JP6679859B2 - Gas detector - Google Patents

Description

  The present invention relates to a low power consumption type gas detection device.

Gas detectors are generally used for gas leak alarms and the like. The gas sensor used in this gas detection device is a device that is sensitive to a specific gas, for example, a reducing gas such as CO, CH ₄ , C ₃ H ₈ , and CH ₃ OH, and has high sensitivity and high selectivity. High responsiveness, high reliability, and low power consumption are essential.

  By the way, gas leak alarms widely used for home use include those for the purpose of detecting combustible gas for city gas and propane gas, those for the purpose of detecting incomplete combustion gas of combustion equipment, Alternatively, there is a device having both of these functions, but the diffusion rate is not so high due to problems of cost and installability. One of the installation problems is that a 100V AC power source is used, and therefore a power source is required around the gas leak alarm. In addition, there is a problem that it cannot be used in an emergency such as a power failure. Therefore, from the viewpoint of improving the diffusion rate of the gas leak alarm device, it is desired to improve the installability, and more specifically, to make the gas leak alarm device battery-less and cordless.

Low power consumption is the most important factor in realizing battery operation. However, when detecting the CH _4, C ₃ H _8, etc. in the gas sensor of the catalytic combustion type, semiconductor type, it is necessary to detect by heating the gas sensing portion to a high temperature of 400 ° C. to 500 ° C.. In order to heat to a high temperature with low power consumption, an intermittent operation is performed in which a gas sensor having a highly adiabatic / low heat capacity structure such as a diaphragm structure is heated according to a detection cycle by using a microfabrication process.

  Now, for such a gas sensor, temperature control is performed to switch the temperature in order to remove a substance that affects gas detection. As a prior art related to an apparatus in which such temperature control is performed, for example, one described in Patent Document 1 (Japanese Patent No. 4450773) is known. In the thin-film gas sensor of Patent Document 1, temperature control is performed to drive the heater layer so as to remove water vapor gas.

  Further, as another prior art related to an apparatus in which such temperature control is performed, for example, one described in Patent Document 2 (JP 2012-172973 A) is known. In the flammable gas detection device of Patent Document 2, temperature control for driving the heater layer is performed so as to remove the poisoning gas.

Japanese Patent No. 4450773 (paragraphs [0044], [0059], [0060], FIGS. 1, 5 and 6) Japanese Unexamined Patent Application Publication No. 2012-172973 (paragraph [0017], FIGS. 3 and 4)

  Gas components in the environment include organic solvents contained in paints and the like, and fuel system gases such as kerosene. For example, octane and tetrahydrofuran. Octane has a combustion heat of 5501 kJ / mol (48.3 kJ / g), and tetrahydrofuran has a combustion heat of 2530 kJ / mol (35.1 kJ / g), which is extremely high. It has been found that such a gas component having an excessively high heat of combustion (hereinafter referred to as overcombustible gas in the present specification) may affect the gas detection unit and is a substance that affects gas detection. Was done.

The reason for this will be described. The thin film gas sensor is provided with a gas selective combustion layer as shown in FIG. 7 of Patent Document 1. This gas selective combustion layer is generally formed of γ-Al ₂ O ₃ or the like, which is a porous body, in order to allow detection target gases such as CH ₄ , C ₃ H ₈ , and CO to pass through and diffuse. Further, in order to efficiently burn and remove the interfering gas that is not the detection target gas, a noble metal catalyst (for example, Pt or Pd) is often carried.

Further, the gas sensing layer made of SnO ₂ also employs a porous body or a columnar structure to increase the specific surface area and enhance the detection sensitivity. By adopting these configurations, the contact area with the gas to be detected is increased and the detection sensitivity is improved.

  In such a porous body or columnar structure, a large number of pores having an opening diameter of several nm to several μm exist. In the pores, water, interfering gas, and gas to be detected tend to be adsorbed by capillary condensation represented by the following formula.

  Now, a large amount of overcombustible gas existing in the environment may be adsorbed to the fine pores of the gas sensing layer or the gas selective combustion layer of the porous body as described above by capillary condensation. In this case, when the heater is turned on (energized) to heat it to a high temperature of 400 ° C. to 500 ° C., the overcombustible gas adsorbed in the fine pores burns, and the high combustion heat causes the gas sensing layer and the gas selective combustion layer of the thin film gas sensor. It is conceivable that the temperature rises above the gas detection temperature and that normal detection characteristics cannot be obtained due to thermal deterioration.

  It has been found that there is a problem to prevent excessive temperature rise of the gas sensing layer and the gas selective combustion layer of the thin film gas sensor even in the environment where such overcombustible gas exists. At this time, it was necessary to prevent excessive temperature rise with low power consumption in order to realize battery driving, but no attention was paid to the problem of performing temperature control to prevent excessive temperature rise.

Patent Document 1 discloses a prior art that realizes low power consumption driving while performing both moisture removal and gas detection, but does not consider prevention of excessive temperature rise.
In addition, Patent Document 2 discloses a prior art that realizes low power consumption driving while performing both removal of poisoning gas and gas detection, but also does not consider prevention of excessive temperature rise.

  Therefore, the present invention is intended to solve the above problems, and an object thereof is to provide a gas detection device that eliminates the influence of excessive temperature rise, enhances reliability, and realizes highly accurate detection. is there.

In order to solve the above problems, the invention according to claim 1 is a gas sensing layer formed of a porous body or a columnar structure for sensing a gas to be detected, and a gas formed of a porous body for burning and removing an interfering gas. selection combustion layer, and a gas detector having a heater layer for heating said gas selective combustion layer and the gas sensing layer,
A heater layer drive unit that energizes and drives the heater layer by a normal drive pattern for detecting the detection target gas or a drive pattern for preventing excessive temperature rise of the gas detection unit,
An overheating detection unit that detects an overheating of the gas sensing layer or the gas selective combustion layer based on the temperature of the heater layer,
A drive switching unit that changes the drive pattern of the heater layer drive unit from the normal drive pattern to the drive pattern against excessive temperature rise when the excessive temperature rise detection unit detects an excessive temperature rise;
Equipped with
The drive pattern against excessive temperature rise is a pattern in which the temperature of the gas detection unit is lowered to vaporize or combust and remove the overcombustible gas.

請 Motomeko according to a second aspect of the present invention, in the gas detection apparatus according to claim 1, wherein the overheat countermeasures driving pattern, the a temperature lower than the detected temperature of the detection target gas, and the over-combustible gases removed It is characterized in that the heater layer is energized for a predetermined overcombustible gas removal time at a given overcombustible gas removal temperature .

請 Motomeko according to third invention, in the gas detection apparatus according to claim 1, wherein the overheat countermeasures driving pattern, pause the current driving of the heater layer, lower than the detected temperature of subsequent said detection target gas It is characterized in that the heater layer is energized for a predetermined overcombustible gas removal time at a temperature and at an overcombustible gas removal temperature at which the overcombustible gas is removed .

The invention according to 請 Motomeko 4, in the gas detection apparatus according to claim 2 or 3, wherein the excessive temperature rise measures driving patterns, the heater layer over the overcombustion gas removal time by repeated pulses having a predetermined pulse width Is a pattern for energizing and driving .

請 Motomeko according to 5 the invention is the gas detector according to claim 1, wherein the overheat countermeasures drive pattern is characterized by a pattern for stopping the energization driving of the heater layer.

請 Motomeko according to sixth invention, in the gas detection apparatus according to claim 1, wherein the overheat countermeasures driving pattern, the heater at a power closer to the temperature of the gas detector to the gas temperature detected by the detection target gas It is characterized in that it is a pattern in which the layers are electrically driven .

The invention according to 請 Motomeko 7, the gas detection apparatus according to any one of claims 1 to 6, wherein the overheat detecting section, a heater layer in measuring electric characteristics to obtain the electrical characteristic values of the heater layer and parts, and the heater layer temperature calculation unit for calculating a temperature of the heater layer on the basis of the electrical characteristic value, characterized in that it consists.

The invention according to claim 8 is a gas detection part having a gas sensing layer formed of a porous body or a columnar structure for sensing a gas to be sensed, and a heater layer for heating the gas sensing layer,
The heater layer has a normal drive pattern for detecting the detection target gas, an overcombustible gas removal pattern for removing the overcombustible gas at a temperature lower than the detection temperature of the detection target gas, and an excessive temperature rise of the gas detection unit. A heater layer drive section that is energized and driven by a drive pattern for preventing excessive temperature rise ,
An overheating detection unit that detects an overheating of the gas sensing layer based on the temperature of the heater layer,
The energization drive is performed by the normal drive pattern after the energization drive by the overcombustible gas removal pattern, and the heater layer drive unit is operated when the excessive temperature rise detection unit detects the excessive temperature rise in the normal drive pattern. A drive switching unit for changing the drive pattern of the normal drive pattern from the drive pattern against excessive temperature rise,
Equipped with
The excessive temperature rise measures driving pattern, the temperature of the gas sensing portion is lowered, and wherein the pattern der Rukoto to vaporize remove or burn off excessive combustible gases.

The invention according to claim 9 is the gas detection device according to claim 8, wherein the overcombustible gas removal pattern has a temperature lower than a detection temperature of the detection target gas, and the overcombustible gas is removed. The heater layer is energized for a predetermined overcombustible gas removal time at the overcombustible gas removal temperature .

According to a tenth aspect of the present invention, in the gas detection device according to the eighth aspect, the overburning gas removal pattern is energized to drive the heater layer for a predetermined overburning gas removal time by a repeating pulse having a predetermined pulse width. It is characterized in that it is a pattern.

The invention according to claim 11 is the gas detection device according to claim 9 or 10 , wherein the overcombustible gas removal pattern is a pattern in which the overcombustible gas removal time is lengthened over a predetermined initial period from the start of gas detection. Is characterized in that.

  According to the present invention, it is possible to provide a gas detection device that eliminates the influence of excessive temperature rise, enhances reliability, and realizes highly accurate detection.

It is a block block diagram of the gas detection apparatus of the 1st, 2nd, 3rd, and 4th forms for implementing this invention. It is sectional drawing of the gas sensor of the gas detection apparatus of the 1st, 2nd, 3rd, and 4th forms for implementing this invention. It is explanatory drawing of the heater layer drive pattern of a 1st form. It is a characteristic view which shows the heater layer resistance change of a gas sensor by the external heating in a high temperature furnace. It is an explanatory view of a drive pattern against excessive temperature rise of the heater layer at the time of detecting overcombustible gas. It is a characteristic view explaining the time change of the heater layer temperature before and behind exposure to an overcombustible gas (tetrahydrofuran). It is a characteristic view explaining the time change of the heater layer temperature at the time of removal of overcombustible gas. It is a characteristic view explaining the time change of the heater layer temperature at the time of driving a heater layer after removal of overcombustible gas. It is explanatory drawing of the heater layer drive pattern of a 2nd form. It is explanatory drawing of the heater layer drive pattern of 3rd form. It is a characteristic view explaining the time change of the heater layer temperature after the overburning gas (tetrahydrofuran) exposure and before and after the overburning countermeasure drive. It is a block block diagram of the gas detection apparatus of the 5th, 6th forms for implementing this invention. It is sectional drawing of the gas sensor of the gas detection apparatus of the 5th, 6th forms for implementing this invention. It is explanatory drawing of the normal drive pattern of the heater layer of 5th form. It is explanatory drawing of the normal drive pattern of the heater layer of 6th form. It is explanatory drawing of the normal drive pattern of the heater layer of the improved form of 5th, 6th, 7th, and 8th form. It is explanatory drawing of the gas sensor of the gas detection apparatus of 10th form for implementing this invention, FIG.17 (a) is a top view of a gas sensor, FIG.17 (b) is AA sectional drawing of a gas sensor, FIG. (C) is a BB sectional view of the gas sensor.

  Hereinafter, a gas detector 1 of a first embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1, the gas detection device 1 includes a gas sensor 10 and a drive control / signal processing unit 20. The drive control / signal processing unit 20 is a device that drives and controls the gas sensor 10 and receives a detection signal from the gas sensor 10 to detect the presence or absence of gas.

Next, details of the gas sensor 10 will be described.
The gas sensor 10 is a thin-film semiconductor type sensor configured as shown in the cross-sectional view of FIG. 2, and further includes a silicon substrate (hereinafter referred to as Si substrate) 11, a heat insulating support layer 12, a heater layer 13, The electrical insulation layer 14 and the gas detection unit 15 are provided. It should be noted that FIG. 2 merely shows the configuration of the thin-film semiconductor gas sensor conceptually in an easy-to-see manner, and the size and thickness of each part are not strict.

Subsequently, the configuration of each part will be described.
The Si substrate 11 is made of silicon (Si), and a through hole is formed at a position directly above the gas detection unit 15.

  The heat insulating support layer 12 is formed on the opening of the through hole to form a diaphragm, and is provided on the Si substrate 11.

Specifically, the heat insulating support layer 12 is formed by forming a three-layer structure of a thermally oxidized SiO ₂ layer 121, a CVD-Si ₃ N ₄ layer 122, and a CVD-SiO ₂ layer 123 on the upper side of the Si substrate 11. It has a diaphragm structure.

The thermally oxidized SiO ₂ layer 121 is formed as a heat insulating layer and has a function of preventing heat generated in the heater layer 13 from being conducted to the Si substrate 11 side and reducing the heat capacity. The thermally oxidized SiO ₂ layer 121 has a high resistance to plasma etching and facilitates formation of through holes in the Si substrate 11 by plasma etching, which will be described later.

The CVD-Si ₃ N ₄ layer 122 is formed on the upper side of the thermally oxidized SiO ₂ layer 121.
The CVD-SiO ₂ layer 123 improves the adhesion with the heater layer 13 and secures electrical insulation. The SiO ₂ layer formed by CVD (chemical vapor deposition) has a small internal stress.

  The heater layer 13 is formed of a thin-film Pt-W film or a Ni-Cr film, and is provided on the upper surface of the heat insulating support layer 12 substantially at the center. Also, a power supply line is formed. This power supply line is connected to the heater layer driving unit 22 as shown in FIGS. The heater layer driving unit 22 drives the heater layer 13 with a heater. Further, the heater layer 13 is electrically connected to a heater layer electric characteristic measuring section 23 which is a specific example of the heater layer temperature measuring section of the present invention, and the heater layer electric characteristic measuring section 23 has an electric resistance of the heater layer 13. To measure.

The electrically insulating layer 14 is a sputtered SiO ₂ layer that ensures electrical insulation, and is provided so as to cover the heat insulating support layer 12 and the heater layer 13. The electrical insulation layer 14 ensures electrical insulation between the heater layer 13 and the sensing layer electrode 152. In addition, the electrically insulating layer 14 improves the adhesion with the gas sensing layer 153 described later.

  The gas detection unit 15 is provided on the upper side of the electrical insulating layer 14, and includes a pair of bonding layers 151, a pair of sensing layer electrodes 152, a gas sensing layer 153, and a gas selective combustion layer 154.

  The bonding layers 151 are, for example, a Ta film (tantalum film) or a Ti film (titanium film), and are provided on the electrical insulating layer 14 in a left-right pair. The bonding layer 151 is interposed between the sensing layer electrode 152 and the electric insulating layer 14 to enhance the bonding strength.

  The sensing layer electrodes 152 are, for example, a Pt film (platinum film) or an Au film (gold film), and are provided as a pair of left and right electrodes so as to serve as sensing electrodes of the gas sensing layer 153.

The gas sensing layer 153 is an Sb-doped tin dioxide layer (hereinafter, SnO ₂ layer), and is formed on the electrically insulating layer 14 so as to pass the pair of sensing layer electrodes 152. Although the gas sensing layer 153 is described as the SnO ₂ layer in the present embodiment, in addition to SnO ₂ , a metal oxide such as In ₂ O ₃ , WO ₃ , ZnO, or TiO ₂ is a main component. It may be a thin film layer.

The gas selective combustion layer 154 is provided so as to cover the surfaces of the electrical insulating layer 14, the bonding layer 151, the pair of sensing layer electrodes 152, and the gas sensing layer 153. The gas selective combustion layer 154 is a sintered body supporting a noble metal catalyst such as palladium oxide (PdO), and is a catalyst-supporting Al ₂ O ₃ sintered material as described above.

Since Al ₂ O ₃ is a porous body, it increases the chance that the gas passing through the pores will come into contact with the noble metal catalyst. Then, the burning reaction of the reducing gas (interfering gas) having a stronger oxidizing activity than the gas to be detected is promoted, and the selectivity of the gas to be detected is increased. That is, the interfering gas can be oxidized and removed from the gas to be detected.

In addition to the Al ₂ O ₃ , the gas selective combustion layer 154 has Cr ₂ O ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , ZrO ₂ , SiO ₂ , or a metal oxide called zeolite as a main component. Is also good. Further, as the noble metal catalyst, platinum (Pt) or palladium (Pd) may be adopted in addition to palladium oxide (PdO).

  The gas detection unit 15 (specifically, the gas detection layer 153 via the detection layer electrode 152) is electrically connected to the gas detection signal processing unit 24, and the drive control / signal processing unit 20 is connected to the gas detection layer 153. Read the sensor resistance value of.

Such a gas sensor 10 adopts a diaphragm structure to have a structure of high heat insulation and low heat capacity. In the gas sensor 10, the heat capacity of each component of the sensing layer electrode 152, the gas sensing layer 153, the gas selective combustion layer 154, and the heater layer 13 is reduced by a technique such as MEMS (micro electro mechanical system). As a result, the temperature change to the gas detection temperature T ₁ becomes faster, and it becomes possible to detect the gas with a short pulse. Therefore, the power consumption is low.

Next, a method for manufacturing the gas sensor 10 and the gas detection device 1 of the present embodiment whose sectional structure is shown in FIG. 2 will be schematically described. First, a plate-shaped silicon wafer (not shown) is thermally oxidized on one side (or both front and back sides) by a thermal oxidation method to form a thermally oxidized SiO ₂ layer 121 which is a thermally oxidized SiO ₂ film.

Then, a CVD-Si ₃ N ₄ film serving as a support film is deposited on the upper surface on which the thermally-oxidized SiO ₂ layer 121 is formed by a plasma CVD method to form a CVD-Si ₃ N ₄ layer 122. Then, on the upper surface of the CVD-Si ₃ N ₄ layer 122, a CVD-SiO ₂ film serving as a heat insulating film is deposited by a plasma CVD method to form a CVD-SiO ₂ layer 123.

Further, a Pt—W film (or Ni—Cr film) is vapor-deposited on the upper surface of the CVD-SiO ₂ layer 123 by a sputtering method to form the heater layer 13. Then, a sputtered SiO ₂ film is vapor-deposited on the upper surfaces of the CVD-SiO ₂ layer 123 and the heater layer 13 by a sputtering method to form the electrical insulating layer 14 which is a sputtered SiO ₂ layer.

A pair of bonding layers 151 and a pair of sensing layer electrodes 152 are formed on the electrical insulating layer 14. The film formation is performed by an ordinary sputtering method using an RF magnetron sputtering device. The film forming conditions are the same for the bonding layer (Ta or Ti) 151 and the sensing layer electrode (Pt or Au) 152. Ar gas (argon gas) pressure is 1 Pa, substrate temperature is 300 ° C., RF power is 2 W / cm ² , and film thickness is The bonding layer 151 / the sensing layer electrode 152 = 500Å / 2000Å. The pair of sensing layer electrodes 152 are electrodes that extract an electric signal from the gas sensing layer 153.

While passing to the pair of sensing layer electrodes 152, a SnO ₂ film is vapor-deposited on the electric insulating layer 14 by a sputtering method to form a gas sensing layer 153. This film formation is performed by a reactive sputtering method using an RF magnetron sputtering device. SnO ₂ containing 0.1 wt% of Sb is used as the target. The film forming conditions are Ar + O ₂ gas pressure 2 Pa, substrate temperature 150 to 300 ° C., RF power 2 W / cm ² , and film thickness 400 nm. The gas sensing layer 153 is formed in a square shape with one side of about 50 μm in a plan view.

  Subsequently, the gas selective combustion layer 154 is formed. The gas selective combustion layer 154 forms a paste by adding the same weight of diethylene glycol monoethyl ether to γ-alumina (average particle diameter 2 to 3 μm) containing 7.0 wt% of PdO and further adding 5 to 20 wt% of silica sol binder. . Then, it is formed by screen printing with a thickness of about 30 μm. Thereafter, the film is baked at 500 ° C. for 12 hours. The gas selective combustion layer 154 has a diameter larger than that of the outer peripheral portion of the gas sensing layer 153 so as to fully cover the gas sensing layer 153. Alternatively, the gas selective combustion layer 154 may be formed on the upper surface of the gas sensing layer 153 so as to have the same size. The gas selective combustion layer 154 is preferably formed in a circular shape having a diameter of about 200 μm in a plan view.

  Finally, a fine processing process of removing silicon from the back surface of a silicon wafer (not shown) by etching is performed to form a Si substrate 11 having through holes. Finally, the gas sensor 10 having a diaphragm structure is obtained. The heater layer 13 is electrically connected to the heater layer driving unit 22 and the heater layer electric characteristic measuring unit 23, and the sensing layer electrode 152 is electrically connected to the gas detection signal processing unit 24. The method of manufacturing the gas sensor 10 is as described above.

  Next, the drive control / signal processing unit 20 will be described. As shown in FIG. 1, the drive control / signal processing unit 20 includes a central processing unit 21, a heater layer driving unit 22, a heater layer electric characteristic measuring unit 23, a gas detection signal processing unit 24, a storage unit 25, and an alarm display unit 26. , An alarm sound output unit 27, an external output unit 28, and a power supply unit 29.

  The central processing unit 21 is connected to the heater layer driving unit 22, the heater layer electric characteristic measuring unit 23, the gas detection signal processing unit 24, the storage unit 25, the alarm display unit 26, the alarm sound output unit 27, and the external output unit 28. . The central processing unit 21 is composed of a CPU such as a microcomputer and its peripherals, and has a heater layer driving unit 211, a city gas detecting unit 212, a CO gas detecting unit 213, a heater layer temperature calculating unit 214, and an excessive temperature rise detection. Each function of the means 215, the drive switching means 216, the correction means 217, the determination means 218, the display control means 219, and the output control means 220 is realized by hardware and software, and various controls and signal processing are performed.

  The heater layer drive unit 22 is a circuit unit that converts the electric power supplied from the power supply unit 29 into heater layer drive electric power for accurately detecting gas and drives the heater layer 13 by energization. The heater layer driving unit 22 is controlled by the heater layer driving unit 211 in the central processing unit 21.

For example, when the heater layer is driven, the heater layer is driven in the normal drive pattern as shown in FIG. In the normal drive pattern, the gas detection time (heater on time) t ₁ is 500 ms and the gas detection period t _d is 60 s, and the current is energized in a repeating pulse form. The details of these drives will be described in the detection process described later.

  The heater layer electric characteristic measuring unit 23 includes means for detecting electric characteristic values such as resistance and voltage of the heater layer 13, and sends a detection signal to the central processing unit 21. As will be described later, the heater layer temperature calculation means 214 of the central processing unit 21 measures the heater layer temperature substantially equal to the gas sensor temperature by a method described later based on the electrical characteristic value of the heater layer 13, mainly the resistance value of the heater layer 13. . When calculating the heater layer temperature, the storage unit 25 is accessed to acquire various data described later.

  The gas detection signal processing unit 24 is connected to the gas sensing layer 153 via the pair of sensing layer electrodes 152, and detects the sensor resistance value of the gas sensing layer 153 that senses the gas to be detected. Based on this sensor resistance value, the city gas detection means 212 and the CO gas detection means 213 in the central processing unit 21 detect the city gas and the CO gas and send them to the correction means 217 as sensor outputs. In addition to the city gas detecting means 212 and the CO gas detecting means 213, other means for detecting various gases can be adopted.

  Since the outputs from the heater layer electrical characteristic measuring unit 23 and the gas detection signal processing unit 24 are analog signals, the central processing unit 21 converts the analog signals into digital signals by an A / D conversion unit (see FIG. (Not shown).

  The storage unit 25 is connected to the central processing unit 21 to read and write various data. The storage unit 25 stores set values such as threshold values for issuing various alarms, correction values according to ambient temperature and ambient humidity acquired by an environment sensor (not shown), and states when the gas detection device 1 issues an alarm. Stores historical data such as data.

  In the central processing unit 21, the correction unit 217 calculates a correction value by using the temperature acquired by the heater layer temperature calculation unit 214 in the non-energized state as the ambient temperature, and outputs it to the sensor outputs of the city gas detection unit 212 and the CO gas detection unit 213. On the other hand, the correction is performed using this correction value, and the corrected sensor output is sent to the determination means 218. The determination unit 218 determines the presence or absence of the detection target gas based on the corrected sensor output. Further, for example, the correction may be performed based on the output from an environment sensor (not shown) (eg, thermometer, hygrometer, barometer, etc.). The correction can be appropriately selected. With such a correction, highly accurate gas detection is performed with the influence of the surrounding environment eliminated as much as possible.

  A method without correction may be adopted. In this case, the correction means 217 may be omitted and the determination means 218 may determine the sensor outputs of the city gas detection means 212 and the CO gas detection means 213.

  When the determination unit 218 of the central processing unit 21 determines that gas has been detected, it performs control to display an alarm on the alarm display unit 26 via the display control unit 219, and also outputs an alarm sound via the output control unit 220. The control is performed so as to output to the unit 27 and the external output unit 28.

  The alarm display unit 26 includes, for example, a display unit such as an LED, a lamp, and an LCD, and a driver for the display unit, and can display an alarm when an abnormality is detected. In the central processing unit 21, the display control unit 219, which receives the output of the determination unit 218, causes the alarm display unit 26 to perform control to display an alarm indicating the detected content that the abnormality has occurred due to the detection of city gas or CO gas. To do.

  The alarm sound output unit 27 is composed of, for example, a speaker and a driver thereof, and can output an alarm sound or a sound by a speaker or the like. In the central processing unit 21, the output control unit 220, which receives the output of the determination unit 218, outputs the alarm sound of the detection content indicating that the abnormality has occurred due to the detection of the city gas or CO gas by the alarm sound output unit. Perform on 27.

  The external output unit 28 is, for example, a contact unit or a communication unit, and can output an alarm to the outside. In the central processing unit 21, the output control unit 220 that receives the output of the determination unit 218 outputs the content of detection that city gas or CO gas is detected to be abnormal as an output signal of voltage or the like or a communication signal to the outside. The output to the external output unit 28 is controlled.

  The power supply unit 29 includes a central processing unit 21, a heater layer driving unit 22, a heater layer electric characteristic measuring unit 23, a gas detection signal processing unit 24, a storage unit 25, an alarm display unit 26, an alarm sound output unit 27, and an external output unit 28. Are connected by a circuit (not shown), and power is supplied to these. The power supply unit 29 is assumed to be a consumable battery such as a built-in dry battery or a rechargeable battery, but may be composed of a commercial power supply such as AC100V and a constant voltage unit. The overall configuration of the gas detection device 1 is as described above.

  Next, the gas detection operation of the gas detection device 1 will be described. The central processing unit 21 controls the entire gas detection device 1. As shown in FIG. 2, the drive signal from the heater layer drive unit 22 is input to the heater layer 13 of the gas sensor 10 through the conductive wire indicated by the thin wire to drive the heater layer.

The central processing unit 21 determines whether the gas sensing layer 153 or the gas selective combustion layer 154 is overheated. If the gas temperature is not overheated, the central processing unit 21 drives in the normal drive pattern as shown in FIG. However, when the excessive temperature rise occurs, the driving is performed according to the excessive temperature rise countermeasure drive pattern described later. The normal drive pattern of FIG. 3 is a pattern in which the gas detection is set as one unit and this one unit is repeatedly made to appear at the gas detection cycle t _d . In the second, third, and fourth modes, which will be described later, the driving is similarly performed using the excessive temperature rise countermeasure drive pattern.

  The determination of the presence or absence of excessive temperature rise will be described. First, in order to explain the principle of temperature detection, the relationship between temperature and heater layer resistance will be described. The gas sensor 10 having the structure shown in FIG. 2 was placed in a high temperature furnace to raise the temperature around the gas sensor 10 and the change in the heater layer resistance value of the heater layer 13 was measured. As shown by the change in the heater layer resistance value in FIG. 4, the heater layer resistance value changes substantially linearly with temperature in the temperature range of 0 to about 500 ° C. The heater layer resistance value increases as the ambient temperature increases, and the heater layer resistance value decreases as the ambient temperature decreases. This tendency was confirmed from a plurality of (8 in FIG. 4) samples.

  From such a tendency, the ambient temperature changes as the temperature of the gas sensing layer 153 and the gas selective combustion layer 154 changes, and therefore, the heater layer resistance value is also affected, in other words, the heater layer resistance value changes. It is assumed that the temperatures of the gas sensing layer 153 and the gas selective combustion layer 154 can be detected. By monitoring the heater layer resistance value, changes in the temperature of the gas sensing layer 153 and the gas selective combustion layer 154 can be grasped.

  Next, a series of operations at the time of gas detection will be described. First, a normal drive pattern when there is no overcombustible gas will be described. As described above, the overcombustible gas is a gas having an excessively high heat of combustion, such as octane (heat of combustion 5501 kJ / mol (48.3 kJ / g)) or tetrahydrofuran (heat of combustion 2530 kJ / mol ( 35.1 kJ / g)) and the like are applicable.

Although this normal drive pattern is used, the heater layer 13 performs repeated pulse drive of gas detection (on) and energization stop (off) as shown in FIG. 3, for example. In this gas detection, more specifically, the heater layer 13 is heated by energizing the heater layer 13 for a gas detection time t ₁ (for example, 500 ms) with electric power having a high gas detection temperature T ₁ (for example, 450 ° C.), and the gas detection layer 153 and the gas are detected. The temperature of the selective combustion layer 154 rises. In such a normal drive pattern, repetitive pulses appear at a predetermined gas detection period t _d (for example, 60 s).

Here, the gas selective combustion layer 154 at high temperature burns a reducing gas such as CO and H _{2 and} other miscellaneous gases, but allows a flammable gas such as CH ₄ and C ₃ H ₈ to pass through. Combustible gas reaches the gas sensing layer 153 of the high-temperature state by the diffusion in the gas selective combustion layer 154 reacts with the SnO ₂ gas sensitive layer 153, changing the sensor resistance of the SnO _2. This change in sensor resistance is detected for detecting the presence or absence of the particular city gas generated during gas leakage, such as gas equipment (CH _4, combustible gas such as C ₃ H _8). The sensor resistance value of the gas sensing layer 153 is measured by the gas sensing signal processing unit 24 by the pair of sensing layer electrodes 152 (High-Off method).

  It should be noted that in gas detection, another method may be adopted instead of the High-Off method. When incomplete combustion (CO) is detected, the temperature of the heater layer 13 is once raised to a high temperature (High 400 to 500 ° C.) for a fixed period of 50 to 500 ms, and the gas sensing layer 153 is cleaned. Then, the temperature is lowered to a low temperature (Low about 100 ° C.) to detect incomplete combustion (CO). This is known to increase CO sensitivity and gas selectivity (High-Low-Off method).

In addition, not only cleaning but also combustible gas detection such as CH ₄ and C ₃ H _{8 in the} High state, combined with detection of incomplete combustion gas such as CO in the Low state, combustible gas A gas sensor that can detect both combustion gas may be used.

Next, the gas detection of the combustible gas and / or the incomplete combustion gas by the normal drive pattern will be described.
The heater layer driving unit 211 of the central processing unit 21 shown in FIG. 1 functions as a unit for driving the heater layer driving unit 22 to heat and drive the heater layer 13 to reach the gas detection temperature, and gas detection is performed.

In parallel with the gas detection shown in FIG. 1, the heater layer temperature calculating means 214 of the central processing unit 21 functions as a means for calculating the heater layer temperature from the electric characteristic value detected by the heater layer electric characteristic measuring section 23. It is assumed that such calculation of the heater layer temperature is continuously repeated during the gas detection time t ₁ . For example, the heater layer temperature is output every 5 ms.

Next, how to calculate the heater layer temperature using the heater layer resistance value, which is a specific example of the electrical characteristic value, will be described.
As shown in FIG. 2, the heater layer electrical characteristic measuring unit 23 is configured to measure the heater layer resistance value from the heater layer 13 through a conducting wire indicated by a thin line, and has a shunt resistance. The resistance value of the shunt resistor is known in advance and is connected in series with the heater layer 13. Further, the circuit is configured so that the voltage across the heater layer 13 and the voltage across the shunt resistor can be measured.

During the gas detection, a predetermined voltage is applied to the heater layer 13 to reach the gas detection temperature T ₁ . In this state, the voltage across the heater layer 13 is measured, and at the same time, the voltage across the shunt resistor arranged in series is also measured. These voltage values at both ends are sent to the central processing unit 21 and are processed by the heater layer temperature calculation means 214.

  The heater layer temperature calculation means 214 calculates the current from the measured voltage value across the shunt resistance and the known shunt resistance value arranged in series. Then, the heater layer resistance value is calculated from this current and the read voltage across the heater layer 13. Then, using the calculated heater layer resistance value of the heater layer 13, the heater layer temperature calculation means 214 calculates the temperature T of the heater layer 13 from the following equation. In this way, the change in the heater layer temperature can be indirectly captured as the change in the heater layer resistance or the change in the heater layer voltage, the change in the heater shunt voltage, or the change in the heater current.

[Equation 2]
R / R ₀ = αT + 1
Here, T: heater layer temperature R: heater layer resistance value at temperature T R ₀ : heater layer resistance value at reference temperature (for example, reference temperature 0 ° C., etc.)
α: Temperature coefficient of resistance of heater layer

Here, the value of the heater layer resistance value R ₀ at the reference temperature is previously obtained by measurement. The value of the temperature coefficient of resistance α of the heater layer is a value determined for each sensor. It should be noted that since there is little variation between wafers on which thin film sensors are made, the same value may be given to thin film sensors that can be obtained from one wafer. Alternatively, when a plurality of wafers are flown in one lot, the same value may be given to the thin film sensors of the same lot.

The heater layer resistance value R ₀ and the resistance temperature coefficient α of the heater layer 13 at the reference temperature are stored in the storage unit 25, and the heater layer resistance value R at the heater layer temperature T is the heater layer electric characteristic measurement unit. 23, the temperature T of the heater layer 13 is calculated by the above equation 2. The temperature of the heater layer 13 is regarded as the temperature of the gas sensing layer 153 and the gas selective combustion layer 154.

The excessive temperature rise detection unit 215 of the central processing unit 21 functions as a unit that detects the presence or absence of excessive temperature rise of the gas sensing layer based on the heater layer temperature calculated by the heater layer temperature calculation unit 214. When the heater layer temperature exceeds a preset upper limit temperature T _ex , an excessive temperature rise of the gas sensing layer 153 is detected. For example, when the upper limit temperature T _ex is set to 455 ° C. (+ 5 ° C.) for heating to 450 ° C. and the heater layer temperature (that is, the sensor temperature) is 450 ° C., the upper limit temperature T _ex is exceeded. Therefore, it is determined that there is no excessive temperature rise.

  The drive switching means 216 of the central processing unit 21 receives the determination that the excessive temperature rise detecting means 215 does not cause the excessive temperature rise, and does not perform the switching, but drives the normal drive pattern as it is.

The city gas detection means 212 and the CO gas detection means 213 of the central processing unit 21 are means for detecting the presence or absence of a detection target gas from the sensor resistance value of the gas sensing layer 153 at high temperature via the gas detection signal processing unit 24. Function. As shown in FIG. 3, the normal drive pattern of the heater layer 13 when the excessive temperature rise is not repeated pulsed, and the heater layer 13 is driven until the end of the gas detection time t _1. is there. This is a pattern in which the gas detection heated by the heater layer 13 to a high temperature of the gas detection temperature T ₁ (450 ° C.) for the gas detection time t ₁ (500 ms) repeatedly appears at every gas detection cycle t _d (for example, 60 s). . The gas sensing layer 153 contacts the gas to be detected in the state of being heated to a high temperature of 450 ° C., and the changing sensor resistance value of the gas sensing layer 153 is detected by the gas detection signal processing unit 24 as a detection signal through a conducting wire indicated by a thin line. The presence or absence of the detection target gas is detected by outputting.
When there is no excessive temperature rise, the heater layer 13 is driven in this way.

Next, a case where there is an excessive temperature rise due to the overcombustible gas will be described. First, the heater layer driving unit 211 of the central processing unit 21 shown in FIG. 1 functions as a unit that drives the heater layer driving unit 22 to heat and drive the heater layer 13 so as to reach the gas detection temperature. Initially, as in the normal drive pattern, as shown in FIG. 3, the heater layer 13 drives the heater layer at a high temperature of, for example, the gas detection temperature T ₁ (for example, 450 ° C.) (gas detection time) t ₁ (for example, 500 ms). Is heated over.

In parallel with the gas detection, the heater layer temperature calculating means 214 of the central processing unit 21 shown in FIG. 1 calculates the heater layer temperature from the electric characteristic value detected by the heater layer electric characteristic measuring section 23 as described above. Function as. It is assumed that such calculation of the heater layer temperature is continuously repeated during the gas detection time t ₁ . For example, the heater layer temperature is output every 5 ms.

The excessive temperature rise detection means 215 of the central processing unit 21 shown in FIG. 1 functions as means for detecting the presence or absence of excessive temperature rise of the gas sensing layer 153 based on the heater layer temperature calculated by the heater layer temperature calculation means 214. Here, as shown in FIG. 5, when the heater layer temperature exceeds a preset upper limit temperature T _ex , overheating of the gas sensing layer 153 is detected. In FIG. 5, when the upper limit temperature is set to 455 ° C. (+ 5 ° C.) to heat the heater layer temperature to 450 ° C. and the heater layer temperature (that is, the sensor temperature) is 460 ° C., Since it exceeds the upper limit temperature T _ex , it is determined that there is an excessive temperature rise.

  The drive switching unit 216 of the central processing unit 21 changes the drive pattern of the heater layer drive unit 22 from the normal drive pattern to the excessive temperature rise countermeasure drive pattern in response to the determination of the excessive temperature rise by the excessive temperature rise detection unit 215. Thus, the heater layer driving means 211 functions as a means for switching the driving. In this case, the heater layer temperature is driven so as to include an excessive temperature rise countermeasure drive pattern as shown in FIG. This is performed at the time of overheating detection (gas detection stop) shown in FIG.

The drive pattern against excessive temperature rise in this embodiment lowers the temperature of the excessively heated gas sensing layer 153 and the gas selective combustion layer 154, and vaporizes or combusts the overcombustible gas that causes the subsequent excessive temperature rise. To remove. That is, as shown in FIG. 5, the heater layer driving means 211 of the central processing unit 21 suspends the gas detection for a while to lower the heater layer temperature even after the gas detection time t ₁ , and then the gas is not detected. At a temperature lower than the detection temperature T _{1 and} at an overcombustible gas removal temperature T ₀ at which the overcombustible gas is removed, the heater layer 13 is heated and driven for the overcombustible gas removal time t _0. It functions as a means for controlling the drive unit 22. It should be noted that the heater layer driving means 211 of the central processing unit 21 does not have to perform the temporary stop, and immediately after the gas detection time t ₁ , the temperature is lower than the gas detection temperature T ₁ and the overcombustible gas is removed. The heater layer driving unit 22 may be controlled to heat and drive the heater layer 13 at the overcombustible gas removal temperature T ₀ for the overcombustible gas removal time t ₀ .

When the gas detection temperature T ₁ and the overcombustible gas removal temperature T ₀ are set here, the condition of T ₀ <T ₁ is satisfied. It is possible to remove the adsorbed overcombustible gas at such an overcombustible gas removal temperature T ₀ . Note that the temperature T ₀ at which the overcombustible gas is removed is not limited to 300 ° C., as long as it is a temperature at which the overcombustible gas can be removed. The temperature may be appropriately determined according to the type of overcombustible gas to be removed.

In the removal of the overcombustible gas in the drive pattern for overheating control in FIG. 5, the heater layer 13 has the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s). Although it is heated, at this time, the overcombustible gas of the gas sensing layer 153 and the gas selective combustion layer 154 is heated at a relatively low temperature, and the overcombustible gas is vaporized at a low temperature and diffused and removed. Further, even when the fuel is removed by combustion, there is no problem that the sensor deteriorates because the temperature is lower than the sensor deterioration temperature.
In this case, the gas detection device 1 reports to the surroundings by, for example, issuing an alarm that the outside air is dirty when the excessive temperature rise detection exceeds the predetermined number.

After the overcombustible gas is removed in this way, the heater layer drive means 211 of the central processing unit 21 shown in FIG. 1 is driven in the normal drive pattern, and again the gas detection temperature shown in FIG. It functions as a means for heating and driving the heater layer 13 so as to be T ₁ . Hereinafter, similar to the above description, the heater layer temperature calculation means 214, the excessive temperature rise detection means 215, and the drive switching means 216 are caused to function, and if the excessive temperature rise is not eliminated, the driving pattern is changed again to the excessive temperature rise countermeasure drive pattern. Then, the overcombustible gas is removed again to detect the gas without deteriorating the gas sensing layer 153 and the gas selective combustion layer 154. Gas detection is performed in this way.

  Subsequently, a verification result of the overcombustible gas removing ability of the gas detection device 1 will be described. The behavior of a gas sensor exposed to tetrahydrofuran, which is an example of an overflammable gas, will be verified. First, the time change of the heater layer temperature of the gas sensor 10 before exposure to tetrahydrofuran is verified. Then, the time change of the heater layer temperature of the gas sensor 10 after exposing to 10 ppm of tetrahydrofuran for 24 hours is verified. At this time, only the heater layer drive for gas detection is performed without removing the overcombustible gas with the gas sensors before and after the exposure to the overcombustible gas, and the time change of the heater layer temperature is verified. FIG. 6 shows the behavior of the heater layer temperature of the gas sensor 10 under such conditions by comparing before and after overexposure gas exposure.

  As shown by the solid line in FIG. 6, the time-dependent change in the heater layer temperature of the normal gas sensor 10 without the adsorption of the over-combustible gas before the over-combustible gas exposure is about 200 ms at the same 450 ° C. as the set detection temperature. Reached and maintained for up to 500 ms. On the other hand, the temporal change in the heater layer temperature of the gas sensor 10 in which the overcombustible gas is adsorbed after the exposure to the overcombustible gas reaches the detection temperature of 450 ° C. in about 200 ms, as shown by the alternate long and short dash line in FIG. After that, the temperature was further raised and reached 550 ° C. at 500 ms. This is a temperature higher than the set heater layer temperature of 450 ° C., and the gas sensor 10 has been overheated after being exposed to the overcombustible gas.

  An example of improvement by the gas detection device 1 of the present invention that solves such an excessive temperature rise will be described. When the overcombustible gas adheres to the gas sensing layer 153 or the gas selective combustion layer 154 due to the overcombustible gas exposure, the temperature rises as shown by the one-dot chain line in FIG. . Therefore, the drive pattern is switched to the excessive temperature rise countermeasure drive pattern as shown in FIG. 5, and the removal of the overcombustible gas is started.

  FIG. 7 shows the behavior of the heater layer temperature when the gas sensor 10 exposed to 10 ppm of tetrahydrofuran for 24 hours is heated to 300 ° C. to remove the overcombustible gas. It is not allowed. FIG. 8 shows the behavior of the heater layer temperature after the removal of the overcombustible gas and during the detection of the gas heated to 450 ° C., but no excessive temperature rise of 450 ° C. or higher is observed. This is the same tendency as the time change of the normal heater layer temperature before the exposure to overburning gas shown by the solid line in FIG. 6 described above. According to the gas detection device 1 of the present invention, the temperature of the gas sensing layer 153 and the gas selective combustion layer 154 is immediately lowered when an excessive temperature rise occurs, and then the gas sensing layer 153 and the gas are removed by removing the overcombustible gas. The overcombustible gas adsorbed to the selective combustion layer 154 is removed, and then the gas detection is performed, thereby eliminating the influence of the excessive temperature rise.

  Next, the second mode will be described. Compared with the first embodiment described above with reference to FIGS. 1 to 8, the second embodiment has the same configuration of the gas detection device 1 shown in FIGS. 1 and 2, and when there is no excessive temperature rise. The same applies to the detection using the normal drive pattern described above with reference to FIG. 3, but only the drive pattern against excessive temperature rise is different. The configuration of the second embodiment is the same as the configuration of the first embodiment described above, the same reference numerals are given, redundant description will be omitted, and only different overheating countermeasure drive patterns will be described.

In the above-described drive pattern for preventing excessive temperature rise of the first embodiment, as shown in FIG. 5, when the excessive temperature rise is detected, the energization is stopped to stop the gas detection, and the overflammable gas temperature lower than the gas detection temperature T ₁ is reached. The heating is continuously performed at the removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s). However, in the excessive temperature rise countermeasure drive pattern of the second embodiment, as shown in FIG. 9, at the time of removing the overcombustible gas, for example, the pulse width t ₃ (500 ms) at the overcombustible gas removal temperature T ₀ (300 ° C.). The pulse drive that causes the pulse of n to appear n times (for example, 6 times) is adopted. Even in such a form, the overcombustible gas is removed without departing from the spirit of the present invention. The overcombustible gas removal time t ₀ , the pulse width t ₃ and the number of pulses can be appropriately selected according to the actual situation. Further, this pulse does not have to be the same pulse in succession, and may have different pulse widths, or may be a pulse whose temperature is initially low and the temperature increases sequentially. Well, you can choose various variations. Such a form may be adopted.

  Next, the third mode will be described. Compared to the first embodiment described above with reference to FIGS. 1 to 8, the third embodiment has the same configuration of the gas detection device 1 shown in FIGS. 1 and 2, and when there is no excessive temperature rise. Is the same in that the detection is performed using the normal drive pattern described above with reference to FIG. 3, but only the drive pattern against excessive temperature rise is different. The configuration of the third embodiment is the same as the configuration of the first embodiment described above, the same reference numerals are given, redundant description will be omitted, and only the excessive temperature rise countermeasure drive pattern will be described. This drive pattern for preventing excessive temperature rise is for performing only the gas detection stop described in FIG. 5, and is a pattern for easily removing the overcombustible gas.

In the above-described drive pattern against excessive temperature rise of the first embodiment, as shown in FIG. 5, when the excessive temperature rise is detected, the energization is stopped and the gas detection is stopped, and the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) The heating is continuously performed for the overcombustible gas removal time t ₀ (for example, 5 s). However, in the excessive heating countermeasure drive pattern of the third embodiment, the heater layer driving is stopped immediately after detecting the excessive heating even during the gas detection time t ₁ , and the overburning gas is not removed. It is a pattern that has been stopped for a while. After that, the normal drive pattern as shown in FIG. 3 is restored.

  In this case, the drive switching means 216 of the central processing unit 21 of FIG. 1 changes to the overheat-up countermeasure drive pattern in response to the judgment that the overheat-up detection means 215 causes the overheat-up, and the heater The driving of the heater layer driving means 211 is switched so as to stop the layer driving. By doing so, it is possible to avoid a situation in which over-combustion is immediately eliminated by stopping the driving of the heater layer, and the heater layer 13 and the gas sensing layer 153 and the gas selective combustion layer 154 that have overheated are destroyed. It Then, even if the excessive temperature rise again occurs during the subsequent gas detection, the heater layer driving is similarly stopped so that the heater layer driving is stopped. The process is repeated until the excessive temperature rise is eliminated. After that, the normal drive pattern as shown in FIG. 3 is maintained.

  Then, a 4th form is demonstrated. Compared with the first embodiment described above with reference to FIGS. 1 to 8, the fourth embodiment has the same configuration of the gas detection device 1 shown in FIGS. 1 and 2, and when there is no excessive temperature rise. Is also the same as that the detection is performed with the normal drive pattern described above with reference to FIG. 3, but the drive pattern against excessive temperature rise is different. The configuration of the fourth mode is the same as the configuration of the first mode described above, the same reference numerals are given, redundant description will be omitted, and only different overheating countermeasure drive patterns will be described.

In the above-described drive pattern for preventing excessive temperature rise of the first embodiment, as shown in FIG. 5, the energization is stopped at the time of detecting the excessive temperature rise to stop the gas detection, and then the overcombustible gas removal temperature T ₀ (for example, 300 (° C), the heating is continuously performed for the overcombustible gas removal time t ₀ (for example, 5 s). However, in the excessive temperature rise countermeasure drive pattern of the fourth embodiment, as shown in FIG. 10, the heater that reduces the power supplied to the heater layer 13 immediately after the excessive temperature rise is detected even during the gas detection time t _1. Layer driving is performed to bring the temperature of the heater layer 13 close to a normal gas detection temperature T ₁ that is equal to or lower than the sensor deterioration temperature. At this time, overcombustible gas removal is performed.

When the excessive temperature rise is detected, the drive switching unit 216 of the central processing unit 21 of FIG. 1 receives the determination that the excessive temperature rise is generated by the excessive temperature rise detection unit 215, and reduces the electric power. The drive pattern of the heater layer drive means 211 is changed to drive the heater layer so as to reduce the electric power by changing to the temperature countermeasure drive pattern. Gas detection is performed after the gas detection time t _{1 has} elapsed.

  Even if the temperature rises again during the subsequent gas detection, the heater layer is driven to reduce the power in the same manner. The process is repeated until the excessive temperature rise is eliminated. After that, the normal drive pattern as shown in FIG. 3 is maintained. If the excessive temperature rise is detected even after the excessive temperature rise countermeasure drive pattern is executed over the predetermined number of times, an alarm is issued.

FIG. 11 shows a comparison of the behavior of the heater layer temperature with and without driving against excessive temperature rise. After the sensor chip has been exposed to 10 ppm of tetrahydrofuran for 24 hours, energization is started. Assuming that the excessive temperature rise determination temperature is + 5 ° C. of the detection temperature, it exceeds 455 ° C. at time t _A. In this case, if the power applied to the heater layer is not reduced, an excessive temperature rise occurs above 500 ° C. as indicated by the dashed line in FIG. 11, but if the power applied to the heater layer is reduced, it is indicated by the solid line in FIG. Thus, the temperature can be maintained at about 450 ° C., which prevents excessive temperature rise.

  By stopping the driving of the heater layer, the influence of over-combustion is reduced, and the situation in which the heater layer 13, the gas sensing layer 153 and the gas selective combustion layer 154 that have overheated are destroyed is avoided. Further, even when the electric power is reduced, the overcombustible gas burns, and the overcombustible gas is also removed.

Next, the fifth mode will be described with reference to FIGS. 12, 13, and 14. The gas detection device 2 of the fifth embodiment shown in FIGS. 12 and 13 includes the heater layer electric characteristic measuring unit 23 and the heater layer of the configuration of the gas detection device 1 of the first embodiment described above with reference to FIGS. The difference is that the temperature calculation means 214, the excessive temperature rise detection means 215, and the drive switching means 216 are removed and the heater layer drive means 211 is changed. Hereinafter, the heater layer driving means 211 and its driving pattern will be described, and the other components will be denoted by the same reference numerals and redundant description will be omitted. The fifth embodiment is first described above, the second, third, than switch overheated measures driving pattern used in the fourth embodiment was intended to include overcombustion measures driving pattern in the driving pattern without ( (Fig. 14).

Specifically, the heater layer driving means 211 of the central processing unit 21 shown in FIG. 12 functions as an overcombustible gas removal driving means 211a and a gas detection driving means 211b.
First, in the overcombustible gas removal driving means 211a, as shown in FIG. 14, at the overcombustible gas removal temperature T ₀ at which the overcombustible gas is removed at a temperature lower than the gas detection temperature T ₁ (described later). The heater layer driving unit 22 is controlled so that the heater layer 13 is heated and driven for the overcombustible gas removal time t ₀ . The heater layer 13 heats at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s).

At this time, the overcombustible gas in the gas sensing layer 153 and the gas selective combustion layer 154 of the gas sensing unit 15 is heated at a relatively low temperature, and the inside of the pores of the gas sensing layer 153 and the gas selective combustion layer 154 are heated. Thus, the overcombustible gas that adheres due to the capillary condensation effect is vaporized and diffused and removed without rapidly increasing the temperature. Further, the overcombustible gas around the outside of the gas selective combustion layer 154 is also vaporized and diffused and removed without rapidly increasing the temperature. Here, the overcombustible gas removal temperature T ₀ is a temperature at which the gas sensing layer 153 and the gas selective combustion layer 154 do not deteriorate during vaporization. Even when removed by combustion, there is no problem that the sensor deteriorates because the temperature is lower than the sensor deterioration temperature.

Subsequently, the gas detection driving unit 211b controls the heater layer drive unit 22 so that the heater layer 13 is driven to be heated at the gas detection temperature T ₁ after the overcombustible gas is removed. The heater layer 13 heats at a high temperature, for example, the gas detection temperature T ₁ (for example, 450 ° C.) for a gas detection time t ₁ (for example, 500 ms).

Here, the gas selective combustion layer 154 at high temperature burns a reducing gas such as CO and H _{2 and} other miscellaneous gases, but allows a flammable gas such as CH ₄ and C ₃ H ₈ to pass through. Combustible gas reaches the gas sensing layer 153 of the high-temperature conditions by diffusing the gas selective combustion layer 154 reacts with the SnO ₂ gas sensitive layer 153, changing the sensor resistance of the SnO _2. This change in sensor resistance is detected for detecting the presence or absence of the particular city gas generated during gas leakage, such as gas equipment (CH _4, combustible gas such as C ₃ H _8). The sensor resistance value of the gas sensing layer 153 is measured by the gas sensing signal processing unit 24 by the pair of sensing layer electrodes 152 (High-Off method).

In gas detection, instead of the High-Off method, the high-low-off method and the detection of incomplete combustion gas such as CO in a low state as described above are combined with one sensor to combustible gas / incomplete combustion gas. A method of detecting both of these may be adopted. Then, in such a drive pattern, one unit consisting of removal of overcombustible gas and gas detection repeatedly appears at a predetermined gas detection cycle t _d (for example, 60 s). In such a gas detection device 2 as well, the overcombustible gas adsorbed by the removal of the overcombustible gas is removed, and the excessive temperature rise is prevented.

  Next, the sixth mode will be described. Compared to the fifth embodiment described above with reference to FIGS. 12, 13, and 14, the sixth embodiment has the same configuration as the gas detection device 2 illustrated in FIGS. 12 and 13, but only the drive pattern. Is different. The configuration of the sixth mode is the same as the configuration of the fifth mode described above, the same reference numerals are given, redundant description will be omitted, and only different drive patterns will be described.

In the fifth embodiment described above, as shown in FIG. 14, heating is continuously performed at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s). However, in the sixth embodiment, as shown in FIG. 15, when removing the overcombustible gas, for example, a pulse having a pulse width t ₃ (500 ms) at the overcombustible gas removal temperature T ₀ (300 ° C.) is n times in one cycle. Pulse drive is performed (6 times in FIG. 15). Even in such a form, the overcombustible gas is removed without departing from the spirit of the present invention. The overcombustible gas removal time t ₀ , the pulse width t ₃ and the number of pulses can be appropriately selected according to the actual situation. Further, this pulse does not have to be the same pulse, may have different pulse widths, or may be a pulse whose temperature is initially low and the temperature is gradually increased. You can select variations. As a result, it is possible to obtain a low power consumption type gas detection device which consumes less power and is driven by a battery. Such a form may be adopted.

Then, a 7th form is demonstrated. Compared to the fifth and sixth embodiments described above with reference to FIGS. 12, 13, 14, and 15, the seventh embodiment is the gas detection device shown in FIGS. 12, 13, 14, and 15. Although the configuration is the same as that of No. 2, only the drive pattern at the beginning of gas detection is different. The configuration of the seventh mode is the same as the configuration of the fifth and sixth modes described above, the same reference numerals are given, the duplicate description will be omitted, and only the drive pattern will be described. The seventh mode is different from the fifth and sixth modes in that the overcombustible gas removal driving means 211a extends the overcombustible gas removal time t ₀ over a predetermined initial period from the start of gas detection. After the lapse of this initial period, the normal over-combustible gas removal time t ₀ is restored.

When it is considered that the non-energization period is long and the amount of adsorption of the over-combustible gas is large due to long-term storage, etc., the over-combustibility gas removal time t ₀ is increased in the initial period immediately after the start of energization. Make sure to remove the gas. This is applicable in the fifth and sixth forms. For example, normally, the heater layer 13 heats at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s), but within a predetermined initial period from the start of gas detection. Is that the heater layer 13 heats at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 10 s). This can enhance the ability to remove the overcombustible gas. Such a drive pattern can be adopted.

Next, the eighth mode will be described. Compared with the fifth, sixth, and seventh modes described above with reference to FIGS. 12, 13, 14, and 15, the eighth mode has the same configuration as that of the invention shown in FIGS. However, only the drive pattern after the lapse of a predetermined period from the beginning of gas detection is different. Since the configuration of the eighth mode is the same as the configurations of the fifth, sixth, and seventh modes described above, the same reference numerals are given, redundant description will be omitted, and only the drive pattern will be described. In the eighth mode, in addition to the fifth, sixth, and seventh modes, the overcombustible gas removal drive means 211a further shortens the overcombustible gas removal time t ₀ after a predetermined drive period has elapsed from the start of gas detection. It is in.

After the overcombustible gas is removed a plurality of times, the overcombustible gas can be sufficiently removed even if the overcombustible gas removal time t ₀ is shortened. As a result, it is possible to obtain a low power consumption type gas detection device which consumes less power and is driven by a battery. This is applicable in the fifth, sixth and seventh forms. For example, normally, the heater layer 13 is heated at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 5 s), but after a predetermined drive period has elapsed from the start of gas detection. Then, the heater layer 13 is heated at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) for the overcombustible gas removal time t ₀ (for example, 3 s). Such a drive pattern can be adopted.

In addition, in the fifth, sixth, seventh, and eighth modes, the overcombustible gas removal driving means 211a operates at the overcombustible gas removal temperature T ₀ (for example, 300 ° C.) in one gas detection cycle t _d . Overcombustible gas removal drive for heating for the combustible gas removal time t ₀ (for example, 5 s) is performed once. However, this overcombustible gas removal drive may be performed intermittently, such as once for each elapse of a plurality of gas detection periods t _d (for example, FIG. 16).

  Next, the ninth mode will be described. Even if the overcombustible gas removal drive is performed in a predetermined cycle, if the overcombustible gas excessively adheres, it may not be removed only by the overcombustible gas removal drive in a predetermined cycle. Therefore, normally, the overcombustible gas removing drive is performed regularly, and the overcombustible gas removing drive is also performed when the excessive temperature rise is detected again thereafter. The ninth mode has the configuration shown in FIGS. Then, normally, it is driven in the normal pattern described as the fifth, sixth, seventh, and eighth modes with reference to FIGS. 14, 15, and 16. During this driving, the presence or absence of excessive temperature rise is detected as described above. If there is no excessive temperature rise, drive in the normal pattern is continued. However, if there is an excessive temperature rise, the pattern is switched to the overcombustible gas removal pattern as shown in FIGS. 5, 9 and 10. Then, the pattern returns to the normal pattern, but if the excessive temperature rise occurs again, the pattern is switched to the overcombustible gas removal pattern. Hereinafter, if the excessive temperature rise is detected even after the driving by the normal pattern and the excessive temperature rise countermeasure driving pattern is executed a predetermined number of times, an alarm is issued. Such a form may be adopted.

Next, a tenth embodiment of the present invention will be described with reference to the drawings. When the first to ninth forms described earlier on purpose comparison, the present embodiment is obtained by employing the gas sensor 10 'of the bridge structure as shown in FIG. 17 as a gas sensor. FIG. 17 conceptually shows the configuration of the gas sensor in an easy-to-see manner, and the size and thickness of each part are not strict.

  Similar to the diaphragm structure, this bridge structure also has a structure with high heat insulation and low heat capacity, and can be used as a gas sensor. The gas sensor 10 ′ includes a Si substrate 11, a heat insulating support layer 12, a heater layer 13, an electric insulating layer 14, a gas detector 15, a through hole 16, and a cavity 17. The Si substrate 11, the thermal insulation support layer 12, the heater layer 13, the electrical insulation layer 14, and the gas detection unit 15 that have the same configuration as the gas sensor 10 described with reference to FIG. The description will be omitted.

  The gas sensor 10 ′ has the Si substrate 11, the heat insulating support layer 12, the heater layer 13, the electric insulating layer 14, and the gas detecting portion 15 as described above, and thereafter four bridges and the central stage are left. As shown in FIG. 17 (b) AA sectional view and FIG. 17 (c) BB sectional view, a quadrangular pyramid or a quadrangular pyramid trapezoidal cavity 17 (not shown) is formed. Form. The gas sensor 10 ′ may be a gas detection device that detects the gas by driving the heater as described above.

  The gas detector of the present invention has been described above with reference to the drawings. Although the first to tenth embodiments described above are all described as being configured to include the gas selective combustion layer 154, the gas detection unit 15 without the gas selective combustion layer 154 may be used. . Also in this case, gas detection is possible with the porous gas sensing layer 153, and the same effect can be expected because the porous gas sensing layer 153 adsorbs the overcombustible gas. A configuration without such a gas selective combustion layer 154 may be adopted.

  According to these gas detection devices described above, the influence of excessive temperature rise is eliminated, reliability is increased, and highly accurate detection is realized.

  INDUSTRIAL APPLICABILITY The gas detection device of the present invention can be applied to applications such as gas leak alarms.

1,2: Gas sensing device 10, 10 ': gas sensor 11: Si substrate 12: heat insulating support layer 121: a thermal oxide SiO ₂ layer 122: _CVD-Si 3 _{N 4} layer 123: CVD-SiO ₂ layer 13: a heater layer 14: Electrical insulating layer 15: Gas detection unit 151: Bonding layer 152: Sensing layer electrode 153: Gas sensing layer 154: Gas selective combustion layer 16: Through hole 17: Cavities 20, 20 ': Drive control / signal processing unit 21: Central processing unit 211: heater layer drive means 211a: overcombustible gas removal drive means 211b: gas detection drive means 212: city gas detection means 213: CO gas detection means 214: heater layer temperature calculation means 215: excessive temperature rise detection means 216: Drive switching means 217: Correction means 218: Judgment means 219: Display control means 220: Output control means 22: Heater layer drive section 23: Heater layer electric characteristics Measuring unit 24: Gas detection signal processing unit 25: Storage unit 26: Warning display unit 27: Warning sound output unit 28: External output unit 29: Power supply unit

Claims (11)

A gas sensing layer formed of a porous body or a columnar structure for sensing a gas to be detected, a gas selective combustion layer formed of a porous body for burning and removing an interfering gas, and the gas sensing layer and the gas selective combustion a gas detector having a heater layer for heating a layer,
A heater layer drive unit that energizes and drives the heater layer by a normal drive pattern for detecting the detection target gas or a drive pattern for preventing excessive temperature rise of the gas detection unit,
An overheating detection unit that detects an overheating of the gas sensing layer or the gas selective combustion layer based on the temperature of the heater layer,
A drive switching unit that changes the drive pattern of the heater layer drive unit from the normal drive pattern to the drive pattern against excessive temperature rise when the excessive temperature rise detection unit detects an excessive temperature rise;
Equipped with
The gas detection device, wherein the drive pattern against excessive temperature rise is a pattern for lowering the temperature of the gas detection unit to vaporize or combust and remove the overcombustible gas.   The drive pattern for preventing excessive temperature rise is a temperature lower than the detection temperature of the gas to be detected, and at the overcombustible gas removal temperature at which the overcombustible gas is removed, over a predetermined overcombustible gas removal time. The gas detection device according to claim 1, wherein the heater layer is a pattern for energizing the heater layer.   The drive pattern for preventing excessive temperature rise is a temperature lower than the detection temperature of the gas to be detected after the energization drive of the heater layer is temporarily stopped, and the overcombustible gas removal temperature at which the overcombustible gas is removed. 2. The gas detection device according to claim 1, wherein the heater layer is energized for a predetermined overcombustible gas removal time.   The gas detection device according to claim 2 or 3, wherein the excessive temperature rise countermeasure drive pattern is a pattern in which the heater layer is energized and driven for a period of the overburnable gas removal time by a repeating pulse having a predetermined pulse width. .   The gas detection device according to claim 1, wherein the excessive temperature rise countermeasure drive pattern is a pattern for stopping energization drive of the heater layer.   The gas according to claim 1, wherein the drive pattern against excessive temperature rise is a pattern for energizing and driving the heater layer with electric power that brings the temperature of the gas detection unit close to the gas detection temperature of the detection target gas. Detection device.   The excessive temperature rise detection unit includes a heater layer electric characteristic measurement unit that acquires an electric characteristic value of the heater layer, and a heater layer temperature calculation unit that calculates a temperature of the heater layer based on the electric characteristic value. The gas detection device according to any one of claims 1 to 6. A gas sensing layer having a porous body or a columnar structure and sensing a gas to be sensed, and a gas sensing part having a heater layer for heating the gas sensing layer;
The heater layer has a normal drive pattern for detecting the detection target gas, an overcombustible gas removal pattern for removing the overcombustible gas at a temperature lower than the detection temperature of the detection target gas, and an excessive temperature rise of the gas detection unit. A heater layer drive section that is energized and driven by a drive pattern for preventing excessive temperature rise ,
An overheating detection unit that detects an overheating of the gas sensing layer based on the temperature of the heater layer,
The energization drive is performed by the normal drive pattern after the energization drive by the overcombustible gas removal pattern, and the heater layer drive unit is operated when the excessive temperature rise detection unit detects the excessive temperature rise in the normal drive pattern. A drive switching unit for changing the drive pattern of the normal drive pattern from the drive pattern against excessive temperature rise,
Equipped with
The excessive temperature rise measures driving pattern, the temperature of the gas sensing portion is lowered, the gas detection apparatus, wherein a pattern der Rukoto to vaporize remove or burn off excessive combustible gases. The overcombustible gas removal pattern has a temperature lower than the detection temperature of the detection target gas, and at the overcombustible gas removal temperature at which the overcombustible gas is removed, for a predetermined overcombustible gas removal time. 9. The gas detection device according to claim 8, wherein the heater layer has a pattern for electrically driving . 9. The gas detection device according to claim 8, wherein the overcombustible gas removal pattern is a pattern in which the heater layer is energized and driven for a predetermined overcombustible gas removal time by a repeating pulse having a predetermined pulse width . The overcombustion gas removal pattern, gas detection apparatus according to claim 9 or 10, characterized in that a pattern to lengthen the overcombustion gas removal time for a predetermined initial period from the gas detection start.

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