Lesson 3/Learning Event 1
The resistance of the load varies depending on the type of load, such as a small lamp compared to
a large motor. However, the resistance of the load is generally less than that of the meter. For this
reason, most of the current in the circuit flows through the load. The two paths are side by side or
parallel. We say the voltmeter is connected parallel to the circuit.
The voltmeter contains a pointer or hand known as the indicating pointer. This pointer is
connected to an electromagnet. The pointer and electromagnet are mounted on a pivot or hinge
pin and can be moved or swung around like a door. A very small coil spring, known as a
hairspring, holds the pointer on zero when the meter is not in use. It also returns the pointer to
zero when the meter is in use if the voltage stops or the meter is disconnected.
When voltage is applied to the voltmeter, it moves the current through the electromagnet. The
electromagnet then forces or moves the pointer away from zero. The amount it moves depends on
how much voltage is applied, because, as the voltage is increased the current will increase, and as
the voltage decreases so does the current. The more pressure or voltage applied to the circuit, the
more current that will flow and the voltmeter will, therefore, change as the voltage changes.
The main thing to remember is that the voltmeter is connected parallel to the main circuit. If the
voltmeter was connected so that all the current within a circuit passed through the meter, it would
be connected in series. If a voltmeter was accidentally connected in this manner, it would in most
cases indicate the source voltage. However, the load component(s) would not operate normally due
to the high resistance the voltmeter placed in the circuit. When the voltmeter is used to test a
battery with no load applied, positive is connected to positive and negative is connected to negative.
However, in that case the meter and the battery make up the complete circuit.
Voltmeters do not all look alike. There are many types and sizes of portable voltmeters. Large,
complex electrical equipment has built-in voltmeters, because slight variations in voltage greatly
affect the operation of this equipment. Operators or service personnel must constantly measure the
voltage on such equipment and make quick adjustments whenever needed.
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