This traditional ampere meter indicates current by moving a needle.
Ampere meters, also called ammeters, measure the electrical current that flows through a wire. Earliest designs used needles that moved by magnetic forces, while modern digital ammeters measure current flow using more direct electronic means.
Magnetism
Most of the early ammeters relied on the force of magnetic repulsion to work. Early scientific work done with magnets and coils revealed a direct relationship between the current flowing through a coil and the strength of its magnetic field.
Moving Coil
The basic electromechanical ammeter uses a wire coil suspended on a pivot between two permanent magnets. A flowing current produces a magnetic repelling force between the coil and the magnets, turning the coil on the pivot. A light needle gauge resting on the coil indicates current on a calibrated scale.
Shunt
A resistor wired in parallel with the meter coil lets the meter handle greater currents than the meter could without it. Most of the current goes through the resistor. If the meter uses a resistor, called a shunt, the scale is calibrated differently to indicate larger currents.
Moving Iron
A moving iron ammeter uses a moving iron vane with an indicator needle and a fixed iron vane inside a wire coil. Current in the coil creates magnetic repulsion in the the two vanes, moving the needle on a scale. This design can indicate either AC or DC current, unlike the moving-coil design, which works only with DC.
Digital
Modern digital ammeters don't have moving parts. An analog-to-digital converter (ADC) circuit translates the current in a resistor to a number, which is shown on the meter's display.
Tags: ammeter uses, ammeters measure, digital ammeters, indicates current, iron vane, magnetic repulsion, moving needle