frantisikas Posted May 31, 2019 Report Share Posted May 31, 2019 Hello, I need help with PID control. Is it possible to make proportional band different around Set Point? For example Set Point is 70°C, I want lower limit to be 63°C (start of proportional band) and upper limit 74°C (end of proportional band). Quote Link to comment Share on other sites More sharing options...
MVP 2022 Joe Tauser Posted May 31, 2019 MVP 2022 Report Share Posted May 31, 2019 The proportional band is symmetrical around the setpoint by definition - you don't get to have one side bigger than the other. Sorry. Joe T. Quote Link to comment Share on other sites More sharing options...
Isakovic Posted June 1, 2019 Report Share Posted June 1, 2019 Maybe if you set up logic to change P parameter when temperature rises over setpoint. Although that would probably be unstable. Quote Link to comment Share on other sites More sharing options...
frantisikas Posted June 3, 2019 Author Report Share Posted June 3, 2019 What if I set up two PID loops? Both works at same time but I take output value from one and when temperature reaches set point I take output value from another? Will this make system unstable too? I can take output value from first PID loop until temperature reaches set point -1°C, then use last output vale until temperature reaches set point+1°C and then take output value from another PID loop. Quote Link to comment Share on other sites More sharing options...
Isakovic Posted June 5, 2019 Report Share Posted June 5, 2019 I guess that too would be unstable. Why do you need unsymmetrical Proportional band? Is overshoot too big if you want it to be more aggressive when temperature gets too high? Maybe try parameters that give softer approach to setpoint. I don't know what kind of process you control, but with temperature it helps to turn off integral part when output reaches 100%, there's a function block for that. Quote Link to comment Share on other sites More sharing options...
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