INSTRUMENT which provides damping force to damp the oscillations of the pointer before it comes to rest.Because of inertia, the pointer of the instrument oscillates AROUND its final deflected position for some time before coming to rest.Damping force acts as a brake to prevent these oscillations of the moving system and brings the pointer to it's final deflected position quickly. Methods of damping are:AIR friction 'or' pneumatic damping:In this system, a light ALUMINUM piston is attached to the spindle of the instrument and is arranged to move in a fixed air chamber closed at one end.The compression and suction action of the piston on the air in the chamber damp the possible oscillations of the moving system.Eddy current damping 'or' Electromagnetic Damping:It is the most efficient type of damping.In this type of damping, a thin disc usually of copper 'or' aluminum is mounted on the spindle. When this disc moves in the magnetic field of the permanent magnet, the line of force are being cut and eddy current is produced.The force that exists between these current and magnetic fields is always in the direction opposing the motion and therefore, provide necessary damping.Fluid friction damping:In this method of damping, a light disc is attached to the spindle of the moving system and completely submerge in the damping oil in a pot.The motion of the disc is always opposed by a frictional drag on the disc.Note:SPRING control method is used to produce controlling torque for measuring instrument.Points to remember:Type of dampingInstruments usedAir friction dampingMoving iron (MI) and EDM (Electro dynamometer) instrumentsFluid friction dampingElectro-static voltmeter (ESV) and Induction type instrumentsEddy current dampingPMMC and induction type (which are used permanent magnet)Electromagnet dampingFlux meter