CA2315556A1 - Method and apparatus for measuring the concentration of a gas - Google Patents
Method and apparatus for measuring the concentration of a gas Download PDFInfo
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- CA2315556A1 CA2315556A1 CA 2315556 CA2315556A CA2315556A1 CA 2315556 A1 CA2315556 A1 CA 2315556A1 CA 2315556 CA2315556 CA 2315556 CA 2315556 A CA2315556 A CA 2315556A CA 2315556 A1 CA2315556 A1 CA 2315556A1
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Abstract
This invention relates to a thermoelectrical method and apparatus for measuring the concentration of a gas, and, in particular, a reactive gas (i.e. gasses that may be reacted to produce by-products and which produce heat or remove heat from a system as a result of the reaction) using the electrical resistance of a member upon exposure to the reactive gas. Examples of such gases include, ozone, oxygen, nitrogen or oxides of nitrogen, and the like. In the instant invention, a thermoelectric means is provided to generate a signal which is associated with a display to provide a readout of the concentration of the gas.
Description
Title: METHOD AND APPARATUS FOR MEASURING THE
CONCENTRATION OF A GAS
FIELD OF THE INVENTION
This invention relates to a thermoelectrical method and apparatus for measuring the concentration of a gas, and, in particular, a reactive gas (i.e. gasses that may be reacted to produce by-products and which produces heat or removes heat from a system as a result of the reaction). Example of such gases include, ozone, oxides of nitrogen, and the like.
BACKGROUND OF THE INVENTION
There are instruments available that measure ozone concentration in a gas mixture. One such instrument is disclosed in United States patent, No. 5,167,927 to Karlson. This patent discloses an apparatus that measures heat energy released when a reactive gas is catalytically converted to a different gas, for example using a catalyst to convert ozone to oxygen. In particular, Karlson discloses an apparatus that directs a stream of a gas mixture containing ozone against thermally conducting heat sinked plates on opposite sides of an axis of the stream with the plates extending upstream at an acute angle to the axis. One plate carries on its upstream facing a coating including a catalyst for ozone, while the other plate includes no catalyst on its upstream facing. A sensor is provided for measuring the temperatures of the respective plates. A
separate chamber, which is provided downstream, has a similar arrangement of plates. The ozone concentration of the gas is electronically measured based on the temperature difference of the two plates in each chamber.
One disadvantage of Karlson is that the flow of the gas mixture stream is important to the instruments sensitivity, and is electronically controlled to be constant for each sample of gas mixture measured. A
further disadvantage is that the instruments sensitivity and time constant is dependent on the velocity of the sample flow through the instrument, its electronic time constant and its thermal time constant.
. ' ' CA 02315556 2000-08-09 A further disadvantage is that a second plate (which is not coated with a catalyst) is required to provide a reference point. This second plate is the same size and weight as the total weight of the active plate with the catalyst. This requires careful manufacturing and handling of the plates.
There is also a need an inexpensive durable and easily calibrated apparatus for determining the concentration of reactive gasses, such as ozone.
SUMMARY OF THE INVENTION
In accordance with the instant invention, a sensor uses the electrical resistance of a member, preferably a catalyst to determine the concentration of a reactive gas.
In accordance with the instant invention, there is provided a method of measuring the concentration of a reactive gas in a gas mixture comprising the steps of exposing at least a portion of the gas mixture to a catalyst, measuring the electrical resistance of the catalyst upon exposure to the reactive gas, and using the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture. The electrical resistance is preferably measured while the member is exposed to the reactive gas. However, it will be appreciated that the electrical resistance may be measured after exposure to the reactive gas while the electrical resistance of the catalyst is still effected by its exposure to the reactive gas.
In one embodiment, the method further comprises the step of correcting the measurement for the initial temperature of the reactive gas prior to the exposure of the reactive gas to the catalyst.
In another embodiment, the measurement is corrected by establishing a value representing the initial temperature of the gas mixture containing the reactive gas and the value and the electrical resistance of the catalyst upon exposure to the reactive gas are used to ~ ~ CA 02315556 2000-08-09 obtain a measurement of the concentration of the reactive gas in the gas mixture.
In another embodiment, the value is the initial temperature of the gas mixture and the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas are used to obtain a measurement of the concentration of the reactive gas in the gas mixture.
In another embodiment, the value is the initial temperature of a reference gas and the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas are used to obtain a measurement of the concentration of the reactive gas in the gas mixture.
The reference gas is preferably at substantially the same temperature as the reactive gas. The method preferably further comprise the step of alternately directing at least a portion of the reference gas and at least a portion of the gas mixture containing the reactive gas to the catalyst to sequentially obtain the value and the electrical resistance of the catalyst after exposure to the reactive gas.
In another embodiment, the method further comprises the step of using a temperature sensor (which may be the catalyst or a second catalyst body) to establish the value.
In another embodiment, the method further comprises the step of first adjusting the temperature of the gas mixture to a predetermined temperature.
In another embodiment, the method further comprises the step of adjusting the temperature of the gas mixture to a predetermined temperature to obtain the initial temperature.
In another embodiment, the method further comprises the step of providing a readout of the concentration of the reactive gas within the gas mixture.
In another embodiment, the method further comprises first converting a specific gas in a gas stream to produce the reactive gas.
In accordance with the instant invention, there is also provided an apparatus for measuring the concentration of a reactive gas in a gas mixture comprising a catalyst positioned in an air flow path of the gas ' ~ CA 02315556 2000-08-09 mixture containing the reactive gas, and an electrical circuit for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas whereby the resistance of the catalyst upon exposure to the reactive gas is used to determine the concentration of the reactive gas in the gas mixture.
In another embodiment, the apparatus further comprises a readout calibrated to represent the concentration of the reactive gas within the gas mixture.
In another embodiment, the apparatus further comprises a generator positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
In another embodiment, the apparatus further comprises a station to establish a first value representing the initial temperature of the gas mixture and a comparator linked to the station to receive and compare the first value with the resistance of the catalyst upon exposure to the reactive gas to produce a second value that represents concentration of the reactive gas.
In another embodiment, the apparatus further comprises a station to establish a first value representing the initial temperature of the gas mixture and a comparator containing, for various temperatures, predetermined values representing the relationship between the electrical resistance of the catalyst upon exposure to various concentrations of the reactive gas, the comparator linked to the station and the catalyst to produce a signal representative of the concentration of the reactive gas.
In another embodiment, the apparatus further comprises a temperature adjusting member to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
In another embodiment, the apparatus further comprises a conduit for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to establish a first value and a comparator to compare the first value with the electrical resistance of the catalyst upon ' CA 02315556 2000-08-09 exposure to the reactive gas to produce a value that represents concentration of the reactive gas. The apparatus may further comprise a valve to alternately direct the reference sample of the gas mixture containing no reactive gas and the gas mixture to the catalyst. Preferably the reference sample is at substantially the same temperature as the gas mixture containing the reactive gas.
In another embodiment, the apparatus further comprises a temperature sensor positioned upstream from the catalyst to measure the initial temperature of the reactive gas.
In another embodiment, the catalyst comprises a self supporting member which is positioned in the air flow path.
In accordance with the instant invention, there is also provided an apparatus for measuring the concentration of a reactive gas in a gas mixture comprising a catalyst positioned in an air flow path of the gas mixture containing the reactive gas, and means for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas and to produce a signal representative of the concentration of the reactive gas in the gas mixture.
In one embodiment, the apparatus further comprises means positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
In another embodiment, the apparatus further comprises means to measure the initial temperature of the gas mixture and means for correcting the signal for the initial temperature the gas mixture.
In another embodiment, the apparatus further comprises means to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
In another embodiment, the apparatus further comprises means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain a first measurement and means for correcting the signal for the first measurement.
' , ' CA 02315556 2000-08-09 In another embodiment, the apparatus further comprises means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain the temperature of the reference gas and means for correcting the signal for the temperature of the reference gas.
In another embodiment, the apparatus further comprises means for providing the reference sample at substantially the same temperature as the gas mixture containing the reactive gas.
In another embodiment, the catalyst comprises a self supporting member which is positioned in the air flow path.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
For a better understanding of the present invention and to show more clearly how it would be carried into effect, reference will now be made, by way of example, to the accompanying drawings that show a preferred embodiment of the present invention, and in which:
Figure 1 is a view of one embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture;
Figure 2 is a view of a second embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture;
Figure 3 is a view of a further embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture; and Figure 4 is a view of a further embodiment of the catalyst which may be used in the apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The instant invention provides a thermoelectrical means for measuring the electrical resistance of a catalyst and providing the concentration of the reactive gas.
' CA 02315556 2000-08-09 The method and apparatus of the present invention may be used in conjunction with any gas which undergoes a reaction to produce a by-product, such as another gas, when exposed to another member which is referred to herein as a "catalyst". Any such gas that undergoes such a reaction is referred to herein as a "reactive gas". The catalyst may be any material which will cause the reactive gas, when exposed to the catalyst to, undergo a chemical conversion to produce one or more by-products. The reactive gas may also produce heat when the by-product is formed or it may adsorb heat when the by-product is formed. A preferred example of such a reactive gas is ozone, which releases heat energy when it comes in contact with a suitable catalyst to form oxygen. The catalyst blend may be a blend of iron, manganese, and tin oxide or any other catalyst which is known in the art. This mixture causes the ozone to undergo an exothermic reaction to form oxygen (the by-product).
A preferred apparatus 10 for measuring the concentration of a reactive gas within a gas mixture is illustrated in Figure 1. Apparatus 10 preferably includes a station 12 for establishing a first value representing the initial temperature of the gas mixture containing the reactive gas.
Station 12 will be discussed in more detail below. Once an initial temperature of the gas mixture is established, however, a gas stream containing the reactive gas is introduced to a first chamber 14 which is linked to station 12 by a conduit 16. The gas stream is drawn from station 12, through conduit 16, and into chamber 14, by a suction pump 18, linked to the chamber 14 by a conduit 20. The gas stream may consist essentially only of the reactive gas. Alternatively, the reactive gas may be present with a mixture of one or more non-reactive gasses. It will be appreciated that suction pump 18 may be positioned at any location in the system and may not be required if the gas mixture entering apparatus 10 is under pressure.
The chamber 14 contains a catalyst 22 which causes some or all of the reactive gas in the gas mixture to undergo a reaction which produces one or more by-products and preferably also releases (or adsorbs) heat energy. The catalyst 22 may be located at any position in the chamber _ 8_ 14 that will come into contact with the gas stream entering the chamber 14, so long as the heat energy released or adsorbed during conversion of the reactive gas heats or cools the catalyst and any member thermally connected to the catalyst such as the walls of chamber 14. The heat produced by the reaction causes catalyst 22 (and consequentially chamber 14 which is in thermal contact with catalyst 22) to become heated, It will be appreciated that in the embodiment of Figure 1, catalyst 22 is in the form of individual particulate members (eg. beads having a diameter ranging from 1-5 mm). Catalyst 22 may be in the form of a solid material. For example, catalyst 22 may be a single catalyst bead or a thin self supporting sheet of catalyst (see Figure 4) or the like. In such a case, chamber 14 would not be required and the solid catalyst member could be positioned in the gas flow stream in conduit 16 by any means known in the art. For example, as shown in Figure 4, catalyst 22 may be mounted in a holder by being affixed to the end of wires 30 and 32 such as by alligator clips.
Subsequent to passing over or through catalyst 22, the flow stream may exit the system from pump 18 for subsequent disposal or uses that would be known to those skilled in the art. For example, in the case of ozone, the heated mixture may be fed to an ozone destructor to convert any remaining ozone to oxygen prior to venting the stream to the ambient. Preferably, catalyst 22 doubles as a ozone destructor so that the concentration of ozone in the flow stream is measured at the same time that the ozone is converted to oxygen.
In the embodiments of the invention as illustrated in the Figures 1-3, chamber 14 is a thermally insulated tube 24 that contains the catalyst 22. End caps 26 and 28 can be placed at either ends of the thermally insulated tube 24. Wires 30 and 32 can link the end caps 26 and 28, respectively, to an electronic circuit 36. The conductive end caps 26 and 28 are preferably of a stainless steel construction. Further, conductive end caps 26 and 28 are preferably meshed (not shown) to allow the gas mixture to pass through as it enters or exits the thermally insulated tube 24 while ' 1 CA 02315556 2000-08-09 holding catalyst 22 in position. A tube containing the catalyst and capped at either end and linked to an electronic circuit, as described, forms a resistance sensor that generates a signal representing the electrical resistance of the catalyst 22.
The thermally insulated tube 24 can be capped at either end by plastic end caps 38 and 40, which include rims 42 and 44, respectively, that fit snugly around the thermally insulated tube 24 and enclose conductive end caps 26 and 28, respectively. Each plastic end cap 38 and 40 has an annulus 46 and 48, respectively, sized to receive there around in a sealing fit respective ends 50 and 52 of the conduits 16 and 20. Each annulus 46 and 48 of the end caps 38 and 40, respectively, includes openings 54 and 56, respectively, to allow the gas mixture to pass through the end caps as it enters the chamber 14 from conduit 16 or exits the chamber 14 by conduit 20. Other constructions for the chamber 14 containing the catalyst 22 would be apparent to those skilled in the art.
Pursuant to the instant invention, the concentration of ozone in the gas stream is determined based on the electrical resistance of catalyst 22. Without being limited by theory, it is believed that the electrical resistance of the catalyst may be affected by one or two effects produced by exposing the catalyst to the reactive gas. First, the reaction of the reactive gas results in a change in temperature of the environment in which the reaction occurs. As the catalyst is part of the environment, it itself undergoes a temperature change (eg. in the case of ozone it is heated by the heat released during the reaction) thereby changing its electrical resistance.
Secondly, the presence of the reactive gas may itself also effect the electrical resistance of the catalyst. In any event, a relationship may be developed for any system by measuring the electrical resistance of a catalyst while it is exposed to varying known concentrations of the reactive gas. Once this data is developed, and, eg., stored in comparator 58, the electrical resistance of the catalyst may then be exposed to an unknown concentration of the reactive gas and electrical resistance of the catalyst may then be measured.
By comparing the electrical resistance of the catalyst to the known data, the concentration of the reactive gas may then be determined.
In this preferred embodiment, only one thermoelectrical means (i.e. catalyst 22) is used to measure the concentration of the reactive gas and therefore the thermoelectrical means defines a self referential gas sensor. For example, it will be appreciated that if the heat produced or adsorbed by the conversion of the reactive gas to the by-product at the concentrations to be measured is substantial compared to the temperature of the gas stream prior to contacting the reactive gas with the catalyst, then correcting for the initial temperature of the gas stream may not be necessary for a usable gas sensor. For example, the sensor could be set to read zero for the initial temperature of the gas stream (eg. at room temperature).
In an alternate preferred embodiment, the temperature of the reactive gas may be taken into account if the temperature of the reactive gas is known in advance. For example, the gas stream which is fed to apparatus 10 may be at approximately a constant temperature (eg. ambient temperature). Alternately, at the point in a process when the concentration of the reactive gas is to be measured, the temperature of the gas stream may be controlled within a narrow temperature range. Comparator 58 may be programmed with the electrical resistance of catalyst 22 at varying concentrations of the reactive gas at such an initial temperature. Catalyst 22 forms part of a circuit for determining the electrical resistance across catalyst 22. There is a relationship between the electrical resistance of the catalyst and the concentration of the reactive gas in the gas stream at any temperature. Using this relationship, which may be predetermined for any catalyst 22, the concentration of the reactive gas in the flow stream to which catalyst 22 is exposed may be determined by measuring the electrical resistance of catalyst 22 on exposure to the reactive gas and comparing it with the preprogrammed values of the electrical resistance of catalyst 22 at the anticipated temperature.
If the temperature of the gas stream containing the reactive gas is not known in advance, or if it is desired to increase the accuracy of apparatus 10, then, in an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by measuring the temperature of the reactive gas. For example, the temperature of the gas stream containing the reactive gas may be measured prior to exposing the catalyst to the reactive gas. Controller 58 may be programmed with the predetermined values representing the relationship between the electrical resistance of catalyst 22 to concentrations of the reactive gas at various temperatures. Once the initial temperature of the gas stream is determined, then the concentration of the reactive gas may be determined by comparing the electrical resistance of catalyst 22 after exposure to the reactive gas with the predetermined relationship between concentration and electrical resistance at the measured initial temperature. This embodiment is demonstrated in Figure 1.
Figure 1 illustrates a self referential sensor wherein the reference point is provided by measuring the initial temperature of the gas stream containing the reactive gas to obtain a first value. The second value represents the electrical resistance of catalyst 22 after exposure to the reactive gas. The first value and the second value are electrical signals that are sent to a comparator 58, which can be part of the electronic circuit 36, to provide a signal corresponding to the concentration of the reactive gas.
The value, representing a measurement of the concentration of the reactive gas within the gas mixture, can be displayed by a suitable display 60. Alternatively, this value can be sent to additional apparatus (not shown) for subsequent use, manipulation, or monitoring. Preferably, comparator 58 provides a readout which may be analog or digital that is the concentration of the reactive gas in the gas stream.
In the embodiment of the invention illustrated in Figure 1, the station 12 for establishing the first value representing the initial temperature of the gas mixture comprises a second chamber 62 linked to the chamber 14 by the conduit 16 at its end 64. The chamber 62 includes an inlet 66 to allow the gas mixture containing the reactive gas to enter the chamber 62 from a supply of the gas mixture (not shown). Further, the chamber 62 includes therein a sensor 68 linked through wires 70 and 72 to provide comparator 58 with an electronic signal representing the temperature of the gas mixture in the chamber 62. Sensor 68 can be either a temperature sensor or a resistance sensor.
The chamber 62 can be thermally insulated from the chamber 14 to ensure that any change in the gas temperature when it reacts due to catalyst 22 does not effect the temperature of the gas mixture in the chamber 62. This can be accomplished by having the conversion of the reactive gas occur inside the thermally insulted tube 24 and/or by providing the chamber 62 remote from the chamber 14. Other means to thermally separate chambers 14 and 62 from one another will be apparent to those skilled in the art.
It will be appreciated that the temperature of a gas that does not contain the reactive gas may be so measured. Such a gas (i.e. a reference gas) is preferably at a similar temperature to the temperature of the gas stream containing the reactive gas.
If the temperature of the gas stream containing the reactive gas is not known in advance, or if it is desired to increase the accuracy of apparatus 10, then, in an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by measuring the temperature of a reference gas which is at about the same temperature as the reactive gas. The reference gas may be fed to catalyst 22 to obtain a first value corresponding to the temperature of the reference gas. The reference gas may be fed alternately with the gas stream containing the reactive gas to catalyst 22 to provide a reference point. The reference gas is preferably at a similar temperature to the temperature of the gas stream containing the reactive gas. In this case, the controller may use the temperature of the reference stream as the initial temperature of the gas stream containing the reactive gas prior to exposing the catalyst to the ' CA 02315556 2000-08-09 reactive gas to determine the concentration of the reactive gas in the gas stream. This embodiment is demonstrated in Figure 2.
In Figure 2, station 12 comprises a valve 74, such as, a solenoid valve. The valve 74 includes an inlet 76 that is connected to a supply of the gas mixture containing the reactive gas (not shown). Further, the valve 74 includes an inlet 78 that is connected to a supply of a reference gas mixture containing no reactive gas (not shown). The gas mixture containing the reactive gas and the reference sample of gas mixture containing no reactive gas are preferably supplied to the valve 74 at substantially the same temperature. The valve 74 is linked through wires 80 and 82 to an additional control circuit 84 that can be included in the electronic circuit 36. The control circuit 84 controls the valve 74 so that it allows either the reference gas mixture containing no reactive gas to enter through the inlet 78, or allows the gas mixture containing the reactive gas to enter through inlet 76.
~In use, the valve 74 is set using control circuit 84 to direct at least a portion of the reference gas mixture containing no reactive gas to the chamber 14. The temperature of catalyst 22 within the chamber 14 would adjust to the temperature of the reference gas mixture which is preferably representative of the initial temperature of the gas mixture containing the reactive gas. In this manner catalyst 22 produces a signal that is representative of the initial temperature of the gas mixture (the first value).
Valve 74 can then be set using control circuit 84 to allow the gas mixture containing the reactive gas to enter the chamber 14. The catalyst 22 reacts with the reactive gas in the chamber 14 thereby causing a temperature change to catalyst 22. The electrical resistance of catalyst 22 may then be measured. Comparator 58 then uses the first value and the measured electrical resistance to obtain the concentration of the reactive gas.
Valve 74 can be set to alternately direct to chamber 14 the reference gas mixture containing no reactive gas and the gas mixture containing the reactive gas. So as to provide intermittent readings of the concentration of the reactive gas in the gas stream wherein the catalyst is adjusted to the initial temperature of the gas stream between each reading.
In an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by bringing the reactive gas to a standard temperature. This embodiment is demonstrated in Figure 3. In this embodiment, the station 12 of apparatus 10 for establishing the first value representing the initial temperature of the gas mixture comprises a second chamber 86 linked to the chamber 14. The chamber 86 includes an inlet 88 to allow the gas mixture containing the reactive gas to enter the chamber 86 from a supply of the gas mixture (not shown). In this embodiment the chamber 86 comprises a temperature controlling apparatus to adjust the temperature of the gas mixture to a fixed predetermined value. For example, the temperature controlling apparatus may comprise a thermoelectric refrigeration module 90 which heats or cools a heat exchanger 92 within the chamber 86. External of the chamber 86, but connected to the thermoelectric refrigeration module, is a heat sink 94 to dissipate excess heat or supply heat. The cooperation of the thermally electric refrigeration module, heat exchanger, and heat sink all act to adjust the temperature of the gas mixture containing the reactive gas to a fixed predetermined value. In the preferred embodiment, the temperature of the gas mixture is set to 20° C.
In this embodiment comparator 58 is programmed with the relationship between the electrical resistance of catalyst and the concentration of the reactive gas at the predetermined temperature.
Comparator 58 then uses the measured electrical resistance of catalyst 22 to determine the concentration of the reactive gas in the gas stream.
As illustrated in Figure 1 a generator 96 can be provided for converting all or a predetermined portion of a specific gas in the gas mixture to an associated reactive gas. In this way, apparatus 10 could be used to measure the temperature of a non-reactive gas by measuring the concentration of a corresponding reactive gas. For example, apparatus 10 could be used to measure the concentration of oxygen in a gas stream by converting the oxygen (or a known portion of it) to ozone and then measuring the electrical resistance of catalyst 22 when it is exposed to the ozone.
Generator 96 may be calibrated to display the electrical resistance of catalyst 22, the concentration of the reactive gas (e.g. ozone) in the flow stream or preferably the concentration of the specific gas (e.g.
oxygen). For example, a generator 96 may convert a known percentage of oxygen in an air flow stream to ozone. Using this information and the predetermined relationship between the electrical resistance of catalyst 22 and the concentration of the reactive gas at various temperatures, display 60 may display the concentration of the specific gas within the gas mixture fed to generator 96.
It can be appreciated that a generator 96 as provided in Figure 1 can also be provided to the embodiments illustrated in Figures 2 or 3, or other alternatives, as would be known to those skilled in the art.
It will also be appreciated that the reactive gas could be an oxide of nitrogen and the display 60 could be a read out of the concentration of NOx in the stream (in the embodiments of Figures 2 or 3) or of nitrogen (in the embodiment of Figure 1).
It can be appreciated that variations to this invention would be readily apparent to those skilled in the art, and this invention is intended to include those alternatives. For example, in an alternate embodiment, two tubes 24 may be provided, only one of which contains catalyst 22. The gas stream may pass sequentially or in parallel through the two tubes.
CONCENTRATION OF A GAS
FIELD OF THE INVENTION
This invention relates to a thermoelectrical method and apparatus for measuring the concentration of a gas, and, in particular, a reactive gas (i.e. gasses that may be reacted to produce by-products and which produces heat or removes heat from a system as a result of the reaction). Example of such gases include, ozone, oxides of nitrogen, and the like.
BACKGROUND OF THE INVENTION
There are instruments available that measure ozone concentration in a gas mixture. One such instrument is disclosed in United States patent, No. 5,167,927 to Karlson. This patent discloses an apparatus that measures heat energy released when a reactive gas is catalytically converted to a different gas, for example using a catalyst to convert ozone to oxygen. In particular, Karlson discloses an apparatus that directs a stream of a gas mixture containing ozone against thermally conducting heat sinked plates on opposite sides of an axis of the stream with the plates extending upstream at an acute angle to the axis. One plate carries on its upstream facing a coating including a catalyst for ozone, while the other plate includes no catalyst on its upstream facing. A sensor is provided for measuring the temperatures of the respective plates. A
separate chamber, which is provided downstream, has a similar arrangement of plates. The ozone concentration of the gas is electronically measured based on the temperature difference of the two plates in each chamber.
One disadvantage of Karlson is that the flow of the gas mixture stream is important to the instruments sensitivity, and is electronically controlled to be constant for each sample of gas mixture measured. A
further disadvantage is that the instruments sensitivity and time constant is dependent on the velocity of the sample flow through the instrument, its electronic time constant and its thermal time constant.
. ' ' CA 02315556 2000-08-09 A further disadvantage is that a second plate (which is not coated with a catalyst) is required to provide a reference point. This second plate is the same size and weight as the total weight of the active plate with the catalyst. This requires careful manufacturing and handling of the plates.
There is also a need an inexpensive durable and easily calibrated apparatus for determining the concentration of reactive gasses, such as ozone.
SUMMARY OF THE INVENTION
In accordance with the instant invention, a sensor uses the electrical resistance of a member, preferably a catalyst to determine the concentration of a reactive gas.
In accordance with the instant invention, there is provided a method of measuring the concentration of a reactive gas in a gas mixture comprising the steps of exposing at least a portion of the gas mixture to a catalyst, measuring the electrical resistance of the catalyst upon exposure to the reactive gas, and using the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture. The electrical resistance is preferably measured while the member is exposed to the reactive gas. However, it will be appreciated that the electrical resistance may be measured after exposure to the reactive gas while the electrical resistance of the catalyst is still effected by its exposure to the reactive gas.
In one embodiment, the method further comprises the step of correcting the measurement for the initial temperature of the reactive gas prior to the exposure of the reactive gas to the catalyst.
In another embodiment, the measurement is corrected by establishing a value representing the initial temperature of the gas mixture containing the reactive gas and the value and the electrical resistance of the catalyst upon exposure to the reactive gas are used to ~ ~ CA 02315556 2000-08-09 obtain a measurement of the concentration of the reactive gas in the gas mixture.
In another embodiment, the value is the initial temperature of the gas mixture and the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas are used to obtain a measurement of the concentration of the reactive gas in the gas mixture.
In another embodiment, the value is the initial temperature of a reference gas and the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas are used to obtain a measurement of the concentration of the reactive gas in the gas mixture.
The reference gas is preferably at substantially the same temperature as the reactive gas. The method preferably further comprise the step of alternately directing at least a portion of the reference gas and at least a portion of the gas mixture containing the reactive gas to the catalyst to sequentially obtain the value and the electrical resistance of the catalyst after exposure to the reactive gas.
In another embodiment, the method further comprises the step of using a temperature sensor (which may be the catalyst or a second catalyst body) to establish the value.
In another embodiment, the method further comprises the step of first adjusting the temperature of the gas mixture to a predetermined temperature.
In another embodiment, the method further comprises the step of adjusting the temperature of the gas mixture to a predetermined temperature to obtain the initial temperature.
In another embodiment, the method further comprises the step of providing a readout of the concentration of the reactive gas within the gas mixture.
In another embodiment, the method further comprises first converting a specific gas in a gas stream to produce the reactive gas.
In accordance with the instant invention, there is also provided an apparatus for measuring the concentration of a reactive gas in a gas mixture comprising a catalyst positioned in an air flow path of the gas ' ~ CA 02315556 2000-08-09 mixture containing the reactive gas, and an electrical circuit for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas whereby the resistance of the catalyst upon exposure to the reactive gas is used to determine the concentration of the reactive gas in the gas mixture.
In another embodiment, the apparatus further comprises a readout calibrated to represent the concentration of the reactive gas within the gas mixture.
In another embodiment, the apparatus further comprises a generator positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
In another embodiment, the apparatus further comprises a station to establish a first value representing the initial temperature of the gas mixture and a comparator linked to the station to receive and compare the first value with the resistance of the catalyst upon exposure to the reactive gas to produce a second value that represents concentration of the reactive gas.
In another embodiment, the apparatus further comprises a station to establish a first value representing the initial temperature of the gas mixture and a comparator containing, for various temperatures, predetermined values representing the relationship between the electrical resistance of the catalyst upon exposure to various concentrations of the reactive gas, the comparator linked to the station and the catalyst to produce a signal representative of the concentration of the reactive gas.
In another embodiment, the apparatus further comprises a temperature adjusting member to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
In another embodiment, the apparatus further comprises a conduit for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to establish a first value and a comparator to compare the first value with the electrical resistance of the catalyst upon ' CA 02315556 2000-08-09 exposure to the reactive gas to produce a value that represents concentration of the reactive gas. The apparatus may further comprise a valve to alternately direct the reference sample of the gas mixture containing no reactive gas and the gas mixture to the catalyst. Preferably the reference sample is at substantially the same temperature as the gas mixture containing the reactive gas.
In another embodiment, the apparatus further comprises a temperature sensor positioned upstream from the catalyst to measure the initial temperature of the reactive gas.
In another embodiment, the catalyst comprises a self supporting member which is positioned in the air flow path.
In accordance with the instant invention, there is also provided an apparatus for measuring the concentration of a reactive gas in a gas mixture comprising a catalyst positioned in an air flow path of the gas mixture containing the reactive gas, and means for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas and to produce a signal representative of the concentration of the reactive gas in the gas mixture.
In one embodiment, the apparatus further comprises means positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
In another embodiment, the apparatus further comprises means to measure the initial temperature of the gas mixture and means for correcting the signal for the initial temperature the gas mixture.
In another embodiment, the apparatus further comprises means to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
In another embodiment, the apparatus further comprises means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain a first measurement and means for correcting the signal for the first measurement.
' , ' CA 02315556 2000-08-09 In another embodiment, the apparatus further comprises means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain the temperature of the reference gas and means for correcting the signal for the temperature of the reference gas.
In another embodiment, the apparatus further comprises means for providing the reference sample at substantially the same temperature as the gas mixture containing the reactive gas.
In another embodiment, the catalyst comprises a self supporting member which is positioned in the air flow path.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
For a better understanding of the present invention and to show more clearly how it would be carried into effect, reference will now be made, by way of example, to the accompanying drawings that show a preferred embodiment of the present invention, and in which:
Figure 1 is a view of one embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture;
Figure 2 is a view of a second embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture;
Figure 3 is a view of a further embodiment of an apparatus of the invention for detecting the concentration of a reactive gas within a gas mixture; and Figure 4 is a view of a further embodiment of the catalyst which may be used in the apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The instant invention provides a thermoelectrical means for measuring the electrical resistance of a catalyst and providing the concentration of the reactive gas.
' CA 02315556 2000-08-09 The method and apparatus of the present invention may be used in conjunction with any gas which undergoes a reaction to produce a by-product, such as another gas, when exposed to another member which is referred to herein as a "catalyst". Any such gas that undergoes such a reaction is referred to herein as a "reactive gas". The catalyst may be any material which will cause the reactive gas, when exposed to the catalyst to, undergo a chemical conversion to produce one or more by-products. The reactive gas may also produce heat when the by-product is formed or it may adsorb heat when the by-product is formed. A preferred example of such a reactive gas is ozone, which releases heat energy when it comes in contact with a suitable catalyst to form oxygen. The catalyst blend may be a blend of iron, manganese, and tin oxide or any other catalyst which is known in the art. This mixture causes the ozone to undergo an exothermic reaction to form oxygen (the by-product).
A preferred apparatus 10 for measuring the concentration of a reactive gas within a gas mixture is illustrated in Figure 1. Apparatus 10 preferably includes a station 12 for establishing a first value representing the initial temperature of the gas mixture containing the reactive gas.
Station 12 will be discussed in more detail below. Once an initial temperature of the gas mixture is established, however, a gas stream containing the reactive gas is introduced to a first chamber 14 which is linked to station 12 by a conduit 16. The gas stream is drawn from station 12, through conduit 16, and into chamber 14, by a suction pump 18, linked to the chamber 14 by a conduit 20. The gas stream may consist essentially only of the reactive gas. Alternatively, the reactive gas may be present with a mixture of one or more non-reactive gasses. It will be appreciated that suction pump 18 may be positioned at any location in the system and may not be required if the gas mixture entering apparatus 10 is under pressure.
The chamber 14 contains a catalyst 22 which causes some or all of the reactive gas in the gas mixture to undergo a reaction which produces one or more by-products and preferably also releases (or adsorbs) heat energy. The catalyst 22 may be located at any position in the chamber _ 8_ 14 that will come into contact with the gas stream entering the chamber 14, so long as the heat energy released or adsorbed during conversion of the reactive gas heats or cools the catalyst and any member thermally connected to the catalyst such as the walls of chamber 14. The heat produced by the reaction causes catalyst 22 (and consequentially chamber 14 which is in thermal contact with catalyst 22) to become heated, It will be appreciated that in the embodiment of Figure 1, catalyst 22 is in the form of individual particulate members (eg. beads having a diameter ranging from 1-5 mm). Catalyst 22 may be in the form of a solid material. For example, catalyst 22 may be a single catalyst bead or a thin self supporting sheet of catalyst (see Figure 4) or the like. In such a case, chamber 14 would not be required and the solid catalyst member could be positioned in the gas flow stream in conduit 16 by any means known in the art. For example, as shown in Figure 4, catalyst 22 may be mounted in a holder by being affixed to the end of wires 30 and 32 such as by alligator clips.
Subsequent to passing over or through catalyst 22, the flow stream may exit the system from pump 18 for subsequent disposal or uses that would be known to those skilled in the art. For example, in the case of ozone, the heated mixture may be fed to an ozone destructor to convert any remaining ozone to oxygen prior to venting the stream to the ambient. Preferably, catalyst 22 doubles as a ozone destructor so that the concentration of ozone in the flow stream is measured at the same time that the ozone is converted to oxygen.
In the embodiments of the invention as illustrated in the Figures 1-3, chamber 14 is a thermally insulated tube 24 that contains the catalyst 22. End caps 26 and 28 can be placed at either ends of the thermally insulated tube 24. Wires 30 and 32 can link the end caps 26 and 28, respectively, to an electronic circuit 36. The conductive end caps 26 and 28 are preferably of a stainless steel construction. Further, conductive end caps 26 and 28 are preferably meshed (not shown) to allow the gas mixture to pass through as it enters or exits the thermally insulated tube 24 while ' 1 CA 02315556 2000-08-09 holding catalyst 22 in position. A tube containing the catalyst and capped at either end and linked to an electronic circuit, as described, forms a resistance sensor that generates a signal representing the electrical resistance of the catalyst 22.
The thermally insulated tube 24 can be capped at either end by plastic end caps 38 and 40, which include rims 42 and 44, respectively, that fit snugly around the thermally insulated tube 24 and enclose conductive end caps 26 and 28, respectively. Each plastic end cap 38 and 40 has an annulus 46 and 48, respectively, sized to receive there around in a sealing fit respective ends 50 and 52 of the conduits 16 and 20. Each annulus 46 and 48 of the end caps 38 and 40, respectively, includes openings 54 and 56, respectively, to allow the gas mixture to pass through the end caps as it enters the chamber 14 from conduit 16 or exits the chamber 14 by conduit 20. Other constructions for the chamber 14 containing the catalyst 22 would be apparent to those skilled in the art.
Pursuant to the instant invention, the concentration of ozone in the gas stream is determined based on the electrical resistance of catalyst 22. Without being limited by theory, it is believed that the electrical resistance of the catalyst may be affected by one or two effects produced by exposing the catalyst to the reactive gas. First, the reaction of the reactive gas results in a change in temperature of the environment in which the reaction occurs. As the catalyst is part of the environment, it itself undergoes a temperature change (eg. in the case of ozone it is heated by the heat released during the reaction) thereby changing its electrical resistance.
Secondly, the presence of the reactive gas may itself also effect the electrical resistance of the catalyst. In any event, a relationship may be developed for any system by measuring the electrical resistance of a catalyst while it is exposed to varying known concentrations of the reactive gas. Once this data is developed, and, eg., stored in comparator 58, the electrical resistance of the catalyst may then be exposed to an unknown concentration of the reactive gas and electrical resistance of the catalyst may then be measured.
By comparing the electrical resistance of the catalyst to the known data, the concentration of the reactive gas may then be determined.
In this preferred embodiment, only one thermoelectrical means (i.e. catalyst 22) is used to measure the concentration of the reactive gas and therefore the thermoelectrical means defines a self referential gas sensor. For example, it will be appreciated that if the heat produced or adsorbed by the conversion of the reactive gas to the by-product at the concentrations to be measured is substantial compared to the temperature of the gas stream prior to contacting the reactive gas with the catalyst, then correcting for the initial temperature of the gas stream may not be necessary for a usable gas sensor. For example, the sensor could be set to read zero for the initial temperature of the gas stream (eg. at room temperature).
In an alternate preferred embodiment, the temperature of the reactive gas may be taken into account if the temperature of the reactive gas is known in advance. For example, the gas stream which is fed to apparatus 10 may be at approximately a constant temperature (eg. ambient temperature). Alternately, at the point in a process when the concentration of the reactive gas is to be measured, the temperature of the gas stream may be controlled within a narrow temperature range. Comparator 58 may be programmed with the electrical resistance of catalyst 22 at varying concentrations of the reactive gas at such an initial temperature. Catalyst 22 forms part of a circuit for determining the electrical resistance across catalyst 22. There is a relationship between the electrical resistance of the catalyst and the concentration of the reactive gas in the gas stream at any temperature. Using this relationship, which may be predetermined for any catalyst 22, the concentration of the reactive gas in the flow stream to which catalyst 22 is exposed may be determined by measuring the electrical resistance of catalyst 22 on exposure to the reactive gas and comparing it with the preprogrammed values of the electrical resistance of catalyst 22 at the anticipated temperature.
If the temperature of the gas stream containing the reactive gas is not known in advance, or if it is desired to increase the accuracy of apparatus 10, then, in an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by measuring the temperature of the reactive gas. For example, the temperature of the gas stream containing the reactive gas may be measured prior to exposing the catalyst to the reactive gas. Controller 58 may be programmed with the predetermined values representing the relationship between the electrical resistance of catalyst 22 to concentrations of the reactive gas at various temperatures. Once the initial temperature of the gas stream is determined, then the concentration of the reactive gas may be determined by comparing the electrical resistance of catalyst 22 after exposure to the reactive gas with the predetermined relationship between concentration and electrical resistance at the measured initial temperature. This embodiment is demonstrated in Figure 1.
Figure 1 illustrates a self referential sensor wherein the reference point is provided by measuring the initial temperature of the gas stream containing the reactive gas to obtain a first value. The second value represents the electrical resistance of catalyst 22 after exposure to the reactive gas. The first value and the second value are electrical signals that are sent to a comparator 58, which can be part of the electronic circuit 36, to provide a signal corresponding to the concentration of the reactive gas.
The value, representing a measurement of the concentration of the reactive gas within the gas mixture, can be displayed by a suitable display 60. Alternatively, this value can be sent to additional apparatus (not shown) for subsequent use, manipulation, or monitoring. Preferably, comparator 58 provides a readout which may be analog or digital that is the concentration of the reactive gas in the gas stream.
In the embodiment of the invention illustrated in Figure 1, the station 12 for establishing the first value representing the initial temperature of the gas mixture comprises a second chamber 62 linked to the chamber 14 by the conduit 16 at its end 64. The chamber 62 includes an inlet 66 to allow the gas mixture containing the reactive gas to enter the chamber 62 from a supply of the gas mixture (not shown). Further, the chamber 62 includes therein a sensor 68 linked through wires 70 and 72 to provide comparator 58 with an electronic signal representing the temperature of the gas mixture in the chamber 62. Sensor 68 can be either a temperature sensor or a resistance sensor.
The chamber 62 can be thermally insulated from the chamber 14 to ensure that any change in the gas temperature when it reacts due to catalyst 22 does not effect the temperature of the gas mixture in the chamber 62. This can be accomplished by having the conversion of the reactive gas occur inside the thermally insulted tube 24 and/or by providing the chamber 62 remote from the chamber 14. Other means to thermally separate chambers 14 and 62 from one another will be apparent to those skilled in the art.
It will be appreciated that the temperature of a gas that does not contain the reactive gas may be so measured. Such a gas (i.e. a reference gas) is preferably at a similar temperature to the temperature of the gas stream containing the reactive gas.
If the temperature of the gas stream containing the reactive gas is not known in advance, or if it is desired to increase the accuracy of apparatus 10, then, in an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by measuring the temperature of a reference gas which is at about the same temperature as the reactive gas. The reference gas may be fed to catalyst 22 to obtain a first value corresponding to the temperature of the reference gas. The reference gas may be fed alternately with the gas stream containing the reactive gas to catalyst 22 to provide a reference point. The reference gas is preferably at a similar temperature to the temperature of the gas stream containing the reactive gas. In this case, the controller may use the temperature of the reference stream as the initial temperature of the gas stream containing the reactive gas prior to exposing the catalyst to the ' CA 02315556 2000-08-09 reactive gas to determine the concentration of the reactive gas in the gas stream. This embodiment is demonstrated in Figure 2.
In Figure 2, station 12 comprises a valve 74, such as, a solenoid valve. The valve 74 includes an inlet 76 that is connected to a supply of the gas mixture containing the reactive gas (not shown). Further, the valve 74 includes an inlet 78 that is connected to a supply of a reference gas mixture containing no reactive gas (not shown). The gas mixture containing the reactive gas and the reference sample of gas mixture containing no reactive gas are preferably supplied to the valve 74 at substantially the same temperature. The valve 74 is linked through wires 80 and 82 to an additional control circuit 84 that can be included in the electronic circuit 36. The control circuit 84 controls the valve 74 so that it allows either the reference gas mixture containing no reactive gas to enter through the inlet 78, or allows the gas mixture containing the reactive gas to enter through inlet 76.
~In use, the valve 74 is set using control circuit 84 to direct at least a portion of the reference gas mixture containing no reactive gas to the chamber 14. The temperature of catalyst 22 within the chamber 14 would adjust to the temperature of the reference gas mixture which is preferably representative of the initial temperature of the gas mixture containing the reactive gas. In this manner catalyst 22 produces a signal that is representative of the initial temperature of the gas mixture (the first value).
Valve 74 can then be set using control circuit 84 to allow the gas mixture containing the reactive gas to enter the chamber 14. The catalyst 22 reacts with the reactive gas in the chamber 14 thereby causing a temperature change to catalyst 22. The electrical resistance of catalyst 22 may then be measured. Comparator 58 then uses the first value and the measured electrical resistance to obtain the concentration of the reactive gas.
Valve 74 can be set to alternately direct to chamber 14 the reference gas mixture containing no reactive gas and the gas mixture containing the reactive gas. So as to provide intermittent readings of the concentration of the reactive gas in the gas stream wherein the catalyst is adjusted to the initial temperature of the gas stream between each reading.
In an alternate preferred embodiment, the temperature of the reactive gas may be taken into account by bringing the reactive gas to a standard temperature. This embodiment is demonstrated in Figure 3. In this embodiment, the station 12 of apparatus 10 for establishing the first value representing the initial temperature of the gas mixture comprises a second chamber 86 linked to the chamber 14. The chamber 86 includes an inlet 88 to allow the gas mixture containing the reactive gas to enter the chamber 86 from a supply of the gas mixture (not shown). In this embodiment the chamber 86 comprises a temperature controlling apparatus to adjust the temperature of the gas mixture to a fixed predetermined value. For example, the temperature controlling apparatus may comprise a thermoelectric refrigeration module 90 which heats or cools a heat exchanger 92 within the chamber 86. External of the chamber 86, but connected to the thermoelectric refrigeration module, is a heat sink 94 to dissipate excess heat or supply heat. The cooperation of the thermally electric refrigeration module, heat exchanger, and heat sink all act to adjust the temperature of the gas mixture containing the reactive gas to a fixed predetermined value. In the preferred embodiment, the temperature of the gas mixture is set to 20° C.
In this embodiment comparator 58 is programmed with the relationship between the electrical resistance of catalyst and the concentration of the reactive gas at the predetermined temperature.
Comparator 58 then uses the measured electrical resistance of catalyst 22 to determine the concentration of the reactive gas in the gas stream.
As illustrated in Figure 1 a generator 96 can be provided for converting all or a predetermined portion of a specific gas in the gas mixture to an associated reactive gas. In this way, apparatus 10 could be used to measure the temperature of a non-reactive gas by measuring the concentration of a corresponding reactive gas. For example, apparatus 10 could be used to measure the concentration of oxygen in a gas stream by converting the oxygen (or a known portion of it) to ozone and then measuring the electrical resistance of catalyst 22 when it is exposed to the ozone.
Generator 96 may be calibrated to display the electrical resistance of catalyst 22, the concentration of the reactive gas (e.g. ozone) in the flow stream or preferably the concentration of the specific gas (e.g.
oxygen). For example, a generator 96 may convert a known percentage of oxygen in an air flow stream to ozone. Using this information and the predetermined relationship between the electrical resistance of catalyst 22 and the concentration of the reactive gas at various temperatures, display 60 may display the concentration of the specific gas within the gas mixture fed to generator 96.
It can be appreciated that a generator 96 as provided in Figure 1 can also be provided to the embodiments illustrated in Figures 2 or 3, or other alternatives, as would be known to those skilled in the art.
It will also be appreciated that the reactive gas could be an oxide of nitrogen and the display 60 could be a read out of the concentration of NOx in the stream (in the embodiments of Figures 2 or 3) or of nitrogen (in the embodiment of Figure 1).
It can be appreciated that variations to this invention would be readily apparent to those skilled in the art, and this invention is intended to include those alternatives. For example, in an alternate embodiment, two tubes 24 may be provided, only one of which contains catalyst 22. The gas stream may pass sequentially or in parallel through the two tubes.
Claims (34)
1. A method of measuring the concentration of a reactive gas in a gas mixture comprising the steps of:
(a) exposing at least a portion of the gas mixture to a catalyst;
(b) measuring the electrical resistance of the catalyst upon exposure to the reactive gas; and, (c) using the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture.
(a) exposing at least a portion of the gas mixture to a catalyst;
(b) measuring the electrical resistance of the catalyst upon exposure to the reactive gas; and, (c) using the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture.
2. A method according to claim 1 further comprising the step of correcting the measurement for the initial temperature of the reactive gas prior to the exposure of the reactive gas to the catalyst.
3. A method according to claim 2 wherein the measurement is corrected by establishing a value representing the initial temperature of the gas mixture containing the reactive gas and step (c) comprises using the value and the electrical resistance of the catalyst upon exposure to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture.
4. A method according to claim 3 wherein the value is the initial temperature of the gas mixture and step (c) comprises using the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture.
5. A method according to claim 3 wherein the value is the initial temperature of a reference gas and step (c) comprises using the initial temperature and the electrical resistance of the catalyst upon exposure to the reactive gas to obtain a measurement of the concentration of the reactive gas in the gas mixture.
6. A method according to claim 5 wherein the reference gas is at substantially the same temperature as the reactive gas.
7. A method according to claim 6 further comprising the step of alternately directing at least a portion of the reference gas and at least a portion of the gas mixture containing the reactive gas to the catalyst to sequentially obtain the value and the electrical resistance of the catalyst after exposure to the reactive gas.
8. A method according to claim 3 further comprising the step of using the catalyst to establish the value.
9. A method according to claim 3 further comprising the step of using a temperature sensor to establish the value.
10. A method according to claim 3 further comprising the step of using a second catalyst to establish the value.
11. A method according to claim 5 further comprising the step of using the catalyst to establish the value.
12. A method according to claim 1 further comprising the step of first adjusting the temperature of the gas mixture to a predetermined temperature.
13. A method according to claim 2 further comprising the step of adjusting the temperature of the gas mixture to a predetermined temperature to obtain the initial temperature.
14. A method according to claim 1 further comprising the step of providing a readout of the concentration of the reactive gas within the gas mixture.
15. A method according to claim 1 wherein the method further comprises first converting a specific gas in a gas stream to produce the reactive gas.
16. An apparatus for measuring the concentration of a reactive gas in a gas mixture comprising:
(a) a catalyst positioned in an air flow path of the gas mixture containing the reactive gas; and, (b) an electrical circuit for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas whereby the resistance of the catalyst upon exposure to the reactive gas is used to determine the concentration of the reactive gas in the gas mixture.
(a) a catalyst positioned in an air flow path of the gas mixture containing the reactive gas; and, (b) an electrical circuit for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas whereby the resistance of the catalyst upon exposure to the reactive gas is used to determine the concentration of the reactive gas in the gas mixture.
17. An apparatus according to claim 16 further comprising a readout calibrated to represent the concentration of the reactive gas within the gas mixture.
18. An apparatus according to claim 16 further comprising a generator positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
19. An apparatus according to claim 16 further comprising a station to establish a first value representing the initial temperature of the gas mixture and a comparator linked to the station to receive and compare the first value with the resistance of the catalyst upon exposure to the reactive gas to produce a second value that represents concentration of the reactive gas.
20. An apparatus according to claim 16 further comprising a station to establish a first value representing the initial temperature of the gas mixture and a comparator containing, for various temperatures, predetermined values representing the relationship between the electrical resistance of the catalyst upon exposure to various concentrations of the reactive gas, the comparator linked to the station and the catalyst to produce a signal representative of the concentration of the reactive gas.
21. An apparatus according to claim 16 further comprising a temperature adjusting member to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
22. An apparatus according to claim 16 further comprising a conduit for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to establish a first value and a comparator to compare the first value with the electrical resistance of the catalyst upon exposure to the reactive gas to produce a value that represents concentration of the reactive gas.
23. An apparatus according to claim 22 further comprising a valve to alternately direct the reference sample of the gas mixture containing no reactive gas and the gas mixture to the catalyst.
24. An apparatus according to claim 22 wherein the reference sample is at substantially the same temperature as the gas mixture containing the reactive gas.
25. An apparatus according to claim 16 further comprising a temperature sensor positioned upstream from the catalyst to measure the initial temperature of the reactive gas.
26. An apparatus according to claim 16 wherein the catalyst comprises a self supporting member which is positioned in the air flow path.
27. An apparatus for measuring the concentration of a reactive gas in a gas mixture comprising:
(a) a catalyst positioned in an air flow path of the gas mixture containing the reactive gas; and, (b) means for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas and to produce a signal representative of the concentration of the reactive gas in the gas mixture.
(a) a catalyst positioned in an air flow path of the gas mixture containing the reactive gas; and, (b) means for measuring the electrical resistance of the catalyst due to the exposure of the catalyst to the reactive gas and to produce a signal representative of the concentration of the reactive gas in the gas mixture.
28. An apparatus according to claim 27 further comprising means positioned upstream of the catalyst for converting at least a portion of a specific gas within the gas mixture to the reactive gas.
29. An apparatus according to claim 27 further comprising means to measure the initial temperature of the gas mixture and means for correcting the signal for the initial temperature the gas mixture.
30. An apparatus according to claim 27 further comprising means to adjust the temperature of the gas mixture to a fixed predetermined value prior to exposing the catalyst to the reactive gas.
31. An apparatus according to claim 27 further comprising means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain a first measurement and means for correcting the signal for the first measurement.
32. An apparatus according to claim 27 further comprising means for providing a reference sample of a gas mixture containing no reactive gas to the catalyst to obtain the temperature of the reference gas and means for correcting the signal for the temperature of the reference gas.
33. An apparatus according to claim 32 further comprising means for providing the reference sample at substantially the same temperature as the gas mixture containing the reactive gas.
34. An apparatus according to claim 27 wherein the catalyst comprises a self supporting member which is positioned in the air flow path.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US37628099A | 1999-08-18 | 1999-08-18 | |
| US09/376,280 | 1999-08-18 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2315556A1 true CA2315556A1 (en) | 2001-02-18 |
Family
ID=23484366
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2315556 Abandoned CA2315556A1 (en) | 1999-08-18 | 2000-08-09 | Method and apparatus for measuring the concentration of a gas |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2315556A1 (en) |
-
2000
- 2000-08-09 CA CA 2315556 patent/CA2315556A1/en not_active Abandoned
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