Method and circuit for monitoring asynchronous motors which are operated from a single-phase alternating-current mains system

摘要

The present invention relates to a method and a circuit for monitoring asynchronous motors which are operated from a single-phase alternating-current mains system, at least two stator windings, which are connected to one another at one end, being provided in the circuit of the relevant asynchronous motor, the free ends of which stator windings are bridged by a capacitor and can alternatively be connected to the phase of an alternating-current mains system. In order to create a method and a circuit for monitoring asynchronous motors which are operated from a single-phase alternating-current mains system, which method ensures reliable monitoring of the torque of an asynchronous motor, it is proposed according to the invention that the voltage (UH) which is applied to the auxiliary phase (1) is detected and is compared with at least one limiting value (G1) the rotation direction of the motor (6) being reversed, or the electrical supply for the drive of the motor (6) being interrupted, once this limiting value (G1) has been undershot. It is provided according to the invention in the case of the relevant circuit that a voltage pick-off (2, 3) is provided for the respective auxiliary phase (1) and that the corresponding auxiliary phase voltage (UH), if appropriate in a voltage divider circuit, is passed to an electrical switching element (10, 11, 19) which in each case assumes one of at least two possible states, which can be distinguished by measurement, as a function of the applied voltage.