Exercise 4: Use of the Multimeter
Objective
At the end of this exercise student should be able to operate the Multimeter to take circuit voltage and current
measurements and to perform continuity testing to troubleshoot a circuit or device.
Introduction
The term Multimeter refers to an electronic device use to measure several
parameters common to electric and electronic circuits. These parameters include
voltage, current, and resistance. More sophisticated devices can also measure
capacitance, inductance, temperature, relative humidity, frequency and sound
intensity (decibels), among other things. Some of these measurements require
special probes.
Most Multimeters can measure voltage and current in AC and DC systems. DC, or
direct current, systems are those typically powered by batteries. Examples include
cars, trucks, remote controls, portable toys, and portable tools. Batteries provide a
constant voltage level, thus current, to the load that can be directly measured by
the Multimeter.
AC, or alternating current, refers to the electric energy system such as the one delivered to our homes or work places by
the local energy supplier (i.e., Electric Energy Authority, AEE, in Puerto Rico). The magnitude or such voltage or current
fluctuates in a sinusoidal way. Because of this fluctuation with time, it is not practical to measure the exact magnitude of
the voltage or current at any given point in time. Instead, AC values are determined in terms of the effective or RMS
value. This value is defined as the peak magnitude of the sinusoidal wave divided by square root of two (√2).
V
RMS
 V Peak
2
Using the Multimeter
The first things to know when using a Multimeter are what are
the main components and how to configure it in order to obtain
the desired measurement. The meter has a digital or analog
display on top where the user gets the reading of the desired
parameter. When reading the dial, the user must be aware of
the range of value the multimeter is set up to read.
Below the display there is a selector dial with various options.
The table below summarizes the definitions of some of the
various symbols in the dial.
Symbol
Meaning
Ũ
AC Voltage
Ū
DC Voltage
Ã
AC Current
Ā
DC Current
Ω
Resistance
))
Continuity Testing
))
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Display
Selector
Dial
Probe
Ports
Exercise 4: Use of the Multimeter
For each parameter, the multimeter might have several ranges of operation. Some multimeters adjust to the proper
range automatically, but many require manual adjustment of such range. The AMPROBE® AM-22 model, for example,
has 4 different ranges for AC voltage measurement: 600V, 200V, 20V and 2V. These values indicate the maximum
possible value the meter can read under such configuration. The user must select the voltage level according to the
expected voltage value. If there is no insight as to what the expected value should be, set the meter to the lowest setting
and start your way up.
Say, for example, there are 24 volts at the desired point of measurement. By setting the meter to 2V and reading, the
meter will display “OL”. OL means over load and implies that the detected voltage is larger than what the meter can read
under such configuration. So, the user must increase the range to the next value (i.e., 20V). Since the value of the
voltage is 24V, the meter will again display “OL” and suggest the user to further increase the range. As we increase the
range, the resolution of the meter decreases.
Continuity Testing
In order for current to flow through a circuit, the circuit must be closed. Continuity testing refers to the use of the
multimeter to determine if the circuit is indeed closed. In other words, continuity testing attempts to establish that a
continuous path exists on the portion of the circuit being tested. This is a very valuable troubleshooting technique to
detect malfunctioning devices and broken wires.
In order to perform a continuity test we first need to properly configure the Multimeter. Start by connecting the black
probe to the COM port. The other probe goes to the port with the omega symbol (Ω). Then, rotate the selection dial to
the continuity testing setting. Always start by checking that the Multimeter works properly when performing continuity
testing. Do this by separating the free probe ends to ensure they are not touching each other. Under this condition, the
display should show display “1.” or “OL” to the left of the display. Then, bring the probe ends together. The display
should change to “0.0” (or close to that) and a beep should be heard. This indicates there is continuity.
Test 1: Checking functionality of devices – Continuity Testing
Materials




Multimeter with probes
Lamp
Single pole switch
Outlet
Procedure
1) Connect your Multimeter probes by inserting the black probe into the COM outlet
2) Connect the red probe to measure resistance (Outlet with Ω symbol)
3) Turn on the Multimeter to read resistance
4) Measure values to complete the tables below.
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Exercise 4: Use of the Multimeter
Lamp
Red Probe to
Black Probe to
Contact screw connected to bottom plate of
lamp (A)
Contact screw connected to inner metal covering
(B)
Contact screw B
Contact screw A
Contact screw A
Inner metal covering of the lamp
Contact screw A
Bottom plate inside lamp socket
Contact screw B
Inner metal covering of the lamp
Contact screw B
Bottom plate inside lamp socket
Is there continuity?
Outlet
Red Probe to
Black Probe to
Dark contact screw (A)
Other dark contact screw
Light contact screw
Other light contact screw
Any dark contact screw
Any light contact screw
Any dark contact screw
Short slot of right outlet
Any dark contact screw
Long slot of right outlet
Any light contact screw
Short slot of right outlet
Any light contact screw
Long slot of right outlet
Is there continuity?
Single Pole Switch
Switch Position
Red Probe to
Black Probe to
OFF
Contact screw A
(assume contact A is the upper screw
when the word OFF can be read up
side up)
Contact screw B
ON
Contact screw A
Contact screw B
OFF
Contact screw A
Exterior plate or green screw
ON
Contact screw A
Exterior plate or green screw
OFF
Contact screw B
Exterior plate or green screw
ON
Contact screw B
Exterior plate or green screw
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Is there continuity?
Exercise 4: Use of the Multimeter
Test 2: Troubleshooting switches
Materials



Multimeter
3-way switch
4-way switch
Procedure
1) Use your Multimeter to determine the interconnection of 3-Way and 4-Way switches.
2) Draw a diagram for each switch showing the interconnection of the switch in both positions.
A
B
A
B
C
D
C
D
A
B
A
B
C
D
C
D
4- way switch.
A
B
A
B
C
D
C
D
A
B
A
B
C
D
C
D
3- way switch
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Exercise 4: Use of the Multimeter
Test 3: Building a circuit
Materials







Lamp and light bulb
Single pole switch
Outlet
Black wire & white wire
Screwdriver
Wire cutters
Pliers
Procedure
1) Connect the circuit as shown below.
2) Measure the voltage and currents shown in the figure and complete the table below for the switch in the
OFF position.
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Description
Symbol
Voltage from source
vT
Voltage across fan
vF
Voltage across lamp
vL
Voltage across switch
vS
Measurement
Exercise 4: Use of the Multimeter
3) Repeat step 3 for the switch in the ON position.
Description
Symbol
Voltage across fan
vF
Voltage across lamp
vL
Voltage from source
vT
Current from source
iT
Voltage across switch
vS
Measurement
Review Questions
1) What is a Multimeter?
2) What is the RMS value?
3) What are the main components of a Multimeter?
4) What is continuity testing?
5) How can we use continuity testing as a tool to troubleshoot circuits or devices?
6) On step 2 of part 3,
a. Is VT = VF = VL? Why?
b. Is VT = VS? Why?
7) On step 3 of part 3,
c.
Is VT = VF = VL? Why?
d. Is VT = VS? Why?
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