Ammeter - Navistar International DT 466 Diagnostic/Troubleshooting Manual

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Figure 556 Checking voltage drop
To check the voltage drop across a load device,
connect the positive lead of the voltmeter to the
positive side of the device and the negative meter
lead to the negative side of the device.
With the device operating, this will measure the
voltage drop across the device. With only one device,
all of the voltage should be dropped at the device. In
any circuit, the voltage applied will equal the voltage
dropped in the circuit. If this circuit only dropped 9 V
across the load, it indicates the wires and connections
dropped 3 V, indicating excessive circuit resistance.

Ammeter

An ammeter measures current flow (amperage) in a
circuit. Amperes (or amps) are units of electron flow
that indicate how many electrons are passing through
the circuit. An amp is the unit of measurement for the
current flow in the circuit.
Ohm's Law states that the current flow is equal to the
circuit voltage divided by the total circuit resistance
(I = E ÷ R). Therefore, increasing the voltage also
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
8 DIAGNOSTIC TOOLS AND ACCESSORIES
EGES-270-1
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
increases the current flow. Any decrease in resistance
will also increase the current flow.
At normal operating voltage, most circuits have a
characteristic amount of current flow (current draw).
Current draw can be measured with an ammeter.
Valuable diagnostic information can be provided
by referring to a specified current draw rating for a
component (electrical device), measuring the current
flow in the circuit, and then comparing the two
measurements (the specified current draw versus the
actual measurement).
Figure 557 Installing the ammeter
An ammeter is connected in series with the load,
switches, resistors, etc., so that all of the current