CA1319833C - Infrared-based gas detector - Google Patents
Infrared-based gas detectorInfo
- Publication number
- CA1319833C CA1319833C CA 615459 CA615459A CA1319833C CA 1319833 C CA1319833 C CA 1319833C CA 615459 CA615459 CA 615459 CA 615459 A CA615459 A CA 615459A CA 1319833 C CA1319833 C CA 1319833C
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- Prior art keywords
- chamber
- gas
- sample
- analyte
- analyzer
- Prior art date
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Links
- 239000007789 gas Substances 0.000 claims abstract description 56
- 230000005855 radiation Effects 0.000 claims abstract description 42
- 239000012491 analyte Substances 0.000 claims abstract description 41
- 239000011261 inert gas Substances 0.000 claims abstract description 25
- 238000012544 monitoring process Methods 0.000 claims abstract description 3
- 239000012080 ambient air Substances 0.000 claims description 4
- 230000005540 biological transmission Effects 0.000 claims 1
- 238000007789 sealing Methods 0.000 claims 1
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 8
- 239000003570 air Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 5
- 229910002092 carbon dioxide Inorganic materials 0.000 description 4
- 239000001569 carbon dioxide Substances 0.000 description 4
- 238000013480 data collection Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 2
- 229910052782 aluminium Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- IOLCXVTUBQKXJR-UHFFFAOYSA-M potassium bromide Chemical compound [K+].[Br-] IOLCXVTUBQKXJR-UHFFFAOYSA-M 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 238000001311 chemical methods and process Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000007405 data analysis Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 229910052594 sapphire Inorganic materials 0.000 description 1
- 239000010980 sapphire Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N2021/3129—Determining multicomponents by multiwavelength light
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A nondispersive gas analyzer for use in monitoring the concentration one or more gases, comprises a body having a cavity having an elliptical reflecting surface, defining a first focus and a second focus, for transmitting radiation between the focuses, a chamber for holding a sample gas to be analyzed, one of the focuses being located within the sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, a radiation source disposed at one of the focuses, and a radiation detector associated with each of the inert gas chamber and the analyte gas chamber for detecting the radiation passing through the sample gas and the inert gas and the radiation passing through the sample gas and the analyte gas being located at the other of the focuses.
A nondispersive gas analyzer for use in monitoring the concentration one or more gases, comprises a body having a cavity having an elliptical reflecting surface, defining a first focus and a second focus, for transmitting radiation between the focuses, a chamber for holding a sample gas to be analyzed, one of the focuses being located within the sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, a radiation source disposed at one of the focuses, and a radiation detector associated with each of the inert gas chamber and the analyte gas chamber for detecting the radiation passing through the sample gas and the inert gas and the radiation passing through the sample gas and the analyte gas being located at the other of the focuses.
Description
FIELD OF THIS INV~NTION
This invention relates to a nondispersive analyzer, which can be used ~o monitor the concentration one or more gases.
BACKGROUND OF THB INVBNTION
Nondispersive analyzers are analyzers which provide discrete radiation paths from a source to one or more means for detecting the intensity of radiation. One of these paths is through the sample to be analyzed as well as through an isolated fixed quantity of the analyte gas, and another of these paths is through the sample to be analyzed only. Therefore, that part of the radiation which is at the wavelengths absorbed by the analyte gas is removed from one path, but not the other, resulting in a difference in the outputs from the energy detecting means associated with these paths. Thus, it is only when the sample contains the analyte gas that the difference between the intensities of the radiation along the two paths will be reduced. Other absorbing compounds affect both detectors equally.
In order to ensure that error is not introduced by reason of some variation between radiation sources, a single source is usually used to generate the beams of radiation over both paths. Thus, a beam splitter or chopper is required. Analyzers of this sort may be relatively large. Further, appreciable energy is consumed, often of the order of tens of watts. This is required to power the source, to operate the chopper motor for the beam splitter, and to power the measuring circuits.
This invention provides a nondispersive analyzer which is relatively small and light in weight, and which does not require either a beam splitter or a mechanical chopper. It requires very little power, approximately one watt, and that only intermittently. It can therefore be operated for several weeks on the energy stored in a lightweight battery. It uses an elliptical reflector to focus light from its energy source.
131q833 DE~CRIPTION OF THE PRIOR ART
Elliptical cylinder and ellipsoidal reflectors are commonly used in optics to focus light. Such reflectors are frequently used in measuring devices. Thus U.S.P. 3,266,313 (Litterest) shows a temperature measuring device where the object whose temperature is to be measured (a wire) is at one focus of an ellipse and the detector is at another focus. U.S.P. 4,810,658 (Shanks) shows in Figure 4a a system where a liquid sample in contact with a solid wave guide is placed at one focus of an ellipse and a light source at the other focus.
Partially elliptical or ellipsoidal mirrors are shown in Canadian Patents 1,126,977 (Hogg) and 1,127,867 (Brunsting) for particle counters. The sample and light source are located at one focus of the ellipse. A detector is located either on the axis of the two foci (in Brunsteig) or is reflected off this axis by a mirror (in Hogg).
C.P. 1,228,748 (Oetliker) shows a variety of light guiding designs for various purposes using ellipsoids. In some of the designs the light source and the sample are at one focus of an ellipsoid and a detector is at the other focus. In other designs, a light source is at one focus and a specimen to be treated by light (as for example in a chemical process) is at the second focus.
Elliptical or ellipsoidal reflectors are not common in spectrometry. Three patents of Oehler, U.S.P.
4,557,603; 4,6S7,397 and 4,740,086 and one of Miyatake (U.S.P. 4,808,825) disclose infrared spectrophotometers.
However, such spectrophotometers are not of the non-dispersive type, and have only one gas cell which is traversed by the light. They do not assist in the design of a non-dispersive gas analyzer, where light rays must pass through several gas cells to give a comparative measurement.
BRIEF DE~CRIPTION OF THE INVENTION
According to the present invention, there is provided an analyzer which comprises a body having a cavity having an elliptical reflecting surface means, which defines a first focus and a second focus, for transmitting radiation between the focuses, a chamber for holding a sample gas to be analyzed, one of the focuses being located within the sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, the inert gas and analyte gas chambers being positioned along a path extending between the second focus and at least a portion of the reflecting surface means; a radiation source dis-posed at one of the focuses; and detector means associated with each inert gas chamber and analyte chamber for detect-ing radiation passing through the sample gas and and its associated gas chamber.
The chambers are so positioned so that radiation focused by the elliptical reflecting surface will always pass through the sample chamber and either the analyte chamber or the inert gas chamber as it travels to a detect-ing means. In certain embodiments of the invention, there is a plurality of analyte chambers and detectors, so that the sample gas can be analyzed for several different components (analytes). This invention can be applied, for example, to monitoring air quality, detecting leakage, or as the sensing element in a flow control system.
Figure 1 is a cross-sectional plan view of one embodiment of the novel analyzer, taken on the line 1-1 of Figure 2.
Figure 2 is a cross-sectional side view of the same embodiment, taken on the line 2-2 of Figure 1.
Figure 3 is a cross-sectional side view similar to Figure 2, of a different embodiment, which can be used to analyze a sample simultaneously for three different gases.
- 3a -DETAILED DE8CRIPTION OF PREFFRRED ENBODINæNT8 Figures 1 and 2 show an analyzer for analyzing the content of one particular gas in an unknown sample.
For example, the sample may be ambient air, and carbon dioxide may be the gas whose concentration is to be measured.
An analyzer housing (not shown) is provided.
Within the housing is a chamber 2 (hereinafter called the sample chamber) to contain the sample to be analyzed, a ,,, , ,~1,~
chamber 3 (hereinafter called the analyte chamber) containing the analyte gas, and a chamber ~ (hereinafter called the inert gas chamber) to contain an inert gas, which may suitably be the sample gas which does not contain the analyte gas. The chamber 2 comprises a side wall 10, two end portions 12a and 12b, top wall 14a and bottom wall l~b. The side wall 10 is a portion of an ellipse, with it~s foci at fl and f2. The end portions terminate in two openings 13a and 13b. The shape of the two end portions 12a and 12b is not critical, and they can be elliptical if desired. Their purpose is to close the open side of the elliptical reflector and to form two openings 13a and 13b which support the detectors. Suitably, the side wall is a material which efficiently reflects radiation, for example polished aluminum, or a composite material coated with a reflective material.
The top portion of the side wall 10 mates with top wall l~a. The bottom portion mates with bottom wall l~b. The top and bottom walls are made of a suitably reflective material, such as polished aluminum.
Each of walls l~a and l~b is provided with a plurality of holes 15, to permit the sample gas to enter and leave the device. If the device is used as an air tester, the sample gas will normally be the ambient air being tested.
In the region bounded by the end portions 12a and 12b there is a divider wall 16, parallel to the top and bottom walls. Preferably, the divider is located midway between the top and bottom walls.
Two windows 17 and 18 extend in gas tight relation between the top wall 14a and the bottom wall l~b and the divider wall 16. These windows can be made from any gas impermeable material that is substantially transparent at the wavelengths at which the analyte absorbs, as is known in the art. For example, sapphire or potassium bromide are suitable materials when measuring the carbon dioxide content of air by infrared absorption.
At the focus fl of the ellipse, within chamber 2, is situated radiation source 2~. The source is preferably 131q833 linear and small in cross section. If the analyzer is to use infrared radiation, it can be a conventional gas chromatograph thermal conductivity detector element. One suitable such element is a Gow-Mac* # 13-470P element.
5 Suitable wiring 25 leads from the source 24 through the bottom and/or top walls to a suitable power source and control circuit.
At the focus f2 of the ellipse, in gas-tight seal in the openings 13a and 13b, are placed two detectors.
10The top wall 14a, elliptical side wall 10 and bottom wall 14b, together with windows 17 and 18, define the sample chamber 2. The detector 27, window 17, top wall 14a and divider wall 16, together with side walls 12, define the analyte chamber 3. The detector 26, the window 1518, bottom wall 14b and divider wall 16, together with side walls 12, define the inert gas chamber 4. These detectors can be any detector compatible with the wavelength of the radiation and the wavelengths absorbed by the analyte. For example, when the analyzer is to be used to analyze carbon 20 dioxide in air, the detectors can be thermopile detectors, thermistors, or pyroelectric detectors. One suitable detector for such analysis is, for example, a model 2 thermopile detector obtained from Dexter Research Centre.
The radiation source 24, and the detectors 26 and 25 27, are placed respectively as precisely as possible on foci fl and f2 of the elliptical reflector 10.
The detectors are connected by suitable wiring 28~ and 28b to a suitable instrument control and data collection apparatus 29. For example, the apparatus 29 can 30 include a microprocessor connected and programmed to control the timing and switching functions necessary for operating the instrument, to store and analyze the data, and to display the processed data as required.
A suitable power supply (not shown) is provided 35 for the radiation source 24 and the instrument control and data collection apparatus 29. Such a suitable power supply can be, for example, several AA size alkaline cells connected in series and/or parallel.
*Trade-mark .~ .
If it is desired to correct for changes in ambient temperature, a thermistor 31 can be placed in close proximity to the detectors, and its response used in the known way to compensate the data collection apparatus 29 by wiring 32.
A suitable means for confirming proper operation of the instrument can be provided if desired. This can be done, for example, by providing a screen with known radiation removal characteristics, which can be moved into the beam passing from the radiation source to one detector.
The detector reading should then vary in the known manner from the screen characteristics.
Prior to operation, the analyte chamber 3 is filled with the analyte gas and the inert gas chamber 4 is filled with inert gas. For example, if it is intended to measure the concentration of carbon dioxide in ambient air, air with the carbon dioxide removed can be used in chamber and chamber 3 is filled with carkon dioxide.
The gas mixture to be analyzed is allowed to diffuse, or is otherwise introduced, into chamber 2 through holes 15. The radiation source is energized. Since sidewall 10 is elliptical in shape, with the source 24 located at one focus fl, the radiation emitted from source 24 is focused at f2. A portion of such radiation passes through sample chamber 2 and analyte chamber 3 to impinge on detector 27 at f2. A further portion passes through sample chamber 2 and inert gas chamber ~ to impinge on detector 26.
This focusing by the elliptical reflector permits detector readings to be obtained with little expenditure of energy, allowing a relatively low-powered radiation source to be used. It has been found, for example, that the source, the detectors and the data collection and analysis device can be operated in one embodiment on a total power of approximately 400 mw.
The data received from the two detectors 26 and 27 are analyzed in known fashion. If the unknown sample in sample chamber 2 does not contain the analyte gas, the difference between the output of detectors 26 and 27 will remain at a fixed known value (when corrected for temperature variation by means of thermistor 31). If, however, there is some of the analyte gas in the sample in sample chamber 2, the difference between the readings of detectors 26 and 27 will exhibit a reduced value characteristic of the concentration of the analyte in sample chamber 2.
Figure 3 shows an embodiment in which analysis is carried out simultaneously for three analyte gases. In that Figure, the same numbering is used as in Figur-s 1 and 2 where parts are the same. However, instead of the single analyte chamber 3, three analyte chambers 3a, 3b, and 3c, for three different analytes are provided, and these are separated by walls 16a, 16b, and 16c. As before, chamber 4 contains a gas which is inert with respect to the measurement to be made. If the device is to analyze air, the inert gas can be air from which the analyte gases have been removed. Four detectors 27a, 27b, 27c, and 2C are provided on the focus f2 to measure the radiation passing through the chambers 3a, 3b, 3c, and ~.
As will be noted from the description, only a portion of wall 10 need be elliptical. Even a small segment of an elliptical wall is helpful, as it will direct some of the energy from the radiation source is a beam directed to the detectors. Generally, it is preferred that the wall ID form at least one-quarter of an ellipse, and that this be at the end of the device proximate to the focus fl and remote from the focus f2. However, the device can be arranged with wall 10 as a full ellipse.
Alternately, walls 10, 14a and 14b can together form an ellipsoid, or a portion of an ellipsoid, to further focus the radiations. However, this is generally not preferred as it results in more difficult construction techniques.
The analyzer has been described with respect to a source of infrared radiation, and a detector for such radiation. However, depending on the intended analyte, it may be preferable to have the radiation source 24 as a visible or ultraviolet light bulb or light pipe from an external bulb, and to have a suitable detector for ultraviolet or visible light.
The invention has been shown with reference to certain embodiments, but it will be obvious that variations can be made by one skilled in the art without departing from the spirit of the invention, which is as set out in the appended claims.
This invention relates to a nondispersive analyzer, which can be used ~o monitor the concentration one or more gases.
BACKGROUND OF THB INVBNTION
Nondispersive analyzers are analyzers which provide discrete radiation paths from a source to one or more means for detecting the intensity of radiation. One of these paths is through the sample to be analyzed as well as through an isolated fixed quantity of the analyte gas, and another of these paths is through the sample to be analyzed only. Therefore, that part of the radiation which is at the wavelengths absorbed by the analyte gas is removed from one path, but not the other, resulting in a difference in the outputs from the energy detecting means associated with these paths. Thus, it is only when the sample contains the analyte gas that the difference between the intensities of the radiation along the two paths will be reduced. Other absorbing compounds affect both detectors equally.
In order to ensure that error is not introduced by reason of some variation between radiation sources, a single source is usually used to generate the beams of radiation over both paths. Thus, a beam splitter or chopper is required. Analyzers of this sort may be relatively large. Further, appreciable energy is consumed, often of the order of tens of watts. This is required to power the source, to operate the chopper motor for the beam splitter, and to power the measuring circuits.
This invention provides a nondispersive analyzer which is relatively small and light in weight, and which does not require either a beam splitter or a mechanical chopper. It requires very little power, approximately one watt, and that only intermittently. It can therefore be operated for several weeks on the energy stored in a lightweight battery. It uses an elliptical reflector to focus light from its energy source.
131q833 DE~CRIPTION OF THE PRIOR ART
Elliptical cylinder and ellipsoidal reflectors are commonly used in optics to focus light. Such reflectors are frequently used in measuring devices. Thus U.S.P. 3,266,313 (Litterest) shows a temperature measuring device where the object whose temperature is to be measured (a wire) is at one focus of an ellipse and the detector is at another focus. U.S.P. 4,810,658 (Shanks) shows in Figure 4a a system where a liquid sample in contact with a solid wave guide is placed at one focus of an ellipse and a light source at the other focus.
Partially elliptical or ellipsoidal mirrors are shown in Canadian Patents 1,126,977 (Hogg) and 1,127,867 (Brunsting) for particle counters. The sample and light source are located at one focus of the ellipse. A detector is located either on the axis of the two foci (in Brunsteig) or is reflected off this axis by a mirror (in Hogg).
C.P. 1,228,748 (Oetliker) shows a variety of light guiding designs for various purposes using ellipsoids. In some of the designs the light source and the sample are at one focus of an ellipsoid and a detector is at the other focus. In other designs, a light source is at one focus and a specimen to be treated by light (as for example in a chemical process) is at the second focus.
Elliptical or ellipsoidal reflectors are not common in spectrometry. Three patents of Oehler, U.S.P.
4,557,603; 4,6S7,397 and 4,740,086 and one of Miyatake (U.S.P. 4,808,825) disclose infrared spectrophotometers.
However, such spectrophotometers are not of the non-dispersive type, and have only one gas cell which is traversed by the light. They do not assist in the design of a non-dispersive gas analyzer, where light rays must pass through several gas cells to give a comparative measurement.
BRIEF DE~CRIPTION OF THE INVENTION
According to the present invention, there is provided an analyzer which comprises a body having a cavity having an elliptical reflecting surface means, which defines a first focus and a second focus, for transmitting radiation between the focuses, a chamber for holding a sample gas to be analyzed, one of the focuses being located within the sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, the inert gas and analyte gas chambers being positioned along a path extending between the second focus and at least a portion of the reflecting surface means; a radiation source dis-posed at one of the focuses; and detector means associated with each inert gas chamber and analyte chamber for detect-ing radiation passing through the sample gas and and its associated gas chamber.
The chambers are so positioned so that radiation focused by the elliptical reflecting surface will always pass through the sample chamber and either the analyte chamber or the inert gas chamber as it travels to a detect-ing means. In certain embodiments of the invention, there is a plurality of analyte chambers and detectors, so that the sample gas can be analyzed for several different components (analytes). This invention can be applied, for example, to monitoring air quality, detecting leakage, or as the sensing element in a flow control system.
Figure 1 is a cross-sectional plan view of one embodiment of the novel analyzer, taken on the line 1-1 of Figure 2.
Figure 2 is a cross-sectional side view of the same embodiment, taken on the line 2-2 of Figure 1.
Figure 3 is a cross-sectional side view similar to Figure 2, of a different embodiment, which can be used to analyze a sample simultaneously for three different gases.
- 3a -DETAILED DE8CRIPTION OF PREFFRRED ENBODINæNT8 Figures 1 and 2 show an analyzer for analyzing the content of one particular gas in an unknown sample.
For example, the sample may be ambient air, and carbon dioxide may be the gas whose concentration is to be measured.
An analyzer housing (not shown) is provided.
Within the housing is a chamber 2 (hereinafter called the sample chamber) to contain the sample to be analyzed, a ,,, , ,~1,~
chamber 3 (hereinafter called the analyte chamber) containing the analyte gas, and a chamber ~ (hereinafter called the inert gas chamber) to contain an inert gas, which may suitably be the sample gas which does not contain the analyte gas. The chamber 2 comprises a side wall 10, two end portions 12a and 12b, top wall 14a and bottom wall l~b. The side wall 10 is a portion of an ellipse, with it~s foci at fl and f2. The end portions terminate in two openings 13a and 13b. The shape of the two end portions 12a and 12b is not critical, and they can be elliptical if desired. Their purpose is to close the open side of the elliptical reflector and to form two openings 13a and 13b which support the detectors. Suitably, the side wall is a material which efficiently reflects radiation, for example polished aluminum, or a composite material coated with a reflective material.
The top portion of the side wall 10 mates with top wall l~a. The bottom portion mates with bottom wall l~b. The top and bottom walls are made of a suitably reflective material, such as polished aluminum.
Each of walls l~a and l~b is provided with a plurality of holes 15, to permit the sample gas to enter and leave the device. If the device is used as an air tester, the sample gas will normally be the ambient air being tested.
In the region bounded by the end portions 12a and 12b there is a divider wall 16, parallel to the top and bottom walls. Preferably, the divider is located midway between the top and bottom walls.
Two windows 17 and 18 extend in gas tight relation between the top wall 14a and the bottom wall l~b and the divider wall 16. These windows can be made from any gas impermeable material that is substantially transparent at the wavelengths at which the analyte absorbs, as is known in the art. For example, sapphire or potassium bromide are suitable materials when measuring the carbon dioxide content of air by infrared absorption.
At the focus fl of the ellipse, within chamber 2, is situated radiation source 2~. The source is preferably 131q833 linear and small in cross section. If the analyzer is to use infrared radiation, it can be a conventional gas chromatograph thermal conductivity detector element. One suitable such element is a Gow-Mac* # 13-470P element.
5 Suitable wiring 25 leads from the source 24 through the bottom and/or top walls to a suitable power source and control circuit.
At the focus f2 of the ellipse, in gas-tight seal in the openings 13a and 13b, are placed two detectors.
10The top wall 14a, elliptical side wall 10 and bottom wall 14b, together with windows 17 and 18, define the sample chamber 2. The detector 27, window 17, top wall 14a and divider wall 16, together with side walls 12, define the analyte chamber 3. The detector 26, the window 1518, bottom wall 14b and divider wall 16, together with side walls 12, define the inert gas chamber 4. These detectors can be any detector compatible with the wavelength of the radiation and the wavelengths absorbed by the analyte. For example, when the analyzer is to be used to analyze carbon 20 dioxide in air, the detectors can be thermopile detectors, thermistors, or pyroelectric detectors. One suitable detector for such analysis is, for example, a model 2 thermopile detector obtained from Dexter Research Centre.
The radiation source 24, and the detectors 26 and 25 27, are placed respectively as precisely as possible on foci fl and f2 of the elliptical reflector 10.
The detectors are connected by suitable wiring 28~ and 28b to a suitable instrument control and data collection apparatus 29. For example, the apparatus 29 can 30 include a microprocessor connected and programmed to control the timing and switching functions necessary for operating the instrument, to store and analyze the data, and to display the processed data as required.
A suitable power supply (not shown) is provided 35 for the radiation source 24 and the instrument control and data collection apparatus 29. Such a suitable power supply can be, for example, several AA size alkaline cells connected in series and/or parallel.
*Trade-mark .~ .
If it is desired to correct for changes in ambient temperature, a thermistor 31 can be placed in close proximity to the detectors, and its response used in the known way to compensate the data collection apparatus 29 by wiring 32.
A suitable means for confirming proper operation of the instrument can be provided if desired. This can be done, for example, by providing a screen with known radiation removal characteristics, which can be moved into the beam passing from the radiation source to one detector.
The detector reading should then vary in the known manner from the screen characteristics.
Prior to operation, the analyte chamber 3 is filled with the analyte gas and the inert gas chamber 4 is filled with inert gas. For example, if it is intended to measure the concentration of carbon dioxide in ambient air, air with the carbon dioxide removed can be used in chamber and chamber 3 is filled with carkon dioxide.
The gas mixture to be analyzed is allowed to diffuse, or is otherwise introduced, into chamber 2 through holes 15. The radiation source is energized. Since sidewall 10 is elliptical in shape, with the source 24 located at one focus fl, the radiation emitted from source 24 is focused at f2. A portion of such radiation passes through sample chamber 2 and analyte chamber 3 to impinge on detector 27 at f2. A further portion passes through sample chamber 2 and inert gas chamber ~ to impinge on detector 26.
This focusing by the elliptical reflector permits detector readings to be obtained with little expenditure of energy, allowing a relatively low-powered radiation source to be used. It has been found, for example, that the source, the detectors and the data collection and analysis device can be operated in one embodiment on a total power of approximately 400 mw.
The data received from the two detectors 26 and 27 are analyzed in known fashion. If the unknown sample in sample chamber 2 does not contain the analyte gas, the difference between the output of detectors 26 and 27 will remain at a fixed known value (when corrected for temperature variation by means of thermistor 31). If, however, there is some of the analyte gas in the sample in sample chamber 2, the difference between the readings of detectors 26 and 27 will exhibit a reduced value characteristic of the concentration of the analyte in sample chamber 2.
Figure 3 shows an embodiment in which analysis is carried out simultaneously for three analyte gases. In that Figure, the same numbering is used as in Figur-s 1 and 2 where parts are the same. However, instead of the single analyte chamber 3, three analyte chambers 3a, 3b, and 3c, for three different analytes are provided, and these are separated by walls 16a, 16b, and 16c. As before, chamber 4 contains a gas which is inert with respect to the measurement to be made. If the device is to analyze air, the inert gas can be air from which the analyte gases have been removed. Four detectors 27a, 27b, 27c, and 2C are provided on the focus f2 to measure the radiation passing through the chambers 3a, 3b, 3c, and ~.
As will be noted from the description, only a portion of wall 10 need be elliptical. Even a small segment of an elliptical wall is helpful, as it will direct some of the energy from the radiation source is a beam directed to the detectors. Generally, it is preferred that the wall ID form at least one-quarter of an ellipse, and that this be at the end of the device proximate to the focus fl and remote from the focus f2. However, the device can be arranged with wall 10 as a full ellipse.
Alternately, walls 10, 14a and 14b can together form an ellipsoid, or a portion of an ellipsoid, to further focus the radiations. However, this is generally not preferred as it results in more difficult construction techniques.
The analyzer has been described with respect to a source of infrared radiation, and a detector for such radiation. However, depending on the intended analyte, it may be preferable to have the radiation source 24 as a visible or ultraviolet light bulb or light pipe from an external bulb, and to have a suitable detector for ultraviolet or visible light.
The invention has been shown with reference to certain embodiments, but it will be obvious that variations can be made by one skilled in the art without departing from the spirit of the invention, which is as set out in the appended claims.
Claims (11)
1. An analyzer, comprising:
a body having a cavity having an elliptical reflecting surface means, defining a first focus and a second focus, for transmitting radiation between said focuses, a chamber for holding a sample gas to be analyzed, one of said focuses being located within said sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, said inert gas and analyte gas chambers being positioned along a path extending between said second focus and at least a portion of said reflecting surface means;
a radiation source disposed at one of said focuses; and detector means associated with each said inert gas chamber and said analyte chamber for detecting radiation passing through said sample gas and and its associated gas chamber.
a body having a cavity having an elliptical reflecting surface means, defining a first focus and a second focus, for transmitting radiation between said focuses, a chamber for holding a sample gas to be analyzed, one of said focuses being located within said sample chamber, a chamber for holding an inert gas and a chamber for holding an analyte gas, said inert gas and analyte gas chambers being positioned along a path extending between said second focus and at least a portion of said reflecting surface means;
a radiation source disposed at one of said focuses; and detector means associated with each said inert gas chamber and said analyte chamber for detecting radiation passing through said sample gas and and its associated gas chamber.
2. An analyzer as defined in claim 1, said radiation means being disposed within said sample chamber, said detector means having an active element disposed at said second focus.
3. An analyzer as defined in claim 2, said sample gas chamber, said inert gas chamber and said analyte chamber being in gas tight relation to one another.
4. An analyzer as defined in claim 1, further including divider wall means for sealingly separating said inert gas chamber and said analyte chamber from one another and preventing the exchange of radiation therebetween.
5. An analyzer as defined in claim 1, further including transparent window means for sealingly separating said sample chamber from each said inert gas chamber and said analyte chamber while permitting the transmission of radiation therebetween.
6. An analyzer as defined in claim 5, further including means for admitting a sample gas into said sample chamber.
7. An analyzer as defined in claim 6, said admitting means including apertures in said body for permitting ambient air to diffuse into said sample chamber.
8. An analyzer as defined in claim 1, further including a plurality of said analyte chambers.
9. An analyzer as defined in claim 1, said body having a side wall and opposed end walls defining said cavity, at least a portion of said side wall having an elliptical cylindrical inner surface defining said reflecting surface whereby each said focus being a focal axis paralleling said side wall, a transparent window extending across said side wall between said focal axes so as to define said sample chamber with said opposed end walls and said side wall, and at least one divider wall extending between said side wall and said window remote from said sample chamber and defin-ing therewith said inert gas chamber and said analyte chamber.
10. An analyzer as defined in claim 9, said radiation source being disposed along said focal axis within said sample chamber and said detector means comprising a gas detector disposed at the focal axis extending through each said inert gas chamber and said analyte chamber.
11. A nondispersive gas analyzer for use in monitoring the concentration one or more gases, comprising:
a body having a side wall and opposed end walls defining a cavity, at least a portion of said side wall having a reflective elliptical cylindrical inner surface defining a first focal axis and a second focal axis paralleling said side wall, a transparent window extending across said cavity transversely of a plane containing said focal axes and being in gas tight engagement between said side wall and said opposed end walls so as to define therewith a sample chamber for a sample gas to be analyzed, at least one divider wall extending perpendicularly of said focal axes and said window on a side thereof remote from said sample chamber, said divider wall being in gas sealing engagement with said body and said window so as to define an inert gas chamber and an analyte chamber, said first focal axis extending through said sample chamber and said second focal axis extending through each said inert gas chamber and said analyte chamber, said body having means for admitting ambient gases into said sample chamber;
a radiation source disposed within said sample chamber along said first focal axis; and a detector associated with said inert gas chamber and said analyte chamber for producing an electrical signal representative of the radiation passing through said sample gas and the analyte gas contained within its associated chamber.
a body having a side wall and opposed end walls defining a cavity, at least a portion of said side wall having a reflective elliptical cylindrical inner surface defining a first focal axis and a second focal axis paralleling said side wall, a transparent window extending across said cavity transversely of a plane containing said focal axes and being in gas tight engagement between said side wall and said opposed end walls so as to define therewith a sample chamber for a sample gas to be analyzed, at least one divider wall extending perpendicularly of said focal axes and said window on a side thereof remote from said sample chamber, said divider wall being in gas sealing engagement with said body and said window so as to define an inert gas chamber and an analyte chamber, said first focal axis extending through said sample chamber and said second focal axis extending through each said inert gas chamber and said analyte chamber, said body having means for admitting ambient gases into said sample chamber;
a radiation source disposed within said sample chamber along said first focal axis; and a detector associated with said inert gas chamber and said analyte chamber for producing an electrical signal representative of the radiation passing through said sample gas and the analyte gas contained within its associated chamber.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 615459 CA1319833C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
| US07/720,428 US5170064A (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector using a cavity having elliptical reflecting surface |
| PCT/CA1990/000288 WO1991005240A1 (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector |
| JP2512096A JP2895622B2 (en) | 1989-09-29 | 1990-09-10 | Gas detector using infrared |
| EP90912732A EP0493401B1 (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector |
| DE69007291T DE69007291T2 (en) | 1989-09-29 | 1990-09-10 | INFRARED GAS DETECTOR. |
| AU62910/90A AU6291090A (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 615459 CA1319833C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1319833C true CA1319833C (en) | 1993-07-06 |
Family
ID=4140909
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 615459 Expired - Fee Related CA1319833C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1319833C (en) |
-
1989
- 1989-09-29 CA CA 615459 patent/CA1319833C/en not_active Expired - Fee Related
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| Date | Code | Title | Description |
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| MKLA | Lapsed |