SELF-DIAGNOSTIC PROCESS CONTROL LOOP FOR A PROCESS PLANT

• US 20070150079A1
• Filed: 12/01/2006
• Published: 06/28/2007
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Wojsznis, Peter, Blevins, Terrence, Wojsznis, Wilhelm, McMillan, Gregory
• Granted Patent: US 8,509,926 B2
• Time in Patent Office: Days
• US Class Current: 700/41
• CPC Class Codes: G05B 23/0251 Abstraction hierarchy, e.g. "complex systems", i.e. system is divided in subsystems, subsystems are monitored and results are combined to decide on status of whole system

Abstract

A method of diagnosing an adaptive process control loop includes measuring process control loop signal data, generating a plurality of process control loop parameters from the process loop signal data and evaluating a condition of the adaptive process control loop from one or more of the plurality of process control loop parameters. The process control loop data is generated as a result of a normal operation of one or more process control devices within the adaptive process control loop when the adaptive process control loop is connected on-line within a process control environment. A self-diagnostic process control loop includes a diagnostic tool adapted to receive a diagnostic index pertaining to a process control loop parameter for each component of the process control loop and for the complete process control loop. Each diagnostic index is generated from signal data by a corresponding index computation tool. The diagnostic tool is further adapted to evaluate a condition of the process control loop from one or more of the diagnostic indices.

Claims

1. A method of diagnosing an adaptive process control loop comprising:

measuring process control loop signal data generated as a result of a normal operation of one or more process control devices within the adaptive process control loop when the adaptive process control loop is connected on-line within a process control environment;

generating a plurality of process control loop parameters from the process loop signal data; and

evaluating a condition of the adaptive process control loop from one or more of the plurality of process control loop parameters.

2. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises independently generating a process control loop parameter for each component of the adaptive process control loop.

3. The method of claim 2, wherein the components of the adaptive process control loop comprises one or more of the group consisting of:

a process control loop performance component, a process control loop device component, an adaptive model quality component and a process control loop stability component.

4. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises:

generating a parameter representing a status of each of the one or more process control devices within the adaptive process control loop; and

generating a parameter representing a status of the complete adaptive process control loop.

5. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating one or more use indices indicating the performance of the adaptive process control loop.

6. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating one or more of the group consisting of:

a variability index, a standard deviation and a capability standard deviation.

7. The method of claim 6, wherein generating the variability index comprises generating one or more of the group consisting of:

a variability index indicating a process control loop tuning condition and a variability index indicating a process control loop device condition.

8. The method of claim 6, wherein generating the standard deviation comprises generating one or more of the group consisting of:

a total process variable standard deviation indicating a process control loop tuning condition and a total process variable standard deviation indicating a process control loop device condition.

9. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating one or more use indices indicating a diagnostic of a process control device within the adaptive process control loop.

10. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating one or more of the group consisting of:

a resolution of a process control loop device within the adaptive process control loop, a dead band of a process control loop device within the adaptive process control loop and a hysteresis of a process control loop device within the adaptive process control loop.

11. The method of claim 10, wherein generating a resolution of a process control loop device in the adaptive process control loop comprises generating a resolution indicating a measure of a minimum process control signal required to cause a response in the process control loop device.

12. The method of claim 10, wherein generating a resolution of a process control loop device in the adaptive process control loop comprises calculating the difference between the hysteresis of the process control loop device and the dead band of the process control loop device.

13. The method of claim 10, wherein generating a dead band of a process control loop device within the adaptive process control loop comprises generating a dead band indicating a measure of a range an input can vary without an observable response in the process control loop device in response to a process control signal.

14. The method of claim 10, wherein generating a dead band of a process control loop device within the adaptive process control loop comprises calculating the difference between the hysteresis of the process control loop device and the resolution of the process control loop device.

15. The method of claim 10, wherein generating a hysteresis of a process control loop device within the adaptive process control loop comprises measuring displacement of the process control loop device based on an input to the process control loop device and an output of the process control loop device.

16. The method of claim 10, wherein generating a hysteresis of a process control loop device within the adaptive process control loop comprises calculating a sum of the dead band of the process control loop device and the resolution of the process control loop device.

17. The method of claim 10, wherein generating a hysteresis of a process control loop device within the adaptive process control loop comprises calculating an average of maximum differences between a process control input signal to the process control loop device and a response signal indicating a state of the process control loop device in response to the process control input signal.

18. The method of claim 10, wherein generating a plurality of process control loop parameters from the process loop signal data comprises comprises:

determining an oscillation amplitude on a process control output signal; and

determining an oscillation amplitude on a process control input signal.

19. The method of claim 18, wherein generating a hysteresis of a process control loop device within the adaptive process control loop comprises calculating the hysteresis of a process control devices as the product of a constant value and the oscillation amplitude on the process control output signal.

20. The method of claim 18, wherein generating a resolution of a process control loop device within the adaptive process control loop comprises calculating the resolution of a process control loop device as a ratio of the oscillation amplitude on the process control input signal to a process gain, wherein the ratio is scaled a constant value.

21. The method of claim 18, wherein generating a dead band of a process control loop device within the adaptive process control loop comprises calculating the difference between the hysteresis of the process control loop device and the resolution of the process control loop device.

22. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating an index indicating a quality of a model of the adaptive process control loop defined during an adaptation cycle of the adaptive process control loop.

23. The method of claim 22, wherein generating an index indicating a quality of an adapted model of the adaptive process control loop comprises comparing a final model output with an actual process variable of the adaptive process control loop.

24. The method of claim 22, wherein generating an index indicating a quality of an adapted model of the adaptive process control loop comprises calculating an error ratio of the best model of the adaptive process control loop to a next best model of the adaptive process control loop.

25. The method of claim 22, wherein generating an index indicating a quality of an adapted model of the adaptive process control loop comprises calculating a squared error of the adapted model of the adaptive process control loop indicating the error from a previous adaptation cycle of the adaptive process control loop

26. The method of claim 1, wherein generating a plurality of process control loop parameters from the process loop signal data comprises generating an index indicating a stability of the adaptive process control loop.

27. The method of claim 1, further comprising performing a function based on the evaluated condition of the adaptive process control loop.

28. The method of claim 27, wherein performing a function based on the evaluated condition of the process control loop comprises setting an alarm.

29. The method of claim 28, wherein setting an alarm comprises setting an alarm for at least one of the group consisting of:

an oscillatory adaptive process control loop, a high process control loop device hysteresis and a high process control loop device resolution value.

30. The method of claim 27, wherein performing a function based on the evaluated condition of the process control loop comprises performing a corrective action within the adaptive process control loop.

31. The method of claim 30, wherein performing a corrective action comprises automatically adjusting a process variable filter.

32. A self-diagnostic process control loop within a process control environment comprising:

a plurality of process control loop devices;

a memory adapted to store signal data from the process control loop, wherein the signal data is generated as a result of a normal operation of the plurality of process control devices within the process control loop when the process control loop is connected on-line within a process control environment; and

a diagnostic tool adapted to receive a diagnostic index pertaining to a process control loop parameter for each component of the process control loop and for the complete process control loop, wherein each diagnostic index is generated from the signal data by a corresponding index computation tool, the diagnostic tool further adapted to evaluate a condition of the process control loop from one or more of the diagnostic indices.

33. The method of claim 32, wherein the components of the process control loop comprises one or more of the group consisting of:

a process control loop performance component, a process control loop device component, an adaptive model quality component and a process control loop stability component.

34. The self-diagnostic process control loop of claim 32, wherein the diagnostic tool is adapted to receive a diagnostic index pertaining to a performance of the process control loop.

35. The self-diagnostic process control loop of claim 34, wherein the diagnostic index pertaining to a performance of the process control loop comprises a variability index indicating a process control loop tuning condition.

36. The self-diagnostic process control loop of claim 34, wherein the diagnostic index pertaining to a performance of the process control loop comprises a variability index indicting a process control loop device condition.

37. The self-diagnostic process control loop of claim 34, wherein the diagnostic index pertaining to a performance of the process control loop comprises a total process control loop standard deviation indicating a process control loop tuning condition.

38. The self-diagnostic process control loop of claim 34, wherein the diagnostic index pertaining to a performance of the process control loop comprises a total process control loop standard deviation indicating a process control loop device condition.

39. The self-diagnostic process control loop of claim 34, wherein the diagnostic index pertaining to a performance of the process control loop comprises a capability standard deviation.

40. The self-diagnostic process control loop of claim 32, wherein the diagnostic tool is adapted to receive a diagnostic index pertaining to a diagnostic of a process control device within the process control loop.

41. The self-diagnostic process control loop of claim 40, wherein the diagnostic index pertaining to a diagnostic of a process control device within the process control loop comprises a resolution of a process control loop device within the process control loop indicating a minimum process control signal required to cause a response in the process control loop device.

42. The self-diagnostic process control loop of claim 40, wherein the diagnostic index pertaining to a diagnostic of a process control device within the process control loop comprises a dead band of a process control loop device within the process control loop indicating a measure of a range an input can vary without an observable response in the process control loop device in response to a process control signal.

43. The self-diagnostic process control loop of claim 40, wherein the diagnostic index pertaining to a diagnostic of a process control device within the process control loop comprises a hysteresis of a process control loop device within the process control loop indicating a displacement of a process control loop device based on an input to the process control loop device and an output of the process control loop device.

44. The self-diagnostic process control loop of claim 40, wherein the diagnostic tool is adapted to calculate the a diagnostic index pertaining to a diagnostic of a process control device within the process control loop based on a back calculation signal from a process control loop device.

45. The self-diagnostic process control loop of claim 32, wherein the diagnostic tool is adapted to receive a diagnostic index pertaining to a quality of an adapted model of the process control loop defined during an adaptation cycle of the process control loop.

46. The self-diagnostic process control loop of claim 45, wherein the diagnostic tool is further adapted utilize the diagnostic index as a diagnostic indicator of the process control loop.

47. The self-diagnostic process control loop of claim 32, wherein the diagnostic tool is adapted to receive a diagnostic index pertaining to a stability of the process control loop.

48. The self-diagnostic process control loop of claim 32, wherein the diagnostic routine is further adapted to set an alarm based on the evaluated condition of the process control loop.

49. The self-diagnostic process control loop of claim 48, wherein the diagnostic routine is adapted to set the alarm for at least one of the group consisting of:

an oscillatory process control loop, a high process control loop device hysteresis and a high process control loop device resolution value.

50. The self-diagnostic process control loop of claim 32, wherein the diagnostic routine is further adapted to initiate a corrective action within the process control loop based on the evaluated condition of the process control loop.

51. The self-diagnostic process control loop of claim 50, wherein the diagnostic routine is adapted to initiate a corrective action to automatically adjust an adapted model of the process control loop.

52. The self-diagnostic process control loop of claim 50, wherein the diagnostic routine is adapted to initiate a corrective action to automatically adjust a process variable filter.

53. The self-diagnostic process control loop of claim 32, wherein the plurality of process control loop devices comprise a valve and a process controller.

54. A method of diagnosing a process control loop comprising a plurality of process control loop devices, wherein the process control loop is controlled based on adaptive process loop parameters calculated from an adapted model of the process control loop for each parameter of the process control loop, the method comprising:

evaluating a performance of the process control loop;

evaluating a condition of a process control loop device within the process control loop;

evaluating a quality of the adapted model of the process control loop;

evaluating a stability of the process control loop;

generating a diagnostic index from each of the evaluations; and

evaluating a condition of the process control loop from one or more of the diagnostic indices.

55. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating a variability index from evaluating a performance of the process control loop.

56. The method of claim 55, wherein generating, a variability index from evaluating a performance of the process control loop comprises calculating the variability index as:

57. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating a minimum standard deviation from evaluating a performance of the process control loop.

58. The method of claim 57, wherein generating a minimum standard deviation from evaluating a performance of the process control loop comprises calculating the minimum standard deviation as:

59. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating a dead band of a process control loop device from evaluating a condition of a process control loop device within the process control loop.

60. The method of claim 59, wherein generating a dead band of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating a dead band of a process control loop device as:

b=avg(maxΔ

_i)

if

|Δ

OUT(t−

1)*Δ

BKCAL_IN(t)|>

0

wherein

Δ

_i(t)=|OUT(t−

i)−

BKCAL_IN(t)|,
Δ

OUT(t−

1)=OUT(t−

i)−

OUT(t−

i−

1),
Δ

BKCAL_IN(t)=BKCAL_IN(t)−

BKCAL_IN(t−

1),

OUT(t)=a process control signal to the process control loop device,

BKCAL_IN(t)=a back calculation signal from a process control loop device,

i=a back calculation signal delay from a process control loop device.

61. The method of claim 59, wherein generating a dead band of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating a dead band of a process control loop device as:

62. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating a hysteresis of a process control loop device from evaluating a condition of a process control loop device within the process control loop.

63. The method of claim 62, wherein generating, a hysteresis of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating a hysteresis of a process control loop device as:

h=b+δ

avg(maxΔ

_i)

wherein;

b=a dead band of the process control loop device,

δ

=a resolution of the process control loop device,

i=back calculation signal delay in process control loop module scans of the adaptive process control loop,

max Δ

_i=a maximum value of a back calculation signal.

64. The method of claim 62, wherein generating a hysteresis of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating a hysteresis of a process control loop device as:

h=2Ampl(OUT)

wherein Ampl(OUT)=the oscillation amplitude on the process control output signal.

65. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating a resolution of a process control loop device from evaluating a condition of a process control loop device within the process control loop.

66. The method of claim 65, wherein generating a resolution of a process control loop device from evaluating, a condition of a process control loop device within the process control loop comprises calculating the resolution of a process control loop device as:

δ

=h−

b

wherein;

b=a dead band of the process control loop device,

h=a hysteresis of the process control loop device.

67. The method of claim 65, wherein generating a resolution of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating the resolution of a process control loop device as:

68. The method of claim 65, wherein generating a resolution of a process control loop device from evaluating a condition of a process control loop device within the process control loop comprises calculating a resolution of a process control loop device from an estimation of an oscillation period of the process control loop, wherein the estimation is expressed as:

69. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating an adapted model quality index from evaluating a quality of the adapted model of the process control loop.

70. The method of claim 69, wherein generating adapted model quality index from evaluating a quality of the adapted model of the process control loop comprises calculating a squared error of the adapted model as:

71. The method of claim 54, wherein generating a diagnostic index from each of the evaluations comprises generating an oscillation index from evaluating a stability of the process control loop.

72. The method of claim 54, further comprising setting an alarm based on evaluating a condition of the process control loop from one or more of the diagnostic indices.

73. The method of claim 54, further comprising automatically adjusting an adapted model of the adaptive process control loop based on evaluating a condition of the process control loop from one or more of the diagnostic indices.

74. The method of claim 54, further comprising automatically adjusting a process variable filter based on evaluating a condition of the process control loop from one or more of the diagnostic indices.

75. The method of claim 74, wherein automatically adjusting a process variable filter comprises calculating a process variable filter time constant as:

76. The method of claim 75, wherein automatically adjusting a process variable filter further comprises applying effective process variable filter values as:

τ

_f=0.8τ

_fold+0.2τ

_fnew