Dear forum, I am looking for a smart way to find parameters for a PID to make a frequency speed controlled pump together with a flow meter to keep a desired flow independent from pressure changes and other adjustments. The values I started with bruoght fluctuation between 6000 l/h and 10000 l/h. The desired value was 8000 l/h. An averaging would have shown that it works.

Has anyone of you ideas how to procedure to find reasonable values for a better PID? Are there things to be considered when controlling a pump by flow? I thought it should be a standard application.

Thanks in advance.

-- Benedikt Sürig (suerig@basecom.de), October 02, 2001

Answers

You can try reducing the gain(increase proportional band) to see if the oscillation stops. Is this a positive displacement pump? Is there any oscillation in manual? You might be exasperating the natural frequency of the system with your controller. If that is the case a little filtering ( a few seconds) or using a band gap controller(very low gain when close to setpoint ,normal gain when out of the natural oscillation(oscillation in manual) region can be used to improve control. typical range for standard flow loop-- gain <1 integral< .5 min/repeat.

-- Jamal Husein (jhusein@attglobal.net), December 19, 2001.