I am using the PID.vi from the PID toolkit within code in a .rtexe on cRIO to control a fluid system via several control valves. We are having an issue with getting large fluctuations (~4%) in the output when the system variables are set such that the control valve should be completely open, PID output of 100%. This occurs even when the inputs to the PID.vi are set as constants. But conversely we get a steady output when the valve is driven all the way shut, PID output of 0%. At first we thought this might be due to noise in the PV or SP input signal but as I mentioned it still occurs even when constants are sent to the PID.vi. The output range in the PID.vi has been set to 0-100%. Has anyone had this issue and if so how did you overcome it? Thanks!
