Speedometer is used to measure and display instantaneous speed of the vehicle.
Speedometer application uses an Alnico magnet which rotates on an axle in an aluminium cup.
As a result of relative motion of the magnet and the cup, eddy currents are induced producing the torque on the cup.
Torque is proportional to the speed of rotation of the magnet.
Aluminium cup rotates against the force of a spring and a pointer fixed on its shaft indicates the speed of the magnet.
The speedometer scale is graduated in accordance with the number of revolutions or, as in motor vehicles, in velocity corresponding to the diameter of the wheels.
At constant speed, Pointer remains steady & will show exact speed on the dial.
Schematic for Speedo magnet assembly
Standard sizes of Speedo Magnets in Alnico 2, Alnico 3 alloy
