A galvanometer is an electromechanical measuring instrument for electric current. It works by deflecting a pointer in response to an electric current flowing through a coil in a constant magnetic field. The movement of the pointer is directly proportional to the intensity of the electric current in the circuit. Galvanometers can be thought of as a kind of actuator. They were the first instruments used to detect and measure small amounts of current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. Galvanometers have also been used as the display components of other kinds of analog meters (e.g., light meters and VU meters), capturing the outputs of these meters sensors.

The main parts of a galvanometer include a coil, a spring, and a needle. The coil is the part of the galvanometer through which the electric current to be measured travels. The spring is the joint between the coil and the needle that gives the measurement. The needle is the part that indicates the value of the measured electric current. There are different types of galvanometers, including the D’Arsonval/Weston type, the moving coil type, tangent galvanometer, astatic galvanometer, mirror galvanometer, and ballistic galvanometer.

The moving coil galvanometer is a highly sensitive instrument that can measure low currents even of the order of a few microamperes. It is mainly divided into two types: suspended coil galvanometer and pivoted-coil or Weston galvanometer. When a current is passed through a coil in a magnetic field, the coil experiences a torque proportional to the current. If the coils movement is opposed by a coil spring, then the amount of deflection of a needle attached to the coil may be proportional to the current passing through the coil.

Galvanometers are used to detect or measure small electric currents by movements of a magnetic needle or of a coil in a magnetic field. They are also used to translate different kinds of electric quantities into pointer movements, making them ideal for turning the output of other sensors that output electricity into something that can be read by a human.