JP2007248356A - Flammable gas detector and flammable gas detecting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flammable gas detector and a flammable gas detecting method made to precisely detect the flammable gas while considering the fluctuation of the thermal conductivity of the atmosphere to be detected depending on the humidity of the atmosphere. <P>SOLUTION: Both the constant temperature control circuits 230, 240 control both the heating resistors 211, 221 exposed to the measurement spaces to mutually different constant temperatures by controlling currents. The thermometric resistor 390 generates the atmospheric temperature in the measurement space as the temperature voltage. Both the operational amplifier circuits 250, 260 amplify both the outputs from both the bridge circuits 210, 220 into the potential difference of both the differential amplifiers. The microcomputer 270 calculates the ratio of both the potential difference as the voltage difference, calculates the humidity based on the relation among the humidity, voltage ratio, and the temperature voltage, and the concentration of flammable gas in the atmosphere to be detected is calculated based on the relation among the concentration of the flammable gas in the measurement space, potential difference of differential amplifier of the operation amplifier circuit 260, and humidity and temperature voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a flammable gas detection device and a flammable gas detection method for detecting a flammable gas in an atmosphere to be detected.

Conventionally, in this type of combustible gas detection device, there is a hydrogen gas sensor for a fuel cell vehicle disclosed in Non-Patent Document 1 below. This hydrogen gas sensor detects the degree of influence of humidity from the difference between detection values of both thermistors controlled to different temperatures, and detects hydrogen gas by correcting the humidity component.
Masaaki Tada and three others, "Hydrogen Sensor for Fuel Cell Vehicles", SAE-2003-01-1137, p7-p8

  By the way, in the detection by the hydrogen gas sensor, even if the concentration of hydrogen gas in the atmosphere to be detected is the same, if the humidity in the atmosphere to be detected fluctuates, the thermal conductivity of the entire atmosphere to be detected fluctuates and the above-mentioned. This causes the problem of changing the concentration of hydrogen gas.

  Therefore, in order to cope with the above, the present invention takes into account that the concentration of the combustible gas in the detected atmosphere varies based on the humidity in the detected atmosphere, and accurately detects the combustible gas. It is an object of the present invention to provide a combustible gas detection device and a combustible gas detection method that can be detected.

  In solving the above-described problems, the combustible gas detection device according to the present invention includes a plurality of heating resistors (211, 221 and 330) exposed to the detected atmosphere.

In the combustible gas detection device,
The two heating resistors are controlled by energization so that the resistance values of at least two heating resistors (211, 221 and 330) among the plurality of heating resistors are maintained at respective values corresponding to different constant temperatures. Constant temperature control means (230, 240) for
Temperature detecting means (390) for detecting the environmental temperature (T) in the detected atmosphere;
Voltage ratio determining means (421) for determining a ratio of terminal voltages (VH, VL) of the two heating resistors generated in the control state by the constant temperature control means as a voltage ratio (RV);
Humidity determination means for determining the humidity based on the voltage ratio and the environmental temperature from the humidity (HUM) in the detected atmosphere, the voltage ratio and the humidity-voltage ratio-environment temperature characteristic representing the relationship between the environmental temperature. (422, 423, 424),
It represents the relationship between the concentration (D) of the combustible gas in the detected atmosphere, the terminal voltage (VH) of the high-temperature side heating resistor (221) of the two heating resistors, the humidity, and the environmental temperature. Concentration calculating means (450, 460, 470, 480) for calculating the concentration of the combustible gas based on the terminal voltage of the high temperature side heating resistor, the humidity and the environmental temperature from the concentration-terminal voltage-humidity-environment temperature characteristics. And with
The combustible gas is detected based on the calculated concentration of the concentration calculating means.

  According to this, as described above, the ratio of the terminal voltages of the two heating resistors generated in a state where each of the heating resistors is controlled to be different from each other by energization as described above is determined as the voltage ratio, and the humidity in the detected atmosphere is It is determined based on the voltage ratio and the environmental temperature from the humidity-voltage ratio-environment temperature characteristic.

  Then, the concentration of the combustible gas in the detected atmosphere is determined based on the terminal voltage of the high temperature side heating resistor, the humidity, and the environmental temperature from the concentration-terminal voltage-humidity-environment temperature characteristics, and this Combustible gas is detected based on the calculated concentration.

  Thus, even if the thermal conductivity of the detected atmosphere varies according to the humidity in the detected atmosphere, the combustible gas is detected by processing so as to eliminate this variation.

  Here, as described above, after determining the humidity based on the humidity-voltage ratio-environment temperature characteristic, the humidity is used to determine the concentration of the combustible gas based on the concentration-terminal voltage-humidity-environment temperature characteristic. Since it did in this way, the detection accuracy of the combustible gas mentioned above can be ensured highly.

Moreover, according to the description of Claim 2, the combustible gas detection apparatus which concerns on this invention,
A semiconductor substrate (310) formed with a plurality of recesses (311) from the back side at intervals, an insulating layer (320) formed on the surface of the semiconductor substrate, and the recesses on the surface of the insulating layer And a plurality of heating resistors (211, 221, 330) formed corresponding to the above, and a protective layer (350, 360) formed on the surface of the insulating layer so as to cover these heating resistors. And a detection element (300) disposed in the atmosphere to be detected.

In the combustible gas detection device,
The two heating resistors are controlled by energization so that the resistance values of at least two heating resistors (211, 221 and 330) among the plurality of heating resistors are maintained at respective values corresponding to different constant temperatures. Constant temperature control means (230, 240) for
Temperature detecting means (390) for detecting the environmental temperature (T) in the detected atmosphere;
Voltage ratio determining means (421) for determining a ratio of terminal voltages (VH, VL) of the two heating resistors generated in the control state by the constant temperature control means as a voltage ratio (RV);
Humidity determination means for determining the humidity based on the voltage ratio and the environmental temperature from the humidity (HUM) in the detected atmosphere, the voltage ratio and the humidity-voltage ratio-environment temperature characteristic representing the relationship between the environmental temperature. (422, 423, 424),
It represents the relationship between the concentration (D) of the combustible gas in the detected atmosphere, the terminal voltage (VH) of the high-temperature side heating resistor (221) of the two heating resistors, the humidity, and the environmental temperature. Concentration calculating means (450, 460, 470, 480) for calculating the concentration of the combustible gas based on the terminal voltage of the high temperature side heating resistor, the humidity and the environmental temperature from the concentration-terminal voltage-humidity-environment temperature characteristics. And with
The combustible gas is detected based on the calculated concentration of the concentration calculating means.

  According to this, unlike the invention according to claim 1, the combustible gas detection device having the detection element having the above-described configuration can also achieve the same operational effects as the invention according to claim 1.

According to a third aspect of the present invention, in the combustible gas detection device according to the first or second aspect,
A voltage ratio initial value (RV0) that is a ratio of terminal voltages of the two heating resistors when the concentration and humidity of the combustible gas are both zero is a dependent variable, and the environmental temperature is an independent variable. Functional characteristics of
The second function characteristic having the humidity as a dependent variable and the voltage ratio difference (ΔRV) representing the difference between the voltage ratio and the initial value of the voltage ratio as an independent variable is stored as the humidity-voltage ratio-environment temperature characteristic. Storage means (270) for
The humidity determining means is
Voltage ratio initial value determining means (422) for determining the voltage ratio initial value based on the environmental temperature from the first function characteristic;
Voltage ratio difference calculating means (423) for calculating the voltage ratio difference based on the voltage ratio and the initial value of the voltage ratio;
Humidity calculating means (424) for calculating the humidity based on the voltage ratio difference from the second function characteristic;
The humidity calculated by the humidity calculating means is the humidity determined by the humidity determining means.

  Thus, the first and second function characteristics are stored in the storage means, the initial value of the voltage ratio is determined from the first function characteristics using the environmental temperature, and the voltage ratio thus determined is determined. The voltage ratio difference is calculated based on the initial value and the voltage ratio, the humidity is calculated from the second function characteristic using the voltage ratio difference, and the calculated humidity is set as the humidity determined by the humidity determining means. I did it.

  Therefore, since the voltage ratio initial value and the humidity can be obtained by using the corresponding function characteristics, the calculation accuracy of the finally obtained humidity is further improved. As a result, the operational effects of the invention described in claim 1 or 2 can be further improved.

Moreover, according to the description of Claim 4, this invention is the combustible gas detection apparatus of Claim 3,
The storage means further includes
A third function in which the environmental temperature is an independent variable, and the first terminal voltage value (VH0), which is the terminal voltage of the high-temperature side heating resistor when the concentration and humidity of the combustible gas are both zero, is a dependent variable. Characteristics,
The second terminal voltage value (VH1) that is the terminal voltage of the high-temperature side heating resistor when the humidity is an independent variable, the first terminal voltage value is an intercept, and the humidity in the detected atmosphere is zero. A fourth function characteristic as a dependent variable;
The fifth function characteristic having the environmental temperature as an independent variable and the gas sensitivity (G) for the combustible gas as a dependent variable is stored as the concentration-terminal voltage-humidity-environment temperature characteristic,
Concentration calculation means
First terminal voltage value determining means (450) for determining the first terminal voltage value based on the environmental temperature from the third function characteristic;
Second terminal voltage value determining means (460) for determining the second terminal voltage value based on the humidity and the first terminal voltage value from the fourth function characteristic;
Gas sensitivity determining means (470) for determining the gas sensitivity based on the environmental temperature from the fifth function characteristic;
Dividing means (480) for dividing the difference between the terminal voltage of the high temperature side heating resistor and the second terminal voltage value by the gas sensitivity;
The result of division by the division means is the concentration of the combustible gas.

  In this way, the third to fifth function characteristics are also stored in the storage means, the first terminal voltage value is determined based on the environmental temperature from the third function characteristics, and the fourth function is determined. From the characteristics, the second terminal voltage value is determined based on the humidity and the first terminal voltage value, the gas sensitivity is determined based on the environmental temperature from the fifth function characteristic, and the high temperature side heating resistor is configured as described above. The difference between the terminal voltage and the second terminal voltage value was divided by the gas sensitivity, and the result of division was taken as the concentration of the combustible gas.

  Therefore, since the first terminal voltage value, the second terminal voltage value, and the gas sensitivity are determined based on the corresponding function characteristics described above, the concentration of the combustible gas can be obtained with higher accuracy. As a result, the function and effect of the invention of claim 3 can be further improved.

Moreover, according to the description of Claim 5, this invention WHEREIN: In the combustible gas detection apparatus as described in any one of Claims 1-4,
Saturated water vapor concentration determining means (425) for determining the saturated water vapor concentration based on the environmental temperature from the characteristic representing the relationship between the saturated water vapor concentration in the detected atmosphere and the environmental temperature;
Humidity that corrects the determined humidity to the saturated water vapor concentration when the humidity determined by the humidity determining means is equal to or higher than the saturated water vapor concentration, and corrects the determined humidity to zero when the humidity determined by the humidity determining means is equal to or lower than zero. And correction means (430, 431, 440, 441).

  Thus, since the humidity is corrected to the saturated water vapor concentration determined as described above or zero, an error occurring in the second terminal voltage value calculated from the fourth function characteristic can be minimized. As a result, the same effect as that of the invention described in any one of claims 1 to 4 can be achieved.

Further, according to the sixth aspect of the present invention, in the combustible gas detection device according to any one of the first to fifth aspects,
Other humidity that corrects the humidity determined by the humidity determining means to a predetermined value selected in advance so as to suppress deterioration in the detection accuracy of the concentration of the combustible gas when the environmental temperature is equal to or lower than the predetermined temperature. A correction unit is provided.

  As described above, the humidity is corrected to a predetermined value selected in advance so as to suppress the deterioration in the detection accuracy of the concentration of the combustible gas as described above, so even when the environmental temperature is equal to or lower than the predetermined temperature. And the effect similar to the invention as described in any one of Claims 1-5 can be achieved, suppressing the deterioration of the detection accuracy of the combustible gas density | concentration.

  According to the present invention, in the combustible gas detection device according to any one of claims 1 to 6, the difference in control temperature between the two heating resistors is 50 ( ° C) or more.

  Thereby, the determination precision of humidity can be made still more favorable, As a result, the effect of the invention as described in any one of Claims 1-6 can be improved further.

  According to the present invention, in the combustible gas detection device according to claim 7, the control temperature of the two heating resistors is 150 (° C.) or more and 500 (° C.) or less. It is characterized by being.

  Thereby, the temperature of the two heat generating resistors can be controlled to a temperature of 150 (° C.) or more that surely exceeds the boiling point of water in the atmospheric pressure atmosphere, and the explosion temperature of the combustible gas in the detected atmosphere It can be controlled to a temperature below 500 (° C.) or less. Accordingly, detection by the gas detection device can be enabled even in a humid environment where the atmosphere to be detected includes condensation.

Further, in the combustible gas detection method according to the present invention, according to the description of claim 9,
The two resistance values of at least two heating resistors (211, 221 and 330) of the plurality of heating resistors exposed to the atmosphere to be detected are maintained at values corresponding to different constant temperatures. The heating resistor is controlled by energization,
A ratio of terminal voltages (VH, VL) of the two heating resistors generated in the controlled state in the detected atmosphere is determined as a voltage ratio (RV);
Based on the voltage ratio and the environmental temperature based on the humidity-voltage ratio-environment temperature characteristic representing the relationship between the humidity (HUM) in the detected atmosphere, the voltage ratio, and the environmental temperature (T) in the detected atmosphere. Determine the humidity,
It represents the relationship between the concentration (D) of the combustible gas in the detected atmosphere, the terminal voltage (VH) of the high-temperature side heating resistor (221) of the two heating resistors, the humidity, and the environmental temperature. The combustible gas is detected by calculating the concentration of the combustible gas from the concentration-terminal voltage-humidity-environment temperature characteristics based on the terminal voltage, the humidity, and the environmental temperature of the high-temperature side heating resistor.

  According to this, it is possible to provide a combustible gas detection method capable of achieving the same function and effect as the first aspect of the invention.

According to the description of claim 10, the present invention provides the method for detecting combustible gas according to claim 9,
A voltage ratio initial value (RV0) that is a ratio of terminal voltages of the two heating resistors when the concentration and humidity of the combustible gas are both zero is a dependent variable, and the environmental temperature is an independent variable. Functional characteristics of
A second function characteristic having the humidity as a dependent variable and a voltage ratio difference (ΔRV) representing a difference between the voltage ratio and the initial value of the voltage ratio as an independent variable is set as the humidity-voltage ratio-environment temperature characteristic. And
And the environmental temperature is an independent variable, and the first terminal voltage value (VH0), which is the terminal voltage of the high-temperature heating resistor when the concentration and humidity of the combustible gas are both zero, is a third variable. Functional characteristics of
The second terminal voltage value (VH1) that is the terminal voltage of the high-temperature side heating resistor when the humidity is an independent variable, the first terminal voltage value is an intercept, and the humidity in the detected atmosphere is zero. A fourth function characteristic as a dependent variable;
A fifth function characteristic having the environmental temperature as an independent variable and a gas sensitivity (G) for the combustible gas as a dependent variable is set as the concentration-terminal voltage-humidity-environment temperature characteristic,
The concentration of the combustible gas is determined based on the first to fifth function characteristics.

  As described above, the first and second functions are set as the humidity-voltage ratio-environment temperature characteristic, and the third to fifth functions are set as the concentration-terminal voltage-humidity-environment temperature characteristic. By determining the concentration of the combustible gas based on the first to fifth function characteristics, there is provided a combustible gas detection method that can achieve the effect of the invention of claim 9 more specifically. It becomes possible.

Further, according to the eleventh aspect of the present invention, in the method for detecting a combustible gas according to the eighth or ninth aspect,
Humidity determined based on the humidity-voltage ratio-environmental temperature characteristics by determining the saturated water vapor concentration based on the environmental temperature from the characteristic representing the relationship between the saturated water vapor concentration in the detected atmosphere and the environmental temperature. The determined humidity is corrected to the saturated water vapor concentration when the water vapor concentration is equal to or higher than the saturated water vapor concentration, and the determined humidity is corrected to zero when the humidity determined based on the humidity-voltage ratio-environment temperature characteristic is less than zero. Features.

  Thus, in achieving the function and effect of the invention described in claim 8 or 9, it is possible to provide a method for detecting a combustible gas that can achieve the same function and effect as the invention described in claim 5.

  Further, according to the twelfth aspect of the present invention, in the flammable gas detection method according to any one of the ninth to eleventh aspects, when the environmental temperature is equal to or lower than a predetermined temperature, the humidity − The humidity determined on the basis of the voltage ratio-environment temperature characteristic is set to a predetermined value selected in advance so as to suppress the deterioration of the detection accuracy of the combustible gas concentration.

  Thereby, when the environmental temperature is equal to or lower than the predetermined temperature, the deterioration of the detection accuracy of the combustible gas concentration can be suppressed by setting the humidity to the predetermined value.

Moreover, according to the description of Claim 13, this invention is the combustible gas detection method as described in any one of Claims 10-12.
Detect the pressure in the detected atmosphere,
From the characteristics representing the relationship between the coefficients of the first to fifth function characteristics determined so as not to be affected by the fluctuation of the pressure and the pressure, the function characteristics are determined in the coefficients based on the pressure. Correct,
The humidity is determined based on the first and second functional characteristics after the correction,
The concentration of the combustible gas is determined based on the determined humidity and the corrected third to fifth function characteristics.

  Thereby, even if there is a pressure fluctuation in the atmosphere to be detected, the humidity is accurately determined to a value that is not affected by the pressure fluctuation. Therefore, by determining the concentration of the combustible gas based on the humidity determined in this way and the corrected third to fifth function characteristics, the concentration of the combustible gas can be determined with higher accuracy. The As a result, even if there exists a pressure fluctuation as mentioned above, the effect of the invention as described in any one of Claims 10-12 can be improved further.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

Hereinafter, each embodiment of the present invention will be described with reference to the drawings.
(First embodiment)
1 and 2 show a first embodiment of a combustible gas detection device according to the present invention. This combustible gas detection device includes an apparatus unit 100 (see FIG. 1) and a control circuit 200 (FIG. 2). For example). The combustible gas detection device is used, for example, for detecting the concentration of hydrogen gas leaking from the fuel cell and flowing into the detected atmosphere in the fuel cell system.

  The device unit 100 is disposed in the detected atmosphere. The device unit 100 includes a casing 110, a detection structure 120, and a connector 130 as shown in FIG. The casing 110 has a casing main body 111 and a lid 112, and the casing main body 111 is closed with a lid 112 at the opening. Here, the casing main body 111 is provided with a gas introduction cylinder 113, and this gas introduction cylinder 113 extends outward from the center of the bottom wall of the casing main body 111 in a cylindrical shape, and at the gas introduction port portion 114, It opens to the direction.

  As shown in FIG. 1, the detection structure 120 is coaxially fitted into the gas introduction tube 113 from the inside of the casing body 111. The detection structure 120 includes a cylindrical member 121 as shown in FIGS. 1 and 3, and this cylindrical member 121 has a gas introduction as shown in FIG. 1 at its bottom wall side small diameter portion 122. A small diameter portion of the tube 113 is coaxially fitted. An annular space is formed between the inner peripheral surface of the small diameter portion of the gas introduction tube 113 and the small diameter portion 122 of the cylindrical member 121.

  The cylindrical member 121 is seated from the inner surface side to the gas inlet 114 (see FIG. 1) at the annular bottom wall 123 (see FIG. 3). The annular bottom wall 123 of the cylindrical member 121 is In the hollow portion, the gas introduction port portion 114 is opened outward.

  Further, the cylindrical member 121 is fitted with a large-diameter hole formed on the proximal end side of the gas introduction tube 113 at the proximal-end-side large-diameter portion 124 via an annular space. As shown in FIG. 1, the annular flange 125 extending radially outward from the proximal-side large-diameter portion 124 has a plurality of screws (not shown) on the inner surface of the bottom wall of the casing body 111 via the O-ring 115. Not fixed). However, the O-ring 115 is seated in an annular recess 116 formed on the bottom wall of the casing body 111 from its inner surface, and the O-ring 115 is interposed between the annular flange 125 and the bottom wall of the casing body 111. The inside of the casing main body 111 is hermetically sealed from the inside of the gas introduction tube 113 by being sandwiched.

  Further, the detection structure 120 includes a water repellent water repellent filter 126 provided in the cylindrical member 121 and two wire meshes 127 for preventing a fire from escaping to the outside of the detection structure 120. The water repellent filter 126 is sandwiched between the annular bottom wall 123 of the cylindrical member 121 and the annular plate spacer 128 at the outer periphery thereof. The water repellent filter 126 includes the gas inlet 114 and the annular bottom. Intrusion of water droplets and intrusion of dust from the hollow portion of the wall 123 into the cylindrical member 121 is prevented.

  The two metal meshes 127 are sandwiched between the annular plate spacer 128 and the annular bottom wall 141 of the cylindrical spacer 140 at the outer periphery thereof, and these metal meshes 127 play the following roles. That is, when a heating resistor 330 (see FIG. 4), which will be described later, is energized, a current flows through the heating resistor 330 and the temperature of the heating resistor 330 exceeds the lower limit explosion temperature of hydrogen gas. When fired in the cylindrical member 121, for example, in the cylindrical spacer 140, the two metal meshes 127 prevent the fire from going out from the inside of the cylindrical member 121.

  The spacer 140 is coaxially fitted into the bottom wall side small diameter portion 122 of the cylindrical member 121 by press-fitting, and at the annular bottom wall 141, the two metal nets 127, the annular plate spacer 128, and the water repellent filter are provided. 126 is fixed on the inner surface of the annular bottom wall 123 of the cylindrical member 121.

  The connector 130 is integrally extended from the right side wall shown in FIG. 1 of the casing main body 111, and this connector 130 includes a plurality of connector pins 131 (only one connector pin is shown in FIG. 1). At the end, it passes through the right side wall of the casing body 111 and is electrically connected to a wiring pattern portion (not shown) of the wiring board 150. The connector 130 may be formed separately from the casing body 111.

  As shown in FIGS. 1 and 3, the device unit 100 includes a detection element 300, a mounting plate 170, and a laying plate 180, and the detection element 300 is installed in the cylindrical member 121 together with the mounting plate 170 and the laying plate 180. It is supported by.

  As shown in FIG. 3, the mounting plate 170 is hermetically sealed via an O-ring 172 in an annular recess 129 formed on the inner peripheral surface of the annular flange 125 of the cylindrical member 121 at the annular flange portion 171. It is fitted and fixed.

  The laying plate 180 is formed of a material having a low thermal conductivity, and this laying plate 180 is bonded to the central portion of the outer surface (surface on the spacer 140 side) of the mounting plate 170 with an adhesive. The detection element 300 is adhered to the outer surface of the laying plate 180 (the surface on the spacer 140 side) with an adhesive, and is exposed in the spacer 140.

  Further, as shown in FIGS. 1 and 3, the device unit 100 includes a plurality of pin-shaped terminals 181 and heaters 190, and each terminal 181 is inserted through a mounting plate 170 (see FIG. 1). ). In FIGS. 1 and 3, only two of the plurality of terminals 181 are shown for convenience.

  As shown in FIGS. 1 and 3, the heater 190 is attached to the annular flange 125 of the cylindrical member 121 from above, and this heater 190 is supplied with power via both terminals 181 (both terminals shown in FIG. 3). The detection element 300 is heated via the annular flange 125, the mounting plate 170 and the laying plate 180.

  As a result, the inside of the cylindrical member 121 (hereinafter also referred to as a measurement space) is warmed, and condensation and impurities attached to the detection element 300 are dried and disappeared. As a result, the gas detection device (mainly device unit 100) can operate well even in a humid environment where condensation is likely to occur. In addition, the detection element 300 is electrically connected to the tip of each terminal (not shown) of the plurality of terminals 181 by wire bonding with each electrode film 370 (see FIG. 4) described later.

  As shown in FIG. 1, the wiring board 150 is provided in the casing 110, and the wiring board 150 is supported by the opening end portion of the casing body 111 at the outer peripheral portion thereof. Each terminal 181 is fitted to the wiring board 150 at the base end portion and is electrically connected to the wiring pattern portion of the wiring board 150.

  As shown in FIG. 1, the control circuit 200 is mounted on the back surface of the wiring board 150 (the lower side in FIG. 1) in the casing 110, and the control circuit 200 is connected to the wiring board 150. It is electrically connected to the connector pin 131 of the connector 130 and each terminal 181 through the pattern portion.

  Next, the configuration of the detection element 300 described above will be described with reference to FIGS. The detection element 300 is manufactured using a micromachining technique, and the detection element 300 includes a silicon semiconductor substrate 310 and upper and lower insulating layers 320 as shown in FIG.

  The upper insulating layer 320 is formed on the surface of the semiconductor substrate 310, while the lower insulating layer 320 is formed on the back surface of the semiconductor substrate 310. The upper insulating layer 320 includes a silicon oxide film 321 formed on the surface of the semiconductor substrate 310 and a silicon nitride film 322 stacked on the silicon oxide film 321. The lower insulating layer 320 includes a silicon oxide film 321 formed on the back surface of the semiconductor substrate 310 and a silicon nitride film 322 stacked on the silicon oxide film 321.

  Here, the left and right concave portions 311 shown in FIG. 4 are formed in the semiconductor substrate 310 at intervals on the back surface side of the upper insulating layer 320. In addition, the lower insulating layer 320 is removed at portions corresponding to the respective recesses 311 and formed as openings of the respective recesses 311.

  As a result, the upper insulating layer 320 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 semiconductor substrate 310 constitutes a substrate portion 312 at a portion other than each recess 311.

  Further, as shown in FIGS. 4 and 5, the detection element 300 includes left and right heat generating resistors 330 and left, center, and right wiring films 340. The left heating resistor 330 is spirally formed on a portion of the surface of the upper insulating layer 320 corresponding to the left recess 311, while the right heating resistor 330 is formed on the right side of the surface of the upper insulating layer 320. A spiral shape is formed on a portion corresponding to the recess 311. In the first embodiment, both the heating resistors 330 are formed of a platinum resistance material together with each wiring film 340 described later.

  As shown in FIG. 4, the left wiring film 340 is located on the left side of the surface of the upper insulating layer 320 corresponding to the substrate portion 312 of the semiconductor substrate 310. As shown in FIG. It is formed so as to be integrated with one end of 330.

  The central wiring film 340 is located on the central portion of the surface of the upper insulating layer 320 so as to correspond to the substrate portion 312 of the semiconductor substrate 310, and has the other end of the left heating resistor 330 and one end of the right heating resistor 330. It is formed so as to be integrated.

  The right wiring film 340 is formed on the right side of the surface of the upper insulating layer 320 so as to correspond to the substrate portion 312 of the semiconductor substrate 310 and to be integrated with the other end of the right heating resistor 330. Has been.

  Further, as shown in FIGS. 4 and 5, the detection element 300 includes an inner protective layer 350 and an outer protective layer 360, and left, center, and right electrode films 370. It is formed on the surface of the upper insulating layer 320 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 stacked form.

  Here, in the inner protective layer 350 and the outer protective layer 360, the contact holes 361 on the left side, the central side, and the right side are provided with the wiring films 340 on the left side, the central side, and the right side of the inner protective layer 350 and the outer protective layer 360, respectively. It is formed in each part corresponding to.

  As a result, the left, center, and right wiring films 340 are exposed outwardly through the left, center, and right contact holes 361 on the surface.

  The left, central and right electrode films 370 are formed on the left, central and right wiring films 340 through the left, central and right contact holes 361.

  In the first embodiment, in the detection element 300, the left heating resistor 330, the left and center wiring films 340, and the left and center electrode films 370 mainly serve as the left heat-conducting gas detection unit 380. In addition, the right heating resistor 330, the central and right wiring films 340, and the central and right electrode films 370 mainly constitute the right heat conduction type gas detector 380 (see FIG. 5). .

  In addition, the detection element 300 is exposed to the measurement space of the cylindrical member 121 (see FIG. 1) via the inner protective layer 350 and the outer protective layer 360 by the left and right heat generating resistors 330. Each terminal voltage of the heating resistor 330 varies with changes in heat conduction based on variations in the concentration of hydrogen gas and the amount of moisture in the measurement space.

  Further, as shown in FIG. 5, the detection element 300 includes a resistance temperature detector 390, and the resistance temperature detector 390 is a resistance temperature detector material containing platinum (Pt). On the upper side in the figure, a thin film resistor is formed between the upper insulating layer 320 and the inner protective layer 350.

  Thereby, the resistance temperature detector 390 detects the temperature in the measurement space of the cylindrical member 121 (hereinafter also referred to as environmental temperature T) and generates a temperature voltage VT. Further, since the resistance temperature detector 390 is provided in the detection element 300 as described above, it is not necessary to provide the resistance temperature detector 390 separately from the detection element 300. Therefore, the measurement space can be reduced. The temperature resistance coefficient of the resistance temperature detector 390 is substantially the same as the temperature resistance coefficient of both the heating resistors 330.

  In the first embodiment, when the relationship between the temperature voltage VT of the resistance temperature detector 390 and the environmental temperature T was examined, a graph illustrated in FIG. 6 was obtained. According to the graph, it is understood that the relationship (quadratic function characteristic) specified by the following quadratic function (quadratic function characteristic) is approximately established between the temperature voltage VT and the environmental temperature T. It was.

VT = VT (T) = A0 · T ² + B0 · T + C0 (1)
According to this equation (1), it can be seen that the environmental temperature T, which is the temperature in the detected atmosphere, is specified by the temperature voltage VT. In equation (1), A0 is a positive coefficient, B0 is a negative coefficient, and C0 is a positive constant.

  Each electrode film 391 is formed on both left and right ends of the resistance temperature detector 390 in each contact hole (not shown) formed in the inner protective layer 350 and the outer protective layer 360. The resistance temperature detector 390 is connected to the wiring pattern portion of the wiring board 150 via both terminals 391 and a terminal (not shown).

  Next, the configuration of the control circuit 200 described above will be described with reference to FIG. The control circuit 200 includes both bridge circuits 210 and 220, and the bridge circuit 210 forms a Wheatstone bridge circuit with the gas detection heating resistor 211 and the fixed resistors 212, 213, and 214. It is configured.

  In the bridge circuit 210, the gas detection heating resistor 211 is configured by a left heating resistor 330 that is a component of the left heat conduction type gas detection unit 380 of the detection element 300. Here, the heating resistor 211 is grounded at one end, and the other end of the heating resistor 211 is grounded via a fixed resistor 212, a fixed resistor 213, and a fixed resistor 214.

  Thus, the bridge circuit 210 includes a constant temperature control circuit between the common terminal (one side power supply terminal) of the heating resistor 211 and the fixed resistor 214 and the common terminal (other side power supply terminal) of the two fixed resistors 212 and 213. Operates in response to a control voltage from 230.

  Then, under this operation, the bridge circuit 210 is based on a change in the resistance value of the gas detection heating resistor 211 and a common terminal of the heating resistor 211 and the fixed resistor 212 (one side output terminal of the bridge circuit 210). And a potential difference (representing the concentration of hydrogen gas) generated between the two fixed resistors 213 and 214 (the other output terminal of the bridge circuit 210).

  The constant temperature control circuit 230 maintains the resistance value of the gas detection heating resistor 211 at a value corresponding to a constant temperature (for example, 300 (° C.)) according to the output (described later) of the operational amplifier circuit 250. The control voltage to the bridge circuit 210 is formed based on the output voltage of the built-in DC power supply (not shown). The heating resistor 211 (330) has a positive resistance characteristic with respect to temperature. That is, the heating resistor 211 (330) increases (or decreases) the resistance value in accordance with an increase (or decrease) in the temperature of the heating resistor 211 (330).

  In the first embodiment, the control temperature of the heating resistor 211 for gas detection is controlled to be 300 (° C.) based on the following grounds.

  In order to enable detection of the concentration of hydrogen gas by the gas detection device even in a humid environment where the measurement space of the cylindrical member 121 includes condensation in the detected atmosphere, the temperature of the heating resistor 211 is set. It is necessary to control the temperature to at least 150 (° C.) that surely exceeds the boiling point of water in an atmosphere of atmospheric pressure. On the other hand, it is necessary to control the temperature of the heating resistor 211 to a temperature of 500 (° C.) or less so as not to exceed the explosion temperature of the hydrogen gas in the detected atmosphere. For this reason, the control temperature of the heating resistor 211 is set to 300 (° C.) as described above.

  Further, as shown in FIG. 2, the bridge circuit 220 is configured to form a Wheatstone bridge circuit with the gas detection heating resistor 221 and the fixed resistors 222, 223, and 224.

  In the bridge circuit 220, the gas detection heating resistor 221 is configured with a right heating resistor 330 that is a component of the right heat conduction type gas detection unit 380 of the detection element 300. Here, the heating resistor 221 is grounded at one end, and the other end of the heating resistor 221 is grounded via a fixed resistor 222, a fixed resistor 223, and a fixed resistor 224.

  Thus, the bridge circuit 220 includes the constant temperature control circuit 240 between the common terminal (one side power supply terminal) of the heating resistor 221 and the fixed resistor 224 and the common terminal (other side power supply terminal) of both the fixed resistors 222 and 223. Operates in response to a control voltage from.

  Under this operation, the bridge circuit 220 is connected to the common terminal (one side output terminal of the bridge circuit 220) of the heating resistor 221 and the fixed resistor 222 based on the change in the resistance value of the gas detection heating resistor 221. A potential difference (representing the hydrogen gas concentration) generated between the common terminals of the fixed resistors 223 and 224 (the other output terminal of the bridge circuit 220) is output.

  The constant temperature control circuit 240 maintains the resistance value of the gas detection heating resistor 221 at a value corresponding to a constant temperature (for example, 400 (° C.)) according to the output (described later) of the operational amplifier circuit 260. The control voltage to the bridge circuit 220 is formed based on the output voltage of the built-in DC power supply (not shown). The heating resistor 221 (330) has a positive resistance characteristic with respect to temperature. That is, the heating resistor 221 (330) increases (or decreases) the resistance value in accordance with an increase (or decrease) in the temperature of the heating resistor 221 (330).

  In the first embodiment, the control temperature of the gas detection heating resistor 221 is maintained at 400 (° C.) because the control temperature of the heating resistor 221 is controlled by the heating resistor 211 described above. This is because the temperature needs to be higher than the temperature, and based on the same reason as described above, the temperature needs to be 150 (° C.) or higher and 500 (° C.) or lower. The output of each control voltage of both constant temperature control circuits 230 and 240 is started in synchronization with the power switch 281 being turned on.

  The reason why the control temperature of the heating resistor 221 is made 100 (° C.) higher than the control temperature of the heating resistor 211 is based on the following grounds. That is, in order to increase the detection accuracy of volume humidity (described later), it is better that the difference in the control temperature between the two heating resistors 211 and 221 of the detection element 300 is larger. Specifically, the temperature is desirably 50 (° C.) or higher.

  For this reason, in the first embodiment, as described above, the control temperature of the heating resistor 221 is increased by 100 (° C.) from the control temperature 300 (° C.) of the heating resistor 211 to 400 (° C.). did.

  The operational amplifier circuit 250 differentially amplifies the potential difference generated between the two output terminals of the bridge circuit 210 and outputs the differential amplified potential difference to the constant temperature control circuit 230 and the microcomputer 270. The operational amplifier circuit 260 differentially amplifies the potential difference generated between the two output terminals of the bridge circuit 220 and outputs the differential amplified potential difference to the constant temperature control circuit 240 and the microcomputer 270.

  The microcomputer 270 operates with power supplied from the DC power source 280 via the power switch 281 and executes the computer program according to the flowcharts shown in FIGS. During this execution, the microcomputer 270 performs various processes required for calculating the concentration of hydrogen gas based on the detection environment temperature of the resistance temperature detector 390 and the differential amplification potential differences of the two operational amplifier circuits 250 and 260. The computer program is stored in the ROM of the microcomputer 270 so as to be readable by the microcomputer.

  In this 1st Embodiment comprised as mentioned above, the apparatus unit 100 of the said combustible gas detection apparatus shall be arrange | positioned in the said to-be-detected atmosphere. In this state, when hydrogen gas leaking into the detected atmosphere flows into the gas introduction tube 113 of the apparatus unit 100 from the gas introduction port 114, the hydrogen gas is repelled by the water repellent filters 126 and 2. The sheet passes through the sheet metal mesh 127 and flows into the cylindrical member 121, and then reaches the detection element 300.

  In such a state, when the power switch 281 is turned on and the microcomputer 270 is supplied with power from the DC power supply 280, the microcomputer 270 starts executing the computer program according to the flowcharts of FIGS. Along with this start, in step 400 of FIG. 7, a soft timer built in the microcomputer 270 is activated. Therefore, the soft timer starts timing by the reset activation.

  Then, the determination of NO is repeated in step 410 until the time measured by the soft timer has exceeded a predetermined waiting time. The predetermined waiting time is the temperature of the heating resistor 211 is controlled to be the constant temperature (300 (° C.)) under the control of the constant temperature control circuit 230 and the heating resistance is controlled under the control of the constant temperature control circuit 240. The time required for the body 221 to reach the constant temperature (400 (° C.)) is set.

  Further, in synchronization with the power switch 281 being turned on, the output of each control voltage by the two constant temperature control circuits 230 and 240 is started. Accordingly, when the constant temperature control circuit 230 outputs a control voltage between both power supply terminals of the bridge circuit 210, the bridge circuit 210 is energized with the control voltage. The potential difference output from both output terminals of the bridge circuit 210 is amplified by the operational amplifier circuit 250 and fed back to the constant temperature control circuit 230.

  Accordingly, the heating resistor 211 is controlled at a constant temperature so that the resistance value of the heating resistor 211 maintains a value corresponding to the constant temperature (300 (° C.)) while the determination of NO in step 410 is repeated. The circuit 230 is controlled by energization.

  When the constant temperature control circuit 240 outputs a control voltage between both power supply terminals of the bridge circuit 220, the bridge circuit 220 is energized with the control voltage. The potential difference output from both output terminals of the bridge circuit 220 is amplified by the operational amplifier circuit 260 and fed back to the constant temperature control circuit 240.

  Therefore, during the repetition of the determination of NO in step 410, the heating resistor 221 is controlled at a constant temperature so that the resistance value of the heating resistor 221 maintains a value corresponding to the constant temperature (400 (° C.)). The circuit 240 is controlled by energization.

  Thereafter, when the time measured by the soft timer has passed the predetermined waiting time, it is determined YES in step 410, and in the next step 411, the temperature voltage VT from the resistance temperature detector 390 is input. . Therefore, the temperature voltage VT is input from the resistance temperature detector 390 to the microcomputer 270 and set.

  Next, in step 412, input processing of each differential amplification potential difference of both operational amplifier circuits 250 and 260 is performed. Along with this, the differential amplification potential differences between the operational amplifier circuits 250 and 260 are input and set to the microcomputer 270 as the low temperature side differential amplification potential difference VL and the high temperature side differential amplification potential difference VH.

  After the processing in step 412 is completed as described above, in the next step 420, it is determined whether or not the temperature voltage VT is equal to or lower than a predetermined threshold voltage VTr. In the first embodiment, the predetermined threshold voltage VTr corresponds to the reference value of the environmental temperature T.

  If VT ≦ VTr is satisfied at the current stage, YES is determined in step 420. Accordingly, in the next step 421, the voltage ratio RV is calculated according to the differential amplified potential difference VH from the operational amplifier circuit 260 and the amplified potential difference VL from the operational amplifier circuit 250 based on the following equation (2). The

RV = VH / VL (2)
Here, the voltage ratio RV refers to the ratio of the terminal voltage of the heating resistor 221 to the terminal voltage of the heating resistor 211. In the first embodiment, the voltage ratio RV corresponds to the ratio (VH / VL) of the differential amplification potential difference VH from the operational amplification circuit 260 to the differential amplification potential difference VL from the operational amplification circuit 250.

  When the process of step 421 is completed as described above, in step 422, the calculation process of the voltage ratio RV = RV0 at the hydrogen gas concentration D = 0 and the volume humidity HUM = 0 is performed.

Here, the voltage ratio RV when the hydrogen gas concentration D = 0 and the volume humidity HUM = 0 is RV0 (hereinafter also referred to as the voltage ratio initial value RV0), but the calculation when D = 0 and HUM = 0. When the differential amplification potential difference VH from the amplification circuit 260 is the first differential amplification potential difference VH0,
This voltage ratio initial value RV0 is a ratio (VH0 / VL0) of the first differential amplification potential difference VH0 (corresponding to the first terminal voltage value of the present invention) to the differential amplification potential difference VL = VL0 from the operational amplification circuit 250. Specified. Note that the differential amplification potential difference VL0 is a value when D = 0 and HUM = 0. In the first embodiment, the volume humidity HUM refers to the amount of water per unit volume when the environmental temperature is T in the detected atmosphere.

  Here, when the relationship between the voltage ratio initial value RV0 and the environmental temperature T in the detected atmosphere, that is, the temperature voltage VT, was examined, the relationship between the voltage ratio initial value RV0 and the temperature voltage VT was 2 It was found that the next function characteristic is approximately specified by the equation (3) including the following quadratic function.

RV0 = RV0 (VT) = A1 · VT ² + B1 · VT + C1 (3)
Therefore, it can be seen that the voltage ratio initial value RV0 can be obtained based on the temperature voltage VT from the above equation (3) without depending on (VH0 / VL0). In Equation (3), A1 represents a positive coefficient, B1 represents a negative coefficient, and C1 represents a positive constant. Further, the above equation (3) is stored in advance in the ROM of the microcomputer 270.

  Therefore, in the processing of step 422, the voltage ratio initial value RV0 is calculated based on the temperature voltage VT from the above equation (3) without directly calculating VH0 / VL0.

  However, the relationship between the voltage ratio initial value RV0 and the temperature voltage VT described above is specified by a curved line graph that protrudes downward to the right, unlike the graphs of FIGS. 9 and 12 described later. The Therefore, the equation (3) is different from the equations (6) and (8) described later, and is different from the equations (6) and (8).

  Thereafter, in step 423 (see FIG. 8), the voltage ratio difference ΔRV is calculated based on the following equation (4).

ΔRV = RV−RV0 (4)
Equation (4) is stored in advance in the ROM of the microcomputer 270.

  Next, in step 424, the volume humidity HUM is calculated based on the voltage ratio difference ΔRV from the equation (5) including the following quadratic function. In Equation (5), A2 and B2 are both positive coefficients, and C2 is a constant (C2 = 0).

HUM = HUM (ΔRV)
= A2 · ΔRV ² + B2 · ΔRV + C2 ··· (5)
Here, the basis of the formula (5) is as follows. That is, when the relationship between the volume humidity HUM and the voltage ratio difference ΔRV was examined, a graph as shown in FIG. 10 was obtained. According to this graph, it was found that the relationship between the volume humidity HUM and the voltage ratio difference ΔRV can be approximated by the above equation (5) as a quadratic function characteristic. Equation (5) is stored in advance in the ROM of the microcomputer 270.

  After the process in step 424, in the next step 425, the maximum value HUMmax (corresponding to saturated water vapor concentration) of the volume humidity HUM is calculated. In this calculation process, the maximum value HUMmax is calculated based on the ambient temperature T from a quartic function formula that specifies the relationship between the maximum value HUMmax and the ambient temperature T. The quadratic function formula is stored in advance in the ROM of the microcomputer 270.

  Next, at step 430, it is determined whether or not the volume humidity HUM is larger than the maximum value HUMmax. Such a determination is made based on the following grounds.

  That is, when the high-temperature differential amplification potential difference VH when the hydrogen gas concentration D = 0 is the second differential amplification potential difference VH1 (corresponding to the second terminal voltage value of the present invention), this second differential amplification potential difference When VH1 is calculated using the volume humidity HUM calculated by the above-described expression (5) based on the expression (7) including a cubic function described later, the error may be a second differential depending on the volume humidity HUM. This occurs so as to increase the amplified potential difference VH1. For this reason, step 430 is employed so that the method of correcting the volume humidity HUM differs depending on the volume humidity HUM.

  At this stage, if the volume humidity HUM calculated by the equation (5) is larger than the maximum value HUMmax, YES is determined in step 430, and in the next step 431, the volume humidity HUM becomes the maximum value HUMmax. Limited correction is made.

  On the other hand, if HUM is equal to or lower than HUMmax, it is determined in step 440 whether HUM <0 is satisfied. If HUM <0 is satisfied, YES is determined in step 440, and in step 441, the volume humidity is limited and corrected so that HUM = 0.

  As described above, by limiting and correcting the volume humidity HUM to the maximum value HUMmax or zero, the second differential amplification potential difference VH1 is calculated based on the equation (7) including a cubic function described later, based on the equation (5). Even if the volume humidity HUM calculated by the above is used, the error generated in the second differential amplification potential difference VH1 can be suppressed to the minimum.

  When the limit correction process in step 431, the limit correction process in step 441, or the determination process of NO in step 440 is performed as described above, the hydrogen gas concentration D and the volume humidity HUM in the detected atmosphere are determined. If the high-temperature differential amplification potential difference VH when both are zero is the first differential amplification potential difference VH0, A3 and B3 are coefficients, and C3 is a constant, the first differential amplification potential difference VH0 is It is calculated based on the temperature voltage VT from equation (6) consisting of the following quadratic function. The coefficient A3 is negative, the coefficient B3 is positive, and the constant C3 is positive.

VH0 = VH0 (VT) = A3 · VT ² + B3 · VT + C3 (6)
Here, the basis of the formula (6) will be described. When the hydrogen gas concentration D and volume humidity HUM in the detected atmosphere are zero, the difference between the first differential amplification potential difference VH0 and the environmental temperature T in the detected atmosphere, and thus the temperature voltage VT, When the relationship was established, a graph as shown in FIG. 9 was obtained.

  According to this graph, it was found that the relationship between the first differential amplification potential difference VH0 and the temperature voltage VT is approximately specified by the above-described equation (6) as a quadratic function characteristic. It should be noted that the above equation (6) is stored in advance in the ROM of the microcomputer 270.

  In the next step 460, the second differential amplification potential difference VH = VH1 is calculated based on the volume humidity HUM from the equation (7) consisting of the following quadratic function. In Equation (7), A4 is a negative coefficient, B4 is a positive coefficient, and C4 is a constant (C4 = VH0).

VH1 = VH1 (HUM)
= A4 · HUM ² + B4 · HUM + C4 (7)
Here, the basis of the formula (7) will be described. When the relationship between the second differential amplification potential difference VH1 and the volume humidity HUM was examined, the graph shown in FIG. 11 was obtained. According to this graph, it was found that the relationship between the second differential amplification potential difference VH1 and the volume humidity HUM can be approximated by the above-described equation (7) as a quadratic function characteristic. The first differential amplification potential difference VH0 calculated based on the equation (6) represents an offset amount with respect to the temperature voltage VT (environment temperature T) as can be seen from the equation (7) and FIG.

  Next, at step 470, the gas sensitivity G is calculated based on the temperature voltage VT from equation (8) consisting of the following quadratic function. In the equation (8), A5 is a negative coefficient, B5 is a positive coefficient, and C5 is a positive constant.

G = G (VT) = A5 · VT ² + B5 · VT + C5 (8)
Here, the basis of Expression (8) will be described. At the ambient temperature T in the detected atmosphere, the high-temperature differential amplification potential difference VH when the moisture in the detected atmosphere is zero (that is, the volume humidity HUM = 0) and the hydrogen gas concentration D is zero. Is the first differential amplification potential difference VH0 as described above, the moisture in the detected atmosphere is zero (that is, the volume humidity HUM = 0), and the hydrogen gas concentration D can be detected by the combustible gas detection device. When the high-temperature side differential amplification potential difference VH when the maximum value Dmax (vol%) is VHmax, the gas sensitivity G (mV / vol%) is expressed by the following equation (9).

G = (VHmax−VH0) / Dmax (9)
Based on this equation (9), when the relationship between the gas sensitivity G and the temperature voltage VT was examined, the graph shown in FIG. 12 was obtained. According to this graph, it has been found that the relationship between the gas sensitivity G and the temperature voltage VT is approximately specified by the above-described equation (8) as a quadratic function characteristic. Therefore, it can be seen that the gas sensitivity G can be obtained from the above equation (8) based on the temperature voltage VT without depending on the equation (9).

  However, when the graph of FIG. 12 is compared with the graph of FIG. 9, the graph of FIG. 12 has a curved line that is convex upward, whereas the graph of FIG. Is slightly curved upwardly convex, and if anything, it is almost linear. Therefore, equation (8) differs in the coefficient from equation (6). As a result, Equation (8) is different from Equation (6). The equation (8) is stored in advance in the ROM of the microcomputer 270.

  Thereafter, in step 480, the hydrogen gas concentration D is determined based on the following equation (10), the high temperature side differential amplification potential difference VH input in step 412, the gas sensitivity G calculated in step 470, and step 460. It is calculated according to the second differential amplification potential difference VH1 calculated in (1).

D = (VH−VH1) / G (10)
Since the equation (10) represents the amount of change in the high temperature side differential amplification potential difference VH with respect to the hydrogen gas concentration D = 1 (vol%), the unit of the hydrogen gas concentration D in the equation (10) is ( vol% H ₂ ). Further, the equation (10) is stored in advance in the ROM of the microcomputer 270.

  As described above, since the concentration of hydrogen gas is calculated after calculating the volume humidity in the detected atmosphere, when temperature voltage VT ≦ reference value VTr, moisture is detected in the detected atmosphere. Even if it exists, the density | concentration of hydrogen gas can be calculated accurately. This means that the concentration of hydrogen gas can be calculated accurately even when the gas detection device is in a humid environment.

  By the way, when the output concentration of the gas detection device is examined with respect to the hydrogen gas concentration D when the temperature in the detected atmosphere is 0 (° C.), both graphs shown in FIG. 1 and 2 were obtained. Graph 1 shows how the output concentration of the gas detection device changes with respect to the hydrogen gas concentration D when the volume humidity HUM is restricted as described above. Graph 2 shows how the output concentration of the gas detection device changes with respect to the hydrogen gas concentration D when the volume humidity HUM is not limited as described above.

  According to this, it can be seen that since the error that increases the second differential amplification potential difference VH1 is suppressed, the output density is ensured accurately without decreasing.

  On the other hand, if VT> VTr is satisfied when the computer program proceeds to step 420 as described above, NO is determined in step 420. Accordingly, in the next step 426, the volume humidity HUM is calculated when the hydrogen gas concentration D = 0 in the detected atmosphere. That is, the volume humidity HUM is calculated according to the temperature voltage VT (> VTr) based on the following equation (11).

HUM = HUM (VT) (11)
The basis of this equation (11) is as follows. When the environmental temperature T is low, the absolute moisture content itself contained in the atmosphere to be detected is small. Therefore, the volume humidity HUM calculated by the above equation (5) deviates from the actual volume humidity. This deviation greatly affects the detection accuracy with respect to the concentration of the hydrogen gas that is the detection target gas, and as a result, the detection accuracy of the hydrogen gas concentration may deteriorate.

  Therefore, in order to suppress the deterioration of the detection accuracy of the concentration of hydrogen gas due to the calculation error of the volume humidity as described above, when the detection environment temperature T of the resistance temperature detector 390 is low, in other words, the temperature voltage VT. Is higher than the predetermined threshold voltage VTr, the volume humidity HUM is calculated from the temperature voltage VT based on the above-described equation (11) without depending on the above-described voltage ratio RV. For example, the HUM (VT) may be a predetermined volume humidity selected in advance so as to suppress the deterioration of the detection accuracy of the hydrogen gas concentration due to the above-described calculation error of the volume humidity. Equation (11) is stored in advance in the ROM of the microcomputer 270.

  When the process of step 426 is completed as described above, the second differential amplification potential difference VH1 is calculated in step 460 according to the volume humidity HUM calculated in step 426 based on the above-described equation (7). .

  In step 470, the hydrogen gas concentration D is calculated based on the equation (10).

Thus, when VT> VTr, that is, when the environmental temperature T is low, even if the absolute moisture content in the detected atmosphere is small, the volume humidity HUM is less likely to deviate from the actual volume humidity, and hydrogen gas Concentration D can be obtained with high accuracy.
(Second Embodiment)
Next, a second embodiment of the present invention will be described. The second embodiment is proposed from the following viewpoints. When the gas detection device is applied to a pipe of a fuel cell system, pressure fluctuation occurs inside the pipe. This pressure fluctuation affects the coefficients in the equations (3), (5), (7) and (8) described in the first embodiment. Therefore, if this influence is prevented, the concentration of hydrogen gas can be obtained with higher accuracy.

  From the above viewpoint, specifically, in the second embodiment, the apparatus unit 100 described in the first embodiment has a configuration in which a pressure sensor (not shown) is additionally employed. The pressure sensor detects the pressure in the atmosphere to be detected described in the first embodiment and inputs it to the microcomputer 270.

  Further, in each of the steps 422, 424, 460 and 470, the pressure sensor so that the coefficients of the equations (3), (5), (7) and (8) are not affected by the fluctuation of the pressure. Are corrected by the detected pressure of the above, and the processing in each step 422, 424, 460 and 470 is performed using the equations (3), (5), (7) and (8) after being corrected in this way. . In the correction, characteristics representing the relationship between the coefficients of the equations (3), (5), (7) and (8) and the detected pressure of the pressure sensor are stored in the ROM of the microcomputer 270 in advance. Has been.

  As a result, even if there is a pressure fluctuation as described above, the volume humidity HUM is accurately calculated to a value that is not affected by the pressure fluctuation. Therefore, by calculating the second differential amplification potential difference VH1 from the equation (7) based on the volume humidity HUM calculated in this way, the concentration of the hydrogen gas can be calculated more accurately from the equation (10). As a result, even if there is a pressure fluctuation as described above, the detection accuracy of the hydrogen gas concentration can be further improved.

In carrying out the present invention, the following various modifications are possible without being limited to the above embodiments.
(1) As a material for forming the heating resistor 330 and the wiring film 340, it is desirable that the chemical durability is high at a high temperature and the temperature resistance coefficient is large.
(2) The present invention may be applied not only to hydrogen gas but also to concentration detection of combustible gas such as city gas and leakage detection of the gas.
(3) Relative humidity may be used instead of the volume humidity HUM.
(4) The resistance temperature detector 390 is not limited to a thin film resistor, and may be various resistors such as a thermistor capable of detecting temperature.
(5) Instead of the resistance temperature detector 390, a temperature resistance resistor or other temperature sensor separate from the detection element 300 may be employed. In this case, it is desirable that the temperature sensor is disposed in the measurement space in which the detection element 300 is disposed.
(6) Unlike the above-described embodiments, the heating resistors 211 and 221 change the resistance value so as to decrease (or increase) in accordance with an increase (or decrease) in the temperature of the heating resistor. It may be. In this case, the voltage ratio RV described in each of the above embodiments is calculated based on the larger one of the resistance values of the two heating resistors 211 and 221.
(7) The predetermined waiting time that is the determination criterion in step 410 of FIG. 7 is, for example, 0.5 (seconds), but is not limited to this, and may be changed as appropriate. 221 may be a time that can be maintained at the corresponding constant temperature by the constant temperature control.
(8) The temperature resistance coefficients of the two heating resistors 211 and 221 do not necessarily have to be the same as the temperature resistance coefficient of the resistance temperature detector 390.

It is sectional drawing of the apparatus unit in 1st Embodiment of the combustible gas detection apparatus which concerns on this invention. It is a block diagram which shows the control circuit in the said 1st Embodiment. It is sectional drawing which shows the assembly | attachment structure of the detection element with respect to the detection structure of FIG. FIG. 6 is a cross-sectional view of the detection element taken along line 4-4 in FIG. It is a top view of the detection element of FIG. It is a graph showing the relationship between a temperature voltage and environmental temperature. It is a front | former part of the flowchart which shows the effect | action of the microcomputer of FIG. FIG. 3 is a latter part of a flowchart showing the operation of the microcomputer of FIG. 2. It is a graph which shows the relationship between 1st differential amplification electric potential difference VH0 and the temperature voltage in the said 1st Embodiment. It is a graph which shows the relationship between volume humidity and a voltage ratio difference. It is a graph which shows the relationship between 2nd differential amplification potential difference VH1 and volume humidity. It is a graph which shows the relationship between the gas sensitivity and temperature voltage in the said 1st Embodiment. It is a graph which shows the relationship between an output density | concentration and the density | concentration of hydrogen gas.

Explanation of symbols

211, 221, 330 ... heating resistor, 230, 240 ... constant temperature control circuit,
250, 260 ... operational amplification circuit, 270 ... microcomputer,
280 ... DC power supply, 300 ... detection element, 310 ... semiconductor substrate, 311 ... concave,
320 ... insulating layer, 350 ... inner protective layer, 360 ... outer protective layer,
390 ... Resistance temperature detector, D ... Hydrogen gas concentration, ΔRV ... Voltage ratio difference,
HUM ... Volume humidity, RV ... Voltage ratio, RV0 ... Voltage ratio initial value, T ... Environment temperature,
VH: high temperature side differential amplification potential difference, VH0: first differential amplification potential difference,
VH1 ... second differential amplification potential difference, VL ... low temperature side differential amplification potential difference, VT ... temperature voltage.

Claims (13)

In the combustible gas detection device comprising a plurality of heating resistors exposed to the atmosphere to be detected,
Constant temperature control means for controlling the two heat generating resistors by energization so as to maintain the resistance values of at least two heat generating resistors among the plurality of heat generating resistors at values corresponding to different constant temperatures. ,
Temperature detecting means for detecting an environmental temperature in the detected atmosphere;
Voltage ratio determining means for determining, as a voltage ratio, a ratio of terminal voltages of the two heating resistors generated in the control state by the constant temperature control means;
Humidity determination means for determining the humidity based on the voltage ratio and the environmental temperature from a humidity-voltage ratio-environment temperature characteristic representing a relationship between the humidity in the detected atmosphere, the voltage ratio, and the environmental temperature;
Concentration-terminal voltage-humidity-environment temperature representing the relationship between the concentration of combustible gas in the detected atmosphere, the terminal voltage of the high-temperature side heating resistor of the two heating resistors, the humidity, and the environmental temperature A concentration calculating means for calculating the concentration of the combustible gas based on the terminal voltage of the high temperature side heating resistor from the characteristics, the humidity and the environmental temperature,
The combustible gas detection apparatus, wherein the combustible gas is detected based on the calculated concentration of the concentration calculation means. A semiconductor substrate formed with a plurality of recesses from the back side at intervals, an insulating layer formed on the surface of the semiconductor substrate, and a plurality of recesses formed on the surface of the insulating layer corresponding to the recesses In the flammable gas detection device comprising a heating element and a detection layer disposed in the atmosphere to be detected, having a protective layer formed on the surface of the insulating layer so as to cover these heating resistors,
Constant temperature control means for controlling the two heat generating resistors by energization so as to maintain the resistance values of at least two heat generating resistors among the plurality of heat generating resistors at values corresponding to different constant temperatures. ,
Temperature detecting means for detecting an environmental temperature in the detected atmosphere;
Voltage ratio determining means for determining, as a voltage ratio, a ratio of terminal voltages of the two heating resistors generated in the control state by the constant temperature control means;
Humidity determination means for determining the humidity based on the voltage ratio and the environmental temperature from a humidity-voltage ratio-environment temperature characteristic representing a relationship between the humidity in the detected atmosphere, the voltage ratio, and the environmental temperature;
Concentration-terminal voltage-humidity-environment temperature representing the relationship between the concentration of combustible gas in the detected atmosphere, the terminal voltage of the high-temperature side heating resistor of the two heating resistors, the humidity, and the environmental temperature A concentration calculating means for calculating the concentration of the combustible gas based on the terminal voltage of the high temperature side heating resistor from the characteristics, the humidity and the environmental temperature,
The combustible gas detection apparatus, wherein the combustible gas is detected based on the calculated concentration of the concentration calculation means. A first functional characteristic having a voltage ratio initial value which is a ratio of terminal voltages of the two heating resistors when the concentration and humidity of the combustible gas are both zero as a dependent variable and the environmental temperature as an independent variable. When,
Storage means for storing, as the humidity-voltage ratio-environment temperature characteristic, a second function characteristic having the humidity as a dependent variable and a voltage ratio difference representing a difference between the voltage ratio and the voltage ratio initial value as an independent variable. With
The humidity determining means includes
Voltage ratio initial value determining means for determining the voltage ratio initial value based on the environmental temperature from the first function characteristic;
Voltage ratio difference calculating means for calculating the voltage ratio difference based on the voltage ratio and the voltage ratio initial value;
Humidity calculating means for calculating the humidity based on the voltage ratio difference from the second function characteristic,
The combustible gas detection device according to claim 1 or 2, wherein the humidity calculated by the humidity calculating means is the humidity determined by the humidity determining means. The storage means further includes
A third function characteristic in which the environmental temperature is an independent variable, and a first terminal voltage value which is a terminal voltage of the high-temperature side heating resistor when the concentration and humidity of the combustible gas are both zero is a dependent variable; ,
The humidity is an independent variable, the first terminal voltage value is an intercept, and the second terminal voltage value, which is the terminal voltage of the high-temperature heating resistor when the humidity in the detected atmosphere is zero, is a dependent variable. And a fourth function characteristic
Storing the fifth function characteristic having the ambient temperature as an independent variable and the gas sensitivity to the combustible gas as a dependent variable as the concentration-terminal voltage-humidity-environment temperature characteristic;
The concentration calculating means includes
First terminal voltage value determining means for determining the first terminal voltage value based on the environmental temperature from the third function characteristic;
Second terminal voltage value determining means for determining the second terminal voltage value based on the humidity and the first terminal voltage value from the fourth function characteristic;
Gas sensitivity determining means for determining the gas sensitivity based on the environmental temperature from the fifth function characteristic;
Dividing means for dividing the difference between the terminal voltage of the high temperature side heating resistor and the second terminal voltage value by the gas sensitivity;
4. The combustible gas detection device according to claim 3, wherein the result of division by the dividing means is set to the concentration of the combustible gas. Saturated water vapor concentration determining means for determining the saturated water vapor concentration based on the environmental temperature from the characteristic representing the relationship between the saturated water vapor concentration in the detected atmosphere and the environmental temperature;
When the humidity determined by the humidity determining means is equal to or higher than the saturated water vapor concentration, the determined humidity is corrected to the saturated water vapor concentration, and when the humidity determined by the humidity determining means is equal to or lower than zero, the determined humidity is corrected to zero. The combustible gas detection apparatus according to claim 1, further comprising a humidity correction unit that performs the correction.   When the environmental temperature is equal to or lower than a predetermined temperature, the humidity determined by the humidity determining unit is corrected to a predetermined value selected in advance so as to suppress deterioration in the detection accuracy of the combustible gas concentration. The combustible gas detection apparatus according to claim 1, further comprising a humidity correction unit.   The combustible gas detection device according to any one of claims 1 to 6, wherein a difference in control temperature between the two heating resistors is 50 (° C) or more.   The combustible gas detection device according to claim 7, wherein a control temperature of the two heating resistors is 150 (° C) or more and 500 (° C) or less. The two heating resistors are controlled by energization so as to maintain the resistance values of at least two of the heating resistors exposed to the detected atmosphere at respective values corresponding to different constant temperatures. And
A ratio of terminal voltages of the two heating resistors generated in the control state in the detected atmosphere is determined as a voltage ratio;
Determining the humidity based on the voltage ratio and the environmental temperature from the humidity-voltage ratio-environment temperature characteristic representing the relationship between the humidity in the detected atmosphere, the voltage ratio and the environmental temperature in the detected atmosphere,
Concentration-terminal voltage-humidity-environment temperature representing the relationship between the concentration of combustible gas in the detected atmosphere, the terminal voltage of the high-temperature side heating resistor of the two heating resistors, the humidity, and the environmental temperature A combustible gas detection method for detecting the combustible gas by calculating the concentration of the combustible gas based on the terminal voltage, the humidity, and the environmental temperature of the high-temperature side heating resistor from characteristics. A first functional characteristic having a voltage ratio initial value which is a ratio of terminal voltages of the two heating resistors when the concentration and humidity of the combustible gas are both zero as a dependent variable and the environmental temperature as an independent variable. When,
A second function characteristic having the humidity as a dependent variable and a voltage ratio difference representing the difference between the voltage ratio and the voltage ratio initial value as an independent variable is set as the humidity-voltage ratio-environment temperature characteristic,
And a third function in which the environmental temperature is an independent variable, and the first terminal voltage value, which is the terminal voltage of the high-temperature heating resistor when the concentration and humidity of the combustible gas are both zero, is a dependent variable. Characteristics,
The humidity is an independent variable, the first terminal voltage value is an intercept, and the second terminal voltage value, which is the terminal voltage of the high-temperature heating resistor when the humidity in the detected atmosphere is zero, is a dependent variable. And a fourth function characteristic
A fifth function characteristic having the ambient temperature as an independent variable and a gas sensitivity to the combustible gas as a dependent variable is set as the concentration-terminal voltage-humidity-environment temperature characteristic,
The method for detecting a combustible gas according to claim 9, wherein the concentration of the combustible gas is determined based on the first to fifth function characteristics.   Humidity determined based on the humidity-voltage ratio-environment temperature characteristic, determining the saturated water vapor concentration based on the environmental temperature from the characteristic representing the relationship between the saturated water vapor concentration in the detected atmosphere and the environmental temperature. When the humidity determined based on the humidity-voltage ratio-environment temperature characteristic is zero or less, the determined humidity is corrected to zero. The method for detecting a combustible gas according to claim 8 or 9, wherein the combustible gas is detected.   When the environmental temperature is equal to or lower than a predetermined temperature, the humidity determined based on the humidity-voltage ratio-environment temperature characteristic is selected in advance so as to suppress deterioration in detection accuracy of the combustible gas concentration. The combustible gas detection method according to any one of claims 9 to 11, wherein the value is set to a value of. Detecting the pressure in the detected atmosphere;
Based on the pressure, the function characteristics are determined based on the pressure from the characteristics representing the relationship between the pressure and the coefficients of the first to fifth function characteristics determined so as not to be influenced by the pressure fluctuation. Correct,
Determining the humidity based on the corrected first and second functional characteristics;
The combustible gas according to any one of claims 10 to 12, wherein the concentration of the combustible gas is determined based on the determined humidity and the third to fifth functional characteristics after the correction. Sex gas detection method.

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