MONITORING METHOD FOR FAULT OF PUBLIC TELEPHONE AND FAULT SIGNAL SENDING CIRCUIT AND FAULT SIGNAL MONITORING CIRCUIT

摘要

PURPOSE:To detect the occurrence of a fault without remodeling a switchboard itself, by flowing a line current when a public telephone set is used, or an intermediate line when the set is not used when the fault is detected. CONSTITUTION:When a fault is detected by the fault detecting circuit 31 of a public telephone set 2, a line current when the telephone set 2 is not used is converted by a current control circuit 32 into a presribed value less than a minumum line current when a switchboard is actuated, and greater than that when the switchboard recovers. This conversion is carried out by making a relay contact by energizing a detection relay 33. On the other hand, the current levels of lines L1 and L2 are monitored by the fault signal monitoring circuit 4 of an exchange all the time, and the current value converted into the prescribed value by the circuit 32 is detected by the circuit 4. Thus, the monitoring circuit which discriminates the value of the line current is only connected in series to the lines L1 and L2 to detect the occurrence of a fault in the public telephone set.