# Different type of Damping

## Damping Torque

Why we use damping torque ??????

• When a deflecting force (initial force) is applied to moving system it deflects from initial position and should comes to rest position when controlling torque equal to deflecting Torque. But due to inertia the pointer keeps oscillating about equilibrium. so remove  the oscillation of the pointer a damping torque is required.

So here over damping torque is divided into three parts:-

## Air friction damping  fluid friction damping  Eddy current damping

### Air friction damping is used to damp of the oscillation of the pointer in this damping we are pointer attach with the piston. This piston is move Inside the air chamber. So when Piston starts moving here its face a small friction. So pointer  Attached with the Piston & piston move slowly so pointer  gives the accurate reading without oscillation. So using this we can damp out the oscillation of the pointer.

• Depending on the pointer movement the air pressure in a chamber change which reduce the damping produced by the pointer
• Air friction damping is preferred value value of magnetic field is used

#### fig.1 Air friction Damping

Example:-Moving iron, Eectrodynamometer Type Instruments

### Fluid friction damping:-

• In fluid friction damping our pointer is attached with a piston mechanism this piston is dipped into the fluid, when we are applying any supply pointer goes to show the reading and Piston starts moving with the pointer and due to fluid this Piston face small amount of friction this friction cannot give the immediate action to the pointer so it damp out the oscillation of the pointer.
• The movement of piston is opposed by the fluid so that the damping is reduced.
Electrostatic instruments uses fluid friction damping.

Fig.2 Fluid Friction Damping

### Eddy Current & Electromagnetic Damping:-

• Emf is induced when a conductor moves in a magnetic field. So according to this principal we can induced EMF. If emf can cause a current loop in the conductor, we say this current is an eddy current.
• The current flowing through the coil produced Eddy current in the code and these eddy current opposes the damping produced by the pointer.

### Example:- PMMC Instruments

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