Greg McMillan shares ways to address slow valves and different time constants between primary and secondary loops.
Recorded deminar (demo/seminar) available for viewing at: http://www.screencast.com/t/YWYxZGUw
PID Control of Slow Valves and Secondary Loops Greg McMillan Deminar Series
1. Interactive Opportunity Assessment Demo and Seminar (Deminar) Series for Web Labs – PID Control of Slow Valves and Secondary Loops May 12, 2010 Sponsored by Emerson, Experitec, and Mynah Created by Greg McMillan and Jack Ahlers
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3. The Latest on Unleashing PID Power for Batch Processes Chapter 3 Features: PID Types and Structures Positive Feedback Integral Mode Dynamic Reset Limiting Cascade Loops Full Throttle Startup Appendix C Features: Unification of Tuning Methods
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9. Volume Booster with Integral Bypass (Furnace Pressure and Surge Control Signal from Positioner Air Supply from Filter-Regulator Air Loading to Actuator Adjustable Bypass Needle Valve
10. Booster and Positioner Setup (Furnace Pressure and Surge Control) Port A Port B Supply ZZZZZZZ Control Signal Digital Valve Controller Must be functionally tested before commissioning! 1:1 Bypass Volume Booster Open bypass just enough to ensure a non-oscillatory fast response Air Supply High Capacity Filter Regulator Increase air line size Increase connection size Terminal Box
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12. Ramping Response of Actuator for a Large Step or a Large Actuator Multiply time by 10 for large actuator without volume booster Time (sec) Stroke (%)
15. Positive Feedback Implementation of Integral Mode with Dynamic Reset Limit SP proportional derivative Gain Rate CO filter filter CV filter Filter Time Rate Time filter Filter Time = Reset Time ER is external reset (e.g. secondary PV) Dynamic Reset Limit ER Positive Feedback
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17. Cascade Control Benefit (self-regulating process) i o i o i o i inner loop process time constant o outer loop process time constant i inner loop process deadtime o outer loop process deadtime
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19. Cascade Control Benefit (integrating process) i o i o i o i inner loop process time constant o outer loop process time constant i inner loop process deadtime o outer loop process deadtime
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21. Effect of Slow Secondary Loop (cascade control integrating process) Secondary loop slowed down by a factor of 5 Secondary SP Secondary CO Primary PV Secondary SP Primary PV Secondary CO
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27. Summary of Demos Demo Sec PID Mode Secondary Dynamic Reset Primary Dynamic Reset Valve Slew Rate Secondary Process Response Primary Process Type 1 CAS Disabled Disabled Fast Fast Self-Reg 2 AUTO Disabled Disabled Slow Fast Self-Reg 3 AUTO Enabled Disabled Slow Fast Self-Reg 4 CAS Disabled Disabled Fast Slow Self-Reg 5 CAS Disabled Disabled Fast Slow Self-Reg 6 CAS Disabled Disabled Fast Fast Integ 7 CAS Disabled Disabled Fast Slow Integ 8 CAS Disabled Enabled Fast Slow Integ
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