JP5091078B2 - Combustible gas detector - Google Patents

Description

  The present invention relates to a flammable gas detection device that includes a heating resistor disposed in a detection atmosphere and detects the gas concentration of a flammable gas present in the detection atmosphere.

  A solid electrolyte body is provided with an air electrode and a fuel electrode, air is supplied to the air electrode and fuel gas is supplied to the fuel electrode, and oxygen in the air and hydrogen in the fuel gas are chemically reacted through the solid electrolyte body. There is known a fuel cell that generates electric power by generating the electric power.

  As described above, since the fuel cell uses hydrogen as the fuel, the safety measures of the fuel cell are important. That is, the fuel cell requires a combustible gas detection device that can detect a low concentration below the explosion limit of hydrogen.

Further, in order to use hydrogen used as a fuel more efficiently, the fuel cell needs a combustible gas detection device that can detect a high hydrogen concentration in the fuel gas.
2. Description of the Related Art Conventionally, there has been known a combustible gas detection device that detects the gas concentration of a combustible gas present in a detection target atmosphere based on voltages between terminals of two heat conduction type heating resistors controlled at different temperatures. (For example, see Patent Document 1). In such a flammable gas detection device, the gas concentration of the flammable gas is calculated based on the voltage between the terminals of one heat conduction type heating resistor, and two heat conduction types controlled to different temperatures from each other. The humidity in the detected atmosphere is calculated based on the voltage between the terminals of the heating resistor. And this combustible gas detection apparatus correct | amends the calculated gas concentration using the calculated humidity, and employ | adopted this correction value as a detection result.

However, the gas concentration detectable range of the combustible gas detection device described in Patent Document 1 is limited to the low concentration region. The reason for this will be described below.
The combustible gas detection device equipped with a heat conduction type heating resistor has a voltage between terminals of the heating resistor controlled to a constant temperature in accordance with a change in the thermal conductivity of the combustible gas present in the detected atmosphere. Based on the change, the concentration of combustible gas is detected.

FIG. 7 is a graph showing the relationship between the terminal voltage and the hydrogen gas concentration of two heat conduction heating elements controlled at different temperatures (150 ° C. and 300 ° C.).
As shown in FIG. 7, as the hydrogen gas concentration increases, the voltage between the terminals of the two heat conduction type heating resistors increases. The higher the control temperature, the greater the change rate of the inter-terminal voltage with respect to the increase in the hydrogen gas concentration. That is, the detection sensitivity of the hydrogen gas concentration can be improved by increasing the control temperature.

  However, when the control temperature is increased, the terminal voltage of the heating resistor increases. A circuit that detects the terminal voltage of the heating resistor (hereinafter referred to as a terminal voltage detection circuit) has an upper limit value of the detectable voltage. For this reason, the higher the control temperature, the narrower the range of the inter-terminal voltage that can be detected by the terminal voltage detection circuit. Thereby, the gas concentration detectable range of the combustible gas detection device is reduced. That is, the higher the detection sensitivity of the hydrogen gas concentration, the narrower the gas concentration detectable range. For this reason, in the combustible gas detection device used in the low concentration region where high concentration detection sensitivity is required, the gas concentration detectable range is limited to the low concentration region.

On the other hand, there is known a combustible gas detection device capable of detecting the gas concentration of the combustible gas not only in the low concentration region but also in the high concentration region (see, for example, Patent Document 2). Such a combustible gas detection apparatus includes a contact combustion type heating resistor and a heat conduction type heating resistor, one heating resistor for detecting a low concentration region, and the other heating resistor for a high concentration region. It is used for detection.
JP 2008-180542 A Japanese Patent No. 3929845

  However, since an organic silicon-based sealing material or piping having heat resistance is used in the above-described fuel cell, a silicon compound generated from the sealing material or piping exists in the detected atmosphere. For this reason, when the combustible gas detection device described in Patent Document 2 is used in a fuel cell, a silicon compound is used as a catalyst used in a catalytic combustion type gas sensor including a catalytic combustion type heating resistor. accumulate. Thereby, in the combustible gas detection apparatus of the said patent document 2, there existed a problem that the precision of the gas concentration detection by a contact combustion type gas sensor fell.

  Alternatively, when the combustible gas detection device described in Patent Document 2 is mounted in a vehicle interior, organic silicon is vaporized from resin components in the vehicle interior and adheres to the catalyst used in the contact combustion type gas sensor. There has been a problem that the accuracy of gas concentration detection by the catalytic combustion type gas sensor is lowered.

  The present invention has been made in view of such problems, and can detect the gas concentration of a combustible gas from a low concentration region to a high concentration region without causing a decrease in gas concentration detection accuracy due to the silicon compound. An object of the present invention is to provide a combustible gas detection device.

  The invention according to claim 1, which is made to achieve the above object, is arranged in an atmosphere to be detected, and changes its own resistance value as its temperature changes due to heat conduction to the combustible gas. A first heat-conducting gas detector that is energized so that the first heat-generating resistor has a resistance value corresponding to a preset first target temperature; And a second heating resistor whose own resistance value changes as its temperature changes due to heat conduction to the combustible gas, and the second heating resistor is set lower than the first target temperature. A second heat-conducting gas detector energized to have a resistance value corresponding to the second target temperature, and a first output detection means for detecting a first output value corresponding to the resistance value of the first heating resistor. And a second output value corresponding to the resistance value of the second heating resistor. A first output gas detector, and a first calculation gas concentration that is a gas concentration of a combustible gas present in the atmosphere to be detected, based on the first output value detected by the first output detector and the first output value detected by the first output detector. Based on the concentration output means and the second output value detected by the second output detection means, a second concentration calculation means for calculating a second calculation gas concentration that is a gas concentration of the combustible gas present in the atmosphere to be detected. And a combustible gas detection device for detecting a gas concentration of a combustible gas existing in a detection atmosphere, wherein the comparison is performed in advance with either the first calculation gas concentration or the second calculation gas concentration. Detection that employs either the first calculated gas concentration or the second calculated gas concentration as the detection result of the combustible gas detection device based on the comparison result by the concentration comparison means for comparing the determination value and the comparison result by the concentration comparison means Result adopter A combustible gas detector, characterized in that it comprises a.

  In the gas sensor configured as described above, the first output detection unit detects the first output value corresponding to the resistance value of the first heating resistor that is energized so as to have the resistance value corresponding to the first target temperature. A second output value corresponding to the resistance value of the second heating resistor that is energized so that the second output detection means has a resistance value corresponding to the second target temperature set lower than the first target temperature. To detect.

  The first concentration calculation means calculates a first calculation gas concentration that is a gas concentration of the combustible gas based on the first output value detected by the first output detection means, and the second concentration calculation means includes the first concentration calculation means. Based on the second output value detected by the two-output detection means, a second calculation gas concentration that is a gas concentration of the combustible gas is calculated.

Further, the concentration comparison means compares either the first calculation gas concentration or the second calculation gas concentration with a preset comparison determination value.
Then, the detection result adoption means employs either the first calculation gas concentration or the second calculation gas concentration as the detection result of the combustible gas detection device based on the comparison result by the concentration comparison means.

  Therefore, either the gas concentration detected using the first heating resistor (first calculation gas concentration) or the gas concentration detected using the second heating resistor (second calculation gas concentration), It can be selected according to the gas concentration of the combustible gas.

  As a result, the first heat generating resistor and the second heat generating resistor are used in the region where high concentration detection sensitivity is required, and the set target temperature is set. Therefore, it is possible to select that the second heating resistor having a low value is used in an area where high density detection sensitivity is not required. And the 2nd heating resistor with a low set target temperature has a detectable gas concentration range wider than the 1st heating resistor with a high set target temperature.

  Therefore, according to the combustible gas detection device of the first aspect, the gas concentration of the combustible gas can be detected with high concentration detection sensitivity in a region where high concentration detection sensitivity is required, and the combustible gas can be detected. The detectable gas concentration range can be widened.

  For example, in a combustible gas detection device that detects the hydrogen gas concentration of a fuel cell, it is necessary to detect a low concentration below the explosion limit of hydrogen with high concentration detection sensitivity. Therefore, based on the comparison result by the concentration comparison means, when the gas concentration is less than the comparison determination value, the first calculated gas concentration is adopted as the detection result of the combustible gas detection device, and the comparison result by the concentration comparison means Based on the above, when the gas concentration is equal to or higher than the comparison determination value, the second calculated gas concentration may be adopted as the detection result of the combustible gas detection device.

  In addition, as a selection condition when the concentration comparison unit selects either the first calculation gas concentration or the second calculation gas concentration as the gas concentration to be compared with the comparison determination value, the following is adopted. May be.

  That is, the concentration comparison means compares the first calculated gas concentration with the comparison determination value in a situation where the detection result adoption means adopts the first calculated gas concentration as the detection result of the combustible gas detection device. In a situation where the detection result adopting means adopts the second calculated gas concentration as the detection result of the combustible gas detection device, the second calculated gas concentration may be compared with the comparison determination value.

  However, when the concentration comparison means performs comparison for the first time immediately after the combustible gas detection device is activated, the detection result adoption means does not employ either the first calculation gas concentration or the second calculation gas concentration. . Therefore, immediately after the combustible gas detection device is activated, either the first calculated gas concentration or the second calculated gas concentration may be determined in advance as the gas concentration to be compared with the comparison determination value. .

  Moreover, the 1st heat conduction type gas detection part and the 2nd heat conduction type gas detection part do not have the catalyst used with a catalytic combustion type gas sensor. For this reason, the situation where the accuracy of gas concentration detection falls due to the silicon compound adhering to the catalyst does not occur.

As described above, the gas concentration of the combustible gas can be detected from the low concentration region to the high concentration region without causing a decrease in gas concentration detection accuracy due to the silicon compound.
In the combustible gas detection device according to claim 1, as described in claim 2, the gas concentration range detectable by the first heating resistor is the gas concentration detectable by the second heating resistor. It may be included in the range.

  Further, in the combustible gas detection device according to claim 1 or 2, as described in claim 3, the combustible gas detection device includes temperature detection means for detecting an environmental temperature in the atmosphere to be detected, and includes first concentration calculation means. Uses the environmental temperature detected by the temperature detection means to calculate the first calculation gas concentration, and the second concentration calculation means also uses the environmental temperature detected by the temperature detection means to calculate the second calculation gas. It is advisable to calculate the concentration.

According to the combustible gas detection device configured as described above, the gas concentration of the combustible gas can be detected more accurately by considering the environmental temperature in the detected atmosphere.
Further, in the combustible gas detection device according to claim 3, as described in claim 4, the first output value detected by the first output detection means and the second output value detected by the second output detection means. Humidity calculation means for calculating the humidity in the detected atmosphere based on the output value and the environmental temperature detected by the temperature detection means is provided, and the first concentration calculation means also uses the humidity detected by the humidity detection means. Thus, the first calculation gas concentration is calculated, and the second concentration calculation means preferably calculates the second calculation gas concentration also using the humidity detected by the humidity detection means.

According to the combustible gas detection device configured as described above, the gas concentration of the combustible gas can be detected more accurately by considering the humidity in the detected atmosphere.
By the way, when only one value is set as the comparison determination value, the detection result employed by the detection result adopting means in a situation where the gas concentration of the combustible gas frequently fluctuates in the vicinity of the comparison determination value. However, there is a possibility that a phenomenon (hunting phenomenon) that frequently switches between the first calculation gas concentration and the second calculation gas concentration may occur.

Therefore, the combustible gas detector according to claim 1, concentration comparing means includes a first determination value set in advance for comparison with the first operational gas concentration is compared with the second calculation gas concentration Therefore, in the case where the second determination value is set to a value smaller than the first determination value and the comparison is made using the first calculated gas concentration, the first determination value is used as the comparison determination value. When the comparison is made using the calculated gas concentration, the second determination value is used as the comparison determination value, and the gas concentration of the combustible gas increases, so that the detection result becomes the first calculated gas concentration and the second calculated gas. The first determination value is used as a comparison determination value when switching between the concentration and the gas concentration of the combustible gas is decreased, so that the detection result is between the first calculation gas concentration and the second calculation gas concentration. as using the second judgment value as a comparison determination value when switched Then good.

  In the combustible gas detection device configured as described above, in a situation where the detection result adopting unit adopts the first calculation gas concentration as the detection result of the combustible gas detection device, the concentration comparison unit includes the first calculation gas. In a situation where the concentration is compared with the first determination value, and the detection result adopting unit adopts the second calculated gas concentration as the detection result of the combustible gas detection device, the concentration comparing unit compares the second calculated gas concentration with the first calculated gas concentration. The second determination value can be compared.

  Since the first determination value and the second determination value are different from each other, the second calculation gas is detected from the situation where the detection result adoption means adopts the first calculation gas concentration as the detection result of the combustible gas detection device. The gas concentration of the combustible gas when transitioning to the situation where the concentration is adopted, and the gas concentration of the combustible gas when transitioning from the situation where the second computation gas concentration is adopted to the situation where the first computation gas concentration is adopted Is different.

  Therefore, the detection result adopted by the detection result adoption means is between the first calculation gas concentration and the second calculation gas concentration because the gas concentration of the combustible gas frequently fluctuates in the vicinity of a certain value. Thus, it is possible to suppress the occurrence of a phenomenon (hunting phenomenon) that frequently switches.

  However, there is a need to have the following magnitude relationship between the first determination value and the second determination value. That is, as the gas concentration of the combustible gas increases, the determination value when the detection result adopted by the detection result adoption means switches between the first calculation gas concentration and the second calculation gas concentration is increased. As a determination value, the determination value when the detection result adopted by the detection result adoption means is switched between the first calculation gas concentration and the second calculation gas concentration by decreasing the gas concentration of the combustible gas. When the decrease direction determination value is used, the increase direction determination value needs to be larger than the decrease direction determination value. Specifically, when the first determination value is an increase direction determination value and the second determination value is a decrease direction determination value, the first determination value is larger than the second determination value. On the other hand, when the second determination value is the increase direction determination value and the first determination value is the decrease direction determination value, the first determination value is smaller than the second determination value.

Further, in the combustible gas detection device according to any one of claims 1 to 4 , as described in claim 5 , the detection result is not adopted as a detection result of the combustible gas detection device. It is preferable to provide energization stopping means for stopping energization of either the first heating resistor or the second heating resistor corresponding to the gas concentration.

  According to the combustible gas detection device configured as described above, it is possible to prevent the heating resistor that is not used for detecting the gas concentration of the combustible gas from being unnecessarily energized. Thereby, while being able to reduce the power consumption of a combustible gas detection apparatus, the lifetime of a combustible gas detection apparatus can be improved.

  In addition, it is good to stop electricity supply to the 1st heating resistor with the high target temperature set. In this way, it is possible to improve the life of the heating resistor that requires high detection accuracy.

Embodiments of the present invention will be described below with reference to the drawings.
1 is a cross-sectional view of a combustible gas detection device 1 to which the present invention is applied, FIG. 2 is a cross-sectional view of the periphery of an element case 20, FIG. 3 is a plan view of a gas detection element 60, and FIG. FIG. 5 is a block diagram showing a schematic configuration of the control circuit 200. FIG.

The combustible gas detection apparatus 1 to which the present invention is applied is a combustible gas detection apparatus that includes a gas detection element 60 that is a heat conduction type gas detection element and detects the concentration of the combustible gas.
This combustible gas detection device 1 is mounted on, for example, a pipe provided in a fuel cell unit of an automobile, and is used for the purpose of detecting hydrogen contained in a gas to be detected discharged through the pipe. The combustible gas detection device 1 includes a control circuit 200 and a microcomputer 94 (hereinafter also referred to as a microcomputer 94) for detecting combustible gas contained in the gas to be detected.

  As shown in FIG. 1, the combustible gas detection device 1 supports an element case 20 that houses a gas detection element 60 that detects a gas to be detected, and supports the element case 20 and is electrically connected to the gas detection element. And a housing case 40 for housing the circuit board 41 formed.

Here, the vertical direction in FIG. 1 will be described as the vertical direction in the combustible gas detection device 1, and the horizontal direction in FIG.
First, the configuration of the housing case 40 will be described.

  The housing case 40 includes a case body 42 and a case lid 44 that is a lid that covers an opening provided at the upper end of the case body 42. The housing case 40 includes a circuit board 41, a microcomputer 94, and heating elements 50 and 51 therein. Hereinafter, each member which comprises the storage case 40 is explained in full detail.

  The case main body 42 is a container having an opening on the upper surface and the lower surface and having a predetermined height, a holding portion 46 that holds the flange portion 38 of the element case 20, and a circuit board that holds the peripheral portion of the circuit board 41. Holding part 45. Moreover, the opening provided in the upper surface of the case main body 42 is configured such that a case lid 44 made of synthetic resin for closing the opening can be disposed.

The case main body 42 includes a flow path forming portion 43 formed at the lower center of the case main body 42 and a connector 55 formed on a side portion of the case main body 42 for external power feeding.
Inside the flow path forming portion 43, an introduction portion 35 of the element case 20 for introducing and discharging the gas to be detected is accommodated. As described above, the element case 20 is held by the holding portion 46 in a state where a part of the element case 20 is disposed inside the housing case 40. A seal member 47 is disposed between the flange portion 38 of the element case 20 and the case body 42 to seal (seal) these gaps.

  The connector 55 is for supplying electricity to the circuit board 41 and the microcomputer 94, and is assembled to the outer surface of the case body 42. A plurality of connector pins 56 and 57 projecting from the side wall of the case body 42 are provided inside the connector 55. The connector pins 56 and 57 are electrically connected to the circuit board 41 and the microcomputer 94 via wiring (not shown) embedded in the side wall of the case main body 42, respectively.

  The circuit board 41 is a plate-like board having a predetermined thickness, and the control circuit 200 (see FIG. 5) for detecting the combustible gas contained in the gas to be detected, and the temperatures of the heating elements 50 and 51. And a temperature control circuit (not shown) for controlling.

  The control circuit 200 is electrically connected to each electrode (electrode films 371, 373, 391 and ground electrode films 372, 392 (see FIGS. 3 and 5) described later) of the gas detection element 60 through the connection terminals 24-28. Connected. The temperature control circuit and the heating elements 50 and 51 are electrically connected by lead wires 52 and 53. Although not shown, two lead wires 52 and 53 are provided. The configuration of the control circuit 200 provided on the circuit board 41 will be described later.

  The microcomputer 94 provided on the lower surface of the circuit board 41 is configured to calculate the concentration of the combustible gas contained in the gas to be detected (sensor output calculation processing) based on the output of the control circuit 200, and to output the temperature control circuit. Based on the above, various processes such as a process (temperature control process) for controlling the heat generation amount (temperature) of the heating elements 50 and 51 are executed. The microcomputer 94 includes at least a storage device that stores a program for executing the sensor output calculation processing and the temperature control processing of the heating elements 50 and 51, and a CPU that executes the program stored in the storage device. It is prepared for.

Next, the heating elements 50 and 51 will be described.
The heating elements 50 and 51 are for heating the element case 20 via the housing case 40 or directly, and maintaining the temperature of the inner surface of the element case 20 at a temperature higher than the dew point. The heating elements 50 and 51 are configured using, for example, a resistor used in an electronic component or the like, a film heater, or the like.

  In order to efficiently heat the inner surface of the element case 20 that forms the detection space 39, the heating elements 50 and 51 apply heat to the member that contacts the detection space 39 in the storage space forming surface 58 that surrounds the storage space 59. It is preferable to arrange it at a site where it can be transmitted. Alternatively, it is preferable that the heating elements 50 and 51 are arranged at a site where heat can be efficiently transmitted to the element case 20 which is a member that contacts the detection space 39. For example, the heating elements 50 and 51 can be arranged in a part of the element case 20 that constitutes the accommodation space forming surface 58, or the element case 20 of the inner side surface of the accommodation case 40 that constitutes the accommodation space forming surface 58. Can be disposed in a region adjacent to (the same surface as the surface on which the holding portion 46 is formed).

  The amount of heat generated by the heating elements 50 and 51 is preferably set so that the temperature of the inner surface of the element case 20 forming the detection space 39 is higher than the dew point of the gas to be detected. As a result, the gas to be detected is cooled below the dew point of the gas to be detected on the inner surface of the element case 20, and it is possible to prevent condensation in the detection space 39. Moreover, since the gas to be detected usually has a temperature higher than the dew point, it is more preferable to set the temperature of the heating elements 50 and 51 to be equal to or higher than the temperature of the gas to be detected. By setting such a temperature, it is possible to prevent the temperature of the gas to be detected from becoming unstable due to cooling of the gas to be detected on the inner surface of the element case 20 that forms the detection space 39.

  Therefore, the combustible gas detection device 1 can reduce the influence of the temperature characteristics of the gas detection element 60 due to the temperature of the gas to be detected, and detect the combustible gas contained in the gas to be detected with higher accuracy. it can.

  The heating elements 50 and 51 are controlled by, for example, known constant voltage control, constant power control, or PWM control (pulse width modulation control). In addition, the control method in the case of providing a plurality of heating elements such as the heating elements 50 and 51 may adopt the same control method for each heating element, or may adopt different control methods. Also good. Moreover, the program which prescribed | regulated the control method of the heat generating bodies 50 and 51 is memorize | stored in the memory | storage device with which the microcomputer 94 is provided, and is performed by CPU.

  Next, the element case 20 which comprises the combustible gas detection apparatus 1 is demonstrated. Here, the vertical direction in FIG. 2 will be described as the vertical direction in the combustible gas detection device 1, and the horizontal direction in FIG. 2 will be described as the horizontal direction in the combustible gas detection device 1.

  As shown in FIG. 2, the element case 20 sandwiches the connection terminal extraction base 21 on which the gas detection element 60 is installed and the peripheral portion of the connection terminal extraction base 21 toward the introduction port for introducing the gas to be detected. And a detection space forming member 22 having a cylindrical wall surface. A seal member 48 that seals (seals) a gap between the element case 20 and the detection space forming member 22 is disposed at the peripheral edge of the connection terminal extraction base 21. A space surrounded by the connection terminal extraction base 21 and the detection space forming member 22 is a detection space 39 for introducing the gas to be detected.

  The connection terminal extraction base 21 is a member for supporting the gas detection element 60, and at least a part thereof is formed of a member having thermal conductivity that conducts heat of the heating element 50 provided on the outer surface. It is preferable. A gas detection element 60 is provided on the inner surface of the connection terminal extraction base 21. Further, the connection terminal take-out base 21 is provided with insertion holes for inserting the connection terminals 24 to 28 individually, and the peripheral edge of each insertion hole is covered with an insulating member.

  The connection terminals 24 to 28 are members for electrically connecting the gas detection element 60 and a circuit provided on the circuit board 41, and are formed in a rod shape by a conductive member. One end of each connection terminal is inserted through an insertion hole provided in the connection terminal extraction table 21 and is supported perpendicular to the connection terminal extraction table 21.

  The detection space forming member 22 includes an outer cylinder 36 that comes into contact with the gas to be detected on the outer surface, an extraction table support 37 that sandwiches the peripheral edge of the connection terminal extraction table 21, and a flange 38 that is supported by the storage case 40. And. In addition, an introduction port 34 that is an opening for introducing a gas to be detected into the detection space 39 is provided at the lower end of the detection space forming member 22.

  In the vicinity of the introduction port 34, an introduction portion 35 is provided that forms a flow path for introducing and discharging the gas to be detected from the gas detection element 60. The introduction portion 35 is loaded with a water repellent filter 29, a spacer 30, and two metal meshes 31 and 32 in order from the introduction port 34. These members are sandwiched and fixed by the detection space forming member 22 and the filter fixing member 33. Hereinafter, members constituting the introducing portion 35 will be described in detail.

  First, the water repellent filter 29 is a filter attached at a position closest to the introduction port 34, and is a thin film having water repellency that removes water droplets contained in the gas to be detected. Accordingly, it is possible to prevent the gas detection element 60 from getting wet even in a humid environment where water droplets or the like fly. Further, the water repellent filter 29 may be any filter that removes water droplets by physical adsorption. For example, a filter using polytetrafluoroethylene (PTFE) can be applied.

  The spacer 30 is provided on the inner peripheral wall of the filter fixing member 33, and is a member having a shape (ring shape in plan view) having an opening through which a gas to be detected is introduced. And the positions of the wire meshes 31 and 32 are adjusted.

  The metal nets 31 and 32 have a predetermined thickness and a predetermined opening, and the temperature of the heating resistor provided in the gas detection element 60 is higher than the ignition temperature of hydrogen gas contained in the gas to be detected. Even when it ignites, it functions as a flame arrester that prevents the flame from going outside.

  The filter fixing member 33 is a member for sandwiching and fixing the water repellent filter 29, the spacer 30, and the two metal nets 31 and 32 to the detection space forming member 22. The filter fixing member 33 has a cylindrical wall surface that comes into contact with the inner wall surface of the detection space forming member 22, and includes a convex portion that protrudes inward from the inner surface of the wall surface. The convex portion is provided to sandwich and fix the water repellent filter 29, the spacer 30, and the two metal meshes 31 and 32 with the detection space forming member 22.

Next, the configuration of the gas detection element 60 described above will be described.
The gas detection element 60 is manufactured using a micromachining technique. As shown in FIG. 4, the gas detection element 60 includes a silicon semiconductor substrate 310 and insulating layers (upper insulating layers) on both upper and lower sides of the silicon semiconductor substrate 310. 323, a lower insulating layer 324). The upper insulating layer 323 is formed on the surface of the silicon semiconductor substrate 310, while the lower insulating layer 324 is formed on the back surface of the silicon semiconductor substrate 310.

  The upper insulating layer 323 includes a silicon oxide film 321 formed on the surface of the silicon semiconductor substrate 310 and a silicon nitride film 322 laminated on the silicon oxide film 321. The lower insulating layer 324 includes a silicon oxide film 321 formed on the back surface of the silicon semiconductor substrate 310 and a silicon nitride film 322 stacked on the silicon oxide film 321.

  In the silicon semiconductor substrate 310, a plurality of recesses 311 are formed at intervals on the back side of the upper insulating layer 323. The lower insulating layer 324 is formed as an opening of the recess 311 by removing portions corresponding to the recess 311. As a result, the upper insulating layer 323 is exposed to the outside through the opening of each recess 311 at each corresponding back surface of the back surface corresponding to each recess 311. The silicon semiconductor substrate 310 constitutes a substrate portion 312 at a portion other than each recess 311.

  3 and 4, the gas detection element 60 includes a plurality of heating resistors 330 (left heating resistor 331 and right heating resistor 332) arranged on both the left and right sides, and the left side and the center. A plurality of wiring films 340 (a left wiring film 341, a central wiring film 342, and a right wiring film 343) are provided on the side and the right side, respectively.

  The left heating resistor 331 is spirally formed on the surface of the upper insulating layer 323 corresponding to the left recess 313, while the right heating resistor 332 is the right of the surface of the upper insulating layer 323. A spiral shape is formed on a portion corresponding to the recess 314. In the present embodiment, the two heating resistors 330 (the left heating resistor 331 and the right heating resistor 332) together with the wiring films 340 (the left wiring film 341, the central wiring film 342, and the right wiring film 343) to be described later. , Made of platinum resistance material.

  As shown in FIG. 4, the left wiring film 341 is located on the left side portion of the surface of the upper insulating layer 323 corresponding to the substrate portion 312 of the silicon semiconductor substrate 310, and as shown in FIG. It is formed so as to be electrically connected to one end of the resistor 331. The central wiring film 342 is located on the central portion of the surface of the upper insulating layer 323 so as to correspond to the substrate portion 312 of the silicon semiconductor substrate 310, and the other end of the left heating resistor 331 and the right heating resistor. It is formed so as to be electrically connected to one end of 332. The right wiring film 343 is located on the right side of the surface of the upper insulating layer 323 so as to correspond to the substrate portion 312 of the silicon semiconductor substrate 310 and is electrically connected to the other end of the right heating resistor 332. It is formed so that.

  3 and 4, the gas detection element 60 includes an inner protective layer 350 and an outer protective layer 360, and includes three electrode films 370 (a left electrode film 371, a central electrode film 372, and a right electrode film). An electrode film 373) is provided. The inner protective layer 350 is formed on the surface of the upper insulating layer 323 so as to cover each wiring film 340 and each heating resistor 330. The outer protective layer 360 is formed on the inner protective layer 350 in a laminated form.

  Next, in each of the inner protective layer 350 and the outer protective layer 360 corresponding to the left, central, and right wiring films 340 (left wiring film 341, central wiring film 342, right wiring film 343), Left, center and right contact holes 361 are formed. As a result, the left, central and right wiring films 340 (the left wiring film 341, the central wiring film 342, and the right wiring film 343) are connected to the inner protective layer via the left, central and right contact holes 361. 350 and the outside of the outer protective layer 360 are provided so as to be electrically connectable.

  In the left, center, and right contact holes 361, left, center, and right electrode films 370 (left electrode film 371, center electrode film 372, and right electrode film 373) are formed, respectively. The left, center, and right electrode films 370 (left electrode film 371, center electrode film 372, and right electrode film 373) are left, center, and right wiring films 340 (left wiring film 341, center side wiring film 342). , The right wiring film 343).

  In the present embodiment, in the gas detection element 60, the left heating resistor 331, the left and center wiring films 340 (left wiring film 341, the center wiring film 342) and the left and center electrode films 370 (left electrode). The film 371 and the central electrode film 372) mainly constitute the left heat conduction type gas detection unit 381. Further, the right side heating resistor 332, the center side and right side wiring films 340 (center side wiring film 342, right side wiring film 343) and the center side and right side electrode films 370 (center electrode film 372, right side electrode film 373) are provided. Primarily, the right heat conduction type gas detection unit 382 is configured.

  Further, the gas detection element 60 includes a resistance temperature detector 390 as shown in FIG. The resistance temperature detector 390 is made of a resistance temperature material containing platinum (Pt), and is formed as a thin film resistor between the upper insulating layer 323 and the inner protective layer 350. Thereby, the resistance temperature detector 390 detects the temperature (hereinafter also referred to as environmental temperature) in the atmosphere to be detected in which the combustible gas detection device 1 is disposed. In the present embodiment, the temperature resistance coefficient of the resistance temperature detector 390 is substantially the same as the temperature resistance coefficient of the two heating resistors 330.

  In addition, an electrode film 391 and a ground electrode film 392 are formed in each contact hole (not shown) formed on the left and right ends of the resistance temperature detector 390 among the inner protective layer 350 and the outer protective layer 360. ing. The resistance temperature detector 390 is connected to the circuit board 41 (control circuit 200) via an electrode film 391, a ground electrode film 392, and a terminal (not shown).

Next, the configuration of the control circuit 200 will be described.
As shown in FIG. 5, the control circuit 200 includes a low temperature side gas detection circuit 91, a high temperature side gas detection circuit 92, and a temperature measurement circuit 93.

The low temperature side gas detection circuit 91 includes a low temperature side bridge circuit 210, a current adjustment circuit 230, and an operational amplification circuit 250.
The low temperature side bridge circuit 210 includes a low temperature heating resistor 211 and three fixed resistors 212, 213, and 214, and is configured to form a bridge circuit. Further, in the low-temperature side bridge circuit 210, the low-temperature heating resistor 211 includes a left-side heating resistor 331 that constitutes the left-side heat conduction type gas detection unit 381 of the gas detection element 60. One end of the low-temperature heating resistor 211 is grounded, and the other end is grounded via a fixed resistor 212, a fixed resistor 213, and a fixed resistor 214.

  The low-temperature side bridge circuit 210 has a current adjustment circuit 230 so that a potential difference generated between the common terminal of the low-temperature heating resistor 211 and the fixed resistor 212 and the common terminal of the fixed resistor 213 and the fixed resistor 214 becomes zero. A control voltage is applied. As a result, the resistance value of the low-temperature heating resistor 211 is controlled to be constant, that is, the temperature of the left heating resistor 331 is controlled to be constant. The voltage generated at the common terminal of the low-temperature heating resistor 211 and the fixed resistor 212 is input to the microcomputer 94 as an output signal (potential VL).

  In addition, the current adjusting circuit 230 is dc-directed so as to maintain the resistance value of the low-temperature heating resistor 211 at a value corresponding to a certain temperature (low-temperature target temperature, for example, 150 ° C.) according to the output of the operational amplifier circuit 250. Using the output voltage Vcc of the power source 280, the control voltage to the low temperature side bridge circuit 210 is formed. Note that the resistance value of the low-temperature heating resistor 211 changes (increases or decreases) in accordance with the control voltage from the current adjustment circuit 230 or the temperature change (increase or decrease) of the low-temperature heating resistor 211.

The operational amplifier circuit 250 includes an operational amplifier 251, a non-inverting input terminal resistor 252, an inverting input terminal resistor 253, a feedback resistor 254, and a capacitor 255.
Next, the high temperature side gas detection circuit 92 includes a high temperature side bridge circuit 220, a current adjustment circuit 240, an energization switching control circuit 241, and an operational amplification circuit 260.

  The high-temperature side bridge circuit 220 includes a high-temperature heating resistor 221 and three fixed resistors 222, 223, and 224, and is configured to form a bridge circuit. Further, in the high-temperature side bridge circuit 220, the high-temperature heating resistor 221 includes a right-side heating resistor 332 that constitutes the right-side heat conduction type gas detection unit 382 of the gas detection element 60. Here, one end of the high-temperature heating resistor 221 is grounded, and the other end is grounded via a fixed resistor 222, a fixed resistor 223, and a fixed resistor 224.

  The high-temperature side bridge circuit 220 has a current adjustment circuit 240 so that a potential difference generated between the common terminal of the high-temperature heating resistor 221 and the fixed resistor 222 and the common terminal of the fixed resistor 223 and the fixed resistor 224 becomes zero. A control voltage is applied. As a result, the resistance value of the high-temperature heating resistor 221 is controlled to be constant, that is, the temperature of the right heating resistor 332 is controlled to be constant. The voltage generated at the common terminal of the high-temperature heating resistor 221 and the fixed resistor 222 is input to the microcomputer 94 as an output signal (potential VH).

  Further, the current adjustment circuit 240 is dc-directed so as to maintain the resistance value of the high-temperature heating resistor 221 at a value corresponding to a certain temperature (high-temperature target temperature; for example, 300 ° C.) according to the output of the operational amplifier circuit 260. Using the output voltage Vcc of the power supply 280, the control voltage to the high temperature side bridge circuit 220 is formed. Note that the resistance value of the high temperature heating resistor 221 changes (increases or decreases) in accordance with the control voltage from the current adjustment circuit 240 or the temperature change (increase or decrease) of the high temperature heating resistor 221.

  The energization switching control circuit 241 is provided in an energization path from the DC power supply 280 (output voltage Vcc) to the current adjustment circuit 240 via the power switch 281, and the energization path is in accordance with a command from the microcomputer 94. Can be switched to a cut-off state or an energized state.

The operational amplifier circuit 260 includes an operational amplifier 261, a non-inverting input terminal resistor 262, an inverting input terminal resistor 263, a feedback resistor 264, and a capacitor 265.
Next, the temperature measurement circuit 93 includes a temperature measurement bridge circuit 931 and an amplifier circuit 932.

  The temperature measurement bridge circuit 931 includes a resistance temperature detector 390 and three fixed resistors 232, 233, and 234, and is configured to form a bridge circuit. Further, in the temperature measurement bridge circuit 931, the resistance temperature detector 390 is composed of the resistance temperature detector 390 of the gas detection element 60. One end of the resistance temperature detector 390 is grounded, and the other end is grounded via a fixed resistor 232, a fixed resistor 233, and a fixed resistor 234.

  The temperature measurement bridge circuit 931 includes a common terminal (one end side power supply terminal) for the resistance temperature detector 390 and the fixed resistor 234 and a common terminal (the other end side power supply terminal) for the fixed resistor 232 and the fixed resistor 233. It operates when the output voltage Vcc of the DC power supply 280 is applied.

  Under this operation, the temperature measurement bridge circuit 931 is based on the change in the resistance value of the resistance temperature detector 390, and is connected to the common terminal of the resistance temperature detector 390 and the fixed resistor 232 (one end side output of the temperature measurement bridge circuit 931). Terminal) and a common terminal of the fixed resistor 233 and the fixed resistor 234 (the other end side output terminal of the temperature measurement bridge circuit 931) is output (represents a value corresponding to the ambient temperature in the detected atmosphere). To do. Further, one end side output terminal and the other end side output terminal of the temperature measurement bridge circuit 931 are connected to the amplifier circuit 932.

  The amplifier circuit 932 amplifies the potential difference generated between the one end side output terminal and the other end side output terminal of the temperature measurement bridge circuit 931, and outputs it to the microcomputer 94. The amplifier circuit 932 includes an operational amplifier 933, a non-inverting input terminal resistor 934, an inverting input terminal resistor 935, a feedback resistor 936, and a capacitor 937.

  The microcomputer 94 has the same configuration as a known microcomputer including an arithmetic processing unit (CPU and the like), a storage unit (RAM and ROM and the like), an input / output unit, and the like.

Although illustration is omitted, the output of each control voltage of the current adjustment circuits 230 and 240 is configured to be started in synchronization with the power switch 281 being turned on.
The operational amplification circuit 250 of the low temperature side gas detection circuit 91 amplifies the potential difference generated between both output terminals of the low temperature side bridge circuit 210 and outputs the amplified potential difference to the current adjustment circuit 230. Further, the low temperature side gas detection circuit 91 has the potential VL (the voltage VL across the low temperature heating resistor 211 at the common terminal (electrode film 371) of the low temperature heating resistor 211 and the fixed resistor 212 in the low temperature side bridge circuit 210. Are output to the microcomputer 94.

  The operational amplification circuit 260 of the high temperature side gas detection circuit 92 amplifies the potential difference generated between both output terminals of the high temperature side bridge circuit 220 and outputs the amplified potential difference to the current adjustment circuit 240. Further, the high temperature side gas detection circuit 92 generates a potential VH (a voltage VH across the high temperature heating resistor 221) at a common terminal (electrode film 373) of the high temperature heating resistor 221 and the fixed resistor 222 in the high temperature side bridge circuit 220. Are output to the microcomputer 94.

  The amplifying circuit 932 of the temperature measuring circuit 93 amplifies the potential difference generated between the two output terminals of the temperature measuring bridge circuit 931 and sets the amplified potential difference VT (a value corresponding to the voltage across the resistance temperature detector 390) to the microcomputer 94. Output for.

  The microcomputer 94 operates by being supplied with power from the DC power source 280 via the power switch 281 and executes a computer program (gas detection process) according to the flowchart shown in FIG. FIG. 6 is a flowchart showing the processing contents of the gas detection processing.

  During this execution, the microcomputer 94 is required to calculate the hydrogen gas concentration based on the environmental temperature detected by the temperature measurement circuit 93, the output potential differences of the low temperature side gas detection circuit 91 and the high temperature side gas detection circuit 92, and the like. Perform various processes. Note that the processing content of the computer program (gas detection processing) is stored in the ROM of the microcomputer 94, and the processing unit (CPU or the like) reads the processing content from the ROM when the processing is executed.

  In the present embodiment configured as described above, when the combustible gas detection device 1 is arranged in the detected atmosphere, the hydrogen gas contained in the detected atmosphere is converted into a flow path forming portion of the combustible gas detection device 1. 43 flows in. Then, the hydrogen gas passes through the introduction portion 35 of the element case 20 and flows into the detection space 39, and then reaches the gas detection element 60.

  In this state, when the power switch 281 is turned on and the microcomputer 94 receives power from the DC power supply 280, the microcomputer 94 starts executing the computer program (gas detection process) according to the flowchart of FIG. .

  When the gas detection process is executed, first, in S10, energization of the low temperature heating resistor 211, the high temperature heating resistor 221 and the temperature measuring resistor 390 is started. As a result, the low temperature heating resistor 211 is maintained at the low temperature target temperature (150 ° C.) under the control of the current adjustment circuit 230, and the high temperature heating resistor is controlled under the control of the current adjustment circuit 240. 221 is maintained at the high temperature target temperature (300 ° C.).

  In S20, the computer program for calculating the hydrogen gas concentration is set as a computer program for calculating the hydrogen gas concentration using the potential VH of the high-temperature heating resistor 221 (hereinafter referred to as a high-temperature calculation program).

  Thereafter, in S30, the potential VL output from the low temperature side gas detection circuit 91, the potential VH output from the high temperature side gas detection circuit 92, and the amplified potential difference VT output from the temperature measurement circuit 93 are respectively set to the low temperature side voltage VL, Input as the high temperature side voltage VH and the temperature voltage VT.

  In S40, a process of calculating the environmental temperature T in the detected atmosphere using the temperature voltage VT is executed. In other words, the microcomputer 94 stores conversion data (conversion map data, conversion calculation formula, etc.) relating to the correlation between the temperature voltage VT and the environmental temperature in the detected atmosphere in a storage unit (ROM, etc.), and S30. The environmental temperature T in the detected atmosphere is obtained by calculating the environmental temperature T corresponding to the temperature voltage VT read in step 1 based on the conversion data.

  Further, in S50, a process of calculating the humidity H in the detected atmosphere using the low temperature side voltage VL, the high temperature side voltage VH, and the temperature voltage VT is executed. That is, the microcomputer 94 stores conversion data (conversion map data, conversion calculation formula, etc.) regarding the correlation between the low temperature side voltage VL, the high temperature side voltage VH, and the temperature voltage VT and the humidity H in the detected atmosphere. (ROM, etc.), and the low temperature side voltage VL, the high temperature side voltage VH, and the humidity H in the detection atmosphere corresponding to the temperature voltage VT read in S30 are calculated based on the converted data, thereby detecting the detection target. Acquire humidity H in the atmosphere.

  Thereafter, in S60, a process of calculating the hydrogen gas concentration D using the high temperature side voltage VH is executed. That is, the microcomputer 94 stores conversion data (conversion map data, conversion formula, etc.) relating to the correlation between the high temperature side voltage VH and the hydrogen gas concentration D in a storage unit (ROM, etc.), and is read in S30. The hydrogen gas concentration D corresponding to the high temperature side voltage VH is calculated based on the converted data, thereby obtaining the hydrogen gas concentration D.

In S70, the hydrogen gas concentration D acquired in S60 is corrected using the environmental temperature T acquired in S40 and the humidity H acquired in S50.
Further, in S80, it is determined whether or not the hydrogen gas concentration D corrected in S70 is less than a preset first determination value (10% in the present embodiment). If the corrected hydrogen gas concentration D is less than the first determination value (S80: YES), the hydrogen gas concentration D corrected in S70 is output in S90, and the process proceeds to S30. On the other hand, when the corrected hydrogen gas concentration D is equal to or higher than the first determination value (S80: NO), the energization to the high-temperature heating resistor 221 is stopped in S100.

  In S110, the computer program for calculating the hydrogen gas concentration is set as a computer program for calculating the hydrogen gas concentration using the potential VL of the low-temperature heating resistor 211 (hereinafter referred to as a low-temperature calculation program).

  In S120, as in S30, the potential VL output from the low temperature side gas detection circuit 91, the potential VH output from the high temperature side gas detection circuit 92, and the amplified potential difference VT output from the temperature measurement circuit 93 are obtained. The low temperature side voltage VL, the high temperature side voltage VH, and the temperature voltage VT are input.

  In S130, similarly to S40, a process of calculating the environmental temperature T in the atmosphere to be detected using the temperature voltage VT is executed. Further, in S140, similarly to S50, a process of calculating the humidity H in the detected atmosphere using the low temperature side voltage VL, the high temperature side voltage VH, and the temperature voltage VT is executed.

  Thereafter, in S150, a process of calculating the hydrogen gas concentration D using the low temperature side voltage VL is executed. That is, the microcomputer 94 stores conversion data (conversion map data, conversion formulas, etc.) relating to the correlation between the low temperature side voltage VL and the hydrogen gas concentration D in a storage unit (ROM, etc.), and is read in S120. The hydrogen gas concentration D is obtained by calculating the hydrogen gas concentration D corresponding to the low temperature side voltage VL based on the conversion data.

In S160, the hydrogen gas concentration D acquired in S150 is corrected using the environmental temperature T acquired in S130 and the humidity H acquired in S140.
Further, in S170, it is determined whether or not the hydrogen gas concentration D corrected in S160 is greater than a preset second determination value (5% in the present embodiment). If the corrected hydrogen gas concentration D is greater than the second determination value (S170: YES), the hydrogen gas concentration D corrected in S160 is output in S180, and the process proceeds to S120. On the other hand, when the corrected hydrogen gas concentration D is less than or equal to the second determination value (S170: NO), energization of the high-temperature heating resistor 221 is started in S190, and the process proceeds to S20.

  In the combustible gas detection device 1 configured as described above, between the terminals of the high temperature heating resistor 221 that is energized by the high temperature side gas detection circuit 92 so as to have a resistance value corresponding to the high temperature target temperature (300 ° C.). The voltage (high-temperature side voltage VH) is detected, and the voltage between the terminals of the low-temperature heating resistor 211 that is energized by the low-temperature side gas detection circuit 91 to have a resistance value corresponding to the low-temperature target temperature (150 ° C.) (Low temperature side voltage VL) is detected.

  Further, the hydrogen gas concentration D is calculated based on the high temperature side voltage VH detected by the high temperature side gas detection circuit 92 (S60), and at the same time hydrogen based on the low temperature side voltage VL detected by the low temperature side gas detection circuit 91. The gas concentration D is calculated (S150).

  Further, the hydrogen gas concentration D calculated based on the high temperature side voltage VH or the hydrogen gas concentration D calculated based on the low temperature side voltage VL is compared with a preset first determination value or second determination value. (S80, S170).

  Based on the comparison result, the hydrogen gas concentration D calculated based on the high temperature side voltage VH (hereinafter also referred to as the high temperature side calculated gas concentration) or the hydrogen gas concentration D calculated based on the low temperature side voltage VL. Any one of them (hereinafter also referred to as a low temperature side calculated gas concentration) is adopted as a detection result of the combustible gas detection device 1 (S90, S180).

  Therefore, either the hydrogen gas concentration D detected using the high-temperature heating resistor 221 or the hydrogen gas concentration D detected using the low-temperature heating resistor 211 is determined according to the gas concentration of the hydrogen gas. Can be selected.

  As a result, among the high-temperature heating resistor 221 and the low-temperature heating resistor 211, the high-temperature heating resistor 221 having a high set target temperature is used and set in an area where high density detection sensitivity is required. It is possible to select that the low-temperature heating resistor 211 having a low target temperature is used in an area where high density detection sensitivity is not required. The low temperature heating resistor 211 having a low set target temperature has a wider detectable gas concentration range than the high temperature heating resistor 221 having a high set target temperature.

  Therefore, according to the combustible gas detection device 1, it is possible to detect the gas concentration of hydrogen gas with high concentration detection sensitivity in an area where high concentration detection sensitivity is required, and to provide a gas concentration range in which hydrogen gas can be detected. Can be wide.

  Further, the left-side heat conduction type gas detection unit 381 and the right-side heat conduction type gas detection unit 382 do not have a catalyst used in the catalytic combustion type gas sensor. For this reason, the situation where the accuracy of gas concentration detection falls due to the silicon compound adhering to the catalyst does not occur.

As described above, the gas concentration of hydrogen gas can be detected from the low concentration region to the high concentration region without causing a decrease in gas concentration detection accuracy due to the silicon compound.
Further, the environmental temperature T in the atmosphere to be detected is calculated using the temperature voltage VT (S40, S130), and the high-temperature side calculation gas concentration or the low-temperature side calculation gas concentration is also calculated using this environmental temperature T. (S70, S160). As a result, the gas concentration of the hydrogen gas can be detected more accurately by considering the environmental temperature T in the atmosphere to be detected.

  Further, the humidity H in the detected atmosphere is calculated using the low temperature side voltage VL, the high temperature side voltage VH, and the temperature voltage VT (S50, S140), and the high temperature side calculated gas concentration or low temperature is also calculated using this humidity H. The side calculated gas concentration is calculated (S70, S160). Thereby, the gas concentration of hydrogen gas can be detected more accurately by considering the humidity H in the atmosphere to be detected.

  In a situation where the hydrogen gas concentration D is calculated based on the high temperature side voltage VH (hereinafter referred to as a high temperature side concentration calculation situation), the hydrogen gas concentration D calculated based on the high temperature side voltage VH and the first determination are determined. In the situation where the value is compared (S80) and the hydrogen gas concentration D is calculated based on the low temperature side voltage VL (hereinafter referred to as the low temperature side concentration calculation state), the hydrogen calculated based on the low temperature side voltage VL is calculated. The gas concentration D is compared with the second determination value (S170).

  Since the first determination value and the second determination value are different, the hydrogen gas concentration when transitioning from the high temperature side concentration calculation state to the low temperature side concentration calculation state and the high temperature side concentration calculation from the low temperature side concentration calculation state are performed. The hydrogen gas concentration at the time of transition to the situation is different.

  Further, as the hydrogen gas concentration increases, the determination value when the detection result employed in the combustible gas detection device 1 switches between the high-temperature side calculation gas concentration and the low-temperature side calculation gas concentration is determined as an increase direction. As the hydrogen gas concentration decreases, the determination value when the detection result employed in the combustible gas detection device 1 switches between the high-temperature side calculated gas concentration and the low-temperature side calculated gas concentration decreases. When the determination value is used, the first determination value (10%) corresponds to the increase direction determination value, and the second determination value (5%) corresponds to the decrease direction determination value. The first determination value (10%) is larger than the second determination value (5%).

  Therefore, the hydrogen gas concentration D output from the combustible gas detection device 1 is the difference between the high-temperature-side calculated gas concentration and the low-temperature-side calculated gas concentration due to frequent fluctuations in the hydrogen gas concentration near a certain value. Occurrence of a phenomenon that frequently switches between them (hunting phenomenon) can be suppressed.

  When the hydrogen gas concentration D calculated based on the low temperature side voltage VL is output as the detection result of the combustible gas detection device 1 (S180), the energization to the high temperature heating resistor 221 is stopped. (S100). For this reason, it can suppress that the heating resistor which is not used for detection of the gas concentration of hydrogen gas is energized wastefully. Thereby, while being able to reduce the power consumption of the combustible gas detection apparatus 1, the lifetime of the combustible gas detection apparatus 1 can be improved. In addition, the life of the high-temperature heating resistor 221 that requires high detection accuracy can be improved.

  In the embodiment described above, the high temperature heating resistor 221 is the first heating resistor in the present invention, the right heat conduction type gas detection unit 382 is the first heat conduction type gas detection unit in the present invention, and the low temperature heating resistor 211. Is the second heat generating resistor in the present invention, the left heat conduction type gas detection unit 381 is the second heat conduction type gas detection unit in the present invention, and the high temperature side gas detection circuit 92 is the first output detection means in the present invention, the low temperature side gas. The detection circuit 91 is the second output detecting means in the present invention, the processes in S60 and S70 are the first density calculating means in the present invention, the processes in S150 and S160 are the second density calculating means in the present invention, and the processes in S80 and S170 are the present. The concentration comparison means in the invention, the processes of S90 and S180 are the detection result adoption means in the present invention, and the processes of S40 and S130 are the temperature detection means in the present invention, 140 humidity calculating means in the present invention process, processing of S100 is deenergized means in the present invention.

  The high temperature target temperature (300 ° C.) is the first target temperature in the present invention, the low temperature target temperature (150 ° C.) is the second target temperature in the present invention, and the high temperature side voltage VH is the first output value and the low temperature side voltage in the present invention. VL is the second output value, the first determination value, and the second determination value in the present invention are comparative determination values in the present invention.

As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said embodiment, As long as it belongs to the technical scope of this invention, a various form can be taken.
For example, in the above embodiment, when the execution of the gas detection process is started, first, the hydrogen gas concentration D is calculated using the high temperature side voltage VH, and then the hydrogen gas concentration D is compared with the first determination value. Showed what to do. However, after the execution of the gas detection process is started, first, the hydrogen gas concentration D may be calculated using the low temperature side voltage VL, and the hydrogen gas concentration D may be compared with the first determination value.

  Moreover, in the said embodiment, after performing the process which calculates hydrogen gas concentration D based on the high temperature side voltage VH or the low temperature side voltage VL, hydrogen gas concentration D is used using the environmental temperature T and the humidity H in a to-be-detected atmosphere. An example of calculating the hydrogen gas concentration D in consideration of the environmental temperature T and the humidity H in the atmosphere to be detected by performing the correction process is shown. However, instead of performing two processes in this way, one process is performed such that a process for calculating the hydrogen gas concentration D is performed based on the high temperature side voltage VH, the low temperature side voltage VL, and the temperature voltage VT. By performing this, the hydrogen gas concentration D in consideration of the environmental temperature T and the humidity H in the atmosphere to be detected may be calculated.

  Alternatively, after performing the process of calculating the humidity H in the detected atmosphere, the hydrogen gas concentration D is calculated based on the high temperature side voltage VH or the low temperature side voltage VL, the temperature voltage VT, and the calculated humidity H. The processing may be performed so that the hydrogen gas concentration D in consideration of the environmental temperature T and the humidity H in the atmosphere to be detected may be calculated.

  Moreover, in the said embodiment, when the hydrogen gas density | concentration D calculated based on the low temperature side voltage VL was output, the electricity supply to the heating resistor 221 for high temperature was stopped. However, when the hydrogen gas concentration D calculated based on the high temperature side voltage VH is output, the energization to the low temperature heating resistor 211 may be stopped.

It is sectional drawing of the combustible gas detection apparatus. FIG. 3 is a cross-sectional view of the periphery of an element case 20. 3 is a plan view of a gas detection element 60. FIG. It is a figure which shows the AA cross-section part of FIG. 2 is a block diagram showing a schematic configuration of a control circuit 200. FIG. It is a flowchart showing the processing content of a gas detection process. It is a graph which shows the relationship between the voltage between terminals of two heat generating resistors controlled by different temperature, and hydrogen gas concentration.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Combustible gas detection apparatus, 20 ... Element case, 40 ... Housing case, 41 ... Circuit board, 42 ... Case main body, 60 ... Gas detection element, 91 ... Low temperature side gas detection circuit, 92 ... High temperature side gas detection circuit, 93 ... Temperature measurement circuit, 94 ... Microcomputer, 200 ... Control circuit, 210 ... Low temperature side bridge circuit, 211 ... Low temperature heating resistor, 220 ... High temperature side bridge circuit, 221 ... High temperature heating resistor, 230 ... Current adjustment circuit , 240 ... current adjustment circuit, 241 ... energization switching control circuit, 250 ... operational amplification circuit, 260 ... operational amplification circuit, 280 ... DC power supply, 310 ... silicon semiconductor substrate, 330 ... heating resistor, 331 ... left heating resistor 332: Right side heating resistor, 340: Wiring film, 350 ... Inner protective layer, 360 ... Outer protective layer, 381 ... Left heat conduction type gas detector, 382 ... Right heat conduction type Scan detector, 390 ... RTD, 931 ... temperature measuring bridge circuit, 932 ... amplifier,

Claims (5)

The first heating resistor is disposed in the atmosphere to be detected and has a first heating resistor whose own temperature changes as its temperature changes due to heat conduction to the combustible gas. This first heating resistor is preset. A first heat conduction type gas detector energized to have a resistance value corresponding to the first target temperature;
A second heating resistor is disposed in the atmosphere to be detected, and changes its own resistance value as its temperature changes due to heat conduction to the combustible gas, and this second heating resistor is the first heating resistor. A second heat-conducting gas detector that is energized to have a resistance value corresponding to a second target temperature set lower than the target temperature;
First output detection means for detecting a first output value corresponding to the resistance value of the first heating resistor;
Second output detecting means for detecting a second output value corresponding to the resistance value of the second heating resistor;
First concentration calculation means for calculating a first calculation gas concentration that is a gas concentration of a combustible gas present in the detected atmosphere based on the first output value detected by the first output detection means;
Second concentration calculation means for calculating a second calculation gas concentration, which is a gas concentration of a combustible gas existing in the detected atmosphere, based on the second output value detected by the second output detection means; A flammable gas detection device for detecting a gas concentration of a flammable gas present in the detected atmosphere,
Concentration comparison means for comparing either the first calculated gas concentration or the second calculated gas concentration with a preset comparison determination value;
Based on the comparison result by the concentration comparison means, comprising a detection result adoption means for employing either the first calculation gas concentration or the second calculation gas concentration as a detection result of the combustible gas detection device ;
The concentration comparison means includes
A first determination value set in advance for comparison with the first calculation gas concentration, and a second determination value set to a value smaller than the first determination value for comparison with the second calculation gas concentration; Have
When comparing using the first calculated gas concentration, the first determination value is used as the comparison determination value, and when comparing using the second calculated gas concentration, the first determination value is used as the comparison determination value. 2 as the comparison determination value when the detection result is switched between the first calculation gas concentration and the second calculation gas concentration by increasing the gas concentration of the combustible gas. As the comparison determination value when the detection result is switched between the first calculation gas concentration and the second calculation gas concentration by reducing the gas concentration of the combustible gas using the first determination value. A combustible gas detection apparatus using the second determination value . The combustible gas detection device according to claim 1, wherein the gas concentration range detectable by the first heating resistor is included in the gas concentration range detectable by the second heating resistor. Temperature detecting means for detecting an environmental temperature in the detected atmosphere;
The first concentration calculation means calculates the first calculation gas concentration using the environmental temperature detected by the temperature detection means,
3. The combustibility according to claim 1, wherein the second concentration calculation means calculates the second calculation gas concentration also using the environmental temperature detected by the temperature detection means. Gas detection device. Based on the first output value detected by the first output detection means, the second output value detected by the second output detection means, and the environmental temperature detected by the temperature detection means, Humidity calculation means to calculate the humidity in the detection atmosphere,
The first concentration calculation means calculates the first calculation gas concentration using the humidity detected by the humidity detection means,
The combustible gas detection device according to claim 3, wherein the second concentration calculation means calculates the second calculation gas concentration also using the humidity detected by the humidity detection means. Energization for stopping energization to either the first heating resistor or the second heating resistor corresponding to the gas concentration not adopted by the detection result adoption means as the detection result of the combustible gas detection device The combustible gas detection apparatus according to claim 1, further comprising a stop unit.

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