ammeter Instrument for measuring electric current in amperes. An ammeter is connected in series in a circuit. In the moving-coil type for direct current (DC), the current to be measured passes through a coil suspended in a magnetic field and deflects a needle attached to the coil. In the moving-iron type for both direct and alternating current (AC), current through a fixed coil magnetizes two pieces of soft iron that repel each other and deflect the needle. Digital ammeters are now also commonly used.

am·me·ter / ˈa(m)ˌmētər/ • n. an instrument for measuring electric current in amperes.