JP2017053786A - Gas detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detection device that eliminates an influence of an excessive temperature rise to enhance reliability, and achieve highly accurate detection.SOLUTION: A gas detection device 1 achieves highly accurate detection by: heater layer temperature calculation means 214 that drives a heater layer drive unit 22 to conduct a heater layer drive of implementing a heating drive of a heater layer so as to be a gas detection temperature, and conduct a heater layer temperature calculation of calculating a heater layer temperature from a value detected by a heater layer electric characteristic measurement unit 23; excessive temperature detection means 215 that conducts excessive temperature detection of detecting presence or absence of an excessive temperature rise of a gas sensing layer based on a change in a temperature rise characteristic of the heater layer temperature; and drive switch means 216 that, when the excessive temperature rise is present, conduct a drive switch of changing a drive pattern of the heater layer drive unit 22 to an excessive temperature rise counter-measure drive pattern.SELECTED DRAWING: Figure 1

Description

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

The gas detection device is generally used for applications such as a gas leak alarm. The gas sensor used in this gas detection device is a device that is selectively 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 indispensable.

  By the way, gas leak alarms that are widely used for household use are intended for detection of flammable gas for city gas and propane gas, for detection of incomplete combustion gas in combustion equipment, Alternatively, there are those having both of these functions, but the spread rate is not so high due to cost and installation problems. One of the problems of installation is that a power source is required around the gas leak alarm because a 100V AC power source is used. In addition, there was a problem that it could not be used in an emergency such as a power failure. Therefore, from the viewpoint of improving the penetration rate of gas leak alarm devices, it is desired to improve the installation property, specifically, to make the gas leak alarm device cordless by driving the battery.

Low power consumption is the most important for realizing battery drive. However, when detecting CH ₄ , C ₃ H ₈ or the like with a catalytic combustion type or semiconductor type gas sensor, it is necessary to detect the gas detection unit by heating it to a high temperature of 400 ° C. to 500 ° C. In order to heat to high temperature with low power consumption, intermittent operation is performed in which a gas sensor having a high heat insulation and low heat capacity structure such as a diaphragm structure is heated in accordance with a detection cycle by using a microfabrication process.

  Now, temperature control for switching the temperature is performed on such a gas sensor in order to remove substances that affect 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 for driving the heater layer is performed so as to remove water vapor gas in particular.

  Further, as another prior art related to an apparatus in which such temperature control is performed, for example, one described in Patent Document 2 (Japanese Patent Laid-Open No. 2012-172773) is known. In the combustible gas detection device of Patent Document 2, temperature control for driving the heater layer is performed so as to remove particularly poisonous gas.

Japanese Patent No. 4450773 (paragraphs [0044], [0059], [0060], FIGS. 1, 5, and 6) JP 2012-172773 A (paragraph [0017], FIGS. 3 and 4)

  Examples of environmental gas components include organic solvents contained in paints and fuel-based gases such as kerosene. For example, octane or 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), and the combustion heat is extremely high. It is known that such a gas component with 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. It was done.

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

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

  In such a porous body or a columnar structure, there are many pores having an opening diameter of several nm to several μm. In these pores, water, interference gas, and detection target gas 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 by capillary condensation into the fine pores of the porous gas sensing layer or gas selective combustion layer as described above. In this case, when the heater is turned on (energized) and heated to a high temperature of 400 ° C. to 500 ° C., the overcombustible gas adsorbed in the micropores is combusted, and the gas detection layer or gas selective combustion layer of the thin film gas sensor is generated by high combustion heat. It is conceivable that the temperature rises above the gas detection temperature, and normal detection characteristics cannot be obtained due to thermal degradation.

  It has been found that there is a need to prevent overheating of the gas sensing layer and the gas selective combustion layer of the thin film gas sensor even in an environment where such an overburning gas exists. At this time, in order to realize battery driving, it was necessary to prevent overheating with low power consumption, but attention was not paid to the problem of performing temperature control to prevent overheating.

Patent Document 1 discloses a prior art that realizes low power consumption driving while performing both water removal and gas detection, but does not take into account prevention of excessive temperature rise.
Further, Patent Document 2 discloses a prior art that realizes low power consumption driving while performing both removal of poisoning gas and gas detection, but it does not take into consideration prevention of excessive temperature rise.

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

In order to solve the above-mentioned problem, in the invention described in claim 1,
A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
A heater layer driving unit that energizes and drives the heater layer with a normal driving pattern for detecting the detection target gas or an excessive temperature rising countermeasure driving pattern for preventing an excessive temperature rising of the gas detection unit;
An excessive temperature rise detection unit for detecting an excessive temperature rise in the gas detection unit;
A drive switching unit that changes the drive pattern of the heater layer drive unit from the normal drive pattern to the over-temperature rise countermeasure drive pattern when an over temperature rise is detected by the over temperature rise detection unit. It was set as a gas detection device.

In the invention described in claim 2,
The overheat temperature countermeasure driving pattern is a temperature lower than the detection temperature of the detection target gas, and the overburning gas removal temperature at which the overburning gas is removed, and the heater layer over the overburning gas removal time. The gas detection device according to claim 1, wherein the gas detection device is a pattern for energization driving.

In the invention described in claim 3,
The excessive temperature rise countermeasure driving pattern is a temperature that is lower than the detection temperature of the detection target gas after the energization driving of the heater layer is temporarily stopped, and at the excessive combustion gas removal temperature at which the excessive combustion gas is removed. The gas detection device according to claim 1, wherein the heater layer is energized and driven over an overburning gas removal time.

In the invention described in claim 4,
3. The heater layer energization drive in the over-temperature-measure countermeasure driving pattern is a pattern in which the heater layer is energized and driven over a period of time for removing the overburning gas by a repetitive pulse having a predetermined pulse width. The gas detection device described in 3 was used.

In the invention described in claim 5,
The gas detection device according to claim 1, wherein the excessive temperature rise countermeasure driving pattern is a pattern for stopping energization driving of the heater layer.

In the invention described in claim 6,
2. The gas according to claim 1, wherein the excessive temperature rise countermeasure driving pattern is a pattern in which the heater layer is energized and driven with electric power that brings the temperature of the gas detection unit close to the gas detection temperature of the detection target gas. The detection device was used.

In the invention described in claim 7,
The excessive temperature rise detection unit,
A heater layer electrical property measuring unit for obtaining electrical property values of the heater layer;
The gas detection device according to claim 1, further comprising a heater layer temperature calculation unit that calculates a heater layer temperature based on the electrical characteristic value.

In the invention described in claim 8,
A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
A heater layer drive unit that electrically drives the heater layer with a normal drive pattern for detecting the detection target gas or a supercombustible gas removal pattern for removing the supercombustible gas at a temperature lower than the detection temperature of the detection target gas; Prepared,
After the energization driving of the overcombustible gas removal pattern, the gas detection apparatus is characterized in that the detection target gas is detected by energization driving with the normal driving pattern.

In the invention described in claim 9,
A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
The heater layer includes a normal driving pattern for detecting the detection target gas, a supercombustible gas removal pattern for removing a supercombustible 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 driving unit that is energized and driven with an excessive temperature rise countermeasure driving pattern to prevent;
An excessive temperature rise detection unit for detecting an excessive temperature rise in the gas detection unit;
After the energization drive of the overburning gas removal pattern, the energization drive is performed with the normal drive pattern, and in the normal drive pattern, when an excessive temperature rise is detected by the overheat detection unit, the heater layer drive unit And a drive switching unit that changes the drive pattern from the normal drive pattern to the excessive temperature rise countermeasure drive pattern.

In the invention described in claim 10,
The overburning gas removal pattern is a temperature lower than the detection temperature of the detection target gas, and the overburning gas removal temperature at which the overburning gas is removed, and the heater layer over the overburning gas removal time. The gas detection device according to claim 8 or 9, wherein the gas detection device is a pattern for energization driving.

In the invention described in claim 11,
The energization drive of the heater layer in the overburning gas removal pattern is a pattern in which the heater layer is energized and driven over a overburning gas removal time by repeated pulses having a predetermined pulse width. A gas detector was used.

In the invention described in claim 12,
The gas detection according to any one of claims 8 to 11, wherein the overcombustible gas removal pattern is means for extending the overcombustible gas removal time over a predetermined initial period from the start of gas detection. The device.

  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 detector of the 1st, 2nd, 3rd, 4th form for implementing this invention. It is sectional drawing of the gas sensor of the gas detector of the 1st, 2nd, 3rd, 4th form 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 the gas sensor by the external heating in a high temperature furnace. It is explanatory drawing of the excessive temperature rising countermeasure drive pattern of a heater layer at the time of overcombustible gas detection. It is a characteristic view explaining the time change of the heater layer temperature before and after overcombustible gas (tetrahydrofuran) exposure. It is a characteristic view explaining the time change of the heater layer temperature at the time of overcombustible gas removal. It is a characteristic figure explaining the time change of the heater layer temperature at the time of heater layer drive after supercombustible gas removal. 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 a 3rd form. It is a characteristic view explaining the time change of the heater layer temperature after the overcombustion gas (tetrahydrofuran) exposure and before and after the overcombustion countermeasure driving. It is a block block diagram of the gas detection apparatus of the 5th and 6th form for implementing this invention. It is sectional drawing of the gas sensor of the gas detection apparatus of the 5th, 6th form for implementing this invention. It is explanatory drawing of the normal drive pattern of the heater layer of a 5th form. It is explanatory drawing of the normal drive pattern of the heater layer of a 6th form. It is explanatory drawing of the normal drive pattern of the heater layer of the improvement form of the 5th, 6th, 7th, 8th form. It is explanatory drawing of the gas sensor of the gas detection apparatus of the 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 BB sectional drawing of a gas sensor.

  Hereinafter, a gas detector 1 according to 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 controls the drive of 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 sensor and is 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, An electrical insulating layer 14 and a gas detector 15 are provided. FIG. 2 conceptually shows the configuration of the thin film semiconductor gas sensor in an easy-to-understand manner, and the size and thickness of each part are not strict.

Next, the configuration of each part will be described.
The Si substrate 11 is formed of silicon (Si), and a through hole is formed at a location where the gas detection unit 15 is located immediately above.

  The thermal insulating support layer 12 is stretched over the opening of the through hole and formed into a diaphragm, and is provided on the Si substrate 11.

Specifically, the thermal 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 reducing the heat capacity by preventing heat generated in the heater layer 13 from being conducted to the Si substrate 11 side. The thermally oxidized SiO ₂ layer 121 exhibits high resistance to plasma etching, and facilitates formation of a through hole in the Si substrate 11 by plasma etching, which will be described later.

The CVD-Si ₃ N ₄ layer 122 is formed above the thermally oxidized SiO ₂ layer 121.
The CVD-SiO ₂ layer 123 improves the adhesion to the heater layer 13 and ensures 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-like Pt—W film or Ni—Cr film, and is provided on the upper surface at substantially the center of the heat insulating support layer 12. A power supply line is also formed. The 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. The heater layer 13 is electrically connected to a heater layer electrical property measuring unit 23 which is a specific example of the heater layer temperature measuring unit of the present invention, and the heater layer electrical property measuring unit 23 is connected to the electrical resistance of the heater layer 13. Measure.

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

  The gas detector 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 layer 151 is, for example, a Ta film (tantalum film) or a Ti film (titanium film), and is provided on the electrical insulating layer 14 in a pair of left and right. The bonding layer 151 is interposed between the sensing layer electrode 152 and the electrical insulating layer 14 to increase 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 in a pair on the left and right sides so as to be sensing electrodes of the gas sensing layer 153.

The gas sensing layer 153 is an Sb-doped tin dioxide layer (hereinafter referred to as SnO ₂ layer), and is formed on the electrically insulating layer 14 so as to pass the pair of sensing layer electrodes 152. In this embodiment, the gas sensing layer 153 has been described as a SnO ₂ layer. However, in addition to SnO ₂ , a metal oxide such as In ₂ O ₃ , WO ₃ , ZnO, or TiO ₂ that is a metal oxide 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-supported 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 contacts the noble metal catalyst. Then, the combustion reaction of a reducing gas (interfering gas) having a stronger oxidation activity than the detection target gas is promoted, and the selectivity of the detection target gas is increased. That is, the interference gas can be oxidized and removed from the detection target gas.

The gas selective combustion layer 154 is composed mainly of a metal oxide such as Cr ₂ O ₃ , Fe ₂ O ₃ , Ni ₂ O ₃ , ZrO ₂ , SiO ₂ , or zeolite in addition to the Al ₂ O _3. Also good. In addition to palladium oxide (PdO), platinum (Pt) or palladium (Pd) may be employed as the noble metal catalyst.

  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.

Such a gas sensor 10 employs a diaphragm structure and has a high heat insulation and low heat capacity structure. 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). Thus, the temperature change of the gas detecting temperature T ₁ is faster, it is possible to gas detection in a short pulse. Therefore, low power consumption is achieved.

Next, the manufacturing method of the gas sensor 10 and the gas detector 1 of the present embodiment whose cross-sectional structure is shown in FIG. First, a plate-like silicon wafer (not shown) is thermally oxidized on one side (or both sides) by a thermal oxidation method to form a thermally oxidized SiO ₂ layer 121 as 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, a CVD-SiO ₂ film serving as a thermal insulating film is deposited on the upper surface of the CVD-Si ₃ N ₄ layer 122 by a plasma CVD method to form a CVD-SiO ₂ layer 123.

Further, a Pt—W film (or Ni—Cr film) is 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 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. Film formation is performed by an ordinary sputtering method using an RF magnetron sputtering apparatus. The film formation conditions are the same for both the bonding layer (Ta or Ti) 151 and the sensing layer electrode (Pt or Au) 152, Ar gas (argon gas) pressure 1 Pa, substrate temperature 300 ° C., RF power 2 W / cm ² , film thickness The bonding layer 151 / the sensing layer electrode 152 = 500/2000 mm. The pair of sensing layer electrodes 152 are electrodes that extract an electrical signal from the gas sensing layer 153.

While being passed to the pair of sensing layer electrodes 152, a SnO ₂ film is deposited on the electrical 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 apparatus. SnO ₂ containing 0.1 wt% Sb is used as the target. The film formation 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 plan view.

  Subsequently, a gas selective combustion layer 154 is formed. The gas selective combustion layer 154 generates paste by adding the same weight of diethylene glycol monoethyl ether and 5-20 wt% of silica sol binder to γ-alumina (average particle diameter of 2 to 3 μm) to which 7.0 wt% of PdO is added. . 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 periphery of the gas sensing layer 153 so as to sufficiently 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 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 plan view.

  Finally, a microfabrication process for removing silicon from the back surface of a silicon wafer (not shown) is performed to form a Si substrate 11 having a through hole. The gas sensor 10 having a diaphragm structure is finally obtained. The heater layer 13 is electrically connected to the heater layer driving unit 22 and the heater layer electrical characteristic measuring unit 23, and the sensing layer electrode 152 is electrically connected to the gas detection signal processing unit 24. The manufacturing method of 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 electrical characteristic measurement 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 electrical characteristic measurement 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 includes a CPU such as a microcomputer and its peripheral part, and includes a heater layer driving unit 211, a city gas detection unit 212, a CO gas detection unit 213, a heater layer temperature calculation unit 214, and an excessive temperature rise detection. The functions 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 are realized by hardware and software, and perform various controls and signal processing.

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

For example, when the heater layer is driven, it is driven with a 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 cycle t _d is energized in a repeated pulse form of 60 s. Details of these driving will be described later in the detection process.

  The heater layer electrical property measurement unit 23 includes means for detecting electrical property values such as resistance and voltage of the heater layer 13 and transmits 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 a 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 and 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 detection layer 153 via the pair of detection layer electrodes 152, and detects the sensor resistance value of the gas detection layer 153 that has detected the detection target gas. 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 city gas and CO gas, and send them to the correction means 217 as sensor outputs. In addition to the city gas detection means 212 and the CO gas detection means 213, other means for detecting various gases can be employed.

  Since the outputs from the heater layer electrical property 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 (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 is a set value such as a threshold for generating various alarms, a correction value according to an ambient temperature / humidity acquired by an environmental sensor (not shown), or a state when the gas detection device 1 issues an alarm. History data such as data is stored.

  In the central processing unit 21, the correction unit 217 calculates a correction value using the temperature acquired by the heater layer temperature calculation unit 214 during non-energization as the ambient temperature, and outputs the correction value to the sensor outputs of the city gas detection unit 212 and the CO gas detection unit 213. On the other hand, 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, correction may be performed based on an output from an environmental sensor (not shown) (for example, a thermometer, a hygrometer, a barometer, etc.). About correction | amendment, it can select suitably. With such correction, highly accurate gas detection is performed by eliminating the influence of the surrounding environment as much as possible.

  A method without correction may be adopted. In this case, the correcting unit 217 may be omitted, and the determining unit 218 may determine the sensor outputs of the city gas detecting unit 212 and the CO gas detecting unit 213.

  The determination unit 218 of the central processing unit 21 performs control to display an alarm on the alarm display unit 26 via the display control unit 219 when it is determined that gas has been detected, and outputs an alarm sound via the output control unit 220. Control is performed 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 thereof, and can display an alarm when an abnormality is detected. In the central processing unit 21, the display control unit 219, which has received the output of the determination unit 218, controls the alarm display unit 26 to perform a warning display of the detected content that the city gas or CO gas has been detected and an abnormality has occurred. Against.

  The alarm sound output unit 27 includes, for example, a speaker and a driver thereof, and can output an alarm sound or a sound through a speaker or the like. In the central processing unit 21, the output control unit 220 that has received the output of the determination unit 218 performs control to output a warning sound of the detected content that an abnormality has occurred due to detection of city gas or CO gas. 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 means 220 that has received the output of the determination means 218 externally detects the detected content that the city gas or CO gas has been detected and the abnormality has occurred as an output signal of voltage or communication signal. To the external output unit 28.

  The power supply unit 29 includes a central processing unit 21, a heater layer driving unit 22, a heater layer electrical characteristic measurement 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) to supply power to them. 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 AC 100 V and a constant voltage unit. The overall configuration of the gas detector 1 is as described above.

  Next, a gas detection operation by 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, a drive signal from the heater layer driving unit 22 is input to the heater layer 13 of the gas sensor 10 through a conducting wire indicated by a thin line, and the heater layer is driven.

The central processing unit 21 determines whether or not an excessive temperature rise has occurred in the gas sensing layer 153 and the gas selective combustion layer 154. If no excessive temperature increase has occurred, the central processing unit 21 is driven with a normal drive pattern as shown in FIG. However, when an excessive temperature rise has occurred, driving is performed with an excessive temperature rise countermeasure driving pattern to be described later. The normal drive pattern of Figure 3, the gas detection as one unit, the one unit is a pattern to appear repeatedly in the gas detection period t _d. In the second, third, and fourth modes to be described later, similarly, driving is performed using the excessive temperature rise countermeasure driving pattern.

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

  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 thus affects the heater layer resistance value. In other words, the change in the heater layer resistance value. It is assumed that the temperature of the gas sensing layer 153 and the gas selective combustion layer 154 can be detected. By monitoring the heater layer resistance value, the temperature change of the gas sensing layer 153 and the gas selective combustion layer 154 can be grasped.

  Subsequently, a series of operations at the time of gas detection will be described. First, the normal drive pattern when there is no overcombustible gas will be described. As described above, the overcombustible gas is a gas having excessively high combustion heat. For example, octane (combustion heat 5501 kJ / mol (48.3 kJ / g)) or tetrahydrofuran (combustion heat 2530 kJ / mol ( 35.1 kJ / g)).

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

Here, the gas selective combustion layer 154 at high temperature burns reducing gases such as CO and H _{2 and} other miscellaneous gases, but allows combustible gases such as CH ₄ and C ₃ H ₈ to pass therethrough. The combustible gas diffuses in the gas selective combustion layer 154, reaches the gas sensing layer 153 in a high temperature state, reacts with SnO ₂ in the gas sensing layer 153, and changes the sensor resistance value of SnO ₂ . The change in the sensor resistance value is detected to detect the presence or absence of city gas (combustible gas such as CH ₄ and C ₃ H ₈ ) that is generated when gas equipment leaks. 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, 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 increased to a high temperature (High 400 to 500 ° C.) for a certain 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.) and incomplete combustion (CO) is detected. This is known to increase CO sensitivity and gas selectivity (High-Low-Off method).

Also, in the High state, not only cleaning but also detection of flammable gases such as CH ₄ and C ₃ H ₈ is performed, and in combination with detection of incomplete combustion gases such as CO in the Low state, flammable gases and incompleteness with one sensor. It is good also as a gas sensor which can detect both combustion gas.

Next, gas detection of combustible gas and / or incomplete combustion gas by the normal drive pattern will be described.
The heater layer driving means 211 of the central processing unit 21 shown in FIG. 1 functions as a means for heating and driving the heater layer 13 so as to drive the heater layer driving section 22 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 electrical property value detected by the heater layer electrical property measuring unit 23. Such calculation of the heater layer temperature is assumed to be performed repeatedly in succession with the duration of 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 property measuring unit 23 measures a heater layer resistance value from the heater layer 13 through a conducting wire indicated by a thin line, and includes a shunt resistance. The shunt resistance has a known resistance value and is connected in series with the heater layer 13. Furthermore, the circuit configuration is such that the voltage across the heater layer 13 and the voltage across the shunt resistor can be measured.

A gas sensing has become a predetermined voltage is applied to the heater layer 13 and 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 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 unit 214 calculates the temperature T of the heater layer 13 from the following equation. As described above, the change in the heater layer temperature can be indirectly regarded as a change in the heater layer resistance or a change in the heater layer voltage, a change in the heater shunt voltage, or a 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.)
α: Resistance temperature coefficient of heater layer

Here, the heater layer resistance value _R0 at the reference temperature is obtained in advance by measurement. The value of the resistance temperature coefficient α of the heater layer is a value determined for each sensor. In addition, since there is little variation for every wafer which produces a thin film sensor, you may give the same value with the thin film sensor which can be taken from one wafer. Alternatively, when flowing a plurality of wafers in one lot, the same value may be given to the thin film sensors in the same lot.

The heater layer resistance value _R0 at the reference temperature and the resistance temperature coefficient α of the heater layer 13 are stored in the storage unit 25, and the heater layer resistance value R at the heater layer temperature T is the heater layer electrical characteristic measurement unit. 23, the temperature T of the heater layer 13 is calculated from 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 means 215 of the central processing unit 21 functions as means for detecting the presence or absence of an excessive temperature rise in the gas sensing layer based on the heater layer temperature calculated by the heater layer temperature calculation means 214. When the heater layer temperature exceeds a preset upper limit temperature T _ex , an excessive temperature rise in 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. 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 has not occurred in the excessive temperature rise detection means 215, and does not perform switching, but directly drives in the normal drive pattern.

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 detection layer 153 at a 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 has not occurred is a pattern in which the heater layer 13 is driven until the end of the gas detection time t ₁ as shown in FIG. is there. This is a pattern in which the gas detection heated by the heater layer 13 to the high temperature of the gas detection temperature T ₁ (450 ° C.) over the gas detection time t ₁ (500 ms) repeatedly appears every gas detection cycle t _d (for example, 60 s). . The gas detection layer 153 comes into contact with the gas to be detected while being heated to a high temperature of 450 ° C., and the gas detection signal processing unit 24 detects the sensor resistance value of the gas detection layer 153 as a detection signal through a conductive wire indicated by a thin line. The presence or absence of detection target gas is detected by outputting.
When there is no excessive temperature rise, the heater layer 13 is driven in this way.

Then, the case where there exists an excessive temperature rise by overcombustible gas is demonstrated. First, 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 13 to drive the heater layer driving unit 22 so that the gas detection temperature is reached. At first, similarly to the normal drive pattern, as shown in FIG. 3, the heater layer 13 is heated to a heater layer drive time (gas detection time) t ₁ (for example, 500 ms) at a high temperature, for example, a gas detection temperature T ₁ (for example, 450 ° C.). Over heated.

In parallel with the gas detection, the heater layer temperature calculation means 214 of the central processing unit 21 shown in FIG. 1 calculates the heater layer temperature as described above from the electric characteristic value detected by the heater layer electric characteristic measurement unit 23. Function as. Such calculation of the heater layer temperature is assumed to be carried out repeatedly in succession between the gas detection time t _1. For example, the heater layer temperature is output every 5 ms.

The overheating detection means 215 of the central processing unit 21 shown in FIG. 1 functions as a means for detecting the presence or absence of overheating 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, it detects the excessive temperature rise of the gas sensing layer 153 to exceed the upper limit temperature T _ex heater layer temperature reaches a preset. In FIG. 5, when the upper limit temperature is set to 455 ° C. (+ 5 ° C.) in order to heat the heater layer to 450 ° C., and the heater layer temperature (ie, sensor temperature) is 460 ° C., it is determined that there is excessive temperature rise to exceed the upper limit temperature T _ex.

  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 over-temperature rise countermeasure drive pattern in response to the determination that the over temperature rise detection unit 215 has overheated. Thus, it functions as a means for switching the drive by the heater layer drive means 211. In this case, the heater layer temperature is driven so as to include an excessive temperature rise countermeasure driving pattern as shown in FIG. This is performed at the time of excessive temperature rise detection (gas detection stop) shown in FIG.

In the present embodiment, the excessive temperature rise countermeasure driving pattern lowers the temperatures of the gas sensing layer 153 and the gas selective combustion layer 154 that have been excessively heated, and vaporizes or removes the overcombustible gas that causes the subsequent excessive temperature increase. To be removed. That is, the heater layer drive means 211 of the central processing unit 21, as shown in Figure 5, even in the middle of the gas detection time t _1, lowering the heater layer temperature stops while temporarily gas detection, then the gas a temperature lower than the detection temperature T ₁ of at overcombustion gas removal temperature T ₀ that over-combustible gases are removed, to heat drives the heater layer 13 over overcombustion gas removal time t _0, the heater layer It functions as a means for controlling the drive unit 22. Incidentally, it is not necessary to perform the pause, the heater layer drive means 211 of the central processing unit 21 is a lower temperature than the gas detection temperatures T ₁ immediately in the middle of the gas detection time t ₁ is over-combustion gas removed in overcombustion gas removal temperature T ₀ being over over-combustible gas removal time t ₀ to heat drives the heater layer 13 may also function as means for controlling the heater layer driving unit 22.

When the gas detection temperature T ₁ and the overburning gas removal temperature T ₀ are set here, the condition of T ₀ <T ₁ is satisfied. In such over-combustible gas removal temperature T _0, it is possible to remove the excessive combustible gas adsorbed. Since may be a temperature capable of removing excessive combustion gases, over-combustible gas removal temperature T ₀ are not intended to be limited to 300 ° C.. What is necessary is just to determine temperature suitably with the kind of overcombustible gas to remove.

In the over-combustible gas removal of the over-temperature rise countermeasure driving pattern of FIG. 5, the heater layer 13 is kept at the over-combustible gas removal temperature T ₀ (eg, 300 ° C.) for the over-combustible gas removal time t ₀ (eg, 5 s). At this time, the overcombustible gas in 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. In addition, even when the combustion is removed, there is no problem that the sensor deteriorates because it is lower than the sensor deterioration temperature.
In this case, the gas detection device 1 reports to the surroundings by issuing an alarm that the outside air is dirty or the like when the excessive temperature rise detection exceeds a predetermined number of times.

After the overcombustible gas is removed in this way, the heater layer driving means 211 of the central processing unit 21 shown in FIG. 1 is driven in the normal driving pattern, and again the gas detection temperature as shown in FIG. such that T ₁ functions as a means for heating drives the heater layer 13. Thereafter, in the same manner as described above, the heater layer temperature calculating unit 214, the over temperature rise detecting unit 215, and the drive switching unit 216 are caused to function, and when the over temperature rise is not eliminated, the drive pattern is changed again to the over temperature rise countermeasure driving pattern. Then, the gas detection is performed without deteriorating the gas sensing layer 153 and the gas selective combustion layer 154 by removing the overburning gas again. Gas detection is performed in this way.

  Then, the verification result of the overcombustible gas removal capability of such a gas detection apparatus 1 is demonstrated. The behavior when the gas sensor is exposed to tetrahydrofuran, which is an example of a supercombustible 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 24 hours in 10 ppm of tetrahydrofuran is verified. At this time, only the heater layer drive for gas detection is performed by the gas sensor before and after the exposure to the overcombustible gas without performing the removal of 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 in comparison with before and after the overcombustion gas exposure.

  As shown by the solid line in FIG. 6, the time change of the heater layer temperature of the normal gas sensor 10 that does not adsorb the overburning gas before the overburning gas exposure is about 200 ms at the same 450 ° C. as the set detection temperature. Has reached 500 ms. On the other hand, the time change of the heater layer temperature of the gas sensor 10 with the adsorption of the overcombustible gas after the overcombustible gas exposure reached the detection temperature of 450 ° C. in about 200 ms as shown by the one-dot chain line in FIG. The temperature was further increased later, and reached 500 ° C. at 500 ms. This is a temperature exceeding the set heater layer temperature of 450 ° C., and overheating occurs in the gas sensor 10 after exposure to the overcombustible gas.

  An improvement example 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 over-temperature raising countermeasure driving pattern as shown in FIG. 5 is switched to start over-removable gas removal.

  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 inflammable gas. It is not allowed. FIG. 8 shows the behavior of the heater layer temperature during the detection of the gas heated to 450 ° C. after the removal of the overcombustible gas, but an excessive temperature increase of 450 ° C. or higher is not particularly observed. This is the same tendency as the time change of the normal heater layer temperature before the overcombustible gas exposure shown by the solid line in FIG. 6 described above. According to the gas detector 1 of the present invention, when an excessive temperature rise occurs, the temperature of the gas sensing layer 153 and the gas selective combustion layer 154 is immediately lowered, and then the gas sensing layer 153 and the gas are removed by removing the overcombustible gas. The overcombustible gas adsorbed by the selective combustion layer 154 is removed, and then gas detection is performed, thereby eliminating the influence of excessive temperature rise.

  Next, the second embodiment will be described. When 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. Is the same in that the detection is performed using the normal drive pattern described above with reference to FIG. 3, but only the excessive temperature rise countermeasure drive pattern is different. The configuration of the second mode is given the same reference numeral as the configuration of the first mode described above, and redundant description is omitted, and only the different excessive temperature rise countermeasure driving pattern will be described.

The overtemperature protection driving pattern of the first embodiment described above, as shown in Figure 5, excessive temperature rise and deenergized to stop the gas detection when the detection, over-combustible gas temperature lower than the gas detection temperatures T ₁ Heating is continuously performed at the removal temperature T ₀ (for example, 300 ° C.) for the overburning gas removal time t ₀ (for example, 5 s). However, in the excessive temperature rise countermeasure driving pattern of the second embodiment, as shown in FIG. 9, when removing the overburning gas, for example, the pulse width t ₃ (500 ms) at the overburning gas removal temperature T ₀ (300 ° C.). The pulse driving is used in which the above-mentioned pulse appears n times (for example, 6 times). Even in such a form, the overburning gas is removed without departing from the spirit of the present invention. The overburning gas removal time t ₀ , the pulse width t _3, and the number of pulses can be appropriately selected according to the actual situation. In addition, this pulse does not have to be the same pulse, and each pulse may have a different pulse width, or may be a pulse whose temperature is low only at the beginning and the temperature rises sequentially. Well, you can choose various variations. It is good also as such a form.

  Next, the third embodiment 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. Is the same in that the detection is performed using the normal drive pattern described above with reference to FIG. 3, but only the excessive temperature rise countermeasure drive pattern is different. The configuration of the third embodiment is given the same reference numeral as being the same as the configuration of the first embodiment described above, and redundant description is omitted, and only the excessive temperature rise countermeasure driving pattern will be described. This excessive temperature rise countermeasure driving pattern is a pattern in which only the gas detection stop explained in FIG. 5 is performed, and the overcombustible gas is simply removed.

In the excessive temperature rise countermeasure driving pattern of the first embodiment described above, as shown in FIG. 5, the energization is stopped when the excessive temperature rise is detected, the gas detection is stopped, and the overcombustible gas removal temperature T ₀ (for example, 300 ° C.). And continuously heating over the overburning gas removal time t ₀ (for example, 5 s). However, the excessive temperature rise measures driving pattern of the third embodiment, even in the middle of the gas detection time t ₁ stops detected immediately after the heater layer driving the excessive temperature rise, and, over-combustible gas removal not perform It is a pattern that has been stopped for a while. Thereafter, 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 in FIG. 1 receives the determination that the excessive temperature rise has occurred in the excessive temperature rise detection means 215, changes to the excessive temperature rise countermeasure drive pattern, 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 overheating immediately disappears due to the heater layer driving stop, and the heater layer 13 or the gas sensing layer 153 and the gas selective combustion layer 154 in which excessive temperature rise has occurred is destroyed. The Then, heater layer driving is performed in which heater layer driving is similarly stopped even when excessive temperature rise occurs again during the subsequent gas detection. Thereafter, the process is repeated until the excessive temperature rise is eliminated. Thereafter, the normal drive pattern as shown in FIG. 3 is maintained.

  Next, the fourth embodiment will be described. Compared to 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. Is the same in that the detection is performed using the normal drive pattern described above with reference to FIG. 3, but the excessive temperature rise countermeasure drive pattern is different. The configuration of the fourth embodiment is given the same reference numeral as being the same as the configuration of the first embodiment described above, and redundant description is omitted, and only the different excessive temperature rise countermeasure driving pattern will be described.

In the excessive temperature rise countermeasure driving pattern of the first embodiment described above, as shown in FIG. 5, the energization is stopped and the gas detection is stopped when the excessive temperature rise is detected, and then the overcombustible gas removal temperature T ₀ (for example, 300). C.) over a combustible gas removal time t ₀ (for example, 5 seconds). However, in the excessive temperature rise countermeasure driving pattern of the fourth embodiment, as shown in FIG. 10, even in the middle of the gas detection time t ₁ , the heater that reduces the power supplied to the heater layer 13 immediately after detection of the excessive temperature rise. it is those that approximate the temperature of the heater layer 13 to the normal gas detection temperature T ₁ of at most sensor deterioration temperature the layers were driving, overcombustion gas removal is performed at this time.

When the excessive temperature rise is detected, the drive switching means 216 of the central processing unit 21 in FIG. 1 receives the determination that the excessive temperature rise has occurred in the excessive temperature rise detection means 215, and reduces the power consumption. Switching to the temperature countermeasure driving pattern is performed to switch the driving of the heater layer driving means 211 to perform heater layer driving to reduce power. Implementing the gas detected after the gas detection time t _1.

  Even when an excessive temperature rise occurs again during the subsequent gas detection, the heater layer driving is performed to reduce the power similarly. Thereafter, the process is repeated until the excessive temperature rise is eliminated. Thereafter, the normal drive pattern as shown in FIG. 3 is maintained. If an excessive temperature rise is detected even if the excessive temperature rise countermeasure driving pattern is executed exceeding 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 the excessive temperature rise countermeasure driving. After the sensor chip is 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 detected temperature, it exceeds 455 ° C. at time t _A. In this case, if the power applied to the heater layer is not reduced, the temperature rises above 500 ° C. as shown by the one-dot chain line in FIG. 11, but if the power applied to the heater layer is reduced, the solid line in FIG. Thus, the temperature can be maintained at about 450 ° C., thereby preventing overheating.

  By stopping the heater layer driving, the influence of overcombustion is reduced, and a situation in which the heater layer 13 or the gas sensing layer 153 and the gas selective combustion layer 154 in which excessive temperature rise has occurred is avoided. Further, even when the power is reduced, the overcombustible gas burns and the overcombustible gas is removed.

  Next, the fifth embodiment will be described with reference to FIG. 12, FIG. 13, and FIG. The gas detector 2 of the 5th form of FIG. 12, FIG. 13 is the heater layer electrical property measurement part 23 among the structures of the gas detector 1 of the 1st form demonstrated previously using 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 driving means 211 is changed. Hereinafter, this heater layer driving means 211 and its driving pattern will be described, and the same reference numerals are assigned to the other components, and redundant description will be omitted. In the fifth embodiment, instead of switching to the excessive temperature rising countermeasure driving pattern used in the first, second, third, and fourth embodiments described above, the driving pattern includes the excessive temperature rising countermeasure driving ( FIG. 14).

In detail, the heater layer driving means 211 of the central processing unit 21 shown in FIG. 12 functions as the overcombustible gas removal driving means 211a and the gas detection driving means 211b.
First, the over-combustible gas removal drive means 211a, as shown in Figure 14, at a gas detection temperatures T ₁ overcombustion gas removal temperature T ₀ that over-combustible gases at a temperature lower than _(described later) is removed over overcombustion gas removal time t ₀ to heat drives the heater layer 13, controls the heater layer driving unit 22. The heater layer 13 heats at the overcombustible gas removal temperature T ₀ (eg, 300 ° C.) for the overcombustible gas removal time t ₀ (eg, 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 The overcombustible gas adhering due to the capillary condensation effect is evaporated and diffused and removed without rapidly becoming a high temperature. Further, the overcombustible gas around the outside of the gas selective combustion layer 154 is vaporized and diffused and removed without rapidly becoming high temperature. Here, the overburning gas removal temperature T ₀ is a temperature at which the gas sensing layer 153 and the gas selective combustion layer 154 are not deteriorated during vaporization. Even when the combustion is removed, there is no problem that the sensor deteriorates because the temperature is lower than the sensor deterioration temperature.

Subsequently, in the gas detecting driving unit 211b, to heat drives the heater layer 13 after over-combustible gas is removed in the gas detection temperature T _1, to control the heater layer driving unit 22. The heater layer 13 is heated at a high temperature, for example, a gas detection temperature T ₁ (eg, 450 ° C.) for a gas detection time t ₁ (eg, 500 ms).

Here, the gas selective combustion layer 154 at high temperature burns reducing gases such as CO and H _{2 and} other miscellaneous gases, but allows combustible gases such as CH ₄ and C ₃ H ₈ to pass therethrough. 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. The change in the sensor resistance value is detected to detect the presence or absence of city gas (combustible gas such as CH ₄ and C ₃ H ₈ ) that is generated when gas equipment leaks. 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 addition, the gas detection is changed to the high-off method, and in combination with the above-described high-low-off method and detection of incomplete combustion gas such as CO in the low state, one sensor is used for combustible gas / incomplete combustion gas. A method for detecting both of them may be adopted. And in such a drive pattern, one unit consisting of overcombustible gas removal 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 overburning gas adsorbed by the removal of the overburning gas is removed, and the prevention of overheating is realized.

  Next, the sixth embodiment will be described. Compared with the fifth embodiment described above with reference to FIGS. 12, 13, and 14, the sixth embodiment has the same configuration as the gas detector 2 shown in FIGS. 12 and 13, but only the drive pattern. Is different. The configuration of the sixth embodiment is given the same reference numeral as being the same as the configuration of the fifth embodiment described above, and redundant description is omitted, and only the driving patterns that are different will be described.

In the fifth embodiment described above, as shown in FIG. 14, heating is continuously performed at the overburning gas removal temperature T ₀ (for example, 300 ° C.) over the overburning gas removal time t ₀ (for example, 5 seconds). However, in the sixth embodiment, as shown in FIG. 15, at the time of removing the overburning gas, for example, a pulse having a pulse width t ₃ (500 ms) at the overburning gas removal temperature T ₀ (300 ° C.) n times in one cycle. Pulse driving is performed (six times in FIG. 15). Even in such a form, the overburning gas is removed without departing from the spirit of the present invention. The overburning gas removal time t ₀ , the pulse width t _3, and the number of pulses can be appropriately selected according to the actual situation. These pulses may not be the same pulse, and may have different pulse widths, or may be pulses that are low in temperature only and gradually increase in temperature. Variations can be selected. Thereby, it can be set as the low power consumption type gas detection apparatus which reduced power consumption and considered battery drive. It is good also as such a form.

Next, the seventh embodiment will be described. Compared to the fifth and sixth embodiments described above with reference to FIGS. 12, 13, 14, and 15, the seventh embodiment is the gas detector shown in FIGS. 12, 13, 14, and 15. Although the configuration is the same as 2, only the drive pattern at the beginning of gas detection is different. The configuration of the seventh embodiment is denoted by the same reference numeral as being the same as the configuration of the fifth and sixth embodiments described above, and redundant description is omitted, and only the drive pattern is described. In the seventh embodiment, the fifth, the sixth embodiment, further, the overcombustion gas removal drive means 211a, in terms of longer overcombustion gas removal time t ₀ for a predetermined initial period from the gas detection start. Return to normal over-combustible gas removal time t ₀ is after this initial period.

When it is considered that the non-energization period is long and the amount of adsorption of the super-combustible gas is large due to long-term storage, etc., in the initial period immediately after the start of energization, the over-combustible gas removal time t ₀ is lengthened, so Make sure to remove gas. This is applicable in the fifth and sixth embodiments. For example, normally, the heater layer 13 is heated at the overcombustion gas removal temperature T ₀ (eg, 300 ° C.) for the overcombustion gas removal time t ₀ (eg, 5 s). The heater layer 13 is heated at the overcombustible gas removal temperature T ₀ (eg, 300 ° C.) for the overcombustible gas removal time t ₀ (eg, 10 s). Thereby, the removal capability of overcombustible gas can be improved. Such a drive pattern can be employed.

Next, the eighth embodiment will be described. Compared to the fifth, sixth, and seventh embodiments described above with reference to FIGS. 12, 13, 14, and 15, the eighth embodiment has the same configuration as the invention shown in FIGS. However, only the drive pattern after the elapse of a predetermined period from the beginning of gas detection is different. The configuration of the eighth embodiment is given the same reference numeral as the configuration of the fifth, sixth, and seventh embodiments described above, and redundant description is omitted, and only the drive pattern is described. In the eighth embodiment, fifth, sixth, the seventh embodiment, further, the overcombustion gas removal drive means 211a, points to reduce the over-combustible gas removal time t ₀ after a lapse of a predetermined driving period from the gas detection start It is in.

After the overburning gas removal is performed a plurality of times, the overburning gas can be sufficiently removed even if the overburning gas removal time t ₀ is shortened. Thereby, it can be set as the low power consumption type gas detection apparatus which reduced power consumption and considered battery drive. This is applicable in the fifth, sixth and seventh embodiments. For example, normally, the heater layer 13 is heated at the overcombustion gas removal temperature T ₀ (eg, 300 ° C.) for the overcombustion gas removal time t ₀ (eg, 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 seconds). Such a drive pattern can be employed.

The fifth, sixth, seventh, the eighth embodiment, overcombustion gas removal drive means 211a, in one of the gas detection period _{t d,} over at overcombustion gas removal temperature _{T 0} (for example 300 ° C.) The overcombustible gas removal driving for heating over the combustible gas removal time t ₀ (for example, 5 seconds) is performed once. However, it may be performed intermittently (for example, FIG. 16) such as that once the overcombustion gas removal drive at every elapse of a plurality of gas sensing period t _d.

  Next, the ninth embodiment will be described. Even if the overburning gas removal driving is performed in a predetermined cycle, if the overburning gas is excessively adhered, it may not be removed only by the overburning gas removal driving in a predetermined cycle. Therefore, normally, the overburning gas removal driving is periodically performed, and the overburning gas removal driving is also performed when the excessive temperature rise is detected again thereafter. The ninth embodiment has the configuration shown in FIGS. And normally, it drives by the normal pattern demonstrated as a 5th, 6th, 7th, 8th form using FIG.14, FIG.15, FIG.16. As described above, the presence or absence of excessive temperature rise is detected during this driving. If there is no excessive temperature rise, the drive with the normal pattern is continued. However, when there is an excessive temperature rise, the over-combustible gas removal pattern as shown in FIGS. 5, 9, and 10 is switched. Then, the pattern returns to the normal pattern, but when the temperature rises again, the pattern is switched to the overburning gas removal pattern. Hereinafter, an alarm is issued when an excessive temperature rise is detected even if the drive by the normal pattern and the excessive temperature rise countermeasure drive pattern is executed more than a predetermined number of times. It is good also as such a form.

  Next, a tenth embodiment of the present invention will be described with reference to the drawings. Compared with the first to ninth modes described above, this embodiment employs a gas sensor 10 'having a bridge structure as shown in FIG. 17 as a gas sensor. FIG. 17 shows the configuration of the gas sensor conceptually in an easy-to-see manner, and the size and thickness of each part are not strict.

  This bridge structure, like the diaphragm structure, has a high heat insulation and low heat capacity structure and can be used as a gas sensor. The gas sensor 10 ′ includes a Si substrate 11, a thermal insulation support layer 12, a heater layer 13, an electrical insulation layer 14, a gas detection unit 15, a through hole 16, and a cavity 17. In addition, about the Si substrate 11, the heat insulation support layer 12, the heater layer 13, the electric insulation layer 14, and the gas detection part 15 which are the same structures as the gas sensor 10 demonstrated using previous FIG. Description to be omitted is omitted.

  The gas sensor 10 ′ forms the Si substrate 11, the heat insulating support layer 12, the heater layer 13, the electric insulating layer 14, and the gas detection unit 15 as described above, and then leaves four bridges and a central stage. As shown in the AA cross section of FIG. 17B and the BB cross section of FIG. 17C, wet etching is performed from above, and a quadrangular pyramid or a truncated pyramid-shaped cavity 17 is formed as shown in FIG. Form. Such a gas sensor 10 ′ may be configured as a gas detection device that detects a gas by driving the heater as described above.

  The gas detection device of the present invention has been described above with reference to the drawings. In the first to tenth embodiments described above, the gas selective combustion layer 154 is described as being configured. However, the gas detection unit 15 without the gas selective combustion layer 154 may be used. . In this case as well, gas detection is possible if the porous gas sensing layer 153 is present, and the porous gas sensing layer 153 adsorbs the overcombustible gas, so that the same effect can be expected. 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, and the reliability is improved and highly accurate detection is realized.

  The gas detection device of the present invention is particularly applicable to uses such as a gas leak alarm.

1, 2: Gas detector 10, 10 ': Gas sensor 11: Si substrate 12: Thermal insulation support layer 121: Thermal oxidation SiO ₂ layer 122: CVD-Si ₃ N ₄ layer 123: CVD-SiO ₂ layer 13: Heater layer 14: Electrical insulation 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: Cavity 20, 20 ′: Drive control / signal processing unit 21: Central processing unit 211: heater layer driving means 211a: overcombustible gas removal driving means 211b: gas detection driving 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: Determination means 219: Display control means 220: Output control means 22: Heater layer drive unit 23: Heater layer electrical characteristics Measuring unit 24: Gas detection signal processing unit 25: Storage unit 26: Alarm display unit 27: Alarm sound output unit 28: External output unit 29: Power supply unit

Claims (12)

A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
A heater layer driving unit that energizes and drives the heater layer with a normal driving pattern for detecting the detection target gas or an excessive temperature rising countermeasure driving pattern for preventing an excessive temperature rising of the gas detection unit;
An excessive temperature rise detection unit for detecting an excessive temperature rise in the gas detection unit;
A drive switching unit that changes the drive pattern of the heater layer drive unit from the normal drive pattern to the over-temperature rise countermeasure drive pattern when an over temperature rise is detected by the over temperature rise detection unit. Gas detection device.   The overheat temperature countermeasure driving pattern is a temperature lower than the detection temperature of the detection target gas, and the overburning gas removal temperature at which the overburning gas is removed, and the heater layer over the overburning gas removal time. The gas detection device according to claim 1, wherein the gas detection device is a pattern for energization driving.   The excessive temperature rise countermeasure driving pattern is a temperature that is lower than the detection temperature of the detection target gas after the energization driving of the heater layer is temporarily stopped, and at the excessive combustion gas removal temperature at which the excessive combustion gas is removed. The gas detection device according to claim 1, wherein the heater layer is energized and driven over an overburning gas removal time.   3. The heater layer energization drive in the over-temperature-measure countermeasure driving pattern is a pattern in which the heater layer is energized and driven over a period of time for removing the overburning gas by a repetitive pulse having a predetermined pulse width. 3. The gas detection device according to 3.   The gas detection device according to claim 1, wherein the excessive temperature rise countermeasure driving pattern is a pattern for stopping energization driving of the heater layer.   2. The gas according to claim 1, wherein the excessive temperature rise countermeasure driving pattern is a pattern in which the heater layer is energized and driven 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,
A heater layer electrical property measuring unit for obtaining electrical property values of the heater layer;
The gas detection device according to any one of claims 1 to 6, further comprising a heater layer temperature calculation unit that calculates a heater layer temperature based on the electrical characteristic value. A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
A heater layer drive unit that electrically drives the heater layer with a normal drive pattern for detecting the detection target gas or a supercombustible gas removal pattern for removing the supercombustible gas at a temperature lower than the detection temperature of the detection target gas; Prepared,
The gas detection device, wherein after the energization driving of the overburning gas removal pattern, the detection target gas is detected by energization driving with the normal driving pattern. A gas detection unit having a gas detection layer for detecting a detection target gas, and a heater layer for heating the gas detection layer;
The heater layer includes a normal driving pattern for detecting the detection target gas, a supercombustible gas removal pattern for removing a supercombustible 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 driving unit that is energized and driven with an excessive temperature rise countermeasure driving pattern to prevent;
An excessive temperature rise detection unit for detecting an excessive temperature rise in the gas detection unit;
After the energization drive of the overburning gas removal pattern, the energization drive is performed with the normal drive pattern, and in the normal drive pattern, when an excessive temperature rise is detected by the overheat detection unit, the heater layer drive unit And a drive switching unit that changes the drive pattern from the normal drive pattern to the excessive temperature rise countermeasure drive pattern.   The overburning gas removal pattern is a temperature lower than the detection temperature of the detection target gas, and the overburning gas removal temperature at which the overburning gas is removed, and the heater layer over the overburning gas removal time. The gas detection device according to claim 8, wherein the gas detection device is a pattern for energizing and driving.   The energization drive of the heater layer in the overburning gas removal pattern is a pattern in which the heater layer is energized and driven over a overburning gas removal time by repeated pulses having a predetermined pulse width. Gas detection device.   The gas detection according to any one of claims 8 to 11, wherein the overcombustible gas removal pattern is means for extending the overcombustible gas removal time over a predetermined initial period from the start of gas detection. apparatus.

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