CA1083380A - Gas concentration measuring device with series radiation paths - Google Patents
Gas concentration measuring device with series radiation pathsInfo
- Publication number
- CA1083380A CA1083380A CA292,710A CA292710A CA1083380A CA 1083380 A CA1083380 A CA 1083380A CA 292710 A CA292710 A CA 292710A CA 1083380 A CA1083380 A CA 1083380A
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- radiation
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- reflecting
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Abstract
ABSTRACT OF DISCLOSURE
A device as described whereby the concentration of a gas such as alcohol vapour can be measured using radiation absorption techniques in a pair of chambers. The chambers are elongated tubes, the first having a window at one end through which infra red radiation can pass with an optical reflector at the two ends of each tube so that radiation from a source and focused by an ellipsoidal reflector passes through the first tube in both directions and thence through the second. The reflected radiation leaves the second tube through a second window in the side of the tube, from where it passes to a detector. Passing the radiation in series through two or more parallel arranged chambers, conveniently located within a common housing increases the sensitivity.
A device as described whereby the concentration of a gas such as alcohol vapour can be measured using radiation absorption techniques in a pair of chambers. The chambers are elongated tubes, the first having a window at one end through which infra red radiation can pass with an optical reflector at the two ends of each tube so that radiation from a source and focused by an ellipsoidal reflector passes through the first tube in both directions and thence through the second. The reflected radiation leaves the second tube through a second window in the side of the tube, from where it passes to a detector. Passing the radiation in series through two or more parallel arranged chambers, conveniently located within a common housing increases the sensitivity.
Description
"- 1083380 Field of invention.
_ This invention relates to a dcvice for measuring the concentration of a 6a6 particularly alcohol vapour. In this specification the term "gas" will be used to mean any gaseous or vaporised subRtance.
Background to invention.
In the known devices for measuring the concentration of gases by radiation absorption at characteristi~ absorption wave lengths for the gas, the gas to be analysed i6 introduced i~to a meaFuring chamber. This is subjected to radiation of the 6pecific wave length which enters the measuring chamber with a flux 0O. Thi~ flux is weakened if gas molecules havin~ a significant absorption characteri6tic at that wave-length are present and if present, the radiation leaves the measuring chamber with a reduced flux 0.
According to Lambert-Beer's law, the relationship ls written:
0 ~ 0Oe mlc where m is a material constant, 1 is the length of the radiation pat~ n the abRorbing medium, and c is the concentration of the absorbing gas in the measuring chamber.
If it is desired to measure very small concentration_, then, for a minimum weakening ratio which is given by the relationship 0/0O and i8 limited by the resolution and ~ensitivity of the detector~ and amplifiers, this is only possible by increasing the path length 1 of the radiation through the chamber.
In known spectrophotometric devices for gas analysis, measuring chamber6 are used in which the radiation path is~bent via an optical sy6tem. For example, a principle given by White makes it possible to . , ' ~
, . :' ,, , '. .: ! , " ' 1(1 83380 produce path lengths of up to ten metres. However, the apertures are small and the volume of the chamber amounts to more than six litres. For measuring the concentration of alcohol molecules in exhaled breath, the measuring chamber must have a very small volume in order to ensure that only air from deep in the lungs fills the measuring chamber. For this reason the chamber volume must not exceed 100 cm3.
A device is described in U.S. Patent Specification 3,319,071 in which a sphere with highly reflective inner walls forms the measuring chamber.
However, this arrangement is quite unsuitable for measuring the concentration of alcohol in the breath, as a sphere has the greatest volume with the smallest outer dimensions and exactly the opposite is desired.
It is the object of the invention to produce a device with a measuring chamber having a small volume, a long radiation path and a high ef f icacy.
More particularly in accordance with a first aspect of the invention there is provided a device for measuring the concentration of gases by radiation absorption comprising - a pair of adjacent chambers in the form of elongate tubes the interior surface of each being highly reflective to infra red (IR) radiation, - inlet and outlet means in the chambers for the inflow and outflow of gases to be analysed, - a first window in one end of a first of the chambers through which infra red (IR) radiation can enter that chamber, - a source of IR radiation, 25 - an ellipsoidal concave reflector for reflecting IR radiation positioned so ' that the radiation source is situated at one of the two focal points thereof and so that IR radiation reflected by the ellipsoidal reflector enters the first ' " 1(~i83380 chamber through the said first window, the second focal point of the ellipsoidal reflector lying on the path of the reflected radiation, - first optically reflecting means at the opposite end of the first chamber for reflecting IR radiation which traverses the first chamber along a first path back towards the said one end of the chamber along a second different path, - second optically reflecting means located on said second path for reflecting IR radiation along at least a third path different from the first and second paths thereby to leave the first chamber and enter one end of the second chamber and pass along a fourth different path through said second chamber and a radiation detector for receiving and responding to radiation which has traversed .
said fourth.path.
Where the measuring chamber is to be fitted to a device for measuring the concentration of alcohol in exhaled breath, the gas inlet means preferably comprises a side tube communicating with an aperture in the wall of the chamber and a sal.iva trap is connected between the said side tube and nozzle into which a sub~ect under test can exhale.
Preferably the source of radiation comprises an ellip.soidal quartz-halogen lamp of the type which is vacuum-coated with gold. The rays are concentrated at the second focal point of the ellipsoid. Due to the length of the coil and irregularities usually present in the surface of the ellipsoidal mirror, a point of focus of approximately 6 mm.diameter is obtained from such lamps. This is sufficiently punctiform and the point of focus is formed on the -said first window in the chamber.
~ith optically reflecting elements arranged at opposite ends of the measuring chamber, radiation entering the chamber is reversed in direction at each end and in a basic embodiment of the invention it can be made to pass by reflection at the first and a third reflecting means through each measuring chamber at least twice. Ideally the image of the ~t _ .
~ .
~ .
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radiation source created at the second focal point of the ellipsoidal concave reflector or lamp will be projected back in approximately the same plane by the first optically reflecting means located at the opposite end of the chamber.
.
This image will appear on the second optically reflecting means which in turn reflects the reduced image from the illuminating surface of the first optically reflecting means into the second chamber and thence onto the detector.
Preferably the interior of the chamber is highly reflective of IR
radiation so that any IR radiatlon falling thereon is reflected and finally impinges on one of the reflecting means so that this radiation also reach,es thedetector, possibly after many reflections but nevertheless increasing the overall efficiency of the device. The radiation losses in a measuring chamber can therefore be small.
In order to keep the losses within the chamber as small as possible the focal length of the first optically reflecting means is preferably equal to half the length of a measuring chamber and that of a fourth optically reflect-ing means is equal to the distance between it and the detector, which typically is short in comparison with the length of the measuring chambers.
It is better if the detector is arranged in such a way that it does not receive any direct irradiation from the source. Consequently the fourth optically reflecting means is preferably offset laterally from the radiation ~' inlet on or in the wall of the measuring chamber and a plane reflector is arranged in the measuring chamber next to the radiation inlet. In this way the reduced image of the radiation source which falls on the detector is created -at a point which can be shielded from the effect of the heat from the radiation ;
source and is removed from the radiation inlet. ~
In order to keep the volume of the measuring chambers as .small as ;~ -as possible, the measuring chambers are made wider at the first ends than at ~. ' .
~ .. - :. . .... .. ..
11)83380 the other ends and the cross-section reduces between these two ends along one plane. This design makes it possible to accommodat~a plane reflector next to the radiation inlet without reducing the size of the aperture of the first and third optically reflecting means within the chambers.
The fourth optically reflecting means may comprise a plane reflector for reflecting the radiation from a fifth path along an intermediate path and a convex reflector on said intermediate path for reflecting the radiation from the said intermediate path along the sixth path. A second window is thus locatedin the side wall of the second tube and the detector is located laterally of the tube beyond the second window and the focal length of the convex reflector is chosen to be short compared with the length of the tubes.
Each of the first and third optically reflecting means may comprise a concave reflector or a plane reflecting element having a convex lens mounted infront thereof. The IR radiation transfers from one ohamber to the next and after traversing each chamber in turn finally leaves the last chamber for the detector~ The length of the overall path is thus long. More than two measuring chambers can be arranged adjacent to each other, the measuring chambers having at one end optically reflecting elements and at the other end plane reflectors directed towards the optically reflecting elements and towards each other, the last of the reflecting means in the radiation path being directed towards the detector. The measuring chambers can thus be considered to be adjacent to each other each having the same length and representing an increase in the `
overall width of the device but a significant multiplication of the path length for the radiation between inlet and outlet is obtained and sensitivity can be increased.
The convèx reflector on the intermediate path may comprise a plane reflector with a focusing lens mounted in front of it.
.. ~ ' , , , ~ , ,: , , , .,:
~083380 - -`;
The disclosed apparatus thus provides a small chamber volume combined with a long effective path length for the infra red radiation through the chambers and a high degree of efficiency can be obtained since the radiation flux beamed into the first chamber through the inlet window is only weakened by ~he small losses of the reflectors and of the highly polished reflecting inner walls.
Specific embodiments of the invention will now be described having reference to the accompanying drawings in which;
Fig. 1 is a cross-section through a messuring device in which the measuring chamber widens out in one plane, from one end to the other, Fig. 2 is a cross-section through the device of Fig. 1 at right angles to the view of Fig. l showing the parallel walls, with inlets and outlets for the gas to be analysed, and Fig. 3 is a cross-section through a device with two measuring chambers which are arranged adjacent to each other in a common housing.
Fig. 1 shows a radiation soorce 1 arranged at a focal point of an ~-ellipsoidal reflector 2~. The radiation flux emitted by this is focused at the second focal point 3. The radiation inlet to the measuring chamber 4 is : . , ".:
located here. An optically reflecting element 5 arranged at the far end of the measuring chamber pro~ects the second Eocal point of the ellipsoidal reflector 2 via a plane reflector 6 to a laterally-located second optically reflecting element 7. The radiating surface of the first optically reflecting element is projected by the second optically reflecting element via an opening 8 onto a detector 9. Thus, the radiation coming from the radiation source l passes through the measuring chamber 4 rather more than twice before it reaches the detector 9.
The arrangement of the two optically reflecting elements 5 and 7 ..
~ _ 7 _ - , : , . . :: .: ;. ,; ,. ", - .. " .. : . :. . .. . ..
~833~
at the opposite ends of the measuring chamber is decisive for the optlcal p~incipl~ of the invention here. The plane reflecto~ 6 serves only to project the radiation via the second optically reflecting element 7 out of the measuring chamber 4 onto the detector 9. This can then be arranged to advantage some distance from the radiation source l.
Fig. 2 shows the tube 4 which forms the measuring chamber with a gas inlet connection 17 which is connected via a piece of tubing 18 to a saliva trap 19. The gas inlet connection 17 is arranged toward6 the narrower end of the tube. In the vicinity of each of the ends there is an air outlet hole 20. These are covered by sprun~ plates 21 which form flap valves. These are approximately 0.05 mm thick and are each held by a screw with a pres6ure disc. They act a9 overflow valve6. When breath i6 blown in via the 6aliva trap 19 the inner pres6ure lifts the 6prung plates 21. ~xcess gas can thus escape from the measuring chamber 4.
Fig. 3 shows a novel double measuring chamber in which the described principle is applied twice. The radiation coming from the radiation source 1 reaches the optically reflecting element 5 in the way described, and from there arrives at a first plane reflector 11, which conducts the radiation via a 6econd plane reflector 12 arranged at 90 to its plane, i~to the second chamber. The dividing wall between the two chambers is necessary so that the radiation which arises due to reflections from the interior wall surface6 can be evaluated at the sa~e time. In the 6econd measuring chamber the principle already described in relation to the single measuring chamber is repeated. The image of the ~econd focal plane is reflected from the optically reflecting element 13 after deflec-tion via the plane r~flector onto the laterally arranged optically re-flecting element 7, which again focuses the radiation on the detector 9. ;.i~
~08338~ ~
In thi~ embodiment, the es6ential point is that the ra~iation traverse6 each measuring chamber twice, 80 that a considerable increase in path length i6 obtained`and the radiation flux is finally focused at a point removed from the radiation source, without the need to proportionally increase the VolUme of the overall device to accommodate the additional path length Modification6 are possible. Th~ls, the optically reflecting elements can be constructed either a8 concave reflectors or as plane reflectors with off~et focusing len~e~. ~imilarly, the spatial positions of the radiation source and the detector can be tran6posed.
As a modiflcation to the ¢onstruction form 6hown in Fig. 1, the plane reflector 6 can also be arranged rotated in a counter-clockwise direction.
The radiation then arrives on the detector 9 after being concentrated through a focusing lens, without interposing the optically reflecting element 7. The same applies for the construction form according to Fig. 3. Here, the plane reflector 14 and the focusing lens deflect the radiation directly onto the dètector 9.
The embodiment shown in Fig. 3 can also be modified so that the optically reflecting element 13 is omitted and the second measuring chamber 10 has a radiation outlet in its place. A focusing lens may then be arranged behind this outlet to project the radiation onto the detector. In thi6 event the second measuring chamber i6 only traversed in one direction.
Similarly, the optically reflecting ele~ent 13 can be rotated 60 that it pro~ects the radiation directly onto a detector. However, for this it mu6t co~prise a concave reflector with a short focal length.
' ' ' . ~
~r,r`^' `` , 9_ .
_ This invention relates to a dcvice for measuring the concentration of a 6a6 particularly alcohol vapour. In this specification the term "gas" will be used to mean any gaseous or vaporised subRtance.
Background to invention.
In the known devices for measuring the concentration of gases by radiation absorption at characteristi~ absorption wave lengths for the gas, the gas to be analysed i6 introduced i~to a meaFuring chamber. This is subjected to radiation of the 6pecific wave length which enters the measuring chamber with a flux 0O. Thi~ flux is weakened if gas molecules havin~ a significant absorption characteri6tic at that wave-length are present and if present, the radiation leaves the measuring chamber with a reduced flux 0.
According to Lambert-Beer's law, the relationship ls written:
0 ~ 0Oe mlc where m is a material constant, 1 is the length of the radiation pat~ n the abRorbing medium, and c is the concentration of the absorbing gas in the measuring chamber.
If it is desired to measure very small concentration_, then, for a minimum weakening ratio which is given by the relationship 0/0O and i8 limited by the resolution and ~ensitivity of the detector~ and amplifiers, this is only possible by increasing the path length 1 of the radiation through the chamber.
In known spectrophotometric devices for gas analysis, measuring chamber6 are used in which the radiation path is~bent via an optical sy6tem. For example, a principle given by White makes it possible to . , ' ~
, . :' ,, , '. .: ! , " ' 1(1 83380 produce path lengths of up to ten metres. However, the apertures are small and the volume of the chamber amounts to more than six litres. For measuring the concentration of alcohol molecules in exhaled breath, the measuring chamber must have a very small volume in order to ensure that only air from deep in the lungs fills the measuring chamber. For this reason the chamber volume must not exceed 100 cm3.
A device is described in U.S. Patent Specification 3,319,071 in which a sphere with highly reflective inner walls forms the measuring chamber.
However, this arrangement is quite unsuitable for measuring the concentration of alcohol in the breath, as a sphere has the greatest volume with the smallest outer dimensions and exactly the opposite is desired.
It is the object of the invention to produce a device with a measuring chamber having a small volume, a long radiation path and a high ef f icacy.
More particularly in accordance with a first aspect of the invention there is provided a device for measuring the concentration of gases by radiation absorption comprising - a pair of adjacent chambers in the form of elongate tubes the interior surface of each being highly reflective to infra red (IR) radiation, - inlet and outlet means in the chambers for the inflow and outflow of gases to be analysed, - a first window in one end of a first of the chambers through which infra red (IR) radiation can enter that chamber, - a source of IR radiation, 25 - an ellipsoidal concave reflector for reflecting IR radiation positioned so ' that the radiation source is situated at one of the two focal points thereof and so that IR radiation reflected by the ellipsoidal reflector enters the first ' " 1(~i83380 chamber through the said first window, the second focal point of the ellipsoidal reflector lying on the path of the reflected radiation, - first optically reflecting means at the opposite end of the first chamber for reflecting IR radiation which traverses the first chamber along a first path back towards the said one end of the chamber along a second different path, - second optically reflecting means located on said second path for reflecting IR radiation along at least a third path different from the first and second paths thereby to leave the first chamber and enter one end of the second chamber and pass along a fourth different path through said second chamber and a radiation detector for receiving and responding to radiation which has traversed .
said fourth.path.
Where the measuring chamber is to be fitted to a device for measuring the concentration of alcohol in exhaled breath, the gas inlet means preferably comprises a side tube communicating with an aperture in the wall of the chamber and a sal.iva trap is connected between the said side tube and nozzle into which a sub~ect under test can exhale.
Preferably the source of radiation comprises an ellip.soidal quartz-halogen lamp of the type which is vacuum-coated with gold. The rays are concentrated at the second focal point of the ellipsoid. Due to the length of the coil and irregularities usually present in the surface of the ellipsoidal mirror, a point of focus of approximately 6 mm.diameter is obtained from such lamps. This is sufficiently punctiform and the point of focus is formed on the -said first window in the chamber.
~ith optically reflecting elements arranged at opposite ends of the measuring chamber, radiation entering the chamber is reversed in direction at each end and in a basic embodiment of the invention it can be made to pass by reflection at the first and a third reflecting means through each measuring chamber at least twice. Ideally the image of the ~t _ .
~ .
~ .
: ,: ,: - . ,. j .,, . :,: :, ,., - ., ,: -, :;. ~ - , . j, ; , ,:
radiation source created at the second focal point of the ellipsoidal concave reflector or lamp will be projected back in approximately the same plane by the first optically reflecting means located at the opposite end of the chamber.
.
This image will appear on the second optically reflecting means which in turn reflects the reduced image from the illuminating surface of the first optically reflecting means into the second chamber and thence onto the detector.
Preferably the interior of the chamber is highly reflective of IR
radiation so that any IR radiatlon falling thereon is reflected and finally impinges on one of the reflecting means so that this radiation also reach,es thedetector, possibly after many reflections but nevertheless increasing the overall efficiency of the device. The radiation losses in a measuring chamber can therefore be small.
In order to keep the losses within the chamber as small as possible the focal length of the first optically reflecting means is preferably equal to half the length of a measuring chamber and that of a fourth optically reflect-ing means is equal to the distance between it and the detector, which typically is short in comparison with the length of the measuring chambers.
It is better if the detector is arranged in such a way that it does not receive any direct irradiation from the source. Consequently the fourth optically reflecting means is preferably offset laterally from the radiation ~' inlet on or in the wall of the measuring chamber and a plane reflector is arranged in the measuring chamber next to the radiation inlet. In this way the reduced image of the radiation source which falls on the detector is created -at a point which can be shielded from the effect of the heat from the radiation ;
source and is removed from the radiation inlet. ~
In order to keep the volume of the measuring chambers as .small as ;~ -as possible, the measuring chambers are made wider at the first ends than at ~. ' .
~ .. - :. . .... .. ..
11)83380 the other ends and the cross-section reduces between these two ends along one plane. This design makes it possible to accommodat~a plane reflector next to the radiation inlet without reducing the size of the aperture of the first and third optically reflecting means within the chambers.
The fourth optically reflecting means may comprise a plane reflector for reflecting the radiation from a fifth path along an intermediate path and a convex reflector on said intermediate path for reflecting the radiation from the said intermediate path along the sixth path. A second window is thus locatedin the side wall of the second tube and the detector is located laterally of the tube beyond the second window and the focal length of the convex reflector is chosen to be short compared with the length of the tubes.
Each of the first and third optically reflecting means may comprise a concave reflector or a plane reflecting element having a convex lens mounted infront thereof. The IR radiation transfers from one ohamber to the next and after traversing each chamber in turn finally leaves the last chamber for the detector~ The length of the overall path is thus long. More than two measuring chambers can be arranged adjacent to each other, the measuring chambers having at one end optically reflecting elements and at the other end plane reflectors directed towards the optically reflecting elements and towards each other, the last of the reflecting means in the radiation path being directed towards the detector. The measuring chambers can thus be considered to be adjacent to each other each having the same length and representing an increase in the `
overall width of the device but a significant multiplication of the path length for the radiation between inlet and outlet is obtained and sensitivity can be increased.
The convèx reflector on the intermediate path may comprise a plane reflector with a focusing lens mounted in front of it.
.. ~ ' , , , ~ , ,: , , , .,:
~083380 - -`;
The disclosed apparatus thus provides a small chamber volume combined with a long effective path length for the infra red radiation through the chambers and a high degree of efficiency can be obtained since the radiation flux beamed into the first chamber through the inlet window is only weakened by ~he small losses of the reflectors and of the highly polished reflecting inner walls.
Specific embodiments of the invention will now be described having reference to the accompanying drawings in which;
Fig. 1 is a cross-section through a messuring device in which the measuring chamber widens out in one plane, from one end to the other, Fig. 2 is a cross-section through the device of Fig. 1 at right angles to the view of Fig. l showing the parallel walls, with inlets and outlets for the gas to be analysed, and Fig. 3 is a cross-section through a device with two measuring chambers which are arranged adjacent to each other in a common housing.
Fig. 1 shows a radiation soorce 1 arranged at a focal point of an ~-ellipsoidal reflector 2~. The radiation flux emitted by this is focused at the second focal point 3. The radiation inlet to the measuring chamber 4 is : . , ".:
located here. An optically reflecting element 5 arranged at the far end of the measuring chamber pro~ects the second Eocal point of the ellipsoidal reflector 2 via a plane reflector 6 to a laterally-located second optically reflecting element 7. The radiating surface of the first optically reflecting element is projected by the second optically reflecting element via an opening 8 onto a detector 9. Thus, the radiation coming from the radiation source l passes through the measuring chamber 4 rather more than twice before it reaches the detector 9.
The arrangement of the two optically reflecting elements 5 and 7 ..
~ _ 7 _ - , : , . . :: .: ;. ,; ,. ", - .. " .. : . :. . .. . ..
~833~
at the opposite ends of the measuring chamber is decisive for the optlcal p~incipl~ of the invention here. The plane reflecto~ 6 serves only to project the radiation via the second optically reflecting element 7 out of the measuring chamber 4 onto the detector 9. This can then be arranged to advantage some distance from the radiation source l.
Fig. 2 shows the tube 4 which forms the measuring chamber with a gas inlet connection 17 which is connected via a piece of tubing 18 to a saliva trap 19. The gas inlet connection 17 is arranged toward6 the narrower end of the tube. In the vicinity of each of the ends there is an air outlet hole 20. These are covered by sprun~ plates 21 which form flap valves. These are approximately 0.05 mm thick and are each held by a screw with a pres6ure disc. They act a9 overflow valve6. When breath i6 blown in via the 6aliva trap 19 the inner pres6ure lifts the 6prung plates 21. ~xcess gas can thus escape from the measuring chamber 4.
Fig. 3 shows a novel double measuring chamber in which the described principle is applied twice. The radiation coming from the radiation source 1 reaches the optically reflecting element 5 in the way described, and from there arrives at a first plane reflector 11, which conducts the radiation via a 6econd plane reflector 12 arranged at 90 to its plane, i~to the second chamber. The dividing wall between the two chambers is necessary so that the radiation which arises due to reflections from the interior wall surface6 can be evaluated at the sa~e time. In the 6econd measuring chamber the principle already described in relation to the single measuring chamber is repeated. The image of the ~econd focal plane is reflected from the optically reflecting element 13 after deflec-tion via the plane r~flector onto the laterally arranged optically re-flecting element 7, which again focuses the radiation on the detector 9. ;.i~
~08338~ ~
In thi~ embodiment, the es6ential point is that the ra~iation traverse6 each measuring chamber twice, 80 that a considerable increase in path length i6 obtained`and the radiation flux is finally focused at a point removed from the radiation source, without the need to proportionally increase the VolUme of the overall device to accommodate the additional path length Modification6 are possible. Th~ls, the optically reflecting elements can be constructed either a8 concave reflectors or as plane reflectors with off~et focusing len~e~. ~imilarly, the spatial positions of the radiation source and the detector can be tran6posed.
As a modiflcation to the ¢onstruction form 6hown in Fig. 1, the plane reflector 6 can also be arranged rotated in a counter-clockwise direction.
The radiation then arrives on the detector 9 after being concentrated through a focusing lens, without interposing the optically reflecting element 7. The same applies for the construction form according to Fig. 3. Here, the plane reflector 14 and the focusing lens deflect the radiation directly onto the dètector 9.
The embodiment shown in Fig. 3 can also be modified so that the optically reflecting element 13 is omitted and the second measuring chamber 10 has a radiation outlet in its place. A focusing lens may then be arranged behind this outlet to project the radiation onto the detector. In thi6 event the second measuring chamber i6 only traversed in one direction.
Similarly, the optically reflecting ele~ent 13 can be rotated 60 that it pro~ects the radiation directly onto a detector. However, for this it mu6t co~prise a concave reflector with a short focal length.
' ' ' . ~
~r,r`^' `` , 9_ .
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A device for measuring the concentration of gases by radiation absorption comprising - a pair of adjacent chambers in the form of elongate tubes the interior surface of each being highly reflective to infra red (IR) radiation, - inlet and outlet means in the chambers for the inflow and outflow of gases to be analysed, - a first window in one end of a first of the chambers through which infra red (IR) radiation can enter that chamber, - a source of IR radiation, - an ellipsoidal concave reflector for reflecting IR radiation positioned so that the radiation source is situated at one of the two focal points thereof and so that IR radiation reflected by the ellipsoidal reflector enters the first chamber through the said first window, the second focal point of the ellipsoidal reflector lying on the path of the reflected radiation, - first optically reflecting means at the opposite end of the first chamber for reflecting IR radiation which traverses the first chamber along a first path back towards the said one end of the chamber along a second different path, - second optically reflecting means located on said second path for reflecting IR radiation along at least a third path different from the first and second paths thereby to leave the first chamber and enter one end of the second chamber and pass along a fourth different path through said second chamber and a radiation detector for receiving and responding to radiation which has traversed said fourth path.
2. A device as set forth in claim 1, comprising third optically reflecting means located at the other end of said second chamber for reflecting IR radiation which traverses said second chamber along the fourth path back towards the one end of the second chamber along a fifth different path and, fourth optically reflecting means located on said fifth path for reflecting IR radiation along at least a sixth different path thereby to leave the second chamber.
3. A device as set forth in claim 1 or 2 wherein the first window is located at the second focal point of the ellipsoidal reflector.
4. A device as set forth in claim 1 or 2 wherein the focal length of the first optically reflecting means located at the end of the first chamber remote from the first window is equal to half the length of the chamber.
5. A device as set forth in claim 2 wherein the fourth optically reflecting means comprises a plane reflector for reflecting the radiation from the fifth path along an intermediate path and a convex reflector on said intermediate path for reflecting the radiation from the said intermediate path along the sixth path and from thence out of the second chamber.
6. A device as set forth in claim 5 wherein a second window is located in the side wall of the second tube and the detector is located laterally of such tube beyond the said second window.
7. A device as set forth in claim 6 wherein the focal length of the convex reflector is short compared with the lengths of the tubes.
8. A device as set forth in claim 1 or 2 wherein the width of the chambers decreases in the direction from the first ends to the other ends thereof.
9. A device as set forth in claim 2 in which the first, third and a fifth optically reflecting means beyond said fourth reflecting means, comprise concave reflectors.
10. A device as set forth in claim 9 wherein each of the first, third and fifth optically reflecting means comprises a plane reflecting element and a convex lens located in front thereof.
11. A device as set forth in claim 1 or 2 for measuring the concentration of alcohol in exhaled breath, in which the gas inlet comprises - a side tube communicating with an aperture in the wall of one of the chambers, - a saliva trap located in said side tube, and - a nozzle at the entrance to the saliva trap into which exhaled breath can pass.
12. A device as set forth in claim 1 or 2 wherein the radiation source comprises a quartz-halogen lamp.
13. A device as set forth in claim 1 or 2 wherein the radiation source is an ellipsoidal quartz-halogen lamp which is vacuum-coated with gold.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA292,710A CA1083380A (en) | 1977-12-08 | 1977-12-08 | Gas concentration measuring device with series radiation paths |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA292,710A CA1083380A (en) | 1977-12-08 | 1977-12-08 | Gas concentration measuring device with series radiation paths |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1083380A true CA1083380A (en) | 1980-08-12 |
Family
ID=4110244
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA292,710A Expired CA1083380A (en) | 1977-12-08 | 1977-12-08 | Gas concentration measuring device with series radiation paths |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1083380A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5170064A (en) * | 1989-09-29 | 1992-12-08 | Atomic Energy Of Canada Limited | Infrared-based gas detector using a cavity having elliptical reflecting surface |
-
1977
- 1977-12-08 CA CA292,710A patent/CA1083380A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5170064A (en) * | 1989-09-29 | 1992-12-08 | Atomic Energy Of Canada Limited | Infrared-based gas detector using a cavity having elliptical reflecting surface |
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