CA2119127C - Improved diffusion-type gas sample chamber - Google Patents

Improved diffusion-type gas sample chamber

Info

Publication number
CA2119127C
CA2119127C CA002119127A CA2119127A CA2119127C CA 2119127 C CA2119127 C CA 2119127C CA 002119127 A CA002119127 A CA 002119127A CA 2119127 A CA2119127 A CA 2119127A CA 2119127 C CA2119127 C CA 2119127C
Authority
CA
Canada
Prior art keywords
radiation
tube
detector
sample chamber
source
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 - Lifetime
Application number
CA002119127A
Other languages
French (fr)
Other versions
CA2119127A1 (en
Inventor
Jacob Y. Wong
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Gaztech International Corp
Original Assignee
Gaztech International Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Gaztech International Corp filed Critical Gaztech International Corp
Publication of CA2119127A1 publication Critical patent/CA2119127A1/en
Application granted granted Critical
Publication of CA2119127C publication Critical patent/CA2119127C/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

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
    • G01N21/3518—Devices using gas filter correlation techniques; Devices using gas pressure modulation techniques
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/031—Multipass arrangements
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/0332—Cuvette constructions with temperature control
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • 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
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B17/00—Fire alarms; Alarms responsive to explosion
    • G08B17/10—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means
    • G08B17/117—Actuation by presence of smoke or gases, e.g. automatic alarm devices for analysing flowing fluid materials by the use of optical means by using a detection device for specific gases, e.g. combustion products, produced by the fire
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
    • G08B29/18—Prevention or correction of operating errors
    • G08B29/20—Calibration, including self-calibrating arrangements
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N21/031—Multipass arrangements
    • G01N2021/0314—Double pass, autocollimated path
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/03—Cuvette constructions
    • G01N2021/0385—Diffusing membrane; Semipermeable membrane
    • 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
    • G01N21/01—Arrangements or apparatus for facilitating the optical investigation
    • G01N21/15—Preventing contamination of the components of the optical system or obstruction of the light path
    • G01N2021/158—Eliminating condensation
    • 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
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/85—Investigating moving fluids or granular solids
    • G01N2021/8578—Gaseous flow
    • G01N2021/8585—Gaseous flow using porous sheets, e.g. for separating aerosols
    • 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
    • G01N21/59—Transmissivity
    • G01N21/61—Non-dispersive gas analysers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/02—Mechanical
    • G01N2201/022—Casings
    • G01N2201/0228—Moulded parts

Abstract

The improved sample chamber includes an elongated hollow tube (12) closed at one end (14) and having specularly-reflective inwardly facing surfaces(16). A source (26) of radiation and a detector (28) of radiation are mounted side by side in the open end of the hollow tube, both facing the closed end. A
plurality of filtering apertures (20) are formed in the tube (12), and each aperture is covered by a sheet (22) of a semipermeable membrane that serves to prevent airborne particles larger than a predetermined size from entering the chamber while not interfering with the free diffusion of the gas to be measured into andout of the chamber. The use of an elongated hollow tube that is closed at one end results in no loss in the efficiency with which the radiation is conducted from the source to the detector while decreasing the external length of the chamber by 50 percent.

Description

INTERNATIONAL APPLICATION
UNDER THE
PATENrr COOPERATION TREATY
FOR
IMPROVED DI~FUSION-TYPE GAS SAMPLE CHAMBER

DESCRIPTION
Technical Field The present invention is in the field of gas analysis, and specifically relates to apparatus using a nondis~e,~ivc infrared gas analysis technique to determine the concenll~tion of a particular type of gas present in a sample chamber by 5 sensing the absorption of infrared radiation passing through the gas.

Background Art A comparatively new development in the field of nondispersive infrared gas analyzers has been the diL~ ion-type gas sample chamber. In a diffusion-type gassample chamber, the gas to be measured enters and leaves the chamber by 10 diffusion.
One example of a diffusion-type gas sample chamber is described in applicant's C~n~ n patent application No. 2,101,082. In that invention, the sample chamber has the form of a tube composed of a gastight material, having apertures covered by semipermeable membranes through which the gas to be measured enters and leaves the sample chamber by diffusion. This same approach is used in the present invention, with some important modifications.
Another example of a diffusion-type gas sample chamber is described in U.S. Patent No. 4,709,150 to Burough et al. In their invention, the body of the sample chamber is composed of a porous material through which the gas to be 2 2~ 1 91 27 measured passes by diffusio~ Burough et al. do not teach or suggest using the walls of the porous tube as reflective radiation-guiding elements.
An example of a non{liffusion-type gas sample chamber is shown in Japanese Patent Publication No. 59-173734(A~ of Miyazaki. In that analyzer, the 5 sample cells have the form of helical tubes. The gas to be measured must be pressulized to force it to flow through the sample tube.
Another example of a non~if~usion-type of gas sample chamber is shown in Japanese Publication No. 6~298031 by Fujilllula, in which air is rammed into the sample chamber by motion of the sample chamber through the air.
In the present application, Ine inventor will describe an improvement on the sample chamber described in the above-mentioned copending application to make it more compact while m~int~ining itS radiation-handling efficiency.

Disclosure of the Invention In the gas sample chamber of the above-mentioned copending application, the gas sample chamber includes a tube that is open at both ends; the source of radiation is centered at one end, and the detector of radiation is centered at the opposite end. In contrast, in accordance with the present invention the gas sample chamber includes a tube that is closed at one end, and both the source of radiation and the detector are mounted proximate the open end.
When the present inventor started his experiments leading up to the present invention, it was not known what the effect would be of closing one end of the tube. Nor was it known what the effect would be of mounting the detector and thesource of radiation at the same end of the tube.
After a series of experiments, the present inventor was able to show that when the end of the tube is closed, the path length of the radiation is effectively doubled as compared with a tube of the same length but open at both ends. The experiments also proved that little loss results from mounting the source of radiation and the detector at the same end of the tube.
Thus, compared with a tube that is open at both ends, the sample chamber -30 of the present invention is twice as sensitive. Alternatively, the tube of the present invention can achieve the same sensitivity with a sample chamber that is only half as long.

_ 3 21 1 91 ~7 The novel features which are believed to be characteristic of the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following descriptionS considered in connection with the accompanying drawing in which a preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only and is not intended as a definition of the limits of the invention.

Brief Description of Drawings Figure 1 is a diagram showing a side elevational cross-sectional view of the improved diffusion-type gas sample chamber of the present invention.

Best Mode for Carrying Out the Invention In a preferred embodiment, the gas sample chamber of the present invention includes a tube 12 having a closed end 14 and having an open end. In 15 the preferred embodiment, the tube 12 is composed of a me$al, and has a square cross section. In other embodiments, the cross section is circular.
The surface of the inner wall 16 of the tube 12 and the inwardly-facing surface 18 of the closed end 14 are specularly-reflective.
In accordance with the present invention, the metal tube 12 is gastight and 20 therefore filtering apertures, of which the filtering aperture 20 is typical, are provided at spaced locations along the tube 12 to permit molecules of the gas tobe detected to enter and to leave the space within the tube. Each of the filtering apertures 20 is covered by a sheet of a semipermeable membrane 2æ In the preferred embodiment, the gas to be detected is carbon dioxide, and the 25 se~ Jelllleable membrane is composed of silicone rubber and is a~rc,~imately 25 to 50 microns thick. Because of its fragility, in the preferred embodiment the sernipermeable membrane 22 is supported by a mesh 24 that spans the aperture 20. At this point in time, the exact number, location, and disposition of the filtering apertures does not appear to be crucial, although some as-yet-undiscov-30 ered arrangement may be optimal.

The open end of the tube 12 is closed by a cap 32 in which are mounted a source 26 of radiation, a detector 28, and a narrow passband filter 30. The passband of the filter 30 is located at a wavelength at which the gas to be detected strongly absorbs radiation and at which any other gases that might be present do5 not absorb. The source 26 emits radiation in the same absorption band. The concentration within the sample chamber of the gas to be detected is related to the extent to which the radiation is absorbed. The plastic cap 32 serves to mount the source 26 and the detector 28 and the filter 30 in the open end of the tube 12 with the source 26 and the detector-28 facing the surface 18.
Some of the radiation emitted by the source 26 is simply reflected from the surface 18 directly back to the detector 28. In Figure 1, this component of the radiation is defined by the bundle 42 of rays. It is clear from Figure 1 that if this were the only mode of propagation, then only an extremely small fraction of the emitted radiation would reach the detector 28. The solid angle of the detector at 15 a distance equal to twice the length of the tube 12 is extremely small.
An important advantage of using the tube 12 is that it permits other modes of propagation from the source to the detector to occur. The amount of radiationcontributed by the various modes of tr~n~mi~sion is additive since the successive modes are characterized by progressively steeper rays. Compared with a simple 20 plane mirror such as the surface 18, the addition of the tube 12 greatly increases the amount of radiation that reaches the detector 28. One might consider the bundle 42 of rays to represent the simplest or fundamental mode, and the ray 40 to represent one of the higher order modes of propagation.
In addition to m~king it possible to utilize the higher order modes of 25 propagation, the addition of the tube 12 produces a secondary benefit, namely, that the radiation travels a greater distance through the space within the tube as the order of the mode of propagation increases. That is, for the higher modes, the rays are steeper resulting in a greater distance of travel back and forth across the tube, notwithstanding that the distance traveled in the longitudinal direction 30 remains constant and simply equals twice the length of the tube.
The purpose of the semipermeable membrane 22 is to prevent airborne particles larger than a predetermined size from entering the space within the tube 12, while at the same time not interfering appreciably with the free diffusion of the gas to be detected into and out of the space within the tube 12. The unwanted particles include minute droplets of moisture or oil and also include fine particulate matter such as particles of dust or smoke. If these unwanted airborne S particles were to enter the space within the tube 12, they would deposit themselves onto the specularly reflective surfaces thereby reducing the reflectivity and destroying its specular nature. The unwanted particles would also deposit onto the source 26 and onto the narrow passband filter 30 reducing the transmission of radiation and possibly causing chemical changes to take place. All 10 of these problems are elimin~ted through the use of the semipermeable membrane which, in the preferred embodiment prevents airborne particles larger than 0.3 microns from entering the space within the tube 12.
Unfortunately, the semipermeable membrane cannot prevent molecules of water from diffusing into the space within the tube 12, and if the components 15 within the space are at a sufficiently low temperature, there is a possibility that the water vapor may condense onto the cold surfaces. To prevent that from happening, heater wires 34 are employed in the preferred embodiment to generate heat by ohmic heating when an electric current is passed through them.
To ~i"i",i:~e the escape of this heat, the metal tube 12, which is an excellent 20 conductor, is provided with an insulative sheath 38. Likewise, the cap 32 is provided with an insulative casing 36. Because of the pro~~ y of the wires 34 to the source 26 and the filter 30, these components are also protected from moisture condensing upon them.
Thus, there has been described an i",~loved diffusion-type gas sample 25 chamber which differs from previous sample chambers in that both the radiation source and the detector are mounted side by side at the same end of the tubular sample chamber. Compared to previously known sample chambers, the chamber of the present invention efficiently collects and conducts the radiation to the detector while using a tube that is only half as long.

30 Industrial Applicability The most prominant applications of the diffusion-type sample chamber -6 2 1 1 9 t 27 have been in the fields of air conditioning and fire detection. In both of theseapplications the gas being detected is carbon dioxide. The improvement of the present invention will increase the accuracy and sensitivity of the instruments in which it is used without increasing the size of the insl~ulllents. In this way, the S present invention advances the state of the art by a factor of two.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. An improved diffusion-type gas sample chamber for transmitting radiation through gases present in the chamber by ambient pressure diffusion, comprising in combination:
a) an elongated hollow tube having an inner wall and having a closed end and an open end, composed of a gastight material and having a specularly-reflective surface on the inner wall and on the inwardly-facing side of the closed end;
b) said tube including a plurality of filtering apertures arrayed along said tube for improving the diffusion into and out of the space within said tube;

c) a sheet of a semipermeable membrane covering each of said plurality of filtering apertures, said semipermeable membrane permitting gases to diffuse through it under ambient pressure into and out of the space within said tube andpreventing airborne particles larger than a predetermined size from entering said space;
d) a source of radiation;
e) a detector of radiation; and f) means for mounting both said source of radiation and said detector of radiation proximate said open end and facing said closed end, whereby some ofthe radiation emitted in various directions from said source of radiation is conducted by at least one reflection from the specularly-reflective surface on the inner wall to the specularly-reflective surface on the inwardly-facing side of the closed end and from the latter by at least one reflection from the specularly-reflective surface on the inner wall to said detector of radiation.
2. The improved diffusion-type gas sample chamber of claim 1 further comprising heater means adjacent the open end of said tube for supplying heat tosaid tube to prevent condensation on said source of radiation, on said detector of radiation and on said specularly-reflective surface.
3. The improved diffusion-type gas sample chamber of claim 1 wherein said predetermined size is 0.3 microns.
4. The improved diffusion-type gas sample chamber of claim 1 wherein said detector of radiation includes a narrow passband filter.
CA002119127A 1992-07-16 1993-07-16 Improved diffusion-type gas sample chamber Expired - Lifetime CA2119127C (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/915,003 US5340986A (en) 1991-11-18 1992-07-16 Diffusion-type gas sample chamber
US07/915,003 1992-07-16

Publications (2)

Publication Number Publication Date
CA2119127A1 CA2119127A1 (en) 1994-01-17
CA2119127C true CA2119127C (en) 1997-01-21

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
CA002119127A Expired - Lifetime CA2119127C (en) 1992-07-16 1993-07-16 Improved diffusion-type gas sample chamber

Country Status (9)

Country Link
US (2) US5340986A (en)
EP (2) EP0997727B1 (en)
JP (1) JPH0666724A (en)
AT (2) ATE199458T1 (en)
AU (1) AU657638B2 (en)
CA (1) CA2119127C (en)
DE (2) DE69329968T2 (en)
DK (1) DK0634009T3 (en)
WO (1) WO1994018546A1 (en)

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DE69329968D1 (en) 2001-04-05
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EP0997727B1 (en) 2005-11-16
EP0634009B1 (en) 2001-02-28
ATE310240T1 (en) 2005-12-15
AU4681993A (en) 1994-08-29
ATE199458T1 (en) 2001-03-15
US5340986A (en) 1994-08-23
EP0997727A1 (en) 2000-05-03
US5502308A (en) 1996-03-26
DE69329968T2 (en) 2001-09-20
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EP0634009A4 (en) 1996-01-03
DK0634009T3 (en) 2001-06-25

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