Method and system for detecting abnormal operation of a level regulatory control loop

• US 8,145,358 B2
• Filed: 07/25/2006
• Issued: 03/27/2012
• Est. Priority Date: 07/25/2006
• Status: Active Grant

• Current Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Original Assignee: Fisher-Rosemount Systems Incorporated (Emerson Electric Company)
• Inventors: Miller, John P.
• Primary Examiner(s): Chaki, Kakali
• Assistant Examiner(s): LAUGHLIN, NATHAN L
• Application Number:
  US11/492,577
• Publication Number:
  US 20080125879A1
• Time in Patent Office: 2,072 Days
• Field of Search: 700/21, 700/29, 700/30, 700/32, 700/80, 700/282, 700/79, 700/281, 702/51
• US Class Current: 700/281
• CPC Class Codes: G05B 23/0254 based on a quantitative model, e.g. mathematical relationships between inputs and outputs; functions: observer, Kalman filter, residual calculation, Neural Networks

Abstract

A system facilitates detecting an abnormal operation associated with a level regulatory control loop in a process plant. A model for modeling at least a portion of the level regulatory control loop may be utilized with respect to first and second signals associated with regulatory control of a level of material in a tank. The model may include a first regression model in a first range corresponding to a first operating region of the level regulatory control loop. The model may be capable of being subsequently configured to include at least a second regression model in at least a second respective range corresponding to at least a second respective operating region different than the first operating region. The model may generate a prediction of the second signal as a function of first signal. It may be determined whether the second signal significantly deviates from the prediction of the second signal generated by the model. If there is a significant deviation, this may indicate an abnormal operation associated with the level regulatory control loop.

Claims

1. A method for detecting abnormal operation associated with a level regulatory control loop, comprising:

generating a first signal associated with regulatory control of a level of material in a tank;

generating a second signal associated with regulatory control of the level of material in the tank;

using a first model to generate a prediction of the second signal as a function of the first signal, the first model including a first regression model in a first range corresponding to a first operating region of the level regulatory control loop and corresponding to a first range of the first signal, the first model capable of being subsequently configured to include at least a second regression model in at least a second respective range corresponding to at least a second respective operating region and corresponding to a second range of the first signal, wherein the first and second ranges of the first signal do not overlap;

determining whether the second signal deviates from the prediction of the second signal to an extent that meets a predetermined condition; and

generating a first indicator of an abnormal operation associated with the level regulatory control loop based on whether the second signal deviates from the prediction of the second signal to the extent that meets the predetermined condition.

2. A method according to claim 1, wherein generating the first signal comprises generating a mean of a first process variable associated with regulatory control of the level of material in the tank.

3. A method according to claim 2, wherein generating the second signal comprises generating a mean of a second process variable associated with regulatory control of the level of material in the tank.

4. A method according to claim 3, wherein the first process variable is a signal indicative of the level of material in the tank;

wherein the second process variable is a control demand signal;

wherein generating the first indicator comprises;

generating the first indicator to indicate that the mean of the control demand signal is low if the mean of the control demand signal is lower than the prediction generated by the first model to the extent that meets the predetermined condition; and

generating the first indicator to indicate that the mean of the control demand signal is high if the mean of the control demand signal is higher than the prediction generated by the first model to the extent that meets the predetermined condition.

5. A method according to claim 3, wherein the first process variable is a signal indicative of the level of material in the tank;

wherein the second process variable is a difference between a valve position signal and a control demand signal;

wherein generating the first indicator comprises generating the first indicator to indicate a valve problem if the mean of the difference between the valve position signal and the control demand signal deviates from the prediction generated by the first model to the extent that meets the predetermined condition.

6. A method according to claim 1, further comprising:

generating a third signal associated with regulatory control of the level of material in a tank;

using a second model to generate a prediction of the third signal as a function of the first signal; and

determining whether the third signal deviates from the prediction of the third signal to an extent that meets an additional predetermined condition;

wherein generating the first indicator comprises generating the first indicator further based on whether the third signal deviates from the prediction of the third signal to the extent that meets the additional predetermined condition.

7. A method according to claim 6, wherein generating the third signal comprises generating a difference between a fourth signal associated with the level of material in the tank and the second signal.

8. A method according to claim 7, wherein generating the first signal comprises generating a mean of a signal indicative of the level of material in the tank;

wherein generating the second signal comprises generating a mean of a control demand signal;

wherein generating the third signal comprises generating a mean of a difference between a valve position signal and the control demand signal.

9. A method according to claim 8, wherein generating the first indicator comprises:

generating the first indicator to indicate a valve problem if the mean of the difference between the valve position signal and the control demand signal deviates from the prediction generated by the second model to the extent that meets the additional predetermined condition; and

generating the first indicator to indicate a measurement drift problem if the mean of the difference between the valve position signal and the control demand signal does not deviate from the prediction generated by the second model to the extent that meets the additional predetermined condition and if the mean of the control demand deviates from the prediction generated by the first model to the extent that meets the predetermined condition.

10. A method according to claim 9, further comprising generating a second indicator of an abnormal operation, wherein generating the second indicator comprises:

generating the second indicator to indicate that the mean of the control demand signal is low if the mean of the control demand signal is lower than the prediction generated by the first model to the extent that meets the predetermined condition;

generating the second indicator to indicate that the mean of the control demand signal is high if the mean of the control demand signal is higher than the prediction generated by the first model to the extent that meets the predetermined condition;

generating the second indicator to indicate that the mean of the control demand signal is not high or low if the mean of the control demand signal does not deviate from the prediction generated by the first model to the extent that meets the predetermined condition;

the method further comprising generating a third indicator of an abnormal operation, wherein generating the third indicator comprises;

generating the third indicator to indicate that the mean of the difference between the valve position signal and the control demand signal is low if the mean of the difference between the valve position signal and the control demand signal is lower than the prediction generated by the second model to the extent that meets the additional predetermined condition;

generating the third indicator to indicate that the mean of the difference between the valve position signal and the control demand signal is high if the mean of the difference between the valve position signal and the control demand signal is higher than the prediction generated by the second model to the extent that meets the additional predetermined condition; and

generating the third indicator to indicate that the mean of the difference between the valve position signal and the control demand signal is not high or low if the mean of the difference between the valve position signal and the control demand signal does not deviate from the prediction generated by the second model to the extent that meets the additional predetermined condition.

11. A method according to claim 1, wherein generating the first indicator comprises generating an indicator of a liquid leak condition.

12. A method according to claim 1, wherein generating the first indicator comprises generating an indicator of a head loss condition.

13. A computer readable memory storing machine readable instructions, the machine readable instructions, when executed by one or more machines, to cause the one or more machines to:

generate a first signal associated with regulatory control of a level of material in a tank;

generate a second signal associated with regulatory control of the level of material in the tank;

use a first model to generate a prediction of the second signal as a function of the first signal, the first model including a first regression model in a first range corresponding to a first operating region of the level regulatory control loop and corresponding to a first range of the first signal, the first model capable of being subsequently configured to include at least a second regression model in at least a second respective range corresponding to at least a second respective operating region and corresponding to a second range of the first signal, wherein the first and second ranges of the first signal do not overlap;

determine whether the second signal deviates from the prediction of the second signal to an extent that meets a predetermined condition; and

generate an indicator of an abnormal operation associated with the level regulatory control loop based on whether the second signal deviates from the prediction of the second signal to the extent that meets the predetermined condition.

14. A system for detecting an abnormal operation of a level regulatory control loop in a process plant, comprising:

a processor; and

a computer readable medium coupled to the processor to store machine readable instructions for execution by the processor;

a first model implemented by the processor to generate a prediction of a second signal associated with regulatory control of a level of material in a tank as a function of a first signal associated with regulatory control of the level of material in the tank, the first model including a first regression model in a first range corresponding to a first operating region of the level regulatory control loop and corresponding to a first range of the first signal, the first model capable of being subsequently configured to include at least a second regression model in at least a second respective range corresponding to at least a second respective operating region and corresponding to a second range of the first signal, wherein the first and second ranges of the first signal do not overlap;

a first deviation detector implemented by the processor, the first deviation detector to generate an output indicative of whether the second signal deviates from the prediction of the second signal to an extent that meets a predetermined condition; and

an indicator generator implemented by the processor, the indicator generator to generate an indicator of an abnormal operation associated with the level regulatory control loop based on whether the second signal deviates from the prediction of the second signal to the extent that meets the predetermined condition.

15. A system according to claim 14, further comprising:

a first mean generator implemented by the processor to generate the first signal as a mean of a first process variable associated with the level of material in the tank; and

a second mean generator implemented by the processor to generate the second signal as a mean of a second process variable associated with the level of material in the tank.

16. A system according to claim 15, wherein the first process variable is a signal indicative of the level of material in the tank;

wherein the second process variable is a control demand signal;

wherein the first deviation detector is configured to;

generate the first deviation detector output to indicate whether the mean of the control demand signal is lower than the prediction generated by the first model to the extent that meets the predetermined condition, and

generate the first deviation detector output to indicate whether the mean of the control demand signal is higher than the prediction generated by the first model to the extent that meets the predetermined condition;

wherein the indicator generator is configured to;

generate the indicator to indicate that the mean of the control demand signal is low if the mean of the control demand signal is lower than the prediction generated by the first model to the extent that meets the predetermined condition, and

generate the indicator to indicate that the mean of the control demand signal is high if the mean of the control demand signal is higher than the prediction generated by the first model to the extent that meets the predetermined condition.

17. A system according to claim 15, wherein the first process variable is a signal indicative of the level of material in the tank;

wherein the second process variable is a difference between a valve position signal and a control demand signal;

wherein the indicator generator is configured to generate the indicator to indicate a valve problem if the output of the first deviation detector indicates that the mean of the difference between the valve position signal and the control demand signal deviates from the prediction generated by the first model to the extent that meets the predetermined condition.

18. A system according to claim 14, further comprising:

a second model implemented by the processor to generate a prediction of a third signal associated with regulatory control of the level of material in the tank as a function of the first signal associated with regulatory control of the level of material in the tank;

a second deviation detector implemented by the processor, the second deviation detector to generate an output indicative of whether the third signal deviates from the prediction of the third signal to an extent that meets an additional predetermined condition; and

wherein the indicator generator is coupled to the second deviation detector, and wherein the indicator generator is configured to generate the indicator further based on whether the third signal deviates from the prediction of the third signal to the extent that meets the additional predetermined condition.

19. A system according to claim 18, further comprising:

a first mean generator implemented by the processor to generate the first signal as a mean of a signal indicative of the level of material in the tank;

a second mean generator implemented by the processor to generate the second signal as a mean of a control demand signal; and

a third mean generator implemented by the processor to generate the third signal as a mean of a difference a difference between a valve position signal and the control demand signal.

20. A system according to claim 19, wherein the indicator generator is configured to:

generate the indicator to indicate a valve problem if the mean of the difference between the valve position signal and the control demand signal deviates from the prediction generated by the second model to the extent that meets the additional predetermined condition, and

generate the indicator to indicate a measurement drift problem if the mean of the difference between the valve position signal and the control demand signal does not deviate from the prediction generated by the second model to the extent that meets the additional predetermined condition and if the mean of the control demand signal deviates from the prediction generated by the first model to the extent that meets the predetermined condition.

21. A system according to claim 20, wherein the first deviation detector is configured to generate the output of the first deviation detector to indicate whether the mean of the control demand signal is lower than the prediction generated by the first model to the extent that meets the predetermined condition, and to indicate whether the mean of the control demand signal is higher than the prediction generated by the first model to the extent that meets the additional predetermined condition;

and

wherein the second deviation detector is configured to generate the output of the second deviation detector to indicate whether the mean of the difference between the valve position signal and the control demand signal is lower than the prediction generated by the second model to the extent that meets the additional predetermined condition, and to indicate whether the mean of the difference between the valve position signal and the control demand signal is higher than the prediction generated by the second model to the extent that meets the additional predetermined condition.

22. A system according to claim 21, wherein the first deviation detector is configured to generate the output of the first deviation detector to indicate whether the mean of the control demand signal does not deviate from the prediction generated by the first model to the extent that meets the predetermined condition;

and

wherein the second deviation detector is configured to generate the output of the second deviation detector to indicate whether the mean of the difference between the valve position signal and the control demand signal does not deviate from the prediction generated by the second model to the extent that meets the additional predetermined condition.

23. A system according to claim 14, wherein the indicator generator is configured to generate an indicator of a liquid leak condition.

24. A system according to claim 14, wherein the indicator generator is configured to generate an indicator of a head loss condition.