Multi-mode input/output circuit and module, and process control system using same.

摘要

A universal I/O circuit is provided to interface a control computer system with remote sensor transmitters which produce outputs representing one or more process variables and with remote controlled devices which control process variables. The circuit uses a pair of terminals (28a, 28c) in series combination with an electrically-controllable variable resistance device (74) and a load means (76) , across which series combination a supply voltage (from 56, 62) is applied. A microcomputer (52) controls the resistance of the variable resistance device (74), as well as of associated circuity, to operate them appropriately to receive current inputs from the remote transmitters or to supply current or voltage outputs to the remote controlled device; in any of these cases, the remote controlled device or remote transmitter is connected directly to the two terminals (28a, 28c) . The variable-resistance device is preferably a transistor, and the load means a resistor. <IMAGE>