Mains-isolated three=phase asynchronous rotary electrical machine speed monitor e.g. for door - has two=channel processing circuits for delivering bit signals to coupling circuit, which generates output signal when speed is above or below limits, if bit signal changes from rest to active within time window

TLDR: In this article, a dual-channel evaluation circuit is used to detect machine speed above or below a given limit value and uses a dual channel evaluation circuit coupled to the three machine winding phases (5,6,7).

Abstract: The monitor detects machine speed above or below a given limit value and uses a dual-channel evaluation circuit (11) coupled to the three machine winding phases (5,6,7). Each channel (12,13) of the evaluated circuit has two inputs (15,16;21,22) coupled to two different phases and a single digital output (17,23) providing a binary signal. The two binary signals are combined to provide an output signal which changes from a rest value to an active value when the limit value is exceeded. Pref. each channel of the evaluation circuit contains a voltage amplifier with a variable amplification and a precision rectifier. USE/ADVANTAGE - For asynchronous motor drive indicating abnormal speed to prevent overloading, without noise problems and without structural interference in or at machine.