Emerson's James Beall presents on some of the advanced capabilities in DeltaV PID blocks

1. Interesting and Useful Features of the DeltaV PID, Ratio and Bias/Gain Control Blocks James Beall Principal Process Control Consultant Emerson Process Management

3. Introduction Provide additional information on useful features of the DeltaV PID, RTO (ratio), and BG (bias-gain) function blocks Discuss some common parameters of these function blocks where the default values can cause poor control. Provide examples of the use of these features. Note – “BOL” is DeltaV Books on Line (the embedded, electronic DeltaV documentation)

4. Topics PID Form PID Structure Integral Dead Band SP Filter/Rate of Change SP Limits Cascade Features Gain Scheduler Non-linear Gain Feed Forward Output Characterization Anti-Reset Windup Limits Adaptive Control Simulated Loops RTO (Ratio Block) BG (Bias Gain)

5. PID “Form” Three Common PID Forms Parallel Form Standard, aka ISA Form, Series, aka Classical Form. DeltaV has Choices Standard Series

6. PID “Form” - PID Function Block DeltaV default is “Standard” Note that if you choose “Nonlinear Gain” in FRSIPID_OPTS then the FORM becomes “Standard” – More on this later

7. Series and Standard Forms Series Standard Output Error + PV + PROCESS SP + D + - P I

8. PID “Form” Choice Prior system experience and/or migration Personal Preference - Standard (RS3, etc) or Series (Provox, etc.) Series is identical to Standard form if Derivative action is NOT used Can impact conversion of tuning constants from previous control system

9. 0 0 TRClassical + TDClassical TRSeries + TDSeries + TDSeries KCStandard= KCSeries * TRClassical* TDClassical TRSeries* TDSeries TRClassical TRSeries ( TRClassical+ TDClassical ) ( TRSeries+ TDSeries ) TRSeries TRStandard = + TDClassical TDStandard = 0 Convert Series (Classical) to Standard Series is identical to Standard form if Derivative action is NOT used TR should be time/rep; units = seconds TD should be in seconds Be sure to convert to your tuning constant units after form conversion

10. PID Function Block “Structure” Parameter Used most. Default

11. PID Function Block “Structure” Parameter SP Change on Reactor feed tank level: PI on error, D on PV Controller Output – Flow to reactor SP

12. PID Function Block “Structure” Parameter SP Change on Reactor feed tank level: I on error, PD on PV Controller Output – Flow to reactor SP

13. PID Structure – 2 Degrees of Freedom BETA - determines the degree of proportional action that will be applied to SP changes. Range = 0-1 BETA=0 means no proportional action is applied to SP change. BETA=1 means full proportional action is applied to SP change. GAMMA - determines the degree of derivative action that will be applied to SP changes. Range = 0-1 GAMMA=0 means no derivative action applied to SP change. GAMMA=1 means full derivative action is applied to SP change.

14. PID Structure – 2 Degrees of Freedom

15. Integral Dead Band IDEADBAND - When the error gets within IDEADBAND, the integral action stops. The proportional and derivative action continue. Same Engineering Units as PV Scale May be used to reduce the movement of the controller output when the error is less than the “IDEADBAND”. For example on a level controller that feeds the downstream unit.

16. Set Point - Filter/Rate of Change SP_FTIME - Time constant (seconds) of the first order SP filter. The Set Point Filter applies in AUTO, CAS and *RCAS (*not specified in BOL). SP_RATE_DN - Ramp rate at which downward setpoint changes are acted on in Auto mode, in PV units per second. If the ramp rate is set to 0.0, then the setpoint is used immediately. For control blocks, rate limiting applies only in Auto (not CAS or RCAS). SP_RATE_UP - Ramp rate at which upward setpoint changes are acted on in Auto mode, in PV units per second. If the ramp rate is set to 0.0, then the setpoint is used immediately. For control blocks, rate limiting applies only in Auto (not CAS or RCAS).

17. Set Point Limits SP_HI_LIM- The highest SP value (EU’s) allowed. SP_LO_LIM - The lowest SP value (EU’s) allowed. CONTROL_OPTS – allow you to specify if SP Limits to be obeyed in “CAS and RCAS” Can use “Output Limits” of Master loop in cascade pair to limit SP to Slave loop ONLY in CAS and RCAS

18. Cascade Features FC 3-5 LC 3-2 Column Tray 6 RSP LT 3-2 FT 3-5 Bottoms Master Loop aka Primary Loop Slave Loop aka Secondary Loop

19. Cascade Features Mode tracking and bumpless transfers are automatically provided through the BKCAL feature Limited conditions in the Slave loop are taken care of through the BKCAL feature Prevent reset windup with external reset by selecting “Dynamic Reset Limit” in FRSIPID_OPTS on the Master loop “Use PV for BKCAL_OUT” in CONTROL_OPTS should be selected on Slave loop for use with Dynamic Reset Limit in Master

20. Enabling PID External Reset Utilized most often in the primary loop of a cascade Compensates for “unexpected” slow secondary loop response or secondary PV limited before OUT limited

21. Gain Scheduler Proves up to 3 regions of different PID tuning parameters based on a selected state variable (output, PV, error, or “other”) Provides a smooth transition between regions Create PID module using Module Templates: Analog Control/PID_GAINSCHED OR, add function to existing PID module Expose Gain, Reset and Rate parameters on PID function block Copy all function blocks from template except the PID FB and link as needed.

22. Gain Scheduler Module Templates: Analog Control/PID_GAINSCHED

23. Gain Scheduler

24. Gain Scheduler – Detail Display

25. FRSIPID_OPTS: Non-linear Gain Modifies the proportional Gain as a function of the error (PV-SP) Can be used to make the tuning more aggressive as the PV is farther from the set point Can create the “error squared” PID function Recall PID Form is set to Standard regardless of config.

26. FRSIPID_OPTS: Non-linear Gain The PID “Gain” is multiplied by “KNL” which has a value between 0 and 1 as a function of the error (SP-PV). = PV-SP

27. FRSIPID_OPTS: Non-linear Gain

28. FRSIPID_OPTS: Non-linear Gain The PID “Gain” is multiplied by “KNL” which has a value between 0 and 1 as a function of the error I typically set NL_HYST = 0 unless it is a for a “valve position controller. Be aware that using this feature on an integrating process, like levels, can cause oscillations at the reduced gain. For these applications, the reset time should be based on “Gain*MINMOD” which will result in a larger reset time to prevent oscillations.

29. FRSIPID_OPTS: Non-linear Gain To provide non-linear “tuning” on integrating processes (like level), consider using the Gain Scheduler (so you can change gain and reset) CAUTION!Up through DeltaV version 11.3, if the Non-linear Gain option is enabled, the “P” action will always be applied to the Error, not PV, regardless of the PID Structure chosen (including 2 degrees of freedom). So if you move the SP such that the error is outside of NL_GAP+NL_HYST, there will be a “proportional kick” of the output

30. FRSIPID_OPTS: Non-linear Gain “Error2” Modified Gain Error “Error squared” PID function – error*abs(error) Proportional = error*abs(error)*gain = error* (abs(error)*gain) Proportional = error*(Modified Gain) Modified Gain = abs(error)*Gain Non-linear Gain Settings for E2 Activate NL Gain NL_MINMOD = 0 NL_GAP = 0 NL_TBAND = 100% of PV Span (EU’s) NL_HYST = 0

31. Feed Forward From BOL:

32. Feed Forward There are several way to interpret the information in BOL but here is the way it works: The FF_VAL is converted to % of the FF_SCALE Normally FF_SCALE is the same as the source of the FF_VAL but it doesn’t have to be! The FF_VAL can exceed the FF_SCALE and the %FF_VAL will be calculated. The “%FF_VAL” is multiplied by the FF_GAIN and added to the %OUT calculated by the PID functions The %OUT is converted to OUT in EU’s using the OUT_SCALE. Note that different choices of FF_SCALE and FF_GAIN could have the same exact feed forward action.

33. Feed Forward MODE BCKCAL_OUT SP OUT_SCALE OUT_HI_LIM OUT_LO_LIM C CAS_IN GAIN, RESET, RATE BYPASS A LIMIT OUTPUT PID CALC + IN OUT 100 % 100 % 100 % 100 % BCKCAL_IN PV_SCALE FF_GAIN FF_VALUE FF_SCALE TRK_IN_D 0 % 0 % 0 % 0 % TRK_VAL TRK_SCALE Converted to % based on FF_SCALE but limited to 0-100% Note: For simplicity, not all modes are shown.

36. Anti-Reset Windup Limits Improves process recovery from saturated conditions On recovery from a saturated condition, when the ARW_HI_LIM and ARW_LO_LIM are set inside the OUT limits, the reset time will automatically be decreased (faster) by 16X until the OUT parameter comes back within the the ARW limits or the control parameter reaches setpoint.

37. Setting ARW limits PV SP ARW_LO_LIM OUT OUT_LO_LIM

42. InSight captures response data and calculates a dynamic process model for each Trigger Event. Models are stored in a database for use in loop diagnostics and adaptive tuning.

44. Adaptive Control Adaptive control adjusts tuning to improve control performance

45. Simulated Loop in DeltaV

46. Simulated Loop in DeltaV This is the training simulator. Assign and download this module to a controller. (Note the Fuzzy Logic Controller and MPC simulations!) This “graphic” is really a special “detail” display for this module

48. Note the PV_FTIME filter is applied to IN (manipulated flow)

50. Ratio Block - Options CONTROL_OPTS “Act on IR” (act on initialization request) If checked, when Ratio Block transitions from non-automatic to automatic, the current Ratio will remain as the SP. If not checked, when Ratio Block transitions from non-automatic to automatic, the Ratio Working SP will start at the current value and ramp to the last automatic SP in the “Balance Time” “Use BKCAL_OUT With IN_1” – check if the OUTPUT of a Controller goes to IN1 AND you want it to operate in Cascade with the Ratio Block (see case 2) FRSRB_OPTS “Treat IN_1 as wild” –if true IN_1 is treated as a non-cascade input and if Use_Bkcal_out_With_IN_1 is true Bkcal_out sub-status will be set to keep cascade closed. Be careful with this one!

51. Ratio Control – Case 2 Check CONTROL_OPTS “Use BKCAL_OUT With IN_1” CONTROL_OPTS “Act on IR” “Don’t Check” if you want the Ratio SP to return to the operator SP in the Balance time after Ratio Block returns to Auto “Check” if you if you want the Ratio SP track the actual ratio when the Ratio Block returns to Auto Do not use FRSIRB_OPTS “Treat IN_1 as wild” Test your application with simulation! IN1 Ratio SP From Operator X TIC Ratio Block OUT SP to Manipulated FIC

52. Ratio Control – Case 3 Don’t Check CONTROL_OPTS “Use BKCAL_OUT With IN_1” CONTROL_OPTS “Act on IR” “Don’t Check” if you want the Ratio SP to return to the operator SP in the Balance time after Ratio Block returns to Auto “Check” if you if you want the Ratio SP equal the actual ratio when the Ratio Block returns to Auto Do not use FRSIRB_OPTS “Treat IN_1 as wild” Test your application with simulation! Main Flow Ratio From Controller IN1 X TIC CAS or RCAS OUT SP to Manipulated FIC

53. Bias-Gain Function Block

54. Bias-Gain Function Block CONTROL_OPTS “Act on IR” (act on initialization request) If checked, when Bias/Gain Block transitions from non-automatic to automatic, the current Bias will remain as the SP. If not checked, when Bias/Gain transitions from non-automatic to automatic, an internal register is used to move the from the actual Bias from the current value the retained Bias SP in the “Balance Time” “Use BKCAL_OUT With IN_1” – check if the OUTPUT of a Controller goes to IN1 AND you want it to operate in Cascade with the Ratio Block (see case 2) FRSRB_OPTS “Treat IN_1 as wild” –if true IN_1 is treated as a non-cascade input and if Use_Bkcal_out_With_IN_1 is true Bkcal_out sub-status will be set to keep cascade closed. Be careful with this one!

55. Bias-Gain Function Block Check ““Use BKCAL_OUT With IN_1” Check “Act on IR” if you want the BIAS’s to stay at the value they are when the B/G transitions to an automatic mode. Don’t check “Act on IR” if you want the BIAS to return to the previous value when the B/G transitions to an automatic mode. Test your application! Example Boiler 1 PIC B/G B/G B/G Boiler 2 Boiler 3

56. Bias-Gain Function Block Good example in BOL Check ““Use BKCAL_OUT With IN_1” Don’t check “Act on IR” Test your application!

57. Bias-Gain Function Block- External FFWD Feedforward continues even if PID is in Man mode PID correction is limited by its output limits

58. Business Results Achieved These features can be used to significantly improved the performance of your control schemes The default ARW limits of 0-100 is a common problems for the master loop in a cascade arrangement. Correcting the ARW limits improves control. These features can be used to customize the response of the PID controller to meet process goals ($$$!) “Difficult” process dynamics can be handled Bottom line – Better control performance = $$$$

59. Summary DeltaV has many useful control features Watch out for default parameters (ARW limits) that don’t match your application “One of the highest ROI in the control field!”

60. Where To Get More Information EGUE Workshops (TBD) EGUE Exhibit Area – Industry Solutions Group Emerson Process Management Education Services DeltaV™ Advanced ControlCourse: # 7201 - CEUs: 3.2 DeltaV™ Operate Implementation I Course: # 7009 - CEUs: 3.2 EnTech - Process Dynamics, Control and Tuning Course: # 9030 CEUs: 2.8 Emerson Process Management, Industry Solutions Group http://www2.emersonprocess.com/en-US/brands/processautomation/consultingservices/ProcessImprovementOptimization/Pages/ProcessImprovementOptimization.aspx James.Beall@Emerson.com, 903-235-7935

61. About the Presenter James Beall is a Principal Process Control Consultant with Emerson Process Management. He has over 28 years experience in process control, including 9 years with Emerson and 19 years with Eastman Chemical Company. His areas of expertise include process instrumentation, control strategy analysis and design, control optimization, DCS configuration and maintenance, control valve performance testing and Advanced Process Control. James is a contributing author to Process/Industrial Instruments and Control Handbook (5th Edition, G.K. McMillan, McGraw-Hill, New York, 1999. He is a member of AIChE and is currently the chairman of ISA Subcommittee 75.25, Control Valve Performance Testing.