Continuous Median Failure Control System and Method

• US 20060291376A1
• Filed: 06/28/2005
• Published: 12/28/2006
• Est. Priority Date: 06/28/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Toth, Carl Raymond
• Granted Patent: US 7,515,995 B2
• Time in Patent Office: Days
• US Class Current: 370/217
• CPC Class Codes: G01D 3/08 with provision for safeguarding the apparatus, e.g. against abnormal operation, against breakdown
• CPC Class Codes: G05B 2219/14126 Redundant I-O points, two sensors, actuators for same point
• CPC Class Codes: G05B 2219/24182 Redundancy
• CPC Class Codes: G05B 2219/24193 Two transducers for same parameter
• CPC Class Codes: G05B 9/03 with multiple-channel loop, i.e. redundant control systems

Abstract

A redundant control system including at least three redundant signals is presented. The redundant control system includes a failure circuit associated with each of the redundant signals. The failure circuit generates a failure signal in response to an occurrence of a failure of a corresponding one of the redundant signals. A select circuit is associated with each of the redundant signals. The select circuit is receptive to a default signal associated with the corresponding one of the redundant signals, to the failure signal, and to the corresponding one of the redundant signals. The select circuit selects the default signal when the failure signal indicates a failure of the corresponding one of the redundant signals and selects the corresponding one of the redundant signals when the failure signal does not indicate a failure for the corresponding one of the redundant signals. A median determination circuit is receptive to the default signals selected and the redundant signals selected to determine a median signal indicative of a median of the default signals selected and the redundant signals selected.

Claims

1. A redundant control system including at least three redundant signals, comprising:

at least three failure circuits, each individual one of said at least three failure circuits being associated with an individual one of said at least three redundant signals, said failure circuit generating a failure signal in response to an occurrence of a failure of a corresponding one of the redundant signals;

a first select circuit associated with each of the redundant signals, said first select circuit receptive to a default signal associated with the corresponding one of the redundant signals, to said failure signal, and to the corresponding one of the redundant signals, said first select circuit selecting said default signal when said failure signal indicates a failure of the corresponding one of the redundant signals, said first select circuit selecting the corresponding one of the redundant signals when said failure signal does not indicate a failure for the corresponding one of the redundant signals; and

a median determination circuit receptive to said default signals selected and the redundant signals selected to determine a median signal indicative of a median of said default signals selected and the redundant signals selected.

2. The redundant control system of claim 1 wherein each of said failure circuits comprises:

a summation circuit receptive to a present signal of the corresponding one of the redundant signals and a previous signal of the corresponding one of the redundant signals, said summation circuit combining said present signal of the corresponding one of the redundant signals and said previous signal of the corresponding one of the redundant signals to provide a difference signal thereof; and

a compare circuit receptive to said difference signal, said compare circuit comparing said difference signal to a constant to generate said failure signal when the difference signal is one of (1) greater than and (2) less than said constant.

3. The redundant control system of claim 1 wherein each of said failure circuits further comprises:

an alarm circuit generating an alarm signal in response said failure signal.

4. The redundant control system of claim 2 wherein said failure signal is also generated when a fixed signal is used for any one of the redundant signals.

5. The redundant control system of claim 2 wherein:

said constant comprises a high constant an a low constant; and

said default signal comprises a high level default signal when said difference signal is greater than said high constant and a low level default signal when said difference signal is less than said low constant.

6. The redundant control system of claim 1 further comprising;

a second select circuit receptive to a present signal of each of the redundant signals, to said median signal, and to a signal indicative of an occurrence of all but one of said failure signals indicating failures of all but one of said redundant signals, said second select circuit selecting a corresponding one of said present signals corresponding to said one of the redundant signals that is the only one of the redundant signals for which said failure signal does not indicate a failure of the corresponding one of the redundant signals as said median signal when said signal indicative of an occurrence of all but one of said failure signals indicates failures of all but one of said the redundant signals, said second select circuit selecting said median signal otherwise.

7. The redundant control system of claim 1 wherein said median signal comprises a present median signal of said median signal as determined from present signals of the redundant signals and a previous median signal of said median signal as determined from previous signals of the redundant signals, and further comprising:

a summation circuit receptive to said present median signal and said previous median signal, said summation circuit combining said present median signal and said previous median signal to provide a difference signal thereof; and

second select circuit receptive to said difference signal and to a signal indicative of an occurrence of any one of said failure signals indicating a failure of any one of said the redundant signals, said second select circuit selecting said difference signal as a second select output signal when said signal indicative of said occurrence of any one of said failure signals indicates a failure of any one of said the redundant signals, said second select circuit selecting a fixed signal as said second select output signal otherwise.

8. The redundant control system of claim 7 further comprising:

a summation circuit receptive to said second select output signal and to said median signal, said summation circuit combining said second select output signal and said median signal to provide a redundant control system output.

9. A redundant control method including at least three redundant signals, comprising:

determining an occurrence of a failure of any one of the redundant signals;

for each of the redundant signals, selecting a default signal associated with the corresponding one of the redundant signals when a failure of the corresponding one of the redundant signals has been determined;

for each of the redundant signals, selecting the corresponding one of the redundant signals when a failure of the corresponding one of the redundant signals has not been determined; and

determining a median signal of said default signals selected and the redundant signals selected.

10. The redundant control method of claim 9 wherein said determining an occurrence of a failure comprises:

for each of the redundant signals, combining a present signal of the corresponding one of the redundant signals and a previous signal of the corresponding one of the redundant signals to provide a difference signal thereof; and

for each of the redundant signals, comparing said difference signal to a constant to generate said failure signal when the difference is one of (1) greater than and (2) than said constant.

11. The redundant control method of claim 9 further comprising:

generating an alarm signal when a failure of any one of the redundant signals has been determined.

13. The redundant control method of claim 10 wherein:

said constant comprises a high constant and a low constant; and

said default signal comprises a high level default signal when said difference signal is greater than said high constant and a low level default signal when said difference signal is less than said low constant.

14. The redundant control method of claim 9 further comprising;

selecting a present signal corresponding to one of the redundant signals when that corresponding one of the redundant signals is the only one of the redundant signals for which said failure has not been determined, wherein said present signal selected is utilized as said median signal; and

selecting said median signal when said failure has been determined for more than one of the redundant signals.

15. The redundant control method of claim 9 wherein said median signal comprises a present median signal of said median signal as determined from present signals of the redundant signals and a previous median signal of said median signal as determined from previous signals of the redundant signals, and further comprising:

combining said present median signal and said previous median signal to provide a difference signal thereof; and

selecting said difference signal when a failure of said the redundant signals has been determined; and

selecting a fixed signal when a failure of said the redundant signals has not been determined.

16. The redundant control method of claim 15 further comprising:

combining one of said difference signal selected and said fixed signal selected with said median signal to provide a redundant control system output.

12. The redundant control method of clam 10 wherein said determining an occurrence of a failure further comprises:

determining an occurrence of a failure when a fixed signal is used for any one of the redundant signals.

17. A redundant control system including at least three redundant signals, comprising:

means for determining an occurrence of a failure of any one of the redundant signals;

first means for selecting associated with each of the redundant signals, said first means for selecting a default signal associated with the corresponding one of the redundant signals when a failure of the corresponding one of the redundant signals has been determined, said first means for selecting the corresponding one of the redundant signals when a failure of the corresponding one of the redundant signals has not been determined; and

means for determining a median signal of said default signals selected and the redundant signals selected.

18. The redundant control system of claim 17 wherein said means for determining comprises:

means for combining associated with each of the redundant signals, said means for combining a present signal of the corresponding one of the redundant signals and a previous signal of the corresponding one of the redundant signals to provide a difference signal thereof; and

means for comparing associated with each of the redundant signals, said means for comparing said difference signal to a constant to generate said failure signal when the difference signal is one of (1) greater than and (2) less than said constant.

19. The redundant control system of claim 17 further comprising:

means for generating an alarm signal when a failure of any one of the redundant signals has been determined.

20. The redundant control system of claim 18 wherein said means for determining further comprises:

means for determining an occurrence of a failure when a fixed signal is used for any one of the redundant signals.