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CHE 185 – PROCESS CONTROL AND DYNAMICS WORKSHOP 4.

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Presentation on theme: "CHE 185 – PROCESS CONTROL AND DYNAMICS WORKSHOP 4."— Presentation transcript:

1 CHE 185 – PROCESS CONTROL AND DYNAMICS WORKSHOP 4

2 The hazard of tuning PI controllers by trial and error WORKSHOP OBJECTIVES: 1.UNDERSTAND THE NEED FOR INTEGRAL ACTION FROM THE TANK LEVEL CONTROL. IT MAKES THE CLOSED LOOP GAIN ONE. (NO OFFSET) 2.DRAW A BLOCK DIAGRAM FOR A SINGLE CLOSED-LOOP CONTROL BASED ON KNOWN TF OF EACH BLOCK.

3 The hazard of tuning PI controllers by trial and error WORKSHOP OBJECTIVES: 3.UNDERSTAND THE REASON FOR TAKING MEASURES AGAINST INTEGRAL WINDUP. 4.KNOW HOW TO IMPLEMENT ANTI-WINDUP MEASURES. 5.DERIVE THE ALGORITHM FOR PI CONTROL, IN T. F., IN ANALOG FORM, AND DIGITAL FORM.

4 ZIEGLER-NICHOLS TUNING METHOD SEE SECTION 9.3 IN TEXT FOR DETAILS. STEP 1 – PUT CONTROLLER IN P-ONLY AUTOMATIC CONTROL STEP 2 – ADJUST K UNTIL LOOP OSCILLATES WITH CONSTANT AMPLITUDE, K U STEP 3 – DETERMINE THE PERIOD, P U, OF OSCILLATION FROM THE LOOP

5 Z_N PARAMETERS GRAPHICAL DETERMINATION

6 ZIEGLER-NICHOLS TUNING METHOD

7 WORKSHEET RESULTS WHEN YOU HAVE DETERMINED BEST TUNING VALUES FOR DISTURBANCE REJECTION, RECORD THEM BELOW. ALSO RECORD THE NUMBER OF TESTS YOU TRIED IN YOUR SEARCH FOR THESE BEST VALUES. K c = T I = NUMBER OF TUNINGS TESTS PERFORMED =

8 WORKSHEET RESULTS IF CLOCK TIME ON THE SIMULATION IS SHOWING MINUTES, HOW MANY HOURS OF PROCESS TIME DID THIS LOOP TUNING EXERCISE TAKE? AT 8 HOURS/SHIFT, HOW MANY LOOPS COULD YOU TUNE PER SHIFT AT THIS RATE? HOURS OF PROCESS TIMED USED = NUMBER OF LOOPS TUNED IN 8 HOUR SHIFT =

9 WORKSHEET RESULTS REPEAT THE ABOVE EXERCISE WITH A SET POINT TRACKING CONTROL OBJECTIVE. START WITH YOUR BEST DISTURBANCE REJECTION TUNING VALUES AND DETERMINE BY TRIAL AND ERROR WHETHER THEY ARE BEST FOR TRACKING SP STEPS FROM 50% UP TO 60% AND BACK AGAIN. RECORD YOUR BEST SP TRACKING TUNING VALUES: KC = T I = NUMBER OF TUNINGS TESTS PERFORMED =

10 WORKSHEET RESULTS IS YOUR BEST TUNING FOR SET POINT TRACKING THE SAME AS YOUR BEST TUNING FOR DISTURBANCE REJECTION? DID HAVING DISTURBANCE REJECTION TUNING VALUES AS A STARTING POINT HELP YOU FIND SET POINT TRACKING TUNING VALUES WITH FEWER TESTS?


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