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Voltage Measurements

With voltage measurements, the total resistance of the voltmeter must be considered. Reading an analog voltmeter scale is like reading an analog ammeter scale. Some multirange voltmeters have only one range marked on the scale and the scale reading must be multiplied by the range switch setting to acquire the accurate voltage reading. Other voltmeters have individual ranges on the scale for every setting of the range switch. When utilizing these meters, ensure that you read the set of values that corresponds to the range switch setting. Many digital meters also have range switches, but they may additionally have a special feature known as autoranging. This means you can either utilize the range switch or let the digital meter set the proper range by itself.

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Current Measurements

Current-measuring meters are called ammeters. There are two ways of measuring the current flowing in a circuit. The first way is to open the circuit being tested and link the meter test leads into the circuit so the current flowing in the circuit flows in series through the meter as well. This is the in-circuit-type of ammeter sometimes referred to as an in-line meter. An external type of ammeter, known as a clamp-on ammeter, can be used without opening the circuit. The clamp-on ammeter has jaws that open and clamp around the sides of one wire in the circuit and measures the magnetic field that the current in the wire produces, to determine the current flow. The clamp-on ammeter is widely used and simplifies the measurement of current from one to hundreds of amperes. It is especially helpful for field testing and troubleshooting AC power lines.

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