WO2006130016A1 - Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers - Google Patents

Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers Download PDF

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Publication number
WO2006130016A1
WO2006130016A1 PCT/NO2006/000200 NO2006000200W WO2006130016A1 WO 2006130016 A1 WO2006130016 A1 WO 2006130016A1 NO 2006000200 W NO2006000200 W NO 2006000200W WO 2006130016 A1 WO2006130016 A1 WO 2006130016A1
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Prior art keywords
gas
liquid
optical
monitor
light source
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PCT/NO2006/000200
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French (fr)
Inventor
Ivar Linnerud
Ove BJORØY
Axel Fredrik Bohman
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Norsk Elektro Optikk As
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Publication of WO2006130016A1 publication Critical patent/WO2006130016A1/en

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    • 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
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
    • G01N21/3504—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing gases, e.g. multi-gas analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/39—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using tunable lasers
    • G01N2021/396—Type of laser source
    • G01N2021/399—Diode laser

Definitions

  • Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers.
  • TDL tuneable diode lasers
  • a second window 3020 on the opposite side of the target gas or process • A detector lens system 3030 focusing the light onto
  • a detector 2000 • A detector 2000.
  • Other parts in a typical gas analyser, but not involved in the optical path is the electronic system 5000 containing: electronics- for temperature control of the laser, modulation of the laser, detector amplifiers, analogue to digital converters for digitising analogue signals like the detector signal and a micro processor with software (firmware) for controlling the instrument as well as calculating a gas concentration based on sampled signals.
  • Water vapour and oxygen as well as other gases are present in the normal atmosphere and will typically be present in the housing of a gas analyser.
  • the absorption signal from the part of the path inside the analyser will typically be much stronger that the absorption from the part of the path inside the process.
  • the signal contribution from the part of the path inside the analyser could change with time due to change in humidity, temperature, and pressure and make it almost impossible to get a reliable measurement of the gas in the process • •
  • the gas mix inside a gas analyser could be a result of the air (atmosphere) where the analyser was assembled, where it is installed (leaks) and contributions could also come from emission of gas from the inside walls of the housing or other components inside the housing.
  • the laser beam 1100 will go through the gas in the analyser from the laser 1000 to the collimating lens 3010 and then to the window 3020 isolating the monitor from the process and the target gas 4000.
  • the light beam then enters the other end of the analyser through another window 3020.
  • the beam will go through more gas from the window to the detector lens 3030 and then to the detector 2000. If the absorption from the gas within the analyser itself is much higher than the absorption of the same gas in the process, then it could in practice be impossible to measure the absorption contribution from the process reliably. This 5. is in particular a problem if the gas concentration in the gas analyser housing changes with time.
  • This invention uses a liquid to deplete the unwanted gases from the optical parts of the gas analyser so that the light beam from the light source goes through the liquid on its way from the light source to the window isolating the analyser from the process.
  • the liquid will replace air or gas between optical components on the receiver side in front of the detector. Liquids will typically have other refractive indexes than air or other gases and therefore the overall optical design will be modified to compensate for this.
  • Displacing gases in the monitor housing optical path will work due to two different effects.
  • the first and obvious effect is that the gas we want to remove is fully depleted by the liquid.
  • the second effect is that, even though the gas we want to remove .still is present to .a certain degree in the liquid, the shape of this gas' absorption lines will be significantly changed due to heavy line broadening. Therefore absorption of the gas in the liquid will not influence the measurement of the same gas in the sealed process. From a spectroscopic point of view it would even work to use water as the liquid for measurement of low water vapour concentrations as long as the transmission through water is sufficient on the wavelength one will use. Oils with satisfactory optical and electrical i.e., isolating properties will the preferred choice.
  • the technique of this invention could be applied to all optical gas measurement methods even though the examples and figures in this patent application show measurements based on tuneable diode lasers .
  • the selected liquid must have a sufficient transmission in the wavelength region where the light source emits light.
  • Other requirement to liquid selection is that it must neither freeze nor boil within the temperature operating range of the gas monitor. This will also apply for the storage and transport temperature range.
  • Other important criteria for liquid selection are that no bubbles or foam are being formed in the liquid under industrial work conditions like severe vibrations.
  • Different parts of the optical path inside the gas monitor might have different requirements to the properties of the liquid.
  • the area around the light source, that in the preferred embodiment is a laser, might require a liquid with high thermal conductivity and good electrical isolating properties while other parts of the optical path requires a liquid with a certain refractive index. Therefore some embodiments of this invention will use different liquids in the different parts of the optical path inside the gas monitor.
  • a setup described in this application where the optical path between the gas monitor and a container like a light bulb or vial has been filled with a liquid, this liquid possibly one of the liquids used inside the gas monitor or possibly yet another liquid. The latter could be selected based on issues like residues on the containers and health, safety and environment considerations .
  • the sealed beam part of the monitor could have the following embodiments: • Completely filled with the liquid i.e., no gas present
  • FIG. 7 One other embodiment with regards to the optical path is shown in figure 7 where a fibre (3200) coupled laser 1000 has been used.
  • Using this embodiment will de-couple temperature control of the laser from the liquid at the cost of possibly introducing a small air or gas gap between the laser and the optical fibre. In this gap isolator lenses that couple the laser light into the fibre normally are present. To compensate for this a fibre splitter and an extra detector could be introduced. Two fibres will then come from the laser and one of them is connected to the gas analyser shown in figure 7 while the other fibre is connected to a second detector. The signal from this second detector is then used to measure the possible interference and this measurement is then used to adjust the measurement in the gas analyser accordingly.
  • Yet another embodiment of the optical system is based on a dual path approach where both the light source and the detector are placed on the same side of the target gas and a retro reflector is placed on the opposite side.
  • a dual gas analyser according to this invention would have a retro reflector possibly filled with liquid and mirror arrangement enabling zero check with a path within the instrument itself and a gain check with an gas cell inserted in the path. The mirror arrangement and gas cell are placed in the liquid filled part of the analyser.
  • a multi-pass cell embodiment of this invention will..have all parts of the multi-pass optical path outside of the gas cell filled with liquid.
  • the gas cell could for instance be a Herriott cell, but is not limited to this design.
  • the laser in a TDL gas monitor is temperature regulated with an accuracy better than 10 mK (1 milli Kelvin equals 1/1000 0 C) .
  • the temperature control of the laser 1000 is done indirectly by temperature controlling the liquid 6100 in the sealed part 6000 while in another embodiment as in figure 7 the laser 1000 is placed outside the sealed part 6000 and temperature regulated as in prior art.
  • this invention could have several embodiments .
  • the preferred embodiment is based on tuneable diode lasers, but other embodiments are also possible.
  • Revolving optical filters selecting two or more spectral ranges, possibly one in the wavelength absorption range of the gas and one outside is one commonly used technique.
  • FTIR techniques could also be applied as well as techniques based on other optical filter techniques like the one described in US patent 5,606,419 (Norsk Hydro) .
  • Figure 1 shows prior art of one method of optical gas measurement using a tuneable diode laser 1000 emitting laser light 1100 being collimated by a lens 3010 and sent through a window 3020 that isolates the internal parts of the gas monitor from the ambient atmosphere and the process gas, target gas 4000.
  • the electronic system 5000 comprising means for control of laser modulation and temperature, means for amplification of detector signal, means for digitisation of analogue signals, means for calculation of a gas concentration and means for house keeping in the instrument.
  • the light beam passes through parts both inside the gas monitor (inside isolating windows 3020) and in the sealed off process measuring target gas 4000.
  • the concentration of the target gas 4000 is extremely low and this same gas also is present inside the monitor in significant amounts the absorption signal from the target gas could be obscured by absorption signal from the gas inside the monitor itself.
  • Figure 2 shows the basic principle of this invention where the light beam 1100 goes through a liquid 6100 inside the housing of the instrument, the liquid depleting possible interfering gases or influences the absorption spectrum significantly due to line broadening effects. This makes it possible to measure extremely' low concentrations of the target gas 4000.
  • Figure 3 shows a possible set-up for measurement in a light bulb 9010 where the ambient atmosphere also is depleted by the liquid 6100.
  • Figure 4 shows a possible set-up for measurement of a target gas (pollutant) 4000 in a medical vial 9020 containing substance 9030 to be protected from pollutant.
  • Figure 5 shows a different set-up for measurement in a vial using flexible seals 9050 to connect the gas analyser to the vial. Means are available to vary the level of the fluid so that nothing is spilled when vials are changed.
  • Figure 6 shows a similar set-up as in figure 5, but for a light bulb.
  • Figure 7 shows modification of the transmitter side of the gas analyser where the laser 1000 has been placed outside the volume 6000 filled with liquid 6100.
  • the laser 1000 has been attached a fibre optical pigtail 3200 entering the liquid filled volume 6000 through a sealed feed-through 6040.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Analytical Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
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  • General Health & Medical Sciences (AREA)
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Abstract

Optical apparatus for the measurement of one or more target gases in sealed off processes or in containers where the optical path inside the apparatus has been filled with a liquid to change or remove the spectroscopic contribution of gases that could be present in the apparatus itself. The liquid either depleting the gas or changing the spectral properties of the gases normally present in the optical path of the apparatus, the gases normally present would make measurement of the target gas difficult or impossible. Method for the optical measurement of one or more target gases in sealed off processes or in containers where the optical path outside the target area or process is filled with a liquid to change or remove the spectrscopic contribution of the gases normally present outside the target area.

Description

Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers.
Background of the invention
In the process of measuring gases using spectroscopic techniques, it is normally difficult to measure low concentrations of gases that also are present in the atmosphere where the gas analyser is mounted or has been assembled. This is a problem typically in processes which are sealed off or isolated from the normal atmosphere, but where part of the optical path that light traverse is within the analyser housing. It is the objective of this invention to reduce the interference from gases that could be present inside the gas analyser ■ itself.
To be able to measure low concentrations of gases one will normally use an optical i.e., spectroscopic technique like laser spectroscopy based on tuneable diode lasers, TDL. A gas analyser or gas monitor based on TDL technology will normally, as shown in figure 1, contain:
• A tuneable laser light source, 1000 • Optics to shape the laser beam, 3010
• A window 3020 to isolate the analyser from the process or target gas, 4000
• A second window 3020 on the opposite side of the target gas or process • A detector lens system 3030 focusing the light onto
• A detector 2000. Other parts in a typical gas analyser, but not involved in the optical path is the electronic system 5000 containing: electronics- for temperature control of the laser, modulation of the laser, detector amplifiers, analogue to digital converters for digitising analogue signals like the detector signal and a micro processor with software (firmware) for controlling the instrument as well as calculating a gas concentration based on sampled signals.
As can be seen from figure 1 presence of a gas in the optical path inside the monitor could also contribute to the optical signal. That applies for the path between laser 1000 and lens 3010, path between lens 3010 and window 3020 (left) , path between window 3020 (right) and lens 3030 and finally path between lens 3030 and detector 2000.
A description of one optical gas monitoring technique based on laser spectroscopy is found in the academic paper published in Applied Physics B 67, pages 297-305, 1998. The title of this publication is "Gas monitoring in the process industry using diode laser spectroscopy. (Linnerud et.al.) This paper also gives a brief summary of optical measurement techniques and their spectroscopic foundation.
In processes sealed off from the normal atmosphere one often wants to measure low concentrations of gases normally present in the atmosphere. These gases will be considered pollutants in the process and could lead to lower yield in the production process, risk of explosion or other unwanted conditions in the process. Two examples of gases one want to measure in such processes are water vapour and oxygen. A few examples of such processes are semiconductor manufacturing, pure gas manufacturing, quality control of light bulbs and medical vials and detection of oxygen in highly explosive processes.
Water vapour and oxygen as well as other gases are present in the normal atmosphere and will typically be present in the housing of a gas analyser. In particular if one wants to measure extremely low concentrations of water vapour in a sealed off process, the absorption signal from the part of the path inside the analyser will typically be much stronger that the absorption from the part of the path inside the process. The signal contribution from the part of the path inside the analyser could change with time due to change in humidity, temperature, and pressure and make it almost impossible to get a reliable measurement of the gas in the process • •
The gas mix inside a gas analyser could be a result of the air (atmosphere) where the analyser was assembled, where it is installed (leaks) and contributions could also come from emission of gas from the inside walls of the housing or other components inside the housing.
From figure 1 we can see that the laser beam 1100 will go through the gas in the analyser from the laser 1000 to the collimating lens 3010 and then to the window 3020 isolating the monitor from the process and the target gas 4000. The light beam then enters the other end of the analyser through another window 3020. The beam will go through more gas from the window to the detector lens 3030 and then to the detector 2000. If the absorption from the gas within the analyser itself is much higher than the absorption of the same gas in the process, then it could in practice be impossible to measure the absorption contribution from the process reliably. This 5. is in particular a problem if the gas concentration in the gas analyser housing changes with time.
Prior Art
One solution normally applied in the industry is to purge 0 the analyser housing with a gas containing none or minute amounts of the gas to be measured. For oxygen measurements nitrogen is normally used. For low level water vapour measurements higher quality nitrogen must be used, typically quality "6.0" which corresponds to a N2 5 purity of 99.9999% (six nines). A continuous purge of the instrument housing with either standard nitrogen or even worse with high purity nitrogen is expensive and therefore not wanted if it could be avoided.
0 Other common methods used to solve the problem include building sealed optical systems that could be emptied using a vacuum pump and then filled with an inert gas like high quality nitrogen. This is a time consuming and labour intensive production process and if the seals in 5 the optical system start to leak, the gas analyser will quickly be malfunctioning. One other snag with a sealed optical system is that the inner surfaces might emit gases like water vapour even after it has been emptied using the vacuum pump and filled with inert gas. 0
The abstracts of the 5th International Conference on Tuneable Diode Laser Spectroscopy to be held on July 11- 15, 2005, in Florence, Italy was published on the following address on the internet in April 2005: http : //www. ino . it/~pwwerle/Download/2005_Abstracts .pdf In one of the abstracts on pages 22-23 namely "State-of- the-art of Diode-Laser based Gas Analysis in Process Industries", by Michael W. Markus of Siemens AG Automation & Drives, Germany, one other method of measuring low concentrations of water vapour is described. This method uses two measurement channels, one for the process gas and the purged parts of the instrument and the second for the purge gas only. Using this set-up they measure the water vapour content in the purge gas and compensate for the same water vapour content in the purged parts of the instrument making it possible to measure low concentrations of water vapour in the process of interest using low cost purging techniques .
US patent 5,804,702 (Hovde et . al . /Southwest Sciences Inc.) describes a process for reducing interfering signals in optical measurements of water vapour. In this patent, normal water vapour (H20) inside the analyser is replaced with heavy water vapour (D20 or DHO) . The heavy water molecules have other absorption lines than normal water vapour that makes it possible to measure low concentrations of normal water vapour in a sealed off system without interference from water vapour inside the analyser itself. After the normal water molecules have been replaced by heavy water, the optical system is sealed. Heavy water isotopes are normally not available for normal instrument manufacturers due to restrictions on its use caused by its potential applications in the nuclear industry. Description of the invention
This invention uses a liquid to deplete the unwanted gases from the optical parts of the gas analyser so that the light beam from the light source goes through the liquid on its way from the light source to the window isolating the analyser from the process. Similarly the liquid will replace air or gas between optical components on the receiver side in front of the detector. Liquids will typically have other refractive indexes than air or other gases and therefore the overall optical design will be modified to compensate for this.
Displacing gases in the monitor housing optical path will work due to two different effects. The first and obvious effect is that the gas we want to remove is fully depleted by the liquid. The second effect is that, even though the gas we want to remove .still is present to .a certain degree in the liquid, the shape of this gas' absorption lines will be significantly changed due to heavy line broadening. Therefore absorption of the gas in the liquid will not influence the measurement of the same gas in the sealed process. From a spectroscopic point of view it would even work to use water as the liquid for measurement of low water vapour concentrations as long as the transmission through water is sufficient on the wavelength one will use. Oils with satisfactory optical and electrical i.e., isolating properties will the preferred choice.
The technique of this invention could be applied to all optical gas measurement methods even though the examples and figures in this patent application show measurements based on tuneable diode lasers . The selected liquid must have a sufficient transmission in the wavelength region where the light source emits light. Other requirement to liquid selection is that it must neither freeze nor boil within the temperature operating range of the gas monitor. This will also apply for the storage and transport temperature range. Other important criteria for liquid selection are that no bubbles or foam are being formed in the liquid under industrial work conditions like severe vibrations.
Different parts of the optical path inside the gas monitor might have different requirements to the properties of the liquid. The area around the light source, that in the preferred embodiment is a laser, might require a liquid with high thermal conductivity and good electrical isolating properties while other parts of the optical path requires a liquid with a certain refractive index. Therefore some embodiments of this invention will use different liquids in the different parts of the optical path inside the gas monitor. A setup described in this application where the optical path between the gas monitor and a container like a light bulb or vial has been filled with a liquid, this liquid possibly one of the liquids used inside the gas monitor or possibly yet another liquid. The latter could be selected based on issues like residues on the containers and health, safety and environment considerations .
Below are listed some possible embodiments of the part of the monitor containing the gas displacing liquid. However this invention is not limited to those embodiments. The sealed beam part of the monitor could have the following embodiments: • Completely filled with the liquid i.e., no gas present
• Completely filled with the liquid and the liquid having an overpressure
• Completely filled with the liquid and comprising means for compensating for variable internal pressure due to temperature expansion
• Filled with the liquid, but leaving some space for inert gas above the liquid
• Filled with the liquid, but leaving some space for inert gas above the liquid, this gas under pressure to avoid foam building and bubbles in the liquid
• Any embodiment as above including means for regulating the temperature of the liquid.
With regards to the light beam both inside and outside of the instruments several embodiments could be applied including a diverging beam, a collimated beam, a focused beam and a diffused beam based on a diffuser component using any available technique.
One other embodiment with regards to the optical path is shown in figure 7 where a fibre (3200) coupled laser 1000 has been used. Using this embodiment will de-couple temperature control of the laser from the liquid at the cost of possibly introducing a small air or gas gap between the laser and the optical fibre. In this gap isolator lenses that couple the laser light into the fibre normally are present. To compensate for this a fibre splitter and an extra detector could be introduced. Two fibres will then come from the laser and one of them is connected to the gas analyser shown in figure 7 while the other fibre is connected to a second detector. The signal from this second detector is then used to measure the possible interference and this measurement is then used to adjust the measurement in the gas analyser accordingly.
Yet another embodiment of the optical system is based on a dual path approach where both the light source and the detector are placed on the same side of the target gas and a retro reflector is placed on the opposite side. A dual gas analyser according to this invention would have a retro reflector possibly filled with liquid and mirror arrangement enabling zero check with a path within the instrument itself and a gain check with an gas cell inserted in the path. The mirror arrangement and gas cell are placed in the liquid filled part of the analyser.
A multi-pass cell embodiment of this invention will..have all parts of the multi-pass optical path outside of the gas cell filled with liquid. The gas cell could for instance be a Herriott cell, but is not limited to this design.
To optimise the optical path when measuring gas in sealed containers like bottles, vials, and light bulbs these items could be designed incorporating an optical window part of the housing with optical properties altered to give a better optical performance of the combination of the analyser and the container.
Normally the laser in a TDL gas monitor is temperature regulated with an accuracy better than 10 mK (1 milli Kelvin equals 1/1000 0C) . In one embodiment of this invention the temperature control of the laser 1000 is done indirectly by temperature controlling the liquid 6100 in the sealed part 6000 while in another embodiment as in figure 7 the laser 1000 is placed outside the sealed part 6000 and temperature regulated as in prior art.
With regards to measurement techniques this invention could have several embodiments . The preferred embodiment is based on tuneable diode lasers, but other embodiments are also possible. Revolving optical filters selecting two or more spectral ranges, possibly one in the wavelength absorption range of the gas and one outside is one commonly used technique. FTIR techniques could also be applied as well as techniques based on other optical filter techniques like the one described in US patent 5,606,419 (Norsk Hydro) .
Description of the figures - .
Figure 1 shows prior art of one method of optical gas measurement using a tuneable diode laser 1000 emitting laser light 1100 being collimated by a lens 3010 and sent through a window 3020 that isolates the internal parts of the gas monitor from the ambient atmosphere and the process gas, target gas 4000. Light passing through target gas 4000 and being picked up by receiver part of gas monitor through isolating window 3020, light beam focused onto detector 2000 by lens 3030. This being controlled by the electronic system 5000 comprising means for control of laser modulation and temperature, means for amplification of detector signal, means for digitisation of analogue signals, means for calculation of a gas concentration and means for house keeping in the instrument. As can be seen from the figure the light beam passes through parts both inside the gas monitor (inside isolating windows 3020) and in the sealed off process measuring target gas 4000.
If the concentration of the target gas 4000 is extremely low and this same gas also is present inside the monitor in significant amounts the absorption signal from the target gas could be obscured by absorption signal from the gas inside the monitor itself.
Figure 2 shows the basic principle of this invention where the light beam 1100 goes through a liquid 6100 inside the housing of the instrument, the liquid depleting possible interfering gases or influences the absorption spectrum significantly due to line broadening effects. This makes it possible to measure extremely' low concentrations of the target gas 4000.
The liquid contained in sealed parts 6000 and 6010.
Figure 3 shows a possible set-up for measurement in a light bulb 9010 where the ambient atmosphere also is depleted by the liquid 6100.
Figure 4 shows a possible set-up for measurement of a target gas (pollutant) 4000 in a medical vial 9020 containing substance 9030 to be protected from pollutant.
Figure 5 shows a different set-up for measurement in a vial using flexible seals 9050 to connect the gas analyser to the vial. Means are available to vary the level of the fluid so that nothing is spilled when vials are changed.
Figure 6 shows a similar set-up as in figure 5, but for a light bulb.
Figure 7 shows modification of the transmitter side of the gas analyser where the laser 1000 has been placed outside the volume 6000 filled with liquid 6100. The laser 1000 has been attached a fibre optical pigtail 3200 entering the liquid filled volume 6000 through a sealed feed-through 6040.
The table below lists the numbers used in the figures:
Number Description . .:
1000 -. Light source, laser in the preferred embodiment
1100 Light beam, laser beam 2000 Detector 3010 Collimating lens 3020 Isolating optical window 3030 Detector lens 3200 Optical fibre 4000 Target gas 5000 Electronic system 6000 Sealed part of optical beam, transmitter part 6010 Sealed part of optical beam, receiver part
6020 Electrical feed through
6030 Electrical feed through 6040 Fibre optical feed through 6100 Liquid
9010 Light bulb 9020 Bottle or vial
9030 Substance to be protected against normal atmosphere 9050 Seals

Claims

Claims
1. Gas analyser based on optical techniques comprising a light source, optical means to direct light from light source through a target gas onto a detector and means to calculate one or more gas concentrations based on the detector signal characterised by that the internal light paths in the gas analyser have been filled with a liquid.
2. Gas monitor as in claim 1 where the liquid fully depletes gases that could interfere with the measurement of the target gas .
3. Gas monitor as in claim 1 where the liquid leads to significant line broadening effects of the interfering gas contained in the liquid so that measurement of the target gas is unaffected by the interfering gas contained in the liquid inside the monitor housing. ■
4. Gas monitor as in claim 1, 2 or 3 characterised by means to fill volume between gas analyser windows and sealed container with a similar liquid as used inside the gas monitor.
5. Gas monitor as in any of claim 1, 2, 3 or 4 where the light source is a tuneable laser diode
6. Gas monitor as in any of claim 1, 2, 3 or 4 where the light source is a broadband light source and the means to direct light comprise optical filters selecting the spectral range of interest.
7. Gas monitor as in any of claim 1, 2, 3, 4, 5 or 6 characterised by that different liquids have been used for different parts of the optical path.
8. Optical method of measurement of gas using a light source, optical means to direct light from light source through a target gas onto a detector and means to calculate one or more gas concentrations based on detector signal characterised by that the internal light paths in the gas analyser are filled with a liquid.
9. Optical method as in claim 8 characterised by that the parts of the optical paths between the gas monitor and a container with the target gas is filled with a similar liquid.
PCT/NO2006/000200 2005-05-31 2006-05-29 Apparatus and method for reducing interfering signals from atmospheric gases in optical measurement of gas in sealed processes or containers WO2006130016A1 (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
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ITBO20100198A1 (en) * 2010-03-31 2011-10-01 Bonfiglioli Engineering S R L METHOD OF ANALYSIS OF A GASEOUS COMPONENT PRESENT IN A HERMETICALLY SEALED CONTAINER.
ITPD20100203A1 (en) * 2010-06-28 2011-12-29 L Pro S R L EQUIPMENT FOR MEASURING A GAS CONCENTRATION IN A CLOSED CONTAINER
CN102519905A (en) * 2011-12-14 2012-06-27 中国农业大学 Method for detecting automobile exhaust gas
CN104874238A (en) * 2015-06-02 2015-09-02 成都虹华环保科技股份有限公司 Discharging passage for organic waste gas treating system

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