The system, a closed-loop control system which consists of single chip computer, control circuit, frequency converter and motor, can not only measure the motor’s speed, but also can set the motor’s speed conveniently and make the motor run at the set speed at last. There need to be three timers/counters to realize this function. As an enhanced 51 series microcontroller AT89S52, There are three such timers/counters (T0, T1, T2) in it. We can determine the motor’s speed with T2 by installing powerful magnet and Hall sensor on the motor’s axle. The Hall sensor generates a pulse when the motor’s axle turn a round. We can get the motor’s speed by calculating the cycle of the pulse. T1 and T2, as pulse width modulation signal generator, produce the pulse signals. Here T1 determines the cycle, and T0 determines the duty ratio. The duty ratio of pulse signals can be regulated according to the deviation between the real speed and set speed. Then the single chip computer generates corresponding DC voltage, which controls the frequency converter and makes the motor run at the set speed finally. The system can be applied to many field that has special requirements to motor’s speed.
