Ammeter

Ammeter, pronounced AM mee tuhr, is an instrument that measures the electric current in a circuit in units called amperes. There are two basic types--analog and digital.

The most widely used direct current analog ammeters consist of a coil of fine wire wound around a soft iron core. The core or shaft is suspended between the poles of a permanent magnet. When a current flows through the coil, the coil and the shaft turn so that their magnetic fields tend to become parallel to those of the permanent magnet. A pointer on the shaft moves along a scale to indicate the reading. A shunt (heavy wire) carries most of the current around the meter. By using different shunts, the ammeter can measure a wide range of currents--from a few millionths of an ampere to several thousand amperes.

The ammeter measures the strength of electric currents. The shunt allows the meter to measure a wide range of currents.
From The World Book^™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved.
World Book illustrations by Sarah Woodward.

A digital ammeter typically contains no moving parts. When a current passes through the meter, it converts the voltage between two points into a digital (numerical) code. The code is then processed electronically to calculate the current.

Contributor: Raymond D. Findlay, Ph.D., Director, Engineering and Management, McMaster Univ.

Ammeter

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