Universiti Malaysia Perlis
DKT 111/3 – ELECTRIC CIRCUITS PRINCIPLES
LAB ASSIGNMENT 2:
OHMMETER
Pn. Nazatul Syima Bt. Saad
Pusat Pengajian Kejuruteraan Komputer Dan Perhubungan
Universiti Malaysia Perlis
DKT 111/3 – Electrical Circuits Principles
Laboratory Session 1: Ohmmeter and its Measurement
Figure 1 – Analog Ohmmeter
Introduction
Ohmmeter
An Ohmmeter is an electrical instrument which is use to measure the resistance
(degree of opposition to current flow).Resistance is measured in unit Ohm, bigger value
indicates strong opposition and less current flow while smaller value indicates lesser
opposition and more current flow.
A simple analog ohmmeter consists of a battery, a moving meter and a red and a black
lead terminals and it measures the resistance in between the leads. Resistance
measurement has NO POLARITY so interchanging position of red and black probe will
not change measurement value.
Ohmmeter fixed current or voltage going out of its lead and measure the change in
voltage or current between both leads.
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DKT 111/3 – Electrical Circuits Principles
Using Ohmmeter
1. Calibration
i.
ii.
Hold both leads together (short).
Adjust calibration knob until needle indicates zero resistance, 0 Ω.
2. Measurement
i.
Power off unit under test.
ii.
Set Ohmmeter to highest resistance range.
iii.
Touch the probe leads to measurement points.
iv.
Adjust resistance range until readable resistance value is obtained.
3. Caution
i.
Ohmmeter may be damaged if connected to voltage source.
ii.
Ohmmeter has internal resistance of 100 MΩ (typical) and may load your
circuit.
Figure 2 –Sanwa’s Multimeter specifications
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DKT 111/3 – Electrical Circuits Principles
Experiment 1
1. Connect the meter's test probes across your body part as such, and note its
indication on the resistance scale:
a) Between fingers in a palm
b) Between both hands
c) Between two person
Experiment 2
Connect the meter's test probes across the resistor as such, and note its indication on
the resistance scale:
Figure 3 – Measuring resistors
If the needle points very close to zero, you need to select a lower resistance range on
the meter, just as you needed to select an appropriate voltage range when reading the
voltage of a battery.
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DKT 111/3 – Electrical Circuits Principles
Experiment 3
Take a piece of paper and draw a very heavy black mark on it with a pencil (not a
pen!). Measure resistance on the black strip with your meter, placing the probe tips at
each end of the mark like this:
Figure 4 – Measuring pencil mark resistance
Move the probe tips closer together on the black mark and note the change in
resistance value. Does it increase or decrease with decreased probe spacing? If the
results are inconsistent, you need to redraw the mark with more and heavier pencil
strokes, so that it is consistent in its density. What does this teach you about resistance
versus length of a conductive material?
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DKT 111/3 – Electrical Circuits Principles
Experiment 4
Connect your meter to the terminals of a light-dependent resistor (LDR) and measure
the change in resistance created by differences in light exposure.
Figure 5 – Measuring LDR
Exercise 1
Use your meter to determine continuity between the holes on a breadboard as in Figure
6. (Use small gauge solid wire to insert into the holes of the breadboard), redraw the
board with line showing its connectivity.
Exercise 2
For the circuit below ( figure 7) , measure the voltage between point ab, when
a) R1 = 1 kΩ, R2 = 2.2 kΩ and R3 = 4.7kΩ.
b) R1 = 200 kΩ and R2 = R3 =10 kΩ.
For the two conditions above:
a) Briefly explains your measurement result to theoretical value.
b) What is your measurement error?
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DKT 111/3 – Electrical Circuits Principles
Figure 6 – Measuring breadboard’s continuity.
Figure 7 – Measuring circuit resistance
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DKT 111/3 – Electrical Circuits Principles
Name :
Matrix Number:
Programs:
Result / Analysis
Experiment 1:
a) Between fingers in a palm
b) Between both hands
c) Between two person
Experiment 2:
Discussion:
a) Between fingers in a palm
Experiment 3:
Discussion:
Experiment 4:
Discussion:
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DKT 111/3 – Electrical Circuits Principles
Exercise 1:
Discussion:
Exercise 2:
a) R1 = 1 kΩ, R2 = 2.2 kΩ and R3 = 4.7kΩ.
b) R1 = 200 kΩ and R2 = R3 =10 kΩ.
Discussion for all Laboratories:
Conclusion:
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