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Remote Switch Position Determination Using Constant Current Signaling

Abstract: 

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.

Patent Number: 
4,652,876
Date Of Issue: 
03/24/1987
Inventors: 

Glenn T. Darilek