Hall element is a magnetic sensitive element. If the rotating speed is to be measured, a magnet must be installed on the measured rotating body. When rotating, as long as the magnet passes through the Hall element, the Hall element will send out a signal, which will be amplified and shaped to get a pulse signal. Some Hall elements can directly output pulse signals and send them to operation. The interval between two pulses is the period, from which the rotational speed can be converted, and the number of pulses per unit time can be counted, and then the rotational speed can be converted.