JP4960136B2 - Gas detection device and gas detection method - Google Patents

Description

  The present invention relates to a gas detection device and a gas detection method for detecting (calculating) the concentration of a detection gas contained in a detection atmosphere.

2. Description of the Related Art Conventionally, a gas detection device that detects the concentration of a combustible gas based on the thermal conductivity of the detected atmosphere when detecting the concentration of the combustible gas contained in the detected atmosphere is known. However, in the conventional gas detection device, even if the concentration of the combustible gas in the detected atmosphere is the same, the thermal conductivity of the entire detected atmosphere varies due to the change in humidity in the detected atmosphere. There was a problem that the detection accuracy of combustible gas was lowered. In view of this, a combustible gas detection device and a combustible gas detection method have been proposed in consideration that the concentration of the combustible gas contained in the detected atmosphere varies based on the humidity of the detected atmosphere (for example, non-patent literature). 1, see Patent Document 1). In the combustible gas detection device proposed in Patent Document 1, the ratio of the respective terminal voltages of the two heating resistors provided in the combustible gas detection device and the temperature of the detected atmosphere (environment temperature) are calculated. The humidity of the detection atmosphere is obtained.
Masaaki Tada, 3 others, “Hydrogen Sensor for Fuel Cell Vehicles”, SAE-2003-01-1137, p7-p8 JP 2006-10670 A

  By the way, in recent years, it has been desired to further improve the detection accuracy of a gas to be detected such as a combustible gas, and the gas detection in which the concentration of the gas to be detected in the atmosphere to be detected considers the influence of the humidity of the atmosphere to be detected. Further development of devices and gas detection methods has become increasingly desirable.

  The present invention has been made in order to solve the above-mentioned problems, and in consideration of the fact that the concentration of the gas to be detected contained in the atmosphere to be detected varies based on the humidity of the atmosphere to be detected, the gas to be detected is accurate. An object of the present invention is to provide a gas detection device and a gas detection method which are well detected.

In order to solve the above-described problem, a gas detection device according to a first aspect of the present invention provides a gas detection device including two heat generation resistors exposed to an atmosphere to be detected so that the two heat generation resistors are set to have different target temperatures. An energizing control means for energizing the body, a temperature detecting means for detecting the environmental temperature of the detected atmosphere, a voltage detecting means for detecting each terminal voltage in the two heating resistors, and the voltage detecting means. From the two terminal voltages and the environmental temperature detected by the temperature detecting means, thermal conductivity calculating means for calculating each thermal conductivity corresponding to the two terminal voltages as a thermal conductivity calculated value, based on the ratio of two of the thermal conductivity calculation value calculated by the thermal conductivity calculating means, calculating of said and humidity calculating means for calculating a humidity of the atmosphere to be detected, by the thermal conductivity calculating means Based on at least one of the two calculated thermal conductivity values and the humidity of the detected atmosphere calculated by the humidity calculating means, the gas concentration of the detected gas contained in the detected atmosphere is calculated. Concentration calculating means for calculating.

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the gas detection device includes a semiconductor substrate in which a plurality of openings are formed, and the openings are shielded on the semiconductor substrate. A gas detection element including an insulating member to be formed is provided, and the two heating resistors are included in the insulating member at portions that are opposed to the different opening portions while being spaced apart from each other.
According to a third aspect of the present invention, in addition to the configuration of the first or second aspect of the invention, the gas to be detected is hydrogen gas, and the concentration of the hydrogen gas under the condition that no moisture exists. And the terminal voltage when the voltage is applied so that the heating resistor reaches the target temperature, and the relationship between the thermal conductivity and the data plotted for each environmental temperature, the terminal voltage and the environment Temperature calculation data for obtaining the thermal conductivity calculation value from the relationship with temperature is prepared in advance for each different target temperature, and the thermal conductivity calculation means is configured to use the two thermal conductivity values based on the temperature calculation data. An operation value is obtained.

According to a fourth aspect of the present invention, there is provided a gas detection method for detecting a gas to be detected contained in a detected atmosphere, wherein a temperature detection step for detecting an environmental temperature of the detected atmosphere and a different target temperature are used. A voltage detection step of detecting each terminal voltage in the two heating resistors controlled to energize, the two terminal voltages detected in the voltage detection step, and the environmental temperature detected in the temperature detection step from the ratio of the respective thermal conductivity corresponding to two terminal voltages and thermal conductivity calculation step of calculating the thermal conductivity calculation value, two of the thermal conductivity calculation value calculated in the thermal conductivity calculating step Based on the above, at least one of the humidity calculation step for calculating the humidity of the detected atmosphere and the two thermal conductivity calculation values calculated in the thermal conductivity calculation step , Based on the humidity of the computed the atmosphere to be detected in the humidity calculation step, and a concentration calculating step of calculating a gas concentration of a gas to be detected in the atmosphere to be detected.
According to a fifth aspect of the present invention, in addition to the configuration of the fourth aspect of the present invention, the gas to be detected is hydrogen gas, and the concentration of the hydrogen gas is changed in the absence of moisture. And the terminal voltage and the environmental temperature based on the data obtained by plotting the relationship between the terminal voltage when the voltage is applied so that the heating resistor becomes the target temperature and the thermal conductivity for each environmental temperature. Temperature calculation data for obtaining the thermal conductivity calculation value from the relationship is prepared in advance for each different target temperature, and in the thermal conductivity calculation step, based on the temperature calculation data, the two thermal conductivity calculation values Is required.

  According to the gas detection device of the first aspect of the present invention, from each thermal conductivity calculation value corresponding to each terminal voltage in the two heating resistors that are energized and controlled so as to have different target temperatures, and the environmental temperature. The humidity of the detected atmosphere is calculated. The calculated value of thermal conductivity corresponding to each terminal voltage includes the contribution of moisture contained in the atmosphere to be detected and the contribution of the gas to be detected. And the change pattern of the thermal conductivity when the gas concentration to be detected is changed in the absence of moisture, and the thermal conductivity when the moisture concentration (humidity) is changed in the absence of flammability It is different from the change pattern. By utilizing the difference between these change patterns, it is possible to appropriately calculate the humidity of the atmosphere to be detected using the thermal conductivity calculation value corresponding to each terminal voltage. Then, based on at least one of the above two thermal conductivity calculation values and the humidity of the detected atmosphere, the gas concentration of the detected gas contained in the detected atmosphere is calculated. As a result, it is possible to accurately detect the gas to be detected by processing so that the thermal conductivity of the heating resistor disposed in the atmosphere to be detected fluctuates according to the humidity of the atmosphere to be detected. .

  According to the gas detector of the invention of claim 2, in addition to the effect of the invention of claim 1, the gas detector comprises a gas having a heating resistor capable of raising and lowering temperature in a short time. Since the detection element is provided, the power consumption of the heating resistor can be reduced.

Moreover, according to the gas detection method of the invention which concerns on Claim 4 , the gas detection method which can achieve the effect similar to the invention of Claim 1 can be provided.

  Hereinafter, an embodiment of a combustible gas detection device 10 embodying a gas detection device according to the present invention will be described with reference to the drawings. The combustible gas detection device 10 exemplified as the present embodiment includes a gas detection element 60 that is a heat conduction type gas detection element, and detects (calculates) the concentration of hydrogen that is a combustible gas contained in the atmosphere to be detected. It is a detection device. This combustible gas detection device 10 corresponds to the “gas detection device” of the present invention. For example, the combustible gas detection device 10 is mounted on a pipe provided in a fuel cell unit of an automobile, and the concentration of hydrogen contained in a detection atmosphere discharged through the pipe is determined. Used for detection purposes. Further, in the present embodiment, hydrogen that is a combustible gas corresponds to the “detected gas” of the present invention.

  First, the configuration of the combustible gas detection device 10 will be described with reference to FIGS. FIG. 1 is a longitudinal sectional view of the combustible gas detection device 10. In FIG. 1, the vertical direction is referred to as the vertical direction, and the horizontal direction is referred to as the horizontal direction. As shown in FIG. 1, the combustible gas detection device 10 supports an element case 20 that houses a gas detection element 60 for detecting the concentration of hydrogen contained in the atmosphere to be detected, and the element case 20. A housing case 40 for housing the circuit board 41 electrically connected to the gas detection element 60 is provided.

  First, the configuration of the housing case 40 will be described with reference to FIG. 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 therein a circuit board 41 on which a microcomputer 94 is mounted, and heating elements 50 and 51. 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. Holding part 45. Further, the opening on the upper surface of the case main body 42 is configured to be able to close the opening and to arrange a case lid 44 made of synthetic resin.

  The case main body 42 includes a flow path forming portion 43 formed in 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. Molded. The flow path forming portion 43 accommodates an introduction portion 35 of the element case 20 for introducing and discharging a detection atmosphere described later with reference to FIG. 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. In addition, a seal member 47 that seals between the flow path of the atmosphere to be detected and the housing case 40 is disposed between the collar portion 38 and the holding portion 46 of the element case 20.

  The connector 55 is a member for supplying power to the circuit board 41 on which the microcomputer 94 is mounted, and is assembled to the outer surface of the case main 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. Each of the connector pins 56 and 57 is connected to the circuit board 41 via the inside of the side wall of the case main body 42.

  The circuit board 41 includes a control circuit 200 (see FIG. 5) for detecting combustible gas in the atmosphere to be detected, and a temperature control circuit (not shown) for controlling the temperature of the heating elements 50 and 51. Each has. The control circuit 200 is electrically connected to the electrodes 371, 373, 391 and the ground electrodes 372, 392 (see FIGS. 3 and 4) of the gas detection element 60 through connection terminals 24 to 28, respectively. Further, 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 control circuit 200 provided on the circuit board 41 will be described later with reference to FIG.

  The microcomputer 94 mounted on the lower surface of the circuit board 41 calculates the concentration of hydrogen in the atmosphere to be detected based on the output from the control circuit 200, and based on the output from the temperature control circuit, the heating elements 50 and 51. The amount of heat generated (temperature) is controlled. The microcomputer 94 has the same configuration as a known microcomputer including an arithmetic processing unit, a storage unit, an input / output unit, and the like. As shown in FIG. 5, the microcomputer 94 according to the present embodiment includes a CPU 941 as an arithmetic processing unit, and includes a ROM 942 and a RAM 943 as storage units. An external storage device may be used as a storage device for storing the program.

  Next, the heating elements 50 and 51 will be described with reference to FIG. The heating elements 50 and 51 are for heating the element case 20 through 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, and are used in electronic parts, for example. A resistor or a film heater is used. The heating elements 50 and 51 are composed of an inner surface of the housing case 40 and an outer surface of the element case 20 in order to efficiently heat the inner surface of the element case 20 forming the detection space 39. It is preferable that the housing space forming surface 58 constituting the housing space 59 for housing the circuit board 41 is fixed to a portion capable of transferring heat to a member in contact with the detection space 39.

  The heating elements 50 and 51 are controlled by, for example, a known constant voltage control or PWM control (pulse width modulation control). A program that defines the control method of the heating elements 50 and 51 is stored in a storage device (ROM 942) included in the microcomputer 94 and executed by the CPU 941.

  Next, the element case 20 which comprises the combustible gas detection apparatus 10 is demonstrated with reference to FIG. FIG. 2 is an enlarged longitudinal sectional view of the periphery of the element case 20 of the combustible gas detection device 10. In FIG. 2, the vertical direction is referred to as the vertical direction, and the horizontal direction is referred to as the horizontal direction.

  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 edge of the connection terminal extraction base 21, and faces the introduction port for introducing the detected atmosphere. And a cylindrical detection space forming member 22 projecting therefrom. A seal member 48 that seals between the flow path of the atmosphere to be detected and the element case 20 is disposed at the periphery of the connection terminal extraction base 21 of the element case 20. A space surrounded by the connection terminal extraction base 21 and the detection space forming member 22 is a detection space 39 for introducing a detection atmosphere.

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

  The connection terminals 24 to 28 are members for electrically connecting a gas detection element 60 described later with reference to FIGS. 3 and 4 and various circuits provided on the circuit board 41. One end of each of the connection terminals 24 to 28 is inserted into an insertion hole provided in the connection terminal extraction base 21 and is supported vertically with respect to the connection terminal extraction base 21.

  Further, the detection space forming member 22 has an outer cylinder 36 that is in contact with the atmosphere to be detected on the outer surface, an extraction table support portion 37 that holds the peripheral portion of the connection terminal extraction table 21, and a collar portion 38 that is supported by the housing case 40. It has. Further, an introduction port 34 that is an opening for introducing the atmosphere 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 atmosphere 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, 32 in order from the introduction port 34, respectively. 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.

  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 atmosphere 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. 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 a ring-shaped member that is provided on the inner peripheral wall of the filter fixing member 33 and has an opening through which the atmosphere to be detected is introduced. The spacer 30 has a predetermined thickness so that the water-repellent filter 29 and the metal mesh 31, The position with 32 is 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 detected atmosphere. 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 with 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 in the axial direction of the wall surface and fixes the filter. The convex portion is provided 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.

  Next, the configuration of the gas detection element 60 disposed in the detection space 39 and exposed to the detected atmosphere will be described with reference to FIGS. 3 and 4. 3 is a schematic plan view for explaining the arrangement state of the left side heating resistor 331 and the right side heating resistor 332 of the gas detection element 60. FIG. 4 is a schematic plan view of the left side heating resistor 331 and the right side heating resistor 332. FIG. 4 is a cross-sectional view taken along the line AA in FIG. 3 for explaining an arrangement state. In FIG. 4, the upper side is the upper side, the lower side is the lower side, and in FIGS. 3 and 4, the left-right direction is the left-right direction.

  As shown in FIG. 3, the gas detection element 60 is a heat conduction type gas detection element having a rectangular planar shape. As shown in FIGS. 3 and 4, the gas detection element 60 is formed on the plate-shaped silicon substrate 310, the upper insulating coating layer 323 formed on the upper surface of the silicon substrate 310, and the lower surface of the silicon substrate 310. And a lower insulating coating layer 324. The upper insulating coating layer 323 includes a left heating resistor 331 and a right heating resistor 332, respectively. The gas detection element 60 is formed by, for example, a micromachining technique. The left heating resistor 331 and the right heating resistor 332 correspond to “two heating resistors” of the present invention. Hereinafter, each member which comprises the gas detection element 60 is explained in full detail.

  The silicon substrate 310 is a flat plate made of silicon and is a member corresponding to the “semiconductor substrate” of the present invention. This silicon substrate 310 is provided with a pair of openings 313 and 314 in which a part of the silicon substrate 310 is removed in an opening at a portion located below the left heating resistor 331 and the right heating resistor 332. In the upper portions of the openings 313 and 314, a part of the upper insulating coating layer 323 is exposed. That is, the left side heating resistor 331 and the right side heating resistor 332 are located at portions facing the different openings 313 and 314 (positioned immediately above in FIG. 4) in the upper insulating coating layer 323 while being spaced apart from each other. It is included. In addition, when the upper insulating coating layer 323 is projected in the thickness direction (vertical direction in FIG. 4) of the silicon substrate 310, an opening 313 larger than the left heating resistor 331 is formed at a position corresponding to the left heating resistor 331. An opening 314 larger than the right heating resistor 332 is provided at a position corresponding to the right heating resistor 332.

The upper insulating coating layer 323 includes insulating layers 321, 322, 350 and a protective layer 360 in order from the silicon substrate 310 side (lower side). This upper insulating coating layer 323 (insulating layers 321, 322, 350 and protective layer 360) corresponds to the “insulating member” of the present invention. On the other hand, the lower insulating coating layer 324 includes insulating layers 325 and 326 in order from the silicon substrate 310 side (upper side). The insulating layers 321 and 325 are made of silicon oxide (SiO ₂ ) and are formed on both surfaces in the thickness direction so as to sandwich the silicon substrate 2. Insulating layers 322 and 326 made of silicon nitride (Si ₃ N ₄ ) are formed on the outer surfaces of the insulating layers 321 and 325, respectively. An insulating layer 350 made of silicon oxide is formed on the upper surface of the insulating layer 322 constituting the upper insulating coating layer 323, and a protective layer 360 made of silicon nitride is further formed on the upper surface.

  The insulating layer 350 constituting the upper insulating coating layer 323 includes a left heating resistor 331 and a right heating resistor 332, respectively. Further, wiring films 341, 342, and 343 formed in the same plane as the plane on which the left heating resistor 331 and the right heating resistor 332 are formed are included in the insulating layer 350, respectively.

  The left heat generating resistor 331 and the right heat generating resistor 332 are resistors that are energized and controlled so as to have different target temperatures, and whose resistance values change according to their own temperature changes. The left heating resistor 331 is formed in a spiral shape in plan view at a portion corresponding to the upper portion of the planar opening 313 parallel to the silicon substrate 310. The left heating resistor 331 is energized and controlled so as to reach a low temperature side target temperature (for example, 300 ° C.). Similarly, the right side heating resistor 332 is formed in a spiral shape in a plan view at a portion corresponding to the upper portion of the planar opening 314 parallel to the silicon substrate 310. The right heating resistor 332 is energized and controlled so as to reach a high temperature side target temperature (for example, 400 ° C.). The left heating resistor 331 and the right heating resistor 332 are made of, for example, platinum (Pt) or an alloy thereof, polysilicon, or the like. In the present embodiment, the left heating resistor 331 and the right heating resistor 332 are formed of a platinum resistance material together with the wiring films 341, 342, and 343.

  The left end of the left heating resistor 331 is electrically connected to the electrode 371 through the wiring film 341. On the other hand, the right end of the left heating resistor 331 is electrically connected to the ground electrode 372 via a wiring film 342 formed integrally with the left heating resistor 331. Similarly, the left end of the right heating resistor 332 is electrically connected to the ground electrode 372 via the wiring film 342. The right end of the right heating resistor 332 is electrically connected to the electrode 373 through the wiring film 343. The electrodes 371 to 373 are wiring lead portions connected to the left heating resistor 331 and the right heating resistor 332, and are exposed through the contact holes 361. For example, gold (Au) is used as the material of the electrodes 371 to 373.

  Further, the gas detection element 60 includes a resistance temperature detector 390 as shown in FIG. The resistance temperature detector 390 is for detecting the temperature of the atmosphere to be detected existing in the detection space 39 (hereinafter also referred to as “environment temperature”), and between the insulating layer 322 and the insulating layer 350. And formed on a plane parallel to the silicon substrate 310. The resistance temperature detector 390 is made of a metal whose electrical resistance value changes approximately in proportion to the temperature. For example, platinum (Pt) is used. In this 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 331 and 332.

  Further, the resistance temperature detector 390 is electrically connected to the electrode 391 and the ground electrode 392 formed on the left and right ends of the resistance temperature detector 390. The electrode 391 and the ground electrode 392 are exposed through a contact hole (not shown). For example, gold (Au) is used as the material of the electrode 391 and the ground electrode 392. The resistance temperature detector 390 is connected to the circuit board 41 through electrodes 391 and 392.

  Next, an outline of the control circuit 200 provided on the circuit board 41 will be described with reference to FIG. FIG. 5 is an explanatory diagram of the control circuit 200 for processing the detection signal of the gas detection element 60. 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. Hereinafter, each circuit included in the control circuit 200 will be described in detail.

  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 left heating resistor 331 provided in the gas detection element 60 and fixed resistors 212 to 214 provided in the circuit board 41. The left heating resistor 331 is grounded on the side connected to the ground electrode 372, and the other end of the left heating resistor 331 is grounded via fixed resistors 212 to 214. The operational amplifier circuit 250 is provided on the circuit board 41 and amplifies the potential difference obtained from the low temperature side bridge circuit 210. 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.

  The low-temperature side bridge circuit 210 is controlled from the current adjustment circuit 230 so that the potential difference generated between the common terminal of the left heating resistor 331 and the fixed resistor 212 and the common terminal of the fixed resistor 213 and the fixed resistor 214 becomes zero. A voltage is applied. The current adjustment circuit 230 uses the output voltage Vcc of the DC power supply 280 to form a control voltage for the low temperature side bridge circuit 210 in accordance with the output from the operational amplifier circuit 250. Thus, the resistance value of the left heating resistor 331 is controlled to be constant, that is, the temperature of the left heating resistor 331 is controlled to be the low temperature side target temperature. The operational amplifier circuit 250 included in the low temperature side gas detection circuit 91 inputs the voltage generated at the common terminal (electrode 371) of the left heating resistor 331 and the fixed resistor 212 to the microcomputer 94 as an output signal (potential VL). .

  Similarly, the high temperature side gas detection circuit 92 includes a high temperature side bridge circuit 220, a current adjustment circuit 240, and an operational amplification circuit 260. The high temperature side bridge circuit 220 includes a right heating resistor 332 provided in the gas detection element 60 and fixed resistors 222 to 224 provided in the circuit board 41. The right heating resistor 332 is grounded on the side connected to the ground electrode 372, and the other end of the right heating resistor 332 is grounded via fixed resistors 222 to 224. The operational amplifier circuit 260 is provided on the circuit board 41 and amplifies the potential difference obtained from the high temperature side bridge circuit 220. 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.

  The high-temperature side bridge circuit 220 is controlled from the current adjustment circuit 240 so that the potential difference generated between the common terminal of the right heating resistor 332 and the fixed resistor 222 and the common terminal of the fixed resistor 223 and the fixed resistor 224 becomes zero. A voltage is applied. The current adjustment circuit uses the output voltage Vcc of the DC power supply 280 to form a control voltage for the high-temperature side bridge circuit 220 according to the output from the operational amplifier circuit 260. Thereby, the resistance value of the right side heating resistor 332 is controlled to be constant, that is, the temperature of the right side heating resistor 332 is controlled to be the high temperature side target temperature. The operational amplifier circuit 260 included in the high temperature side gas detection circuit 92 inputs the voltage generated at the common terminal (electrode 373) of the right heating resistor 332 and the fixed resistor 222 to the microcomputer 94 as an output signal (potential VH). .

  The temperature measurement circuit 93 includes a temperature measurement bridge circuit 931 and an operational amplifier circuit 932. The temperature measurement bridge circuit 931 includes a resistance temperature detector 390 provided in the gas detection element 60 and fixed resistors 232 to 234 provided in the circuit board 41. The resistance temperature detector 390 is grounded on the side connected to the ground electrode 392, and the other end side of the resistance temperature detector 390 is grounded via fixed resistors 232 to 234. This temperature measurement bridge circuit 931 includes a common terminal (one end side output terminal) of the resistance temperature detector 390 and the fixed resistor 232, 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. This potential difference indicates a value corresponding to the environmental temperature of the atmosphere to be detected. The operational amplifier circuit 932 is provided on the circuit board 41 and amplifies the potential difference obtained from the temperature measurement bridge circuit 931. The operational 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 operational amplifier circuit 932 amplifies a potential difference generated between both output terminals of the temperature measurement bridge circuit 931 and inputs the amplified signal to the microcomputer 94 as an output signal (potential VT). This output signal is used to calculate the environmental temperature, and the calculated environmental temperature is further included in the atmosphere to be detected and subjected to arithmetic processing for detecting combustible gas.

  Next, an outline of the detection principle of the gas detection process of the gas detection process that calculates the concentration of hydrogen as the combustible gas executed by the microcomputer 94 based on the output value of the control circuit 200 having the above configuration. This will be described with reference to FIGS. FIG. 6 shows the relationship between the terminal voltage and the thermal conductivity when the hydrogen concentration is changed to 0 to 4% by volume in the absence of moisture and the voltage is applied so that the heating resistor has a target temperature of 400 ° C. It is the graph which plotted the relationship for every environmental temperature. FIG. 7 shows the relationship between the terminal voltage and the thermal conductivity when the hydrogen concentration is changed to 0 to 4% by volume in the absence of moisture and the voltage is applied so that the heating resistor has a target temperature of 300 ° C. It is the graph which plotted the relationship for every environmental temperature. In FIGS. 6 and 7, when a voltage is applied so that the heating resistor has a target temperature at five different concentrations of 0, 1, 2, 3, and 4% by volume in the absence of moisture. The relationship between the terminal voltage and the thermal conductivity is plotted for each environmental temperature, and an approximate expression (primary expression) is obtained based on each measurement point. In the graph 500 shown in FIG. 6, data 501, 20 ° C. are data 502, and data 503, 80 ° C. are data 501, 20 ° C. and data 504, respectively. Similarly, in the graph 550 shown in FIG. 7, when the environmental temperature is −20 ° C., the data 551, 20 ° C. is the data 552, 50 ° C., the data 553, 80 ° C. is the data 554, respectively. ing.

  In the combustible gas detection device 10 of the present embodiment, there is a positive correlation between the hydrogen concentration and the terminal voltage in a situation where no moisture exists. Further, as shown in FIGS. 6 and 7, there is a positive correlation represented by a linear expression between the terminal voltage under the above conditions and the thermal conductivity. When the target temperature of the heating resistor is constant, the intercept in the primary expression representing the relationship between the terminal voltage and the thermal conductivity under the above conditions becomes smaller as the environmental temperature is higher than when the environmental temperature is lower. . Therefore, the thermal conductivity of the atmosphere to be detected can be obtained from the terminal voltage and the environmental temperature. On the other hand, when the hydrogen concentration is changed in the absence of moisture, the thermal conductivity corresponding to the high temperature side target temperature of 400 ° C. (high temperature side thermal conductivity) and the thermal conductivity corresponding to the low temperature side target temperature of 300 ° C. Taking a ratio (high temperature side thermal conductivity / low temperature side thermal conductivity) to (low temperature side thermal conductivity), this ratio takes a substantially constant value regardless of the hydrogen concentration and the environmental temperature.

  On the other hand, the thermal conductivity (high temperature side thermal conductivity) with respect to the high temperature side target temperature 400 ° C. and the low temperature side target temperature 300 when the moisture concentration (humidity) is changed in a situation where no flammable gas exists. When the ratio (high temperature side thermal conductivity / low temperature side thermal conductivity) with the thermal conductivity (low temperature side thermal conductivity) corresponding to ℃ is taken, regardless of the environmental temperature, the moisture concentration (humidity) and the above thermal conductivity There is a positive correlation with the ratio.

  In the gas detection method of this embodiment, as described above, the ratio of thermal conductivity corresponding to two heating resistors that are energized and controlled to have different target temperatures (high temperature side thermal conductivity / low temperature side thermal conductivity). Rate) is almost constant when the gas concentration of the flammable gas is changed, but it has a positive correlation when the moisture concentration (humidity) is changed. Calculate humidity. The positive correlation also varies depending on the configuration of the gas detection element 60 such as the material and shape of the heating resistor, the target temperature of the heating resistor, the gas to be detected, and the like. For this reason, various information such as map data and calculation formulas necessary for setting the target temperature of the two heating resistors in accordance with the detection target gas to be detected and executing the above positive correlation and gas detection processing. Is set in advance.

  Next, the gas detection process performed in the combustible gas detection apparatus 10 explained in full detail above is demonstrated with reference to the flowchart of FIG. FIG. 8 is a flowchart showing the flow of the gas detection process of the present embodiment. A program for executing each process shown in the flowchart of FIG. 8 is stored in the ROM 942, and is read into the RAM 943 and executed by the CPU 941 shown in FIG. Various information such as map data and calculation formulas necessary for executing the gas detection process is stored in the ROM 942, and is read from the ROM 942 and stored in the RAM 943 when the program is executed. In addition, data acquired or calculated during execution of the gas detection process is stored in a predetermined storage area of the RAM 943 as needed. This gas detection process is started by the CPU 941 when the power switch 281 is turned ON and the microcomputer 94 is supplied with power from the DC power supply 280.

  As shown in the flowchart of FIG. 8, in this gas detection process, first, an initialization process is executed (S5). In the initialization process, a process for starting a soft timer that manages a time-dependent process that is separately executed and a process for setting initial values of various variables used in the gas detection process are executed. Also, the output of each control voltage of the current adjustment circuits 230 and 240 is started.

  Subsequently, it is determined whether or not a predetermined initial waiting time has elapsed from the start timing of the gas detection process (S10). This process is a process for executing the gas detection process after the two heating resistors 331 and 332 reach the target temperature. In the present embodiment, the target temperature of the left heating resistor 331 is set to the low temperature side target temperature 300 ° C., and the target temperature of the right heating resistor 331 is set to the high temperature side target temperature 400 ° C. Thus, the target temperature is set to a different temperature between the two heating resistors (the left heating resistor 331 and the right heating resistor 332), and the difference between the high temperature side target temperature and the low temperature side target temperature is the detected atmosphere. From the viewpoint of accurately detecting moisture contained in the water, it is preferably 50 ° C. or higher. Moreover, it is preferable that the lower limit value of the target temperature is 150 ° C. or higher that surely exceeds the boiling point of water, and the upper limit value of the target temperature is preferably lower than the ignition temperature of the combustible gas.

  In S10, when the predetermined initial waiting time has not elapsed since the start timing of the gas detection process (S10: No), the predetermined initial waiting time elapses from the start timing of the gas detection process. Wait until. On the other hand, when a predetermined initial waiting time has elapsed from the start timing of the gas detection process (S10: Yes), the temperature voltage VT reading process is subsequently executed (S15).

  In the reading process of the temperature voltage VT, the potential VT output from the temperature measuring circuit 93 shown in FIG. 5 is read as the temperature voltage VT and stored in the RAM 943 (S15). This temperature voltage VT shows a value corresponding to the environmental temperature of the atmosphere to be detected.

  Subsequently, based on the temperature voltage VT read in S15, a temperature conversion process for obtaining the environmental temperature T of the detected atmosphere is executed (S20). In the combustible gas detection device 10 of the present embodiment, the relationship between the temperature voltage VT and the ambient temperature T of the atmosphere to be detected is predetermined as temperature conversion data and is stored in a predetermined storage area of the ROM 942. Yes. As the temperature conversion data, for example, temperature conversion map data or a temperature conversion calculation formula is used. Therefore, in S20, the environmental temperature T of the detected atmosphere is obtained based on the temperature voltage VT acquired in S15 and the temperature conversion data. The processes of S15 and S20 correspond to the “temperature detection step” of the present invention.

  Subsequently, a process of reading the potential VH output from the high temperature side gas detection circuit 92 shown in FIG. 5 as the high temperature side voltage VH and reading the potential VL output from the low temperature side gas detection circuit 91 as the low temperature side voltage VL is executed. (S25). The read high-temperature side voltage VH and low-temperature side voltage VL are stored in predetermined storage areas of the RAM 943, respectively. The process of S25 corresponds to the “voltage detection step” of the present invention, and the high temperature side voltage VH and the low temperature side voltage VL correspond to “two terminal voltages” of the present invention.

Subsequently, a high temperature side thermal conductivity calculated value λH corresponding to the high temperature side voltage VH read in S25 and a low temperature side thermal conductivity calculated value λL corresponding to the low temperature side voltage VL are respectively calculated (S30). The high-temperature-side thermal conductivity calculation value λH is calculated using the high-temperature-side thermal conductivity calculation data such as calculation map data and calculation formulas stored in advance in a storage unit such as the ROM 942 and the high-temperature-side voltage VH read in S25. Calculated based on Calculation equation to be used as a high-temperature-side heat conductivity computed data, such as those of the formula (1) is represented by _{λH = (VH measure -VH 0 (} t)) × αH (t) + λH 0.

Here, VH _measure in the equation (1) is the high temperature side voltage VH read in S25. Further, VH ₀ (t) was obtained in advance under the condition where there was no flammable gas (hydrogen) and moisture (hereinafter, the situation where there was no flammable gas (hydrogen) and moisture was referred to as “dry air condition”). From the correlation data (map data, calculation formula represented by a quadratic equation, etc.) indicating the correlation between the terminal voltage when the voltage is applied so that the heating resistor reaches the high temperature side target temperature and the environmental temperature t The calculated reference terminal voltage. In the combustible gas detection device 10 of the present embodiment, the terminal voltage obtained in advance under the dry air condition is used as the reference terminal voltage. Although not shown, there is a negative correlation expressed by a calculation expression such as a quadratic expression between the terminal voltage under the dry air condition and the environmental temperature t. The correlation data is preset based on the correlation and stored in the ROM 942.

ΑH (t) is a terminal voltage change ΔV (VH when a voltage is applied so that a heating resistor is at a high temperature target temperature in a state where moisture is not present in advance. _This is a coefficient for converting measurement −VH ₀ (t)) into a thermal conductivity change ΔλH. As shown in the graph 500 of FIG. 6, 0-4% by volume of flammable gas (hydrogen) is added in the absence of moisture, and a voltage is applied so that the heating resistor has a high temperature side target temperature of 400 ° C. In this case, the relationship between the terminal voltage and the thermal conductivity depends on the environmental temperature t. For this reason, the coefficient αH (t) is obtained from temperature calculation data (map data, a calculation formula represented by a linear equation or the like) determined in advance according to the environmental temperature t.

Further, λH ₀ is the thermal conductivity (constant) when a voltage is applied so that the heating resistor has a high temperature side target temperature under dry air conditions. In this embodiment, the target temperature (high temperature side target temperature) of the right side heating resistor 332 to which a voltage is applied so as to be the high temperature side target temperature is 400 ° C., and λH ₀ is 50.518 [mW / (m · K)].

As in the case of the high temperature side thermal conductivity calculation value λH, the low temperature side thermal conductivity calculation value λL is the low temperature side thermal conductivity such as calculation map data or calculation formulas stored in advance in a storage unit such as the ROM 942. The calculation is performed based on the calculation data and the low temperature side voltage VL read in S25. Calculation equation to be used as low-temperature heat conductivity computed data, such as those of the formula _{(2), λL = (VL} measure -VL 0 (t)) is calculated on the basis of the _{× αL (t) + λL 0} . Here, VL _measurement is the low-temperature side voltage VL read in S25, and VL ₀ (t) is a case where a voltage is applied so that the heating resistor is the low-temperature side target temperature obtained in advance under the dry air condition. Is a reference terminal voltage calculated from correlation data between the terminal voltage and the ambient temperature t. In addition, αL (t) is a terminal voltage change ΔV (when a voltage is applied so that a heating resistor is at a low-temperature target temperature in a state where moisture is not present in advance. VL _{its measure} -VL ₀ a (t)) is a coefficient for converting the thermal conductivity change DerutaramudaL, determined by the temperature calculation data. Further, λL ₀ is a thermal conductivity (constant) when a voltage is applied so that the heating resistor has a low temperature side target temperature under dry air conditions. In the present embodiment, the target temperature of the left heating resistor 331 to which the voltage is applied so as to be the low temperature side target temperature is 300 ° C., and λL ₀ is 44.038 [mW / (m · K)]. The process of S30 corresponds to the “thermal conductivity calculation step” of the present invention, and the high temperature side thermal conductivity calculated value λH and the low temperature side thermal conductivity calculated value λL are the two heat conductivity values of the present invention. It corresponds to “calculated value”.

  Subsequently, the thermal conductivity ratio Rλ is calculated by dividing the high temperature side thermal conductivity calculated value λH obtained in S30 by the low temperature side thermal conductivity calculated value λL (S35).

Then, it calculates a thermal conductivity ratio R [lambda] determined in S35, a difference ΔRλ the thermal conductivity ratio R [lambda] ₀ of the reference (S40). The reference thermal conductivity ratio Rλ ₀ is calculated by the equation (3), Rλ ₀ = λH ₀ / λL ₀ , and is 1.147 in the combustible gas detection device 10 of the present embodiment.

Subsequently, moisture H ₂ O (humidity of the detected atmosphere) contained in the detected atmosphere is calculated (S45). Although not shown, there is a positive correlation represented by a calculation formula such as a quadratic equation between ΔRλ and moisture H ₂ O contained in the atmosphere to be detected. Based on this correlation, relational calculation data (map data, a calculation formula represented by a quadratic expression, etc.) for moisture calculation is set in advance and stored in the ROM 942. Therefore, the moisture in the atmosphere to be detected (humidity of the atmosphere to be detected) is calculated based on the relational calculation data and ΔRλ obtained in S40. The processes of S35, S40, and S45 correspond to the “humidity calculation step” of the present invention.

Subsequently, a change ΔλH _H2O due to moisture contained in the high temperature side thermal conductivity calculated value λH obtained in S30 is calculated (S50). Although not shown, there is a positive correlation represented by a calculation formula such as a quadratic equation between the moisture H ₂ O contained in the atmosphere to be detected and the change ΔλH _{H2O in} thermal conductivity due to moisture. Based on this correlation, relational calculation data (map data, a calculation formula represented by a quadratic expression, etc.) for calculating a change ΔλH _H2O due to moisture is set in advance and stored in the ROM 942. Therefore, the ΔλH _H2O is calculated based on the relation calculation data and the moisture H ₂ O contained in the detected atmosphere obtained in S45.

Subsequently, a change ΔλH _H2 due to the combustible gas (hydrogen) included in the high temperature side thermal conductivity calculated value λH obtained in S30 is calculated (S55). In this process, the change ΔλH _H2 due to the combustible gas (hydrogen) included in the high temperature side thermal conductivity calculated value λH obtained in S30 is calculated using Equation (4), ΔλH _H2 = λH−ΔλH _H2O −λH _0. To do. Here, λH is the high temperature side thermal conductivity calculated value obtained in S30, and ΔλH _H2O is a change due to moisture contained in the high temperature side thermal conductivity calculated value λH obtained in S50. ΛH ₀ is the thermal conductivity (constant) under dry air conditions.

Subsequently, the combustible gas (hydrogen) contained in the detected atmosphere is calculated (S60). Although not shown, between the combustible gas (hydrogen) contained in the atmosphere to be detected and the change ΔλH _{H2 in the} thermal conductivity due to the combustible gas (hydrogen), a positive expression such as a linear expression is used. There is a correlation. Based on this correlation, relational calculation data (map data, a calculation formula represented by a primary expression, etc.) for calculating the combustible gas (hydrogen) is set in advance and stored in the ROM 942. Therefore, the combustible gas (hydrogen) contained in the atmosphere to be detected is calculated based on the relational calculation data and the change ΔλH _H2 due to the combustible gas (hydrogen) obtained in S55. The processes of S50, S55 and S60 correspond to the “density calculation step” of the present invention.

  Subsequently, it is determined whether a predetermined waiting time has elapsed (S65). This process is a process for executing the gas detection process at every predetermined time. When the waiting time has not elapsed (S65: No), it waits until the waiting time elapses. On the other hand, when the waiting time has elapsed (S65: Yes), the process returns to S15 and the process is repeated.

  As described above in detail, in the combustible gas detection device 10 of the present embodiment, the gas detection process shown in the flowchart of FIG. 8 is performed. In the gas detection process, the current adjusting circuit 230, the operational amplifier circuit 250, and the current amplifier circuit 250 shown in FIG. 5 are energized and controlled so as to have different target temperatures (high temperature side target temperature, low temperature side target temperature). The current adjustment circuit 240 and the operational amplifier circuit 260 correspond to the energization control means of the present invention. Further, the temperature measuring circuit 93 and the CPU 941 shown in FIG. 5 that detect the ambient temperature T of the atmosphere to be detected in S15 of the flowchart shown in FIG. 8 correspond to the temperature detecting means of the present invention. Further, in S25 of the flowchart shown in FIG. 8, the CPU 941 shown in FIG. 5 that detects the terminal voltages VH and VL in the two heating resistors 331 and 332 functions as the voltage detection means of the present invention.

  Further, in S30 of the flowchart shown in FIG. 8, from the two terminal voltages VH and VL read in S25 and the environmental temperature T converted in S20, each thermal conductivity calculation value λH corresponding to the two terminal voltages VH and VL. , ΛL is calculated, and the CPU 941 shown in FIG. 5 functions as the thermal conductivity calculating means of the present invention. Further, in S35, S40 and S45 in the flowchart shown in FIG. 8, the CPU 941 shown in FIG. 5 calculates the humidity of the detected atmosphere based on the two thermal conductivity calculated values λH and λL calculated in S30. Functions as humidity calculation means. Further, in S50, S55 and S60 of the flowchart shown in FIG. 8, among the two thermal conductivity calculated values λH and λL calculated in S30, the high temperature side thermal conductivity calculated value λH and the detected atmosphere humidity calculated in S45. Based on the above, the CPU 941 shown in FIG. 5 that calculates the gas concentration of the combustible gas contained in the atmosphere to be detected functions as the concentration calculation means of the present invention.

  According to the combustible gas detection device 10 of the present embodiment described in detail above, the two heating resistors 331 and 332 that are energized and controlled so as to have different target temperatures (high temperature side target temperature and low temperature side target temperature). From the thermal conductivity calculated values λH and λL corresponding to the terminal voltages and the environmental temperature T, the humidity of the detected atmosphere is calculated (S35, S40, S45). The thermal conductivity calculation values λH and λL corresponding to each terminal voltage include a contribution of moisture contained in the atmosphere to be detected and a contribution of combustible gas, respectively. And the change pattern of the thermal conductivity when the flammable gas concentration is changed in the absence of moisture, and the thermal conductivity when the moisture concentration (humidity) is changed in the absence of flammability It is different from the change pattern. By utilizing the difference between these change patterns, it is possible to appropriately calculate the humidity of the detected atmosphere using the thermal conductivity calculation values λH and λL corresponding to each terminal voltage. Based on the high temperature side thermal conductivity calculation value λH and the humidity of the detected atmosphere among the above two calculated thermal conductivity values λH and λL, the gas concentration of the combustible gas contained in the detected atmosphere is calculated. Calculate (S50, S55, S60). As a result, the thermal conductivity of the heating resistor disposed in the detection space 39 is processed so as to avoid fluctuations according to the humidity of the detected atmosphere, and the combustible gas that is the detected gas is accurately detected. Can be detected.

  In the combustible gas detection device 10, when hydrogen is detected as the combustible gas, the target temperature of the heating resistors 331 and 332 is set to 150 ° C. or higher so that the boiling point of water is reliably exceeded in the detected atmosphere. The temperature range can be controlled, and the hydrogen gas concentration can be detected even if the atmosphere to be detected is a humid environment. In addition, by setting the target temperature of the heating resistors 331 and 332 to 500 ° C. or lower, it is possible to suppress the detected atmosphere from rising to the ignition (explosion) temperature of the hydrogen gas and to prevent the hydrogen gas from igniting. .

  Moreover, since the combustible gas detection apparatus 10 is provided with the gas detection element 60 which can perform temperature rise and temperature fall for a short time, it can reduce the power consumption of the heating resistors 331 and 332.

  The present invention is not limited to the embodiment described in detail above, and various modifications may be made without departing from the scope of the present invention. For example, in the above-described embodiment, the combustible gas detection device 10 is exemplified as being mounted on a fuel cell unit of an automobile and used for the purpose of detecting leakage of hydrogen. Various locations and applications can be selected, and the present invention is not limited to this.

  In the above embodiment, the gas detection process for detecting the concentration of hydrogen, which is a combustible gas, is described as the gas to be detected. However, the gas to be detected is not limited to the combustible gas, and a gas other than the combustible gas may be used. It may be a gas to be detected. Further, when the flammable gas is a detected gas, the flammable gas is not limited to the hydrogen exemplified in the above embodiment, and a flammable gas containing at least a hydrogen atom, such as methane or propane, may be used as the detected gas. Good. Therefore, for example, the present invention may be applied to a gas detection device used for leak detection or concentration detection of combustible gas such as city gas.

  The configuration of the gas detection element 60 may be any as long as it detects the concentration of the gas to be detected by utilizing the change in the electrical resistance value of the heating resistor according to the concentration of the gas to be detected. It is not limited to. Therefore, for example, instead of the resistance temperature detector 390 of the present embodiment, a resistance temperature detector different from the gas detection element 60 and other temperature sensors may be adopted. When using a resistance temperature detector or other temperature sensor separate from the gas detection element 60, it is preferably installed in the detection space 39.

  The number, material, shape, arrangement, and the like of each member constituting the combustible gas detection device 10 and the gas detection element 60 can be appropriately changed. For example, the planar shape of the gas detection element 60 is not limited to a rectangle, but may be a polygon or a circle. Further, for example, the gas detection element 60 may include three or more heating resistors. Further, for example, when the flammable gas detection device 10 is used in a condition in which no component that corrodes the heating resistor exists in the detection space 39, the gas detection element 60 does not include the protective layer 360, and the heating resistor is in the atmosphere to be detected. You may make it expose to.

  Further, for example, the humidity of the detected atmosphere may be calculated by a predetermined calculation method based on the two thermal conductivity calculation values λH and λL calculated in S30, and is not limited to the gas detection method of the above embodiment. .

  Further, for example, the gas concentration of the combustible gas contained in the detected atmosphere is set to at least one of the two thermal conductivity calculated values λH and λL calculated in S30 and the humidity of the detected atmosphere calculated in S45. What is necessary is just to calculate by the predetermined calculation method based on this, and is not limited to the gas detection method of the said embodiment. For example, in S50, S55, and S60 of the flowchart of FIG. 8, the detected atmosphere is determined based on the low temperature side thermal conductivity calculated value λL calculated in S30 and the moisture concentration (humidity) of the detected atmosphere determined in S45. You may calculate the gas concentration of the combustible gas contained. Further, for example, the gas concentration of the combustible gas contained in the detected atmosphere may be calculated based on the difference or ratio between the two calculated thermal conductivity values λH and λL and the humidity of the detected atmosphere.

1 is a longitudinal sectional view of a combustible gas detection device 10. FIG. 3 is an enlarged longitudinal sectional view of the periphery of an element case 20 of the combustible gas detection device 10. FIG. 4 is a schematic plan view for explaining the arrangement state of a left heating resistor 331 and a right heating resistor 332 of a gas detection element 60. FIG. FIG. 4 is a cross-sectional view in the direction of the arrows in the line AA in FIG. 3 for explaining the arrangement state of the left heating resistor 331 and the right heating resistor 332. It is explanatory drawing of the control circuit 200 for processing the detection signal of the gas detection element. The relationship between the terminal voltage and the thermal conductivity when the hydrogen concentration is changed to 0 to 4% by volume in the absence of moisture and the voltage is applied so that the heating resistor has a target temperature of 400 ° C. is the environmental temperature. It is the graph plotted for every. The relationship between the terminal voltage and the thermal conductivity when the hydrogen concentration is changed to 0 to 4% by volume in the absence of moisture and the voltage is applied so that the heating resistor reaches the target temperature of 300 ° C. is the environmental temperature. It is the graph plotted for every. It is a flowchart which shows the flow of the gas detection process of this embodiment.

1 Combustible Gas Detection Device 60 Gas Detection Element 93 Temperature Measurement Circuit 94 Microcomputer 230, 240 Current Adjustment Circuit 250, 260 Operational Amplification Circuit 331 Left Heating Resistor 332 Right Heating Resistor 310 Silicon Substrate 311, 312 Opening 321, 322 350 Insulating layer 323 Upper insulating coating layer 360 Protective layer 941 CPU
942 ROM
943 RAM

Claims (5)

In a gas detection device comprising two heating resistors exposed to the atmosphere to be detected,
Energization control means for energizing the two heating resistors so as to have different target temperatures;
Temperature detecting means for detecting the environmental temperature of the detected atmosphere;
Voltage detecting means for detecting each terminal voltage in the two heating resistors;
Heat that calculates each thermal conductivity corresponding to the two terminal voltages as a thermal conductivity calculation value from the two terminal voltages detected by the voltage detection unit and the environmental temperature detected by the temperature detection unit Conductivity calculating means;
Humidity calculation means for calculating the humidity of the detected atmosphere based on the ratio of the two thermal conductivity calculation values calculated by the thermal conductivity calculation means;
Based on at least one of the two thermal conductivity calculated values calculated by the thermal conductivity calculating means and the humidity of the detected atmosphere calculated by the humidity calculating means, the detected atmosphere And a concentration calculating means for calculating the gas concentration of the gas to be detected. A gas detection element comprising a semiconductor substrate having a plurality of openings formed thereon and an insulating member formed on the semiconductor substrate so as to block the openings;
2. The gas detection device according to claim 1, wherein the two heat generating resistors are included in the insulating member at portions that are opposed to the different opening portions while being spaced apart from each other. The detected gas is hydrogen gas,
The relationship between the terminal voltage and the thermal conductivity when the voltage is applied so that the concentration of the hydrogen gas is changed in a state where moisture does not exist and the heating resistor becomes a target temperature is set for each environmental temperature. Based on the plotted data, temperature calculation data for obtaining the thermal conductivity calculation value from the relationship between the terminal voltage and the environmental temperature is created in advance for each different target temperature,
The gas detection device according to claim 1 or 2, wherein the thermal conductivity calculation means obtains two thermal conductivity calculation values based on the temperature calculation data. In a gas detection method for detecting a detected gas contained in a detected atmosphere,
A temperature detecting step for detecting an environmental temperature of the detected atmosphere;
A voltage detection step for detecting each terminal voltage in the two heating resistors that are energized and controlled to have different target temperatures;
Heat that calculates each thermal conductivity corresponding to the two terminal voltages as a thermal conductivity calculation value from the two terminal voltages detected in the voltage detection step and the environmental temperature detected in the temperature detection step Conductivity calculation step;
A humidity calculating step of calculating the humidity of the detected atmosphere based on the ratio of the two calculated values of the thermal conductivity calculated in the thermal conductivity calculating step;
Based on at least one of the two calculated thermal conductivity values calculated in the thermal conductivity calculation step and the humidity of the detected atmosphere calculated in the humidity calculation step, And a concentration calculating step for calculating the gas concentration of the detection gas. The detected gas is hydrogen gas,
The relationship between the terminal voltage and the thermal conductivity when the voltage is applied so that the concentration of the hydrogen gas is changed in a state where moisture does not exist and the heating resistor becomes a target temperature is set for each environmental temperature. Based on the plotted data, temperature calculation data for obtaining the thermal conductivity calculation value from the relationship between the terminal voltage and the environmental temperature is created in advance for each different target temperature,
5. The gas detection method according to claim 4, wherein, in the thermal conductivity calculation step, two of the thermal conductivity calculation values are obtained based on the temperature calculation data.

Images