Ammeter

It's Electronic device in which we measure current in amperes (A)in close Circuit. It is connected in series with circuit.

The effective resistance of ammeter is low

The Resistance of an ammeter is zero. A moving coil of galvanometer is converted in to an ammeter by connected a suitable low resistance in parallel to it. Circuit must be disconnected in order to attach

the ammeter. Ammeter considered as less accurate value.

Type of ammeter

There are 7 type of ammeter.

1.Moving coil 

2-Moving magnet

 3-Electrodynamic

 4-Moving iron 

5-Hot wire

 6-Digital 

7-Integrating

Moving coil ammeter:

                                  The D'Arsonval galvanometer is a moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The modern form of this instrument was developed by Edward Weston, and uses two spiral springs to provide the restoring force. The uniform air gap between the iron core and the permanent magnet poles make the deflection of the meter linearly proportional to current. These meters have linear scales. Basic meter movements can have full-scale deflection for currents from about 25 microamperes to 10 milliamperes. Because the magnetic field is polarised, the meter needle acts in opposite directions for each direction of current. A DC ammeter is thus sensitive to which way round it is connected; most are marked with a positive terminal, but some have centre-zero mechanisms and can display currents in either direction. A moving coil meter indicates the average (mean) of a varying current through it, which is zero for AC. For this reason moving-coil meters are only usable directly for DC, not AC.This type of meter movement is extremely common for both ammeters and other meters derived from them, such as voltmeters and ohmmeters. Although their use has become less common in recent decades, this type of basic movement was once the standard indicator mechanism for any analogue displays involving electrical machinery. Moving Coil Instruments are used for measuring DC quantities. They can be used on AC systems when fed through bridge rectifiers, but some products are rectified moving coil and can be used in ac systems directly.