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10 Tips for Tuning of Pid Looops

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10 Tips for Tuning of Pid Looops

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10 Tips for Tuning of Pid Looops

  1. 1. Technology Training that Workswww.idc-online.com/slideshare 10 Tips for: Tuning of PID Loops By Steve Mackay
  2. 2. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Welcome to this webinar There are at least 3 ways to interact with your presenter today: 1. Use the Text tab, near bottom left of your screen. Type the message in the space next to the “Send” button, then enter or click Send. (Ensure “All” is selected in the drop- down menu under the typing area) 2. Use the Emoticons selection in the text window – choose an emoticon then click send or enter. 3. Talk! Click the Push To Talk button. The button will change to yellow when you are queued, then green to show that your microphone is live. Remember to click it again when you have spoken This 45 minute session will commence shortly! RH
  3. 3. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Objectives • Concept of tuning • Ziegler Nichols classical rules • Practical closed and open loop strategies • Cascade loops • Dead time issues
  4. 4. Technology Training that Workswww.idc-online.com/slideshare Concept of Tuning
  5. 5. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 1 - Minimize Integral of error Objectives of Tuning (1)
  6. 6. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 2 - Minimize Amplitude of error squared Objectives of Tuning (2)
  7. 7. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 3 - Minimize wear and tear 4 - No overshoot at Start Up 5 - Minimize effect of known disturbances Other Aspects of Tuning (3,4,5)
  8. 8. Technology Training that Workswww.idc-online.com/slideshare Ziegler Nichols and others
  9. 9. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Loop Controller and Process
  10. 10. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 1. Put controller in manual mode 2. Make a step change to the OP value 3. Observe Reaction Curve 4. Calculate timing constants Reaction curve Steps of Open Loop Tuning (Reaction Curve)
  11. 11. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare P - Control PI - Control PID - Control ( )= × OP N L % ( )= × × = × 09 3 . % int OP N L T L ( )= × × = × = × 12 2 05 . % . int OP N L T L T Lder KC KC KC Reaction Curve Calculations
  12. 12. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare • Find critical value of K for continuous oscillations • Do not use I or D - control • Observe critical frequency for 180° phase shift • Stabilize loop by reducing K and ensure that I & D • Control still gives a phase lead Continuous Cycling - Ziegler & Nichols
  13. 13. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare P-only for Continuous Cycling Method
  14. 14. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 1. Put controller in P - control only 2. P - control on ERR = (SP - PV) 3. Controller in Auto 4. Step change to SP 5. Double value of K until continuous cycling 6. Calculate tuning constants Continuous Cycling Method
  15. 15. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare P - Control PI - Control PID - Control K KC U= ×05. K K T P C U U = × = 0 45 12 . .int K K T P T P C U U der U = × = = 0 6 2 8 . int Calculation of Tuning Constants
  16. 16. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare First Order Lag
  17. 17. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare First Order Lag Response Curve
  18. 18. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Variation on continuous cycling .... to avoid danger to process ... but damped oscillations are acceptable requires some subjective evaluation Damped Cycling Method
  19. 19. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Damped Oscillation Decay Ratio
  20. 20. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare 1. Put controller in P - control 2. P - control on ERR = (SP - PV) 3. Controller into Auto 4. Double K until oscillations. 5. Terminate immediately 6. Calculate tuning constants Steps of Damped Cycling Method Estimate damping of oscillation Convert P into Pu using diagram
  21. 21. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Convert P into Pu using diagram Estimate damping of oscillation (d) ... 0.5 acceptable
  22. 22. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare PI - Control PID - Control ( )T P Rd d int .= × 12 R P pd u =       ( ) ( ) T P R T P R d d der d d int = × = × 2 8 K determined by good judgement..... Calculate Tuning Constants
  23. 23. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Tuning for NO Overshoot on Start-up Variation of continuous cycling method When no overshoot even for start-up is permitted (manual ⇒ auto)
  24. 24. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Same as for continuous cycling Formula for PID – control: K K T P T P C U U der U = × = = 0 2 3 2 . int Formula for NO Overshoot on Start-up
  25. 25. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Variation of continuous cycling method No overshoot during normal modulating control only Tuning for SOME Overshoot on Start-up
  26. 26. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Same as for continuous cycling Formula for PID - control K K T P T P C U U der U = × = = 033 2 3 . int Formula for Some Overshoot on Start-up
  27. 27. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Cascade Control
  28. 28. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Single Loop Temperature Control
  29. 29. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Two Controller Basic Cascade Control
  30. 30. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Tuning of Cascade Loops (cont…) • Cascade Control - Secondary Controllers – Mainly flow controller – No D - control as mainly stable – K < 1 • Cascade Control - Primary Controllers – Mainly PID controller – Careful stability considerations
  31. 31. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Long Process Deadtime in Closed Loop Control & The Smith Predictor
  32. 32. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Process Deadtime • Difficult problem to overcome long deadtime in feedback control loop • Especially when deadtime more than 20% of total time taken for PV to settle to its new value after last setpoint change
  33. 33. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Example of Process Deadtime Illustration of a long conveyor system giving an excessive deadtime to the control loop
  34. 34. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Overcoming Process Deadtime • Depends on operating requirements of process • Easiest solution: de-tune controller to slower response rate so that controller will not over compensate unless deadtime excessively long • Integral mode of controller very sensitive to deadtime since during period of PV inactivity, integrator ramps output
  35. 35. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Level Control Maintain flow as constant as possible to downstream equipment Medium response Tune as slowly as possible without overfilling or emptying the tank Choice of Tuning Constant (1)
  36. 36. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Flow Control Maintain constant flow Aim for fast response Small process lag in system Tune for fast as possible response Choice of Tuning Constants (2)
  37. 37. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Temperature Control Maintain a steady temperature Major process lag and dead time in the system Tune as quickly as possible without causing oscillations TC PV SP T2 O utlet Inlet Choice of Tuning Constants (3)
  38. 38. www.eit.edu.au Technology Training that Workswww.idc-online.com/slideshare Thank You For Your Interest If you are interested in further training, please visit: IDC Technologies Short Courses: Two-day practical courses available to the public: http://www.idc-online.com/slideshare

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