WO2011126476A1

WO2011126476A1 - Toxic gas detector

Info

Publication number: WO2011126476A1
Application number: PCT/US2010/030037
Authority: WO
Inventors: Thierry Carriere; Marcin Piech; Meredith B. Colket; Max D. Allsworth; Brian Powell; Gary Follett; John King
Original assignee: Utc Fire & Security Corporation
Priority date: 2010-04-06
Filing date: 2010-04-06
Publication date: 2011-10-13

Abstract

An exemplary gas detector includes an elongated chamber configured to allow a fluid to enter the chamber. A lamp is positioned to project radiation into the chamber. At least one mirror is near an end of the chamber. The mirror reflects radiation from the lamp toward a second, opposite end of the chamber. At least two detectors are positioned to receive at least some of the radiation reflected from the mirror. The radiation moves through the chamber at least once in each of the opposite directions before the detectors receive it. An indication from the detectors provides information regarding a gas of interest in the fluid within the chamber.

Description

TOXIC GAS DETECTOR

BACKGROUND

[oooi] There are a variety of situations in which the level of toxic gases needs to be monitored. For example, it is necessary to be able to determine a level of hydrogen sulfide, which can be found in petrochemical sites. Current regulations require detecting low concentrations of such a gas to limit human exposure. For example, it is required to determine a concentration on the order of ten parts per million quickly and reliably.

[0002] Proposed sensors for this purpose include electrochemical cells and metal oxide sensors. Each of these have a limited life because they degrade in harsh environments. Moreover, such devices are not fail safe and an operator needs to take additional steps using a sensor tester to determine whether the sensor is functioning properly.

[0003] Other sensors are considered optical detectors. These provide the advantage of a longer lifetime and they are generally fail-safe. One example optical sensor is shown in United States Patent No. 5,936,250. There are several limitations with such an arrangement. A highly polished tube as required in that patent tends to be expensive. Another drawback associated with the type of tube recommended in that patent is that there are openings in the tube to allow gas penetration. Those openings can result in a loss of light, which corresponds to a decrease in sensitivity. Another relatively expensive component of that arrangement is a xenon flash lamp. Additionally, the driver that is required for operating a xenon flash lamp introduces electromagnetic interference, which is undesirable. A relatively complex control approach is required for timing operation of the lamp and data acquisition with the arrangements shown in that patent.

SUMMARY

[0004] An exemplary gas detector includes an elongated chamber configured to allow a fluid to enter the chamber. A lamp is positioned to project radiation into the chamber. At least one mirror is near an end of the chamber. The mirror reflects radiation from the lamp toward a second, opposite end of the chamber. At least two detectors are positioned to receive at least some of the radiation reflected from the mirror. The radiation moves through the chamber at least once in each of the opposite directions before the detectors receive it. An indication from the detectors provides information regarding a gas of interest in the fluid within the chamber.

[0005] The various features and advantages of disclosed examples will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 schematically shows a gas detector designed according to an embodiment of this invention.

[0007] Figures 2a and 2b are cross-sectional illustrations taken along the lines 2-2 in Figure 1.

[0008] Figure 3a schematically illustrates an example gas detector arrangement.

[000 ] Figure 3b schematically illustrates another example gas detector arrangement.

[oooio] Figure 4 schematically illustrates another example gas detector configuration.

[oooii] Figure 5 schematically illustrates another gas detector configuration.

[00012] Figure 6 schematically illustrates another example gas detector configuration.

[00013] Figure 7 schematically illustrates another example gas detector configuration.

[00014] Figure 8 schematically illustrates another example gas detector configuration.

[00015] Figure 9 schematically illustrates another example gas detector configuration.

DETAILED DESCRIPTION

[00016] Figure 1 schematically shows a gas detector 20. An elongated chamber

22 is associated with electronic components 24 to detect at least one selected gas from within a fluid 26 such as air that is allowed to enter the chamber 22. As can be appreciated from Figure 2a, one example chamber 22 includes solid sidewalls 30, 32 and 34. A gas-permeable membrane 36 extends across at least a portion of one of the sides of the chamber 22 to allow the fluid 26 to enter the chamber. In some examples, a membrane is provided on at least one other side of the chamber so that the fluid 26 is allowed to pass through the chamber from one side to another. Figure 2b shows another example chamber configuration. This example has two curvilinear sidewalls 30 and 32 and gas-permeable members 36.

[00017] Figure 3 a schematically illustrates selected portions of an example gas detector 20. This example includes a lamp 40 that is a source of radiation. In one example, the radiation from the lamp 40 is in the ultraviolet range of the spectrum and the lamp 40 does not generate any electromagnetic interference (EMI). In one example, the lamp 40 comprises a glow discharge lamp.

[00018] One feature of using a UV source, such as a glow discharge lamp, is that there is no EMI associated with such a lamp. This allows for placing other electronic components in close proximity to the lamp and relaxes any need to shield electronics from the source of radiation used for the gas detection. Another feature of using a UV glow discharge lamp is that it has a relatively small footprint and is lower in cost compared to other radiation sources, for example. Another feature of using a UV glow discharge lamp is that there is no requirement for high speed integration, fast data acquisition or triggering as is required with some other types of lamps.

[0001 ] As schematically shown in Figure 3 a, radiation 42 from the lamp 40 travels in a direction from a first end 43 of the chamber 22 near which the lamp 40 is located toward a mirror 44 supported near an opposite end 45 of the chamber 22. Radiation 46 and 47 is reflected from the mirror 44 back toward the first end 43 of the chamber 22.

[00020] A first detector 50, which has an associated optical filter 51, is positioned to detect at least some of the reflected radiation 46. Another detector 52, which has an associated filter 53, also detects at least some of the reflected radiation 47. In this example, one of the filters 51 or 53 is selected to have a wavelength corresponding to a wavelength of the radiation at which the gas of interest would absorb the radiation. In one example, hydrogen sulfide is the gas of interest and one of the filters is selected to allow the corresponding detector to detect radiation on the order of 200 nm and the other filter is selected to allow the corresponding detector to detect radiation on the order of 254 nm. Given this description, those skilled in the art will be able to select appropriate filters and detectors to meet their particular needs. [00021] In the example of Figure 3 a, the mirror 44 directs the reflected radiation 46 and 47 toward each of the detectors 50 and 52. A collimating lens 58 is provided in this example between the lamp 40 and the mirror 44 for guiding the radiation 42 on the mirror 44. Optional focusing lenses 56 and 57 (shown in phantom) are positioned between the mirror 44 and the detectors 50 and 52 for focusing the reflected radiation 46 and 47 for detection by the detectors 50 and 52. Alternatively, mirror 44 can serve to focus the reflected radiation 46 and 47 for detection by the detectors 50 and 52.

[00022] A controller 60 receives an indication from each of the detectors 50 and 52 and uses known techniques for making a determination regarding a level of at least one gas of interest within the fluid that enters the chamber 26. In one example, the detector is intended to detect hydrogen sulfide gas. The controller 60 in such an example provides an output indicating a number of parts per million of hydrogen sulfide within the fluid (i.e., air) inside the chamber 26.

[00023] In one example, the chamber 22 has a 25 centimeter length and the detector 20 has a sensitivity on the order of ten parts per million. In such an example, the distance traveled by the radiation within the chamber is on the order of 50 centimeters between the lamp 40 and the detectors 50 and 52. Having a two-pass path within the chamber 22 allows for a more sensitive detector with a relatively shorter chamber 22. In other words, the mirror 44 increases the length of the path within the fluid through which the radiation passes before arriving at the detectors 50 and 52, which increases the sensitivity of the detector 20. Another examples shown in Figures 8 and 9 are able to detect hydrogen sulfide gas levels on the order of two parts per million using a chamber 22 with a length of approximately 25 centimeters. Having more than a two-pass path within the chamber 22 allows for an even more sensitive detector with a further shortened chamber 22. In other words, the mirrors 44 and 47 increase the length of the path within the fluid through which the radiation passes before arriving at the detectors 50 and 52, which increases the sensitivity of the detectors 20.

[00024] Another feature of the example of Figure 3a is a humidity sensor 64 that provides an indication of a humidity or moisture level within the fluid inside the chamber 22. The controller 60 uses information regarding the humidity level and determines whether the humidity level would cause interference with the ability to detect the gas of interest. The controller 60 is programmed to recognize appropriate threshold humidity levels and to correct for such humidity levels by adjusting how indications from the detectors 50 and 52 are processed for purposes of determining a level of the selected gas within the chamber 22. Given this description, those skilled in the art will be able to determine appropriate humidity level thresholds and corresponding corrections to meet the needs of their particular situation.

[00025] One feature of the humidity detector 64 is that it allows for minimizing any affect of signal distortion based on humidity. It also allows for the sampling wavelength to be relatively lower and within a range where vapor or water present within the fluid 26 could potentially cause interference. The programmed controller 60 can correct for any such interference and this allows for effectively increasing the sensitivity of the detector 20 by allowing it to make determinations at a wider range of wavelengths. In one example, the sample wavelength is below 200 nm. One example includes using a range between 180 nm and 200 nm for the sample wavelength.

[0002 ] Another feature of the example of Figure 3 is a temperature sensor 65 that provides an indication of a temperature within the fluid inside the chamber 22. The controller 60 uses information regarding the chamber temperature and determines whether the temperature level would cause interference with the ability to detect the gas of interest. The controller 60 is programmed to recognize appropriate threshold temperature levels and to correct for such temperature levels by adjusting how indications from the detectors 50 and 52 are processed for purposes of determining a level of the selected gas within the chamber 22. Given this description, those skilled in the art will be able to determine appropriate temperature level thresholds and corresponding corrections to meet the needs of their particular situation.

[00027] In the example of Figure 3b, a mirror 44 directs the reflected radiation 46 toward each of the detectors 50 and 52. A collimating lens 58 is provided in this example between the lamp 40 and the mirror 44 for guiding the radiation 42 on the mirror 44. Reflected radiation 46 is divided into two beams by a beam splitter 54. One beam is directed towards detector 50 and the second beam is directed toward detector 52. An optional focusing lens 56 is positioned between the mirror 44 and the detectors 50 and 52 for focusing the reflected radiation 46 for detection by the detectors 50 and 52. Alternatively, mirror 44 can serve to focus the reflected radiation 46 for detection by the detectors 50 and 52. The other features of the example shown in Figure 3b are the same as those included in the example of Figure 3a.

[00028] Another example arrangement is shown in Figure 4. Much of the operation of the example of Figure 4 is like that described for Figures 3a and 3b. This example includes additional detector 70 that is situated to detect radiation from the lamp 40 in a manner that provides an indication whether there is drift in the performance of the lamp 40. In this example, a beam splitter 72 is positioned to direct at least some of the radiation from the lamp 40 onto the drift detector 70 before that radiation reaches the mirror 44. Alternatively, lens 58 may be used to reflect portion of the light directly onto detector 70 without the use of a beam splitter 72. In this example, the detector 70 monitors the radiation 42 before it enters the chamber 22.

[00029] Utilizing a UV glow discharge lamp as the source of radiation allows for positioning the detector 70 close to the lamp along with the controller 60 and the detectors 50 and 52. There is no concern with EMI issues when a UV glow discharge lamp is utilized. This allows for locating more of the electronic control components within a single housing near one end of the chamber 22.

[00030] An optical filter 71 associated with the detector 70 is tuned to the appropriate wavelength to monitor the output from the lamp 40. With the detector 70, it is possible for the controller 60 to make appropriate corrections based upon signal drift resulting from changes in the output or operation of the lamp 40.

[00031] Another example arrangement is shown in Figure 5. Much of the operation of the example of Figure 5 is like that described for Figure 4. This example includes an additional detector 73 that is situated to detect radiation from the lamp 40 in a manner that provides an indication whether there is drift in the performance of the lamp 40 at another wavelength. In this example, a beam splitter 72 is positioned to direct at least some of the radiation from the lamp 40 onto the detectors 70 and 73 before that radiation reaches the mirror 44. Another beam splitter 75 is positioned to direct the radiation from beam splitter 72 onto the detectors 70 and 73. Alternatively, lens 58 may be used to reflect a portion of the radiation 42 directly onto detectors 70 and 72 without the use of beam splitters 72 and 75.

[00032] Optical filters 71 and 74 are tuned to the appropriate wavelength to monitor the output from the lamp 40. Optical filters 71 and 74 may for example, pass the same wavelength radiation as filters 51 and 53. With the detectors 70 and 73, it is possible for the controller 60 to make appropriate corrections based upon signal drift resulting from changes in the output or operation of the lamp 40.

[00033] Figure 6 schematically shows another example arrangement in which the detectors 70 and 73 are positioned to detect some of the reflected radiation 46. This example configuration can be expanded to include an arbitrary number of drift detectors with associated optical filters. The advantage of such an arrangement is increased selectivity for a target gas especially when the optical filters 51, 71, and 74 are appropriately selected. Given this description and knowledge of a gas of interest, those skilled in the art will be able to choose appropriate filters to meet their particular needs..

[000 4] One alternative configuration is shown schematically in Figure 7. Radiation 42 from the lamp 40 travels in a direction from a first end 43 of the chamber 22 near which the lamp 40 is located toward the opposite end 45 of the chamber 22 without reflection.

[00035] In the example of Figure 7, a collimating lens 58 is positioned between the lamp 40 and the first end 43 of the chamber 22 for guiding the radiation 42 onto the beam splitter 54. An optional focusing lens 56 is positioned between the opposite end 45 of the chamber 22 and the beam splitter 54 for focusing the radiation for detection by the detectors 50 and 52.

[00036] While Figure 7 has fewer passage of the radiation through the chamber

22, Figure 8 shows an example that increases it. In this example, radiation 42 from the lamp 40 passes through a hole in mirror 47 and travels in a direction from a first end 43 of the chamber 22 near which the lamp 40 is located toward a mirror 44 supported near an opposite end 45 of the chamber 22. The radiation is reflected from the mirror 44 toward the mirror 47. This reflected radiation is subsequently reflected by the mirror 47 supported near the first end 43 of the chamber back toward the mirror 44. The reflection process from mirror 47 towards the mirror 44 and back to the mirror 47 occurs multiple times. Upon a last reflection from the mirror 47, the radiation is directed through a hole in the mirror 44. This multi-pass arrangement affords significant decrease in detector footprint and increase in sensitivity.

[00037] In the example of Figure 8, a collimating lens 58 is positioned between the lamp 40 and the mirror 47 for guiding the radiation 42 onto the mirror 44. An optional focusing lens 56 is positioned between the mirror 44 supported on the opposite end 45 of the chamber 22 and the beam splitter 54 for focusing the radiation for detection by the detectors 50 and 52.

[00038] Alternatively, as shown schematically in Figure 9, radiation 42 from the lamp 40 passes through a hole in mirror 47 and travels in a direction from a first end 43 of the chamber 22 near which the lamp 40 is located toward a mirror 44 supported near an opposite end 45 of the chamber 22. The radiation is reflected by the mirror 44 and is subsequently reflected by the mirror 47 supported near the first end 43 of the chamber back toward the mirror 44. The reflection process from the mirror 47 towards the mirror 44 and back to the mirror 47 may occur multiple times. Upon a last reflection from the mirror 44, the radiation is directed through a hole in the mirror 47. This example is another multi-pass arrangement that affords significant decrease in detector footprint and increase in sensitivity.

[0003 ] In the example of Figure 9, a collimating lens 58 is positioned between the lamp 40 and the mirror 47 for guiding the radiation 42 onto the mirror 44. An optional focusing lens 56 is positioned between the mirror 47 and the beam splitter 54 for focusing the radiation for detection by the detectors 50 and 52.

[00040] Although the illustrated examples schematically show detectors, filters and beam splitters as individual components, those skilled in the art will realize that it is possible to utilize a variety of assembly configurations including multiple filters and detectors for purposes of detecting enough information to make a determination regarding the presence of a selected gas within a fluid 26 in the chamber 22 in a quick and reliable manner.

[00041] There are various features of the disclosed examples that render them superior to previous detector designs. One such feature is the use of a collimating lens for focusing the light to travel in a desired direction instead of using a light- guiding, highly polished tube. The collimating lens approach does not suffer from a loss of light or sensitivity that otherwise results from the required openings in the polished tube style of detector. Another feature is the use of at least one mirror for directing the light through the detection chamber along a longer path. This increases detector response. Additionally, the expense associated with a polished tube is avoided with the disclosed examples.

[00042] Another feature of the disclosed example is the use of a lower cost source of radiation that has a smaller footprint to allow a more compact sensor design. A glow discharge lamp, which can be referred to as a crater lamp, instead of a xenon flash lamp also reduces the complexity of the sensor design because there is no need for a high speed integrator and there is no concern with electromagnetic interference from a xenon flash lamp driver. Additionally, the style of lamp or source of radiation used in the disclosed examples provide more data that is useful for signal processing. [00043] Another feature of some of the disclosed examples is a humidity sensor that corrects any variation in the signal that would occur from water vapor interference, for example.

[000 4] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the scope of legal protection given to this invention, which can only be determined by studying the following claims.

Claims

We claim: 1. A gas detector, comprising:

an elongated chamber configured to allow a fluid to enter the chamber;

a lamp positioned to project radiation into the chamber;

at least one mirror near an end of the chamber, the mirror reflecting radiation from the lamp towards an opposite end of the chamber; and

at least two detectors positioned to receive at least some of the radiation reflected from the mirror, the received radiation having moved through the chamber at least once in each of two opposite directions, an indication from the at least two detectors providing information regarding a gas of interest in the fluid within the chamber.

2. The detector of claim 1, comprising

a controller that determines an amount of a toxic gas in the fluid in the chamber based on an indication from each of the at least two detectors, the toxic gas having absorption in the ultraviolet light range and comprising at least one of hydrogen sulfide, ammonia, sulfur dioxide, nitrogen dioxide, nitrogen oxide, toluene, benzene or xylene.

3. The detector of claim 1, comprising

a drift detector positioned to detect radiation from the lamp before it enters the chamber.

4. The detector of claim 3, comprising

a controller that determines any changes in output of the lamp based on an indication from the drift detector, the controller responsively adjusting an interpretation of indications from the at least two detectors.

5. The detector of claim 1, comprising

at least one collimating lens between the lamp and the mirror for guiding radiation from the lamp onto the mirror.

6. The detector of claim I, comprising

a humidity sensor that provides a humidity level indication ; and

a controller that automatically corrects an output regarding the gas of interest based on an indication from the at least two detectors responsive to the humidity level indication being in a range that corresponds to interference with accuracy of the indication from the at least two detectors.

7. The detector of claim 6, wherein a wavelength of radiation detected by the at least two detectors is in a range from 180nm to 300nm.

8. The detector of claim 1 , wherein the chamber is configured to allow air to pass through the chamber and to allow diffusion of toxic gas.

9. The detector of claim 8, wherein the chamber comprises at least one solid wall and a gas-permeable membrane that collectively define an interior of the chamber.

10. The detector of claim 9, comprising a plurality of planar walls.

11. The detector of claim 9, wherein the solid wall is generally curvilinear.

12. The detector of claim 1, wherein the lamp comprises a glow discharge lamp.

13. The detector of claim 1, wherein the radiation comprises ultraviolet light.

14. The detector of claim 1, wherein the lamp is near the opposite end of the chamber.

15. The detector of claim 14, wherein the detectors are near the opposite end of the chamber.

16. The detector of claim 1, comprising

a second mirror near the opposite end of the chamber, the radiation reflected from the mirror reflecting off the second mirror toward the mirror.

17. The detector of claim 16, wherein the radiation reflects off each of the mirror and the second mirror a plurality of times before being received by the detectors.

18. The detector of claim 1, wherein the lamp and the detectors are all positioned near one of the ends of the chamber.

19. A gas detector, comprising:

an elongated chamber configured to allow a fluid to enter the chamber;

a lamp positioned to project radiation into the chamber;

a collimating lens positioned to direct the radiation projected from the lamp in a desired direction through the chamber; and

at least two detectors positioned to receive at least some of the radiation from the chamber, an indication from the at least two detectors providing information regarding a gas of interest in the fluid within the chamber.

20. The detector of claim 19, comprising

a humidity sensor that provides a humidity level indication; and