec/Div = .6mSec = .0006Sec. Period Time = 0.0006Sec.
Period Time = ……. Div * …….mSec/Div = …….… mSec = …..………µsec
Frequency = 1/Period = 1/………… = …………….Hz or ……………kHz.
What is the frequency setting of the function generator? ……………..
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8. Count the number of divisions from the 0V reference line (the mid point of the sine
wave) to the maximum positive voltage peak, and multiply this by the channel A V/Div
setting. Record this as VPK. e.g. 2.5 Div * 2V/Div = 5V.
VPEAK = ……….Div * …………V/Div = …………….Volts
What is the function generator Amplitude setting? ……... Do they agree?…...…
9. Click and drag the Red Cursor 1 and Blue Cursor 2 lines to the start and finish points of
one of the cycles as shown below.
10. The small windows under the main scope display will show the horizontal and vertical
position of both cursors and the difference between each. Look at the far right window
(pictured above right) and record the T2 – T1 figure (approximately 1000µSec or
1mSec) as Period Time in the table below. (Ignore the VA2-VA1 figure at this time,
yours will differ from the example). Calculate the reciprocal (1/Period time) and record
this as Frequency in the same table.
11. Move the 1 and 2 cursors again to the maximum positive and negative peaks of the
sine wave and record the VA2-VA1 voltage as VPK PK in the table. This figure may be a
minus quantity and to change it to a positive, simply interchange the Red and Blue
cursor positions. Divide the VPK PK by 2 and record this as VPK.
Period Time
Frequency
VPK PK
VPK
12. Click on the Reduce button and then close the scope window (click on the X at top right
of scope window).
13. Double click on the Function Generator and set it for a Square wave of 10kHz, 50%
duty cycle and amplitude 3V. Close the Function Generator window.
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14. Repeat 6 to 10 above for the square wave and record the results below. (You will have
to adjust the scope Timebase setting to compensate for the change to 10kHz from
1kHz).
By Divisions
Period = …....Divs * …...… Secs/div = ……….Secs. Frequency (1/T) =……...….Hz
VPK = ………Divs * ………V/div = ……..…..V. VP-P (2*VPK) = ………..V
By Curser
Period = …………………Secs. Frequency (1/T) =…………………Hz
VPK PK = …………………….V.
VPK (VP-P /2)= …………………….V
15. Sketch the 50% Duty cycle squarewave in the scope facsimile below.
16. Go back to the function generator and set the duty cycle to 75%. Sketch the scope
waveform in the appropriate75% space below.
Duty cycle = 50%
Duty cycle = 75%
17. Go back to the function generator and set the duty cycle to 25%. Sketch the scope
waveform in the 25% facsimile below.
Duty cycle = 25%
Procedure - Part B
1. Click on the File menu, choose New and create the
circuit at right. The AC Source can be found in the
Sources bin. Drag it onto the work area, double click
on it and change the voltage to 2.12 V (this is RMS)
and set the frequency to 2kHz. When the 50Ω resistor
is added in series with it, it will emulate the function
generator used in lab 12 and the 100Ω resistor will be
the load resistor (RL).
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2. Double click on the scope and set it up as follows:
• Time Base = 0.10 mSec/Div
• X Position = 0.00
• Channel A = 1V/Div
• Y Position = 0.00
• AC – 0 – DC = DC
3. Ensure the switch is in the open position, click on the power, double click on the
scope, click on the Expand button and then click the power off. You should see a
sine wave.
4. By counting division and multiplying by the settings, measure and record the
parameters listed in the table below under ‘No Load’. Calculate and record the VRMS
and Frequency.
5. Close the switch and repeat steps 7
and 8. Record these results in the
100Ω column.
6. Double click on the 100Ω resistor
and change it’s value to 50Ω.
No Load
100Ω
50Ω
VPK
VPK - PK
Period
VRMS CALC
FreqCALC
7. With the switch still closed, repeat steps 7 and 8. Record these results in the 50Ω
column.
8. Compare the above results with those you obtained in lab 12 by entering the lab 10
step 4, 10, 12 and 13 results below:
• Step 4 ‘No Load’ VPK =…….…… VPk to Pk = ……..……. VRMS = ……………..
• Step 10 ‘100Ω’
VPK =…….…… VPk to Pk = ……..……. VRMS = ……………..
• Step 12 50Ω
VPK =…….…… VPk to Pk = ……..……. VRMS = ……………..
• Step 13 Period/Freq Period……………………… Freq …………………
Do they agree? ………………………
Save the circuit as TEC101Lab14.ewb
Have your teacher or assistant sign off your completed lab below.
Signature ……………………………….…………
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Date …………………………..