JP2005214677A - Gas sensor and hydrogen concentration detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized sensor capable of detecting gas and temperature by using integrally a thermocouple and a gas reaction body (a catalyst material and either of an electrochemical device and a surface acoustic wave device of its application). <P>SOLUTION: This gas sensor is constituted of a complex element means by a conductor bonding point on the temperature measuring junction side of the thermocouple and the gas reaction body; a detachment/attachment means for storing the complex element means in a detachment/attachment vessel; and an electronic control means by an electronic control part comprising a Thompson effect control system, a Seebeck effect control system or the like including a power source for controlling the complex element means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an apparatus for detecting a gas concentration by applying a thermocouple effect of a thermocouple and a function of a gas reactant, and particularly enables downsizing, cost reduction, use in an extreme environment, etc. of a gas sensor. Is.

In the field of gas sensors, particularly for hydrogen sensors, early practical application of fuel cells is desired along with measures to reduce global warming effect gas. For hydrogen sensors that are indispensable for these, Document 1 (Patent Publication No. 8-128992), Document 2 (Patent Publication 2002-535651), Document 3 (Patent Publication 2002-193861), and the like.

Such conventional methods include a hydrogen interaction metal film method, an ion detection method, a proton conductor method, etc., and the apparatus is large, and members for temperature measurement and control are separately required. Then there are problems such as high costs.

In addition, gas sensors using surface acoustic wave (SAW) devices are susceptible to the heat and pressure of the measurement environment, and thus have problems in use in extreme environments and correction control of measurement values.

The present invention makes it possible to reduce the size of the apparatus, reduce the price, and cope with extreme environments, which are problems of the prior art. Another object of the present invention is to combine the functions of gas concentration detection and temperature detection.

The present invention relates to a composite element means using a conductor junction on the temperature measuring contact side of a thermocouple and a gas reactant, a detaching / attaching means in which the composite element means is housed in a detachable attachment container, and a power source for controlling the composite element means. The main feature is that it is composed of electronic control means by an electronic control unit including a Thomson effect control system and a Seebeck effect control system.

In the case of using a hydrogen storage alloy as the catalyst material, the gas reactant of the composite element means in the hydrogen gas detection is a polymer, metal, oxide, carbide, etc. in the hydrogen storage alloy powder mounted around the conductor junction of the thermocouple By applying a thin film using, the poisoning phenomenon of the hydrogen storage alloy can be avoided.

The detaching / attaching means can detach / attach the element part by storing the element part of the composite element means in the container and separating it from the conductor part.

The Thomson effect control system can easily control the temperature of the gas reactant by applying a direct current to the conductor using the Thomson effect of the thermoelectric effect to heat or cool the conductor junction.

The Seebeck effect control system can detect the measurement environment temperature and the calorific value of the gas reactant from the thermoelectromotive force due to the temperature difference between the conductor junction and the reference contact using the Seebeck effect of the thermoelectric effect.

The electronic control unit is operated by the electronic control unit based on values preset in the electronic control unit, temperature control of the Thomson effect control system, values measured by the Seebeck effect control system, values detected by the gas reactant, etc. And by controlling it, gas concentration and temperature can be detected.

In addition, gas and temperature can be detected by combining the catalytic element and any of the gas reactants of the electrochemical device or surface acoustic wave (SAW) device of the application with the conductor junction of the thermocouple to integrate the element. It has a function and can downsize the sensor.

Referring to the embodiment of FIG. 1, a gas sensor for detecting hydrogen gas using a catalyst material for the gas reactant 3, which is a conductor junction 2 of a thermocouple in which conductor ends of two kinds of metal wires are joined. As a gas reactant 3, a hydrogen storage alloy powder of a catalyst material is fixed around the gas sensor 1, and a gas sensor 1 is formed that is housed in the release / detachment container 4.

Further, the detachable container 4 in which the gas sensor 1 is accommodated is inserted into the socket 5, and the two kinds of conductors 8 joined to the conductor end of the gas sensor 1 in the socket 5 are Thomson effect control systems including a power source 15. 10 and the Seebeck effect control system 12 and the like are connected to an electronic control unit 20 to constitute the whole.

The thermocouple conductor material is widely used in general industrial applications. For example, chromel: alumel, iron: constantan, copper: constantan, etc. are joined together, and the thermocouple wire material is particularly limited. Not what you want.

In addition, the conductor 8 is a metal pipe that incorporates a thermocouple conductor through an insulating tube, or a tube that contains a thermocouple conductor that is filled with magnesium oxide and insulated. Generally known.

In the room temperature / normal pressure region shown in FIG. 2, the release / detachment container 4 is provided with a plurality of fine holes through which hydrogen molecules can flow on the plate surface of the injection-molded container made of a plastic material. The sensor 1 is housed and integrally formed.

Further, the release / advancement container 4 is made of a metal material for the heat and pressure resistance shown in FIG. 3, and the portion that houses the gas sensor 1 allows hydrogen gas molecules to pass through the plate surface of the container. A container formed with a plurality of fine holes and more preferably made of a ceramic material is also functional.

As the hydrogen storage alloy for the catalyst material, for example, in addition to metals such as Cu, Ca, La, Mg, Ni, and Ti, LaNi and MgTi alloys of eutectic mixture (eutectic) are known. In particular, the type of the catalyst material and the production method are not limited.

This hydrogen storage alloy powder coating is applied to the powder in which hydrogen is stored in the hydrogen storage alloy and the particle size is adjusted to about 20μ by passing through an initial pulverization process, in addition to wet plating, CVD, PVD and other discharges. It is manufactured by applying a thin film with a metal such as Cu, Ca, La, Mg, Ni, Ti, polymer, oxide, carbide, etc. using the formula.

In addition, hydrogen storage alloys can be used over a wide range of -100 ° C to 500 ° C, but the equilibrium dissociation pressure characteristics are different for each alloy material. An occlusion alloy material is selected and used.

The mounting method of the hydrogen storage alloy powder is to mix the alloy powder coated with polymer, metal, oxide, carbide, etc. and the metal powder as the heat conductor according to the environmental conditions to be used. 2 is pressed and solidified using a mold around 2 or a paste obtained by mixing an alloy powder and a polymer adhesive material such as silicon rubber is applied around the conductor junction 2 of the thermocouple and then solidified by heating and mounted. .

In such a gas sensor, when the hydrogen storage alloy powder is mixed with a film or a polymer adhesive, the hydrogen is selected and permeated, so that the normal hydrogen storage alloy using carbon dioxide, oxygen, nitrogen, etc. This is convenient because it can be avoided from the poisoning phenomenon that is said to deteriorate the quality of the material.

The electronic control unit 20 includes a Thomson effect control system 10 including a power source 15, a Seebeck effect control system 12, and the like. In the electronic control unit 20 and the socket 5 in contact with the conductor end of the gas sensor 1 through the conductor 8. Are connected and can be energized.

The Thomson effect control system 10 switches the direction of the direct current from the power supply 15 to change the temperature of the temperature compensation circuit side of the Seebeck effect control system in the electronic control unit 20 and the conductor junction 2 on the temperature measuring contact side, which is called the Thomson effect. By appropriately using the action of heat generation or heat absorption from the energy gap with the reference contact, the hydrogen storage alloy of the catalyst material to be mounted is heated or cooled to control hydrogen release or hydrogen storage of the hydrogen storage alloy.

Since the thermoelectric effect in this metal wire is extremely small compared to a semiconductor or the like, an electric heater or a Peltier element can be used in combination when the amount of hydrogen storage alloy increases or the amount of heat becomes insufficient.

Further, the Seebeck effect control system 12 generates heat due to the hydrogenation reaction when the hydrogen storage alloy of the gas sensor 1 generates a hydride inside the hydrogen storage alloy by dissociating surrounding hydrogen molecules into hydrogen atoms by the catalytic action. A temperature difference occurs between the conductor junction 2 on the temperature measuring contact side of the received gas sensor 1 and the reference contact on the temperature compensation circuit side of the Seebeck effect control system in the electronic control unit 20, and a potential difference phenomenon called the Seebeck effect. The thermoelectromotive force is measured.

In addition, although not shown in the drawings, an electrochemical device using a catalyst material as a diffusion catalyst layer in a catalyst material is an electrochemical device in which a diffusion catalyst layer is provided on the outer surface of a proton conducting membrane (body) having electrode layers on both sides. The conductor junction points of the thermocouple are joined or inserted to be integrated, and housed in a release / receptacle container, and the thermocouple and the lead wires of the electrochemical device are connected to the electronic control unit via the attach / detach container.

In addition, in a cylindrical electrochemical device, functional membranes such as a diffusion catalyst layer, an electrode layer, and a proton conducting membrane (body) are provided on the outer peripheral surface of the thermocouple conductor junction, and are integrated and accommodated in a release / adsorption container. The conductors of the thermocouple and the electrochemical device are connected to the electronic control unit via the release / attachment container.

The catalyst material of the functional membrane that forms the diffusion catalyst layer of this electrochemical device is not a known material and is generally not specified, and generally has a catalytic function such as metal or alloy, oxide, carbon-containing carbide, enzyme, etc. It is a powder of any substance, and the powder is uniformly dispersed and supported as fine particles by a method such as sputtering using a metal or alloy, oxide, carbide containing carbon, polymer, or CVD, In addition to using a PVD discharge type or the like, it is used after being coated with a solvent.

In addition, in a gas sensor using a surface acoustic wave (SAW) device, a diffusion catalyst layer made of an electrode and a catalyst material is formed on the surface of a sphere or a face using a method such as sputtering, CVD, PVD, and the like. A conductor junction of a thermocouple is joined or inserted into and integrated with the reactant, and is accommodated in a detachable container, and the thermocouple and the surface acoustic wave device conductor are connected to the electronic control unit via the detachable container.

In the case of a gas sensor in which such a gas reactant (electrochemical device, surface acoustic wave device) 3 and a thermocouple conductor junction are combined, the gas reactant 3 itself measures the gas concentration and sends the data to the controller. The thermocouple outputs and improves the detection accuracy of the gas sensor by measuring the temperature using the Seebeck effect and controlling the temperature of the measurement environment using the Thomson effect.

Further, in such a gas reactant (electrochemical device, surface acoustic wave device) 3, it is possible to cope with various types of gas detection by appropriately selecting and using a catalyst material. The sensor can be downsized.

As shown in the fluctuation graph for each hydrogen concentration in FIG. 4, the hydrogen storage alloy of a type having a small hysteresis has an equilibrium dissociation pressure characteristic in which the reversible reaction heat quantity is equal and the hydrogen pressure and temperature have a constant relationship. A hydrogen concentration detection method using a hydrogen storage alloy as a catalyst material in the body and utilizing the hydrogenation function and the thermoelectric effect of a thermocouple will be described.

Measurement environment standards (mode data) can be set basically at room temperature and normal pressure environments by measuring the environmental temperature based on the potential difference of the Seebeck effect of the thermocouple before measurement to determine the zero point of the measurement environment standard. Thus, the denominator data and the preliminary data are recorded in the storage device of the electronic control unit.

In this case, in a special environment where the measured environmental pressure is other than normal pressure, especially in a special environment where the pressure fluctuates, the storage device of the electronic control unit is used as data for measuring the environmental pressure using a pressure sensor and determining the zero point of the measured environmental standard. It is necessary to record in advance.

For this reason, the type of hydrogen storage alloy suitable for the measurement environment is determined in advance, taking into account the equilibrium dissociation pressure characteristics, and the maximum heat (denominator data) and minimum as the measurement environment standard (mode data) for each assumed pressure stage. The amount of heat (preliminary data) is measured and recorded in the storage device of the electronic control unit.

The maximum calorific value (denominator data) is the hydrogen detection denominator data for the temperature tracking and time measurement of the hydrogenation heat generation of the hydrogen storage alloy from P1 to P4 of the B graph when the hydrogen concentration is 100%. It records in the memory | storage device of an electronic control part. Note that P1 to P5 up to the temperature H2 level are measurement points for security (for early detection of risk).

The minimum amount of heat (preliminary data) is the amount of heat that is dissipated mainly by components such as hydrogen storage alloys and thermocouples, and the hydrogenation heat generation of the hydrogen storage alloys installed from P1 to P2 in the A graph when the hydrogen concentration is 0%. Temperature tracking and time are measured and recorded in the storage device of the electronic control unit as minimum heat quantity data. Note that P1 to P3 up to the temperature H2 level are measurement points for security (for early detection of risk).

In the procedure for detecting the hydrogen concentration, first, the electronic control unit selects a suitable measurement environment standard (mode data) from the temperature and pressure information and recognizes the zero point of the measurement environment standard.

Next, in order to completely release the hydrogen of the attached hydrogen storage alloy, the conductor junction on the temperature measuring contact side of the direct current and thermocouple is caused to generate heat by the Thomson effect, and the temperature of the hydrogen storage alloy is raised to the temperature H3 level or higher. After completing the hydrogen release, stop the direct current and let the temperature drop naturally.

Next, as the measurement of calorie (data for molecules), the temperature tracking and time of the hydrogenation exotherm of the hydrogen storage alloy attached from P1 to P6 of the C graph are measured, and the hydrogen detection molecules are stored in the storage device of the electronic control unit. Sent as data for storage. Note that P1 to P7 up to the temperature H2 level are measurement points for security (for early detection of risk).

The electronic control unit that has received the measured calorific value (numerator data) uses the value obtained by subtracting the minimum calorific value (preliminary data) from the maximum calorific value (denominator data) of the selected measurement environment standard (mode data) as the denominator. Data) is calculated by subtracting the minimum amount of heat (preliminary data) from the numerator, and the hydrogen concentration is calculated and detected.

In addition, when hydrogen explosion-proof detection is intended, especially when hydrogen leaks such as hydrogen-related facilities and secondary batteries are overcharged, calorific value is measured from temperature levels H3 to H2 (risk level). By using (for early detection), the measurement time can be shortened and explosion prevention can be avoided, and inexpensive microcomputer control is facilitated by minimizing the amount of data set in advance.

Although the present invention has been described, the present invention is not limited to the above embodiment, and can be improved or modified within the scope of the purpose of the improvement or the idea of the present invention.

  As described above, when the gas sensor is configured, the gas sensor can be miniaturized, used in an extreme environment, and reduced in price. In particular, in a small device, there is an advantage that it is easy to use.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole schematic diagram of one Example of this invention, Comprising: The system outline | summary of the gas sensor and electronic control is shown. 1 shows an embodiment of the present invention, and mainly shows a cross-sectional structure of a gas sensor 1 in a release / attachment container 4 for normal temperature and normal pressure regions. 1 shows an embodiment of the present invention, and mainly shows a cross-sectional structure of a gas sensor 1 in a heat-resistant / pressure-resistant release / attachment container 4. FIG. 3 shows the temperature tracking of the hydrogenation reaction heat measured by the gas sensor 1 of the present invention and the fluctuation of each hydrogen concentration with respect to time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas sensor 2 Conductor junction 3 Gas reactant 4 Detachment receptacle 5 Socket 8 Conductor 10 Thomson effect control system 12 Seebeck effect control system 15 Power supply 20 Electronic control part

Claims (5)

Composite element means by a conductor junction on the temperature measuring contact side of the thermocouple and a gas reactant,
Detachment / attachment means for accommodating the composite element means in a release / removal container;
A gas sensor comprising: a Thomson effect control system including a power source for controlling the composite element means; and an electronic control means by an electronic control unit comprising a Seebeck effect control system. 2. The gas sensor according to claim 1, wherein the gas reactant is any one of the following items 1 to 4 and constitutes a gas detection element.
1. It is a catalyst material and must be attached around the conductor junction of the thermocouple.
2. It is an electrochemical device in which a diffusion catalyst layer made of a catalyst material is formed on the outer surface of a proton conducting membrane (body) having electrode layers on both sides, and a conductor junction point of a thermocouple is joined or inserted.
3. A cylindrical electrochemical device in which a diffusion catalyst layer made of a catalyst material, an electrode layer, and a proton conductive membrane (body) are formed on the outer periphery of the conductor junction of the thermocouple.
4). It is a spherical or planar surface acoustic wave (SAW) device, and has a thermocouple conductor junction joined or inserted. The catalyst material is a powder of any substance having a catalytic function such as a metal or alloy, oxide, carbon-containing carbide, enzyme, etc., and the powder is any of metal, alloy, oxide, carbide, or polymer. 3. The gas sensor according to claim 1, wherein the gas sensor is supported as a fine particle by using a material or is subjected to a coating treatment. 4. The gas sensor according to claim 1, 2 or 3, wherein the conductor junction and the gas reactant are integrally stored in the container, and the element portion is detached and attached. In order to determine the zero point of the measurement environment standard by measuring the environmental pressure with the environmental temperature and pressure sensor based on the potential difference of the Seebeck effect of the thermocouple, the type of hydrogen storage alloy that suits the measurement environment is determined in advance. As the measurement environment standard (mode data) for each assumed pressure stage, the maximum heat value (denominator data) at a hydrogen concentration of 100% and the minimum heat value (preliminary data) at a hydrogen concentration of 0% are kept at a constant temperature. The temperature tracking and time of the hydrogenation exotherm of the hydrogen storage alloy attached to is measured, recorded in the storage device of the electronic control unit, and set.
In the hydrogen concentration detection procedure, first, the electronic control unit selects a suitable measurement environment standard (mode data) from the temperature and pressure information, and recognizes zero point of the measurement environment standard.
Next, in order to completely release the hydrogen of the attached hydrogen storage alloy, the conductor junction point on the temperature measuring contact side of the direct current and thermocouple is caused to generate heat by the Thomson effect, and the temperature of the hydrogen storage alloy is raised above a certain temperature. After completing the hydrogen release, the direct current is stopped and the temperature drops naturally.
Next, as measurement of calorific value (molecular data), the temperature tracking and time of the hydrogenation exotherm of the hydrogen storage alloy mounted at a fixed temperature is measured and sent to the storage device of the electronic control unit as molecular data for hydrogen detection. Remember.
Next, the electronic control unit that has received the measured calorific value (numerical data) uses the value obtained by subtracting the minimum calorific value (preliminary data) from the maximum calorific value (denominator data) of the selected measurement environment standard (mode data) as the measured calorific value. A hydrogen concentration detection method in which a value obtained by subtracting the minimum calorific value (preliminary data) from (molecule data) is used as a numerator to calculate and detect hydrogen concentration.

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