INFRARED TWO GAS ANALYZER

• US 3,735,127 A
• Filed: 09/15/1971
• Issued: 05/22/1973
• Est. Priority Date: 09/15/1971
• Status: Expired due to Term

• Current Assignee: Robert W. Astheimer
• Original Assignee: Robert W. Astheimer
• Inventors: Astheimer, Robert W.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Church, C. E.
• Application Number:
  US05/180,583
• Time in Patent Office: 615 Days
• Field of Search: 250/43.5R
• US Class Current: 250/346
• CPC Class Codes: F02D 41/1451 the sensor being an optical sensor
• CPC Class Codes: G01N 21/314 with comparison of measurements at specific and non-specific wavelengths dual wavelength spectrometry G01J3/427
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis

Abstract

A radiation absorption analyzer is disclosed for the measurement of two gases in a gas sample being analyzed utilizing the same equipment, and for simultaneous measurement of the two gases with some duplication in the electronic processing. A source of infrared radiation is applied through a sample or absorption cell containing the gas to be measured, and through a rotating optical filter wheel onto an infrared detector. The filter wheel contains two analytic filters passing absorption regions of the gases desired to be measured, and two reference filters in nonabsorbing regions. Two reference pickups are utilized, which generate two signals as the filter wheel rotates, which are out of phase with each other by 90*. The signals from the detector and from the reference pickups are fed to a synchronous rectifier which rejects signals 90* out of phase with the reference signal, thereby providing a rectified output representing the quantity of gas in the sample cell under test. A switch may be utilized to apply the reference signals to a single synchronous rectifier, or a separate synchronous rectifier and meter may be utilized, with the reference pickups applied one to each channel for providing simultaneous two-gas analysis. The two-gas analyzer is provided with aperture trimming to radiometrically balance each analytic filter with respect to its reference filter. The two-gas analyzer is suitable for the measurement of auto emissions from the tail pipe of a car for use in inspection stations, garages, etc.

Claims

1. An infrared two gas analyzer comprising a. a sample cell containing a sample of the gas to be analyzed, b. an infrared detector, c. a source of infrared radiation directed through said sample cell and onto said infrared detector, d. a rotating filter wheel having a pair of analytic filters, each having transmissive areas which pass radiation in an absorption region of a different gas whose presence is desired to be detected, and a pair of reference filters having transmissive areas interspersed between said analytic filters for passing radiation in a non-absorbing region of said pair of analytic filters, said filter wheel being positioned between said source and said infrared detector, e. two reference pick-ups for generating time reference signals in accordance with the position of said filter wheel, f. synchronous demodulator means coupled to said infrared detector and said reference pick-ups for rectifying and selecting the signal for the gas desired to be detected;

and g. means for indicating the amount of the gas which is detected.

2. The two-gas analyzers set forth in claim 1 wherein said two reference pick-ups are positioned in quadrature around said filter wheel.

3. The infrared two-gas analyzer set forth in claim 1 including compensation means for radiometrically balancing said analytic filter with its reference filter to provide no signal when no absorber gases are present.

4. The infrared two-gas analyzer set forth in claim 3 wherein said compensation means includes a masking means comprising an adjustable mask for trimming the transmissive areas of said filters.

5. The infrared two-gas analyzer set forth in claim 4 wherein said adjustable mask has arcuate end portions which project uniformly in the transmissive of said filters to prevent radiation chopping by said mask.

6. The infrared two-gas analyzer set forth in claim 1 in which said synchronous demodulator means comprises two synchronous demodulators, one for each gas with the output of the detector being coupled to each synchronous demodulator and the output from each of said reference pick-ups being applied to a different synchronous demodulator and separate meter means coupled to each synchronous demodulator for providing a simultaneous reading for the two gases being analyzed.

7. The two-gas analyzer set forth in claim 6 wherein said filters on said filter wheel and the reference pick-ups around said filter wheel are positioned in phase quadrature, and masking means are provided to trim the transmissive areas of said filters for providing a radiometric balance between the analytic and the reference filters.

8. The two-gas analyzer set forth in claim 1 wherein one said analytic filter passes radiation in a hydrocarbon absorption region on the order of 3.4 microns and the other analytic filter passes radiation in a carbon monoxide region on the order of 4.7 microns and said reference filters are clear for both these gases.