Electrical Engineering ⇒ Topic : Eddy Current Damping

Eddy current damping. Eddy current damping  is the most efficient form of damping. Two methods of eddy current damping are shown in Fig. (a) and Fig. (b) In Fig. (a), a thin *aluminium or copper disc attached to the moving system is allowed to pass between the poles of a permanent magnet. As the pointer moves, the disc cuts across the magnetic field and **eddy cun-ents are induced in the disc.These eddy currents react with the field of the magnet to produce a force which opposes the motion (Lenz's Law )in this way eddy current provide damping torque to reduce the oscillations of the pointer.

                                                                           (a)                                                                                                    (b)

                                                                                                                figure

In Fig. (b), the operating coil (i.e. the coil which produces the deflecting torque) is wound on the aluminium former. As the coil moves in the field of the instrument, eddy currents are induced in the aluminium former to provide the necessary damping torque.

Note. The moving system of an indicating instrument experiences three torques while in motion and two torques when it has come to rest in the final deflected position.

• During motion, the deflecting torque due to the quantity being measured is opposed by controlling torque and damping torque.
• When the pointer comes to rest in the final deflected position, damping torque is zero and the controlling torque is equal to the deflecting torque

Eddy Current Damping

When a conductor moves in a magnetic field, an e.m.f. is induced in it. If a closed path is provided, current flows through it. Now, this induced current interacts with the magnetic field and produces a torque which is called electromagnetic torque. It depends upon the strength of the magnetic field and the current through it. This torque opposes the motion. Eddy current damping is the most efficient form of damping. It is usually used in instruments having metallic former and permanent magnet is already present as a part of the operating system.