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17 Cards in this Set
- Front
- Back
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P Control affects time constant and damping coefficient of a second order process by
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Kc is indirectly proportional to both.
As Kc is increased, both decrease. |
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No lag from PI controller results from
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Excess P action. Too aggressive , Kc should be reduced. Results in faster response of closed loop process
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Maximum controller output occurs at _________, corresponding to ____-____ (___-___)
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Max output occurs at max deviation from set point, which corresponds to zero-lag (in-phase)
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Lag from PI controller results from
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Too much integral action, tI too small. Increase reset time. Offset elimination is slow.
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ITSE
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Integral Time Square Error. Penalizes both late deviations and large deviations
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ITSE equation
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t[ysp(t) - ys(t)]^2 dt
Error squared weights for large deviations. t accounts for late deviations |
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ITAE
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Integral Time Absolute Error penalizes late deviations. t accounts for late deviations
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Characteristic Eqn for 1st order process with PI control
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Kc[1+ 1/tIs]*Kp/tPs +1 = 0
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IAE
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Integral of Absolute Error. Any error is a problem, suppress ALL
ysp(t) - ys(t)] dt |
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ISE
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Integral Square Error
Larger deviations/errors penalized, weight by squaring for specific error. |
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Field Tuning Procedure used for ______.
Based on ________ |
fast responding loops.
Based on trial and error selection of tuning parameters |
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Field Tuning Procedure
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1. Set D and I off
0 and infinity 2. Use initial estimate of Kc (e.g. 1/2Kp) estimating Kp from process knowledge 3. Using SP changes, increase Kc incrementally until response meets tuning criteria 4. For PI controller, decrease Kc by 10% 5. Use initial value of tI (e.g. tI = 5tP) 6. Decrease tI until offset is eliminated and tuning criteria met for SP changes 7. Check P and I action levels |
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ATV method: Ku =
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4(h)/pi(a)
where h = relay height a = resulting amplitude of standing wave |
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ATV tuning method
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Autotune variation method determines ultimate gain and period without upsetting process
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ATV tuning procedures
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Select h (change in MV applied) so that process is not unduly upset but an accurate a results.
Controller output is switched when ys crosses y0 It usually take 3-4 cycles before standing is established Values a and Pu can be measured |
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Ziegler Nichols
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Uses experimental measurements of the ultimate gain, Ku and ultimate period, Pu to calculate controller settings
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Ziegler Nichols procedure
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P only controller
Increase Kc until oscillations are sustained for relatively small SP change Ku = P only controller gain resulting in sustained oscillations Pu = Period of sustained oscillations Calculate controller settings based on Ku and Pu |
