Tangent galvanometer consists of a circular coil of wire wound over a non-magnetic frame of brass or wood. The vertical frame is mounted on a horizontal circular turntable provided with three levelling screws. The vertical frame can be rotated about its vertical diameter.
There is a small upright projection at the centre of the turntable on which a compass box is supported.
The compass box consists of a small pivoted magnet to which a thin long aluminium pointer is fixed at right angles. The aluminium pointer can move over a circular scale graduated in degrees. The scale consists of four quadrants. The compass box is supported such that the centre of the pivoted magnetic needle coincides with the centre of the coil. Since the magnetic field at the centre of the coil is uniform over a very small area, a small magnetic needle is used so that it remains in a uniform field even in deflected position. Usually, the coil consists of three sections of 2,5 and 50 turns, which are of different thickness, used for measuring currents of different strength.
