Ammeter

An Ammeter is a measuring instrument used to measure the flow of electric current in a circuit?. The most common implementation uses magnetic? deflection, where increased current passing through a coil causes a small magnet to be increasingly deflected. The deflective force operates against a spirally wound spring such that instrument reurns to zero when the current is switched off. A key design parameter is that the voltage drop across the coil is kept to a minimum thereby causing minimal distrubance to any circuit into which the meter is inserted.

Because the device is extremely sensitive to small currents and yet needs to be [in circuit]? with the current in order to measure it, ammeters are usually built to measure say 100 milli-amps and can measure larger currents though the use of a shunt? placed in parallel with the meter in the circuit. With this solution, large currents can be measured with only a fraction of the current passing through the meter.

One problem with the use of an ammeter is the need for the meter to be inserted into the circuit and become part of it. For use in [high voltage]? circuits a special design allows the meter to form a single turn around one of the circuit conductors and through the [inductive coupling]? a small current is induced in the meter circuit.