GB2102942A - Spectrometric gas analysis - Google Patents
Spectrometric gas analysis Download PDFInfo
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- GB2102942A GB2102942A GB08134519A GB8134519A GB2102942A GB 2102942 A GB2102942 A GB 2102942A GB 08134519 A GB08134519 A GB 08134519A GB 8134519 A GB8134519 A GB 8134519A GB 2102942 A GB2102942 A GB 2102942A
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- 238000004868 gas analysis Methods 0.000 title description 2
- 230000005855 radiation Effects 0.000 claims abstract description 133
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 20
- 230000003595 spectral effect Effects 0.000 claims description 30
- 238000012545 processing Methods 0.000 claims description 19
- 239000005083 Zinc sulfide Substances 0.000 claims description 6
- 230000005540 biological transmission Effects 0.000 claims description 6
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical group [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 claims description 6
- 230000000694 effects Effects 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 230000005684 electric field Effects 0.000 claims description 4
- 230000005670 electromagnetic radiation Effects 0.000 claims description 4
- 239000004973 liquid crystal related substance Substances 0.000 claims description 4
- 238000000034 method Methods 0.000 claims description 4
- 238000001228 spectrum Methods 0.000 claims description 4
- 238000012546 transfer Methods 0.000 claims description 4
- 238000001514 detection method Methods 0.000 abstract description 9
- 239000004215 Carbon black (E152) Substances 0.000 abstract description 4
- 229930195733 hydrocarbon Natural products 0.000 abstract description 4
- 150000002430 hydrocarbons Chemical class 0.000 abstract description 4
- JBRZTFJDHDCESZ-UHFFFAOYSA-N AsGa Chemical compound [As]#[Ga] JBRZTFJDHDCESZ-UHFFFAOYSA-N 0.000 abstract description 3
- 229910001218 Gallium arsenide Inorganic materials 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 39
- 230000010354 integration Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 4
- 239000002360 explosive Substances 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 2
- 229910052720 vanadium Inorganic materials 0.000 description 2
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000011324 bead Substances 0.000 description 1
- 229910052980 cadmium sulfide Inorganic materials 0.000 description 1
- CJOBVZJTOIVNNF-UHFFFAOYSA-N cadmium sulfide Chemical compound [Cd]=S CJOBVZJTOIVNNF-UHFFFAOYSA-N 0.000 description 1
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000009795 derivation Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 230000007096 poisonous effect Effects 0.000 description 1
- 230000002285 radioactive effect Effects 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 229910001220 stainless steel Inorganic materials 0.000 description 1
- 239000010935 stainless steel Substances 0.000 description 1
- 230000001360 synchronised effect Effects 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
Landscapes
- Physics & Mathematics (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
Abstract
Apparatus for determining the concentration of a gas, particularly a hydrocarbon gas, in the atmosphere employs a non-dispersive infra-red spectrometer priciple of transmitting a beam of infra-red radiation through the atmosphere and examining the signals produced as a result of its detection at a wavelength lambda 1, at which the sought-for gas absorbs radiation, and at a wavelength lambda 2 to which the gas is transparent. The detector 25 emits a pulsed beam containing the two wavelengths alternately in sequence from source means 27, 28 associated with the respective wavelengths. The radiation source in each source means is a gallium arsenide l.e.d. 29, 30 emitting at a shorter wavelength to excite a phosphor 32, which emits at the wavelength associated with that source means. A filter 33, 34 may be employed to limit radiation to a narrow band at the associated wavelength. By employing two electrically switched sources rugged and simple apparatus is possible. <IMAGE>
Description
SPECIFICATION
Non-dispersive optical determination of gas concentration
This invention relates to the determination of the concentration of a gas component identifiable in a gas mixture by non-dispersive optical analysis and in particular to the measurement of the concentration of a sought-for gas in the atmosphere.
It is widely known to detect the presence of small quantities of explosive or poisonous gases in an atmosphere by catalytic "bead" sensors.
Such sensors are not inherently suited for use in a potentially explosive atmosphere where failure of a sensor is not readily detected without frequent manual inspection.
It has been proposed to use infra-red techniques in the form of a non-dispersive infrared analyser in which a beam of infra-red radiation from an incandescent glow lamp contained within a flameproof enclosure is directed onto a detector, also contained within the enclosure, by way of a window in the enclosure wall and a reflector in the atmosphere where the gas may be found. The beam emitted from the source is interrupted by a constantly rotating apertured disc, alternate apertures comprising filters by which the emitted beam is caused to consist of intermittent pulses or radiation alternatively at a first wavelength (A,) absorbed by the sought-for gas and radiation at a second wavelength (ss2) passed by the gas and any other constituents of the atmosphere.Disc rotation is synchronised with detection of the returned beam at the two wavelengths and the ratio or change in ratio of the signals derived from the returned beam used as a measure of the gas concentration within the atmosphere.
Examples of gas analysis arrangements employing such mechanically positioned filters are shown in British Patent Specification Nos.
1,531,844, 1,566,436 and 2,026,687A and demonstrate also the use of a reference beam to mitigate the events of variation in source intensity.
The cost of providing precision and/or rugged mechanical parts in such apparatus invariably leads to a design choice between a competitively priced but relatively delicate apparatus, suitable only for use in laboratory or other controlled conditions, or to an environmentally rugged apparatus which is inaccurate or expensive to manufacture.
To avoid the use of mechanically interposed filters to change the wavelength of the beam by its has been proposed to use two detectors for each beam e.g. as shown in British Patent
Specification No. 1,416,182, each detector having associated therewith a filter to limit radiation to one only of the two wavelengths and produce signals for processing.
The ability to detect radiation at the two wavelengths simultaneously using a wideband source has been modified as shown in British
Patent Specification No. 1,221,463 in which two sources having emissions only over the narrow spectral bands of interest are employed.
Whereas the above described arrangements avoid the use of mechanical parts to select filters for defining the wavelength in use they are also complicated by the duplication of optical elements and detection means and the necessity to obtain comparable responses of each.
It is an object of the present invention to provide apparatus for determining the concentration of a gas in the atmosphere which is of simpler and more rugged construction than known arrangements.
According to the present invention for determining the concentration of a gas in the atmosphere apparatus comprises an enclosure from which electromagnetic radiation at first and second wavelengths, to which the sought-for gas is absorptive and transmissive respectively, is passed as a beam by way of the atmosphere to a principal detector responsive to radiation received at both of said wavelengths to produce principal signals having magnitudes related to the intensity of the received radiation at each said wavelength, beam splitting means contained in the enclosure and arranged to deflect part of the beam to a reference detector within the enclosure responsive to radiation at both of said wavelengths not transmitted through the atmosphere to produce a reference signal having a magnitude related to the intensity of detected radiation at each of said wavelengths, processing means operable to determine the function definable as the product of the ratio of reference signals at second and first wavelengths and the ratio of the principal detector signals at the first and second wavelengths and to calculate from said function the concentration of said gas in the atmosphere, and separate source means associated with radiation of each of said wavelengths each source means being operable to produce radiation in a narrow spectral band including the associated wavelength and switchable in intensity level by controlling means alternately with the other source means.
The wavelengths at which any gas or family of gas is absorptive of the radiation and transmissive of it are readily determined from tables of physical constants and it will be understood that the present invention is suitable for detection of any gas for which each wavelength can be determined and for which emission and detection is possible.Of particular interest is the detection of small and potentially explosive concentrations of hydrocarbon gases which as a family absorb infra-red with a wavelength such as 2350 nm (first wavelength A1) and transmit infra-red with wavelength such as 2100 nm (second wavelength
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:: Figure 1 is a schematic representation of a known atmospheric gas detector arrangement,
Figure 2 is a schematic representation of apparatus for determining the concentration of gas in the atmosphere according to the present invention, showing a first form of source means,
Figures 3(a) to 3(c) are schematic representations of different forms of source means, and
Figure 4 is a schematic representation of an alternative form of source means.
Referring to Figure 1 which shows in schematic form 10 the known non-dispersive infra red gas detector outlined hereinbefore, infrared radiation, including components at the above mentioned wavelengths A1 and A2, is emitted by a source 11 comprising an incandescent lamp powered by supply circuit 12. The emitted radiation is passed by way of a window 13, a mirror 14 and window 13 again to a photodetector 1 5 sensitive at the infra-red wavelengths concerned.A filter wheel 1 6 comprising an opaque mask containing spaced apertures 17, 18 in which filter material limits transmission to include different ones of the wavelengths A1 and A2 respectively, is located such that one aperture at a time is in the path of the emitted radiation and is rotated by a motor 1 9 controlled by drive circuitry 20. The motor drive circuitry 20 supplies timing or synchronisation signals to a computing circuit 21 which also receives signals from detector 1 5 by way of an amplifier 22.
The detector 1 5 thus receives intermittently pulses of radiation comprising components at the two wavelengths A1 and A2 in alternate pulses.
Assuming that the changes in photo-detector signals due to reception of the pulses of radiation at wavelengths A, and A2 are 1D1 and 1D2 respectively, then the relationships
hold where T is related to the transmissivity of the window, x is the path length of the radiation through the atmosphere and a is proportional to the gas concentration. Division of equations (1) and (2) enables T to be eliminated showing a to be a function of the ratio ID1/iD2 determined by computing circuitry 21. The arrangement may be caused to provide an analogue output related to a at terminal 23 or an alarm signal when a exceeds a predetermined threshold level at 24.
Referring now to Figure 2 which shows a schematic representation of apparatus 25 according to the present invention. The apparatus is mainly contained within a flame proof enclosure 26 and consists of radiation source means 27, 28 each including a radiation source in the form of a gallium arsenide light emitting diode 29, 30 caused to emit pulses of radiation intermittently and alternately by means of intermittent energisation by a power supply 31.
Considering the source means 27, the l.e.d. 29, emits radiation over a range of wavelengths which does not include the wavelength A1 but which is able to excite a phosphor 32 to emit in a spectral band including said wavelength. For the wavelengths of 2350 nm and 2100 nm considered for hydrocarbon gases the phosphor may be zinc sulphide containing a trace of vanadium which is excited by radiation in the 930-940 nm wavelength band (at which high efficiency gallium arsenide l.e.d.'s emit) to emit radiation at the wavelengths A1 and A2.
Because the phosphor emits in a wide spectral band which includes both wavelengths A1 and A2 the l.e.d. and phosphors of each source means may be identical.
In source means 27 a filter 33 is located to receive the radiation emitted by the phosphor 32 and limit transmission to radiation in an narrow spectral band centred on wavelength A1 while excluding radiation particularly at wavelength A2 but also any other wavelength absorbed by components of atmospheric gas. The source means 27 thus comprises an l.e.d. 29 phosphor 32 and filter 33, and when energised intermittently by supply 31 causes at each energisation a beam of radiation at wavelength A to be emitted. The source means 28 is similar but includes a filter 34 which limits radiation emission substantially to wavelength A2 when l.e.d. 30 is energised.
The beam emitted by each source means is intercepted by a beam splitter 35 and a part of the beam is directed by optics 36 on to a reference detector 37 responsive to radiation at A1 and A2 to produce reference signals 1R1 and 1R2 related to the intensity of the radiation received to amplifier 38.
The part of the beam not diverted by splitter 30 is transmitted by window 39 in the enclosure wall and incident upon a reflector means 40 located a predetermined distance x/2 from the window. The distance x/2 is conveniently chosen to be 7.5 cms giving a path length through the atmosphere of 1 5 cms. The reflector 40 is formed of stainless steel and concave to direct the radiation back into the enclosure by way of window 39 and concentrate it on principal detector 41. The principal detector is similar to the reference detector and consists of a photodetector responsive to radiation at both wavelengths A1 and A- 2 and provides principal signals IP1 and 1P2 to amplifier 42.
The signals from amplifiers 38 and 42 are fed to processing means indicated generally at 43 and contained within the enclosure 26, although it will be appreciated that the processing means may be located remotely of the detection means.
Considering firstly the relationships existing between the principal and reference beams at the two wavelengths,
and,
where as for equations (1) and (2) T is the transmissivity of the window, x is the radiation path length in the atmosphere and a is proportional to the gas concentration.Using the approximatibn of e-""=(l-ax) for low concentration, equations (3) and (4) may be combined to eliminate T giving
and,
The product of the ratios,
may be written as PR and equation (5) written more simply as a=(1-PR)/x (6) The processing means 43 comprises a reference signal integration and storage device 44 which stores the sequentially produced reference signals IR1 or 1R2 and makes them available simultaneously at outputs 45 and 46. A principal signal integration and storage device 47 provides similarly principal signals IP1 and 1P2 at outputs 48, 49.
The outputs 45 and 46 of reference signal integration and storage device 44 and fed to a reference division circuit 50 and corresponding outputs 48, 49 of device 47 are fed to a principal division circuit 51. Outputs 52, 53 from the division circuits 50, 51 respectively are fed as inputs to a multiplication circuit 54, the output 55 of which is fed to a scaling and threshold circuit 56. The integration and storage devices, division, multiplication and scaling circuits and l.e.d. supply 31 are all operated under the control of a synchronising circuit 57. The division circuits 50 and 51 contain means for processing the signals, which are produced at different times into a form suitable for division.The signals received from amplifier 38 which consist alternately of signals due to detection of a reference beam at one of two wavelengths and detector output when no radiation is present for each wavelength the signals are first integrated stored and subtracted to remove the effects of detector variations and stored again for access via outputs 45 and 46 respectively. Similarly the signals from amplifier 42 are treated in this way in device 47 so as to be available concurrently for division at outputs 48, 49.
In operation for each pulse of radiation emitted the division circuit 50 produces an updated value for the ratio lR2/1R1 and the division circuit 51 produces an updated value for the ratio 1P1/1P2 The multiplication circuit 54 produces the product of these ratios to give a signal on line 55 representing the term PR of equation (6). The circuit 56 subtracts this term from a maximum value and with a gain of 1/x produces at an output terminal 58 a value for a in accordance with equations (5) and (6). Threshold devices 59 may also be employed to respond to a value of a in excess of predetermined threshold values set therein.
It will be appreciated that the function represented by PR and definable from the above derivation as the product of the ratio of the reference signals at the second and first wavelengths and the ratio of the principal signals at the first and second wavelengths, that is,
may be represented in other ways and circuitry to evaluate it formed accordingly. For instance the function PR may be derived by determining the ratio 1P1I1R1 and either the ratio IP2/lR2 and their ratio, or the ratio 1A211P2 and their product, or by determining the products IP1'lR2 and IP2'lR1 and the ratio of these products.
It will be appreciated that equation (5) instead of relying upon an absolute measurement of the detector signal at each wavelength effectively compares it with the radiation emitted by the ratios 1P1/1R1 and 1P211R2 for each pulse. Thus any variation of emitted power over a time period, whether due to source aging or supply fluctuations, introduces no errors in the measurement of a. Similarly the absence of moving parts enables a rugged and compact instrument to be constructed.
The phosphor 29 is described above as being of zinc sulphide. Other materials may also be employed, such as cadmium sulphide or cadmium selenide each containing a trace of vanadium.
It will be appreciated that the above described embodiment is suitable for measurement of hydrocarbon gas concentrations in atmospheric air and the operating wavelengths of the radiation chosen accordingly. Other gases and or other atmospheric mixtures may require different wavelengths for which component parts of the source means are related to have appropriate characteristics and may be varied from those described above, depending upon the availability of components with suitable characteristics.
For instance, as shown in Figure 3(a), the source means 27' may comprise an l.e.d. 61 or other source which emits radiation in a spectral band excluding the wavelength A1 and excites a phosphor 62 to emit radiation in a narrow spectral band including the wavelength . The source means 28' comprises a source 63 and a phosphor 64 which is excited to emit radiation in a narrow spectral band including the wavelength A2. If the phosphors have suitable characteristics for producing radiation at the wavelengths A1, A2 respectively the sources 61 and 62 may be identical.
Alternatively, as shown in Figure 3(b), each source means may comprise a single radiation source, such as an l.e.d. which is able to emit radiation in a narrow spectral band at the relevant wavelength A1 or.82. If in such an arrangement the spectral band of one or both sources is too wide, while not actually including both wavelengths, simple filter means 65, 66, as shown in Figure 3(c) may be used with each radiation source 67, 68.
In all of the above described embodiments each source means comprises an electrically switched radiation source to effect sequential pulsed transmission. As an alternative each source means, e.g. 27, may include in the radiation path an electro-optic shutter 70 composed of a panel of an electrically conditionable medium, such as a liquid crystal, which is caused to change between a first state, in which it is transparent to radiation at the first and/or second wavelengths, and a second state, in which it is opaque to the radiation, by means of an electric field applied by the supply 31 under the control of the synchronising circuit 57.The radiation source is continuously energised or modulated at high frequency so that the source means produces an intermittent beam of radiation containing components at wavelength A1 which is detected in the same manner described above in relation to Figure 2. Source means 28 also may contain a similar electro-optic shutter 71. The position of the shutter in the components forming each source means is immaterial providing there is no transfer of radiation between the source means.
Such a shutter arrangement and continuously emitting sources may be applied to the variations shown in Figures 3(a) to (c).
In a situation wherein the radiation sources of both source means produce radiation in the same wide spectral band and are both continuously illuminated while an electro-optic shutter performs beam switching the source means may share a common modulation source. As illustrated in Figure 4, each source means 72, 73 the common radiation source 74 is coupled with separate phosphor 75 and/or filter 76 as appropriate and an electro-optic shutter 77. As the source is continuously energised there is no requirement for it to have suitable switching characteristics and may be any device having requisite physical characteristics.
One form the source may take is a luminescent radioactive source, such as known by the trade name Betalight.
All of the embodiments described above may be provided with a self-test facility (not shown) in which at predetermined intervals the level of signal Ip1 (that is at A1) is reduced in value to simulate absorption of the radiation by a soughtfor gas. The system is then arranged to check that an alarm condition is generated, while inhibiting the output of such an alarm condition for the duration of the test. Such a test facility monitors not only the responses of the apparatus system but also the timing sequences employed.
It will be appreciated that the prevailing feature in the various embodiments described is the detection of reference signals which renders the value obtained for gas concentration independent of source emission variations and the truly solid state nature, and inherent ruggedness of the source means, enabling results to be produced with a high degree of reliability and repeatability.
In all of the embodiments described the processing means 43 described as comprising discrete functional elements may be formed by a computer having fixed in the storage medium thereof the instruction sequences necessary to operate on the signals produced by the detectors.
Claims
1. Apparatus for determining the concentration of a gas in the atmosphere comprising an enclosure from which electromagnetic radiation at first and second wavelengths, to which the sought-for gas is absorptive and transmissive respectively, is passed as a beam by way of the atmosphere to a principal detector and responsive to radiation received at both of said wavelengths to produce principal signals having magnitudes related to the intensity of the received radiation at
each said wavelength, beam splitting means contained in the enclosure and arranged to deflect part of the beam to a reference detector within the enclosure responsive to radiation at both of said wavelengths not transmitted through the atmosphere to produce a reference signal having a magnitude related to the intensity of detected radiation at each of said wavelengths, processing means operable to determine the function definable as the product of the ratio of reference signals at second and first wavelengths and the ratio of the principal detector signals at the first and second wavelengths and to calculate from said function the concentration of said gas in the atmosphere, and separate source means associated with radiation of each of said wavelengths each source means being operable to produce radiation in a narrow spectral band including the associated wavelength and switchable in intensity level by controlling means alternately with the other source means.
2. A detector as claimed in claim 1 in which at
least one source means comprise a source of
radiation in a wide spectral band excluding the
first or second wavelength associated with the
source and including phosphor means located so
as to be excited by radiation from the source to
emit radiation in a different spectral band
including the associated first or second wavelength.
3. A detector as claimed in claim 2 in which the phosphor is arranged to emit radiation in a narrow spectral band including said associated first or second wavelength.
4. A detector as claimed in claim 1 or claim 2 in which the radiation is in a wide spectral band including both of said first and second wavelength and/or wavelengths affected by other non-sought components of the atmosphere, and the source means includes a filter operable to restrict radiation passage therethrough to a narrow spectral band including only the associated first or second wavelength.
5. A detector as claimed in claim 1 in which at least one source means comprises a source of radiation in a narrow spectral band including one only of said first or second wavelengths.
6. A detector as claimed in claim 1 or claim 2 in which the source means is operable to emit radiation in the visible and/or near infra-red part of the spectrum and the phosphor is zinc sulphide.
7. A detector as claimed in any one of the preceding claims in which the source of radiation of the source means is a light emitting diode.
8. A detector as claimed in any one of the preceding claims in which the source of radiation in each source means is responsible to an electrical signal applied thereto to produce radiation at different switched intensity levels.
9. A detector as claimed in any one of claims 1 to 7 in which in at least one source means the source of radiation is a continuous emitter means and the controlling means includes an electrooptic shutter comprising an electrically conditionable medium by way of which radiation is passed to form the beam and means operable to condition the medium to interrupt transmission of the beam to effect switching of intensity of the radiation emitted by the source means.
10. A detector as claimed in claim 9 in which the electrically conditionable medium is a liquid crystal material switchable, by the application of an electric field, between transparency and opacity to radiation of the associated first or second wavelength.
11. A detector as claimed in claim 10 in which both source means share a common continuous emitter.
12. A detector of gas as claimed in any one of the preceding claims in which the processing means is arranged to process the reference and principal signals at said first and second wavelengths in synchronisation with the alternate emission of the radiation at said first and second wavelengths.
13. A detector of gas as claimed in any one of the preceding claims in which the beam splitting means comprises a partly reflective mirror.
14. A detector of gas as claimed in any one of the preceding claims in which the processing means includes means to produce an output signal a in accordance with the transfer function a=(1-PR)/x, where PR is the product of the ratio of the reference signals at the second and first wavelengths and the ratio of the principal signals at the first and second wavelengths and x is the path length of the radiation through the atmosphere outside of the enclosure.
1 5. A detector of gas as claimed in any one of the preceding claims in which the processing means is contained within the enclosure.
1 6. A detector of gas in the atmosphere substantially as herein described with reference to any one of Figures 2 to 5 of the accompanying drawings.
New Claims or Amendments to Claims filed on 24
June, 1982.
Superseded Claims 1 to 16.
New or Amended Claims: 1. Apparatus for determining the concentration of a gas in the atmosphere comprising an enclosure from which electromagnetic radiation at first and second wavelengths, to which the sought-for gas is absorptive and transmissive
respectively, is passed as a beam by way of the atmosphere to a principal detector and responsive to radiation received at both of said wavelengths to produce principal signals having magnitudes related to the intensity of the received radiation at each said wavelength, beam splitting means contained in the enclosure and arranged to deflect part of the beam to a reference detector within the enclosure responsive to radiation at both of said wavelengths not transmitted through the atmosphere to produce a reference signal having a magnitude related to the intensity of detected radiations at each of said wavelengths, processing means operable to determine the function definable as the product of the ratio of reference signals at second and first wavelengths and the ratio of the principal detector signals at the first and second wavelengths and to calculate from said function the concentration of said gas in the atmosphere, and separate radiation source means associated one each with the first and second radiation wavelengths suitable by controlling means to emit radiation alternately at different intensities, at least one of said source means comprising a source of radiation emitted in a spectral band excluding the first or second wavelength associated with the source means and phosphor means located to be excited by radiation from the source to emit radiation in a different spectral band including the associated first or second wavelengths.
2. A detector as claimed in claim 1 in which the phosphor is arranged to emit radiation in a narrow spectral band including said associated first or second wavelength.
3. A detector as claimed in claim 1 in which the radiation is in a wide spectral band including both of said first and second wavelength and/or wavelengths affected by other non-sought components of the atmosphere, and the source means includes a filter operable to restrict radiation passage therethrough to a narrow spectral band including only the associated first or second wavelength.
4. A detector as claimed in claim 1 in which the source means is operable to emit radiation in the visible and/or near infra-red part of the spectrum and the phosphor is zinc sulphide.
5. A detector as claimed in any one of the preceding claims in which the source of radiation of the source means is a light emitting diode.
6. A detector as claimed in any one of the preceding claims in which the source of radiation in each source means is responsible to an
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (1)
- **WARNING** start of CLMS field may overlap end of DESC **.spectral band including only the associated first or second wavelength.5. A detector as claimed in claim 1 in which at least one source means comprises a source of radiation in a narrow spectral band including one only of said first or second wavelengths.6. A detector as claimed in claim 1 or claim 2 in which the source means is operable to emit radiation in the visible and/or near infra-red part of the spectrum and the phosphor is zinc sulphide.7. A detector as claimed in any one of the preceding claims in which the source of radiation of the source means is a light emitting diode.8. A detector as claimed in any one of the preceding claims in which the source of radiation in each source means is responsible to an electrical signal applied thereto to produce radiation at different switched intensity levels.9. A detector as claimed in any one of claims 1 to 7 in which in at least one source means the source of radiation is a continuous emitter means and the controlling means includes an electrooptic shutter comprising an electrically conditionable medium by way of which radiation is passed to form the beam and means operable to condition the medium to interrupt transmission of the beam to effect switching of intensity of the radiation emitted by the source means.10. A detector as claimed in claim 9 in which the electrically conditionable medium is a liquid crystal material switchable, by the application of an electric field, between transparency and opacity to radiation of the associated first or second wavelength.11. A detector as claimed in claim 10 in which both source means share a common continuous emitter.12. A detector of gas as claimed in any one of the preceding claims in which the processing means is arranged to process the reference and principal signals at said first and second wavelengths in synchronisation with the alternate emission of the radiation at said first and second wavelengths.13. A detector of gas as claimed in any one of the preceding claims in which the beam splitting means comprises a partly reflective mirror.14. A detector of gas as claimed in any one of the preceding claims in which the processing means includes means to produce an output signal a in accordance with the transfer function a=(1-PR)/x, where PR is the product of the ratio of the reference signals at the second and first wavelengths and the ratio of the principal signals at the first and second wavelengths and x is the path length of the radiation through the atmosphere outside of the enclosure.1 5. A detector of gas as claimed in any one of the preceding claims in which the processing means is contained within the enclosure.1 6. A detector of gas in the atmosphere substantially as herein described with reference to any one of Figures 2 to 5 of the accompanying drawings.New Claims or Amendments to Claims filed on 24 June, 1982.Superseded Claims 1 to 16.New or Amended Claims:1. Apparatus for determining the concentration of a gas in the atmosphere comprising an enclosure from which electromagnetic radiation at first and second wavelengths, to which the sought-for gas is absorptive and transmissive respectively, is passed as a beam by way of the atmosphere to a principal detector and responsive to radiation received at both of said wavelengths to produce principal signals having magnitudes related to the intensity of the received radiation at each said wavelength, beam splitting means contained in the enclosure and arranged to deflect part of the beam to a reference detector within the enclosure responsive to radiation at both of said wavelengths not transmitted through the atmosphere to produce a reference signal having a magnitude related to the intensity of detected radiations at each of said wavelengths, processing means operable to determine the function definable as the product of the ratio of reference signals at second and first wavelengths and the ratio of the principal detector signals at the first and second wavelengths and to calculate from said function the concentration of said gas in the atmosphere, and separate radiation source means associated one each with the first and second radiation wavelengths suitable by controlling means to emit radiation alternately at different intensities, at least one of said source means comprising a source of radiation emitted in a spectral band excluding the first or second wavelength associated with the source means and phosphor means located to be excited by radiation from the source to emit radiation in a different spectral band including the associated first or second wavelengths.2. A detector as claimed in claim 1 in which the phosphor is arranged to emit radiation in a narrow spectral band including said associated first or second wavelength.3. A detector as claimed in claim 1 in which the radiation is in a wide spectral band including both of said first and second wavelength and/or wavelengths affected by other non-sought components of the atmosphere, and the source means includes a filter operable to restrict radiation passage therethrough to a narrow spectral band including only the associated first or second wavelength.4. A detector as claimed in claim 1 in which the source means is operable to emit radiation in the visible and/or near infra-red part of the spectrum and the phosphor is zinc sulphide.5. A detector as claimed in any one of the preceding claims in which the source of radiation of the source means is a light emitting diode.6. A detector as claimed in any one of the preceding claims in which the source of radiation in each source means is responsible to aneiectrical signal applied thereto to produce radiation at different switched intensity levels.7. A detector as claimed in any one of claims 1 to 5 in which in at least one source means the source of radiation is a continuous emitter means and the controlling means includes an electrooptic shutter comprising an electrically conditionable medium by way of which radiation is passed to form the beam and means operable to condition the medium to interrupt transmission of the beam to effect switching of intensity of the radiation emitted by the source means.8. A detector as claimed in claim 7 in which the electrically conditionable medium is a liquid crystal material switchable, by the application of an electric field, between transparency and opacity to radiation of the associated first or second wavelength.9. A detector as claimed in claim 8 in which both source means share a common continuous emitter.10. A detector of gas as claimed in any one of the preceding claims in which the processing means is arranged to process the reference and principal signals at said first and second wavelengths in synchronisation with the alternate emission of the radiation at said first and second wavelengths.11. A detector of gas as claimed in any one of the preceding claims in which the processing means includes means to produce an output signal a in accordance with the transfer function a=( 1 -PR)/x, where PR is the product of the ratio of the reference signals at the second and first wavelengths and the ratio of the principal signals at the first and second wavelengths and x is the path length of the radiation through the atmosphere outside of the enclosure.12. A detector of gas as claimed in any one of the preceding claims in which the processing means is contained within the enclosure.1 3. A detector of gas in the atmosphere substantially as herein described with reference to any one of Figures 2 to 5 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08134519A GB2102942B (en) | 1981-07-03 | 1981-11-16 | Spectrometric gas analysis |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8120552 | 1981-07-03 | ||
| GB08134519A GB2102942B (en) | 1981-07-03 | 1981-11-16 | Spectrometric gas analysis |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2102942A true GB2102942A (en) | 1983-02-09 |
| GB2102942B GB2102942B (en) | 1985-06-26 |
Family
ID=26280007
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08134519A Expired GB2102942B (en) | 1981-07-03 | 1981-11-16 | Spectrometric gas analysis |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2102942B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1993002367A1 (en) * | 1991-07-18 | 1993-02-04 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | An electro-optical detection system for reflection free underwater images from aircraft |
| EP0584519A1 (en) * | 1992-08-21 | 1994-03-02 | Siemens-Elema AB | Spectrophotometric method and spectrophotometer for performing the method |
| GB2274163A (en) * | 1993-01-12 | 1994-07-13 | Pollution Monitor Syst Ltd | Gas analyser |
| WO1999013303A1 (en) * | 1997-09-09 | 1999-03-18 | Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno | Gas sensor |
| WO2011042628A1 (en) * | 2009-10-08 | 2011-04-14 | Centre National De La Recherche Scientifique | Chemical species optical sensor operating in infrared |
-
1981
- 1981-11-16 GB GB08134519A patent/GB2102942B/en not_active Expired
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1993002367A1 (en) * | 1991-07-18 | 1993-02-04 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | An electro-optical detection system for reflection free underwater images from aircraft |
| GB2273155A (en) * | 1991-07-18 | 1994-06-08 | Secr Defence | An electro-optical detection system for reflection free underwater images from aircraft |
| GB2273155B (en) * | 1991-07-18 | 1995-04-19 | Secr Defence | An electro-optical detection system for reflection free underwater images from aircraft |
| US5444441A (en) * | 1991-07-18 | 1995-08-22 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Briatin And Northern Ireland | Electro-optical detection system for reflection free underwater images from aircraft |
| EP0584519A1 (en) * | 1992-08-21 | 1994-03-02 | Siemens-Elema AB | Spectrophotometric method and spectrophotometer for performing the method |
| US5387979A (en) * | 1992-08-21 | 1995-02-07 | Siemens-Elema Ab | Spectrophotometric method and spectrophotometer for performing the method |
| GB2274163A (en) * | 1993-01-12 | 1994-07-13 | Pollution Monitor Syst Ltd | Gas analyser |
| GB2274163B (en) * | 1993-01-12 | 1996-11-20 | Pollution Monitor Syst Ltd | Gas analyser |
| WO1999013303A1 (en) * | 1997-09-09 | 1999-03-18 | Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno | Gas sensor |
| WO2011042628A1 (en) * | 2009-10-08 | 2011-04-14 | Centre National De La Recherche Scientifique | Chemical species optical sensor operating in infrared |
| FR2951270A1 (en) * | 2009-10-08 | 2011-04-15 | Centre Nat Rech Scient | OPTICAL SENSOR OF CHEMICAL SPECIES OPERATING IN INFRARED |
| US8779363B2 (en) | 2009-10-08 | 2014-07-15 | Centre National De La Recherche Scientifique | Chemical species optical sensor operating in infrared |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2102942B (en) | 1985-06-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |