what is ammeter

An ammeter is an instrument used to measure the current in a circuit, which is measured in amperes (A) . It is designed to be connected in series with the circuit in which the current is to be measured. An ammeter usually has low resistance so that it does not cause a significant voltage drop in the circuit being measured. Ammeters must not be connected directly across a voltage source since their internal resistance is very low and excess current would flow. Ammeters are designed for a low voltage drop across their terminals, much less than one volt; the extra circuit losses produced by the ammeter are called its "burden" on the measured circuit. A portable hand-held clamp-on ammeter is a common tool for maintenance of industrial and commercial electrical equipment, which is temporarily clipped over a wire to measure current. Ammeters vary in their operating principles and accuracies. The D’Arsonval-movement ammeter measures direct current flowing through a coil 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 to convert the AC to DC) with accuracies of 0.1 to 0.25 percent. An ideal ammeter has zero resistance so that it does not affect the circuit it is measuring.