# CHE 185 – PROCESS CONTROL AND DYNAMICS

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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) 2. Draw a block diagram for a single closed-loop control based on known TF of each block.

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.

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

Z_N PARAMETERS Graphical determination

ZIEGLER-NICHOLS TUNING METHOD

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 =

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 =

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 =

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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