Alternative to PID

[roydm]

Many years ago I used a Ramsey controller they called Pulsed Error. The application was controlling the power draw of a crusher located after a vibrating screen. We tried without success to replace the controller with a more modern PID but it never came close to achieving the same results.
Are there other alternatives to PID besides Fuzzy Logic?
Roy

 

[sreid]

You have to know what your control requirements are. Most home heaters and ovens are Bang Bang (On or Off). This still works well for many applications (and is unconditionally stable; sometimes call Histerisis Control).

Maybe for the rock crusher they sense motor currents and underexcite the motor when no crushing is happening (phase controlled SCRs).

 

[dcasto]

here's one in use daily. It uses a pulse signal to a valve to open and close it for flow control, no PID, if to high pulse on solenoid, to low the other.

http://www.emersonprocess.com/daniel/products/liquid/Controlvalves/Productlevel2.htm

 

[roydm]

The controller would look at the power draw and then make a change in the rock feed rate. The change would show as a change in power about 20 seconds later.
Unlike a PID where the Integral term would continue ramping the output to reduce the error, the Pulsed Error controller made no change to the output until a timer (e.g. 25 seconds) had expired. The 4-20 mA was derived from a motorized potentiometer.
From memory the controller had only 2 settings, Proportional and Time delay.
Sreid, The crusher was part of 100,000 t/d plant. The controller setpoint would typically be 95-98% of motor nameplate kW and they would run non-stop for several weeks between maintenance shutdowns.
Dcasto, I think you may have posted the wrong link.
This is the only time I have seen that type of control although I have sometimes copied the "wait and see" strategy in PLC logic.
Roy

 

[sreid]

Another PID variant that could be used is to "Square the Error." Use low PID gains. With low errors. sloppy control but as the error gets larger, the control gets more aggressive.

 

[hacksaw]

pulse error works fine where you have large dead-times. Continuous p&id can be made to work, but you have to turn off the D and lower the gain quite abit. Digital is the best.