Presented by Greg McMillan on December 7, 2010 to the ISA St. Louis section.

1. ISA Saint Louis Short Course Dec 6-8, 2010 Exceptional Process Control Opportunities - An Interactive Exploration of Process Control Improvements - Day 2

4. Block Diagram of “Series”, “Real”, or “Interacting” PID Form Nearly all analog controllers used the “Series” or “Real” Form   SP   proportional integral derivative  Gain     Reset (1  T i )  Rate    CO filter filter CV filter Filter Time   Rate Time Improving Controllers

5. Block Diagram of “Standard”, “Ideal”, or “Non-interacting” PID Form Nearly all digital controllers have the “standard” or “Ideal” form as the default Improving Controllers   SP   proportional integral derivative  Gain     Reset (1  T i )  Rate    CO filter filter CV filter Filter Time   Rate Time

6. Positive Feedback Implementation of Integral Mode Improving Controllers   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

8. PID Controller Forms PB = 100%  K c CO n = P n  I n + D n + CO i CO i = controller output at transition to AUTO, CAS, or RCAS modes (%) CO n = controller output at execution n (%) CV n = controlled variable at execution n (%) D n = contribution from derivative mode for execution n (%) I n = contribution from integral mode for execution n (%) K c = controller gain (dimensionless) P n = contribution from proportional mode for execution n (%) R i = reset setting (repeats/minute) PB = controller proportional band (%) SP n = set point at execution n (%) T d = derivative (rate) time setting (seconds) T i = integral (reset) time setting (seconds/repeat)  = rate time factor to set derivative filter time constant (1/8 to 1/10)  = set point weight for proportional mode (0 to 1)  = set point weight for derivative mode (0 to 1) R i = (60  T i ) Conversion of settings: Improving Controllers (K c  T d )  SP n – SP n-1 ) – (CV n  CV n-1 ) ]  T d  D n-1 D n = -------------------------------------------------------------------------------  T d  t P n = K c  SP n – CV n ) I n = (K c  T i )  SP n – CV n )  t  I n-1 Standard P n = K c  SP n – D n ) I n = (K c  T i )  SP n – D n )  t  I n-1 Series

10. Flow Setpoint Response - PIDPlus vs. Traditional PID Improving Controllers

11. Flow Load Response - PIDPlus vs. Traditional PID Improving Controllers

12. Flow Failure Response - PIDPlus vs. Traditional PID Improving Controllers

13. pH Setpoint Response - PIDPlus vs. Traditional PID Improving Controllers

14. pH Load Response - PIDPlus vs. Traditional PID Improving Controllers

15. pH Failure Response - PIDPlus vs. Traditional PID Improving Controllers

19. Control Valve Watch-outs dead band Deadband Stick-Slip is worse near closed position Signal (%) 0 Stroke (%) Digital positioner will force valve shut at 0% signal Pneumatic positioner requires a negative % signal to close valve The dead band and stick-slip is greatest near the closed position Deadband is 5% - 50% without a positioner ! Plugging and laminar flow can occur for low Cv requirements and throttling near the seat Consider going to reagent dilution. If this is not possible checkout out a laminar flow valve for an extremely low Cv and pulse width modulation for low lifts Improving Valves

20. Direct Connection Piston Actuator Less backlash but wear of piston O-ring seal from piston pitch is concern Improving Valves

21. Significant backlash from link pin points 1 and 2 Link-Arm Connection Piston Actuator Improving Valves

22. Stick-slip from rack and gear teeth - particularly bad for worn teeth Rack & Pinion Connection Piston Actuator Improving Valves

23. Lots of backlash from slot Scotch Yoke Connection Piston Actuator Improving Valves

24. Diaphragm Actuator with Solenoid Valves Improving Valves Port A Port B Supply ZZZZZZZ Control Signal Digital Valve Controller Must be functionally tested before commissioning! SV Terminal Box

25. Piston Actuator with Solenoid Valves Improving Valves Port A Port B Supply Digital Valve Controller SV SV Volume Tank Must be functionally tested before commissioning! Piston W Check Valve Air Supply Terminal Box

26. Size of Step Determines What you See Improving Valves Maintenance test of 25% or 50% steps will not detect dead band - all valves look good for 10% or larger steps

27. Effect of Step Size Due to Sensitivity Limit Improving Valves

28. Response to Small Steps (No Sensitivity Limit) Improving Valves Stroke (%) Time (sec)

29. Response to Large Steps (Small Actuator Volume) Improving Valves Time (sec) Stroke (%)

30. Installed Characteristic (Linear Trim) Improving Valves Valve pressure drop ratio (  P R ) for installed characteristic: Characteristic 1:  P R  0.5 Characteristic 2:  P R  0.25 Characteristic 3:  P R  0.125 Characteristic 4:  P R  0.0625

31. Installed Characteristic (Equal Percentage Trim) Improving Valves Valve pressure drop ratio (  P R ) for installed characteristic: Characteristic 1:  P R  0.5 Characteristic 2:  P R  0.25 Characteristic 3:  P R  0.125 Characteristic 4:  P R  0.0625

32. Improving Valves Installed Characteristic (Modified Parabolic Trim) Valve pressure drop ratio (  P R ) for installed characteristic: Characteristic 1:  P R  0.5 Characteristic 2:  P R  0.25 Characteristic 3:  P R  0.125 Characteristic 4:  P R  0.0625

33. Limit Cycle in Flow Loop from Valve Stick-Slip Improving Valves Controller Output (%) Saw Tooth Oscillation Process Variable (kpph) Square Wave Oscillation

34. Limit Cycle in Level Loop from Valve Deadband Improving Valves Manipulated Flow (kpph) Clipped Oscillation Controller Output (%) Rounded Oscillation Level (%)

35. Real Rangeability Improving Valves Minimum fractional flow coefficient for a linear trim and stick-slip: Minimum fractional flow coefficient for an equal percentage trim and stick-slip: Minimum controllable fractional flow for installed characteristic and stick-slip: C xmin  minimum flow coefficient expressed as a fraction of maximum (dimensionless)  P r  valve pressure drop ratio (dimensionless) Q xmin  minimum flow expressed as a fraction of the maximum (dimensionless) R v  rangeability of control valve (dimensionless) R  range of the equal percentage characteristic (e.g. 50) X vmin  maximum valve stroke (%) S v  stick-slip near closed position (%)

37. Volume Booster with Integral Bypass (Furnace Pressure and Surge Control) Improving Valves Signal from Positioner Air Supply from Filter-Regulator Air Loading to Actuator Adjustable Bypass Needle Valve

38. Booster and Positioner Setup (Furnace Pressure and Surge Control) Improving Valves 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

44. Dynamic Response to Step Improving Measurements Time (seconds) Theoretical Transmitter Response Actual Transmitter Response True Process Variable  m  m deadtime measurement time constant Process Variable and Measurement

45. Dynamic Response to Ramp Improving Measurements Time (seconds) Actual Transmitter Response True Process Variable  m  m Process Variable and Measurement

46. Attenuation of Oscillation Amplitude by Transmitter Damping or Signal Filters: When a measurement or signal filter time (  f ) becomes the largest time constant in the loop, the above equation can be solved for (A o ) to get the Amplitude of the original process variability from the filtered amplitude (A f ) Improving Measurements Effect of Transmitter Damping and Signal Filters

47. Effect of Transmitter Damping or Filter for Surge Improving Measurements  m  m  m  m

51. Temperature Sensor Performance Improving Measurements

52. Temperature Sensor Lag Improving Measurements

53. Thermowell Lags Improving Measurements

56. Elimination of Ground Noise by Wireless pH Improving Measurements Wired pH ground noise spike Temperature compensated wireless pH controlling at 6.9 pH set point Incredibly tight pH control via 0.001 pH wireless resolution setting still reduced the number of communications by 60%

64. Effect of MEA Solvent on pH Improving Measurements

65. Effect of PZ Solvent on pH Improving Measurements

67. Cascade Loop Block Diagram  p1  p2  p2 K p2  p1  m2  m2 K m2  c2  f2 Primary Process K v  v  v K L2  L2  L2 Primary Load Upset  CV p  CO p  MV  PV p2 Delay Lag Delay Delay Delay Delay Delay Lag Lag Lag Lag Lag Gain Gain Gain Gain Local Set Point  DV p2 % % % Delay <=> Dead Time Lag <=>Time Constant K L1  L1  L1 Delay Lag Gain  DV p1 Secondary Load Upset  CO s Secondary PID Cascade Set Point % % K p1 Gain  CV s  m2  m2 K m2 Delay Lag Gain  c2  f2 Delay Lag Secondary Process Primary PID Primary:  o2  v  p1  p2  m2  c2  f2  v  p1  Secondary:  o1  v  p1  m1  c1  f1  v Improving Loops - Part 1 K c2 T i2 T d2 K c1 T i1 T d1

68. Cascade Control Benefit (self-regulating process) Improving Loops - Part 1  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

69. Cascade Control Benefit (integrating process) Improving Loops - Part 1  i  inner loop process time constant  o  outer loop process time constant  i  inner loop process deadtime  o  outer loop process deadtime  i   o   i   o   i   o 

70. Cascade Control Benefit (runaway process) Improving Loops - Part 1  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

71. Secondary loop slowed down by a factor of 5 Secondary SP Secondary CO Primary PV Secondary SP Primary PV Secondary CO Effect of Slow Secondary Tuning (cascade control) Improving Loops - Part 1

72. Triple Cascade Loop Block Diagram Improving Loops - Part 1 Control Valve AO PID PID AI AI Flow Meter Process Process Sensor Secondary (Inner) Loop Feedback Primary (Outer) Loop Feedback Process SP Flow SP Out PV PV Relay PID * Position Loop Feedback DCS Valve Positioner Position (Valve Travel) I/P Drive Signal * most positioners use proportional only

76. Bias Correction of Ratio Control For information on Ratio Control, see April 7, 2009 Post on website http://www.modelingandcontrol.com/2009/04/what_have_i_learned_-_ratio_co_1.html Improving Loops - Part 1