Damping Torque

Damping force or torque is also necessary to avoid oscillations of the moving system about its final deflected position owing to the inertia of the moving parts and to bring the moving system to rest in its deflected position quickly.  In the absence of damping, the moving system and instrument would oscillate about the position at which the deflecting and restoring torques are equal. The function of damping is to absorb energy form the oscillating system and to bring it to rest promptly in its equilibrium position so that its indication may be observed.

If the instrument is under damped, the moving system will oscillate about its final position and take some time to come to rest in its steady position.  If the instrument is over damped, the moving system will become slow and lethargic and when the degree of damping is such that the pointier (moving system) rises quickly to its deflected position without oscillations; the damping is said to be ‘critical’ and the instrument is said to be "dead beat".In practice to obtain best results the damping is adjusted to the value slightly less than the critical value.

Depending upon the degree of damping introduced in the moving system, the instrument may have

any one of the following conditions:

1. Under damped condition: The response is oscillatory.

      2.   Over damped condition: The response is sluggish and it rises very slowly from its zero

             position to final position.

    3. Critically damped condition: When the response settles quickly without any oscillation, the

         system is said to be critically damped.