galvanometer

/gal'veuh nom"i teuhr/, n.

an instrument for detecting the existence of small electric currents and determining their strength.

[1795-1805; GALVANO- + -METER]

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Instrument for measuring small electric currents by deflection of a moving coil.

A common galvanometer consists of a light coil of wire suspended from a metallic ribbon between the poles of a permanent magnet. As current passes through the coil, the magnetic field it produces reacts with the magnetic field of the permanent magnet, producing a torque. The torque causes the coil to rotate, moving an attached needle or mirror. The angle of rotation, which provides a measure of the current flowing in the coil, is measured by the movement of the needle or by the deflection of a beam of light reflected from the mirror.

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▪ measurement instrument

      instrument for measuring a small electrical current or a function of the current by deflection of a moving coil. The deflection is a mechanical rotation derived from forces resulting from the current.

      The most common type is the D'Arsonval galvanometer, in which the indicating system consists of a light coil of wire suspended from a metallic ribbon between the poles of a permanent magnet. The magnetic field produced by a current passing through the coil reacts with the magnetic field of the permanent magnet, producing a torque, or twisting force. The coil, to which an indicating needle or mirror is attached, rotates under the action of the torque; the angle through which it rotates to balance the torsion of the suspension provides a measure of the current flowing in the coil. The angle is measured by the movement of the needle or by the deflection of a beam of light reflected from the mirror.

      The ballistic galvanometer is designed to deflect its indicating needle (or mirror) in a way that is proportional to the total charge passing through its moving coil or to a voltage pulse of short duration. Any conventional galvanometer may also be employed as a ballistic type, but the latter has smaller torque and higher inertia in the coil.

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