GB2178841A - Gas detection systems - Google Patents
Gas detection systems Download PDFInfo
- Publication number
- GB2178841A GB2178841A GB08519971A GB8519971A GB2178841A GB 2178841 A GB2178841 A GB 2178841A GB 08519971 A GB08519971 A GB 08519971A GB 8519971 A GB8519971 A GB 8519971A GB 2178841 A GB2178841 A GB 2178841A
- Authority
- GB
- United Kingdom
- Prior art keywords
- gas
- radiation
- detector
- vapour
- sensor
- 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- Withdrawn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
- 238000001514 detection method Methods 0.000 title description 5
- 230000005855 radiation Effects 0.000 claims abstract description 49
- 238000010521 absorption reaction Methods 0.000 claims abstract description 25
- 238000000034 method Methods 0.000 claims description 4
- 230000005670 electromagnetic radiation Effects 0.000 claims description 2
- 238000012544 monitoring process Methods 0.000 claims description 2
- 230000035945 sensitivity Effects 0.000 abstract description 14
- 230000001419 dependent effect Effects 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 39
- 230000009102 absorption Effects 0.000 description 21
- RJCQBQGAPKAMLL-UHFFFAOYSA-N bromotrifluoromethane Chemical compound FC(F)(F)Br RJCQBQGAPKAMLL-UHFFFAOYSA-N 0.000 description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 8
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- 239000011521 glass Substances 0.000 description 3
- 229910052750 molybdenum Inorganic materials 0.000 description 3
- 239000011733 molybdenum Substances 0.000 description 3
- JCXJVPUVTGWSNB-UHFFFAOYSA-N nitrogen dioxide Inorganic materials O=[N]=O JCXJVPUVTGWSNB-UHFFFAOYSA-N 0.000 description 3
- 238000005070 sampling Methods 0.000 description 3
- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 description 2
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 2
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- LELOWRISYMNNSU-UHFFFAOYSA-N hydrogen cyanide Chemical compound N#C LELOWRISYMNNSU-UHFFFAOYSA-N 0.000 description 2
- 150000002903 organophosphorus compounds Chemical class 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- JLGADZLAECENGR-UHFFFAOYSA-N 1,1-dibromo-1,2,2,2-tetrafluoroethane Chemical compound FC(F)(F)C(F)(Br)Br JLGADZLAECENGR-UHFFFAOYSA-N 0.000 description 1
- MGWGWNFMUOTEHG-UHFFFAOYSA-N 4-(3,5-dimethylphenyl)-1,3-thiazol-2-amine Chemical compound CC1=CC(C)=CC(C=2N=C(N)SC=2)=C1 MGWGWNFMUOTEHG-UHFFFAOYSA-N 0.000 description 1
- HGINCPLSRVDWNT-UHFFFAOYSA-N Acrolein Chemical compound C=CC=O HGINCPLSRVDWNT-UHFFFAOYSA-N 0.000 description 1
- KAKZBPTYRLMSJV-UHFFFAOYSA-N Butadiene Chemical compound C=CC=C KAKZBPTYRLMSJV-UHFFFAOYSA-N 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 239000004338 Dichlorodifluoromethane Substances 0.000 description 1
- CBENFWSGALASAD-UHFFFAOYSA-N Ozone Chemical compound [O-][O+]=O CBENFWSGALASAD-UHFFFAOYSA-N 0.000 description 1
- 101100054666 Streptomyces halstedii sch3 gene Proteins 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- BZHJMEDXRYGGRV-UHFFFAOYSA-N Vinyl chloride Chemical compound ClC=C BZHJMEDXRYGGRV-UHFFFAOYSA-N 0.000 description 1
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 229940124326 anaesthetic agent Drugs 0.000 description 1
- 230000003444 anaesthetic effect Effects 0.000 description 1
- 229940058344 antitrematodals organophosphorous compound Drugs 0.000 description 1
- 125000003118 aryl group Chemical group 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- MEXUFEQDCXZEON-UHFFFAOYSA-N bromochlorodifluoromethane Chemical compound FC(F)(Cl)Br MEXUFEQDCXZEON-UHFFFAOYSA-N 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- PXBRQCKWGAHEHS-UHFFFAOYSA-N dichlorodifluoromethane Chemical compound FC(F)(Cl)Cl PXBRQCKWGAHEHS-UHFFFAOYSA-N 0.000 description 1
- 235000019404 dichlorodifluoromethane Nutrition 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 150000008282 halocarbons Chemical class 0.000 description 1
- BCQZXOMGPXTTIC-UHFFFAOYSA-N halothane Chemical compound FC(F)(F)C(Cl)Br BCQZXOMGPXTTIC-UHFFFAOYSA-N 0.000 description 1
- 238000005286 illumination Methods 0.000 description 1
- 239000003317 industrial substance Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 210000005036 nerve Anatomy 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 150000003003 phosphines Chemical class 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 239000003507 refrigerant Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 239000000779 smoke Substances 0.000 description 1
- CYTQBVOFDCPGCX-UHFFFAOYSA-N trimethyl phosphite Chemical compound COP(OC)OC CYTQBVOFDCPGCX-UHFFFAOYSA-N 0.000 description 1
- 229930195735 unsaturated hydrocarbon Natural products 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
- G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light
-
- 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
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/10—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void
- G01J1/16—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void using electric radiation detectors
- G01J1/1626—Arrangements with two photodetectors, the signals of which are compared
-
- 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
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/10—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void
- G01J1/16—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void using electric radiation detectors
- G01J2001/161—Ratio method, i.e. Im/Ir
-
- 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
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
- G01J1/44—Electric circuits
- G01J2001/4413—Type
- G01J2001/4426—Type with intensity to frequency or voltage to frequency conversion [IFC or VFC]
-
- 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
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
A gas sensor for detecting the concentration of a gas or vapour which has an absorption wavelength in the UV radiation band of approximately 130 to 250 nm comprises a UV source (2) at a fixed distance from a housing containing two UV detectors (6, 8) which each receive a part of the radiation transmitted from the source through the gas or vapour. One detector (8) has a sensitivity which includes the absorption wavelength of the gas to be detected. The other detector (6) has a sensitivity which is close but excludes the absorption wavelength. The ratio of radiation falling on the two detectors is measured by circuit 20 and from this the concentration of the gas is calculated. The detectors are gas discharge UV photocells which produce pulses at a frequency dependent on the amount of radiation received. <IMAGE>
Description
SPECIFICATION
Gas detection systems
The present invention relates to gas detection systems.
In many applications, it is necessary to detect the presence of gases and vapours. For example, in industrial installations, it may be required to monitor the atmosphere for gas leaks. In automatic fire control systems, it may be required to monitor the concentration of an organic fire extinguishing agent.
All gases and vapours exhibit absorptions at various characteristic wavelengths in the electromagnetic spectrum. In particular, strong absorptions are found for many common gases and vapours in the ultraviolet (UV) portion of the electromagnetic spectrum.
The present invention accordingly provides a sensor for a gas or vapour which has a strong absorption of electromagnetic radiation at a predetermined wavelength, the detector comprising a source of radiation including said predetermined wavelength, two detectors disposed at a fixed distance from said source, one detector being adapted to detect radiation within a range including the predetermined wavelength, and the second detector being adapted to detect radiation within a range produced by the source but which is not absorbed by the gas or vapour to be detected, the relative values of the outputs of the detectors providing an indication of the concentration of the gas or vapour.
Preferably the predetermined wavelength is in the ultraviolet range of wavelengths between substantially 130 and 250 nm. In this way the sensor can be utilised in the open without shielding as no solar radiation is produced in this range of wavelengths. Accordingly, such a sensor is insensitive to sunlight.
In a preferred embodiment the detectors are gas discharge UV photocells which produce a pulsed output, the frequency of which is proportional to the intensity of received radiation within the range of the detector, and the sensor further comprises concentration measuring means comprising a counter connected to the output of each said detector, and means connected to said counters for producing an output representative of the ratio of the counts for each detector. An alarm signal may be produced if the ratio falls below a threshold value. Alternatively, processing means may be provided to derive the true concentration of the gas or vapour from the output ratio.
The present inventionfurther provides a method of sensing the concentration of a gas or vapour which strongly absorbs radiation at a predetermined wavelength, comprising the steps of providing a source of a range of radiation including said predetermined wavelength, monitoring the received radiation at a fixed distance from said source at at least two wavelengths, one being said predetermined wavelength, the other being a wavelength not being absorbed by the gas or vapour, and producing a signal representing the ratio of the intensities of radiation at the two monitored wavelengths.
A gas or vapour sensor embodying the invention and a method of sensing the concentration of a gas or vapour in accordance with the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:
Figure 1 is a schematic diagram of the sensor; and
Figure 2 is a plot of wavelength against the percentage transmission of radiation for the gas Halon 1301 (bromotrifluoromethane), and a plot of wavelength against relative sensitivity for two gas discharge photocells.
The gas sensor illustrated diagrammatically in Figure 1 comprises a source 2 of UV radiation, such as a gas discharge device. The source is contained in a housing with a lens 4 which collimates the radiation into a beam. The source 2 is spaced a fixed distance along the path of the beam from a detector housing containing two UV detectors 6 and 8.
The housing has a UV transparent window 10 through which the incident radiation from the source 2 enters the housing. A beam splitter 12 is positioned behind the window 10 so as to cause part of the received radiation to fall on each of the detectors 6,8.
The detectors are sensitive to different radiation bands within the range of radiation emitted by the source 2. The detector 6 has a sensitivity band which does not include an absorption wavelength of the gas or vapour to be detected. Therefore, the intensity of radiation falling on this detector should remain constant if the radiation from the source is constant. The detector 8 has a sensitivity band which includes the absorption wavelength and, therefore, the intensity of radiation falling on this detector will fluctuate with the concentration of gas or vapour between the source and this detector.
Ideally the bands of the two detectors are relatively close so that fluctuations in intensity of the source equally affect both detectors.
The radiation falling on the detector 6 is passed from the beam splitter 12 via a filter 14. The filter 14 is provided to modify the range of sensitivity of the detector 6. The filter 14 is not necessary if a detector 6 is available with the required range of sensitivity. A filter may also be provided for the detector 8 if necessary.
Where the detectors 6, 8 are gas discharge UV photocells, their output is in the form of pulses, the frequency of which is proportional to the amount of radiation falling on the detector within its range of sensitivity. The pulses from the detectors 6 and 8 are fed to respective counters 16, 18. The outputs of the counters are fed to a ratio measuring circuit 20 which produces an output at 22 representative of the ratio of the counts accumulated in the two counters. This ratio is proportional to the ratio of the intensi ties of radiation falling on the respective detectors 6,8.
The output of the counter 16 is also fed to a digital to analogue converter (DAC) 24 which has a long time constant. The output of the DAC 24 is fed to a control input of a power supply 26 which supplies power to the source 2. As the counter 16 is driven from the detector 6 which responds to fluctuations in the intensity of radiation emitted from the source 2, the DAC 24 provides a feedback path so that, as the intensity of radiation received from the source 2 drops, the control input to the power supply causes the power to the source 2 to be increased thereby bringing the intensity of radiation back to its original level.
The feedback operates similarly to compensate for an increase in intensity of radiation from the source.
The output of the DAC 24 is also fed to one input of a comparator 28. The other input 30 of the comparator 28 is provided with a reference voltage. The output of the comparator at 32 is used to provide an indication of the occurrence of a optical fault. Therefore, if the radiation received by the detector 6 falls below a reference value set by the reference voltage fed to input 30, a fault is indicated at output 32. This may arise if the window 10 has become unduly soiled or the source 2 has failed.
The source 2 produces UV radiation in the range of wavelengths from substantially 130 to 250 nm. For detection of certain gases the wavelength range of the source can be selected to be more restricted, for example 180 to 250 nm. When a gas discharge device is used it is operated by a continuous discharge at a current level set by the power supply 26. If the radiation produced by the source 2 is represented as 1o then the radiation (I) received by a detector will be represented by Beer-Lambert's equation: Ia exp (-iicx) where pd = the absorption coefficient for a particular gas at the wavelength at which the intensities l,lo are measured.
c = the concentration of the gas or vapour,
x = the distance between the source and the detector.
As stated, the detector 6 has a band of wavelength sensitivity which does not include an absorption wavelength of the gas or vapour to be detected. Therefore the absorption coefficient will be low for this detector. However, the detector 8 has a sensitivity range which includes a wavelength at which the gas or vapour absorbs strongly and therefore the absorption coefficient for this detector is relatively high and much greater than the absorption coefficient for the other detector.
A large variety of gaseous vapours exhibit strong absorption in the UV range of wavelengths between 160 and 250 nm. Therefore, all such gases and vapours can be detected by the sensor described. Such gases include hydrogen sulphide, sulphide dioxide, nitric oxide, nitrogen dioxide, ozone, hydrogen cyanide, ammonia, and carbon monoxide. Oxygen has a broad absorption band between about 180 and 130 nm with a peak at about 145 nm. Certain organic gases and vapours particular can also be detected, such as the halogenated hydrocarbons; this has particular relevance to fire extinguishing agents such as bromotrifluoromethane, bromochlorodifluoromethane and dibromotetrafluoroethane; to refrigerants such as dichlorodifluoromethane; to anaesthetics such as bromochlorotrifluoroethane; and to industrial chemicals such as vinyl chloride or chloroform. Other organic vapours which can readily be detected are unsaturated hydrocarbons, particularly those containing aromatic or conjugated ethylenic and acetylenic groupings. Since many organophosphorus compounds have UV absorption bands in this wavelength range these can also be detected by this means; this applies to simple phosphines and P(llI) compounds and also to organophosphorous compounds containing the phyosphoryl group (P=O), thus, for example, the equipment could be used to detect the presence of anticholoinesterase nerve agents.
Table 1 give below gives a list of samples of substances which can be detected with a sensor as described together with their peak absorption wavelength (A max).
TABLE 1
UVAbsorption Bands of some Gases and Vapours
Substance A max
nm N2O 190
NO 192 NO2 206
H2S 197 SO, 199
NH3 194 O3 145 o3 200,250
CF3Br 205
CF2CIBr 205 C6H6 183,204
CH2=CH-CH=CH2 217
CH2=CHCHO 210 C10H8 190,220 PH3 191
POCI3 195
P(OCH3)3 190 C2H5PO(OC2Hs) (SCH3) 185,221
A sensor which is specifically adapted for the detection of Halon 1301 (bromotrifluoromethane) will now be described as an example of how the sensor can be adapted for particular gases or vapours.
In Figure 2 the plot labelled A shows the absorption curve for Halon 1301 (measured at a concentration of 10% by volume over a path length of 75mm). As shown, there is strong absorption at approximately 205nm. The plot marked B shows the wavelength sensitivity of the detector 8. The plot marked C shows the wavelength sensitivity of the detector 6.
The detector 8 is a photocell with a nickel electrode and a UV transmitting glass envelope. The high work function of nickel ensures that the photocell does not respond to wavelengths longer than about 240nm and the envelope does not transmit radiation of wavelengths shorter than about 190 nm. This range of wavelengths includes the strong absorption wavelength of approximately 205 nm which is characteristic of Halon 1301. The detector 6 is a molybdenum electrode which is mounted behind a glass UV cut off filter (Schott WG295, 1 mm thick). The lower work function of molybdenum relative to nickel means that this photocell has a wavelength sensitivity out beyond 270 nm while the glass filter 14 cuts off the short wave response to about 220 nm. This ensures that within the wavelength sensitivity of the detector 6 there is very little absorption by Halon 1301.
In the sensor of this example the detectors 6 and 8 are distanced 75mm from the source 2. Therefore, for these two detectors 6,8 the Beer-Lambert equation can be written as follows.
Ini = Ioni exp (- 12.4c) (1)
Imo = Iomo exp (- 0.62c) (2) where Ini is the incident radiation received by the nickel electrode photocell detector 8 and I is the radiation received by the molybdenum electrode photocell detector 6, Ioni represents the intensity of radiation within the band of the detector 8 produced by the source 2. 1a,, represents the corresponding quantity for detector 6. Ideally the source 2 is arranged such that 1a = lomo. If this is not possible then the ratio may be measured as a calibration constant of the sensor. The figure 12.4 is the absorption coefficient within the wavelength band of the detector 8 multiplied by the path length of 75mm.Similarly 0.62 represents the much lower absorption coefficient for the detector 6 multiplied by the same path length.
Dividing equation (1) by equation (2) gives the following.
The output 22 from the sensor circuit shown in Figure 1 provides a ratio Inj/lmo. This output can be fed to a further processing circuit for calculating the gas concentration c. The processing circuit may com prise logarithmic amplifiers or use a microprocessor or microcomputer to perform the necessary calculations. Where the ratio 1,,,/1,,, is not equal to 1, this ratio must be provided to the processing circuit.
If the absolute gas concentration is not required then the output 22 representing the ratio In,lmo can be fed to a threshold detector circuit so that an alarm signal can be produced if the ratio falls below a predetermined threshold indicative of an excess concentration of the gas or vapour to be detected.
The minimum concentrations of the gas or vapour that can be detected by the sensor described depend on various factors, including the intensity of the absorption band, the path lengths x between the source 2 and the detectors, the bandwidth of the source and detectors, the possible presence of interfering gases or background radiation, and the signal to noise ratio.
Gas discharge photocells are suitable for use as the detectors 6, 8. Such detectors may be made responsive to wavelengths down to 160 nm by using a pure silica envelope.
The system is particularly advantageous in that it is solar blind since the UV radiation band of 130 to 250nm is not present in normal sunlight. Therefore, the sensor requires no shielding from ambient illumination. This ensures that the atmosphere to be sampled has easy access to the space between the source and the detectors of the sensors.
The described sensor can readily be accommodated in a rugged housing so that it can tolerate hostile environments including high temperatures and high vibration levels. Therefore, it is possible to install such a sensor directly at the sampling point. This avoids the need for sampling pipes and pumps required by some prior art sensors for conveying a sample of the atmosphere to be monitored to the sensor location. The absence of such sampling pipes and pumps clearly minimises the reaction time of the sensor.
Another particular advantage of this sensor is that there are no moving parts.
The use of the feedback provided by the DAC 24 to the power supplies 26 for the source 2 enables the sensor to be relatively intolerant to the presence of smoke, dust, condensation and other contaminations which may prevent radiation effectively reaching the detectors 6,8. The comparator 28 fed from the DAC 24 and the reference voltage 30 provides a simple and effective way of detecting failure of the source or excessive contamination.
Claims (8)
1. A sensor for a gas or vapour which has a strong absorption of electromagnetic radiation at a predetermined wavelength, the detector comprising a source of radiation including said predetermined wavelength, two detectors disposed at a fixed distance from said source, one detector being adapted to detect radiation within a range including the predetermined wavelength, and the second detector being adapted to detect radiation within a range produced by the source but which is not absorbed by the gas or vapour to be detected, the relative values of the outputs of the detectors providing an indication of the concentration of the gas or vapour.
2. A sensor as claimed in claim 1, wherein the predetermined wavelength is in the ultraviolet range of wavelengths between substantially 130 and 250nm.
3. A sensor as claimed in claim 1 or 2, wherein the detectors are gas discharge UV photocells which produce a pulsed output, the frequency of which is proportional to the intensity of received radiation within the range of the detector, and the sensor further comprises concentration measuring means comprising a counter connected to the output of each said detector, and means connected to said counters for producing an output representative of the ratio of the counts for each detector.
4. A sensor as claimed in claim 3, further comprising means for producing an alarm signal if the ratio falls below a predetermined threshold value.
5. A sensor as claimed in claim 3, further comprising processing means for deriving the true concentration of the gas or vapour from the output ratio.
6. A sensor for a gas or vapour substantially as herein described with reference to the accompanying drawings.
7. A method of sensing the concentration of a gas or vapour which strongly absorbs radiation at a predetermined wavelength, comprising the steps of providing a source of a range of radiation including said predetermined wavelength, monitoring the received radiation at a fixed distance from said source at at least two wavelengths, one being said predetermined wavelength, the other being a wavelength not being absorbed by the gas or vapour, and producing a signal representing the ratio of the intensities of radiation at the two monitored wavelengths.
8. A method of sensing the concentration of a gas or vapour substantially as herein described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08519971A GB2178841A (en) | 1985-08-08 | 1985-08-08 | Gas detection systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08519971A GB2178841A (en) | 1985-08-08 | 1985-08-08 | Gas detection systems |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8519971D0 GB8519971D0 (en) | 1985-09-18 |
| GB2178841A true GB2178841A (en) | 1987-02-18 |
Family
ID=10583524
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08519971A Withdrawn GB2178841A (en) | 1985-08-08 | 1985-08-08 | Gas detection systems |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2178841A (en) |
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5281816A (en) * | 1991-07-04 | 1994-01-25 | Spectronix Ltd. | Method and apparatus for detecting hydrocarbon vapors in a monitored area |
| EP0802430A2 (en) * | 1996-04-18 | 1997-10-22 | Sick AG | Opto-electronic sensor |
| EP0836091A1 (en) * | 1996-10-09 | 1998-04-15 | Osaka Gas Company Limited | Method and apparatus for measuring odorant concentration and odorant adding system |
| US5961314A (en) * | 1997-05-06 | 1999-10-05 | Rosemount Aerospace Inc. | Apparatus for detecting flame conditions in combustion systems |
| US8469700B2 (en) | 2005-09-29 | 2013-06-25 | Rosemount Inc. | Fouling and corrosion detector for burner tips in fired equipment |
| FR3001292A1 (en) * | 2013-01-24 | 2014-07-25 | Airbus Operations Sas | METHOD AND DEVICE FOR MEASURING THE EXTINGUISHING AGENT CONCENTRATION IN A FIRE AREA |
| NL2015580B1 (en) * | 2015-10-07 | 2017-05-02 | Aquacolor Sensors B V | Sensor system for spectrophotometric measurement of components and method there for. |
| CN109085044A (en) * | 2018-08-14 | 2018-12-25 | 武汉敢为科技有限公司 | A kind of portable ultralow ultraviolet flue gas analysis pretreatment detection system |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3843256A (en) * | 1972-03-03 | 1974-10-22 | Michele Catellono | Press for exposure and photoengraving |
| GB1416182A (en) * | 1972-02-28 | 1975-12-03 | Ici Ltd | Photometric analyser |
| GB1420044A (en) * | 1972-09-13 | 1976-01-07 | Us Energy Research Dev Adminis | Zeeman effect absorption spectrometer |
| US3935463A (en) * | 1974-12-05 | 1976-01-27 | Milton Roy Company | Spectrophotometer |
| US4193694A (en) * | 1978-07-03 | 1980-03-18 | Smith Charles R | Photosensitive color monitoring device and method of measurement of concentration of a colored component in a fluid |
| GB2144849A (en) * | 1983-08-12 | 1985-03-13 | Hochiki Co | Gas sensor |
-
1985
- 1985-08-08 GB GB08519971A patent/GB2178841A/en not_active Withdrawn
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1416182A (en) * | 1972-02-28 | 1975-12-03 | Ici Ltd | Photometric analyser |
| US3843256A (en) * | 1972-03-03 | 1974-10-22 | Michele Catellono | Press for exposure and photoengraving |
| GB1420044A (en) * | 1972-09-13 | 1976-01-07 | Us Energy Research Dev Adminis | Zeeman effect absorption spectrometer |
| US3935463A (en) * | 1974-12-05 | 1976-01-27 | Milton Roy Company | Spectrophotometer |
| US4193694A (en) * | 1978-07-03 | 1980-03-18 | Smith Charles R | Photosensitive color monitoring device and method of measurement of concentration of a colored component in a fluid |
| GB2144849A (en) * | 1983-08-12 | 1985-03-13 | Hochiki Co | Gas sensor |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5281816A (en) * | 1991-07-04 | 1994-01-25 | Spectronix Ltd. | Method and apparatus for detecting hydrocarbon vapors in a monitored area |
| EP0802430A2 (en) * | 1996-04-18 | 1997-10-22 | Sick AG | Opto-electronic sensor |
| EP0802430A3 (en) * | 1996-04-18 | 1999-06-23 | Sick AG | Opto-electronic sensor |
| US6091071A (en) * | 1996-04-18 | 2000-07-18 | Sick Ag | Opto-electronic sensor |
| EP0836091A1 (en) * | 1996-10-09 | 1998-04-15 | Osaka Gas Company Limited | Method and apparatus for measuring odorant concentration and odorant adding system |
| US5844124A (en) * | 1996-10-09 | 1998-12-01 | Osaka Gas Co., Ltd. | Method and apparatus for measuring odorant concentration and oderant adding system |
| US5961314A (en) * | 1997-05-06 | 1999-10-05 | Rosemount Aerospace Inc. | Apparatus for detecting flame conditions in combustion systems |
| US8469700B2 (en) | 2005-09-29 | 2013-06-25 | Rosemount Inc. | Fouling and corrosion detector for burner tips in fired equipment |
| FR3001292A1 (en) * | 2013-01-24 | 2014-07-25 | Airbus Operations Sas | METHOD AND DEVICE FOR MEASURING THE EXTINGUISHING AGENT CONCENTRATION IN A FIRE AREA |
| NL2015580B1 (en) * | 2015-10-07 | 2017-05-02 | Aquacolor Sensors B V | Sensor system for spectrophotometric measurement of components and method there for. |
| CN109085044A (en) * | 2018-08-14 | 2018-12-25 | 武汉敢为科技有限公司 | A kind of portable ultralow ultraviolet flue gas analysis pretreatment detection system |
| CN109085044B (en) * | 2018-08-14 | 2021-01-12 | 武汉敢为科技有限公司 | Portable ultralow ultraviolet flue gas analysis preliminary treatment detecting system |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8519971D0 (en) | 1985-09-18 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5464983A (en) | Method and apparatus for determining the concentration of a gas | |
| EP0480753B1 (en) | Optical analytical instrument and method | |
| US5281816A (en) | Method and apparatus for detecting hydrocarbon vapors in a monitored area | |
| EP2092289B1 (en) | Leak detection system and method | |
| US5604298A (en) | Gas measurement system | |
| US3935463A (en) | Spectrophotometer | |
| CS90191A3 (en) | Fire detector | |
| EP0084726B1 (en) | Monitoring gaseous ammonia concentration in flue gases | |
| US5936250A (en) | Ultraviolet toxic gas point detector | |
| GB2178841A (en) | Gas detection systems | |
| US5818598A (en) | Nondispersive optical monitor for nitrogen-oxygen compounds | |
| Korolkoff | Survey of toxic gas sensors and monitoring systems | |
| US8077316B2 (en) | Chlorine dioxide sensor | |
| NO159424B (en) | PHOTOELECTRIC SMOKE DETECTOR. | |
| WO2014143049A1 (en) | Gas sensing with tunable photonic radiation filter element | |
| KR20200055236A (en) | A NDIR analyzer using Two Functional Channels and method thereof | |
| US7166843B2 (en) | Technique for detecting ethylene oxide in air | |
| GB2264169A (en) | Collinear-beam drift-compensated methane detector | |
| Thomas et al. | Instruments for methane gas detection | |
| JP2008232918A (en) | Gas detector | |
| US11841317B2 (en) | Device and process for detecting a gas, especially a hydrocarbon | |
| US6320199B1 (en) | Process for improving the reliability of operation of optical gas sensors | |
| JPS6120808B2 (en) | ||
| Zientkiewicz | Self referenced fiber optic Methane detection system | |
| KR100254935B1 (en) | Method and apparatus for measuring moisture using near-infrared ray with short wavelength as light source |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |