description about dead beat galvanometer
A galvanometer is said to be dead beat if its coil quickly returns to its mean position of rest without oscillating after being deflected.
The main conditions for a moving coil galvanometer to be dead beat are as:
1. The period of oscillations of the coil should be as small as possible. This condition can be achieved by using the coil of low moment of inertia and a suspension fibre of low torsional constant.
2. The damping should be high. The damping in the coil can be made high by winding the coil on the conducting frame e.g., copper or aluminum, and a soft iron core be placed between the pole pieces of the permanent magnet. This increases the electromagnetic damping.
3. The resistance of the coil should be small.
When current is passed through a galvanometer, the coil oscillates about its mean position before comes to rest. To bring the coil to rest immediately, the coil is wound on a metallic frame. Now, when the coil oscillates, eddy currents are set up in a metallic frame, which opposes further oscillations of the coil. This inturn enables the coil to attain its equilibrium position almost instantly. Since the oscillations of the coil die out instantaneously, the galvanometer is called dead beat galvanometer