POWER FAILURE DETECTION SYSTEM

摘要

PURPOSE:To detect a power failure at a terminal device side by transmitting a power failure signal combining a mark signal, a space signal and a line interruption signal at power failure occurrence from a terminal device and detecting it at a center side. CONSTITUTION:When a terminal device detects a power failure, a power failure signal generating circuit 14 outputs [1], [0] signal corresponding DC +48V, -48V and a line interruption signal 0V to a voltage converting circuit 4. The circuit 4 converts the [1], [0] signal into + or -48V, 0V signals and transmits them to the center side. On the other hand, a level converting circuit converts the DC +48V into [1] and the DC -48V into [0] via an isolation circuit 5. Further, a line interruption signal detecting circuit 7 supervises whether or not the DC + or -48V signals are a specified voltage or below, and when the signal is below the voltage, a base hold circuit 8 applies space-hold to the input of an S/P converting circuit and a ower failure signal detection circuit 15. The detection circuit 15 uses an output of the space hold circuit 8 and the line interruption signal to detect a power failure signal.