MONITORING ARRANGEMENT FOR A STEP-BY-STEP SWITCHING TRAIN

摘要

An arrangement is disclosed for identifying which switch in a plurality of selector switches arranged in a switching train may be operating incorrectly. All of the selector switches of the step-by-step switching train are modified so that each switch superimposes a distinctive combination of audio frequency tones on the sleeve holding ground that the selector normally applies during the temporary interval that it is responding to dial pulses. Scanning the trunks at the input of the switching train for the appearance of the tone frequencies enables a record to be made of any tone which persists for longer than the normal selector operate time.