Emergency telephone installation for traffic road system - with by=pass circuit maintaining connection to emergency control centre in event of power failure

摘要

Each telephone (FSE) of a motorway emergency telephone installation is associated with a line (OVST) to the local automatic exchange. By operating a pushbutton (AT) a caller initiates an automatic number selection process which connects him with the emergency control centre for the motorway. A switching unit (ASS) at the individual telephone controls the number selection and connection of the control centre operator with the caller. A supervisory circuit (SPU) monitors the power supply which is drawn from the exchange. In the event of a failure an already connected caller is automatically reconnected by the supervisory circuit to bypass the switching unit and thus avoid interruption. At the same time the loss of supply is signalled to the control centre for rectification.