PID Input: Square Root


Hi Optoers,

I have a quick question regarding PID inputs. I hope the answer is obvious, and possibly indicative of my poor internet-search and manual-reading skills.

I’m getting dangerously close to clicking the “Square Root” checkbox option for one of my PID inputs. (I’m pumping liquid out of a spherical volume, which unfortunately is nonlinear when performing level control.) I’d simply like to know if I need to refactor the setpoint and gains to account for the square root math. Or, is all this handled behind-the-scenes, maintaining a friendly 12-inches-as-a-setpoint-means-12-inches interface.



Update: The answer is Opto performs as advertised. Clicking the “square root” checkbox simply takes the square root of the input process value and compares that value to the setpoint for calculation of the PID error. So if I want to maintain a setpoint level of 9 inches in my vessel and I am taking the square root of the level transmitter to linearize the pump behavior, I’d have to adjust my SP = sqrt(9 in) = 3 in^(1/2). Cool.