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Electrical
Instrumentation
Unit 6
We have already learned about current (amps – A),
voltage (volts - V) and resistance (R). In order to do
his or her job properly, an electrician, electronics
technician, maintenance technician, HVAC
technician, or engineer must be able to measure all
three of these quantities. The various crafts use an
ammeter to measure current, a voltmeter to
measure voltage, and a ohmmeter to measure
resistance.
Multimeter
An easier way to do
this job is to use a
meter that combines
all three meter types
into one device. This
device is called a
multimeter. There is a
multimeter in the
MB100 Kit. 
Most analog meters use a D’
Arsonval meter movement,
also called a moving coil
meter. To the right is a
pictorial vies of the inside. A
horseshoe magnet provides a
magnetic field. A moving coil,
suspended on a pivot is
mounted between the poles
of the magnets. The coil is
wound around a light
aluminum frame, called a
bobbin, which is not shown in
the picture.
Functions of a Multimeter
• An analog multimeter has a dial, an adjustment knob, and a
combined display. The dial selects the type of measurement to be
made: current (DCmA), voltage (DCV or ACV), or resistance (OHM).
The adjustment know is used when measuring resistance (OHM). It is
used to zero the scale before making a measurement. Part of the
display is used with each setting. You will learn about these setting in
the Experiments.
• Multimeters are the most important electronic testing instruments.
They have many uses around the home and on the job. An electrician
may use a multimeter when working with appliances and motor
vehicles.
Two Types of Multimeters
Digital Multimeters have a digital readout.
They are very accurate and easy to read.
They are best for finding the exact value of
a current, voltage or resistance.
Analog multimeters use a moving coil meter.
They are less expensive and slightly less precise
than digital types. Analog multimeters are best
for observing the trend of a slowly changing
current, voltage, or resistance.
Current Measurement
In order to use the multimeter to
measure current (amperage), there
are two things you must
understand. First, to measure
current all the electricity must flow
through he meter. So the meter is
connected in series with the rest of
the devices in a circuit as shown in
the Figure. We will learn more
about series circuits in Unit 12, but
for now notice that only one path
exists for the current to flow.
The second thing you need to remember is that the
current does not have its own scale on the multimeter.
It shares the scale for DC voltage and is marked V+mA.
Since you will be measuring small electrical currents,
the measurements are taken in milliamps (mA). The
dial is marked DCmA for direct current milliamps and
has two settings. When you use the multimeter dial,
you will need to select the 10 or 250 DCmA scale. (You
are not able to measure AC current with this meter).
• When setting the multimeter to
measure current, you should always
start on the higher setting (250
DCmA) so you don’t ruin the meter.
(The meter in our MB100 Kit is
protected so that it cannot be
ruined). When the meter is set this
way, you read the scale shown in
Figures 6-4a. Each small mark on
this scale is 5 mA.
• When you switch the meter to the
10 DCmA scale, you read the scale
shown on Figure 6—4b. Every small
line is now 0.2 mA.
Voltage Measurement
In order to use the
multimeter to measure
voltage, the multimeter
must be connected
across the device being
measured as shown in
the Figure
This arrangement is
called parallel. We will
discuss this more in unit
13.
Resistance Measurement
• In order to use the multimeter to measure resistance, the meter must be
connected across the device, in parallel, as for voltage. When measuring
resistance, no source voltage can be connected to the component.
• A measure of resistance is also a measure of the circuit’s ability to conduct.
In addition measuring the amount of resistance , you can also make a
check of continuity. A very low reading, or near zero resistance, is an
indicator of continuity between the points being examined.
• This fact is used when zeroing the meter. Before measuring resistance, the
meter must be zeroed. There should be zero resistance when two probes of
the multimeter are connected. In the Experiment, you will learn how to
zero the meter.
Additional Electrical
Instruments
• Fluke Clamp-On Amp Meter.
• Allows for the measurement of
current by just clamping around
the wire.
• Fluke VoltAlert Tester
• Easy to carry and has
continuous self-test so
you always know it’s
working, the Fluke 1ACII non-contact voltage
detector allows you to
quickly test for
energized circuits in the
workplace or at home.
Electrical Multimeter Use Video
Digital Multimeter Tutorial