GB2290139A - Gas concentration measurement - Google Patents
Gas concentration measurement Download PDFInfo
- Publication number
- GB2290139A GB2290139A GB9511854A GB9511854A GB2290139A GB 2290139 A GB2290139 A GB 2290139A GB 9511854 A GB9511854 A GB 9511854A GB 9511854 A GB9511854 A GB 9511854A GB 2290139 A GB2290139 A GB 2290139A
- Authority
- GB
- United Kingdom
- Prior art keywords
- filter
- gas
- angle
- detector
- wavelength
- 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.)
- Withdrawn
Links
- 238000005259 measurement Methods 0.000 title description 3
- 230000005855 radiation Effects 0.000 claims abstract description 16
- 230000010355 oscillation Effects 0.000 claims abstract description 10
- 238000010521 absorption reaction Methods 0.000 claims abstract description 8
- 230000003534 oscillatory effect Effects 0.000 claims abstract description 5
- 230000005540 biological transmission Effects 0.000 claims description 7
- 238000000034 method Methods 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 18
- BOTDANWDWHJENH-UHFFFAOYSA-N Tetraethyl orthosilicate Chemical compound CCO[Si](OCC)(OCC)OCC BOTDANWDWHJENH-UHFFFAOYSA-N 0.000 description 12
- 238000000862 absorption spectrum Methods 0.000 description 3
- 150000002902 organometallic compounds Chemical class 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 229910052733 gallium Inorganic materials 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- XCAUINMIESBTBL-UHFFFAOYSA-N lead(ii) sulfide Chemical compound [Pb]=S XCAUINMIESBTBL-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 150000002894 organic compounds Chemical class 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 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
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
- G01J3/42—Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry
- G01J3/433—Modulation spectrometry; Derivative spectrometry
-
- 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
- G01N21/314—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry with comparison of measurements at specific and non-specific wavelengths
-
- 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
- G01N21/359—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using near infrared light
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- General Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
A gas or vapour can be detected and measured using a source 14 arranged to send a beam 15 of radiation through a sample chamber 12 to a detector 18. The beam 15 is also passed through a narrow bandwidth multi-layer filter 16, and the angle of incidence to the filter 16 is oscillated so that the transmitted wavelength varies in an oscillatory fashion over a range in which the absorption of the gas varies. The resulting signal variations from the detector 18 at the frequency of the filter oscillation, or at an integral multiple of that frequency, enable the gas to be detected and measured. <IMAGE>
Description
Gas Concentration Measurement
The invention relates to an apparatus and to a method for detecting, and for measuring the concentration of, a gas or vapour. The measured gas may be a component of a mixture of gases or vapours. In this specification the term gas is to be interpreted as including vapour.
According to the present invention there is provided an apparatus for detecting, or measuring the concentration of, a gas, the apparatus comprising means for generating a beam of radiation having a range of wavelengths, means for causing the beam to pass through a region in which the gas is to be detected, and means to detect the beam after its passage through the region, and also comprising a narrow bandwidth filter onto which the beam is incident, and means to cause oscillation of the angle of incidence of the beam on the filter and so an oscillatory variation in the wavelength of radiation received by the detector, the variation in the wavelength occurring over a range of wavelengths within which the gas varies in its absorption, and means responsive to signals from the detector to detect or to measure the concentration of the gas.
The radiation might be infrared, visible, or ultraviolet, but the preferred radiation is nearinfrared. For sample the gas might be an organometallic compound having one or more C-H bonds. Such bonds have a vibration mode with a first overtone at a wavenumber of about 6000 cm-1 (i.e. wavelength of about 1.67 rum), which is in the near-infrared region of the electromagnetic spectrum.
The filter may be a reflecting filter, but is preferably a transmission filter as this enables simpler optical paths to be used. It is preferably a multi-layer filter. The bandwidth (measured at half the peak transmission) is desirably no more than 1/20 the wavelength of peak transmission, more preferably less than 1/50, for example 1/150, of the said wavelength.
The filter may allow radiation over a narrow bandwidth to be propagated while preventing propagation of other wavelengths, or may prevent propagation of radiation over a narrow bandwidth while allowing propagation of radiation of other wavelengths, the latter being known as a notch filter.
The angle of incidence of the beam onto the filter may be varied by varying the direction of the beam while leaving the filter fixed, but in the preferred apparatus the beam direction is fixed while the filter is oscillated, as this provides a simpler apparatus. The wavelength of the radiation passed by the filter varies with the angle of incidence (being approximately proportional to cos of the angle of incidence); the filter might for example be oscillated through an angle of no more than 600, preferably no more than 300, for example 200, and the oscillation might be either side of the plane perpendicular to the incident beam direction, or might be primarily or entirely to one side of that plane.
The filter may be oscillated at less than 10 Hz, for example 1 or 2 Hz. The detector preferably includes means sensitive to signal oscillations at an integral multiple of the filter oscillation frequency, preferably one, two, or four times the filter oscillation frequency.
Absorption by the gas will cause signal oscillations at such frequencies and so these signals enable the gas to be detected. By being sensitive only to such frequencies the signal to noise ratio for the apparatus is enhanced, because background noise is substantially eliminated.
The invention will now be further described by way of example only and with reference to the accompanying drawings in which:
Figure 1 shows a diagrammatic representation of a
gas measuring apparatus; and
Figure 2 shows the near-infrared absorption
spectrum of an organic vapour.
Referring to Figure 1 there is shown a gas measuring apparatus 10 for measuring the concentration of tetraethoxysilane (TEOS) vapour in a transparent-walled container 12. The apparatus 10 includes a light-emitting diode 14 which emits a beam 15 of radiation in the nearinfrared part of the spectrum over the wavelength range about 1.5 to 2.1 Wm. The beam 15 passes through a filter 16, through the gas container 12, and is then incident upon a lead sulphide detector 18 whose optimum sensitivity is in the wavelength range 1 to 3 Wm. The filter 16 is a glass plate of diameter 20 mm and with a multi-layer coating such that it transmits a narrow band of wavelengths about 1.70 Clam. It is supported on a motorized turntable 20 so the angle of incidence, i, of the beam 15 to the filter 16 can be varied.
The apparatus 10 also includes a computer 22. The computer 22 controls the light-emitting diode 14 via a drive circuit 24, which supplies a 200 mA peak, 1 kHz square wave current. The computer 22 also controls the rotary turntable 20 via a driver circuit 26; the turntable 20 is driven to turn to and fro through an angle of 190 at a frequency of 1 Hz, so the angle of incidence i varies between 90 and 280. Signals from the detector 18 are supplied via a driver and pre-amplifier circuit 30 to a lock-in amplifier 28. The lock-in amplifier 28 selectively amplifies any signals varying at a frequency of 1 Hz (i.e. the same frequency as the driver circuit 26). The output from the lock-in amplifier 28 is supplied to the computer 22.
Referring now to Figure 2 there is shown part of the infrared absorption spectrum of TEOS vapour, as a graph showing the variation of absorption (A) with wavelength t It is apparent that there are peaks of absorption at wavelengths in the vicinity of 1.677 ,um and 1.726 pm.
The filter 16 has a central wavelength of about 1.70 pm for radiation incident normally; as it oscillates between i = 90 and i = 280 the peak wavelength varies between about 1.699 Rm and 1.657 Rm (the filter's bandwidth is about .02 um at i = 0, and this also varies with the angle of incidence, as does its peak transmission).
Consequently as the filter 16 is oscillated, the wavelength of the radiation passing through the gas container 12 varies over a range of wavelengths for which the TEOS vapour absorption varies significantly. Hence the amplitude of the signal from the detector 18 varying at 1 Hz may be used to measure the concentration of TEOS vapour in the container 12. There will also be a variation at 1 Hz due solely to the changes in the transmission of the filter 16 with angle, even in the absence of TEOS, and this must be determined separately, to be subtracted from the 1 Hz signal obtained when TEOS is present. The apparatus 10 is sensitive down to about 200 ppm of TEOS at a pressure of 1 atmosphere.
It will be appreciated that the apparatus 10 may be modified in various ways while remaining within the scope of the present invention. For example the lock-in amplifier 28 might be arranged to selectively amplify signals at twice or four-times the frequency of the driver circuit 26. Detecting signals at twice the driver circuit frequency has the advantage that at that frequency no signal is expected in the absence of TEOS.
Clearly the source of radiation 14, the filter 16, and the detector 18 must be chosen in accordance with the nature of the gas to be detected, so that a range of wavelengths are observed over which the gas varies in its absorption. It may also be beneficial to provide means to maintain the temperature of the source of radiation 14 at a desired value during operation, for example to keep it at room temperature by means of a Peltier cooler. The turntable 20 might be replaced by a different oscillatory support, for example a pivoted support and an oscillatory drive linkage; the multi-layer filter 16 might be replaced by a different type of filter for which the wavelength varies with the angle of incidence, for example a holographic filter.
Although the apparatus 10 has been described in relation to the detection and measurement of TEOS it might also be used to measure the concentrations of other materials, in particular other organo-metallic compounds (e.g. organic compounds of gallium, aluminium, silicon, or phosphorus) because the wavelength range around 1.7 ,um corresponds to the frequencies at which vibration overtones of C-H bonds occur, so that all these compounds can be expected to have similar absorption spectra in this range. It will also be appreciated that the apparatus 10 may be used to provide feedback in equipment supplying TEOS vapour, for example for chemical vapour deposition plant, so ensuring more accurate control of the TEOS concentration during operation of the plant.
Claims (7)
1. An apparatus for detecting, or measuring the concentration of, a gas, the apparatus comprising means for generating a beam of radiation having a range of wavelengths, means for causing the beam to pass through a region in which the gas is to be detected, and means to detect the beam after its passage through the region, and also comprising a narrow bandwidth filter onto which the beam is incident, and means to cause oscillation of the angle of incidence of the beam on the filter and so an oscillatory variation in the wavelength of radiation received by the detector, the variation in the wavelength occurring over a range of wavelengths within which the gas varies in its absorption, and means responsive to signals from the detector to detect or to measure the concentration of the gas.
2. An apparatus as claimed in Claim 1 wherein the filter is a multi-layer filter.
3. An apparatus as claimed in Claim 2 wherein the filter has a bandwidth, measured at half the peak transmission, less than 1/50 of the wavelength of peak transmission.
4. An apparatus as claimed in any one of the preceding
Claims wherein the angle of incidence of the beam onto the filter is varied by oscillating the filter.
5. An apparatus as claimed in any one of the preceding
Claims wherein the detector includes means sensitive to signal oscillations at an integral multiple of the frequency of oscillation of the angle of incidence.
6. An apparatus for detecting, or measuring the concentration of, a gas, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings, and as shown in Figure 1.
7. A method for detecting, or measuring the concentration of, a gas by use of an apparatus as claimed in any one of the preceding Claims.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9511854A GB2290139A (en) | 1994-06-11 | 1995-06-12 | Gas concentration measurement |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9411824A GB9411824D0 (en) | 1994-06-11 | 1994-06-11 | Gas concentration measurement |
| GB9511854A GB2290139A (en) | 1994-06-11 | 1995-06-12 | Gas concentration measurement |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9511854D0 GB9511854D0 (en) | 1995-08-09 |
| GB2290139A true GB2290139A (en) | 1995-12-13 |
Family
ID=26305061
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9511854A Withdrawn GB2290139A (en) | 1994-06-11 | 1995-06-12 | Gas concentration measurement |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2290139A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5793043A (en) * | 1995-12-29 | 1998-08-11 | Instrumentarium Oy | Method and apparatus for determining the alcohol concentration in a gas mixture |
| WO2003102520A1 (en) * | 2002-06-04 | 2003-12-11 | Baker Hughes Incorporated | Method and apparatus for a derivative spectrometer |
| US6798518B2 (en) | 2002-06-04 | 2004-09-28 | Baker Hughes Incorporated | Method and apparatus for a derivative spectrometer |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2163251A (en) * | 1984-07-19 | 1986-02-19 | Elektrisk Bureau As | Infrared gas detector |
| US5070245A (en) * | 1988-11-04 | 1991-12-03 | Instrumentarium Corporation | Apparatus and method for the identification of gases |
| GB2247525A (en) * | 1990-07-18 | 1992-03-04 | Secretary Trade Ind Brit | Optical long-path gas monitoring apparatus using wavelength modulation |
| EP0510856A2 (en) * | 1991-04-26 | 1992-10-28 | Siemens Plessey Controls Limited | Improvements in or relating to optical gas detectors |
-
1995
- 1995-06-12 GB GB9511854A patent/GB2290139A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2163251A (en) * | 1984-07-19 | 1986-02-19 | Elektrisk Bureau As | Infrared gas detector |
| US5070245A (en) * | 1988-11-04 | 1991-12-03 | Instrumentarium Corporation | Apparatus and method for the identification of gases |
| GB2247525A (en) * | 1990-07-18 | 1992-03-04 | Secretary Trade Ind Brit | Optical long-path gas monitoring apparatus using wavelength modulation |
| EP0510856A2 (en) * | 1991-04-26 | 1992-10-28 | Siemens Plessey Controls Limited | Improvements in or relating to optical gas detectors |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5793043A (en) * | 1995-12-29 | 1998-08-11 | Instrumentarium Oy | Method and apparatus for determining the alcohol concentration in a gas mixture |
| WO2003102520A1 (en) * | 2002-06-04 | 2003-12-11 | Baker Hughes Incorporated | Method and apparatus for a derivative spectrometer |
| US6798518B2 (en) | 2002-06-04 | 2004-09-28 | Baker Hughes Incorporated | Method and apparatus for a derivative spectrometer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9511854D0 (en) | 1995-08-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732E | Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977) | ||
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |