Communications system with remote control of outstations - can interrupt sequential transmissions to interrogate one specific outstation

摘要

A control centre (1) with a transmitter (S) and receiver (E) controls substations (US1, US2...) via a communications link comprising a monitoring channel and a control channel. The substation logic circuitry (L) controls switches (R1, R2...) in the monitoring channel. Normally the switches (R1, R2...) are all closed so that the substations can sequentially send process information to the control centre. A message from the control centre can interrupt the sequence to allow a substation to transmit data. In such cases the logic (L) opens the relevant switch, to prevent substations further down the line from transmitting.