Correction of collision broadening in non-dispersive absorption measurement of gases
First Claim
1. A method for determining the concentration of a given gas in a mixture of gases by means of non-dispersive absorption of radiation, the method providing compensation for the effects of collision broadening of absorption lines in the absorption spectrum of the given gas, said method comprising the steps of:
- (a) providing a sample of the gas mixture;
(b) passing radiation through the gas mixture, the radiation having a wavelength range including an absorption spectrum band for determining the concentration of the given gas;
(c) applying the radiation exiting the gas mixture to a first optical transmission band filter, the first filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value substantially equal to the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band;
(d) detecting the intensity of the radiation transmitted through the first optical transmission band filter to provide a first signal, the detected radiation, and hence the first signal, being subject to the effects of collision broadening occurring from the mixture of gases;
(e) providing a compensation filter, the compensation filter including a compensating gas including a known concentration of the given gas at a known pressure, any collision broadening effects occurring in the compensating gas usually differing from those occurring in the gas mixture;
(f) passing radiation through both the gas mixture and the compensating gas;
(g) applying the radiation passed through the gas mixture and compensating gas to a second optical transmission band filter, the second filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value greater than the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band;
(h) detecting the intensity of the radiation transmitted through the second filter to provide a second signal, the detected radiation, and hence the second signal, being subject to the differing collision broadening effects resulting from passage through the compensating gas; and
(i) providing an output from the first and second signals which is compensated for the effects of collision broadening in the absorption spectrum of the given gas and is, thus, an accurate determination of the concentration of the given gas in the gas mixture.
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Accused Products
Abstract
A method of non-dispersive analysis of gas mixtures for determining the concentration of some gas component therein. A radiation source is arranged which emits, through the gas mixture being analyzed, radiation within a wavelength range within which the absorption spectrum band used in the determination of the concentration of the said gas component is located; an optical transmission band filter the transmission band of which coincides with the said spectrum band is provided in the path of the radiation traversing the gas mixture being analyzed; a detector is used for detecting the radiation which has traversed the gas mixture being analyzed and the optical transmission band filter, whereby a first signal is obtained from the detector; a different second signal is generated in the detector by means of an additional gas or an additional gas mixture interposed between the radiation source and the detector; and the result of the concentration measurement is formed computationally by using the different measurement signals. Furthermore, in the method the transmission bands of the said transmission band filters are arranged within the same measuring range; as the additional gas there is used a compensation gas or a compensation gas mixture in which the compensation gas is the gas component the concentration of which is being determined or a corresponding other gas or a compensation filter. The absorption properties of the compensation filter are selected to be such, or the amount of the compensation gas is selected to be such, that the broadening of the absorption lines in the absorption spectrum band used will change the said different second signal.
29 Citations
27 Claims
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1. A method for determining the concentration of a given gas in a mixture of gases by means of non-dispersive absorption of radiation, the method providing compensation for the effects of collision broadening of absorption lines in the absorption spectrum of the given gas, said method comprising the steps of:
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(a) providing a sample of the gas mixture; (b) passing radiation through the gas mixture, the radiation having a wavelength range including an absorption spectrum band for determining the concentration of the given gas; (c) applying the radiation exiting the gas mixture to a first optical transmission band filter, the first filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value substantially equal to the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band; (d) detecting the intensity of the radiation transmitted through the first optical transmission band filter to provide a first signal, the detected radiation, and hence the first signal, being subject to the effects of collision broadening occurring from the mixture of gases; (e) providing a compensation filter, the compensation filter including a compensating gas including a known concentration of the given gas at a known pressure, any collision broadening effects occurring in the compensating gas usually differing from those occurring in the gas mixture; (f) passing radiation through both the gas mixture and the compensating gas; (g) applying the radiation passed through the gas mixture and compensating gas to a second optical transmission band filter, the second filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value greater than the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band; (h) detecting the intensity of the radiation transmitted through the second filter to provide a second signal, the detected radiation, and hence the second signal, being subject to the differing collision broadening effects resulting from passage through the compensating gas; and (i) providing an output from the first and second signals which is compensated for the effects of collision broadening in the absorption spectrum of the given gas and is, thus, an accurate determination of the concentration of the given gas in the gas mixture. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An apparatus for providing an indication of the concentration of a given gas in a mixture of gases, said apparatus employing non-dispersive absorption of radiation and providing an output compensated for the effects of collision broadening of absorption lines in the absorption spectrum of the given gas, said apparatus comprising:
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a sample chamber containing the gas mixture; a radiation source means providing radiation to first and second radiation paths in said apparatus, the radiation having a wavelength range including an absorption spectrum band for determining the concentration of the given gas, said sample chamber being located in said first and second paths so that radiation from said radiation source means passes through said sample chamber; a first optical transmission band filter located in said first radiation path for receiving radiation passed through said sample chamber, said first filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value substantially equal to the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band; a compensation filter means located in said second radiation path, the compensation filter means including a compensating gas including a known concentration of the given gas at a known pressure, any collision broadening effects occurring in the compensating gas as usually differing from those occurring in the gas mixture; a second optical transmission band filter in said second radiation path for receiving the radiation passed through said sample chamber and compensation filter means, said second filter having a transmission bandwidth selected from a range of bandwidth values having a maximum value substantially equal to the width of the absorption spectrum band and a minimum value less than the width of the absorption spectrum band; detector means for detecting the intensity of the radiation transmitted through said first filter to provide a first signal, the detected radiation, and hence the first signal, being subject to the effects of collision broadening occurring from the mixture of gases, said detector means further detecting the intensity of the radiation transmitted through said second filter to provide a second signal, the detected radiation, and hence the second signal, being subject to the differing collision broadening effects resulting from passage through the compensating gas; and means for applying the second signal to the first signal to provide an output which is compensated for the effects of collision broadening in the absorption spectrum of the given gas and is, thus, an accurate indication of the concentration of the given gas in the gas mixture. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification