Binary gas analyzer instrument and analysis method

• US 4,891,629 A
• Filed: 05/16/1988
• Issued: 01/02/1990
• Est. Priority Date: 05/16/1988
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Wroblewski, Craig A., Gajjar, Jagdish T., Roman, Michael F., Underkoffler, Edwin C.
• Primary Examiner(s): Williams, Hezron E.
• Application Number:
  US07/194,635
• Time in Patent Office: 596 Days
• Field of Search: 73/25, 73/26, 73/27 R, 73/23, 422/90, 422/95, 422/96, 340/632
• US Class Current: 340/632
• CPC Class Codes: G01N 25/18 by investigating thermal conductivity by calorimetry G01N25/20; by measuring change of resistance of an electrically-heated body G01N27/18

Abstract

A binary gas analyzer instrument and analysis method for determining percent composition of a cooling gas within a turbine generator is disclosed. The instrument includes a measurement block having a plurality of cells therein, some of which comprise sealed cells containing a known reference gas. One of the cells comprises a measurement cell and contains the binary gas mixture to be evaluated. Each of the cells contains a thermistor and a heater is provided for keeping the cells at a substantially constant temperature. An electric current supply provides a constant current to each thermistor for selfheating, and the gas within each cell conducts heat away from the thermistor at a distinctive rate. Measuring apparatus is selectably connectable across each cell thermistor to measure the voltage drop across said thermistors, and computational apparatus is provided to automatically translate the measured voltage drop across the measurement cell thermistor into a percent compositional reading of the binary gas constituents. Translation is accomplished by the computational apparatus with reference to the voltage drop across at least one of the reference cell thermistors.

Claims

1. A gas analyzer instrument capable of determining the percent composition of a binary gas mixture of known constituents, said analyzer instrument comprising:

a first reference cell having a first gas therein, said first gas having a thermal conductivity near the thermal conductivity of one of said constituent gases;

a measurement cell having said binary gas mixture therein;

means for maintaining said cells at a substantially constant temperature;

a thermistor positioned within each of said cells;

means for supplying a substantially constant electrical current to each of said thermistors for heating thereof, the gas in each of said cells conducting heat away from the thermistor;

voltage measuring means selectably connectable across each of said thermistors to measure voltage drop across said thermistors; and

computational means for automatically translating the voltage drop across said measurement cell thermistor into a percent compositional reading of said binary gas constituents, said computational means utilizing the voltage drop across said first cell thermistor as a reference.

2. The analyzer instrument of claim 1, further comprising:

a second reference cell having a second gas therein, said second gas having a thermal conductivity near the thermal conductivity of the other of said constituent gases; and

wherein the computational means automatically translates the voltage drop across said measurement cell thermistor into a percent compositional reading of said binary gas constituents utilizing the voltage drop across at least one of said first and second cell thermistors as a reference.

3. The analyzer instrument of claim 2, wherein said instrument is capable of being used to determine percent composition of the constituents within each of a plurality of different known binary gas mixtures.

4. The analyzer instrument of claim 3, further comprising at least three reference cells, each of said reference cells having a gas therein with a thermal conductivity near the thermal conductivity of a constituent gas in one of said plurality of mixtures.

5. The analyzer instrument of claim 3, further comprising means for displaying the percent compositional reading of said binary gas constituents.

6. The analyzer instrument of claim 5, wherein said display means includes a plurality of selectable display scales, the appropriate display scale being manually selected based upon of the binary gas mixture under analysis.

7. The analyzer instrument of claim 2, wherein said first gas is sealed in said first reference cell and said second gas is sealed in said second reference cell.

8. The analyzer instrument of claim 2, wherein said first gas comprises one of said constituent gases.

9. The analyzer instrument of claim 8, wherein said second gas comprises the other of said constituent gases.

10. The analyzer instrument of claim 2, further comprising a substantially solid block within which said cells are located, said block being manufactured of metal.

11. The analyzer instrument of claim 10, wherein said temperature maintaining means maintains said block at a substantially constant temperature.

12. The analyzer instrument of claim 11, wherein said cells are arranged in a triangular shaped configuration within said block.

13. The analyzer instrument of claim 12, wherein said maintaining means includes heating means positioned substantially central said triangular shaped configuration of cells.

14. The analyzer instrument of claim 11, wherein said substantially constant block temperature is above standard room temperature.

15. The analyzer instrument of claim 13, wherein said substantially constant block temperature is approximately 50 degrees Celsius.

16. The analyzer instrument of claim 13, wherein said thermistors comprise negative temperature coefficient of resistivity thermistors.

17. The analyzer instrument of claim 3, wherein said instrument is used for monitoring a hydrogen gas cooled turbine driven electrical generator, and wherein said first gas comprises helium and said second gas comprises nitrogen.

18. The analyzer instrument of claim 17, wherein said instrument is capable of being used to determine percent composition of the constituents within each of three different binary gas mixtures, said different mixtures comprising carbon dioxide and air, hydrogen and carbon dioxide, and hydrogen and air.

19. The analzyer instrument of claim 18, further comprising alarm means for providing an indication when the percent composition of said hydrogen and air mixture is at a dangerous level.

20. The analyzer instrument of claim 18, wherein said measurement cell includes a gas inlet for continuously introducing a binary gas mixture of unknown percent composition from said electrical generator into said measurement cell and a gas outlet for continuously exhausting said gas mixture.

21. The analyzer instrument of claim 18 further comprising:

means for calculating and storing standard nitrogen reference cell and standard helium reference cell readings;

means for calibrating nitrogen gas in said measurement cell and for storing said nitrogen calibration reading in memory;

means for calibrating hydrogen gas in said measurement cell and for storing said hydrogen calibration reading in memory; and

means for calibrating carbon dioxide in said measurement cell and for storing said carbon dioxide calibration reading in memory.

22. The analyzer instrument of claim 21, wherein said computational means utilizes said stored nitrogen and helium reference standard readings and said stored nitrogen, hydrogen and carbon dioxide calibration readings in translating the voltage drop across said measurement cell thermistor into a percent compositional reading of said binary gas constituents.

23. The analyzer instrument of claim 22, wherein said percent hydrogen in air composition is calculated from:

##EQU2## wherein;

READN=present nitrogen cell reading

READH=present helium cell reading

READX=present measurement cell reading

NSTD=nitrogen standard reading from memory

HSTD=helium standard reading from memory

NCALIB=nitrogen calibration reading from memory

HCALIB=hydrogen calibration reading from memory

CCALIB=carbon dioxide calibration reading from memory.

24. The analyzer instrument of claim 23, wherein said percent hydrogen in carbon dioxide composition is calculated from:

##EQU3##

25. The analyzer instrument of claim 24, wherein said percent carbon dioxide in air composition is calculated from:

##EQU4##

26. The analyzer instrument of claim 25, wherein said NSTD, HSTD, NCALIB, HCALIB and CCALIB readings are stored in nonvolatile memory.

27. A percent composition determining instrument for use with a binary gas mixture of known constituents, said instrument comprising in combination:

a block;

means for maintaining said block at a substantially constant temperature;

a plurality of gas cells positioned within said block;

some of said gas cells comprising sealed reference chambers with known gases therein;

means for introducing the binary gas mixture into one of said cells;

a thermistor within each of said cells;

means for supplying a substantially constant electrical current to each of said thermistors for heating thereof, the gas in each of said cells conducting heat away from said thermistor;

voltage measuring means selectably connectable across each of said cells to measure voltage drop across said thermistors; and

computational means for automatically correlating the voltage drop across the thermistor within said cell containing the binary gas mixture with a percent compositional reading of said binary gas constituents, said computational means utilizing the voltage drop across the thermistor within at least one of said sealed chambers as a reference.

28. The instrument of claim 27, wherein said instrument is capable of being used to determine percent composition of the constituents within each of a plurality of different binary gas mixtures.

29. The instrument of claim 27, wherein said block is substantially solid and manufactured of metal.

30. The analyzer instrument of claim 29, wherein said temperature maintaining means maintains said block at a substantially constant temperature.

31. The instrument of claim 30, wherein said substantially constant block temperature is approximately 50 degrees Celius.

32. The instrument of claim 27, wherein said thermistors comprise negative temperature coefficient of resistivity thermistors.

33. A method for determining the percent composition of a gas mixture of two known constituents, said method comprising the steps of:

(A) providing a first reference cell having a first gas and a thermistor sealed therein, said first gas having a thermal conductivity near the thermal conductivity of one of said two constituent gases;

(B) providing a second reference cell having a second gas and a thermistor sealed therein, said second gas having a thermal conductivity near the thermal conductivity of the other of said two constituent gases;

(C) providing a measurement cell and a thermistor therein;

(D) introducing said binary gas mixture into said measurement cell;

(E) maintaining said cells at a substantially constant temperature;

(F) supplying a substantially constant electric current to each of said thermistors for heating thereof, the gas in each of said cells conducting heat away from the thermistor;

(G) measuring the voltage drop across each of said thermistors; and

(H) correlating the voltage drop across said measurement cell thermistor with a percent compositional reading of said binary gas mixture constituents, said correlation step utilizing the voltage drop across at least one of said first and second cell thermistors as a reference.

34. The method of claim 33, wherein said method is capable of being used to determine percent composition of the constituents within each of a plurality of different binary gas mixtures, and wherein said providing step (A) includes providing a first gas having a thermal conductivity near the thermal conductivity of a constituent gas in one of said plurality of mixtures, and said providing step (B) includes providing a second gas having a thermal conductivity near the thermal conductivity of another constituent gas in one of said plurality of mixtures.

35. The method of claim 34, further comprising displaying the percent compositional reading of said binary gas constituents.

36. The method of claim 35, further comprising manually selecting a display scale from one of a plurality of scales based upon the binary gas mixture under analysis.

37. The method of claim 34, wherein said temperature maintaining step (E) includes maintaining said cells at approximately 50 degrees Celius.

38. The method of claim 34, wherein said method is capable of being used to determine percent composition of the constituents within each of three different binary gas mixtures, said different mixtures comprising carbon dioxide and air, hydrogen and carbon dioxide, and hydrogen and air.

39. The method of claim 38 further comprising initially calibrating said cells.

40. The method of claim 39 wherein said method is used for monitoring a hydrogen gas cooled electrical generator, and wherein said first gas provided in step (A) comprises helium and said second gas provided in step (B) comprises nitrogen.

41. The method of claim 40, wherein said calibration step includes:

calculating and storing standard nitrogen reference cell and helium reference cell readings;

calibrating nitrogen gas in said measurement cell and storing said nitrogen calibration reading in memory;

calibrating hydrogen gas in said measurement cell and storing said hydrogen calibration reading in memory; and

calibrating carbon dioxide in said measurement cell and storing said carbon dioxide calibration reading in memory.

42. The method of claim 41, wherein said correlating step (H) includes calculating the hydrogen in air gas composition from:

##EQU5## wherein;

READN=present nitrogen cell reading

READH=present helium cell reading

READX=present measurement cell reading

NSTD=nitrogen standard reading from memory

HSTD=helium standard reading from memory

NCALIB=nitrogen calibration reading from memory

HCALIB=hydrogen calibration reading from memory

CCALIB=carbon dioxide calibration reading from memory.

43. The method of claim 42, wherein said correlating step includes calculating the percent hydrogen in carbon dioxide composition from:

##EQU6##

44. The method of claim 43, wherein said correlating step includes calculating the percent carbon dioxide in air from:

##EQU7##

45. The method of claim 44, further comprising initially storing said NSTD, HSTD, NCALIB, HCALIB and CCALIB readings in nonvolatile memory.