Signalling sticking relay contacts in DC motor controller

摘要

A test potential is checked on the changeover contact of one relay (RV,RR) at a test time point after each time at which the motor (M) is switched off. Another relay is activated during the stop time while the test potential measurement indicates that the contacts of the first relay have not opened.During the stop time the first relay is periodically switched on for a short period and then switched off again for a wait period, during which a signal tone indicating this state is generated. The short period is at least equal to the pull-in time of the changeover relay.