A system and method for sensing the status of a plurality of valves by detecting the total current flowing through a network of constant current devices connected in series with a plurality of limit switches responsive to the open and closed positions of the valves. The system uses a binary constant current encoding network to provide a total current that is a unique binary weighted indication of which switches are closed. The system includes a current measurement circuit that converts the current to a voltage, filters out noise and amplifies the voltage for input to an analog to digital converter. The output of the analog to digital converter is then decoded by a logic hardware or by a computer to derive a digital output indicative of the position of the switches. A bipolar voltage source energizes the constant current encoding network and interacts with the current measurement and decoding circuits to ensure a sufficient voltage level for constant current operation.
Glenn T. Darilek