CA2067049A1 - Gas sensor - Google Patents
Gas sensorInfo
- Publication number
- CA2067049A1 CA2067049A1 CA 2067049 CA2067049A CA2067049A1 CA 2067049 A1 CA2067049 A1 CA 2067049A1 CA 2067049 CA2067049 CA 2067049 CA 2067049 A CA2067049 A CA 2067049A CA 2067049 A1 CA2067049 A1 CA 2067049A1
- Authority
- CA
- Canada
- Prior art keywords
- gas
- gas sensor
- filter
- interferant
- filter material
- 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.)
- Abandoned
Links
- 239000000463 material Substances 0.000 claims abstract description 13
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000011347 resin Substances 0.000 claims abstract description 6
- 229920005989 resin Polymers 0.000 claims abstract description 6
- 230000001427 coherent effect Effects 0.000 claims abstract description 4
- 239000012528 membrane Substances 0.000 claims description 12
- 230000003197 catalytic effect Effects 0.000 claims description 8
- 239000012491 analyte Substances 0.000 claims description 5
- 229910052709 silver Inorganic materials 0.000 claims description 4
- 239000004332 silver Substances 0.000 claims description 4
- 239000007789 gas Substances 0.000 description 35
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- RWSOTUBLDIXVET-UHFFFAOYSA-N Dihydrogen sulfide Chemical compound S RWSOTUBLDIXVET-UHFFFAOYSA-N 0.000 description 3
- 239000004809 Teflon Substances 0.000 description 3
- 229920006362 Teflon® Polymers 0.000 description 3
- 239000006185 dispersion Substances 0.000 description 3
- 229910000037 hydrogen sulfide Inorganic materials 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 229920000544 Gore-Tex Polymers 0.000 description 2
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 2
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 2
- 239000008187 granular material Substances 0.000 description 2
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000008188 pellet Substances 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000004065 semiconductor Substances 0.000 description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 238000007084 catalytic combustion reaction Methods 0.000 description 1
- 230000005465 channeling Effects 0.000 description 1
- 238000002485 combustion reaction Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 229920000295 expanded polytetrafluoroethylene Polymers 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- JRTYPQGPARWINR-UHFFFAOYSA-N palladium platinum Chemical compound [Pd].[Pt] JRTYPQGPARWINR-UHFFFAOYSA-N 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 1
- 239000002574 poison Substances 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 229920000515 polycarbonate Polymers 0.000 description 1
- 239000004417 polycarbonate Substances 0.000 description 1
- 239000012286 potassium permanganate Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
Landscapes
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
- Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A gas sensor incorporates between the source of the gas to be analyzed and the detecting element a filter to remove interferants from the gas reaching the detecting element. The filter comprises a porous coherent sinter of fluorocarbon resin and a finely divided filter material that removes the interferant.
A gas sensor incorporates between the source of the gas to be analyzed and the detecting element a filter to remove interferants from the gas reaching the detecting element. The filter comprises a porous coherent sinter of fluorocarbon resin and a finely divided filter material that removes the interferant.
Description
2~67Q~9 GA E; SENSOR
FIELD OF THE INVENTION
This invention relates to gas sensors and more particularly, to gas sensors in which interferants are removed from the gas to be sensed.
BACKGROUND OF THE INVENTION
Active gas sensing elements, such as electrochemical cells, gas responsive semiconductors, or catalytic combustion elements, are conventionally contained in a housing having a gas pervious wall that permits the gas being analyzed to reach the sensing elements. In addition to the analyte, the gas being analyzed may contain interferants that the sensing elements respond to by giving a false indication of analyte or that poison the sensing element so it does not properly respond to the analyte. Conventionally interferants have been removed by passing the gas through a bed of granular material that absorbs or reacts with the interferant, such as, for example, described in U.S. Pat. 5,633,704. An inherent 4 l~ 33/~
~ 6 problem with such filter beds is that a filter bed sufficiently dense to efficiently remove interferants also slows gas transfer through the filter to substantially reduce the response of the sensor. Granular filter beds are also . .
' ' ' , , ' , ' ' ~ ~ ~' ' , , :
.' ' ' ~. . ,~ . ' ' ' ' " ~ , . ', ' ' ' ' `` 2067~9 subject to channeling and may shed granules that contaminate the sensor.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a gas sensor having a filter for removing interferant gas from the gas being analyzed that exhibits both high removal efficiency and high porosity. In accordance with this invention, a gas sensor responsive to an analyte gas and an interferant gas comprises a source of gas to be analyzed, a sensing element and a filter means interposed between the source and the sensing element, the filter means comprises a porous coherent sinter of a fluorocarbon resin and finely divided filter material that removes the interferant gas. On the preferred filter, the sinter is supported and bonded to a porous fluorocarbon membrane.
, ~
- . : .: , .- ., , -` 20~7~9 BRIEF DESCRIPTION OF TEIE DRAWINGS
FIG. 1 is partly a section view of and partly a schematic of a gas sensor in accordance with this invention for measuring combustible gases.
FIG. 2 is an enlarged section of the interferant filter means of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a catalytic combustible gas detector incorporating the new interferant filter in an otherwise lQ conventional configuration. The gas detector comprises a detecting element 2 and a compensating element 4 of the kind described in U.S. Pat. 3,092,799. The detecting element is a helical coil of platinum wire embedded in a pellet of aluminum oxide and an oxidation catalyst, suitably palladium or a palladium-platinum mixture. The compensating element is a helical coil of wire embedded in a pellet that has no catalytic activity.
The detecting and compensating elements are electrically connected by leads 6, 8 and common lead 10 in a bridge circuit comprising fixed resistors 12 and 14 and 21D~70~9 voltmeter 16. The meter zero can be adjusted by potentiometer 18. Power source 20 provides power for heating the detecting and compensating elements as well as for the bridge. When the heated detecting element is exposed to a combustible gas, combustion increases the temperature of the element with a consequent change of resistance. The gas does not burn on the non-catalytic compensating element so the resistance of the compensating element does not change. The resultant imbalance of the bridge, indicated by meter 10, is a measure of the combustible gas concentration. If an interfering gas reaches the detecting element, an erroneous indication will result.
Metal housing 22 contains an inner polycarbonate housing 24 with chambers 26 and 28 having Teflon cylindrical liners 30 and 32. The interferant filter 34 is positioned between the inner housing and sintered metal porous disc 36 to cover the chamber openings. The edge 38 o~ the housing 22 is formed over the edge of the disc making a tight assembly.
Referring to FIG. 2, the interferant filter includes a gas diffusion membrane 40 having bonded thereto a filter 42 that reacts with or absorbs the interferant gas. The membrane ; 40 is preferably a Zitex or Goretex porous fluorocarbon membrane. Other membrane materials may be used that have - similar characteristics, includlng having a large number of , . .
` - 20~0~
pores, between about 40-70% porous, of small pore size (0.2 micron), and being thin enough to avoid significant increase in the response time of the sensor to changes in the concentration of the gas being measured. The filter 42 is made up of a mixture of a finely divided powder filter material mixed with a fluorocarbon resin dispersion (e.g.
Teflon dispersion). The mixture is painted onto the membrane, dried-and sintered to form a good bond.
Catalytic elements of the type described for measuring combustible gases are poisoned by hydrogen sulfide.
Exemplary of the invention is a sensor incorporating a filter comprising silver that removes hydroyen sulfide thus prolonging the life of the sensor. A Goretex expanded polytetrafluoroethylene membrane having a O.lO" thickness, 0.7 g/cc density and 68% porosity is held between identical toroidal flanges defining a central filter area of about 0.95 inches in diameter. A mixture of 500 mg of silver powder of 4 to 7 micron particle size with 250 microliters of Teflon 30, an aqueous dispersion of TFE fluorocarbon resin, is spread over the central area of the membrane. The assembly is heated in an oven from about lOOoC to 2900C over a 45-minute period to form a coherent, porous sinter of filter material and fluorocarbon resin and securely bond the sinter to the membrane. The cooled membrane is removed from the fixture and ., . .. , . . : , , .
2~7~
trimmed to remove the uncoated portion. The filters provide intimate and effective contact of the filter material with gas passing through the filter with substantially no flow restriction that changes the response time of the element.
For example, sensors as shown in FIG.
incorporating the above described filter were exposed to (1) air containing 50~ LEL methane to establish a sensor response base, (2) air containing 23 ppm hydrogen sulfide for 14 hours and then (3) air containing 50~ LEL methane to determine any change in response. The loss of response was less than 6%.
In contrast, sensors without the interference filters, under the same conditions, showed a loss of response from 40-60%.
The interferant filter does not restrict flow to interfere with the normal operation of the sensor; typically the output of the new sensor incorporating the interferant filter is 97-99% of the output of the sensor without the interferant filter.
It will be recognized by those skilled in the art that this invention can be used with sensors other than the exemplified catalytic combustible gas sensor, such as, for example, electrochemical gas detecting elements and semi-conductor gas det cting elements. The selection of filter material will depend on the interferant gas to be removed and may be an absorbent, such as activated carbon or silica ~el , :
, ~
~. . ' ` ' ~' ', : .
, 2~704~
or a material that chemically reacts with and removes the interferant. Illustrative reactants are manganese dioxide to remove sulfur dioxide or potassium permanganate to remove hydrogen sulfide when measuring carbon monoxide with an electrochemical cell.
- .: , .
"
- - ~ - ~.
FIELD OF THE INVENTION
This invention relates to gas sensors and more particularly, to gas sensors in which interferants are removed from the gas to be sensed.
BACKGROUND OF THE INVENTION
Active gas sensing elements, such as electrochemical cells, gas responsive semiconductors, or catalytic combustion elements, are conventionally contained in a housing having a gas pervious wall that permits the gas being analyzed to reach the sensing elements. In addition to the analyte, the gas being analyzed may contain interferants that the sensing elements respond to by giving a false indication of analyte or that poison the sensing element so it does not properly respond to the analyte. Conventionally interferants have been removed by passing the gas through a bed of granular material that absorbs or reacts with the interferant, such as, for example, described in U.S. Pat. 5,633,704. An inherent 4 l~ 33/~
~ 6 problem with such filter beds is that a filter bed sufficiently dense to efficiently remove interferants also slows gas transfer through the filter to substantially reduce the response of the sensor. Granular filter beds are also . .
' ' ' , , ' , ' ' ~ ~ ~' ' , , :
.' ' ' ~. . ,~ . ' ' ' ' " ~ , . ', ' ' ' ' `` 2067~9 subject to channeling and may shed granules that contaminate the sensor.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a gas sensor having a filter for removing interferant gas from the gas being analyzed that exhibits both high removal efficiency and high porosity. In accordance with this invention, a gas sensor responsive to an analyte gas and an interferant gas comprises a source of gas to be analyzed, a sensing element and a filter means interposed between the source and the sensing element, the filter means comprises a porous coherent sinter of a fluorocarbon resin and finely divided filter material that removes the interferant gas. On the preferred filter, the sinter is supported and bonded to a porous fluorocarbon membrane.
, ~
- . : .: , .- ., , -` 20~7~9 BRIEF DESCRIPTION OF TEIE DRAWINGS
FIG. 1 is partly a section view of and partly a schematic of a gas sensor in accordance with this invention for measuring combustible gases.
FIG. 2 is an enlarged section of the interferant filter means of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a catalytic combustible gas detector incorporating the new interferant filter in an otherwise lQ conventional configuration. The gas detector comprises a detecting element 2 and a compensating element 4 of the kind described in U.S. Pat. 3,092,799. The detecting element is a helical coil of platinum wire embedded in a pellet of aluminum oxide and an oxidation catalyst, suitably palladium or a palladium-platinum mixture. The compensating element is a helical coil of wire embedded in a pellet that has no catalytic activity.
The detecting and compensating elements are electrically connected by leads 6, 8 and common lead 10 in a bridge circuit comprising fixed resistors 12 and 14 and 21D~70~9 voltmeter 16. The meter zero can be adjusted by potentiometer 18. Power source 20 provides power for heating the detecting and compensating elements as well as for the bridge. When the heated detecting element is exposed to a combustible gas, combustion increases the temperature of the element with a consequent change of resistance. The gas does not burn on the non-catalytic compensating element so the resistance of the compensating element does not change. The resultant imbalance of the bridge, indicated by meter 10, is a measure of the combustible gas concentration. If an interfering gas reaches the detecting element, an erroneous indication will result.
Metal housing 22 contains an inner polycarbonate housing 24 with chambers 26 and 28 having Teflon cylindrical liners 30 and 32. The interferant filter 34 is positioned between the inner housing and sintered metal porous disc 36 to cover the chamber openings. The edge 38 o~ the housing 22 is formed over the edge of the disc making a tight assembly.
Referring to FIG. 2, the interferant filter includes a gas diffusion membrane 40 having bonded thereto a filter 42 that reacts with or absorbs the interferant gas. The membrane ; 40 is preferably a Zitex or Goretex porous fluorocarbon membrane. Other membrane materials may be used that have - similar characteristics, includlng having a large number of , . .
` - 20~0~
pores, between about 40-70% porous, of small pore size (0.2 micron), and being thin enough to avoid significant increase in the response time of the sensor to changes in the concentration of the gas being measured. The filter 42 is made up of a mixture of a finely divided powder filter material mixed with a fluorocarbon resin dispersion (e.g.
Teflon dispersion). The mixture is painted onto the membrane, dried-and sintered to form a good bond.
Catalytic elements of the type described for measuring combustible gases are poisoned by hydrogen sulfide.
Exemplary of the invention is a sensor incorporating a filter comprising silver that removes hydroyen sulfide thus prolonging the life of the sensor. A Goretex expanded polytetrafluoroethylene membrane having a O.lO" thickness, 0.7 g/cc density and 68% porosity is held between identical toroidal flanges defining a central filter area of about 0.95 inches in diameter. A mixture of 500 mg of silver powder of 4 to 7 micron particle size with 250 microliters of Teflon 30, an aqueous dispersion of TFE fluorocarbon resin, is spread over the central area of the membrane. The assembly is heated in an oven from about lOOoC to 2900C over a 45-minute period to form a coherent, porous sinter of filter material and fluorocarbon resin and securely bond the sinter to the membrane. The cooled membrane is removed from the fixture and ., . .. , . . : , , .
2~7~
trimmed to remove the uncoated portion. The filters provide intimate and effective contact of the filter material with gas passing through the filter with substantially no flow restriction that changes the response time of the element.
For example, sensors as shown in FIG.
incorporating the above described filter were exposed to (1) air containing 50~ LEL methane to establish a sensor response base, (2) air containing 23 ppm hydrogen sulfide for 14 hours and then (3) air containing 50~ LEL methane to determine any change in response. The loss of response was less than 6%.
In contrast, sensors without the interference filters, under the same conditions, showed a loss of response from 40-60%.
The interferant filter does not restrict flow to interfere with the normal operation of the sensor; typically the output of the new sensor incorporating the interferant filter is 97-99% of the output of the sensor without the interferant filter.
It will be recognized by those skilled in the art that this invention can be used with sensors other than the exemplified catalytic combustible gas sensor, such as, for example, electrochemical gas detecting elements and semi-conductor gas det cting elements. The selection of filter material will depend on the interferant gas to be removed and may be an absorbent, such as activated carbon or silica ~el , :
, ~
~. . ' ` ' ~' ', : .
, 2~704~
or a material that chemically reacts with and removes the interferant. Illustrative reactants are manganese dioxide to remove sulfur dioxide or potassium permanganate to remove hydrogen sulfide when measuring carbon monoxide with an electrochemical cell.
- .: , .
"
- - ~ - ~.
Claims (6)
1. A gas sensor responsive to an analyte gas and an interferant gas comprising a source of gas to be analyzed, a sensing element and a filter means interposed between the source and the sensing element, said filter means comprising a porous coherent sinter of fluorocarbon resin and finely divided filter material that removes interferant.
2. A gas sensor according to claim 1 in which the sensing element is a catalytic combustible gas sensor and the filter material is silver.
3. A gas sensor according to claim 1 in which the filter material is bonded to a porous fluorocarbon membrane.
4. A gas sensor according to claim 3 in which the sensing element is a catalytic combustible gas sensor and the filter material is silver.
5. A gas sensor according to claim 3 in which the membrane is between about 40% and 70% porous.
6. A gas sensor according to claim 5 in which the sensing element is a catalytic combustible gas sensor and the filter material is silver.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2067049 CA2067049A1 (en) | 1992-04-24 | 1992-04-24 | Gas sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2067049 CA2067049A1 (en) | 1992-04-24 | 1992-04-24 | Gas sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2067049A1 true CA2067049A1 (en) | 1993-10-25 |
Family
ID=4149697
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2067049 Abandoned CA2067049A1 (en) | 1992-04-24 | 1992-04-24 | Gas sensor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2067049A1 (en) |
-
1992
- 1992-04-24 CA CA 2067049 patent/CA2067049A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |