Testing emergency call system with subscribers - generating preset number of test pulses within preset time interval and transmitting to evaluator circuit

摘要

The subscribers are connectable over a two-core signal line and a subscriber circuit in an exchange to an interrogating station. The d.c. feed for the exchange hearing, speaking and control devices takes place over the signal line. Testing pulses are generated by an evaluating circuit in the subscriber circuit. Within a preset time interval a preset number of identical testing pulses are generated in the same time intervals, and supplied to the evaluation circuit. The automatic evaluation is so carried out that the testing is considered positive, when at least one of the transmitted test pulses is received in the evaluating circuit and identified during the preset time interval. ADVANTAGE - Interference transmission only when real interference has occured.