İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT
LABORATORY
LECTURER: ASST. PROF. DR. GÖKHAN ÇINAR
LAB ASSISTANTS: RES. ASST. ESRA SAATÇI
RES. ASST. ERTUĞRUL BAŞAR
2007
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
TABLE OF CONTENTS
Lab Rules and Procedures
Laboratory Safety Rules
Laboratory Report Rules
Experiment 1
Errors in Measurement and Basic Statistical Sampling
Experiment 2
DC Current and Voltage Measurement
Experiment 3
Resistor Characteristics and Ohms Law
Experiment 4
Oscilloscope
Experiment 5
AC Voltage Measurement
Experiment 6
Measurement Using DC Bridges
Experiment 7
Measurement Using AC Bridges
Experiment 8
Measurement of Semiconductor Devices with Multimeter
Experiment 9
Thermistor Characteristics and Temperature Controlled Circuits
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LABORATORY RULES AND PROCEDURES
1. Students have to attend all the scheduled experiments. If anybody misses an
experiment, he/she will make it up during the last week of the semester. Students who
miss more than two experiments shall have to repeat the course; i.e. they will have an
“F” grade automatically.
2. Experiments are done by groups of students (a maximum of three).
3. Experiments start at the scheduled time of the laboratory session when all the
members of the group are ready. Any one who fails to join the group in 15 minutes will
be assumed absent.
4. “Experiment sheets” is given to the students at least one week prior to the
experiments. Students are supposed to study the experiment sheets, read the
necessary references, do the preliminary calculations –if necessary-, and collect
enough knowledge about the experiment before coming to the laboratory. This will be
checked by the instructor and will affect the student’s grade.
5. Two copy of the, blank “Experiment Data Sheet” should be prepared before the
experiment. “Experiment Data Sheet” is found at the end of each experiment section.
All the experimental data (and graphics if necessary) must be written on these sheets.
The laboratory instructor must sign the sheets. One copy of this sheet will be handed
to the instructor after the experiment. The other will be kept by the students to be
used in prepare the report.
6. Students must take all precautions for their own and instruments safety. They will be
liable to replace the instruments or the components, which are damaged due to misuse.
7. Students should obey all the “Laboratory Safety Rules” in the lab.
8. Students should leave the bench clean and tidy after the experiment. Cleanliness and
orderliness of the laboratory should always be maintained. All instruments should be
switched off before leaving the lab.
9. Students repeating a course should attend laboratories fully including submitting the
report. (They will not be exempted from the laboratories).
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LABORATORY SAFTY RULES
1. Eating, drinking, smoking, sleeping are not allowed inside the laboratory.
2. Excessive noise must be avoided (i.e. when talking etc...) must be avoided.
3. Jewellery, ties and clothing which, in the opinion of the Laboratory Staff, is hazardous
must not be worn while working with machinery in the Laboratory. All users must wear
full shoes (not sandals) and at least a shirt and full-length trousers. Long hair must be
held back securely with a head band or a net. Medallions or jewellery hanging from the
neck must not be worn.
4. The bench is for experimental equipment only. Do not leave coats, sweaters,
briefcases and other irrelevant personal belongings on the bench.
5. Keep your workspace tidy and set aside all equipment and leads that are not actually
part of the test being conducted.
6. Move around slowly to avoid knocking things over.
7. Make sure that there are at least three persons in the lab all the time.
8. Never open (remove cover) of any equipment in the lab.
9. Use the proper power cord and correct fuse. Replace the power cord if it is cracked or
broken or has any pins missing. Make sure that all devices are using a three-wire power
cable when powered from a 220V outlet. Use extension cords only when necessary and
only on a temporary basis.
10. Voltages above 50 V rms ac and 50 V dc are always dangerous. Extra precautions
should be considered as voltage levels are increased.
11. Always be careful when electricity is applied to the experiment circuit. Some circuit
elements such as capacitors and inductors may produce high voltages even when the
power supply voltage is low.
12. Never handle “live” equipment when hands, feet, or body are wet or perspiring, when
standing on a wet floor or on a metal surface.
13. While manipulating a circuit with an applied voltage or current, put one hand in your
pocket or behind your back.
14. All accidents, including minor injuries and all hazardous conditions are to be reported
immediately to the Laboratory Staff or the Director.
15. Laboratory shall remain locked other than laboratory hours.
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LABORATORY REPORTS RULES
Each student of each group should submit a report of the experimental work with
“Experiment Data Sheet” in one week after the experiment completion date. Grades
will be reduced by 5 points-per-each delayed day. The reports will not be accepted
after two weeks of delay. The first report will be given in a wired file for archiving
whereas the rest will be given in the transparent file.
The laboratory reports should include the following items:
1. Report cover page: Blank cover page of the experiment can be found at the
appendix. Students should complete this page and make it the first page of the
report.
2. Preliminary work: Should contain the short theory and method of the
experiment. It must not be a repetition of the “background section of the
experiment”, given in the “Experiment sheets”. Below items must be written in
your own words:
a. The technical objective of the experiment,
b. Calculations and questions’ answers found in the “Experiment sheets”.
3. Experimental setup: This section should include following:
a. Neat drawing of the experimental setup (indicating all the measuring
instruments, with types and brand names),
b. Equipment list: the list should include the names, manufacturer’s brand
names and model numbers of the instrument,
c. List of the electronic components and other related tools, instruments
used in the experiment.
4. Experimental results: This section should contain following:
a. Calculated data in the preliminary work section in tabular form,
b. All measured values in tabular form,
c. All curves with suitable titles, units and scales on both coordinate axes,
on each graph.
5. Conclusion: It includes:
a. All discussion of the experimental results,
b. Comments on differences between the experimental and theoretical
results,
c. Probable sources of errors and the ways of reducing these errors,
d. Personal opinions about the experiments.
Even though lab reports might be handwritten in pen or in ink, clarity and neatness are
required. Marks can be lost for reports that are not presented in a convenient way.
Marks are not given for the quantity of material written but for its quality. Comments,
which show that you understand or have thought about what is going on, are valuable.
Clarity of ideas, thoughts and understanding are essential for increasing your mark.
Lack of these will reduce your mark. Your report should be legible but does not have to
be a work of art. It is your ideas and experimental ability you will be graded on.
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FACULTY OF ENGINEERING AND ARCHITECTURE
ELECTRONIC ENGINEERING
ELECTRONIC MEASUREMENT
LABORATORY REPORT
EXPERIMENT NO :
...........
EXPERIMENT NAME :
...........
LABORATORY GROUP NO :
...........
LABORATORY PARTNERS :
...........
Prepeared by
STUDENT NO :
STUDENT NAME :
Experiment Date:
Report Grade:
...........
...........
Report Submission Date:
Delay Grade:
Result:
Submission Delay:
Signature
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İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 1
ERRORS IN MEASUREMENT
AND BASIC STATISTICAL
SAMPLING
OBJECTIVES
To investigate sources of error in measurements,
To observe the value of statistical analysis.
EQUIPMENT & COMPONENTS
1. 30 composition resistors of the same color-coded value
2. 1 digital multimeter
BACKGROUND
Error is defined as the deviation of a reading (or set of readings) from the expected value
of the measure variable. When we make measurements, some error is inevitable because no
measurement can yield the exact value of any quantity. There are several sources of error in
any experimental data. The primary concerns about analysing experimental data are the
sources of error and the extent to which the error has affected the validity of the data.
The error of measurement consists of three major components:
1. Gross error,
2. Systematic error,
3. Random error.
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In order to eliminate gross error, good measurement practice must be applied. Always obey
the rules of the measurement, do not relay on only one measurement, do many measurements
and judge the results.
Systematic errors are resulted from the measuring instruments (Instrumental error) and
external conditions (Environmental error). Experiment 2 covers Instrumental errors
A statistical analysis is performed on samples of very large quantities of the measurements
to determine the probable variation in values of the entire measurement, which is resulted in
Random errors. The percentage of the entire measurement, which will fall within a specific
range of values, can be predicted quite accurately from the statistical analysis of the sample.
Under ideal conditions, a very large number of measurements will provide a distribution of
readings, with the greatest number of readings approximately equal to the actual value. On
either side of the actual value, the frequency of readings will decrease, producing an
approximately normal distribution as shown in Figure 1.1.
Arithmetic mean of the n measurement is the best estimate of the true value. It can be
formulated as:
n
x + x + x + ... + xn
x= 1 2 3
=
n
∑x
i =1
i
n
(1.1)
Where n is the number of measurement, xi is the reading of the i’th measurement.
Standard Deviation or root-mean-square deviation of the n measurement is the best estimate
of the precision. It can be formulated as:
n
σ=
d + d 2 + d3 + ... + d n
=
n −1
2
1
2
2
2
∑d
i =1
2
i
n −1
for n → ∞
where n is the number of measurement, di is the deviation from the mean ( di = xi − x ).
2
(1.2)
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−
1
F ( x) =
e
2πσ
( x − x )2
2σ 2
Figure 1.1
PROCEDURE
□
1. Measure the value of each resistors by digital multimeter. Record the values in the
Table 1.1 (Resistance values).
□
2. Select 8 resistors at random from the total lot and measure and record their values
in Table 1.1 (Sample 1).
□
3. Mix all the resistors together and select, at random, any 12 resistors. Your selection
may or may not include resistors from the previous sample. Measure and record the
values of the 12 resistors in Table 1.1 (Sample 2).
□
4. Mix all the resistors together and select, at random, a sample of 16 resistors and
measure an record their vales in Table 1.1 (Sample 3).
□
5. On one sheet of graph paper, plot the value of each resistor in the total lot and
make a bar graph, or histogram.
□
6. Divide a second sheet of graph paper three ways vertically. Plot a histogram
(resistance values versus frequency) for each of the three samples of the resistors.
□
7. Connect the maximum points of each histogram by a smooth curve. If the numbers
of resistors in the samples were much larger, this would give an approximate normal
distribution curve such as the one shown in Figure 1.1. However, your curves may be
skewed because samples are small.
□
8. Compute and record in Table 1.1 the standard deviation
each of the three samples.
□
9. Record in Table 1.2 which sample (1, 2, or 3) most neatly describes the total lot with
regard to standard deviation.
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σ for the entire lot and for
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QUESTIONS
1. What is average deviation? Calculate the average deviation of the samples in Table 1.1 and
find out the best sample with regard the average deviation.
2. What is probable error? Calculate the probable error of the samples in Table 1.1 and find
out the best sample with regard the probable error.
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EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
Date of the Experiment
Name of the Lab Assistant
:Errors in Measurement and Basic Statistical Sampling
:
........
:
........
........
........
:
........
:
........
Signed
:
........
Experiment Data
Resistance
Values
Sample 1
Table 1.1 Results
Sample 2
Sample 3
Best sample
Second Best
Sample
Worst Sample
5
Sample 1
σ
Sample 2
σ
Sample 3
σ
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İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 2
DC CURRENT AND VOLTAGE
MEASUREMENT
OBJECTIVES
To learn how to measure DC voltages and current through the circuit,
To learn how to use multimeter properly.
EQUIPMENT & COMPONENTS
1. Digital Multimeter
2. Analog Multimeter
3. DC Power Supply (12 V)
4. Resistors (100Ω, 1kΩ, 10kΩ)
BACKGROUND
The two most important commonly used quantities are the current and the voltage. The
current is a serial quantity and measured by using ampermeter. The voltage is defined
between two nodes and measured by connecting a voltmeter across those two nodes.
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Figure 2.1 (a) The electronic circuit, (b) measuring current and (c) voltage: Current is measured by connecting
the ammeter in series to the resistor; the voltage is measured by connecting the voltmeter in parallel to it.
In order to eliminate the loading effect, the internal resistance of the ammeter should be
very small and the resistance of the voltmeter should be very high compared to the circuit
resistance. Otherwise the ammeter or the voltmeter changes the circuit operation conditions
and an error is introduced.
The error of measurement consists of three major components:
1. Gross error,
2. Systematic error,
3. Random error.
In order to eliminate gross error, good measurement practice must be applied. Always obey
the rules of the measurement, do not relay on only one measurement, do many measurements
and judge the results.
Systematic errors are resulted from the measuring instruments (Instrumental error) and
external conditions (Environmental error). Instrumental error is given in the user’s manual of
the instrument for maximum reading:
ε0 =
ΔV
Vmax
(2.1)
where ε0 is the error or accuracy of the instrument. Error of the analogue instrument is
usually expressed as the class of the instrument. The class of the instrument shows the
relative error for full-scale deflection (maximum reading).
Lading error is the other type of instrumental error. When measuring system is connected to
the system to be measured, some loading effects happen due to the power sharing of the two
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systems. The loading error for an ammeter and voltmeter can be calculated as follows,
respectively.
ΔI
r
=
(2.2)
I
r + Rn
Rth
ΔV
=
V
r + Rth
(2.3)
where r is the internal resistance of the meter and Rn is the Norton and Rth Thevenin
equivalent resistance of the circuit. Since the internal resistance of analog voltmeter change
with the selected range, instead of the internal resistance usually the sensitivity of the
instrument, S (input resistance-per-volt), is given such as “20kΩ/V”. This value is indicated
on the panel of the instrument. If the range of the voltmeter is set to VR, then the internal
resistance of analog voltmeter is:
r = VR × S
(2.4)
The internal resistance of a digital voltmeter is usually constant and greater than 1MΩ. The
internal resistance of an ammeter changes with the range of the instrument and should be
obtained from the users manual of the instrument.
The relative worst case or limiting error of a measurement is the sum of the loading error
and instrument (accuracy) error assuming other errors are negligible:
ΔX
X
=
worst case
ΔX
X
+
instrument
ΔX
X
(2.5)
loading
PROCEDURE
□
1. Calculate the current and the voltages across the resistors R1 and R2 of Figure 2.2
for (a) R2=10kΩ and (b) R2=100Ω.
Figure 2.2
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□
2. Connect the circuit given in Figure 2.2. Set R2=10kΩ. Measure the exact value of
the voltage source, using the digital voltmeter.
□
3. Open one end of R1. Connect the analog ammeter in series and measure the current
I1.
□
4. Open one end of R2. Connect the analog ammeter in series and measure the current
I2.
□
5. Connect the analog voltmeter across the resistor R1 and measure V1.
□
6. Connect the analog voltmeter across the resistor R2 and measure V2.
□
7. Repeat steps 3 to 6 using digital multimeter.
□
8. Set R2= 100Ω. Repeat steps 3 to 7.
□
9. Calculate the errors of measurements and fill in the Table 2-1, 2-2.
QUESTIONS
1. Calculate the minimum input resistance of the voltmeter which will introduce a 1% loading
error when measuring V2 of Figure 2.2 with R2=100Ω.
2. What are other methods to measure a DC voltages? Explain their operation and compare
with the simple “voltmeter” measurement method.
3. Is there a method to measure the current of a circuit without cutting the current
carrying line? Explain the method(s) briefly.
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EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
DC Current and Voltage Measurement
........
........
........
........
........
........
Signed
:
........
Experiment Data
2. V = . . . . . . . .
Table 2.1 Results
THEORICAL
R2=10kΩ
EXPERIMENTAL
R2=10kΩ
Analog
Digital
Meter
Meter
R2=100Ω
R2=100Ω
Analog
Digital
Meter
Meter
V1
I1
V2
I2
Table 2.2 Measurement Errors
R2=10kΩ
Analog Meter
Instrument Loading
Error
Error
Total
Error
Instrument
Error
Digital Meter
Loading
Error
Total
Error
Digital Meter
Loading
Error
Total
Error
V1
I1
V2
I2
R2=100Ω
Analog Meter
Instrument Loading
Error
Error
Total
Error
Instrument
Error
V1
I1
V2
I2
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İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 3
RESISTOR CHARACTERISTICS
AND OHM’S LAW
OBJECTIVES
To learn how to use ohmmeter properly,
To study characteristics of resistance,
To learn how to use Ohm’s Law in circuit analysis.
EQUIPMENT & COMPONENTS
1. Digital Multimeter
2. Adjustable DC Power Supply
3. Potentiometer
4. Resistors
BACKGROUND
All materials possess electrical resistance which is the opposition to the flow of electrical
current in a circuit. The unit of measure for electrical resistance is the ohms (Ω). One ohm
may be defined as the electrical resistance of a copper wire which is 300 m long and 2.5 mm
in diameter. The instrument used to measure electrical resistance is called an ohmmeter. The
ohmmeter must be connected to any circuit element under no power conditions.
The resistors can be simply divided into two types: fixed resistors and variable resistors.
The fixed resistor has two terminals and its resistance is constant. A variable resistor (VR)
or potentiometer has three terminals and its resistance is variable.
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The circuit symbol of a variable resistor is shown in Figure 3.1. The three terminals are the
end terminals A,C and a wiper terminal B. The resistance between the end terminals RAC is
fixed and is always equal to its nominal value. The wiper resistances between the wiper
terminal and the end terminals, RAB and RBC, are variable. The wiper resistances correspond
to a given position of the potentiometer shaft.
A
B
C
Figure 3.1 Symbol of a variable resistor
Ohm’s law, discovered by a German physicist Simon Ohm (1787 – 1854), is an important law
that describes the relationship of voltage E to current I and resistance R. It is often
referred to as the foundation of circuit analysis and can be expressed by three different
ways:
E
R
E = I ×R
E
R =
I
I =
(3.1)
where E is the potential difference from one end of a resistance element to the other (volt),
I is the current through the same resistance element (amperes), R is the resistance of the
same element (ohm).
Remember that lowering the resistance raises the current, and raising the voltage also raises
the current.
PROCEDURE
□
1. Using the ohmmeter measure the resistance of resistors given to you and record the
results in the column of measured value in Table 3.1.
□
2. Read the resistor values by using color codes. Compare the measured values with the
reading values and tolerances for determining whether each measured value is within
the tolerance or not. Complete Table 3.1.
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□
3. Designate three terminals of VR1 on the KL-21001 as A (the right), B (the middle)
and C (the left).
□
4. Using the ohmmeter, measure the resistance between terminals A and C and record
the value on Table 3.2.
□
5. Turn the VR1 control knob completely to the left. Measure and record the
resistance between terminals A and B, and A and C on Table 3.2.
□
6. Turn the VR1 control knob completely to the right. Measure and record the
resistance between terminals A and B, and A and C on Table 3.2.
□
7. Turn the VR1 control knob to middle position. Measure and record the resistance
between terminals A and B, and A and C on Table 3.2.
□
8. Set the circuit shown in Figure 3.2 by using R1 = 100Ω and Vs = 12 V. Using Ohm’s
Law calculate the current through resistor R1.
I
+
Vs
R1
+
V
-
Figure 3.2.
□
9. Connect the ammeter to the circuit shown in Figure 3.2. Measure the current
through resistor R1. and record the result on the Table 3.3 Is there good agreement
between your measured and calculated current values?
□
10.Change Vs as you read 150 mA on the ammeter. Measure the voltage across the
resistor R1 by using voltmeter. Calculate and record the voltage value (V) on the Table
3.3. Is there good agreement between your measured and calculated voltage values?
□
11. It is simple to build an equivalent ammeter by connecting a known resistor in parallel
with a voltmeter, see Figure 3.3. According to this build your own ammeter with RA =
4.7 Ω. To measure the current in this ammeter you measure the voltage (V) and by
using the Ohm’s Law you calculate the current through RA ( I = V RA ). You assume that
the internal resistance of voltmeter is very high and loading effect is negligible.
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+
RA
V
Figure 3.3
□
11. Connect your ammeter to the circuit shown in Figure 3.2 V (R1 = 100Ω and Vs = 12
V.). Calculate the current through the resistor R1 by considering your ammeter
connected to the circuit. Record the result on the Table 3.4.
□
12.Measure the current through resistor R1 and record the result on the Table 3.4. Is
there good agreement between your measured and calculated current values?
QUESTIONS
1. How can you design a voltmeter with full scale of 100V by using an ammeter and a
resistance.
2. Explain basic construction of an ohmmeter.
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EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
Resistor Characteristics and Ohm’s Law
........
........
........
........
........
........
Signed
:
........
Experiment Data
Resistor
Table 3.1
1st Band
2nd Band
3rd Band
4th Band
Reading
Value (Ω)
Tolerance
(%)
Measured
Value (Ω)
within
Tolerance?
R1
R2
R3
R4
Table 3.2
RAC=----Shaft Position
Fully left
Fully right
At the middle
RAB
RBC
RAB+RBC
Table 3.3
Vs = 12 V
R1 = 100Ω
Ical
Im
I = 150 mA
R1 = 100Ω
Table 3.4
Ical
Vm
Vs = 12 V
R1 = 100Ω
17
Im = Vm RA
Vcal
Vm
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İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 4
OSCILLOSCOPE
OBJECTIVES
To learn how to use oscilloscope properly,
To measure amplitude, frequency and phase angle by using oscilloscope,
EQUIPMENT & COMPONENTS
1. Dual Trace Oscilloscope
2. Digital Multimeter
3. Signal Generator
4. Resistors
5. Capacitor
BACKGROUND
The cathode ray oscilloscope is the most versatile instrument to measure electrical
quantities. It is possible to use an oscilloscope to measure the following quantities of a
voltage;
1. Instantaneous value, v(t)
2. The positive and negative peak value, Vp+, Vp3. The peak-to-peak value, Vpp
4. The average value, VA
5. The period, T
6. The phase difference between two voltages, φ
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Figure 4.1. Sinusoidal wave.
Probe:
The imput impedance of an oscilloscope is very high. 1MΩ paralel 20pF input impedance is an
industry standart for oscilloscopes. To compensate the large input capacitance and to
increase the input resistance of an oscilloscope it is necessary to use a serial cable and
circuit that is called “PROBE”. The probe is made of a co-axial shielded cable and
compensated attenuator as shown in Figure 4.2.
input
C1
Probe cable
Oscilloscope
R1
ground
C2
R2
x10
Figure 4.2. Oscilloscope probe.
The large input time constant R2C2 creates a low pass filter (with single pole) and attenuates
all high frequency (HF) signals. To compensate this “pole” it is necessary to create a zero at
the same frequency by R1C1, satisfying:
R1C1 = R2C 2
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(4.1)
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To obtain x10 attenuation R1 = 9MΩ is selected. It is necessary to adjust either C1, to obtain
the equality, since C2 is not exactly known. This adjustment must be done once, for every
oscilloscope and every probe connected to the specific input of this oscilloscope.
Note: Compensation works only on x10 position. Therefore HF signals can only be used by
using a compensated x10 probe.
Measurement using an Oscilloscope
Since it has a very large input resistance, an oscilloscope can only be used to measure
voltages and time. The vertical axes of an oscilloscope are calibrated to indicate volts/cm
and the horizontal axes are calibrated as s/cm.
Instantaneous and peak value:
Measuring the first three quantities, Instantaneous, Peak and Peak-to-Peak Voltage value is
straightforward. Be sure that zero level adjustment is done properly and DC or AC input
selection is correctly set.
Average value:
To measure the average value first the input connection is made AC coupled and one extreme
of the waveform is set to the reference line. Then the input is set to Dc coupled mode and
the voltage shift is measured. This shift is equal to the average value of the voltage.
Period:
The period can also be directly measured by measuring the time difference between two
zero crossing points, and frequency can be easily calculated by taking the reciprocal of the
period.
Phase:
The phase measurement can be performed in two different ways.
1. If the oscilloscope has dual trace facility two voltages are displayed simultaneously and
the time difference, tD, is measured between two identical points of the waveforms. The
phase difference is then:
φ = 2π
tD
T
where T is the period of the signal.
21
(4.2)
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
2. If one of the signals applied to the horizontal input while the other is connected to
vertical input an elliptical trace is obtained on the screen as shown in Figure 4.3. The phase
difference can be calculated using this trace as follows:
φ = arcsin
(4.3)
Y
VY(Ө)
Ө
0 Ф
b
a
b
a
X
2п
b = VY (φ ) = a sin(φ )
VX(Ө)
φ = arcsin(b a )
2п
Ө
Figure 4.3. The Lissajou curve.
PROCEDURE
□
1. Read the short instruction for the oscilloscope given in appendix 1.
□
2. Set all push buttons to OUT position. Then turn on the oscilloscope according to the
procedures in appendix.
□
3. Connect the x10 probe to the CAL output of the oscilloscope. Adjust the
TIME/DIV. and VOLT/DIV. knobs to obtain a suitable square wave on the screen. Then
adjust the compensation capacitor by using a suitable screwdriver. Try to obtain an
ideal square wave.
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Electronic Engineering
Over compensated
Under compensated
Critically compensated
C1R1 > C 2R2
C1R1 < C2R2
C1R1 = C 2R2
□
4. Apply 1 kHz sinewave to the INP.-I input of the oscilloscope. Adjust the TIME/DIV.
to obtain approximately one full period, and set VOLTS/DIV.-I to 0.2V/cm and adjust
the output of the signal generator to obtain 1.2V peak-to-peak amplitude. Measure the
period of the waveform and calculate the frequency.
□
5. Measure RMS output voltage of the signal generator using the digital voltmeter.
Calculate peak-to-peak amplitude. Compare the result with the oscilloscope.
□
6. Connect the circuit in Figure 4.4. using R = 1kΩ and C = 100nF. Connect node A to
vertical input CH.I and node B to vertical input CH.II. Adjust VOLTS/DIV.-II to
obtain reasonable amplitude. Measure the time difference between the zero crossing
points of the waveforms and calculate the phase difference for (i) f=100Hz, (ii)
f=1kHz, (iii)=f=10kHz.
Oscilloscope
B
Signal
Generator
A
R
CH.I GND CH.II
C
Figure 4.4.
□
7. Push “Hor/MENU” button and obtain the Lissajou pattern. Measure the phase using
Equation 4.3 for (i) f=100Hz, (ii) f=1kHz, (iii)=f=10kHz.
QUESTIONS
1. Calculate the theoretical errors for the measurement done in steps 4 and 5. Compare the
results with the measured values. Explain the reasons for disagreements (if there are any).
2. Explain the operation of Digital Storage Oscilloscope by drawing block diagrams.
3. Draw the Lissajou curve if v x (t ) = 5 sin(628t ) and v y (t ) = 5 sin(942t ) .
23
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
Oscilloscope
........
........
........
........
........
........
Signed
:
........
Experiment Data
4. T = . . . . . . . . . . .
f=..........
5. VRMS = . . . . . . . VPP(calculated) = . . . . . . VPP(set) = . . . . . . . ∆VPP =. . . . . . .
6.
f = 100Hz
f = 1kHz
f = 10kHz
t=.......
t=.......
t=.......
Ф=.......
Ф=.......
Ф=.......
7.
f = 100Hz
f = 1kHz
f = 10kHz
a=.......
a=.......
a=.......
b= . . . . . . . .
b= . . . . . . . .
b= . . . . . . . .
24
Ф=.......
Ф=.......
Ф=.......
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 5
AC VOLTAGE MEASUREMENT
OBJECTIVES
To learn how to measure AC voltages,
To become familiar with the use of AC voltmeters.
EQUIPMENT & COMPONENTS
1. Dual Trace Oscilloscope
2. Digital Multimeter
3. Analog Multimeter
4. Signal Generator
BACKGROUND
The important parameters of a time varying AC voltage, v(t), to be measured are the
following;
1. Instantaneous value, v(t)
2. The positive and negative peak value, Vp+, Vp3. The peak-to-peak value, Vpp
4. The average value, VA
5. The RMS value, VRMS
5. The period, T
6. The frequency, f
25
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Electronic Engineering
Figure 5.1. Sinusoidal wave.
The oscilloscope is the most versatile instrument to measure most of these electrical
quantities. An oscilloscope can measure all of the above mentioned properties except the
RMS value and the frequency. The frequency may be easily calculated after measuring the
period since f = 1 T .
The phase diffrence between two voltages may be also measured by an oscilloscope.
Measurement using a Voltmeter:
To measure the average value, VA, of an AC signal a DC voltmeter may be used directly. An
AC voltmeter must be used for measuring the RMS value. However, an AC voltmeter can work
properly only in a limited frequency range for which it is designed. Outside of this range, the
measuremnet results will be wrong. Therefore, for AC measurements, it is important to know
the ferquency of the signal to be measured and the frequency characteristics of the
voltmeter to be used.
The waveform also effects the measurement’s result. Ordinary AC voltmeters are designed
and calibrated to measure the RMS values of sinisoidal signals only. For other waveforms the
result is not usually correct.
The RMS value of a waveform is defined as follows:
VRMS =
1
T
T
∫v
0
26
2
(t )dt
(5.1)
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
It is fairly difficult to perform the squaring operation to obtain the true RMS value. Only
expensive voltmeters measure the true RMS value. The ordinary voltmeters measure the
absolute average of a voltage, which is defined:
VAA 1
T
T
∫ v (t ) dt
(5.2)
0
as the average of the absolute value. The absolute average value can be easily be obtained by
a full wave rectifying the input voltage. The The converison from the absolute average to the
RMS value can be done by scaling the readout (or the input voltage) by a factor called the
shape factor. But a Shape Factor is only valid for a certain waveform. For a sinusoidal
waveform thsi factor is 1.11.
SF ≡
VRMS
π
=
= 1.11 (for sinewave)
VAA
2 2
(5.3)
After measuring the Absolute Average voltage, the RMS value can be easily determined if
the waveform is known. For complex waveforms, such as speech and noise, it is not possible
to determine the shape factor and it is necessary to use a True RMS voltmeter.
AC Voltmeter must be connected in parallel with the terminals of the circuit elements whose
ac voltages will be measured. Besides the polarity, AC voltmeters use the same rules as DC
voltmeters do. Since AC voltage reverses its polarity periodically, AC voltmeters are
therfore designed without limit in polarity.
Measurement using an Oscilloscope
Since it has a very large input resistance, an oscilloscope can only be used to measure
voltages and time. The vertical axes of an oscilloscope are calibrated to indicate volts/cm
and the horizontal axes are calibrated as s/cm.
Instantaneous and peak value:
Measuring the first three quantities, Instantaneous, Peak and Peak-to-Peak Voltage value is
straightforward. Be sure that zero level adjustment is done properly and DC or AC input
selection is correctly set.
Average value:
To measure the average value first the input connection is made AC coupled and one extreme
of the waveform is set to the reference line. Then the input is set to Dc coupled mode and
the voltage shift is measured. This shift is equal to the average value of the voltage.
27
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Period:
The period can also be directly measured by measuring the time difference between two
zero crossing points, and frequency can be easily calculated by taking the reciprocal of the
period.
Phase:
The phase measurement can be performed in two different ways.
1. If the oscilloscope has dual trace facility two voltages are displayed simultaneously and
the time difference, tD, is measured between two identical points of the waveforms. The
phase difference is then:
φ = 2π
tD
T
(5.4)
where T is the period of the signal.
2. If one of the signals applied to the horizontal input while the other is connected to
vertical input an elliptical trace is obtained on the screen as shown in Figure 5.3. The phase
difference can be calculated using this trace as follows:
φ = arcsin
Y
VY(Ө)
Ө
0 Ф
b
a
b
a
X
2п
b = VY (φ ) = a sin(φ )
VX(Ө)
φ = arcsin(b a )
2п
Ө
Figure 5.2. The Lissajou curve.
28
(5.5)
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
CALCULATIONS
Calculate the shape factor of a triangular and square wave. The standard AC voltmeters are
calibrated to indicate the RMS value of a sine wave. Using the calculated shape factors
calculate the voltage to be displayed by an absolute average reading meter when the input is
10 V peak (i) sine, (ii) square and (iii) triangular waveform.
Calculate the theoretical RMS values for the procedure steps 4, 5 and fill in the blanks in
table.
PROCEDURE
□
1. Read the short instruction for the oscilloscope given in appendix 1. Set all push
buttons to OUT position. Then turn on the oscilloscope according to the procedures in
appendix
□
2. Apply 1 kHz sinewave to the INP.-I input of the oscilloscope. Adjust the TIME/DIV.
to obtain approximately one full period, and set VOLTS/DIV.-I to 2V/cm and adjust
the output of the signal generator to obtain 12V peak-to-peak amplitude. Measure the
period of the waveform and calculate the frequency.
□
3. Connect the analog and digital voltmeters and the oscilloscope to the signal
generator as shown in Figure 5.3. Set the waveform to Sinewave, output voltage to 12V
peak-to-peak on the oscilloscope. Change the frequency and note the voltmeter
readings in Table 5.1 (Check the voltage on the oscilloscope to remain constant, 12V,
peak-to-peak for every frequency).
Figure 5.3
□
4. Set the frequency to 50 Hz. Adjust the output voltage to 10V peak-to-peak on the
oscilloscope. Then read the voltage with digital and analog voltmeter. Compare the
result with the theoretical values. Complete Table 5.2.
29
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
□
5. Change the signal to square and triangular waveforms then repeat step-4. Complete
Table 5.3.
□
6. Draw the frequency response of the voltmeters, using the measured values (Table
5.1), for the sinusoidal input, on a lin-log graph-paper.
QUESTIONS
1. Is it possible to measure the phase difference of two sine waves with a single-input
oscilloscope? Explain how.
2. Which instrument is more accurate at 500 Hz and 5000 Hz? Explain the reason.
3. Are Digital and analog Voltmeters used in the Experiment True RMS Voltmeter?
30
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
AC Voltage Measurement
........
........
........
........
........
........
Signed
:
........
Experiment Data
2. T = . . . . . . . . . . .
f=..........
3.
50
Table 5.1. The Frequency response of the instruments
Frequency (Hz)
100
200
500
1K
2K
5K
10K
20K
50K
Oscilloscope
Analog VM
Digital VM
4.
Sine Wave
Table 5.2. Sinewave measurement of the instruments
Digital VM
Analog VM
Oscilloscope
Theoretical
Measured
5.
Table 5.3. Square and Triangle Wave measurement of the instruments
Digital VM
Analog VM
Oscilloscope
Square Wave
Theoretical
Measured
Triangle Wave
Theoretical
Measured
31
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
32
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 6
MEASUREMENT USING DC BRIDGES
OBJECTIVES
To study resistance measurement techniques using DC Bridge circuits
EQUIPMENT & COMPONENTS
1. Digital Multimeter
2. 12V DC power supply
3. Potentiometer
4. Resistors
BACKGROUND
Accurate measurements of resistances may be performed by using impedance-measuring
Bridges. There are a number of bridges, which are called usually by their inventor’s name, to
measure different type of resistances and impedances.
Typical bridge circuit is given in Figure 6.1.
33
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Z1
+
Z2
A
B
Z3
Z4
Figure 6.1. The basic impedance bridge.
When the equation
Z 1 Z 4 = Z 2Z 3
(6.1)
is satisfied, the voltages of nodes A and B are equal and the current of the detector, is zero.
The unknown impedance, Z4 is:
Z4 =
Z2
Z3
Z1
(6.2)
For measuring real impedances, i.e. resistors, all impedances are resistors and the bridge is
called Wheastone Bridge. For measuring capacitance, inductance or complex impedances at
least one of the Z1, Z2, Z3 must also be complex in order to satisfy the balance equation.
Resistance Measurement using the Wheastone Bridge
The basic bridge circuit called Wheastone Bridge is suitable to measure medium range
resistance. A DC voltage source and DC meter may be used in this case, since the impedances
to be used are real.
R1
E
A
R2
B
G
R3
Rx
Figure 6.2 Wheastone Bridge.
34
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
For the resistive case the Equation 6.2 becomes:
Rx =
R2
R3
R1
(6.3)
For the maximum sensitivity of the bridge all resistance values should be in the same range
(as close to each other as possible) as a result of maximum power transfer theorem.
Resistance Measurement using the Kelvin Double Bridge
G
b
a
Figure 6.3. The Kelvin Double Bridge.
The Kelvin Double Bridge is a modification of the Wheatstone Bridge and provides greatly
increased accuracy in the measurement of low-value resistances, generally below 1Ω. The
term double bridge is used because the circuit contains a second set of ratio arms. . The
unknown resistance Rx can be calculated as follows:
Rx =
bR y
⎛ R1 a ⎞
R1 R3
⎜
⎟
+
(a + b + R y ) ⎜⎝ R2 − b ⎟⎠
R2
(6.4)
where Ry is the yoke resistance measured between the node connecting R3 and b and the
node connecting Rx and a.
PROCEDURE
□
1. Connect the Wheatstone bridge circuit shown in Figure 6.2. Set R1=R2= 1kΩ. Use an
unkown resistor with a relatively low resistance value, a potentiometer for R3 and 12V
DC power supply for the voltage source. Connect a DC voltmeter between nodes A-B as
the detector.
□
2. By adjusting Rv obtain the balance of the bridge.
35
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
□
3. Calculate the value of unknown resistance Rx
□
4. Replace R1=R2= 100Ω and repeat steps 2, 3.
□
5. Connect the Kelvin double bridge circuit shown in Figure 6.3. Set R1=R2=R3=a=b= 1kΩ
and an unknown resistor having a relatively low resistance value. Connect a 12V DC
power supply for the voltage source.
□
6. Calculate the value of unknown resistance Rx.
QUESTIONS
1. Compare the accuracy of the Wheatstone and Kelvin double bridges.
2. Which bridge would you prefer to use for the measurement of a test resistor having a
value around 50 kΩ?
36
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
Measurement using DC Bridges
........
........
........
........
........
........
Signed
:
Experiment Data
2. R3= . . . . . . . . . . .
3. Rx= . . . . . . . . . . . ±. . . . . . . . . . . .
4. R3= . . . . . . . . . . .
Rx= . . . . . . . . . . . ±. . . . . . . . . . . .
6. Rx= . . . . . . . . . . . ±. . . . . . . . . . . . .
37
........
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
38
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITESI
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 7
MEASUREMENT USING AC BRIDGES
OBJECTIVES
To study impedance measurement techniques using AC Bridge circuits
EQUIPMENT & COMPONENTS
1. Digital Multimeter
2. Signal Generator
3. Potentiometers
4. Resistors, Capacitors and Inductors
BACKGROUND
Accurate measurements of complex impedances and frequencies may be performed by using
impedance-measuring AC Bridges. There are a number of bridges, which are called usually by
their inventor’s name, to measure different types of impedances and frequencies.
Typical bridge circuit is given in Figure 7.1.
39
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Z1
+
Z2
A
B
Z3
Z4
Figure 7.1. The basic impedance bridge.
When the equation
Z 1 Z 4 = Z 2Z 3
(7.1)
is satisfied, the voltages of nodes A and B are equal and the current of the detector, is zero.
The unknown impedance, Z4 is:
Z4 =
Z2
Z3
Z1
(7.2)
For measuring capacitance, inductance or complex impedances at least one of the Z1, Z2, Z3
must also be complex in order to satisfy the balance equation.
Capacitance Measurement using the Schering Bridge
R1
R2
C1
E
+
A
B
Detector
C3
Rx
Cx
Figure 7.2. The Schering Bridge.
The Schering Bridge is a complex impedance bridge to measure capacitance. The complex
balance equation yields two real equation. Using these two equations the unknown capacitance
and its equivalent series resistor (which corresponds to the losses of the capacitor) can be
calculated as follows:
40
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
R1
C3
R2
C
Rx = 1 R2
C3
Cx =
(7.3)
(7.4)
The error of measurement can be calculated as:
ΔC x
Cx
ΔR1
=
R1
+
ΔR2
+
R2
ΔC 3
C3
(7.5)
The relative error on the Cx should be treated as the sum of the accuracy of the component
ΔC x C x acc , which is given by the manufacturer and the minimum relative variation,
ΔC x det C x , that can be detected by the detector.
ΔC x
Cx
=
ΔC x
Cx
+
ΔC x det
Cx
acc
(7.6)
The accuracy of the detector does not effect the error of measurement. But its sensitivity
determines the minimum detectable difference between the voltages of the nodes A and B,
hence, minimum detectable variation of adjustable components, ∆Cxdet. The best sensitivity is
obtained if the values of the impedances of the arms of the bridge on the operating
frequency are close to each other.
The losses of a capacitor can either be represented by a shunt or series equivalent resistors.
The Schering Bridge measures the series equivalent capacitor and resistor. To obtain the
parallel equivalent capacitor and leakage resistor (representing the losses):
D=
1
Q
= wC s Rs =
C p = Cs
Rp = Rs
1
wCD RD
1
1 + D2
1 + D2
(7.7)
(7.8)
D2
The result of measurement should be given as:
C = C ± ΔC
41
(7.9)
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Inductance Measurement using the Maxwell Bridge
The Maxwell Bridge is a complex impedance bridge to measure an unknown inductance in
terms of a known capacitance. The complex balance equation yields two real equation. Using
these two equations the unknown inductance and the resistor in series with it can be
calculated as follows:
R3
Lx
Figure 7.3 Maxwell Bridge.
Lx = R2 R3C1
(7.10)
and
Rx =
R 2 R3
R1
(7.11)
respectively.
PROCEDURE
□
1. Connect the Schering bridge circuit shown in Figure 7.2. Set C3 to 47nF, R1 to 1kΩ.
and oscillator frequency to 1kHz. Connect an AC voltmeter between nodes A-B as the
detector.
□
2. Set C1 as 22nF and by adjusting R2 obtain the balance of the bridge. Can you balance
the bridge? Then change C1 to 47nF and adjust R2 to obtain balance of the bridge. Can
you balance the bridge?
□
3. Calculate the value of unknown capacitor Cx and equivalent resistance Rx.
□
4. Calculate the value of unknown capacitor Cp and equivalent resistance Rp.
42
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
□
5. Set the frequency of the generator to 50 Hz and repeat step 3 and 4.
□
6. Connect the Maxwell bridge circuit shown in Figure 7.2. Set C1 to 47nF, R2 to 1kΩ.
and oscillator frequency to 1kHz. Connect an AC voltmeter between nodes A-B as the
detector.
□
7. By adjusting R1 and R3 obtain the balance of the bridge. Can you balance the bridge?
□
8. Calculate the value of unknown capacitor Lx and resistance Rx.
□
9. Calculate the value of unknown capacitor Lp and resistance Rp.
□
10. Set the frequency of the generator to 50 Hz and repeat step 8 and 9.
QUESTIONS
1. Derive the balance equations of the Schering Bridge.
2. Can an inductor be measured by using a Schering Bridge?Why?
3. Derive the balance equations of the Maxwell Bridge.
4. Can a capacitor be measured by using a Maxwell Bridge?Why?
43
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:
:
:
Date of the Experiment
Name of the Lab Assistant
:
:
Measurement using AC Bridges
........
........
........
........
........
........
Signed
:
Experiment Data
2. R2= . . . . . . . . . . .
C1= . . . . . . . . . . .
3. Cx= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rx=. . . . . . . . . . . ±. . . . . . . . . . . . .
4. Cp= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rp= . . . . . . . . . . . ±. . . . . . . . . . . . .
5. Cx= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rx=. . . . . . . . . . . ±. . . . . . . . . . . . .
Cp= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rp= . . . . . . . . . . . ±. . . . . . . . . . . . .
7. R1= . . . . . . . . . . .
R3= . . . . . . . . . . .
8. Lx= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rx=. . . . . . . . . . . ±. . . . . . . . . . . . .
9. Lp= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rp= . . . . . . . . . . . ±. . . . . . . . . . . . .
10. Lx=. . . . . . . . . . . ±. . . . . . . . . . . . .
Rx=. . . . . . . . . . . ±. . . . . . . . . . . . .
Lp= . . . . . . . . . . . ±. . . . . . . . . . . . .
Rp= . . . . . . . . . . . ±. . . . . . . . . . . . .
44
........
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 8
MEASUREMENT OF SEMICONDUCTOR
DEVICES WITH MULTIMETER
OBJECTIVES
To understand the construction of the analog and digital multimeter,
To learn how to test semiconductor devices by using the multimeter
EQUIPMENT & COMPONENTS
1. KL 100 main unit KL-21001
2. KL 100 breadboard module
2. KL 100 module KL-13007
3. 1 analog multimeter
4. 1 1N4001 diode, 1 2N3906 BJT
BACKGROUND
The analog (VOM - Volt-Ohm-Miliammeter) and digital (DMM) multimeters is the most
popular instruments for electrical parameter measurements. As the name implies, the
multimeter can be considered as a test instrument which assembles some separate
instruments such as the ac voltmeter, dc voltmeter, dc miliammeter, and the ohmmeter into a
unit. Each separate function can be accomplished through the control of a selector switch.
With specific circuits and scales added, the multimeter can also perform the measurements
of inductance, capacitance and dB. In this experiment the use of the multimeter will be
exercised in the tests for diode, bipolar junction transistor (BJT) and Field Effect
Transistor (FET).
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Analog and Digital meters behave quite differently when testing nonlinear devices like diodes
and transistors. DMMs can result in false readings as the current may be too low to
adequately bias the junctions of diodes and transistors. Thus, VOM may be most suitable for
semiconductor device test. However, since lowest resistance range of VOM may put out too
much current for smaller devices possibly damaging them, next higher resistance range
should be considered first.
Testing Diode with VOM.
A diode is a two-terminal element, usually made by using a p-n junction. The symbol for a
diode is shown in Figure 8.1(a). Which terminal is which matters very much in a diode. Usually,
the terminal indicated by a horizontal line in Fig. 8.1 (a), called the cathode, is marked on a
real diode (Fig. 8.1 (b)). Voltage (vD) and the current (iD) of a diode are defined as shown in
Figure 8.1(c). When the voltage vD is positive, the diode is said to be forward-biased; a large
current can then flow, and the diode is said to conduct. When the voltage vD is negative, the
diode is said to be reverse-biased; the diode current is extremely small, and it is assumed to
be zero; the diode is then said to be turned off. Thus, the diode effectively conducts
current in only one direction; it “refuses” to conduct current in the other direction.
Figure 8.1. (a) the symbol of the diode, (b) real diode, (c) i-v characteristic of a diode.
To test the functionality and polarity of the diode are very important. Battery powered VOM
can be used to test the diode and determine the way it conducts the current. To test the
diode, VOM is used on low scale range. When black probe (GND probe) is connected to the
cathode and red probe to anode of the diode, the diode is forward biased by the battery
inside the VOM and should show very low resistance, for instance couple of ohms for regular
diode (but not zero). On the contrary, if the probes are interchanged, the VOM measures
very high resistance (nearly infinite resistance) as VOM battery reverse
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
bised the diode. However, it should be emphasized that the measured resistance is a
resistance at particular (at low current) operating point.
On a (digital) DMM, there will usually be a diode test mode, which displays the actual forward
voltage drop of the diode in volts, rather than a "resistance" figure in ohms. These meters
work by forcing a small current through the diode and measuring the voltage dropped
between the two test leads. Using this, a silicon diode should read between 0.5 to 0.8 V in
the forward direction and open in reverse.
Testing BJT with WOM
A Bipolar Junction Transistor (BJT) has three terminals connected to three doped
semiconductor regions. In n-p-n transistor, a thin and lightly doped p-type material is
sandwiched between two thicker n-type materials; while in a pnp transistor, a thin and lightly
doped n-type material is sandwiched between two thicker p-type materials (Figure 8.2).
Figure 8.2. Bipolar transistor types.
The three terminals of a transistor are typically used as the input, output and the common
terminal of both input and output. Depending on which of the three terminals is used as
common terminal, there are three different configurations: common emitter (CE), common
base (CB) and common collector (CC). The common emitter (CE) is the most typical
configuration: Two voltages VBE and VCB are applied to the base and collector of the
transistor with respect to the common emitter. In normal operation, the BE junction is
forward biased while the CB junction is reverse biased (Figure 8.3).
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Figure 8.3. Common emitter configuration of the n-p-n BJT.
To test BJTs, 6 configuration of the VOM leads present with 2 diode junction. Only two
configuration should show low resistance, i.e. black lead is on base and red lead is on the
emitter and collector. Rest should indicate very high resistance.
Testing FET with VOM
BJT has the disadvantage of a low input impedance because the base of the transistor is the
signal input and the base-emitter diode is forward biased. Another device achieved
transistor action with the input diode junction reversed biased, and this device is called a
Field Effect Transistor (FET). FETs are subdivided between two major classes: Junction
Field Effect Transistors (JFETs) and Metal Oxide Semiconductor Field Effect Transistors
(MOSFETs). With the reverse biased input junction, FET has a very high input impedance.
Having a high input impedance minimizes the interference with or "loading" of the signal
source when a measurement is made. For an n-channel FET (Figure 8.4), the device is
constructed from a bar of n-type material, with the shaded areas composed of a p-type
material as a Gate. Between the Source and the Drain, the n-type material acts as a resistor.
The current flow consists of the majority carriers (electrons for n-type material).
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Figure 8.4. N-channel junction field effect transistor.
The difference between JFETs and MOSFETs is that the thin layer of SiO2 is applied to
insulate the gate and the n-channel. Due to this insulation there is no gate current to either
to source or drain. FETs can be both n-channel and p-channel.
The control element for the JFET comes from depletion of charge carriers from the nchannel. When the Gate is made more negative, it depletes the majority carriers from a
larger depletion zone around the gate. This reduces the current flow for a given value of
Source-to-Drain voltage. Modulating the Gate voltage modulates the current flow through
the device.
Figure 8.5. N-channel JFET.
To test FETs first, it should be verified that the gate has infinite resistance to both drain
and source. If the gate and source are connected, drain and source should act like a diode.
PROCEDURE
□
1. Set the range selector switch of the multimeter to Rx1K range, put the tested
diode on the breadboard, and connect the red probe to diode terminal 1 and the black
probe to diode terminal 2. Record the value indicated by the multimeter to experiment
data sheet. Interchange the probes and record the result.
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
□
2. From the results of step 1, name the terminals of the diode (anode or cathode).
□
3. Set the range selector switch of the multimeter to Rx1K range, put the tested BJT
on the breadboard connect the red probe to BJT terminal 1 and the black probe to
BJT terminal 2. Record the value indicated by the multimeter to experiment data
sheet. Interchange the probes and record the result.
□
4. Connect the black probe to p-n-p BJT terminal 1 and red probe to BJT terminal 3.
Measure and record the reading on the multimeter to experiment data sheet.
Interchange the probes and record the result.
□
5. Connect the black probe to BJT terminal 2 and red probe to BJT terminal 3.
Measure and record the reading on the multimeter to experiment data sheet.
Interchange the probes and record the result.
□
6. From the results of steps 3, 4 and 5, name the terminals of the BJT (collector,
base, emitter).
□
7. Set the module KL-13007 on the main unit KL-21001.
□
8. Locate FET terminals on the block e.
□
9. Set the range selector switch of the multimeter to Rx1K range, connect the red
probe to FET terminal S and the black probe to terminal G. Record the value indicated
by the multimeter to experiment data sheet. Interchange the probes and record the
result.
□
10. Connect the black probe to G and red probe to D. Measure and record the reading
on the multimeter to experiment data sheet. Interchange the probes and record the
result.
□
11. From the results of steps 3 and 4, which type of the FET is (n-channel or pchannel)?
□
12. Connect to black probe to D and the red probe to S. Measure and record the
resistance indicated by the multimeter. Interchange the probes and record the result.
Is there good agreement between the two?
□
13. Connect to black probe to D and the red probe to S, then touch G by your index
finger and observe the change on the reading. The resistance is decreased or
increased? Is the FET sure good?
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Electronic Engineering
QUESTIONS
1. If a physical diode is modelled as shown below with VPN = 0.6 V and Rf = 10 Ω: (a) What
voltage is developed across the diode when If = 100 mA? (b) How much power is dissipated in
the diode at this current?
VPN
Rf
2. When testing BJTs what effects the actual resistance values?
3. Which kind of problems you come across when you test the transistors?
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Electronic Engineering
EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
:Measurement of semiconductor devices with multimeter
:
........
:
........
........
........
:
........
:
........
Signed
:
........
Date of the Experiment
Name of the Lab Assistant
Experiment Data
Table 8.1 Diode
Table 8.2 BJT
Resistance (Ω)
Terminal 1-2
Reverse
Terminal 1
Terminal 2
anode cathode
anode cathode
Resistance (Ω)
Terminal 1-2
Reverse
Terminal 1-3
Reverse
Terminal 2-3
Reverse
Terminal 1
Terminal 2
Terminal 3
Table 8.3 FET
Resistance (Ω)
Terminal S-G
Reverse
Terminal G-D
Reverse
FET
Terminal D-S
Reverse
agreement
Terminal D-S
terminal G
ground
FET ok
n channel
p channel
yes
resistor
increased
no
resistor
decreased
yes
no
52
C
C
C
B
B
B
E
E
E
İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
İSTANBUL KÜLTÜR UNIVERSITY
DEPARTMENT OF ELECTRONIC ENGINEERING
ELECTRICAL MEASUREMENT LABORATORY
EXPERIMENT 9
THERMISTOR CHARACTERISTICS
AND TEMPERATURE-CONTROLLED
CIRCUIT
OBJECTIVES
To understand the characteristics of a thermistor,
To construct a temperature-controlled switch circuit by using a thermistor
EQUIPMENT & COMPONENTS
1. KL 100 main unit KL-21001
2. KL 100 module KL-13010
3. 1 soldering iron
BACKGROUND
Thermistors (RT) are thermally sensitive resistors used in a variety of applications, including
temperature measurement. A thermistor is a piece of semiconductor made from metal oxides
which exhibits an electrical resistance that varies with temperature. There are two types of
thermistors – negative temperature coefficient (NTC) thermistors, whose resistance
decreases with increasing temperature, and positive temperature coefficient (PTC)
thermistors, whose resistance increases with increasing temperature. NTC thermistors are
much more commonly used than PTC thermistors, especially for temperature measurement
applications.
A main advantage of thermistors for temperature measurement is their extremely high
sensitivity. For example, a 2252 W thermistor has a sensitivity of -100 W/°C at room
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Electronic Engineering
temperature. Another advantage of the thermistor is its relatively high resistance.
Thermistors are available with base resistances (at 25° C) ranging from hundreds to millions
of ohms. This high resistance diminishes the effect of inherent resistances in the lead wires.
The major tradeoff for the high resistance and sensitivity of the thermistor is its highly
nonlinear output and relatively limited operating range (Figure 9.1). Depending on the type of
thermistors, upper ranges are typically limited to around 300° C. Figure 1 shows the
resistance-temperature curve for a 2252 W thermistor.
Figure 9.1. Resistance-temperature curve for thermistor, resistance temperature detector (RTD) and
thermocouple.
The thermistor has been used primarily for high-resolution measurements over limited
temperature ranges. The classic example of this type of application is medical thermometry.
However, continuing improvements in thermistor stability, accuracy, and interchangeability
have prompted increased usage of thermistors in all types of industries.
The resistance-temperature behaviour of thermistors is highly dependent upon the
manufacturing process. Therefore, thermistor manufacturers have not standardized
thermistor curves to the extent that thermocouple or RTD curves have been standardized.
Typically, thermistor manufacturers supply the resistance-versus-temperature curves or
tables for their particular devices. The thermistor curve, however, can be approximated
relatively accurately with the Steinhart-Hart equation :
T ( °K ) =
1
a0 + a1 ln (Rt ) + a2 ⎡⎣ln (Rt ) ⎤⎦
3
(9.1)
where T(°K) is the temperature in degrees Kelvin, equal to T(°C) + 273.15, and RT is the
resistance of the thermistor. The coefficients a0, a1, and a2 can be provided by the
thermistor manufacturer, or calculated from the resistance-versus-temperature curve.
Temperature-controlled circuits
An application of the characteristics of a thermistor is shown in Figure 9.2. The
temperature-controlled switch is composed of the resistor bridge, silicon controlled
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
rectifier (SCR) and lamps. The resistive bridge is constituted by a thermistor and resistors
VR2, R3, R4 and R5. Its output between A and B provides the triggering voltages VAB to the
gate of SCR. Two lamps are controlled by the SCR.
If the bridge is in balance (
RT
VR 2 + R 3
=
R4
) VAB is zero. This will turn off the SCR and the
R5
lamps. When an increase in temperature decreases the resistance of RT, the bridge circuit is
unbalanced and the positive output voltage VAB turning on SCR. Then ac current flows through
SCR and both lamps. The D1 acts as a protection diode to pass the negative VAB. The VR2 is
used to balance the bridge at a specific temperature, such as at room temperature.
Figure 9.2. Temperature-controlled circuit.
PROCEDURE
□
1. Set the module KL-13010 on the main unit KL-21001, and locate the block b.
□
2. Locate the terminals of the thermistor RT shown in Figure 9.3.
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
Figure 9.3.
□
3. Measure and record the resistance of RT at room temperature.
□
4. Hold RT by your thumb and the index finger and observe the change of resistance
indicated by the ohmmeter. Is the resistance of RT decreased?
□
5. Warm up RT with a soldering iron of 25W-35W until resistance reaches a constant
value and measure the resistance of RT.
□
6. According to Figure 9.4, complete the experiment circuit with short circuit clips.
Figure 9.4.
□
7. Apply the ac power source 9V-0-9V to terminals AC9V, 0, AC9V.
□
8. Apply +5V to V+.
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İSTANBUL KÜLTÜR UNIVERSITY
Electronic Engineering
□
9. Turn VR2 to the point that the lamps L1 and L2 are just turned off. At this time,
SCR is turned on or off?
□
10. Approach a heated soldering iron to RT and observe the states of lamps. Record
the results in Table 9.1 and identify the states of SCR.
□
11. Take away the soldering iron from RT and observe the states of lamps. Record the
results in Table 9.2 and identify the states of SCR.
QUESTIONS
1. What is silicon controlled rectifier (SCR)? Explain briefly.
2. Explain the differences between thermistor and RTD and thermocouple.
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EXPERIMENT DATA SHEET
Name of the Experiment
Group #
Names of the Students
Date of the Experiment
Name of the Lab Assistant
:Thermistor characteristics and
temperature-controlled circuit
:
........
:
........
........
........
:
........
:
........
Signed
:
Experiment Data
3. RT at room temperature
:
........
4. RT decreased with increasing temperature
5. max resistance of RT
:
........
9. SCR at room temperature
:
on
off
Table 9.1
L1 state
:
yes
no
Table 9.2
L2 state
SCR state
L1 state
58
L2 state
SCR state
........