PID instruction: bit 03 of C+5

[tingxing 1]

Hello, I am trying to use PID instruction (PIDAT). I have a question about the usage of bit 03 of C+5, i.e. "Manipulated variable output designation". And the manual states it "Designates the manipulated variable output for when the PV equals the SV." And also said 0 means output 0%, and 1 means 50%. I did some experiments, and could not discern any difference between using or disabling the bit. What actual effect will be there if I set the bit to 0 or 1? Thanks in advance. Ting

[Geir 4]

It is hard to see any effect due to the integral and derivative action of the controller, to see it you must disable the I and D action and set the P-band to 100. Then you should be able to give the setpoint (SV) a value of 50% and observe the output (MV) follow the input (PV). When the bit is 1, the output should start at approx 0% and follow the input proportionally to 100%. (Assuming direct control action). When the bit is 0, I think you will only see the output change when the input is higher than the setpoint. Normally when you design a simple process, you try to have it balanced when there is as much energy going out as is coming in at 50% MV and SV. Otherwise, if you have for example a process with a heating and a cooling circuit with one controller for each circuit, the process would be in balance when both outputs are at 0%, and you need to set the control bit to 0. Note that you have to turn the control action off and on again for this control bit (+C5 03) to take action.

[Jay Anthony 118]

Awesome answer!

[Geir 4]

Thanks