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Hi, I have to make logic were one PID loop controls two series-connected valves (look File 2). In logic, PID SP is temperature what comes from dynamical graph (depend on the external air temp), PV is outgoing temperature (after valves), PID CV is used to activate PLC relay outputs- OPEN, CLOSE (look File 1) There is no feedback from valves, from technical data is known that OPEN position to CLOSE position takes 150 sec (both valves are same type). Actions: 1. If its needed to raise water temperature, then its activated OPEN output, which is linked to valve "Direct" (look File 2, 11GM1). When valve "Direct" is full-open, but temp. isnt still high then end- switch Open will be electrically close valve "Bypass". 2. If its needed to lower water temperature, then its activated CLOSE output, which is linked to valve "Bypass" (look File 2, 11GM2). When valve "Bypass" is full-open, but temp. isnt still low then end- switch Open will be electrically close valve "Direct". First positions (physically) are , before PID Auto -tuning 40/60: "Direct" valve start position is 60% opened and "Bypass" valve start position is 40% opened (maybe 50/50 would be better?). I have looked U90 Ladder example "PID with motorized valve". It seemed very helpful, in example primary loop PID is looking SP-PV error and secondary loop compares PID CV and Virtual Valve Position. In example there is only one valve, how to do it with two valves what are series-connected? OK, in logic OPEN output is increasing "Direct" valve position and CLOSE output is increasing "Bypass" valve position, but what to do in logic when movement physically goes over to series-connected valve (look algorithm and File 2)? Ylle
