Method for safety-related monitoring of speed of three-phase alternating current motor, involves determining value from time intervals, and comparing value with safety-related limit value transmitted from safety controller

摘要

The method involves determining time intervals between flanks of a signal e.g. digitally evaluated control signal. A value is determined from the time intervals and is compared with another value i.e. safety-related limit value, which is transmitted from a safety controller or a signal electronic circuit to another signal electronic circuit. The comparison result is evaluated. Pulse-pause ratio of the signal is determined as a pulse width modulation ratio, where frequency of lateral characteristics of the ratio represents the safety-related limit value. An independent claim is also included for a device to perform a method for safety-related monitoring of speed of an electric machine.