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Digital volt ohm meter
Digital volt ohm meters or DVOMs are the most useful
tool to troubleshoot any electrical system. Depending
on the model of DVOM used, DVOMs can measure
Volts, Amps, Ohms and more. DVOMs are a must
when working on circuits with solid state components
(microchips). They have very high impedance, that
means they have very high resistance and pull very lit-
tle current from the circuit. Use of analog equipment or
test lights will pull enough current to damage the micro-
chips in the circuit. See Figure 2.3.
Figure 2.3
When measuring volts, always hook the meter in par-
allel with the circuit. That means do not disconnect the
component where measuring voltage.
When measuring current the meter must be connected
in series with the component to be measured. That
means opening the circuit and having the circuit go
through the meter.
NOTE: The only exception to this is when using
an inductive amp clamp.
When measuring resistance, the component must be
isolated from the circuit.
CAUTION: The meter has it's own power source
to measure resistance. connecting the meter to
a component that has current going through it
will damage the meter (usually beyond repair).
NOTE: When measuring resistance and there is
no continuity, the meter will read infinity. This is
represented in a few different ways like: OL
(open line) or 1.0 displayed to the far left. Check
the operator's manual for the DVOM to see how
it is represented on your meter..
Inductive amp meter
An inductive amp meter, sometimes referred to as an
"amp clamp" or clamp meter, measures current follow-
ing through a wire by the magnetic field created around
the wire. Clamp meters are very important when deal-
ing with currents over 10 amps. A DVOM typically can
not measure current over 10 amps. Clamp meters are
also helpful because they can read current in a circuit
without opening it up to hook the meter into the circuit.
See Figure 2.4.
Wiring or a schematic diagram
A wiring or a schematic diagram is very important in
troubleshooting a circuit. The diagram shows how the
circuit was designed and what paths the electricity is
suppose to flow.
Fused jumper wires
Fused jumper wires are handy to help find bad grounds
or to jump across switches for testing purposes.
CAUTION: Only use fused jumper wires. If there
is a short in the circuit, using an unfused jump
could damage components in the circuit further.
Types of circuits
There are three ways a circuit can be wired. They are:
•
Series
•
Parallel
•
Series/parallel
5
ELECTRICAL SYSTEM
Figure 2.4
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