Exam Question

(a) Functioning of Revolution Pick-up Sensor:
A magnetic pick-up unit (MPU), also known as a revolution pick-up sensor, consists of a permanent magnet and an external coil winding. It's positioned a precise distance from ferrous gear teeth or flywheel teeth. As the flywheel rotates, the proximity of the teeth to the MPU creates a constantly changing magnetic field within the sensor. This fluctuating magnetic field induces an AC voltage in the coil. The frequency of this AC voltage is directly proportional to the engine's rotational speed – higher engine speed results in a higher frequency and voltage. The formula for induced frequency is:
$$F=\frac{Number\:of\:gear\:teeth\:\times Gear\:RPM}{60}$$
This frequency signal is then used by the engine's control system to determine engine speed.