Flow meter diagnostics

• US 20070192046A1
• Filed: 02/15/2006
• Published: 08/16/2007
• Est. Priority Date: 02/15/2006
• Status: Active Grant

• Current Assignee: Natural Gas Solutions North America, LLC (Baker Hughes Company)
• Original Assignee: Dresser Incorporated (Nagano Keiki Company Limited)
• Inventors: Hairston, Ronald
• Granted Patent: US 7,295,934 B2
• Time in Patent Office: Days
• US Class Current: 702/45
• CPC Class Codes: F04B 51/00 Testing machines, pumps, or pumping installations
• CPC Class Codes: F04C 14/28 Safety arrangements; Monitoring
• CPC Class Codes: G01F 25/15 specially adapted for gas meters G01F25/11 - G01F25/14, G01F25/17 take precedence
• CPC Class Codes: G01F 3/065 sliding-vane meters
• CPC Class Codes: G01F 3/10 Geared or lobed impeller meters
• CPC Class Codes: G01M 3/00 Investigating fluid-tightness of structures

Abstract

Apparatus and associated systems, methods and computer program products relate to monitoring the performance of an operating gas meter by automatic and substantially continuous differential pressure (dP) measurement. Measured dP may be compared against a baseline dP characteristic to determine if the measured dP exceeds a threshold value above a baseline dP characteristic. If the threshold is exceeded, then the system may generate a signal to request repair or replacement of the meter. After installation, some embodiments collect dP data over time and/or over a range of flow rates to automatically learn a baseline dP characteristic under installation conditions. A system may switch from a default baseline dP characteristic to a learned baseline dP characteristic. Some embodiments may further correct volume or flow rate signals for line pressure and/or temperature. Further embodiments provide a passive apparatus to protect a dP sensor against transients in line pressure and/or differential pressure.

Claims

1. A system for continuously monitoring performance of a gas meter, the system comprising:

a differential pressure (dP) sensor to measure a differential pressure across a rotary gas flow meter, the differential pressure sensor having a first input port to be in continuous uninterruptible fluid communication with an inlet of the meter and a second port to be in continuous uninterruptible fluid communication with an outlet of the meter;

a first plurality of memory locations containing baseline dP characteristic information; and

a second plurality of memory locations containing instructions that, when executed by a processor, cause the processor to perform operations to;

determine a flow rate through the meter when the differential pressure was measured; and

determine whether the measured differential pressure exceeds a threshold differential pressure above the baseline dP characteristic at the determined flow rate.

2. The system of claim 1, wherein the differential pressure based on the determined flow rate is determined by interpolating a plurality of values associated with the baseline dP characteristic.

3. The system of claim 1, wherein the baseline dP characteristic comprises a function to determine differential pressure based on measured flow rate information.

4. The system of claim 3, wherein the baseline dP characteristic further comprises a function to determine differential pressure based on measured line pressure information.

5. The system of claim 4, wherein the baseline dP characteristic further comprises a function to determine differential pressure based on measured line temperature information.

6. The system of claim 1, wherein the baseline dP characteristic information is determined during commissioning of the meter in the field.

7. The system of claim 1, wherein the baseline dP characteristic information is determined before the meter is installed in the field.

8. The system of claim 1, wherein the baseline dP characteristic information is determined after the meter is installed, the operations further comprising storing differential pressure measurement information at each of a plurality of measured flow rates to define a second performance characteristic.

9. The system of claim 1, further comprising a first flow restriction element and a second flow restriction element, each flow restriction element to protect the differential pressure sensor against some gas line pressure transients, the first input port to be in continuous uninterruptible fluid communication with the inlet of the meter through the first flow restriction element and the second port to be in continuous uninterruptible fluid communication with the outlet of the meter through the second flow restriction element.

10. The system of claim 1, further comprising a differential pressure limiter to limit the differential pressure between the first and second ports.

11. The system of claim 1, the operations further comprising determining a corrected volume output signal.

12. The system of claim 11, further comprising a line pressure sensor to measure a line pressure of the gas at the inlet or outlet of the meter.

13. The system of claim 12, wherein the corrected volume output signal is corrected according to the line pressure and gas temperature.

14. The system of claim 1, further comprising operations to remove a DC offset from the dP sensor during a substantially zero flow rate condition.

15. The system of clam 14, wherein the operations to determine whether the measured differential pressure exceeds a pressure based on the performance characteristic at the determined flow rate by more than a threshold value are substantially performed only within limits selected based on a most recent operation to remove the DC offset.

16. The system of claim 15, wherein the selected limits comprise a selected period of time after the most recent operations to remove the DC offset.

17. A method to adaptively learn a baseline differential pressure characteristic of a meter in an installation, the method comprising:

(a) measuring differential pressure (dP) across a rotary gas flow meter over a period of time;

(b) for each dP measurement, determining a flow rate through the meter;

(c) comparing the measured dP information to a threshold differential pressure that is greater than an initial baseline dP characteristic at the determined flow rate;

(d) monitoring the performance of the meter based on the comparison; and

(e) generating at least one baseline dP characteristic based on the measured differential pressure and determined flow rate information.

18. The method of claim 17, further comprising repeating steps (a)-(d) until at least one baseline dP characteristic has been generated.

19. The method of claim 18, further comprising:

(f) measuring differential pressure across the rotary gas flow meter;

(g) for each dP measurement in step (g), determining a flow rate through the meter;

(h) comparing the measured dP information to a threshold differential pressure that is greater than the generated baseline dP characteristic at the determined flow rate; and

(i) monitoring the performance of the meter based on the comparison in (h).

20. The method of claim 17, wherein the threshold differential pressure comprises a differential pressure that is based on a selected ratio of the baseline dP characteristic at the determined flow rate, wherein the selected ratio is between about 1.1 and 5.0.

21. The method of claim 20, wherein the selected ratio is about 1.5.

22. The method of claim 17, wherein the threshold differential pressure comprises a differential pressure that is based on a function of one or more measured variables selected from the group consisting of:

flow rate, line pressure, and line temperature.

23. The method of claim 17, wherein generating at least one baseline dP characteristic comprises generating two or more baseline dP characteristics, each baseline dP characteristic being associated with a different combination of line pressure and line temperature.

24. A computer program product tangibly embodied in an information carrier and containing instructions that, when executed, cause a processor to perform operations to automatically learn a baseline dP characteristic for a meter installed to measure a gas being transported in a gas line, the operations comprising:

selecting a predetermined baseline dP characteristic for a rotary gas meter;

determining a differential pressure across the meter at each of a plurality of measured flow rates;

determining at each measured flow rate whether any of the determined differential pressures exceeds the selected baseline dP characteristic by more than a threshold value; and

storing the determined differential pressure at each of the plurality of measured flow rates to define a second baseline dP characteristic.

25. The computer program product of claim 24, further comprising determining that sufficient differential pressure data points have been determined according to a set of acceptance criteria.

26. The computer program product of claim 24, further comprising determining at each of a second plurality of measured flow rates whether a differential pressure measurement exceeds the second performance characteristic by more than a second threshold value.

27. The computer program product of claim 24, wherein the predetermined performance characteristic comprises a plurality of pairs of differential pressure and flow rate measurements.

28. The computer program product of claim 24, wherein the predetermined performance characteristic comprises information determined in a meter shop or factory.

29. The computer program product of claim 24, wherein the determined baseline dP characteristic comprises information determined upon installing the meter in a distribution system.

30. The computer program product of claim 24, further comprising substantially simultaneously measuring the flow rate of gas through the meter and the differential pressure of gas at an inlet and an outlet of the meter.