Electrical Measurements—Meters:Introduction to Meters

In the field of electricity, accurate quantitative measurements are essential. A technician com- monly works with current, voltage, and resistance. Ammeters, voltmeters, and ohmmeters are used to provide the essential measurements. A good under- standing of the design and operation of electrical measuring meters is important.

This chapter describes the more commonly used analog meters, including the multimeter, or multi- function meter.

Introduction to Meters

Meters are the means by which the invisible action of electrons can be detected and measured. Meters are indispensable in examining the operation of a circuit. Two types of meters are available. One type is the analog meter, which uses a graduated scale with a pointer (Figure 15-1). The other type is the digital m e t e r , which provides a reading in numbers (Figure 15-2). Digital meters are easier to read and provide a more accurate reading than analog meters. However, analog meters provide a better graphic display of rapid changes in current or voltage.

Most meters are housed in a protective case. Terminals are provided for connecting the meter to the circuit. The polarity of the terminals must be observed

for proper connection. A red terminal is positive and a black terminal is negative.

Before using an analog meter, the pointer should be adjusted to 0. A small screw is located on the front of the meter to permit this adjustment (Figure 15-3). To zero the meter, place the meter in the position where it is to be used. If the needle does not point to 0, use a screwdriver to turn the screw until it does. The meter should not be connected to a circuit while this adjustment is being made.