Question about a PID controller

[chensley1975]

Everyone, I am fairly new to LabView programming. I have created a program that gathers and sends data to a PXI system. I have a VFD controller that drives a blower motor based on the mA output (4-20mA). I have a PID controller that works great when I am using the CFM input; however, when I switch and use the static pressure input instead (some tests will use CFM and some will use static) there will be an issue. The response for static pressure is different than CFM so I am not sure how to modify the code. With CFM, an increase in output will result in an increase in the CFM reading, while with static pressure, an increase in output will result in a decrease in static pressure. I know that this can be done through a reverse acting PID; however, I am not sure how to implement this in LabView. Any help that you can give would be greatly appreciated.

[wiebe@CARYA]

I'd try to reverse the output range. Output high = -100, Output low = 100, or similar.

Not sure how well that will work, or if it's the proper way to do it, but worth a try.

[RavensFan · Accepted solution]

Can you use a negative gain factor?