Gas analyzing

• US 4,008,394 A
• Filed: 06/28/1973
• Issued: 02/15/1977
• Est. Priority Date: 06/28/1973
• Status: Expired due to Term

• Current Assignee: Sensors, Inc.
• Original Assignee: Sensors, Inc.
• Inventors: Arnold, Charles B., Risgin, Ojars
• Primary Examiner(s): Borchelt, Archie R.
• Assistant Examiner(s): Anderson, B. C.
• Application Number:
  US05/374,553
• Time in Patent Office: 1,328 Days
• Field of Search: 250/343, 250/344, 250/345, 356/246
• US Class Current: 250/345
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

Dual-beam comparison of gas absorption characteristics in which a single source and single detector of radiant energy and single chopper disc are used in sample gas and reference gas paths. Ambient atmosphere or gas directed through a sample gas chamber can be analyzed. Multiple gas analyses, of a plurality of gases or a plurality of constituents of a gas, can be performed simultaneously utilizing the single chopper disc with a plurality of optical gas assemblies. Each such assembly includes a single source of radiant energy, means for directing the radiant energy along sample and reference gas paths to a single detector for such radiant energy. The multiple units are mounted so that the single chopper disc cyclically interrupts radiant energy in the respective sample and reference gas paths in predetermined phase relationship. The combined sample gas and reference gas path response of the single detector for each gas analyzing unit is directed to phase-sensitive signal-separation circuit means. The single chopper disc is also used to generate phase reference signals for gating the phase-sensitive signal separation circuit means to produce a voltage output for the sample and reference gas paths, V_s and V_r, respectively. An automatic gain control function, to eliminate or minimize variations in source intensity, detector characteristics, and circuit components influencing both gas paths equally, is provided by electronic ratio circuit means or feedback circuit means.

Claims

1. Gas analyzing structure for use in simultaneously performing multiple gas anaylses comprising

frame means supporting a plurality of individual optical gas analysis assemblies located to dispose portions of each such assembly along an arcuate path,

each such assembly of said plurality of assemblies including a single source of radiant energy, a single radiant energy detector having an electrical output, means for directing the radiant energy from the single source for passage along a sample gas and a reference gas path, and means for directing such radiant energy after passage along the reference gas and sample gas paths to the single detector for such radiant energy,

means for predetermined cyclic interruption of radiant energy in the sample and reference gas paths of each such assembly including a single chopper disc rotatable about a fixed central axis located in predetermined positional relationship to the arcuate path disposition of gas analysis assemblies,

the chopper disc including a plurality of windows predeterminedly spaced radially from the fixed central axis with a portion of the windows being spaced from the central axis a predetermined distance to permit passage of radiant energy in the sample gas path and a portion of the windows being spaced radially from the central axis to permit passage of radiant energy in the reference gas path of each optical gas analyzer assembly upon rotation of the chopper disc about the fixed central axis, and

said radiant energy detector of each of said assemblies being adapted to be connected to circuitry for processing the electrical output of a detector.

2. The structure of claim 1 in which the predetermined arcuate path of disposition of the portion of each optical gas analysis assembly is along a substantially circumferential path about the fixed central axis, and further including

drive means for rotating the chopper disc.

3. The structure of claim 1 including in combination

phase reference signal generating means on said frame means and responsive to rotation of the single chopper disc for generating electrical phase reference output in predetermined synchronous relationship with cyclic interruption of radiant energy in the sample and reference gas paths.

4. The combination of claim 3 further including

circuit means connected to the detector of each optical gas analysis assembly for providing phase-sensitive separation of the electrical output from the single detector in each such optical assembly into electrical signals indicative of radiant energy passage in the sample and reference gas paths, and

means connecting the output of the phase reference signal generating means to the circuit means providing the phase-sensitive separation of the electrical output of the detector in such gas analysis assembly.

5. The device of claim 1 in which the sample and reference gas paths are defined by cell structure with divider means separating the cell structure into a sample gas chamber and a reference gas chamber, such chambers being in contiguous aligned relationship extending longitudinally between the single source of radiant energy and the single detector for such radiant energy.

6. The structure of claim 1 in which the single source of radiant energy comprises an infrared source and the single detector comprises an infrared detector.

7. The structure of claim 6 including

filter means for selective passage of infrared radiation in both the reference and sample gas paths of at least one of the gas analysis assemblies, said filter means having common infrared transmitting characteristics.

8. The device of claim 6 in which at least one of the optical gas analysis assemblies includes

selective frequency filters for infrared energy, such selective frequency filters defining the sample and reference gas paths such that ambient gas being analyzed flows in the space between the single infrared source and the single infrared detector of such assembly.

9. The device of claim 1 in which at least one of the optical gas analysis systems includes a reference gas chamber extending longitudinally between the source and detector so as to define the reference gas path, and

the sample gas path is open for analysis of ambient atmosphere between the source and detector.

10. Gas analyzing apparatus providing sample and reference gas path comparison data comprising

single source means for radiant energy to be absorbed by the gas under analysis,

means for directing such radiant energy from the single source means along a sample gas path and a reference gas path,

chopper disc means located in the sample and reference gas paths providing predetermined cyclic interruption of radiant energy in each such path,

synchronizing means cyclically actuated by the chopper disc means to generate electrical output in predetermined phase relationship with passage of radiant energy in the sample gas path and in the reference gas path,

single detector means positioned to receive radiant energy from each such path after cyclic interruption and to generate electrical output responsive to the radiant energy passage along both the sample and reference gas paths,

circuit means electrically connected to the single detector means,

such circuit means including a separate electrical channel means for the sample gas path and for the reference gas path,

each such separate electrical channel means including amplifier means,

each such amplifier means having input juncture means and output juncture means,

the circuit means electrically connected to the single detector means further including phase-sensitive circuit means for each electrical channel means,

each such phase-sensitive circuit means including an electrical gating device actuated by the electrical output of the synchronizing means of its respective gas path in predetermined phase relationship to actuation of the gating device in the remaining gas path to gate signals from the detector means to the amplifier means along a predetermined path,

each said gating device being connected to the input juncture means of its respective electrical channel amplifier means to define one electrical path from the detector means to such amplifier means,

each such electrical channel means including an additional electrical path from the detector means to the input juncture means of its respective amplifier means such that each channel amplifier means operates responsively to sample and reference gas path signals with the result that

the sample gas path electrical channel means combines sample path gating device signals and the additional electrical path signals at the channel amplifier means to effectively eliminate reference gas path detector output signals to produce a signal, V_s, indicative of the signal generated by the detector as a result of radiant energy passage along the sample gas path, and

the reference gas path channel combines reference gas path gating device signals and the additional electrical path signals at its channel amplifier means to effectively eliminate sample gas path detector output signals to produce a signal, V_r, indicative of the signal generated by the detector as a result of radiant energy passing along the reference path,

said V_s and V_r signal appearing at the output juncture means of the respective amplifier means, means connected to the output juncture means of the amplifier means for averaging respective V_s and V_r signals,

and output circuit means for producing an output representative of a comparison of the passage of radiant energy through the reference gas and the sample gas paths.

11. The gas analyzing apparatus of claim 10 in which the output circuit means includes

means for determining the algebraic difference between V_s and V_r.

12. The gas analyzing apparatus of claim 10 in which the output circuit means includes

electronic ratio means providing an automatic gain control function to compensate for variations in the intensity of the radiant energy source, attenuation in the optical path, and component variations.

13. The gas analyzing apparatus of claim 12 in which the electronic ratio means provides a ratio based on the values of V_s and V_r.

14. The gas analyzing apparatus of claim 12 in which the electronic ratio means provides a ratio based on the values (V_s - V_r) and V_r.

15. The gas analyzing apparatus of claim 12 in which the electronic ratio means provides a ratio based on the values (V_s - V_r) and (V_s + V_r).

16. The gas analyzing apparatus of claim 10 further including

feedback means connected to an output of the electrical channel means for the reference gas path, and

means connecting the feedback means to the circuit means electrically connected to the single detector means to provide automatic gain control to compensate for variation source intensity, attenuation in the optical path, and component variations which influence both gas paths equally.

17. The gas analyzing apparatus of claim 10 in which the synchronizing means includes

a light-sensitive device for producing synchronizing signals in synchronism with the cyclic interruption of radiant energy for each gas path,

bistable latch means for each light-sensitive device for shaping output signals of such devices,

symmetrical circuit means connecting the light-sensitive device of each gas path to its bistable latch means,

the bistable latch means each having dual outputs in negative symmetry, and

means for connecting one output of each bistable latch means to the gating device of its corresponding electrical channel means.

18. The gas analyzing apparatus of claim 10 in which the synchronizing means includes

first and second light sensitive devices,

shaping circuit means connected to each light-sensitive device for shaping output signals of such devices,

circuit means for switching such shaping circuit means in response to a change in illumination of its light-sensitive device,

window means in the chopper disc for chopping the sample gas path, and

window means in the chopper disc for chopping the reference gas path,

means mounting one of the light-sensitive devices adjacent to the travel path of the window means for the sample gas path,

means mounting the other light sensitive device adjacent the travel path of the window means for the reference gas path,

said light sensitive devices being in spaced relation to the sample and reference gas paths,

such shaping circuit means connected to one light-sensitive device gating the gating device of one electrical channel means "ON" in response to illumination received by its light-sensitive device, and

such shaping circuit means connected to the other light sensitive device gating the gating device of the other electrical channel "OFF" in response to illumination received by its light-sensitive device.