US Patent 7693080 Network loop monitor

A network loop monitor (10) is disclosed which comprises an RS485 port (16) for connection to a host which receives and transmits data. The port (16) comprises termination jumpers (14), a transmitter/receiver (34) and an isolator (36). The monitor (10) includes two further RS485 ports (18, 20) each of which has a termination (26, 28), a transmitter/receiver (42, 44) and an isolator (38, 40). A relay (22) controls contacts (24) in the line pair (12). Router logic (32) controlled by a microprocessor (30) determines the status of the loop monitor.