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CHE 185 – PROCESS CONTROL AND DYNAMICS

CHE 185 – PROCESS CONTROL AND DYNAMICS. WORKSHOP 4. 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)

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CHE 185 – PROCESS CONTROL AND DYNAMICS

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  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 , KU • STEP 3 – DETERMINE THE PERIOD, PU, 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. • Kc= tI = • 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 = tI = 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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