A communicator for field instruments connected to a transmission line for transmitting electric signals from the field instruments to a host instrument. The communicator operates on electric power fed from an external power supply over the transmission line. The external power supply is arranged in the...http://www.google.ca/patents/US5995021?utm_source=gb-gplus-sharePatent US5995021 - Communicator for field instruments and method for supplying power to this communicator
