Concentrator for telephone emergency call facility - has pair of relays reversing polarity to supply speech current and connect engaged tone generator to subsequent callers

摘要

A concentrator stage, i.e a stage having more inputs than outputs, can couple a subscriber for an emergency call. It allows line-engaged signals to be generated for subsequent callers. Subscribers are connected over pairs of inputs with relays normally set to supply a specified current level. When connected, one pair of relays connects one subscriber to an output and reverses the polarity of the supply to allow conversation to take place. Any other subscriber calling during this period is connected with an engaged signal generator.