SPEED CONTROLLER OF INDUCTION MOTOR

PURPOSE:To immediately judge the normal or abnormal state of a circuit when a motor is rotated at a low speed by using a ritriggerable monostable multivibrator which generates a pulse of long period longer than the synchronization of a firing pulse. CONSTITUTION:When a circuit operates normally, a monostable multivibrator 15 is triggered by a firing pulse from a firing pulse generator G, and since the multivibrator 15 is retriggerable, its outputs Q, Q respectively continue high and low states, a light emitting diode 18 is fired slightly delay from the energization of a power source, and continues firing as long as the circuit operation is normal. When the circuit operation becomes abnormal and the firing pulse is defected, the multivibrator 15 is operated to irregularly flash the diode 18 or extinguish it to notify the abnormal state.