PID tuning

Much has been said and written about the PID tuning.

Some people argue that tuning is best done manually and can never be done by computer programs.

 

For the beginners, in process control , one of the basic questions will be "can PID loops be really tuned by softwares?" ( well, atleast , I had this question in my mind, during my initial years)

Is it true ?

Well it is both true and false .

True in the sense, for a given control objective , it is possible to "calculate" the tuning constants for the specific PID algorithms by computer programs

And False in the sense, it is the user who has to decide the control objective , because the software can not.

What is meant by control objectives ?

Well we know , that a loop can be tuned "slowely" to get a smooth response or tuned aggressively to quickly reject the disturbances. So there exists a trade off between the "robustness" and "aggressiveness" .

So this "degree of robustness or aggressiveness" must be measureable by some parameter , like "Closed loop time constant " or "Integrated absolute error" or % overshoot etc. If we know this , then we can calculate the tuning constants.