Loop monitoring circuit for telephone exchange - includes comparator for interrogation cycle, and counter storing loop state duration

摘要

The loop monitoring circuit cyclically detects the state of each connection line and junction line loop and compares it with the state of the corresponding loop obtained for the previous interrogation cycle. A memory unit has respective locations containing the previously detected state of each loop and the count value of a counter, which represents the duration of each loop state. The counter is indexed after each interrogatin cycle with a signal provided when a given count value is reached. For each interrogation of a connection line or junction line, an indicator for the connection circuit, representing the count value for which the signal is supplied to a subsequent central processor is provided together with the actual state of the loop.