Gas analysis transducers with electromagnetic energy detector units

• US 5,146,092 A
• Filed: 04/16/1991
• Issued: 09/08/1992
• Est. Priority Date: 05/23/1990
• Status: Expired due to Term

• Current Assignee: NTC Technology, Inc. (Dixtal Medical, Inc.)
• Original Assignee: NTC Technology, Inc. (Dixtal Medical, Inc.)
• Inventors: Bang, Gary M., Labuda, Lawrence L., Apperson, Jerry R., Knodle, Daniel W., Russell, James T.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US07/687,012
• Time in Patent Office: 511 Days
• Field of Search: 250/237, 250/343, 250/345, 250/352, 128/719
• US Class Current: 250/343
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 3/36 Investigating two or more bands of a spectrum by separate detectors
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A transducer for nondispersive infrared gas analysis has heaters for the data and reference detectors to maintain the detectors at a selected temperature. A heater is also provided to heat the casing of an airway adapter associated with the transducer to a temperature high enough to keep condensation from forming. The detector unit is surrounded and electrostatically shielded by a boxlike component with barndoor extensions which are closed to shield the installed detector unit at that end of the shield through which the detector unit is installed. The detector unit, electrostatic shield, and a circuit board which carries power supply and preamplifier circuits are installed in the transducer housing which has separate end closures sealed thereto with a through fastener and internal guides for locating the shielded detector unit in the housing.

Claims

1. A transducer for non-dispersive infrared radiation gas analysis which comprises:

a detector unit which includes a detector for outputting a signal indicative of the concentration of a designated gas flowing through an airway adapter physically associated with the transducer;

means for so heating the detector as to keep it at a selected temperature and thereby eliminate detector temperature-related changes in the signal outputted by the detector;

means for heating the casing of an airway adapter associated with the transducer to a temperature high enough to keep condensation from forming and interfering with the operation of the detector; and

means for independently controlling the operation of the detector heating means and the airway adapter casing heating means so that the heating of said casing will not interfere with the temperature regulating supply of power to the detector.

2. A transducer as defined in claim 1 in which the detector unit comprises:

a housing;

reference and data detectors, said data detector being the detector which outputs the signal indicative of the concentration of the designated gas; and

detector supporting means for so supporting said detectors in said housing that said detectors can be maintained at the same, selected temperature, said detector supporting means comprising a monolithic, isothermal member fabricated of a material having a high coefficient of thermal conductivity.

3. A transducer as defined in claim 2 wherein the detector heating means includes means for heating both the reference and data detectors, said detector heating means including:

reference detector and data detector heaters supported from, and in conductive heat transfer relationship to, said detector supporting means; and

control means for regulating the flow of current through said heaters, said control means comprising a temperature responsive, current flow limiter in conductive heat transfer relationship to said detector supporting means.

4. A transducer as defined in claim 3 in which there are heater receiving recesses in the detector supporting means of the detector unit, said recesses being configured to complement the external configurations of the data and reference detector heaters.

5. A transducer as defined in claim 3 in which the reference detector heater is proximate to the reference detector and the data detector heater is proximate to the data detector.

6. A transducer as defined in claim 3 in which the detector heating means comprises a power supply for making operating voltage and biasing voltage respectively available at selected, precise levels to said detector heaters and to the reference and data detectors.

7. A transducer as defined in claim 6 in which the power supply includes an inverter so connected that biasing voltages of opposite polarity are supplied to opposite sides of the reference detector and the data detector.

8. A transducer as defined in claim 3 in which the detector supporting means is dimensioned and configured to direct thermal energy emitted from the reference detector and data detector heaters first past the reference and data detectors, then past the temperature responsive, current flow limiter, and then overboard from the detector supporting means.

9. A transducer as defined in claim 2 which includes detector heating means for heating the reference and data detectors, said detector heating means including:

a detector heater mounted in said detector supporting means in conductive heat transfer relationship to the supporting means and in equidistantly spaced relationship to the reference and data detectors; and

control means for so regulating the flow of current through the detector heater as to keep the detectors at the desired temperature, said control means comprising a temperature responsive current flow limiter in conductive heat flow relationship to the detector supporting means and in equidistantly spaced relationship to the reference and data detectors.

10. A transducer as defined in claim 2 in which the detector unit includes a beam splitting means for reflecting that energy in a beam impinging thereon and above a designated wavelength onto one of the detectors in that unit and for transmitting energy of a shorter wavelength from the same compass of the beam to the other of the detectors, said beam splitting means being supported from the detector supporting means midway between, and in mirror image relationship to, the reference and data detectors.

11. A transducer as defined in claim 10 in which:

the beam splitting means has front and back sides and a generally parallelepipedal configuration; and

the longitudinal axes of the detector heating means and the temperature responsive current limiter and the plane of symmetry between the sides of the beam splitter are in the same plane.

12. A transducer as defined in claim 2 in which:

the reference and data detectors of the detector unit have electrically conductive electrodes on their exposed surfaces;

the detector supporting means has detector receiving recesses in which the detectors are installed; and

the edges of the detector receiving recesses are spaced from the exposed surfaces to prevent shorting between the detectors and the detector supporting means.

13. A transducer as defined in claim 2 which comprises:

light trap means in the housing of the detector unit for keeping electromagnetic energy other than that making up a particular beam from reaching said reference and data detectors.

14. An transducer as defined in claim 13 in which:

the detector supporting means of the detector unit has first and second detector receiving recesses which open onto an exterior surface of the supporting means;

said reference detector and said data detector are respectively seated in said first and second recesses; and

said light trap means comprises means extending toward the axis of symmetry of the beam from said housing on those sides of the detector receiving recesses facing that aperture in the housing via which the of electromagnetic energy is admitted to interior of the housing.

15. A transducer as defined in claim 13:

which has a beam splitter for reflecting that electromagnetic energy in said beam which is above a selected wave length toward one of said detectors and for transmitting the remainder of the energy making up said beam to the other of the detectors, said beam splitter having a parallelepipedal configuration and being supported at one edge thereof from said detector supporting means; and

said light trap means is configured and dimensioned to support the opposite edge of the beam splitter.

16. A transducer as defined in claim 1 which comprises:

a housing; and

an electromagnetic shield in the housing of the transducer in surrounding relationship to said detector unit.

17. A transducer as defined in claim 16 in which:

the detector unit also comprises a printed circuit board assembled to said transducer housing; and

said electrostatic shield comprises means operable after said shield and said detector unit have been installed in the transducer housing to make an electrical connection between the shield and the backplane of the printed circuit board.

18. A transducer as defined in claim 17 in which the electrostatic shield has side walls and means at one end of the shield for closing that end thereby completing the shielding of said detector unit/printed circuit board assembly, the means at said one end of the shield comprising foldable extensions which are integral with said side walls at said one shield end.

19. A transducer as defined in claim 16 in which:

the transducer housing has a member with top, bottom, and side walls;

said transducer housing member has internal guides for spacing the electrostatic shield from the top, bottom, and side walls of the housing and for locating the shield lengthwise in the housing; and

said electrostatic shield has internal guides for positioning a detector unit in the shield.

20. A transducer as defined in claim 19 in which the housing also comprises:

first and second end closures configured to complement the housing member;

a seal between the housing member and each of the end closures; and

means for retaining the end closures, the seals, and the housing member in assembled relationship with the electrostatic shield and the detector unit installed therein, said retaining means comprising a fastener extending from the first end closure through that end closure and the housing member to the second end closure.

21. A transducer as defined in claim 1 in which:

said detector unit comprises;

a printed circuit board;

a housing mounted on the printed circuit board; and

a support in said housing, said detector, said detector heating means, and a temperature responsive current flow limiter being integrated with said support in conductive heat transfer relationship thereto; and

said printed circuit board has circuits for connecting said detector and said detector heating means to a power supply and for connecting the current flow limiter in controlling relationships to the power supply and the detector heating means.

22. A transducer as defined in claim 21 wherein:

said detector unit comprises a reference detector and a data detector;

the detector heating means comprises a reference detector heater and a data detector heater; and

the printed circuit board has circuits for connecting the reference and data detectors to the power supply and for connecting the temperature responsive current flow limiter to the power supply.

23. A transducer for non-dispersive electromagnetic radiation gas analysis which comprises:

a housing;

an electromagnetic energy detector unit in said housing; and

an electrostatic shield in said housing in surrounding relationship to said detector unit;

the detector unit comprising detector means in said housing and a printed circuit board assembled to said housing; and

said electrostatic shield comprising means operable after said shield and said detector unit have been installed in the transducer housing to make an electrical connection between the shield and the backplane of the printed circuit board.

24. A transducer as defined in claim 23 in which the electrostatic shield has side walls and means at one end of the shield for closing that end and thereby completing the shielding of said detector unit/printed circuit board assembly, the means at said one end of the shield comprising foldable extensions which are integral with said side walls at said one shield end.