Methods of Production of Damping Torque

Methods of Production of Damping Torque Points : Methods of Production of Damping Torque, Air friction damping, Fluid friction damping, Eddy current damping, Electromagnetic damping The methods of production of damping torque are:
(a) Air friction damping
(b) Fluid friction damping
(c) Eddy current damping
(d) Electromagnetic damping (a) Air Friction Damping The arrangement of consists of a light alumunium piston which is attached to the moving system. This piston moves in a fixed air chamber which is closed at one end, The clearance between piston and chamber walls is uniform throughout and is very small. When there are oscillations the piston moves into and out of an air chamber. When the piston moves into the chamber, the air chamber. When the piston moves into the chamber, the air inside is compressed and the pressure of air, thus built up, opposes the motion of piston and hence of whole of the moving system. When the piston moves out of air chamber, pressure in the closed space fails, and the pressure on the open side of piston is greater than on the other side. Thus there is again an opposition to motion.

The arrangement of consists of an aluminium vane which moves in a quadrant (sector) shaped air chamber. This air chamber is a recess cast in a bakelite moulding or diecasting. The chamber is completed by providing a cover plate at the top. The aluminum piston should be carefully fitted so that it does not touch the wall otherwise a serious error will be caused in readings.

(b) Fluid Friction Damping This form of damping is similar to air friction damping. Oil is used in place of air and as the viscosity of oil is greater, the damping force is also correspondingly greater. A disc is attached to the moving system as, this disc dips into an oil pot and is completely submerged in oil. When the moving system moves in oil and a frictional drag is produced. This frictional drag always opposes the motion.

In the arrangement, a number of vanes are attached to the spindle. These vanes are submerged in on and move in a vertical plane. This arrangement gives a greater damping torque.

(c) Eddy Current Damping This is also known as electromagnetic damping. When a conductor moves in a magnetic field an emf is induced in it and if a closed path is provided, a current (known as eddy current) flows. This current interacts with the magnetic field to produce an electromagnetic torque which opposes the motion. This torque is proportional to the strength of magnetic field and the current produced. The current is proportional to emf which is turn is proportional to velocity of the conductor. Thus if the strength of the magnetic field is constant (if it is produced by a permanent magnet).

(d) Electromagnetic Damping The movement of a coil in a magnetic field produces a current in the coil, which interacts with the magnetic field to produce a torque. This torque opposes the movement of the coil and slows the response. The magnitude of the current and hence the damping torque is dependent upon the resistance of the circuit to which the instrument is connected. The electromagnetic damping is used in galvanometers.