A telemetering system for a data transmission line having a sequence of repeaters controls sequential operation from a centralized single supervisory terminal. The supervisory terminal sends an interrogation signal forward to a first repeater which sends back an answer signal relating to the status of...http://www.google.com.hk/patents/US4635260?utm_source=gb-gplus-share專利 US4635260 - Data transmission telemonitoring equipment and system
