NONDISPERSIVE INFRARED GAS ANALYZER EMPLOYING SOLID STATE EMITTERS AND PHOTODETECTORS

• US 3,734,631 A
• Filed: 05/28/1971
• Issued: 05/22/1973
• Est. Priority Date: 05/28/1971
• Status: Expired due to Term

• Current Assignee: Egon E. Loebner, Gregory Justice
• Original Assignee: Egon E. Loebner, Gregory Justice
• Inventors: Justice, Gregory, Loebner, Egon E.
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): McGraw, V. P.
• Application Number:
  US05/147,788
• Time in Patent Office: 725 Days
• Field of Search: 250/43.5R,220 356/51,74,88,93,95,205
• US Class Current: 356/434
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A nondispersive infrared gas analyzer employing a pair of solid state radiation emitters and a pair of solid state photoconductors is arranged in an optoelectronic network comprising two branches, each branch including a separate optical radiation beam, both beams passing through the sample. The spectrum of one beam is such that the detected radiation from that beam is substantially independent of the concentration of the absorbent to be measured, the detected radiation of the other beam thereby being differentially modulated relative to that of the first beam by the absorbent under analysis. Means are provided including said photoconductors for converting the differential modulation into an output signal indication of the concentration of the absorbents. One embodiment employs a selective radiation source stage and another embodiment employs a selective detector stage. Control circuits are employed for regulating the relative radiation fluxes in the two branches of the networks. Additional control circuits are used for controlling the absolute amplitude of the fluxes in the two branches of the network.

Claims

1. A nondispersive optical radiation analyzer for measuring the concentration of a specific absorbent in a sample, said analyzer comprising:

source means for providing a first optical radiation beam and a second optical radiation beam, both beams passing through the sample;

detection means for independently detecting radiation of the two beams after they have passed through the sample, the detected radiation of the first beam being substantially independent of the concentration of the specific absorbent in the sample and the detected radiation of the second beam being modified by the specific absorbent in the sample, the detection means providing an electrical output signal indicative of the first beam and an electrical output signal indicative of the modified second beam;

first optoelectronic control means for controlling the level of the electrical output signal indicative of the second beam relative to the level of the electrical output signal indicative of the first beam;

electronic modulating means for electronically modulating the beams provided by the source means; and

electronic output means for electronically demodulating the electrical output signals from the detection means and for providing an output indication of the modified second beam relative to the first beam to obtain a measure of the concentration of the specific absorbent in the sample.

2. An analyzer as in claim 1 including second optoelectronic control means for controlling the absolute amplitude of the fluxes in the two beams.

3. An analyzer as in claim 1 wherein said electronic modulating means comprises a time multiplexing circuit.

4. An analyzer as in claim 1 wherein said electronic modulating means comprises a frequency multiplexing circuit.

5. An analyzer as in claim 1 wherein:

said source means comprises a pair of solid state radiation emitters;

said detection means comprises a solid state radiation detector positioned to intercept the two beams after passage through the sample; and

said first optoelectronic control means comprises another solid state radiation detector positioned to sample the radiation of the two beams before passage through the sample.

6. An analyzer as in claim 5 including second optoelectronic control means for controlling the absolute amplitude of the fluxes in the two beams.

7. An analyzer as in claim 5 wherein said electronic modulating means comprises a time multiplexing circuit.

8. An analyzer as in claim 5 wherein said electronic modulating means comprises a frequency multiplexing circuit.

9. An analyzer as in claim 6 wherein a quantity of the specific absorbent is positioned so that the first beam passes therethrough, the spectrum of the first beam being selectively absorbed thereby before passing through the sample.

10. An analyzer as in claim 9 including second optoelectronic control means for controlling the absolute amplitude of the fluxes in the two beams.

11. An analyzer as in claim 10 wherein said electronic modulating means comprises a time multiplexing circuit.

12. An analyzer as in claim 1 wherein:

said source means comprises a first solid state emitter;

said detection means comprises a first solid state radiation detector positioned to intercept the first beam and a second solid state radiation detector positioned to intercept the second beam; and

said first optoelectronic control means comprises a second solid state radiation emitter positioned to direct radiation onto the first and second solid state radiation detectors without passing through the sample.

13. An analyzer as in claim 12 wherein a quantity of the specific absorbent is positioned so that after passing through the sample the first beam then passes through this quantity of the specific absorbent before impinging on the first solid state radiation detector.

14. An analyzer as in claim 12 including second optoelectronic control means for controlling the absolute amplitude of the fluxes in the two beams.

15. An analyzer as in claim 14 wherein said electronic modulating means comprises a time multiplexing circuit.

16. An analyzer as in claim 15 wherein said first and second solid state radiation detectors have spectral responses that track each other with changes in ambient conditions.