The Digital Multimeter
Science Learning Center
University of Michigan – Dearborn
Modified from a presentation written by Dr. John Devlin by: Donald Wisniewski,
Dawn Wisniewski, Huzefa Mamoola, Shohab Virk, Saadia Yunus
Under the direction of: Dr. Ruth Dusenbery, Dr. Paul Zitzewitz and Mr. Henry
Povolny
And further modified by Jim Hetrick and Annette Sieg.
With funds from the Office of the Provost, UM-D, and NSF CCLI grant # DUE
9952827 to RD and PZ.
Welcome to The Digital Multimeter Module!
To complete the module you must work through the hands-on
tutorial described in this document then pass a follow-up mastery
test.
The goal of the module is to leave you with the ability to confidently
use a digital multimeter to measure, without any assistance, three
quantities: 1) electric voltage, 2) electric current and 3) electric
resistance.
These important electrical instrumentation skills naturally appear in
the context of the analysis, design, construction and use of electric
circuits. That being so, electric circuit vocabulary and diagrams will
appear throughout the module.
Many of the terms and diagrams may appear unfamiliar if you
haven’t covered them in class yet. Keep in mind that you are not
expected to obtain a full understanding of electric circuit theory
from this module.
The module has the specific and limited goal of teaching you the
three electrical instrumentation skills described above. These skills
will be valuable for your electric circuit labs when you take up the
study of electric circuits in your course.
DIGITAL MULTIMETER (DMM) OVERVIEW
DIGITAL MULTIMETER (DMM) OVERVIEW
Introduction
The digital multimeter, sometimes referred to as simply the
multimeter or DMM, is a versatile instrument. It contains
three different meters in one case:
1. A voltmeter measures the electric potential difference
between two points. (in volts).
2. An ammeter measures the electric current through a
device (in amperes, or amps).
3. An ohmmeter measures the electric resistance of a device
(in ohms).
DIGITAL MULTIMETER (DMM) OVERVIEW
Layout
• The top portion of the meter contains
the digital readout area, which
resembles the digital display of many
pocket calculators.
• Below the digital readout is a large
gray knob, called the Function Switch.
This switch determines which function
the multimeter will perform
(voltmeter, ammeter, or ohmmeter).
DIGITAL MULTIMETER (DMM) OVERVIEW
Function Switch – Overview
• The Function Switch has eight
positions.
• The first is OFF. The meter should
always be returned to this position
when not in use.
• The next three marked with V
measure voltage, the one marked Ω
measures electrical resistance, the
one marked
checks for
continuity, and the last two marked
with A measure current.
DIGITAL MULTIMETER (DMM) OVERVIEW
Function Switch – Voltage
• V~ (*) is for measuring
alternating-current voltages,
or simply AC voltage.
• V= (*) is for measuring direct
current voltage, or simply DC
voltage.
• 300mV= (*)is for measuring
low voltages of direct current
in the millivolt (mV) range.
*
*
*
DIGITAL MULTIMETER (DMM) OVERVIEW
Function Switch – Ohms & Amps
•  (*) is used for measuring
electrical resistance (in
ohms).
•
(*) is for continuity
testing. It will not be covered
here.
• A~ (*) is for measuring AC
current (in amps).
• A= (*) is for measuring DC
current (in amps).
*
*
*
*
DIGITAL MULTIMETER (DMM) OVERVIEW
Function Switch – Summary
•
•
•
•
•
•
•
V~ for AC voltage
V= for DC voltage
300 mV for low DC voltages (millivolts)
A~ for AC current
A= for DC current
 for resistance
for continuity (not used in this module)
DIGITAL MULTIMETER (DMM) OVERVIEW
Starting Up
• When the digital multimeter is first turned on, it spends a few
seconds conducting a self-analysis of its battery and its
internal circuits.
• While this is proceeding, the meter will light up almost all of
the digital segments including a tiny battery symbol in the
upper left hand portion of the display.
• If you turn it on and it does not look like the image below,
notify the SLC personnel.
THE DESIGN BOARD AND POWER SUPPLY
THE DESIGN BOARD AND POWER SUPPLY
Introduction
• Measurements with the digital multimeter will be made on
an electric circuit you will build.
• The circuit will be assembled on the Design Board and
powered by an adjustable DC Voltage Supply. (A battery
could be used to power the circuit, but the DC Voltage
Supply, which plays the same role as a battery, is being used
instead.)
DC Voltage
Supply
Design
Board
THE DESIGN BOARD AND POWER SUPPLY
Power Supply Connections
• Check that a red cable is connected from the red (+)
terminal on the DC Voltage Supply to the red socket on
the Design Board.
• Check that a black cable is connected from the black (-)
terminal on the DC Voltage Supply to the black socket on
the Design Board.
-+
+
-
THE DESIGN BOARD AND POWER SUPPLY
Power Supply – Settings
• The DC Voltage Supply has four
knobs that can be turned.
• Check that the left-most knob
is turned fully clockwise. Do
not touch this knob for the
remainder of the module.
• Check that the next knob to
the right is turned fully
counter-clockwise. Do not
touch this knob for the
remainder of the module.
THE DESIGN BOARD AND POWER SUPPLY
Power Supply – Settings
• The DC Voltage Supply has a
display that can read voltage
and current.
• Check that it is set to read
voltage by ensuring the black
slider-switch at the right of
the display is in the “up”
position.
THE DESIGN BOARD AND POWER SUPPLY
Power Supply – Voltage
• Turn on the DC Voltage Supply
by pressing the green button at
the lower left.
• For all of this module’s activities
the DC Voltage Supply should be
set to supply 3.00 V.
• If its display already reads 3.00 V
it is ready to go!
• If not, turn the two right voltageadjust knobs until the display
reads 3.00 V. Do not touch
these knobs for the remainder of
the tutorial.
Voltage Adjust
Knobs
MEASURING DC VOLTAGE
MEASURING DC VOLTAGE
Introduction
• In this portion of the module you will use the digital
multimeter to measure an electric potential difference or
“voltage” between two points.
• The basic unit of electric potential is the volt. The symbol
for a volt is “V”.
• When the multimeter is used to measure electric
potential difference (voltage) it is called a voltmeter.
MEASURING DC VOLTAGE
Measuring the Supply Voltage
• Your first measurement will be using the digital multimeter
to determine the potential difference maintained by the DC
Voltage Supply.
• The DC Voltage Supply is connected
across the terminals labeled A and B
on the Design Board.
• Terminal A is at a higher potential
with respect to terminal B, which is
why terminal A is labeled with a “+”
sign on the DC Voltage Supply.
• You will measure the potential
difference between these terminals.
It should be close to 3.00 V, the
supply voltage.
A
B
MEASURING DC VOLTAGE
Configure the Multimeter – Step 1
• To carry out this measurent you
must configure the multimeter
to measure a DC voltage. This
involves three steps.
• First, turn the DMM’s Function
Switch to the V= position.
MEASURING DC VOLTAGE
Configure the Multimeter – Step 2
• Second, connect voltage probes to the
multimeter.
• At the bottom of its front cover the
multimeter has four sockets for
connecting probes. Only two are used
at a time.
• To measure voltage, probes are
connected to the two sockets on the
right.
• Connect a red probe to the red socket
on the meter (labeled V) and a black
probe to the socket labeled COM.
MEASURING DC VOLTAGE
Configure the Multimeter – Step 3
• Third, the probes must
be connected to the
points across which
the potential
difference is to be
measured.
• To measure the supply
voltage, connect the
red test lead from the
DMM to point A, and
the black test lead to
point B.
A
B
MEASURING DC VOLTAGE
Measure the Voltage
• Read the value on your
display, which should be
about 3.000 V.
• The type of voltage is
indicated by ‘VDC’ to the
right of the number
displayed, which means a
DC voltage as opposed to
AC.
A
B
MEASURING DC VOLTAGE
Review of Method
• First set the Function Switch to the desired position
(V= in this case).
• Then connect the two probes to the proper terminals of
the meter.
• Lastly, connect the probes to the points in the circuit
across which the voltage change is to be measured, and
read the displayed value.
MEASURING DC VOLTAGE
Determining Polarity
• Now, reverse how the DMM’s probes are connected to the
Design Board. Connect the red probe to point B and the black
probe to point A.
• Notice the display shows nearly the same numerical value, but
now has a negative (-) sign in front of it. The DMM not only
measures the magnitude of the voltage, but it also senses
which terminal is at the higher potential.
• Positive readings indicate the red (or
VΩ) terminal is at the higher potential,
while negative readings indicate the
COM terminal is at the higher potential.
A
• Now disconnect the probes from the
Design Board.
B
MEASURING DC VOLTAGE
Circuit Diagrams
• This figure is called a circuit diagram.
It is a symbolic representation of a
physical electric circuit.
• The symbol between points A and B
represents the DC Voltage Supply (or a
battery).
• The symbol between points C and D
and E and F represents a resistance in
the circuit.
• The solid black lines represent wires
connecting the DC Voltage Supply and
two resistances.
MEASURING DC VOLTAGE
A Complete Circuit
• The connections form a closed loop
called a complete circuit.
• Because a complete circuit is formed
the DC Voltage Supply drives a steady
flow of charge around the loop.
• The rate of charge flow is called
electric current (labeled I).
• Charge flow through a resistance
indicates a voltage change occurs
across the resistance.
• You will build this circuit and use the
DMM to measure the voltage change
across each resistance.
MEASURING DC VOLTAGE
Build the Circuit
• To build this circuit the two
resistances must be incorporated.
• The resistances are supplied by
objects called resistors. Find the
resistors labeled R1 and R2 and
place them as shown.
• Using three of the short black
connector wires establish
connections between the points A-C,
D-E and F-B.
• This completes what is called a
series circuit. The battery and two
resistors are in series with one
another.
A C
D R1
E
B
F
R2
MEASURING DC VOLTAGE
Measuring VAB
• Check that the DMM’s
Function Switch is still set to
the V= position.
• Now, connect the red probe to
point A, and the black probe to
point B. Record your results as
VAB, the voltage between
points A and B. This is the
supply voltage.
• Is it the same as when the
resistors were not connected?
A
R1
R2
B
MEASURING DC VOLTAGE
Measuring VCD
• Next you will measure the
voltage across R1.
• To do so connect the red probe
to point C and the black probe
to point D.
• The meter is now connected
across resistor R1, so you are
measuring the potential change
across it. Record this value as
VCD.
C
D R1
R2
MEASURING DC VOLTAGE
Measuring VEF
• Next you will measure the
voltage across R2.
• To do so connect the red
probe to point E and the
black probe to point F.
• The meter is now connected
across resistor R2, so you are
measuring the potential
change across it. Record this
value as VEF.
R1
E
F
R2
MEASURING DC VOLTAGE
A Consistency Check
• Add the voltage results for VCD and VEF.
• Kirchoff’s Voltage Law, called the “loop law”, states that the
sum of potential changes around a circuit is zero. In this
circuit the loop law gives the following equation.
VCD + VEF = VAB
• If this rule does not hold within 10% of your measurements,
you have probably measured something wrong. If so, redo
the measurements.
• When you are finished, disconnect the two DMM probes and
the three small black connector wires and turn the meter off.
MEASURING DC VOLTAGE
Summary of Voltage Measurement
•
•
•
•
Set Function Switch to V=.
Connect red probe to V terminal.
Connect black probe to COM terminal.
Connect the probes to the two points across which the
voltage change is to be measured.
• Read the meter and record result in volts.
MEASURING DC CURRENT
MEASURING DC CURRENT
Introduction
• In this portion of the module you will use the digital
multimeter to measure electric current, a quantity that
gives the rate of charge flow.
• The basic unit of electric current is the ampere, or amp.
The symbol for an amp is an “A”. A current of 1 A at some
point in a circuit indicates charge is flowing past that point
at a rate of 1 Coulomb every second.
• When the multimeter is used to measure electric current it
is called an ammeter.
• It is critical to learn that to measure current the multimeter
must be connected in an entirely different fashion than for
measuring voltage! It is not enough to simply change the
Function Switch!
• Read carefully and note the difference as you proceed.
MEASURING DC CURRENT
Build the Circuit
• Build the circuit shown below using
resistor R1 and two short black
connecting wires.
• The single resistor is in series with
the DC Voltage Supply.
• This is a complete circuit and there
will be a steady flow of charge. The
rate of charge flow is electric
current, labeled with an I in the
diagram. Soon you will measure I.
A
C
D
B
R1
MEASURING DC CURRENT
Configure the Multimeter – Step 1
• To measure DC current the
multimeter must be
reconfigured.
• First, the Function Switch must
be set to measure DC current.
• Do so by turning the Function
Switch to the A= position.
MEASURING DC CURRENT
Configure the Multimeter – Step 2
• Second, the red probe must be relocated, because a different
pair of sockets on the multimeter is used to measure current.
• Insert the red probe in the socket on the lower left labeled
300 mA. This socket is used for measuring currents up to a
maximum of 300 mA. (Higher currents, up to 10 A, can be
measured with this meter by using the socket labeled 10 A.)
• The black probe should remain inserted in the COM socket.
MEASURING DC CURRENT
Configure the Multimeter – Step 3
• Third, the probes must be
connected to the circuit, but in a
fashion that is different from a
voltage measurement.
• The circuit must be “broken” to
connect the ammeter. Do so by
first removing the short black
wire that connects point A to
point C.
• Then…
A
Wire has been
removed.
C
R1
MEASURING DC CURRENT
Configure the Multimeter – Step 3
• …replace the short black wire
with the ammeter by
connecting the multimeter in
its place. That is, connect the
red probe of the multimeter
to point A and the black
probe of the multimeter to
point C.
A
C
R1
MEASURING DC CURRENT
Measure the Current
• Once again a complete
circuit has been established,
but now the ammeter is part
of the circuit, connected in
series with R1 and the DC
Voltage Supply.
• By placing the ammeter in
series, charge flowing
through the circuit also flows
through the meter where its
rate of flow is measured.
• Record what the display
reads. This is the current in
units of mA. It should read
between 2.73 and 3.33 mA.
R1
MEASURING DC CURRENT
Determining Direction of Flow
• Reverse how the DMM’s probes are connected to the Design
Board. Connect the red probe to point C and the black probe
to point A.
• Notice the display shows nearly the same numerical value, but
now has a negative (-) sign in front of it. The DMM not only
measures the magnitude of the current, but it also senses the
direction of flow.
A
• A positive reading indicates
conventional charge flow into the
300 mA socket and out of the COM
socket.
• A negative reading indicates
conventional charge flow into the COM
socket and out of the 300 mA socket.
C
R1
MEASURING DC CURRENT
What Does it Mean?
• In this circuit the DC Voltage Supply, the ammeter, R1, and the
wires form a single complete loop. We say all of these
elements are in series.
• A SERIES RULE TO REMEMBER: The current through all
elements in series is the same!
• Therefore, the current you just measured is not just the
current through the ammeter, but is also the current through
R1, all the wires, and the DC Voltage Supply.
• Reset the circuit by disconnecting the ammeter from the circuit
and reconnecting the short black wire between points A and C.
MEASURING DC CURRENT
A Consistency Check
• Let’s propose a test to check this
rule. If you measure the current on
the other side of R1, the rule says
you should get the same result.
• But don’t start the test right away.
You will conduct this test using a
different technique for connecting
the ammeter to the circuit. Read
carefully, learn the new technique,
and note the difference.
What is the current here?
R1
MEASURING DC CURRENT
The Two-Point-Break
• A key step in creating a test to
measure current in a circuit is
“breaking the circuit” to insert the
ammeter in series.
• In the measurement you just
completed this was accomplished by
removing the wire connecting points
A and C and replacing it with the
ammeter.
• This remove-and-replace method
should be recognized as a “twopoint-break”. The circuit was broken
at two points: at point A one end of
the black wire was disconnected,
and at point C the other end of the
wire was disconnected.
A
C
R1
MEASURING DC CURRENT
The One-Point-Break
• An ammeter can also be
connected to a circuit with a
“one-point-break”. Let’s try it.
• To measure the current on the
other side of R1, first disconnect
the other short black wire at
point D. This is the one-pointbreak.
• Do not disconnect the other end
from point B; this wire will
remain part of the circuit.
• Then…
R1
D
B
MEASURING DC CURRENT
The One-Point-Break
• …connect the ammeter’s
red probe to point D and its
black probe to the free end
of the short black wire.
(This requires two hands so
both hooks can be made to
protrude simultaneously.)
R1
D
MEASURING DC CURRENT
Measure the Current
• Once again, but this time
using a one-point-break, a
complete circuit has been
established with the
ammeter inserted in
series.
• Record what the display
reads. The current on this
side of R1 should be the
same as what you
measured on the other
side. Is it?
R1
MEASURING DC CURRENT
Two Ways to Break a Circuit
• To recap, the diagrams below contrast the two-point-break
and the one-point-break methods for connecting an ammeter.
• Both accomplish the same goal in slightly different ways. Be
aware of the difference.
symbol for
ammeter
two-point-break
one-point-break
MEASURING DC CURRENT
Summary
To measure DC current with the multimeter:
• Set the function switch to A=.
• Connect the red probe to the socket labeled 300 mA (or the
socket labeled 10 A if the current is greater than 300 mA.)
• Connect the black probe to the socket labeled COM.
• Connect the meter in series with the elements through
which the current is to be measured. Use either the onepoint-break or two-point-break method.
• Read the display and record the result. When the 300 mA
socket is used, the units of your results are milliamps.
(When the 10 A socket is used the units are amps.)
MEASURING DC CURRENT
Voltage vs. Current
• The circuit diagrams below contrast the connections
needed to measure the voltage across R1 (left) and the
current through R1 (right).
• The voltmeter is connected in parallel with (across) R1.
No break in the circuit needed. (Easy!)
symbol for
• The ammeter is connected in series (in line) with R1. voltmeter
The circuit must be broken. (More difficult.)
Measuring Voltage
R1
Measuring Current
R1
MEASURING RESISTANCE
MEASURING RESISTANCE
Introduction
• In this final portion of the module you will use the digital
multimeter to measure electrical resistance.
• Electrical resistance is a property of objects that depends
on many things including an object’s size and shape, its
structure and composition, and the temperature.
• The basic unit of resistance is the ohm. The symbol for an
ohm is a capital omega, Ω.
• When the multimeter is used to measure electrical
resistance it is called an ohmmeter.
MEASURING RESISTANCE
Measuring Resistance – Step 1
• You will use the digital multimeter
to measure the resistance of
resistors labeled R1, R2 and R3.
This requires four steps.
• First, set the DMM’s Function
Switch to measure resistance.
• Do so by turning it to the Ω
position.
• In this position, the display will
show an “O.L.” reading when first
turned on. This indicates that there
is an “over load” or off-scale
resistance. This occurs when the
resistance is higher than the meter
is capable of reading, such as when
no device is connected.
MEASURING RESISTANCE
Measuring Resistance – Step 2
• Second, connect the probes to the
DMM for a resistance measurement.
The same sockets as for a voltage
measurement are used for a
resistance measurement.
• Insert the red probe in the VΩ
socket.
• Insert the black probe in the COM
socket.
MEASURING RESISTANCE
Measuring Resistance – Step 3
• Third, electrically isolate the object
whose resistance is to be measured.
• For example, let’s measure the
resistance of the resistor labeled R1
first.
• R1 must be completely isolated
before its resistance can be
measured. This means if it is still
connected in a circuit on the Design
Board you must disconnect all wires
from it.
• Resistance of an object cannot be
measured when the object is still in
a circuit, even if the circuit’s power
source is off. It must be removed
from the circuit.
R1
MEASURING RESISTANCE
Measuring Resistance – Step 4
• Fourth, connect the DMM’s
probes across the object
whose resistance is being
measured.
• Here connect the red probe to
one side of R1 and the black
probe to the other side of R1.
• Note that, just like a voltage
measurement, this step
connects the multimeter in
parallel with the object.
• Read the display showing R1’s
resistance. It should be within
10% of 1000 Ω.
R1
MEASURING RESISTANCE
Measuring R2
• Repeat this procedure to
measure the resistance of
the resistor labeled R2. Its
resistance should be within
10% of 2200 Ω.
R2
MEASURING RESISTANCE
Measuring R3
• Repeat this procedure to
measure the resistance of
the resistor labeled R3. Its
resistance should be within
10% of 3300 Ω.
• (Note: the multimeter
automatically switches to
the kΩ scale when the
resistance exceeds about
3000 Ω.)
R3
MEASURING RESISTANCE
Summary
Turn the DMM’s Function Switch to .
Insert the red probe in the V socket.
Insert the black probe in the COM socket.
Electrically isolate the object whose resistance is to be
measured.
• Connect the probes across (in parallel with) the object.
• Read the display and record the resistance in , k, or
M.
•
•
•
•
MEASURING RESISTANCE
Equivalent Resistance
• Next you will use your resistancemeasurement-skills in a more
complex example.
• Sometimes it is necessary to know
the combined resistance of a group
of resistors, called the equivalent
resistance of the group. The
ohmmeter is capable of measuring
this resistance as well.
• The circuit diagram shows one way
of connecting resistors R1, R2 and R3
together.
• What is the equivalent resistance of
this combination?
C
R1
D
G
E
R2
F
R3
H
MEASURING RESISTANCE
Connect the Resistors
• Lay out the three resistors on the design board.
• Using three short black
connecting wires establish links
between the pairs of points: DC
E, E-G and F-H.
R1
D
• Do not connect the resistors to
the DC Voltage Supply. You will
E
not be powering this circuit.
G
R2
• Remember, you will be
F
H
measuring resistance with the
multimeter which means the
object, in this case a
combination of three resistors,
must be electrically isolated.
R3
MEASURING RESISTANCE
Measure the Equivalent Resistance
• Check that the DMM is still configured to measure
resistance.
• Then connect the red probe to point C and the black
probe to point F.
• Read the DMM’s display;
it shows the resistance
between points C and F.
This is the equivalent
resistance of the three
resistors in this
configuration.
• Your result should be
between 2088 Ω and
2552 Ω.
C
D
R1
E
F
R2
G
H
R3
CONCLUSION
CONCLUSION
Mastery Test
• You have completed the tutorial portion of the Digital
Multimeter Module.
• To complete the module you must pass the Digital
Multimeter Mastery Test.
• Disconnect all of your wiring. Turn the Function Switch on
the multimeter to the OFF position. Turn off the DC
Voltage Supply.
• Return resistors R1, R2 and R3 to the SLC personnel. The
Design Board, DC Voltage Supply and short black
connecting wires remain at the station.
• When you are ready to take the Mastery Test obtain a
new set of “testing resistors”, two 3-way splitters, the test
instructions, and answer sheet from the SLC personnel.