1. Control Using Two Manipulated Parameters Terry Blevins (Principal Technologist) and Greg McMillan (Principal Consultant)

2. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 2 Presenters Terry Blevins Greg McMillan

3. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 3 Introduction Overview – Typical Examples Split-Range Control –Concept, variations in implementation –Setup in field vs. Splitter Block and IO for each valve. –Using Splitter Block, Example. Valve Position Control –Concept and typical implementation –Setup of I-only control in implementation –Impact of mode/status, Example. Combining Split Range and Valve Position Control –How to implement in DeltaV –Example Utilizing Predict/PredictPro for Control Using Two Manipulated Parameters –Advantage if process has large deadtime, difference in dynamics –Setup of MPC and MPC-Pro Blocks –Example Applications Summary References

4. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 4 Control Using Two Manipulated Parameters Under specified problem that has multiple solutions for unlimited operation. Extra degree of freedom is used to achieve unique solution that satisfied specific control objective. Most common techniques are: split range, valve position control. Combination of these technique and MPC offer new capability to address this class of problems ControllerProcess SP Unmeasured Disturbance One(1) Controlled Parameter Two(2) Manipulated Parameters

5. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 5 Split Range – Traditional Implementation IP 101 TT 101 TIC 101 Process Sequencing of valve accomplished through calibration of positioner, selection of actuator (A/O or A/C) Pro – Less expensive installation (1 pair of wires to field and 1 I/P) Con – You are not using the best technology for valve performance (e.g. digital positioners). Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain. Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem. Con – The actuator, pneumatic positioner, and I/P performance shift with time and field conditions Con – I/P failure disables 2 valves Con - Replacements in the night may not have the special settings Temperature Example 4-20ma Heating Cooling 3-15PSI Valve Position (% of Span) IP Output ( PSI ) 15 3 0 100 Cooling Heating A/C A/O

6. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 6 Split Range – Traditional Implementation Sequencing of fine and coarse valve requires pressure switch, two solenoid valves and associated wiring and tubing Con – Complex installation Con – You are not using the best technology for valve performance (e.g. digital positioners). Con -Difficult to initially calibrate and continuously improve to get best gap and most constant gain. Con -Individual valves not accessible for trouble shooting loop and actuator/valve problem. Con – The switch, actuator, pneumatic positioner, and I/P performance shift with time and field conditions Con – I/P failure disables 2 valves Con - Replacements in the night may not have the special settings IP 102 AT 102 AIC 102 Process pH Example 4-20ma Coarse Valve Fine Valve 3-15PSI A/O pH Valve Position (% of Span) I/P Output ( PSI ) 15 3 0 100 Fine Valve Coarse Valve A/O PS 102

7. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 7 Split Range – DeltaV Implementation Splitter bock is used to implement split range control. When using traditional valves, split range control may implemented in DeltaV Controller using two(2) current outputs Split range control may be partially or fully assigned to fieldbus devices. AI PID SPLT AO AI PID SPLT AO

8. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 8 Split Range Control in DeltaV

9. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 9 Splitter Block Calculation

10. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 10 IN_ARRAY Parameter The SP range associated with each output is defined by IN_ARRAY. SP range of outputs may be defined to overlap The SP upper end of range must be greater that lower end of range for each output SP range associated with OUT1 SP range associated with OUT2

11. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 11 OUT_ARRAY Parameter When SP is outside defined range, then the value at the end of range is used to determine the output. LOCKVAL determines if OUT1 value is held if SP is greater that the upper end of range defined for OUT1. No restrictions are placed on the output range. OUT1 Range for associated SP range

12. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 12 Splitter Block SP 0 100 0 0 0 0 0 OUT_1 OUT_2 LOCK_VAL “holds ” LOCK_VAL“is zero ” OUT_ARRAY 0 100 0 100 IN_ARRAY 0 100 0 100 OUT_ARRAY 100 0 0 100 IN_ARRAY 0 40 35 100 OUT_ARRAY 0 100 0 100 IN_ARRAY 0 40 35 100 HYSTVAL

13. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 13 AI PID SPLT AO IP 103A IP 103B TT 103 FY 103 TIC 103 COOLER HEATER TT103 TIC103 FY103 IP103A IP103B Heating-Cooing Example

14. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 14 Valve Position (% of Span) TIC103 Output (% of Span) 100 0 0 Cooling (IP103B) Heating (IP103A) Split Range Output (FY103)

15. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 15 AI PID SPLT AO IP 104A IP 104B PT 104 FY 104 PIC 104 PT104 PIC104 FY104 IP104A IP104B Steam Header Example 400# Header 1475# Header Boiler Turbo Generator

16. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 16 Valve Position (% of Span) PIC104 Output (% of Span) 100 0 0 Valve 104A Valve 104B Split Range Output (FY104) - Capacity

17. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 17 Basic Neutralizer Example Neutralizer Discharge Reagent AI PID SPLT AO AT105 AIC105 FY105 IP105A IP105B AIC 105 AT 105 IP 105B FY 105 IP 105A Coarse Valve Fine Valve

18. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 18 pH Nonlinearity and Sensitivity pH Reagent Flow Influent Flow 6 8

19. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 19 Split Range Output – Valve Sequencing Valve Position (% of Span) AIC105 Output (% of Span) 100 0 0 Fine Valve (IP105B) Coarse Valve (IP105A) HYSTVAL

20. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 20 Calculating Splitter SP Ranges A 1% change in controller output to the splitter should have the same impact on control parameter when operating with either valve. When manipulating the same or similar material e.g. steam flow to header, then the range may be calculated based on valve rating. Tests may be performed to determine impact of each valve on the controlled parameter. Example: Steam flow to Header, splitter interfacing directly to PRV’s, no overlap Valve 1 rating = 50kph Valve2 rating = 150kph Desired Splitter Span valve 1 = 100*(50/(150+50)) = 25% SP range for valve 1 = 0-25% SP range for valve 2 = 25-100%

21. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 21 Testing Process to Determine Splitter SP Ranges With the process at steady state and AO’s in Auto mode, determine the magnitude of change in the controlled parameter for a 1 percent change in each valve. Calculate the splitter SP span and range for each output based on the observed response Time Cooling Heating 1% 1.1degF 2.2degF Desired Splitter Span cooling valve = 100*(1.1/(1.1+2.2)) = 33% SP range for cooling valve = 0-33% SP range for heating valve = 33-100% Controlled Temperature Example: Slaker feed temperature controlled using heating and cooling valves

22. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 22 Example – Split Range

23. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 23 Response to SP Change – Split Range Output To Large Valve/Small Valve Small Valve Large Valve PID OUT SP PV

24. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 24 Split Range – Strengths and Weaknesses Pro - Process operation in simplified since two actuators are treated as one control manipulated parameter. Pro – immediate change in target actuator position can be achieved over the entire operating range independent of the size of change in the splitter SP Con – To achieve stable control over the entire operating range, Controller tuning must be established based on the slower responding manipulated parameter. Con- Does not take advantage of difference in resolution of actuator e.g. fine vs. coarse valve. Valve position control may be used in place of split range control when there are differences in dynamic response or resolution in actuators.

25. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 25 Valve Position Control – Traditional Implementation IP 106A AT 106 AIC 106 Process PID control is implemented using the actuator with finer resolution or fastest impact on controlled parameter The actuator with coarse resolution or slower impact on the controlled parameter is adjusted by an I-only controller to maintain the long term output of the PID controller at a given target I-Only controller must be disabled when the PID controller is not in an Automatic mode. pH Example Fine Valve A/O ZC 106 IP 106B Coarse Valve I-Only Controller Mode Target Valve Position Time pH Fine Valve Coarse Valve Target Valve Position

26. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 26 Valve Position Control – DeltaV Implementation I-Only control is achieved by configuration of the PID Block STRUCTURE, GAIN and RESET parameters. It is possible to implement valve position control in the DeltaV controller or for this function to be distributed to fieldbus devices. AI PID AO AI PID AO I-Only AO I-Only Traditional field devices Fieldbus devices

27. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 27 Valve Position Control in DeltaV Actuator with fastest impact or highest resolution is used to maintain the controlled parameter at setpoint. The OUT of the PID used for control is wired to IN on the PID block used for I- Only regulation of slower responding or coarse resolution. PID configured for I- Only control

28. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 28 Configuring PID for I-Only Control The STRUCTURE parameter should be configured for “I action on Error, D action on PV” The GAIN should be set to 1 to allow normal tuning of RESET (even though proportional action is not implemented. RESET should be set significantly slower than that the product of the PID gain and reset time used for control e.g. 5X slower

29. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 29 AI PID AO IP 107A IP 107B FT 107 FIC 107 FT107 FIC107 IP107A Precise Flow Using Big/Small Valve ZC107 I-Only AO IP107B ZC 107

30. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 30 Neutralizer Using Valve Position Control Neutralizer Discharge Reagent AIC 108 AT 108 IP 108A IP 108B Coarse Valve Fine Valve AI PID AO AT108 AIC108 IP108A ZC108 I-Only AO IP108B ZC 108

31. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 31 Example -Boiler BTU Demand Example -Boiler BTU Demand ZC 109 FT 109A IP 109B AI PID AO FT109B FIC109 IP109A ZC109 I-Only AO IP109B FIC 109 FT 109B IP 109A FY 109 Low BTU – Waste Fuel HI BTU Fuel Boiler BTU Demand AI FT109A SUM FY109

32. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 32 Example –Reformer Air Demand Example –Reformer Air Demand ZC 110 AI PID AO FT110 FIC110 IP110 ZC110 I-Only AO SC110 FIC 110 FT 110 SC 110 Air Machine Secondary Reformer Total Air Demand IP 110

33. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 33 Example – Valve Position Control

34. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 34 Response to SP Change - Valve Position Control with Large Valve/Small Valve Fine Valve Coarse Valve SP PV Target position for fine valve is 30%. When the fine valve saturates, then response is limited to be reset of the I-Only control Limited

35. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 35 Valve Position Control – Strengths and Weaknesses Pro – Immediate control response is based on actuator with finest resolution and/or faster impact on controlled parameter. Pro – Actuator with coarse resolution or slower impact on controlled parameter is automatically adjusted to maintain the output of the controller output long term at a specified operating point. Con – The controller output may become limited in response to a large disturbance or setpoint change. For this case, the dynamic response becomes limited by the slower tuning of the I-only controller. Con – Since stick-slip or resolution limits are a % of stroke, the big valve will go into a slow limit cycle The features of split range control and valve position control may be combined to provide immediate response to large changes in demand while retaining the features of valve position control for normal changes.

36. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 36 Combining the Best Features of Split Range and Valve Position Control A composite Block can be created that combines the features of split range and valve position control Support for BKCAL_IN and BKCAL_OUT can be implemented to provide bumpless transfer

37. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 37 Composite Algorithm Filter CAS_IN MODE SP x + x x T Scaling RANGE SPAN NORMAL OUT_1 OUT_2 BKCAL_OUT BKCAL_IN1 BKCAL_IN2 Balance Calculation - - FILTER_TC

38. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 38 Composite Implementation Parameters that must be configure are: FILTER_TC, SPAN (of SP), RANGE (of OUT1), and NORMAL (desired position of The FILTER_TC should be configured similar to the reset time of the I-Only Controller that would be used for valve position control.

39. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 39 Demo – Composite Combining Valve Position and Split Range Control

40. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 40 Example: Response to SP Change SP, PV OUT of PID Fine Valve Coarse Valve For small changes in SP or load disturbance, the response is similar to that provided by valve position control For large changes in SP or load disturbance, the immediate response is similar to split range control Small change Large change

41. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 41 Composite for Valve Position/Split Range Control – Strengths and Weaknesses Pro – All the advantage of valve position control without the dynamic limitations on large setpoint change or load disturbance. Con – If there is a significant delay in the control parameter response to changes in the two valves, then this limits the response that can be achieved using PID for the control. Model Predictive control automatically compensates for process dynamic and may be configured to provide the best features of valve position and split range control and can also address operating constraints.

42. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 42 Example of Different Dynamic Response – Waste Fuel Boiler Control Objective: Maximize use of bark, only use gas when required to maintain Steam SP. Steam response to change in bark is much slower than for a change in gas. Bark alone may not be sufficient to address a sudden increase in steam demand. o o o MPC Steam Flow Constraints BarkGas Hi Cost Fast Fuel Gas Lo Cost Slow Waste Bark Steam Flow Steam SP 20 Desired Response to unmeasured disturbance

43. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 43 Example of Different Dynamic Response – Bleach Plant Control Objective: Maintain KAPPA target though the addition of Chemical 1 and Chemical 2. Minimize the use of Chemical 2. Desired operation is for Chemical 2 to be used for short term correction in KAPPA to replace Chemical 2 with Chemical 1 in the longer term. AT MPC 20 minutes 60 minutes Lo Cost Slow Chemical 1 Hi Cost Fast Chemical 2 Lo Cost Slow Chemical 1 KAPPA KAPPA SP Desired response to unmeasured disturbance

44. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 44 Utilizing MPC for Control Both Predict and PredictPro can be configured and tuned for maintaining the critical controlled variable (CV), such as steam or composition, at its target and maximizing the low cost slow MV set point as an optimization variable.

45. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 45 MPC Guidelines for This Application The best load and set point response for the critical CV is obtained with a short term tradeoff in efficiency by reducing the penalty on error (PE) for the optimization variable. When riding the low cost MV maximum set point, this PE lets both the slow and fast MV to move to improve the load and set point response of the critical CV. When riding the high cost MV low set point limit, it does not slow down the response of the other MV to upsets and set point changes to the critical CV. Only the response of the optimization variable is slowed down. This is consistent with the general theme that disturbance rejection must be fast while optimization can be slow. For coarse and fine valve control, the small valve is a low cost (low stick-slip) fast MV and the big valve is a high cost (high stick-slip) slow MV. The optimization variable is fine valve set point with a strategy of keeping it within limits (mid range throttle position). The PE for the optimization variable is reduced rather then the PM increased for the coarse valve so that both are available for load disturbance rejection. For the following examples, the slow MV has a lower cost, so its optimization strategy is maximization.

46. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 46 DeltaV Predict Configuration MPC block should be configured for two control and two manipulate parameters. The controlled measurement is wired to CNTRL1

47. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 47 DeltaV Predict Configuration (Cont) CNTRL2 is configured as an optimized parameter - Maximize (not wired)

48. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 48 Control Generation - DeltaV Predict In Predict, the Penalty on Error (PE) is significantly decreased on the “Controller Generation” screen as shown in this example. The PE was lowered form 1.0 to 0.1 to make the optimization of the slow MV much less important than the control of the critical PV at its target

49. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 49 MPC Response to Disturbance and Set Point Changes In this example, low cost MV initially is riding its maximum set point, which leaves the fast cost MV free to respond Later, the maximum for the low cost MV has been increased to the point where it is no longer achievable, which drives the high cost MV to its low set point limit. Riding Max SP on Lo Cost MV Riding Min SP on Hi Cost MV Critical CV Lo Cost Slow MV Hi Cost Fast MV Load Upsets Set Point Changes Load Upsets Set Point Changes Low Cost MV Maximum SP Increased Low Cost MV Maximum SP Decreased Critical CV

50. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 50 When configuring the MPC-Pro block, selects “Target” in the optimize column for the critical PV, and “Maximize” for the low cost MV. Browse to specify the RCAS_IN of the low cost slow MV (FC1- 2) to specify the measurement associated with the low cost slow MV.. DeltaV PredictPro Configuration

51. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 51 Control Parameter - MPC-Pro Block

52. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 52 Control Generation - DeltaV PredictPro The Penalty on Error (PE) is significantly decreased on the “Controller Generation” screen In this example, the PE was lowered form 1.0 to 0.1 to make the optimization of the slow MV much less important than the control of the critical PV at its target.

53. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 53 MPC-Pro Response to Disturbance and Set Point Changes In this example, the low cost MV initially is riding its maximum set point, which leaves the fast cost MV free to respond Later, the maximum for the low cost MV has been increased so it is no longer achievable, which drives the high cost MV to its low set point limit. Riding Max SP on Lo Cost MV Riding Min SP on Hi Cost MV Critical CV Lo Cost Slow MV Hi Cost Fast MV Load Upsets Set Point Changes Load Upsets Set Point Changes Low Cost MV Maximum SP Increased Low Cost MV Maximum SP Decreased Critical CV

54. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 54 SummarySummary Split range control allows fully dynamic response to major setpoint of load disturbance changes. Valve position control may be used to takes advantage of any difference in control response or resolution in the manipulated parameters. A composite block has been demonstrated that combines the best features of split range and valve position control. DeltaV Predict and PredictPro and the associated MPC and MPC-Pro blocks may be effective used to address control using two manipulated parameters. Improved performance over PID is expected if the process has significant dead time or the manipulated variables have significantly different dynamics. Also, using this approach allow operating constraints and feedforward to be easily incorporated into the control strategy. Please direct questions or comments on this presentation to Terry Blevins (Terry.Blevins@EmersonProcess.com) or Greg McMillan (Greg.McMillan@EmersonProcess.com ).Terry.Blevins@EmersonProcess.comGreg.McMillan@EmersonProcess.com

55. [File Name or Event] Emerson Confidential 27-Jun-01, Slide 55 Where To Get More Information “Effectively Addressing Control Applications”, Terry Blevins, Emerson Exchange, 2004. “Addressing Multi-variable Process Control Applications”, Dirk Thiele, Willy Wojsznis, Pete Sharpe, Emerson Exchange, 2004 “Advanced Control Unleashed, Plant Performance Management for Optimum Benefit”. Terry Blevins, Gregory McMillan, Willy Wojsznis, Mike Brown, ISA Publication, ISBN 1-55617-815-8, 2003.