Synchronous motor speed controller - has tuning fork oscillator and astable multivibrator with lower natural frequency

摘要

The tuning for oscillator sets the frequency of the multivibrator for normal operation and thus governs the speed of the motor. The multivibrator is designed to be astable and to have a natural oscillation frequency slightly below that of the tuning fork. When the combined system is subject to a disturbance, for example, mechanical shock, which transiently interrupts the tuning fork output the motor drive is automatically taken up by the multivibrator without serious loss of motor speed. The exciter winding of the synchronous motor is switched between the outputs of the oscillator and the multivibrator. The centre connection of the exciter winding is joined to a d.c. power source.