Ammeter

An ammeter is used to measure electrical current (in amperes).

There are several types of analogue ammeters (they are increasingly being replaced by digital ammeters):

* The commonest ammeter is the moving coil type, in which a current passing through the coil causes the coil to move in a magnetic field.

* In moving magnet ammeters it is the magnet that moves like in a current presence detector.

* The moving iron ammeter contains two soft iron vanes inside a coil. One of the vanes is fixed, the other is mounted on a pivot. When current passes through the coil, the two vanes are magnetised and repel each other whatever the direction of the current. This ammeter is therefore not polarised - it can be used for AC and DC.

* In the hot wire ammeter the current flows through a wire. The wire heats and lengthens causing the needle to rotate. Hot wire ammeters are not polarised.