Ammeter unit：Ammeter | Definition, Types

ammeter, instrument for measuring either direct[1] (DC) or alternating[2] (AC) electric current[3], in amperes. An ammeter can measure a wide range of current values[4] because at high values only a small portion of the current is directed through the meter[5] mechanism; a shunt in parallel with the meter carries the major portion. In circuit[6] diagrams, the symbol for an ammeter is a circle with a capital A inside.

Ammeters vary in their operating principles and accuracies. The D’Arsonval-movement ammeter measures direct current flowing through a coil[7] suspended between the poles of a magnet with accuracies of from 0.1 to 2.0 percent. The electrodynamic ammeter uses a moving coil rotating in the field produced by a fixed coil. It measures direct and alternating current (by using a rectifier[8] to convert the AC to DC) with accuracies of 0.1 to 0.25 percent. In the thermal (or hot-wire) ammeter, used primarily to measure AC w...