CA1318520C - Infrared-based gas detector - Google Patents
Infrared-based gas detectorInfo
- Publication number
- CA1318520C CA1318520C CA 615091 CA615091A CA1318520C CA 1318520 C CA1318520 C CA 1318520C CA 615091 CA615091 CA 615091 CA 615091 A CA615091 A CA 615091A CA 1318520 C CA1318520 C CA 1318520C
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- CA
- Canada
- Prior art keywords
- gas
- chamber
- sample
- sealed
- sample gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 239000007789 gas Substances 0.000 claims abstract description 131
- 230000005855 radiation Effects 0.000 claims abstract description 56
- 239000012491 analyte Substances 0.000 claims abstract description 27
- 239000011261 inert gas Substances 0.000 claims abstract description 15
- 238000005192 partition Methods 0.000 claims 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 6
- 238000013480 data collection Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229910002092 carbon dioxide Inorganic materials 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 239000003570 air Substances 0.000 description 2
- 239000012080 ambient air Substances 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
- 238000007405 data analysis Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012544 monitoring process Methods 0.000 description 1
- 239000002245 particle 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
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- 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, infrared gas analyzer comprises a body having a chamber for holding a sample gas to be analyzed, the sample gas chamber having a reflective inner surface, at least a portion of the inner surface being elliptical and defining a first focus and a second focus within the sample gas chamber and being operable to reflect radiation between the focuses, a sealed inert gas chamber for holding an inert gas, a sealed analyte gas chamber for holding an analyte gas, an infrared radiation source disposed at the first focus in the sample gas chamber, a reflector disposed at or around the second focus for reflecting radiation emitted by the radiation source and reflected by the reflective inner surface toward each sealed gas chamber, and a detector associated with each sealed gas chamber for detecting radiation, emitted by the source, which has travelled through the sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in the sample gas of the gas contained in its associated sealed gas chamber.
A nondispersive, infrared gas analyzer comprises a body having a chamber for holding a sample gas to be analyzed, the sample gas chamber having a reflective inner surface, at least a portion of the inner surface being elliptical and defining a first focus and a second focus within the sample gas chamber and being operable to reflect radiation between the focuses, a sealed inert gas chamber for holding an inert gas, a sealed analyte gas chamber for holding an analyte gas, an infrared radiation source disposed at the first focus in the sample gas chamber, a reflector disposed at or around the second focus for reflecting radiation emitted by the radiation source and reflected by the reflective inner surface toward each sealed gas chamber, and a detector associated with each sealed gas chamber for detecting radiation, emitted by the source, which has travelled through the sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in the sample gas of the gas contained in its associated sealed gas chamber.
Description
131~5~0 FIELD OF THE INVEN~ION
This invention relates to a nondispersive analyzer, which can be used to monitor the concentration of one or more gases.
BACXGRO~D ~F THE INV~NT~ON
Nondispersive analyzers are analyzers which provide discrete radiation paths from a radiation source to one or more means for detecting the intensity of radiation.
One of these paths is through an isolated fixed quantity of the analyte gas as well as through the sample to be analyzed, 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 dif~erence 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 sources of radiation, a single source is usually used to generate the beams of radiation over both light paths. Thus, a beam splitter or chopper is required. Analyzers of this sort may be rela-tively large. Further, appreciable energy is consumed, often of the order of tens of watts. This is require~ 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 1 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 radiation source.
. r 1 31 852n DESCRIPTION OF ~'HE PRIOR ART
Elliptical cylinder and ellipsoidal reflectors are commonly use~ in optics to focus radiation. such reflectors are frequently used in measuring devices. Thus U.S.P. 3,226,313 (Litterst) shows a temperature measuring device where the object whose temperature is to be measured (a wire) at one focus o an el:Liptical re~lector and the detector at the other focus. U.S.P. 4,810,658 (Shanks) shows in Figure 4a a system ~here a liquid sample in contact with a solid waveguide is placed at one focus of an elliptical reflector and a light source at the other focus.
Partially elliptical or ellipsoidal reflectors 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 source of the elliptical reflector. A detector is located either on the axis of the two foci (in Brunsting) 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 ellipsoidal reflectors. In some of the designs the light source and the sample are at one focus of an ellipsoidal reflector 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 Oehler; U.S.P.
4,557,603; 4,657,397 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 radiation. They do not assist in the design of a non-dispersive gas analyzer, where the radiation must pass through at least two gas cells to give a comparative measurement.
~r ", ~. "
131~520 BRIEF ~ESCRIPTION OF TH2 INVENTION
According to the present invention, there is provided a nondispersive, infrared gas analyzer, c~mprising a body having a chamber for holding a sample gas to be analyzed, the sample gas chamber having a reflective inner surface, at least a portion of the inner surface being elliptical and defining a first focus and a second focus within the sample gas chamber and being operable to reflect radiation between the focuses, a sealed inert gas chamber lo for holding an inert gas, a sealed analyte gas chamber for holding an analyte gas, an infrared radiation source disposed at the first focus in the sample gas chamber, a reflector disposed around the second focus for reflecting radiation emitted by the radiation source and focused by the reflective inner surface toward each sealed gas chamber, and a detector associated with each sealed gas chamber for detecting radiation, emitted by the source, which has travelled through the sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in the sample gas of the gas contained in its associated sealed gas chamber.
In various embodiments of the invention, a reflector, or a plurality of reflectors, or a single moveable reflector, or a plurality of moveable reflectors are located at or around the second focus of the ellipse, and such reflector or reflectors direct the light beam to a plurality of analyte chambers and detectors.
This invention can be applied, for example, to monitoring air ~uality, detecting leakage, or as the sensing element in a flow control system.
1 31 ~3520 DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional plan view of one embodiment of the novel analyzsr, taken on the line 1-1 of Figure 2.
5~igure 2 is a cross-sectional side view of the same embodiment, taken on the line 2-2 of Figure 1.
Figur~ 3 is a cut-away perspective view of a further embodiment in which an ellipsoidal reflector is used to further increase the number of gases which can be measured simultaneously.
DETAILED DESC~IPTION OF PREFERRED ~MBODIMEN~
Figure~ 1 and 2 show an analyzer for analyzing the content of several gases in an unknown sample.
15An 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, chambers 3, 3~, 3b, 3c, and 3d (hereinafter called the analyte chambers) each containing one of the plurality of gases to be analyzed for, and a chamber 4 (hereinafter called the inert gas chamber) to contain an inert gas, which may suitably be the sample gas in which none of the analyte gases are present. The chamber 2 comprises a side wall ~0, top wall 14 and bottom wall 14a. The side wall 10 is an ellipse, with its foci at fl and f2, although it may be made as a portion of an ellipse, with a non-elliptical or several non-elliptical portions if desired. This reduces the effectiveness of the device; but may be usable if some additional power loss can be tolerated. Suitably, the side wall 10 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 a top wall 14. The bottom portion mates with a bottom wall 14a. The two walls are made of a suitable reflective material, such as polished aluminum.
Each of walls 14 and 14a is provided with a plurality of holes 15, to permit the sample gas to enter and leave the device.
~' .
1 31 ~520 At the focus fl o~ the ellipse, within chamber 2, is situated a radiation source 2~. The source i5 preferably linear and small in cross section, as can be a conventional gas chromatograph thermal conductivity detector element. One suitable such element is a Gow-Mac*
# 13-470P element.
A multi-faceted reflective column 31 is centered at focus f2. Column 31 is approximately hexagonal in cross section. It is preferrecl to deviate from a true hexagon in that a slight curvature of the reflective faces 31a, 31b, 31c, 31a, 31e, 31~, i5 needed to focus the radiation reflected ~rom these faces toward the corresponding detectors 26, 27, 27~, 27b, 27c, and 27d.
The column is of a suitable material and is polished, so that the faces corresponding to the sides of the hexagon reflect radiation. For example, the column can be polished aluminum.
When the source 24 is energized, radiation is focused toward the center of column 31. Each of the faces of column 31 reflects a beam of radiation toward a specific location on wall 10. For example, two rays o~ radiation are shown emanating from the source 2~. These rays are focused toward f2 by the elliptical reflector 10. They are then reflected by face 31d toward hole 40 which penetrates wall 10. Behind hole 40 are oriented one behind the other window 50 and detector 27b, which define between them, in combination with a cylindrical side wall 60, a chamber 3b.
Similarlyl other holes 41, 42, 43, 44, and 45 are shown, which receive reflections from faces 31e, 31f, 31a, 31b, and 310 respectively. In such a structure, a multiplicity of detectors and their corresponding chambers can be provided.
With a device having six chambers, it is possible to simultaneously measure the concentrations of five analytes in the sample in chamber 2. The sixth chamber contains an inert gas, for example, the sample gas which does not contain the analyte gases.
The detectors are connected by suitable wiring 2~
to a suitable instrument control and data collection *Trademark l3l~s2n apparatus 29. For example, the apparatus 2g can 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 for the source 24 and the instrument control and data collection apparatus 2g. A suitable power supply is, for example, several AA size alkaline cells connected in series and/or parallel to supply the different voltages required.
If it is desired to correct for changes in ambient temperature/ a thermistor 31 can be installed, and its response used in the known way to compensate the data collection apparatus 2g 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 removing a known and reproducible part of the radiation from one beam by introducing a screen into one beam, as is known in the art.
Prior to operation, the analyte chambers 3, 3a, 3b, 3c, and 3d are filled with the analyte gases and gas chamber 4 is filled with inert gas~ For example, air with the carbon dioxide removed can be used in chamber 4 where the analyte is carbon dioxide, and it is intended to measure the concentration of carbon dioxide in ambient air.
The gas mixture to be analyzed is allowed to diffuse, or is otherwise introduced, into chamber 2 through holes 15. The source is energized. Sinca sidewall 10 is elliptical in shape, with the source 24 located at one focus fl, the radiation emitted from source 2~ is focused at f2. Such radiation is then reflected by reflectors 31a, 31b, 31c, 31d, 31e, and 31~ through analyte chambers 3, 3a, 3b, 3c, 3d, and inert gas chamber 4.
This focusing by the elliptical reflector onto reflecting surfaces of column 31 permits detector readings to be obtained with little expenditure of energy, allowing a relatively low-powered 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 detectors 26, 27, 27a, 27b, ~7c, and 27d are analyzed in known fashion. If the unknown sample in sample chambe~r 2 does not contain the analyte gas, the difference between the output of detector 26 and the other detectors wil:L remain at a fixed known value (when corrected for temperature variation by means of thermistor 31). If, however, there is some amount of one of the analyte gases in the sample in sample chamber 2, the difference between the output of detector 26 and the detector associated with that analyte ~as will exhibit a reduced value characteristic of the concentration of the analyte in sample chamber 2.
In Figure 3 the reflector is an ellipsoid (rather than an elliptical cylinder) with f3 and f4 being the foci of the ellipsoid. Thus, the entire wall 50 is formed as an ellipsoid. A source 51, which is as close as possible being a point source, is placed at focus f3. A
multifaceted reflector 52 is placed at focus ~, and holes are made in the ellipsoid at the points on the wall 50 to which the facets of reflector 52 direct the beams of radiation. Behind each of these holes is placed an analyte or inert gas chamber and a detector. Two holes 53 and 54 are shown, and one associated chamber/detector assembly 55 is shown schematically.
In the example given, only two of many possible radiation paths are shown, and the sample gas could flow, for example, through porous supports 56 and 57.
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 departiny from the spirit of the invention, which is as set out in the appended claims.
,~ , 1 ,
This invention relates to a nondispersive analyzer, which can be used to monitor the concentration of one or more gases.
BACXGRO~D ~F THE INV~NT~ON
Nondispersive analyzers are analyzers which provide discrete radiation paths from a radiation source to one or more means for detecting the intensity of radiation.
One of these paths is through an isolated fixed quantity of the analyte gas as well as through the sample to be analyzed, 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 dif~erence 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 sources of radiation, a single source is usually used to generate the beams of radiation over both light paths. Thus, a beam splitter or chopper is required. Analyzers of this sort may be rela-tively large. Further, appreciable energy is consumed, often of the order of tens of watts. This is require~ 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 1 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 radiation source.
. r 1 31 852n DESCRIPTION OF ~'HE PRIOR ART
Elliptical cylinder and ellipsoidal reflectors are commonly use~ in optics to focus radiation. such reflectors are frequently used in measuring devices. Thus U.S.P. 3,226,313 (Litterst) shows a temperature measuring device where the object whose temperature is to be measured (a wire) at one focus o an el:Liptical re~lector and the detector at the other focus. U.S.P. 4,810,658 (Shanks) shows in Figure 4a a system ~here a liquid sample in contact with a solid waveguide is placed at one focus of an elliptical reflector and a light source at the other focus.
Partially elliptical or ellipsoidal reflectors 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 source of the elliptical reflector. A detector is located either on the axis of the two foci (in Brunsting) 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 ellipsoidal reflectors. In some of the designs the light source and the sample are at one focus of an ellipsoidal reflector 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 Oehler; U.S.P.
4,557,603; 4,657,397 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 radiation. They do not assist in the design of a non-dispersive gas analyzer, where the radiation must pass through at least two gas cells to give a comparative measurement.
~r ", ~. "
131~520 BRIEF ~ESCRIPTION OF TH2 INVENTION
According to the present invention, there is provided a nondispersive, infrared gas analyzer, c~mprising a body having a chamber for holding a sample gas to be analyzed, the sample gas chamber having a reflective inner surface, at least a portion of the inner surface being elliptical and defining a first focus and a second focus within the sample gas chamber and being operable to reflect radiation between the focuses, a sealed inert gas chamber lo for holding an inert gas, a sealed analyte gas chamber for holding an analyte gas, an infrared radiation source disposed at the first focus in the sample gas chamber, a reflector disposed around the second focus for reflecting radiation emitted by the radiation source and focused by the reflective inner surface toward each sealed gas chamber, and a detector associated with each sealed gas chamber for detecting radiation, emitted by the source, which has travelled through the sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in the sample gas of the gas contained in its associated sealed gas chamber.
In various embodiments of the invention, a reflector, or a plurality of reflectors, or a single moveable reflector, or a plurality of moveable reflectors are located at or around the second focus of the ellipse, and such reflector or reflectors direct the light beam to a plurality of analyte chambers and detectors.
This invention can be applied, for example, to monitoring air ~uality, detecting leakage, or as the sensing element in a flow control system.
1 31 ~3520 DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-sectional plan view of one embodiment of the novel analyzsr, taken on the line 1-1 of Figure 2.
5~igure 2 is a cross-sectional side view of the same embodiment, taken on the line 2-2 of Figure 1.
Figur~ 3 is a cut-away perspective view of a further embodiment in which an ellipsoidal reflector is used to further increase the number of gases which can be measured simultaneously.
DETAILED DESC~IPTION OF PREFERRED ~MBODIMEN~
Figure~ 1 and 2 show an analyzer for analyzing the content of several gases in an unknown sample.
15An 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, chambers 3, 3~, 3b, 3c, and 3d (hereinafter called the analyte chambers) each containing one of the plurality of gases to be analyzed for, and a chamber 4 (hereinafter called the inert gas chamber) to contain an inert gas, which may suitably be the sample gas in which none of the analyte gases are present. The chamber 2 comprises a side wall ~0, top wall 14 and bottom wall 14a. The side wall 10 is an ellipse, with its foci at fl and f2, although it may be made as a portion of an ellipse, with a non-elliptical or several non-elliptical portions if desired. This reduces the effectiveness of the device; but may be usable if some additional power loss can be tolerated. Suitably, the side wall 10 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 a top wall 14. The bottom portion mates with a bottom wall 14a. The two walls are made of a suitable reflective material, such as polished aluminum.
Each of walls 14 and 14a is provided with a plurality of holes 15, to permit the sample gas to enter and leave the device.
~' .
1 31 ~520 At the focus fl o~ the ellipse, within chamber 2, is situated a radiation source 2~. The source i5 preferably linear and small in cross section, as can be a conventional gas chromatograph thermal conductivity detector element. One suitable such element is a Gow-Mac*
# 13-470P element.
A multi-faceted reflective column 31 is centered at focus f2. Column 31 is approximately hexagonal in cross section. It is preferrecl to deviate from a true hexagon in that a slight curvature of the reflective faces 31a, 31b, 31c, 31a, 31e, 31~, i5 needed to focus the radiation reflected ~rom these faces toward the corresponding detectors 26, 27, 27~, 27b, 27c, and 27d.
The column is of a suitable material and is polished, so that the faces corresponding to the sides of the hexagon reflect radiation. For example, the column can be polished aluminum.
When the source 24 is energized, radiation is focused toward the center of column 31. Each of the faces of column 31 reflects a beam of radiation toward a specific location on wall 10. For example, two rays o~ radiation are shown emanating from the source 2~. These rays are focused toward f2 by the elliptical reflector 10. They are then reflected by face 31d toward hole 40 which penetrates wall 10. Behind hole 40 are oriented one behind the other window 50 and detector 27b, which define between them, in combination with a cylindrical side wall 60, a chamber 3b.
Similarlyl other holes 41, 42, 43, 44, and 45 are shown, which receive reflections from faces 31e, 31f, 31a, 31b, and 310 respectively. In such a structure, a multiplicity of detectors and their corresponding chambers can be provided.
With a device having six chambers, it is possible to simultaneously measure the concentrations of five analytes in the sample in chamber 2. The sixth chamber contains an inert gas, for example, the sample gas which does not contain the analyte gases.
The detectors are connected by suitable wiring 2~
to a suitable instrument control and data collection *Trademark l3l~s2n apparatus 29. For example, the apparatus 2g can 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 for the source 24 and the instrument control and data collection apparatus 2g. A suitable power supply is, for example, several AA size alkaline cells connected in series and/or parallel to supply the different voltages required.
If it is desired to correct for changes in ambient temperature/ a thermistor 31 can be installed, and its response used in the known way to compensate the data collection apparatus 2g 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 removing a known and reproducible part of the radiation from one beam by introducing a screen into one beam, as is known in the art.
Prior to operation, the analyte chambers 3, 3a, 3b, 3c, and 3d are filled with the analyte gases and gas chamber 4 is filled with inert gas~ For example, air with the carbon dioxide removed can be used in chamber 4 where the analyte is carbon dioxide, and it is intended to measure the concentration of carbon dioxide in ambient air.
The gas mixture to be analyzed is allowed to diffuse, or is otherwise introduced, into chamber 2 through holes 15. The source is energized. Sinca sidewall 10 is elliptical in shape, with the source 24 located at one focus fl, the radiation emitted from source 2~ is focused at f2. Such radiation is then reflected by reflectors 31a, 31b, 31c, 31d, 31e, and 31~ through analyte chambers 3, 3a, 3b, 3c, 3d, and inert gas chamber 4.
This focusing by the elliptical reflector onto reflecting surfaces of column 31 permits detector readings to be obtained with little expenditure of energy, allowing a relatively low-powered 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 detectors 26, 27, 27a, 27b, ~7c, and 27d are analyzed in known fashion. If the unknown sample in sample chambe~r 2 does not contain the analyte gas, the difference between the output of detector 26 and the other detectors wil:L remain at a fixed known value (when corrected for temperature variation by means of thermistor 31). If, however, there is some amount of one of the analyte gases in the sample in sample chamber 2, the difference between the output of detector 26 and the detector associated with that analyte ~as will exhibit a reduced value characteristic of the concentration of the analyte in sample chamber 2.
In Figure 3 the reflector is an ellipsoid (rather than an elliptical cylinder) with f3 and f4 being the foci of the ellipsoid. Thus, the entire wall 50 is formed as an ellipsoid. A source 51, which is as close as possible being a point source, is placed at focus f3. A
multifaceted reflector 52 is placed at focus ~, and holes are made in the ellipsoid at the points on the wall 50 to which the facets of reflector 52 direct the beams of radiation. Behind each of these holes is placed an analyte or inert gas chamber and a detector. Two holes 53 and 54 are shown, and one associated chamber/detector assembly 55 is shown schematically.
In the example given, only two of many possible radiation paths are shown, and the sample gas could flow, for example, through porous supports 56 and 57.
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 departiny from the spirit of the invention, which is as set out in the appended claims.
,~ , 1 ,
Claims (16)
1. A gas analyzer, comprising:
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a reflective inner surface, at least a portion of said inner surface being elliptical and defining a first focus and a second focus within said sample gas chamber and being operable to reflect radiation between said focuses;
a sealed inert gas chamber for holding an inert gas;
a sealed analyte gas chamber for holding an analyte gas;
a radiation source disposed at said first focus in said sample gas chamber;
means disposed around said second focus for reflecting radiation emitted by said radiation source and focused by said reflective inner surface toward each said sealed gas chambers; and detector means associated with each said sealed gas chambers for detecting radiation which was emitted by said source and which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a reflective inner surface, at least a portion of said inner surface being elliptical and defining a first focus and a second focus within said sample gas chamber and being operable to reflect radiation between said focuses;
a sealed inert gas chamber for holding an inert gas;
a sealed analyte gas chamber for holding an analyte gas;
a radiation source disposed at said first focus in said sample gas chamber;
means disposed around said second focus for reflecting radiation emitted by said radiation source and focused by said reflective inner surface toward each said sealed gas chambers; and detector means associated with each said sealed gas chambers for detecting radiation which was emitted by said source and which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
2. A gas analyzer as defined in claim 1, said portion of said reflective inner surface being in the form of an elliptic cylinder, said first focus and said second focus being first and second axes, respectively.
3. A gas analyzer as defined in claim 2, said reflector means being a multi-sided column coaxially disposed along said second focal axis and defining a plurality of reflective surfaces paralleling said second focal axis and each being operable to reflect radiation emitted by said source and focused by said reflective inner surface toward a predetermined one of said inert gas and analyte chambers.
4. A gas analyzer as defined in claim 3, said column being hexagonal.
5. A gas analyzer as defined in claim 2, further including a plurality of said analyte gas chambers for holding one of a plurality of different analyte gases.
6. A gas analyzer as defined in claim 2, said radiation means being disposed within said sample gas chamber.
7. A gas analyzer as defined in claim 2, further including means for admitting a sample gas into said sample gas chamber.
8. A gas analyzer as defined in claim 7, said admitting means including apertures in said body for permitting ambient gas to diffuse into said sample gas chamber.
9. A nondispersive, infrared gas analyzer, comprising:
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a top wall, a bottom wall and a reflective side wall in the form of an elliptical cylinder extending between said top and bottom walls and defining a first focal axis and a second focal axis, and means for admitting a sample gas into said sample gas chamber;
a linear infrared radiation source of small cross section disposed along said first focal axis in said sample gas chamber;
a column coaxially disposed along said second focal axis, said column having a plurality of reflective surfaces, each of said plurality of reflective surfaces being operable to reflect radiation emitted by said radiation source and reflected by said side wall to a predetermined location on said side wall;
a plurality of sealed gas chambers disposed outside of said sample gas chamber for containing one of a plurality of gases, one of said sealed gas chambers being operable to contain an inert gas, each said sealed gas chamber having a partition transparent to radiation emitted by said radiation source and disposed at one of said locations on said side wall; and a detector associated with each said sealed gas chambers for detecting radiation source originating radiation which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a top wall, a bottom wall and a reflective side wall in the form of an elliptical cylinder extending between said top and bottom walls and defining a first focal axis and a second focal axis, and means for admitting a sample gas into said sample gas chamber;
a linear infrared radiation source of small cross section disposed along said first focal axis in said sample gas chamber;
a column coaxially disposed along said second focal axis, said column having a plurality of reflective surfaces, each of said plurality of reflective surfaces being operable to reflect radiation emitted by said radiation source and reflected by said side wall to a predetermined location on said side wall;
a plurality of sealed gas chambers disposed outside of said sample gas chamber for containing one of a plurality of gases, one of said sealed gas chambers being operable to contain an inert gas, each said sealed gas chamber having a partition transparent to radiation emitted by said radiation source and disposed at one of said locations on said side wall; and a detector associated with each said sealed gas chambers for detecting radiation source originating radiation which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
10. A gas analyzer as defined in claim 1, said portion of said inner surface being in the form of an ellipsoid.
11. A gas analyzer as defined in claim 10, said reflector means being a polygon centered at said second focus and having a plurality of reflective surfaces, each reflective surface of said plurality of reflective surfaces being operable to reflect radiation emitted by said source toward a predetermined one of said sealed gas chambers.
12. A gas analyzer as defined in claim 10, further including a plurality of said analyte gas chambers for holding one of a plurality of different analyte gases.
13. A gas analyzer as defined in claim 10, said radiation source being disposed within said sample gas chamber.
14. A gas analyzer as defined in claim 10, further including means for admitting a sample gas into said sample gas chamber.
15. A gas analyzer as defined in claim 14, said admitting means including apertures in said body for permitting ambient gas to diffuse into said sample gas chamber.
16. A nondispersive, infrared gas analyzer, comprising:
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a top wall, a bottom wall and a reflective side wall in the form of an ellipsoid, said side wall defining a first focus and a second focus, and said body having means for admitting a sample gas into said sample gas chamber;
a infrared radiation source of small cross section disposed at said first focus in said sample gas chamber;
a polygonal body centered on said second focus and having a plurality of reflective surfaces, each surface of said plurality of reflective surfaces being operable to reflect radiation emitted by said radiation source and focused by said inner wall to a predetermined location on said inner wall;
a plurality of sealed gas chambers disposed on the outside of said sample gas chamber containing one of a plurality of gases, one of said sealed gas chambers being operable to contain an inert gas, each said sealed gas chamber having a partition transparent to radiation emitted by said radiation source and disposed at one of said locations on said inner wall;
and a detector associated with each said sealed gas chambers for detecting radiation originating at said radiation source which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
a body having a chamber for holding a sample gas to be analyzed, said sample gas chamber having a top wall, a bottom wall and a reflective side wall in the form of an ellipsoid, said side wall defining a first focus and a second focus, and said body having means for admitting a sample gas into said sample gas chamber;
a infrared radiation source of small cross section disposed at said first focus in said sample gas chamber;
a polygonal body centered on said second focus and having a plurality of reflective surfaces, each surface of said plurality of reflective surfaces being operable to reflect radiation emitted by said radiation source and focused by said inner wall to a predetermined location on said inner wall;
a plurality of sealed gas chambers disposed on the outside of said sample gas chamber containing one of a plurality of gases, one of said sealed gas chambers being operable to contain an inert gas, each said sealed gas chamber having a partition transparent to radiation emitted by said radiation source and disposed at one of said locations on said inner wall;
and a detector associated with each said sealed gas chambers for detecting radiation originating at said radiation source which has travelled through said sample gas and the gas in its associated sealed gas chamber and for producing a signal representative of the concentration in said sample gas of the gas contained in its associated sealed gas chamber.
Priority Applications (7)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 615091 CA1318520C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
| PCT/CA1990/000288 WO1991005240A1 (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector |
| DE69007291T DE69007291T2 (en) | 1989-09-29 | 1990-09-10 | INFRARED GAS DETECTOR. |
| EP90912732A EP0493401B1 (en) | 1989-09-29 | 1990-09-10 | 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 |
| AU62910/90A AU6291090A (en) | 1989-09-29 | 1990-09-10 | Infrared-based gas detector |
| JP2512096A JP2895622B2 (en) | 1989-09-29 | 1990-09-10 | Gas detector using infrared |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 615091 CA1318520C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1318520C true CA1318520C (en) | 1993-06-01 |
Family
ID=4140871
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 615091 Expired - Fee Related CA1318520C (en) | 1989-09-29 | 1989-09-29 | Infrared-based gas detector |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1318520C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2982026A1 (en) * | 2011-11-02 | 2013-05-03 | Ethylo | Cuvette for fluid analysis device e.g. colorimeter, has line passing through point and forming angle with another line, where bisector of angle is perpendicular to tangent of inner wall in point and passes through focal zone |
-
1989
- 1989-09-29 CA CA 615091 patent/CA1318520C/en not_active Expired - Fee Related
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2982026A1 (en) * | 2011-11-02 | 2013-05-03 | Ethylo | Cuvette for fluid analysis device e.g. colorimeter, has line passing through point and forming angle with another line, where bisector of angle is perpendicular to tangent of inner wall in point and passes through focal zone |
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