Passive and active infrared analysis gas sensors and applicable multichannel detector assembles

• US 5,721,430 A
• Filed: 01/11/1996
• Issued: 02/24/1998
• Est. Priority Date: 04/13/1995
• Status: Expired due to Fees

• Current Assignee: Edwards Systems Technology, Inc.
• Original Assignee: Engelhard Sensor Technologies, Inc. (BASF SE)
• Inventors: Wong, Jacob Y.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US08/583,993
• Time in Patent Office: 775 Days
• Field of Search: 250/343, 250/339.13, 250/339.01, 250/339.02, 250/338.5
• US Class Current: 250/339.13
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques

Abstract

Multichannel infrared detector assemblies for use in the detection and monitoring of gas concentrations are provided. The detector assemblies include a detector housing having a port for receiving infrared radiation therethrough; a substrate mounted within the detector housing, the substrate having three apertures therein to transmit radiation entering the detector assembly therethrough; a first, a second and a third thermopile detector fabricated on the bottom side of the substrate, the hot junctions of each thermopile detector positioned over one of the apertures in the substrate so as to receive radiation transmitted through the aperture, and the cold junctions of each thermopile detector positioned over the substrate; a first interference bandpass filter mounted on the top side of the substrate so that the first filter covers the aperture above the first detector and the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first spectral band; a second interference bandpass filter mounted on the top side of the substrate so that the second filter covers the aperture above the second detector and the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a second spectral band; and a third interference bandpass filter mounted on the top side of the substrate so that the third filter covers the aperture above the third detector and the third filter is interposed between the port and the third detector, the third interference bandpass filter designed to pass radiation at a third spectral band. The disclosed infrared detector assemblies can be used in traditional NDIR gas sensors having an active source or in passive infrared analysis gas sensors which use a passive infrared temperature source and the space between the detector assembly and the source as the sample chamber.

Claims

1. An infrared detector assembly comprising:

a. a detector housing having a port for receiving infrared radiation therethrough;

b. a substrate mounted within the detector housing, the substrate having three apertures therein;

c. a first, a second and a third thermopile detector fabricated on the bottom side of the substrate, the hot junctions of each thermopile detector positioned over one of the apertures in the substrate so as to receive radiation transmitted through the aperture, and the cold junctions of each thermopile detector positioned over the substrate;

d. a first interference bandpass filter mounted on the top side of the substrate so that the first filter covers the aperture above the first detector and the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first spectral band;

e. a second interference bandpass filter mounted on the top side of the substrate so that the second filter covers the aperture above the second detector and the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a second spectral band; and

f. a third interference bandpass filter mounted on the top side of the substrate so that the third filter covers the aperture above the third detector and the third filter is interposed between the port and the third detector, the third interference bandpass filter designed to pass radiation at a third spectral band.

2. An infrared detector assembly according to claim 1, further comprising output leads extending through the detector housing and electrically connected to the first, second and third thermopile detectors.

3. An infrared detector assembly according to claim 2, wherein the substrate is comprised of a semiconductor material and the first, second and third thermopile detectors are selected from the group consisting of thin film thermopile detectors and micromachined thermopile detectors.

4. An infrared detector assembly according to claim 1, wherein the substrate is comprised of a semiconductor material and the first, second, and third thermopile detectors are micromachined thermopile detectors.

5. An infrared detector assembly according to claim 4, further comprising:

a. a signal processor fabricated on the substrate, the signal processor electrically connected to the first, second, and third thermopile detectors; and

b. leads extending through the detector housing and electrically connected to the signal processor.

6. An infrared detector assembly according to claim 1, wherein each of the first, second, and third infrared thermopile detectors is formed on an electrically insulating diaphragm that spans the aperture the detector is positioned over.

7. An infrared detector assembly according to claim 6, wherein the electrically insulating diaphragm is comprised of a plastic film.

8. An infrared detector assembly according to claim 7, wherein the plastic film is polyester.

9. An infrared detector assembly according to claim 6, wherein the electrically insulating diaphragm is comprised of an inorganic dielectric membrane selected from the group consisting of silicon oxide, silicon nitride, and a multilayer structure of silicon oxide and silicon nitride.

10. An infrared detector assembly according to claim 1, wherein the first, second, and third interference bandpass filters are bonded to the substrate using a thermally conductive material.

11. An infrared detector assembly according to claim 10, further comprising heat sink means to improve the thermal shunt between the substrate and the first, second, and third interference bandpass filters.

12. An infrared detector assembly according to claim 1, further comprising a light transmissive window mounted within the port.

13. An infrared detector assembly according to claim 12, wherein the substrate, filters, and detectors are hermetically sealed within the detector housing.

14. An infrared detector assembly comprising:

a. a detector housing having a port for receiving infrared radiation therethrough;

b. a semiconductor substrate mounted within the detector housing, the substrate having three apertures therein;

c. a dielectric membrane spanning each of the three apertures and formed on the bottom of the substrate;

d. a first, a second and a third thermopile detector, the hot junctions of each thermopile detector being formed over one of the apertures on the dielectric membrane spanning the aperture, and the cold junctions of each thermopile detector formed over the substrate;

e. a first interference bandpass filter mounted on the top side of the substrate so that the first filter covers the aperture above the first detector and the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first spectral band;

f. a second interference bandpass filter mounted on the top side of the substrate so that the second filter covers the aperture above the second detector and the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a second spectral band;

g. a third interference bandpass filter mounted on the top side of the substrate so that the third filter covers the aperture above the third detector and the third filter is interposed between the port and the third detector, the third interference bandpass filter designed to pass radiation at a third spectral band; and

h. leads extending through the detector housing and electrically connected to the first, second, and third thermopile detectors.

15. An infrared detector assembly according to claim 14, wherein the dielectric membrane is selected from the group consisting of silicon oxide, silicon nitride, and a multilayer structure of silicon oxide and silicon nitride.

16. An infrared detector assembly according to claim 14, further comprising a signal processor fabricated on the substrate, and wherein the first, second and third thermopile detectors are electrically connected to the signal processor and the leads are electrically connected to the signal processor.

17. An infrared detector assembly according to claim 14, wherein the first, second, and third interference bandpass filters are bonded to the substrate using a thermally conductive material.

18. An infrared detector assembly comprising:

a. a detector housing having a port for receiving infrared radiation therethrough;

b. a semiconductor substrate mounted within the detector housing, the substrate having three apertures therein and a raised rim on the top of the substrate surrounding each of the apertures;

c. a dielectric membrane spanning each of the three apertures and formed on the bottom of the substrate;

d. a first, a second and a third thin film thermopile detector, the hot junctions of each thermopile detector being formed over one of the apertures on the dielectric membrane spanning the aperture, and the cold junctions of each thermopile detector being formed over the substrate;

e. a first interference bandpass filter mounted on top of the raised rim surrounding the aperture the first detector is formed over so that the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first spectral band;

f. a second interference bandpass filter mounted on top of the raised rim surrounding the aperture the second detector is formed over so that the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a second spectral band; and

g. a third interference bandpass filter mounted on top of the raised rim surrounding the aperture the third detector is formed over so that the third filter is interposed between the port and the third detector, the third interference bandpass filter designed to pass radiation at a third spectral band.

19. An infrared detector assembly according to claim 18, further comprising an active infrared light source operatively mounted within the detector assembly.

20. An infrared detector assembly according to claim 19, wherein the dielectric membrane is selected from the group consisting of silicon oxide, silicon nitride, and a multilayer structure of silicon oxide and silicon nitride.

21. An infrared detector assembly according to claim 19, further comprising output leads extending through the detector housing and electrically connected to the first, second and third thermopile detectors.

22. An infrared detector assembly according to claim 19, further comprising:

a. a signal processor fabricated on the substrate, the signal processor being electrically connected to the thermopile detectors; and

b. leads extending through the detector housing and electrically connected to the signal processor.

23. An infrared detector assembly according to claim 19, wherein the first, second, and third interference bandpass filters are bonded to the substrate using a thermally conductive material.

24. An infrared detector assembly according to claim 19, wherein the active infrared light source comprises a tungsten filament.

25. A passive source infrared gas sensor, comprising:

a. a detector housing having a port for receiving infrared radiation therethrough;

b. a substrate mounted within the detector housing, the substrate having three apertures therein;

c. a first, a second and a third thermopile detector fabricated on the bottom side of the substrate, the hot junctions of each thermopile detector positioned over one of the apertures in the substrate so as to receive radiation transmitted through the aperture, and the cold junctions of each thermopile detector positioned over the substrate;

d. a first interference bandpass filter mounted on the top side of the substrate so that the first filter covers the aperture above the first detector and the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first non-neutral spectral band which is absorbable by a preselected gas to be monitored;

e. a second interference bandpass filter mounted on the top side of the substrate so that the second filter covers the aperture above the second detector and the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a first neutral spectral band;

f. a third interference bandpass filter mounted on the top side of the substrate so that the third filter covers the aperture above the third detector and the third filter is interposed between the port and the third detector, the third interference bandpass filter designed to pass radiation at a second neutral spectral band; and

g. signal processing circuitry connected to the electrical outputs produced by the first, second, and third detectors for producing a signal in response thereto representative of the concentration of the gas being measured.

26. A passive source infrared gas sensor according to claim 25, wherein the gas being monitored is at least one selected from the group consisting of CO, CO₂, H₂ O, and TVOC.

27. A passive source infrared gas sensor according to claim 25, wherein the first, second, and third bandpass filters are about 0.1 μ

m wide at FWHM.

28. A passive source infrared gas sensor according to claim 27, wherein the second and third bandpass filters have a center wavelength selected from the group consisting of 3.91 μ

m, 5.00 μ

m, and 9.00 μ

m.

29. A passive source infrared gas sensor according to claim 28, wherein the first bandpass filter has a center wavelength selected from the group consisting of about 4.26 μ

m and about 4.67 μ

m.

30. An infrared gas sensor, comprising:

a. a detector housing having a port for receiving infrared radiation therethrough;

b. a substrate mounted within the detector housing, the substrate having three apertures therein;

c. a first, a second and a third thermopile detector fabricated on the bottom side of the substrate, the hot junctions of each thermopile detector positioned over one of the apertures in the substrate so as to receive radiation transmitted through the aperture, and the cold junctions of each thermopile detector positioned over the substrate;

d. a first interference bandpass filter mounted on the top side of the substrate so that the first filter covers the aperture above the first detector and the first filter is interposed between the port and the first detector, the first interference bandpass filter designed to pass incident radiation at a first spectral band;

e. a second interference bandpass filter mounted on the top side of the substrate so that the second filter covers the aperture above the second detector and the second filter is interposed between the port and the second detector, the second interference bandpass filter designed to pass radiation at a second spectral band;

f. a third interference bandpass filter mounted on the top side of the substrate so that the third filter covers the aperture above the third detector and the third filter is interposed between the port and tile third detector, the third interference bandpass filter designed to pass radiation at a third spectral band;

g. an active infrared light source operatively mounted within the detector assembly;

h. a source driver electrically connected to the active infrared source for driving the active infrared light source at a predetermined frequency; and

i. signal processing circuitry connected to the electrical outputs produced by the first, second, and third detectors for producing a signal in response thereto representative of the concentration of at least one gas being monitored.

31. An infrared gas sensor according to claim 30, wherein the gas being monitored is at least one selected from the group consisting of CO, CO₂, H₂ O, and TVOC.

32. An infrared gas sensor according to claim 30, wherein the first, second, and third bandpass filters are about 0.1 μ

m wide at FWHM.

33. An infrared gas sensor according to claim 32, wherein the second and third bandpass filters have a center wavelength selected from the group consisting of 3.91 μ

m, 5.00 μ

m, and 9.00 μ

m.

34. An infrared gas sensor according to claim 33, wherein the first bandpass filter has a center wavelength selected from the group consisting of about 4.26 μ

m and about 4.67 μ

m.

35. A passive source infrared gas sensor, comprising:

a passive infrared source comprising an infrared black surface;

b. a three channel infrared detector assembly centered in the passive infrared source, the detector assembly having a port for receiving infrared radiation therethrough; and

c. a concave mirror facing the port of the detector assembly and the infrared black surface, the concave mirror being positioned such that radiation emitted from the passive infrared source is reflected from the mirror into the port.

36. A passive source infrared gas detector according to claim 35, wherein the infrared black surface comprises a material selected from the group consisting of black chrome oxide, bismuth oxide and carbon black.

37. A passive source infrared gas detector according to claim 35, wherein the passive infrared source comprises a concave infrared black surface.

38. A passive source infrared gas detector according to claim 35, wherein the three channel detector assembly comprises three infrared thermopile detectors and three interference bandpass filters, each filter being disposed in the optical path between the passive infrared source and one of the thermopile detectors.