Infrared method and apparatus for measuring gas concentration of a plurality of component gases in a sample
An automatic calibration technique for a gas analyzer includes applying electrical energy to a source that is different from the level used to detect gas concentration in order to produce a different level of radiation from that used to detect gas concentration. The reduced level is applied with a non-absorbing gas in the gas sample chamber. The detector output at the reduced level is resolved to a calibration factor. The instrument can be linearized by repeating the calibration procedure at multiple different levels of reduced source radiation. In one embodiment, a source assembly is provided that includes a plurality of infrared emitters to which is applied modulated electrical energy in a timed sequence in order to produce output levels for three component gas concentrations. A filter between each one of the sources and a detector pass radiation at an absorption line of one of the component gases.
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Claims
4. The infrared gas analyzer in claim 1 wherein each of said plurality of filters correspond with an absorption line of an exhaust gas emitted from a vehicle engine.
5. The infrared gas analyzer in claim 1 wherein said at least one detector is a single detector.
6. The infrared gas analyzer in claim 1 wherein said at least one detector includes a separate detector for each of said plurality of infrared emitters.
7. The infrared gas analyzer in claim 1 wherein said at least one digital-to-analog converter includes a separate digital-to-analog converter for each of said plurality of infrared emitters..Iadd.8. The infrared gas analyzer in claim 1 wherein said computer energizes each of said plurality of infrared emitters at a pulse repetition rate of approximately 1/N where N is the number of said plurality of infrared emitters..Iaddend..Iadd.9. An infrared gas analyzer for detecting a plurality of component gases in a sample, comprising:
- a sample chamber having opposite ends thereof;
- a source assembly having at least one infrared emitter at one of said opposite ends and at least one detector at the other of said opposite ends, said at least one emitter being a lamp made up of a filament in an evacuated chamber;
- at least one of said at least one infrared emitter and said at least one detector comprising a plurality thereof defining a plurality of radiation pathways between said at least one infrared emitter and said at least one detector;
- a plurality of filters in said sample chamber, each in one of said radiation pathways and passing radiation at an absorption line of one of the plurality of component gases;
- a digital computer;
- at least one digital-to-analog converter having a digital input connected with said digital computer and having an analog output connected with said at least one, infrared emitter; and
- at least one analog-to-digital converter having an analog input connected with said at least one detector and a digital output connected with said digital computer:
- wherein said computer energizes said at least one infrared emitter in time-division multiplexed sequence by supplying digital signals sequentially to said at least one digital-to-analog converter in order to sequentially apply electrical energy to said at least one infrared emitter at energy levels determined by the values of said digital signals including pulsing said at least one infrared emitter between energized and
non-energized conditions..Iaddend..Iadd.10. The infrared gas analyzer in claim 9 in which said detector output is a linear function of energy applied to said at least one infrared emitter..Iaddend..Iadd.11. The infrared gas analyzer in claim 9 wherein each of said plurality of filters correspond with an absorption line of an exhaust gas emitted from a vehicle engine..Iaddend..Iadd.12. The infrared gas analyzer in claim 9 wherein said at least one detector is a single detector..Iaddend..Iadd.13. The infrared gas analyzer in claim 9 wherein said at least one detector includes a separate detector for each said at least one
infrared emitter..Iaddend..Iadd.14. The infrared gas analyzer in claim 9 wherein said at least one digital-to-analog converter includes a separate digital-to-analog converter for each said at least one infrared emitter..Iaddend..Iadd.15. The infrared gas analyzer in claim 9 wherein said computer energizes said at least one emitter at a pulse reptition rate of approximately 1/N where N is the number of said at least one emitter..Iaddend..Iadd.16. An infrared gas analyzer for detecting a plurality of component gases in a sample, comprising:
- a sample chamber having opposite ends thereof;
- a source assembly having at least one infrared emitter at one of said opposite ends and at least one detector at the other of said opposite ends;
- at least one of said at least one infrared emitter and said at least one detector comprising a plurality thereof defining a plurality of radiation pathways between said at least one infrared emitter and said at least one detector;
- a plurality of filters in said sample chamber, each in one of said radiation pathways and passing radiation at an absorption line of one of the plurality of component gases;
- a digital computer;
- at least one digital-to-analog converter having a digital input connected with said digital computer and having an analog output connected with said at least one infrared emitter; and
- at least one analog-to-digital converter having an analog input connected with said at least one detector and a digital output connected with said digital computer;
- wherein said computer energizes said at least one infrared emitter in time-division multiplexed sequence by supplying digital signals sequentially to said at least one digital-to-analog converter in order to sequentially apply electrical energy to said at least one infrared emitter at energy levels determined by the values of said digital signals;
- wherein said computer reduces the level of electrical energy applied to said at least one infrared emitter, with a gas in said sample chamber that is non-absorbent of radiation of said absorption line of each of said plurality of gases, in order to determine a calibration factor for each of
said plurality of gases..Iaddend..Iadd.17. An infrared gas analyzer for detecting at least one component gas in a sample, comprising:
- a sample chamber having opposite ends thereof;
- a source assembly having at least one infrared emitter at one of said opposite ends and at least one detector at the other of said opposite ends, said at least one emitter being a lamp made up of a filament in an evacuated chamber;
- at least one filter in said sample chamber between said at least one emitter and said at least one detector and passing radiation at an absorption line of one component gas;
- a digital computer;
- at least one digital-to-analog converter having a digital input connected with said digital computer and having an analog output connected with said at least one infrared emitter; and
- at least one analog-to-digital converter having an analog input connected with said at least one detector and a digital output connected with said digital computer;
- wherein said computer energizes said at least one infrared emitter by supplying at least one digital signal to said at least one digital-to-analog converter in order to apply electrical energy to said at least one infrared emitter at at least one energy level determined by the value of said at least one digital signal including pulsing said at least one infrared emitter between energized and non-energized conditions..Iaddend..Iadd.18. The infrared gas analyzer in claim 17 in which said detector output is a linear function of energy applied to said at least one infrared emitter..Iaddend..Iadd.19. The infrared gas analyzer in claim 17 wherein said at least one filter corresponds with an absorption line of an exhaust gas emitted from a vehicle engine..Iaddend..Iadd.20. The infrared gas analyzer in claim 17 wherein said at least one detector is a single detector..Iaddend..Iadd.21. The infrared gas analyzer in claim 17 wherein said at least one detector includes a separate detector
for each said at least one infrared emitter..Iaddend..Iadd.22. The infrared gas analyzer in claim 17 wherein said at least one digital-to-analog converter includes a separate digital-to-analog converter for each said infrared emitter..Iaddend..Iadd.23. The infrared gas analyzer in claim 17 wherein said computer energizes said at least one emitter at a pulse repetition rate of approximately 1/N where N is the
number of said at least one emitter..Iaddend..Iadd.24. An infrared gas analyzer for detecting at least one component gas in a sample, comprising:
- a sample chamber having opposite ends thereof;
- a source assembly having at least one infrared emitter at one of said opposite ends and at least one detector at the other of said opposite ends;
- at least one filter in said same chamber between said at least one emitter and said at least one detector and passing radiation at an absorption line of one component gas;
- a digital computer;
- at least one digital-to-analog converter having a digital input connected with said digital computer and having an analog output connected said at least one infrared emitter; and
- at least one analog-to-digital converter having an analog input connected with said at least one detector and a digital output connected with said digital computer;
- wherein said computer applies electrical energy to said at least one infrared emitter by supplying at least one digital signal to said at least one digital-to-analog converter in order to apply electrical energy to said at least one infrared emitter at at least one energy level determined by the value of said at least one digital signal;
- wherein said computer reduces the level of electrical energy applied to said at least one infrared emitter, with a gas in said sample chamber that is non-absorbent of radiation at said absorption line of said gas, in order to determine a calibration factor for each said gas..Iaddend.
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Type: Grant
Filed: Aug 26, 1997
Date of Patent: Aug 24, 1999
Assignee: Sensors, Inc. (Saline, MI)
Inventors: Karl H. Black, deceased (late of Dexter, MI), Walter I. Armstrong (Saline, MI)
Primary Examiner: Constantine Hannaher
Law Firm: Van Dyke, Gardner, Linn & Burkhart, LLP
Application Number: 8/920,074
International Classification: G01N 2161;