Gas detectors and gas analyzers utilizing spectral absorption

• US 4,746,218 A
• Filed: 09/05/1986
• Issued: 05/24/1988
• Est. Priority Date: 06/12/1984
• Status: Expired due to Term

• Current Assignee: David Padilla, Martha Nungaray-Silva, Syconex Corp.
• Original Assignee: Syconex Corp.
• Inventors: Lord, Harry C. III
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US06/904,163
• Time in Patent Office: 627 Days
• Field of Search: 356/51, 356/414, 356/416, 356/418, 356/419, 356/437, 250/338 GA, 250/339, 250/343, 250/347
• US Class Current: 356/437
• CPC Class Codes: G01N 21/031 Multipass arrangements
• CPC Class Codes: G01N 21/3518 Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
• CPC Class Codes: G01N 2201/0231 Thermostating

Abstract

Instrumentation to detect the presence of, or to measure the concentration of, a gas or pollutant in a gaseous environment. With the use of gas filter correlation techniques and energy beams having suitable wavelengths, the presence and concentrations of these can be detected and measured, not only in flowing streams such as in exhaust stacks, but above a ground area and around its perimeter. A calibration means using a retrodirective reflector is also shown.

Claims

1. In an instrument for detecting the presence of, or for measuring the concentration of a gas in a stream of other gases, utilizing a beam of spectral energy which has passed through or emanated from at least some part of said stream, an analyzer comprising:

a plurality of nararow band pass filter means;

an initial reflector;

a rotatable deflector, comprising a pair of deflecting reflectors rotatably carried by it, said deflecting reflectors forming an angle with one another, the center of rotation of said deflector lying inside said angle;

means for rotating said deflector;

a spectral source or a spectral detector, said filter means, initial reflector, rotatable deflector and source or detector being fixedly located relative to one another such that fixed beam segments of said beam are formed between the initial reflector and the rotatable deflector, and between the rotatable deflector and the source or detector, and an angularly movable beam segment of said beam is formed between each of the deflecting reflectors of the rotatable deflector and the locus of said filter means which movable beam segments can be moved from filter means to filter means as the consequence of rotation of the rotatable deflector, a first of said movable beam segments extending from one of said deflecting reflectors to said locus, and the other of said movable beam segments extending from the said locus to the other of said deflecting reflectors; and

reflecting means adjacent to each said filter means for reflecting the beam from one of said deflecting reflections movable beam segments to the other, after the beam has passed through the respective filter means at least once.

2. Apparatus according to claim 1 in which said plurality of filter means includes filter means for correlation, reference, and calibration

3. Apparatus according to claim 1 in which a narrow band pass filter is disposed in said beam to limit wavelengths impinging on said detector to those of interest to the subject gas.

4. In combination:

apparatus according to claim 1; and

means for directing a beam through a gas stream, said means receiving said beam from said analyzer, or directing it to said initial reflector, and whichever of said source or detector is not carried by said analyzer disposed on said beam spaced from said analyzer.

5. A combination according to claim 4 in which said detector, filter means, reflector, reflecting means and rotatable deflector are fixedly mounted to common structure, and in which said beam is passed twice through said gas stream.

6. A combination according to claim 4 in which a separate calibration beam path is provided from said source to said deflector to provide a beam to or from said analyzer which does not pass through the gas stream.

7. A combination according to claim 6 in which said plurality of filter means includes filter means for correlation, reference, and calibration.

8. In an instrument for detecting the presence of, or for measuring the concentration of a gas in a stream of other gases, utilizing spectral energy which has passed through or emanated from at least some part of said stream;

an analyzer comprising a plurality of narrow band pass filter means through which a beam of said energy is to be passed;

beam forwarding means to direct an energy beam through or from said stream to said analyzer, said beam being fixed as it enters said analyzer; and

means in said analyzer to cause said beam to encounter selected ones of said filter means;

said beam forming forwarding means comprising a pair of axially spaced apart Cassegrainean reflecting systems.

9. In an instrument for detecting the presence of, or for measuring the concentration of a gas in a stream of other gases, utilizing spectral energy which has passed through or emanated from at least some part of said stream;

an analyzer comprising a plurality of filter means through which a beam of said energy is to be passed;

beam forwarding means to direct an energy beam through or from said stream to said analyzer, said beam being fixed as it enters said analyzer; and

means in said analyzer to cause said beam to encounter selected ones of said filter means;

said beam forwarding means comprising a two-element mirror, a focal mirror, and a Cassegrainean mirror so disposed and arranged that one element of said two element mirror and one half of said focal mirror and of said Cassegrainean mirror occupying substantially an entire half-tubular path, a single retrodirective reflector in said half-tubular path which returns and rotates by 180 degrees the entire energy beam which it receives, and directs it to the other one half of the Cassegrainean mirror, which reflects it to the other half of the focal mirror and the other element of the two-element mirror, which in turn forwards the energy beam to the analyzer as said fixed beam.

10. In an instrument for detecting the presence of, or for measuring the concentration of a gas in a stream of other gases, utilizing spectral energy which has passed through or emanated from at least some part of said stream;

an analyzer comprising a plurality of filter means through which a beam of said energy is to be passed;

beam forwarding means to direct an energy beam through or from said stream to said analyzer, said beam being fixed as it enters said analyzer; and

means in said analyzer to cause said beam to encounter selected ones of said filter means;

said plurality of filter means includes a correlation filter, a reference filter, and a calibration filter.

11. Apparatus according to claim 10 in which at least some of said filter means are optical narrow band filters, one of which passes only wavelengths pertinent to the absorption lines of the subject gas, and another filter which passes only wavelengths near to, but not including, the foregoing.

12. Apparatus according to claim 10 in which said apparatus includes an optical narrow band pass filter which includes wavelengths not included within the absorption spectra of the gases, and nearby wavelengths.

13. Apparatus according to claim 12 in which said beam forwarding means includes a single retroreflector to return and rotate an entire beam which has passed through the gas stream.

14. Apparatus according to claim 10 in which said beam forwarding means includes a single retroreflector to return and rotate an entire beam which has not passed through the gas stream, said retroreflector being mounted for selective insertion into and removal from the path of the beam.

15. Apparatus according to claim 14 in which another single reflector is placed in the beam so as to rotate and return an entire bam which has passed through the gas stream.

16. A surveillance system for detecting the presence of, or measuring the concentration of, a gas in a stream of other gases, utilizing spectral energy which has passed through or emanated from at least part of said stream, comprising an instrument according to claim 10 whose beam tracks through said stream and which is analyzed by said instrument for purposes of said detection or measurement.

17. A surveillance system according to claim 16 in which the path of said beam is closed, whereby to form the perimeter of an area whose emanations are of concern as evidenced by the presence of concentration of said subject gas along said perimeter.

18. A surveillance system according to claim 17 in which said path includes plurality of reflecting means to deflect the beam in said closed path.

19. A surveillance system according to claim 16 in which said path is linear, and includes reflecting means to return said beam along its initial path.

20. A surveillance system according to claim 19 in which said beam comprises a barrier responding to the presence or concentration of said subject gas.