System for measuring gases dissolved in a liquid

• US 6,037,592 A
• Filed: 02/14/1997
• Issued: 03/14/2000
• Est. Priority Date: 02/14/1997
• Status: Expired due to Fees

• Current Assignee: Underground Systems, Inc.
• Original Assignee: Underground Systems, Inc.
• Inventors: Bliven, David C., Sunshine, Steven S., Mattis, John Seymour
• Primary Examiner(s): Porta, David P.
• Application Number:
  US08/800,678
• Time in Patent Office: 1,124 Days
• Field of Search: 250/339.03, 250/339.04, 250/339.13, 250/341.6, 250/343, 250/345
• US Class Current: 250/343
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 33/2841 gas in oil, e.g. hydrogen in insulating oil

Abstract

A method and apparatus for continuously monitoring and measuring the concentration of gases in a gas-containing liquid such as a transformer oil. The method and apparatus employ a passive gas extraction technique which comprises a high performance membrane material to extract dissolved gases from the oil, and an IR-based sensor to detect gases present. The passive gas extractor extracts dissolved gas from the gas-containing liquid, there being a known relationship between the concentration of a constituent gas in the extracted gas and the concentration of the constituent gas remaining dissolved in the gas-containing liquid. The gas sensor senses the concentration of a constituent gas in the extracted gas, in the presence of other constituent gases. The gas sensor comprises a sample chamber which receives the extracted gas, a non-dispersive infrared (IR) absorption sensing system which generates an electrical signal corresponding to the light absorption, at one or more specified IR wavelengths, of the extracted gas in the chamber, and an electrical output comprising the electrical signal generated by the non-dispersive IR absorption sensing system. A processor having receives the electrical signal corresponding to the light absorption, at the one or more specified IR wavelengths, of the extracted gas in the chamber, and computes the concentration of at least one gas constituent present in the extracted gas.

Claims

1. A sensor system for measuring the concentration of gas dissolved in a liquid, the gas comprising one or more constituent gases in a distribution, the system comprising:

a. a passive extractor which extracts dissolved gas from the gas-containing liquid, there being a known relationship between the concentration of a constituent gas in the extracted gas and the concentration of the constituent gas remaining dissolved in the gas-containing liquid; and

b. a gas sensor which senses the concentration of a constituent gas in the extracted gas, in the presence of other constituent gases, the gas sensor comprising

(1) a sample chamber having plural tubes which receive the extracted gas,

(2) a non-dispersive infrared (IR) absorption sensing system which generates an electrical signal corresponding to the light absorption, at one or more specified IR wavelengths, of the extracted gas in the chamber, and

(3) an electrical output comprising the electrical signal generated by the non-dispersive IR absorption sensing system comprising a respective IR emitter disposed at one end of a respective tube, each IR emitter comprising a blackbody source for emitting IR light with wavelengths in the range 2.5 to 15 μ

m, a filter for limiting the IR light transmitted in each tube to a respective sub-range of wavelengths, and plural IR detectors disposed at an opposite end of each of said tubes for receiving the light transmitted in said tube to produce an electrical output signal as a function of the intensity of the received light, each IR detector being tuned to a predetermined wavelength in said respective sub-range corresponding to a respective one of said constituent gases to produce a detection signal representing the presence of said one constituent gas if IR light at said predetermined wavelength is of reduced intensity.

2. The sensor system according to claim 1 comprising a compressor receiving the detection signals produced by said IR detectors, and therefrom computing the concentration of at least one constituent gas present in the extracted gas.

3. The system according to claim 1 comprising:

a. means for receiving a gas-containing liquid from a liquid reservoir; and

b. means for returning liquid to the liquid reservoir.

4. The system according to claim 1 comprising:

a. means for passing extracted gas to the gas sensor; and

b. means for returning extracted gas to the liquid.

5. The system according to claim 1 comprising means for regulating the temperature of the liquid in the system.

6. The system according to claim 5, wherein the temperature regulating means comprises at least one of

a. a heat exchanger;

and

b. a thermoelectric device.

7. The system according to claim 1 comprising means for measuring the temperature of the liquid in the system.

8. The system according to claim 1, wherein the liquid reservoir comprises an electrical transformer and the gas-containing liquid comprises a transformer oil.

9. The system according to claim 1, wherein the IR detectors detect IR light at respective ones of the following wavelengths:

(1) 2.59 μ

m,

(2) 3.32 μ

m,

(3) 4.25 μ

m,

(4) 4.67 μ

m,

(5) 7.65 μ

m,

(6) 10.6 μ

m, and

(7) 13.7 μ

m.

10. The system according to claim 1, wherein the gas sensor comprises a thermal conductivity sensor.

11. The system according to claim 9, wherein selected ones of the IR detectors detect light at respective ones of the following wavelengths:

a. 3.91 μ

m, and

b. 9 μ

m.

12. The system according to claim 9, wherein the IR emitter is separated from the IR detectors in a tube by an optical path of at least one inch.

13. The system according to claim 9, wherein each IR detector comprises a broadband detector and a narrow band filter, the narrow band filter having a full width half maximum (FWHM) bandwidth of less than 0.5 μ

m.

14. The system according to claim 10, wherein the thermal conductivity sensor comprises a bridge circuit, the bridge circuit comprising:

a. an electrical input;

b. a first negative temperature coefficient (NTC) thermistor;

c. a second NTC thermistor; and

c. an electrical output;

wherein the resistance of the first NTC thermistor varies as a function of the temperature of the extracted gas present in the sample chamber, the resistance of the second NTC thermistor varies as a function of the temperature of the sample chamber, and the electrical output of the thermal conductivity sensor comprises an electrical signal which is representative of the difference between the resistances of the first and second NTC thermistors.

15. The system according to claim 14, wherein the processor has an input coupled with the electrical output of the thermal conductivity sensor, the processor receiving the electrical signal corresponding to the difference between the resistances of the first and second NTC thermistors, and therefrom computing the thermal conductivity of the extracted gas and the concentration of hydrogen present in the extracted gas.

16. A sensor system for measuring the concentration of gas dissolved in a liquid, the gas comprising one or more constituent gases in a distribution, the system comprising:

a. a passive gas extractor which extracts dissolved gas from the gas-containing liquid, there being a known relationship between the concentration of a constituent gas in the extracted gas and the concentration of the constituent gas remaining dissolved in the gas-containing liquid; and

b. a gas sensor which senses the concentration of a constituent gas in the extracted gas, in the presence of other constituent gases, the gas sensor comprising

(1) a sample chamber which receives the extracted gas,

(2) a non-dispersive infrared (IR) absorption sensing system which generates an electrical signal corresponding to the light absorption, at one or more specified IR wavelengths, of the extracted gas in the chamber, the non-dispersive IR absorption sensing system comprising an IR emitter assembly and an IR detector assembly, wherein;

a. the IR emitter assembly comprises a blackbody source which emits light from 2.5 to 15 μ

m; and

b. the IR detector assembly comprises six IR detectors with each IR detector detecting light at a different one of the following wavelengths;

2.59 μ

m, 3.32 μ

m, 4.25 μ

m, 4.67 μ

m, 7.65 μ

m, 10.6 μ

m, and 13.7 μ

m; and

(3) an electrical output comprising the electrical signal generated by the non-dispersive IR absorption sensing system.

17. The sensor system according to claim 16 comprising a processor having an input coupled with the electrical output of the gas sensor, the processor receiving the electrical signal corresponding to the light absorption, at the one or more specified IR wavelengths, of the extracted gas in the chamber, and therefrom computing the concentration of at least one gas constituent present in the extracted gas.

18. The system according to claim 16 comprising:

a. means for receiving a gas-containing liquid from a liquid reservoir; and

b. means for returning liquid to the liquid reservoir.

19. The system according to claim 16 comprising:

a. means for passing extracted gas to the gas sensor; and

b. means for returning extracted gas to the liquid.

20. The system according to claim 16 comprising means for regulating the temperature of the liquid in the system.

21. The system according to claim 20, wherein the temperature regulating means comprises at least one of

a. a heat exchangerl and

b. a thermoelectric device.

22. The system according to claim 16 comprising means for measuring the temperature of the liquid in the system.

23. The system according to claim 16, wherein the IR detector assembly comprises an IR detector which detects light at one of the following wavelengths:

a. 3.91 μ

m.; and

b. 9 μ

m.

24. The system according to claim 16, wherein the IR detector assembly has an optical path of at least one inch.

25. The system according to claim 16, wherein the IR detector comprises a broadband detector and a narrow band filter, the narrow band filter having a full width half maximum (FWHM) bandwidth of less than 0.5 μ

m.

26. The system according to claim 16, wherein the gas sensor further comprises a thermal conductivity sensor.

27. The system according to claim 26, wherein the thermal conductivity sensor comprises a bridge circuit, the bridge circuit comprising:

a. an electrical input;

b. a first negative temperature coefficient (NTC) thermistor;

c. a second NTC thermistor; and

c. an electrical output;

wherein the resistance of the first NTC thermistor varies as a function of the temperature of the extracted gas present in the sample chamber, the resistance of the second NTC thermistor varies as a function of the temperature of the sample chamber, and the electrical output of the thermal conductivity sensor comprises an electrical signal which is representative of the difference between the resistances of the first and second NTC thermistors.

28. The system according to claim 27, wherein the processor has an input coupled with the electrical output of the thermal conductivity sensor, the processor receiving the electrical signal corresponding to the difference between the resistances of the first and second NTC thermistors, and therefrom computing the thermal conductivity of the extracted gas and the concentration of hydrogen present in the extracted gas.

29. The system according to claim 16, wherein the liquid reservoir comprises an electrical transformer and the gas-containing liquid comprises a transformer oil.

30. The system according to claim 16, wherein the passive gas extractor comprises a permselective membrane comprising an amorphous perfluoro-2,2-dimethyl-1,3-dioxole polymer.