Measuring and testing – Gas analysis – With compensation detail
Patent
1997-06-13
1999-03-23
Williams, Hezron
Measuring and testing
Gas analysis
With compensation detail
25033913, 356437, G01N 700, G01N 2100, G01J 502
Patent
active
058862471
ABSTRACT:
Apparatus and a method for detecting the presence of a predetermined target gas (e.g. CO) is disclosed. The gas has a predetermined pattern of peaks of absorbance to radiation lying within a particular radiation range (e.g. infrared), the absorbance peaks alternating with gaps in which the gas transmits the radiation. A source (12) passes IR radiation through a comb filter (5) and a measurement cell (22) containing the target gas. The comb filter (5) has successive passbands separated by absorbance gaps. The passbands of the comb filter are repeatedly shifted relative to the IR radiation between a correlation position in which they coincide with at least some of the absorbance peaks of the target gas and an anti-correlation position in which the passbands coincide with at least some of the absorbance gaps of the gas. A detector (26) produces a measurement output corresponding to the radiation received through the cell (22) as the comb filter (5) is moved between the correlation and anti-correlation positions, the measurement output being a function of the presence of the target gas in the measurement cell (22). The comb filter is scanned smoothly and continuously between the two positions and the outputs corresponding to predetermined points in each scan may be accumulated over a period to increase the signal to noise ratio. A reference cell (20) receives some of the radiation passing through the comb filter (5) and contains a predetermined gas which may be the target gas. The output of the reference cell is detected is detected by a detector (44) and can be used to correct for drift in the comb filter (5) which may be an etalon.
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Forney Corporation
Politzer Jay L.
Williams Hezron
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