rslogix 500 mulitple pid conflict

Have program written by someone else that has multiple pid written to control hydraulic proportional valves. The pid is to control 4-20 ma signal to prevent valve ocillation. When running the program on valve runs correctly opening and returning to closed postion waiting for additional signal from program, while the other moves to fully open postion and will not return and it does respond to program signal but instead of starting at closed position tries to run form open position. suggestions?

The pid's for one valve appear to affect the other valve.

mr. p said:

while the other moves to fully open postion and will not return and it does respond to program signal but instead of starting at closed position tries to run form open position. suggestions?

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This sounds like a wiring problem. Either the feedback wires are crossed or the control output wires are crossed. This results in positive feed back instead of negative feedback and the actuator will extend to one end or the other and just sit there.

First you need to have a standard for how the control signal is wired. Make sure that when a positive voltage is sent to the valve that the actuator extends. Then make sure that when the actuator extends that the feed back voltage increases. If the two are opposite you will have problems.

Thanks, I have correct voltage signals from transducer as valves move. i will check to see if wiring to the one valve is correct from plc.