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Guide to Using
the Multimeter
2033-01
This guide was produced by the Société de formation à distance
des commissions scolaires du Québec.
Production Coordinator :
Alain Pednault
Development :
Dorcotek inc.
Translation : Direction de la production en langue anglaise Services à la communauté anglophone Ministère de l'Éducation
Scientific Proofreading :
Interscience
Proofreading :
Francine Cardinal
Layout :
Michèle Gagné
© Société de formation à distance des commissions scolaires du Québec, 2013
All rights for translation and adaptation, in whole or in part, reserved for all
countries. Any reproduction by mechanical or electronic means, including
microreproduction, is forbidden without the written permission of a duly
authorized representative of the Société de formation à distance des commissions
scolaires du Québec.
This guide accompanies the multimeter, which is included in the experiment kit. The description and instructions may differ slightly for instruments made by another manufacturer. The
safety rules, however, apply to all multimeters.
1.
DESCRIPTION OF THE MULTIMETER
Your multimeter allows you to measure the voltage (voltmeter function), current intensity
(ammeter function) and resistance (ohmmeter function) of certain components of an electric circuit. Its specialized functions also allow you to perform other types of tests, such as
circuit continuity and diode polarity tests.
This guide is limited to the study of the measurement of voltage, current and resistance,
since these three types of measurements are the most useful in analyzing circuits. Also,
they are the only measurements you will need to make in the experiments in this course.
Your multimeter is powered by a 9-V cell, without which it cannot operate. The cell is inside
the instrument; to reach it, you must remove the back of the multimeter by unscrewing the
two screws. Near the cell is a 0.2-A, 250-V fuse, which protects the multimeter against surges.
The multimeter has three main parts: the digital display, the function and range selector,
and the jacks.
Figure 1
Display
DCV
1000
OFF
ACV
750
200
200
20
DCA
200 U
2000m
2000 U
200m
20m
2000k
200m
Selector
200k
DCA
20k
W
2000
200
10A
VWmA
500Vmax
Jacks
COM
On the front of the multimeter, the digital display is on top, the selector is in the middle, and the three jacks
are in the bottom right-hand corner.
guide to using the multimeter
3
1.1
The Digital Display
The display represents the measurements taken by the multimeter. When the power is on,
it indicates a number that corresponds to the measurement; the unit will depend on the
function selected: volts or millivolts for voltage, amperes or milliamperes for current, and
ohms or kilo-ohms for resistance. These units are accepted worldwide and are part of the
international system of measurement (SI) used in all countries.
Your multimeter's display can display numbers from 0 to 1999, as well as any combination
of these numbers and a decimal point. It can also display the negative sign and the number
"1" may appear on the left when the measurement exceeds the maximum allowable in any
given range.
1.2
The Selector
The selector is used to choose the function (voltmeter, ammeter or ohmmeter) and the most
appropriate range for the measurement. The choice of function determines the section in
which the selector must be positioned to take the measurement. The choice of range determines the exact position of the selector when the reading is taken.
There are seven distinct sections around the dial: Ω, DCV, ACV, DCA (0 - 200 mA), DCA
(10 A) and two specialized functions identified by symbols. The functions corresponding
to the first five sections are indicated below. While reading, have your multimeter handy
to establish the correspondence between the sections and their function.
– To measure a resistance, select a position in the "Ω" section.
– To measure a DC voltage, select a position in the "DCV" section.
– To measure an AC voltage, select a position in the "ACV" section.
– To measure a direct current whose intensity is less than 200 mA (0.200 A), select a posi tion in the section identified in black as "DCA."
– To measure a direct current whose value is between 200 mA and 10 A, select a position
in the section identified in red as "DCA - 10 A."
Note: In the experiments, you will use only the sections Ω, DCV, DCA (0 - 200 mA) and DCA
(10 A). You will not be called upon to take measurements in AC voltage.
Once the section has been determined, you need to select the range, that is, the exact position at which the selector must be placed to take the measurement. The choice of range
determines the accuracy of the mea- surement taken. The number indicated at a given posi-
4
guide to using the multimeter
tion corresponds to the maximum value that can be measured in that range: for example,
in the "DCV" section, "20" is for measuring DC voltages under 20 V; however, "200 m" is the
best choice for voltages under 200 mV.
Note: In the experiments, the procedure always indicates the range to use for a given measurement. If you want to take measurements in another context, however, follow the instructions
in Section 3 of this guide to determine the most appropriate range.
1.3
The Jacks
Your multimeter has three jacks, labelled, from top to bottom, "10 A," "V-Ω-mA" and "COM."
The jacks are used to connect the multimeter to the circuit or component to be measured.
To connect the multimeter to the circuit, you will find two probes, that is, two special wires
with a banana plug on one end to be connected directly to the multimeter and a thin metal
rod at the other, to be applied to a point in the circuit.
Like any other electrical component, the multimeter must be connected at two points in
the circuit. That is why there are two wires. For all measurements, one wire, usually the
black one, is connected to the "COM" jack of the multimeter. The second jack depends on
the section you selected: if you are working in the "DCA - 10 A" section, to measure a current between 200 mA and 10 A, you must connect the second wire (red) to the jack labelled
"10 A;" for all other measurements, connect the second wire to the middle jack, labelled
"V-Ω- mA." Thus, the circuit is connected either between the "V-Ω-mA" and "COM" jacks or
between the "10 A" and "COM" jacks. The combination "10 A"/"V-Ω-mA" should be avoided,
since it might damage the multimeter.
2. Safety instructions
Measurements of voltage, current and resistance are by nature different. Even if your multimeter is a quality instrument, protected against surges, you must pay attention to a few
important rules in order to avoid damaging it.
Measurements of voltage can be taken safely. An error in the connections will give the
wrong measurement, but will not affect the multimeter.
Measurements of resistance are easy to take, but you must always make sure that the
component to be measured is not already live. To take the measurement, the multimeter
provides a certain voltage at its terminals in order to inject a current into the component to
be measured. It is therefore the ideal instrument for measuring the resistance of a resistor
or a wire. If the resistor is already live, however, the multimeter cannot correctly measure
the resistance.
Measurements of current are more delicate than measurements of voltage or resistance.
guide to using the multimeter
5
For measurements of current, the multimeter must be inserted in series with the component in which the measurement is to be taken, so that the same current flows through the
multimeter and the component.
Ideally, the ammeter function of the multimeter has 0 resistance, so as to avoid increasing
the total resistance of the circuit. If you make the mistake of connecting the multimeter in
parallel with a component of the circuit, the instrument will short-circuit the component;
the total resistance of the circuit will decrease and, at the same time, the current in the
multimeter may increase sufficiently to damage it. Most often, however, the fuse will burn
and the instrument remains intact.
Note: The fuse is not connected to every function of your multimeter. If it is burned, the display will still work; you can take measurements of voltage and resistance. Measurements of
current, however, will be affected.
3.
How to take measurements
3.1Resistance
Your multimeter measures resistances between 0.1 and 2 000 000 Ω. As mentioned in the
preceding section, it is essential that the component to be measured not be already live.
To measure the resistance of a component:
1) connect the red wire provided with the multimeter to the "V-Ω-mA" jack and the
black wire to the "COM" jack;
2)
apply the two probes to the terminals of the component whose resistance you are
measuring;
Figure 2
DCV
1000
OFF
ACV
750
200
200
20
DCV
DCA
1000
OFF
ACV
750
200
200
200 U
20
2000m
2000 U
200m
20m
2000k
200m
DCA
200 U
2000m
2000 U
200m
20m
2000k
200m
6V
200k
DCA
20k
W
2000
200k
DCA
20k
200
W
2000
200
10A
10A
VWmA
500Vmax
VWmA
COM
a) Measurement of resistance
500Vmax
b) When you measure resistance, the component to be measure 6
COM
should not be live
guide to using the multimeter
3) – if you already know the most appropriate range for the measurement to be taken,
turn the selector counterclock- wise to the corresponding position in the "Ω" section;
– if you do not know the most appropriate range, turn the selector counterclockwise
to "2000 K" in the "Ω" section. If the value of the resistance is small, the multimeter
will display a very small number or zero. This is normal, since you chose a very
large range. Turn the selector counterclockwise successively through "200 K", "20 K",
"2000" and "200". When you have passed the range allowing for maximum accuracy,
the multimeter will display the number "1" on the left. Turn the selector clockwise
to the previous position and you will obtain the most accurate reading.
3.2 DC Voltage
Cells and batteries generate DC voltage. Multimeters can measure DC voltages between 0
and 1000 V. Measurements of voltage must always be taken in parallel with the component
to be measured. A faulty connection, however, would not cause any ill effects.
To measure DC voltage:
1) connect the red wire provided with the multimeter to the "V-Ω-mA" jack and the black
wire to the "COM" jack;
2) apply the two probes to the ends of the component whose voltage you wish to measure;
Figure 3
DCV
1000
OFF
ACV
750
200
200
20
-
DCA
200 U
2000m
2000 U
200m
20m
2000k
200m
+
6V
200k
DCA
20k
W
2000
200
10A
VWmA
500Vmax
COM
Measurement of DC voltage
guide to using the multimeter
7
3) – if you already know the most appropriate range for the measurement to be taken,
turn the selector counterclock-wise to the corresponding position in the "DCV"
section;
– if you do not know the most appropriate range, turn the selector counterclockwise
to "1000" in the "DCV" section. If the value of the voltage is small, the multimeter
will display a very small number or zero. This is normal, since you chose a very large
range. Turn the selector counterclockwise successively through "200," "20," "2000 mΩ"
and "200 mΩ."
When you have passed the range allowing for maximum accuracy, the multimeter
will display the number "1" on the left. Turn the selector clockwise to the previous
position and you will obtain the most accurate reading.
3.3 Direct Current
Your multimeter allows you to measure direct current between 0 and 10 A. Note that the
procedure differs depending on whether you are measuring a current between 200 mA and
10 A or a current under 200 mA. If you are uncertain of the intensity of the current you are
measuring, begin by using the 10-A range. If you believe that the current may exceed 10 A,
do not use the multimeter, since you may damage it.
To measure a direct current between 200 mA and 10 A:
1)
connect the red wire provided with the multimeter to the "10 A" jack and the black wire
to the "COM" jack;
2)
disconnect the circuit at the point at which you wish to take the measurement;
3)
connect the multimeter in series by applying a probe to each of the disconnected
extremities of the circuit;
Figure 4
DCV
1000
OFF
+
ACV
750
200
200
20
DCA
200 U
2000m
2000 U
200m
20m
2000k
200m
-
6V
200k
DCA
20k
W
2000
200
10A
VWmA
500Vmax
COM
a) Measurement of a current between 200 mA and 10 A.
8
guide to using the multimeter
DCV
OFF
1000
ACV
750
200
200
DCA
20
200 U
2000m
2000 U
200m
20m
2000k
200m
6V
200k
DCA
20k
W
2000
200
10A
VWmA
COM
500Vmax
b) When you measure current, you risk damaging the multimeter if you connect it in parallel.
4) turn the selector clockwise to "10 A" in the "DCA" section. If the value of the current is
under 0.2 on the 10-A range, you may follow the procedure for measuring a direct current
between 0 and 200 mA described below. If the multimeter displays a number greater than
0.2, it is displaying the most accurate reading possible. If the multimeter is displaying
the number "1" on the left, you have passed the appropriate range. You cannot take the
measurement, since this multimeter, as mentioned previously, does not allow you to take
measurements over 10 A.
To measure a direct current under 200 mA:
1) bconnect the red wire provided with the multimeter to the "V-Ω-mA" jack and the
black wire to the "COM" jack;
2) disconnect the circuit at the point at which you wish to take the measurement;
3) connect the multimeter in series by applying a probe to each of the disconnected
ends of the circuit;
Figure 5
DCV
1000
OFF
ACV
750
200
200
20
DCA
200 U
2000m
2000 U
200m
20m
2000k
200m
6V
200k
DCA
20k
W
2000
200
10A
VWmA
500Vmax
COM
Measurement of a current under 200 mA
guide to using the multimeter
9
4) – if you already know the most appropriate range for the measurement to be taken,
turn the selector clockwise to the corresponding position in the "DCA" section;
– if you do not know the most appropriate range, turn the selector clockwise to "200 m"
in the "DCA" section. If the value of the current is small, the multimeter will display
a very small number or zero; the range chosen may be too large. Turn the selector
counterclockwise successively through "20 m," "2000 μ" and "200 μ," until the multimeter displays the num- ber "1" on the left. This indicates that you have passed the
range. Turn the selector to the previous position and you will obtain the most accurate
reading.
Note: If the multimeter displays "0" in every range, check the connections. If everything seems
normal, check the fuse (see Section 1 of this guide). If it is burned, it must be replaced
10
guide to using the multimeter