Instantaneous Speed ‒ Tachometer

A tachometer or speedometer is a device used to measure the speed of a vehicle. The analog eddy current speedometer operates by measuring the number of revolutions or speed per unit of time. The rotation of the vehicle's wheels is transmitted to the tachometer via a flexible shaft. A permanent magnet, connected to the measuring shaft, rotates within an aluminum cup (also known as a speed cup). This rotation generates eddy currents in the aluminum cup, which exert a force proportional to the speed of rotation. A pointer attached to the cup moves accordingly, and a fine torsion spring returns the pointer to its zero position when the vehicle is stationary. The ribbon speedometer uses a two-color ribbon or tape, which is wrapped around two coils to display the current speed. The drum speedometer replaces the traditional pointer with a two-color drum that rotates to indicate the current speed.