Non-dispersive optical determination of gas concentration
First Claim
1. Apparatus for non-dispersive optical determination of the concentration of an identifiable gas in an atmosphere comprising a sample chamber arranged to communicate with the atmosphere by flow limiting means in the form of a plug of porous material operable to limit the rate of gas flow between the chamber and atmosphere to a value whereby after a pressure change is induced in the chamber and for a time period thereafter there is no substantial restoration of gas pressure within the sample chamber towards atmospheric, transducer means operable to change the pressure of the gas mixture in the sample chamber by a predetermined amount between first and second pressures, a source of a beam of radiation at a wavelength absorbed by the identifiable gas only of the mixture, window means by which the radiation is passed through the sample chamber, a detector responsive to radiation at said wavelength after passage through the sample chamber to produce a signal related to the intensity level of the radiation detected, and signal processing means operable to derive a signal representing the fractional change in intensity (Δ
- I/I) of the detected radiation due to the pressure change in the sample chamber and calculate from said derived signal, the chamber pressure change (Δ
p), radiation path length through the gas mixture (x) and an absorption constant characteristic of the specific gas (α
o), a representation of the gas concentration g in accordance with the formula
space="preserve" listing-type="equation">g=-Δ
I/(I·
Δ
pα
.sub.o ·
x).
1 Assignment
0 Petitions
Accused Products
Abstract
Apparatus (FIG. 1) for non-dispersive optical determination of the concentration of an identifiable gas, such as a hydrocarbon, in a mixture such as atmospheric air comprises a sample chamber 13 to contain a sample of the mixture, a source 21 of IR radiation at a wavelength absorbed by the gas beamed through the sample chamber to a detector 22 and transducer means to change the gas pressure within the chamber to determine the change in radiation intensity detected at different pressures. One wall of the sample chamber is formed by a flexible diaphragm 25 driven by a voice-coil type transducer 26 whereby the pressure is switched repetitively between the values above and below atmospheric. Atmospheric gas is admitted to the chamber by a porous plug 24 which restricts flow to a low level permitting a pressure change in the chamber. Absorption by the gas relates the intensity of source radiation IS and measured radiation IM by IM oc IS ·e-α o.sup.·g·p·x where x is the radiation path length through the sample, αo is a constant, p the total pressure of the gas mixture and g the concentration of the hydrocarbon gas. By measuring intensity at different pressure involving a change Δp and a fractional change in intensity of measured radiation ΔI/I, the gas concentration g is determined by applying the relationship:- g=-ΔI/(I·Δp·αo ·x).
32 Citations
13 Claims
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1. Apparatus for non-dispersive optical determination of the concentration of an identifiable gas in an atmosphere comprising a sample chamber arranged to communicate with the atmosphere by flow limiting means in the form of a plug of porous material operable to limit the rate of gas flow between the chamber and atmosphere to a value whereby after a pressure change is induced in the chamber and for a time period thereafter there is no substantial restoration of gas pressure within the sample chamber towards atmospheric, transducer means operable to change the pressure of the gas mixture in the sample chamber by a predetermined amount between first and second pressures, a source of a beam of radiation at a wavelength absorbed by the identifiable gas only of the mixture, window means by which the radiation is passed through the sample chamber, a detector responsive to radiation at said wavelength after passage through the sample chamber to produce a signal related to the intensity level of the radiation detected, and signal processing means operable to derive a signal representing the fractional change in intensity (Δ
- I/I) of the detected radiation due to the pressure change in the sample chamber and calculate from said derived signal, the chamber pressure change (Δ
p), radiation path length through the gas mixture (x) and an absorption constant characteristic of the specific gas (α
o), a representation of the gas concentration g in accordance with the formula
space="preserve" listing-type="equation">g=-Δ
I/(I·
Δ
pα
.sub.o ·
x). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- I/I) of the detected radiation due to the pressure change in the sample chamber and calculate from said derived signal, the chamber pressure change (Δ
-
11. A method of non-dispersive optical determination of the concentration of an identifiable gas in the atmosphere comprising holding a sample of the atmospheric gas mixture in a sample chamber in communication with the atmosphere by means of a porous plug operable to limit the rate of gas flow between the atmosphere and the sample chamber to a level at which a pressure change may be effected and radiation intensities measured before any significant flow of gas through the plug restores the pressure within the chamber to atmospheric, passing radiation at a wavelength absorbed by the identifiable gas through the sample chamber, detecting the intensity of radiation at said wavelength received after passage through the chamber with the gas mixture at a first pressure, changing the pressure in the chamber by a predetermined amount (Δ
- p) to a second pressure, detecting the intensity of radiation at said wavelength after passage through the chamber with the gas mixture at the second pressure, determining the fractional change in intensity of detected radiation (Δ
I/I) consequent upon the change of gas pressure, and calculating the value of the gas concentration g of the identifiable gas in accordance with the formula;
space="preserve" listing-type="equation">g=-Δ
I/(I·
Δ
p·
α
.sub.o ·
x)where x is the path length of the radiation through the sample and α
o is an absorption coefficient constant for the identifiable gas. - View Dependent Claims (12, 13)
- p) to a second pressure, detecting the intensity of radiation at said wavelength after passage through the chamber with the gas mixture at the second pressure, determining the fractional change in intensity of detected radiation (Δ
Specification