Monitoring and sending of calls from emergency station - using calling frequency generator connected to central control unit via concentrator

摘要

The alarm system uses a concentrator, i.e a central unit having more inputs than outputs, which individual telephone lines are star-like connected through branch lines to a central control unit. The branch lines are supplied with a closed-circuit current, whose change causes the central control to send to a monitoring station a message recognisable as an error signal. Calling is signalled by a telephone station by operation of a frequency generator whose signals are transmitted through the branch lines to the central control unit which then switches signals through to an emergency answering unit.