in order to automatically restore a normal switching position of a relay armature from an accidental off switching induced by external impact or the like , the output of the relay is monitored and is applied to a differentiating circuit . a comparator is provided to reflect on and off operations of a main switch . in the event that the output of the relay falls suddenly , the differentiating circuit outputs a pulse to a wave - shaping circuit . a gate circuit is supplied with the outputs of the wave - shaping circuit and the comparator . the output of the gate circuit momentarily allows a relay driver to actuate the relay in response to the undesired change in relay status , and hence the relay armature resumes on switching position .