JP2010266265A - Combustible gas detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustible gas detector which has a high accuracy of combustible gas detection by correcting the effect of the absolute humidity of an atmosphere to be detected and which is designed to lower the cost and to improve the productivity by reducing the number of components. <P>SOLUTION: The combustible gas detector 1 includes: a heating resistor exposed to the atmosphere to be detected, the temperature of the heating resistor changing depending on the concentration of the combustible gas in the atmosphere to be detected; a gas detection unit 100 for controlling the current in the heating resistor so that the heating resistor is kept at a predetermined temperature and for detecting a voltage between terminals of the heating resistor; a concentration calculation means 3a for calculating the combustible gas concentration in the atmosphere to be detected as a calculated gas concentration value from the voltage between the terminals based on a first relation between the combustible gas concentration and the voltage between the terminals; a main temperature detection means 3a, 50 for detecting the temperature of the atmosphere to be detected, and a correction means 3a for correcting the calculated gas concentration value or the voltage between the terminals from the temperature detected by the main temperature detection means based on a second relation between the calculated gas concentration value or the voltage between the terminals and the temperature of the atmosphere to be detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a combustible gas detection device used for measuring the concentration of combustible gas, detecting leakage, and the like.

  In recent years, research on fuel cells has been actively conducted as a highly efficient and clean energy source in response to social demands such as environmental protection and nature protection. In particular, polymer electrolyte fuel cells (PEFC) and hydrogen internal combustion engines that operate at a low temperature and have a high output and a high density are expected for home use and in-vehicle use. However, since these energy sources use hydrogen as a fuel, it is necessary to detect the presence or absence of hydrogen leakage.

Conventionally, as a device for detecting the concentration of combustible gas contained in the atmosphere to be detected, utilizing the fact that the thermal conductivity of the atmosphere to be detected changes according to the concentration of the combustible gas, a heating resistor placed in the atmosphere to be detected is used. One that measures the voltage between terminals is known. However, even if the concentration of the combustible gas is the same, if the relative humidity of the atmosphere to be detected changes, the thermal conductivity also changes, which affects the detection accuracy of the combustible gas.
Therefore, the resistance values of the two heating resistors are controlled so as to correspond to different constant temperatures, the voltage ratio of the terminal voltage of each heating resistor is obtained, and the relative humidity of the detected atmosphere is set to this voltage ratio. A technique for determining from the relationship between temperature has been developed (see Patent Document 1). According to this technique, it is possible to increase the detection accuracy of the combustible gas in consideration of the variation in the thermal conductivity of the detected atmosphere due to the relative humidity of the detected atmosphere.

JP 2006-10670 A

However, even in an environment where the relative humidity of the atmosphere to be detected is stable, such as a fuel cell with water generation, the detection accuracy may decrease due to the influence of absolute humidity. In the case of the technique described in Patent Document 1, since it is necessary to provide two heating resistors in the gas detection device, the number of parts increases, and there is room for improvement in terms of cost reduction and productivity.
Accordingly, the present invention corrects the influence of the absolute humidity of the atmosphere to be detected to increase the detection accuracy of the combustible gas and reduce the number of parts to reduce the cost and improve the productivity. The purpose is to provide.

In order to solve the above problems, the combustible gas detection device of the present invention is exposed to a detected atmosphere in a stable relative humidity environment, and the temperature changes according to the concentration of the combustible gas in the detected atmosphere. One heating resistor, a gas detection unit for controlling energization of the heating resistor so that the heating resistor is maintained at a predetermined temperature, and detecting a voltage between terminals of the heating resistor at this time, and the combustibility A concentration calculating means for calculating a concentration of the combustible gas in the detected atmosphere as a gas concentration calculated value from the voltage between the terminals based on a first relationship between a gas concentration and the terminal voltage; Detected by the main temperature detection means based on the second relationship between the main temperature detection means for detecting the temperature of the detection atmosphere, the gas concentration calculated value or the voltage between the terminals, and the temperature of the detection atmosphere. The gas concentration from the temperature And a, and correcting means for correcting the calculated value or the inter-terminal voltage.
Here, if the relative humidity is stable, there is a certain relationship between the absolute humidity and the temperature, so that the influence of the absolute humidity can be corrected using the temperature of the detected atmosphere. Therefore, the temperature of the detection atmosphere is measured under a stable relative humidity environment, and the output of the combustible gas detection device is calculated based on the second relationship between the temperature of the detection atmosphere and the calculated gas concentration or the voltage between the terminals. The gas detection accuracy can be improved by performing the correction.
Furthermore, since only one heat generating resistor of the gas detection element is required, the number of parts can be reduced to reduce costs and improve productivity. The stable relative humidity environment can be exemplified by an environment where the relative humidity fluctuation is ± 5% or less.

You may further provide the dew condensation prevention heater which prevents dew condensation of the said heating resistor.
With such a configuration, for example, when detecting a hydrogen leak in a fuel cell, when the atmosphere to be detected is at or near the saturated state of water vapor, detection by condensation of the heating resistor exposed to the atmosphere to be detected A reduction in accuracy can be prevented.

The heating resistor is installed in a measurement chamber formed in the combustible gas detection device and communicated with the detected atmosphere, and the main temperature detection means is arranged outside the measurement chamber, And a second temperature detecting means for detecting the temperature in the measurement chamber, wherein the concentration calculating means may change the first relationship based on the temperature detected by the second temperature detecting means. Good.
With such a configuration, when a dew condensation prevention heater is provided in the vicinity of the heating resistor, the temperature in the measurement chamber reflecting the temperature in the vicinity of the heating resistor is measured by the second temperature detecting means, and the temperature is Since the first relationship is changed, the gas concentration calculation value can be accurately calculated from the inter-terminal voltage.
Moreover, since the correction by the second relationship is based on the temperature of the main temperature detection means outside the measurement chamber reflecting the temperature of the atmosphere to be detected, the correction accuracy is also improved.

You may further provide the casing member which forms the said measurement chamber and forms the main temperature detection means attachment part for attaching the said main temperature detection means on the outer side of the said measurement chamber integrally.
With such a configuration, the measurement chamber and the main temperature detecting means can be easily arranged on the casing member, and productivity is improved.

  According to this invention, the influence of the absolute humidity of the atmosphere to be detected is corrected to improve the detection accuracy of the combustible gas, and the number of parts can be reduced to reduce costs and improve productivity. Can be obtained.

It is sectional drawing of the combustible gas detection apparatus which concerns on embodiment of this invention. It is a top view of a gas detection element. It is sectional drawing which follows the III-III line of FIG. It is a figure which shows the structure of a control part. It is a figure which shows the relationship between the temperature of to-be-detected atmosphere, and humidity. It is a figure which shows the relationship between the output (hydrogen gas concentration) of a combustible gas detection apparatus, and the amount of water vapor | steam (humidity). It is a figure which shows the relationship between the output of a combustible gas detection apparatus, and temperature. It is a figure which shows the relationship between the voltage between terminals of a heating resistor, and the hydrogen concentration in to-be-detected atmosphere. It is a figure which shows the flow of calculation and correction | amendment processing of the hydrogen gas concentration in to-be-detected atmosphere by a microcomputer. It is a figure which shows the relationship between the output of a combustible gas detection apparatus when not performing correction | amendment processing, and the hydrogen concentration in model gas. It is a figure which shows the relationship between the output of a combustible gas detection apparatus when a correction | amendment process is performed, and the hydrogen concentration in model gas.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 shows a cross-sectional view of a combustible gas detection device 1 according to an embodiment of the present invention. The combustible gas detection device 1 houses a circuit board 2 on which a gas detection element 100 described later is mounted. FIG. 1 is a cross-sectional view taken along a direction perpendicular to the surface of the circuit board 2.
In addition, the combustible gas detection apparatus 1 measures the hydrogen concentration in the atmosphere to be detected. Further, a connector (not shown) for inputting / outputting signals to / from the outside is provided on the side surface of the combustible gas detection device 1.

  The combustible gas detection device 1 includes a casing 10 including a substantially rectangular box-shaped casing member 11 integrally formed of plastic or the like, and a back plate 12 that closes the back surface of the casing member 11. A step portion 11 f that extends outward is formed on the upper portion of the side wall of the casing member 11, and the circuit board 2 is attached to the casing member 11 while the edge of the circuit board 2 is locked to the step portion 11 f. A control unit 3 (including a microcomputer) for controlling the combustible gas detection device 1 is mounted at the center of the lower surface of the circuit board 2 (the surface opposite to the back plate 12 on the front side of the casing member 11). The control unit 3 will be described later.

A substantially cylindrical element fixing wall 11a rises on the inner surface on the right side of the casing member 11, and a gas inlet 11b is formed at the center of the element fixing wall 11a in the axial direction. Further, a concave portion 11c that is recessed inward is formed on the left side of the casing member 11, and a main temperature sensor mounting portion (main temperature detecting means mounting portion) 11d protrudes from the bottom surface of the concave portion 11c toward the outside of the casing member 11. ing.
The main temperature sensor mounting portion 11d has a cylindrical shape whose tip is closed in a hemispherical shape, and a main temperature sensor 50 made of a thin film resistor is disposed in the cylinder. The front end of the main temperature sensor mounting portion 11 d is substantially flush with the surface of the casing member 11. Then, two pin-like terminals 51 and 52 project from the main temperature sensor 50 toward the circuit board 2 side, and the terminals 51 and 52 are inserted into the through-holes of the circuit board 2 and soldered. A temperature sensor 50 is mounted on the circuit board 2.
By attaching an element holder 21 (described later) to the element fixing portion 11a, the internal space of the element holder 21 forms the measurement chamber 21s, and the main temperature sensor 50 is located outside the measurement chamber 21s. That is, in this embodiment, the casing member 11 itself does not form a measurement chamber, and the element holder 21 forms a measurement chamber. However, in the present invention, the measurement chamber is directly attached to the casing member. Or it shall be formed via other members (for example, element holder 21).

The element holder 21 has a substantially cylindrical shape and is fitted coaxially to the inner surface of the element fixing wall 11a. Further, a stepped portion 21f extending outward is formed on the upper portion of the side wall of the element holder 21, and the edge of the disk-shaped terminal plate 40 is locked to the stepped portion 21f. The gas detection element 100 is fixed at the center of the lower surface of the terminal plate 40, and three pin-shaped terminals 41 to 43 electrically connected to electrode pads (described later) of the gas detection element 100 project. Each terminal 41 to 43 is inserted through the terminal board 40 in a state where it is electrically insulated from the terminal board 40. And the gas detection element 100 is mounted in the circuit board 2 by inserting each terminal 41-43 in the through hole of the circuit board 2, and soldering.
As will be described in detail later, the gas detection element 100 includes a heating resistor 110 and a second temperature sensor (second temperature detecting means) 130, and terminals 41 and 42 are connected to the heating resistor 110 and the second temperature, respectively. This is a positive electrode side terminal of the sensor 130. The terminal 43 serves as a common ground for the heating resistor 110 and the second temperature sensor 130.

  And the disk-shaped element holder back plate 22 which has the insertion hole of the terminals 41-43 is covered on the back surface of the terminal plate 40, and the element holder back plate 22 is put together with the terminal plate 40 through an unillustrated packing or the like. The terminal plate 40 and the gas detection element 100 are mounted in the element holder 21 by fitting in an airtight manner to the upper end of the holder 21.

On the other hand, the lower surface of the element holder 21 has an annular shape having a central opening communicating with the gas introduction port 11b, and a disk-shaped water-repellent filter 31 and a metal mesh 32 are laminated and press-fitted inside the lower surface of the element holder 21. The water repellent filter 31 is located outside. An internal space surrounded by the side wall of the element holder 21, the wire mesh 32, and the lower surface of the terminal plate 40 forms a measurement chamber 21s, and the gas detection element 100 faces the measurement chamber 21s.
The water repellent filter 31 prevents intrusion of water droplets or dust from the gas inlet 11c into the measurement chamber 21s. The metal mesh 32 is used when the temperature of the heating resistor 110 exceeds the lower limit explosion temperature of the hydrogen gas and the hydrogen gas is ignited in the measurement chamber 21s when the heating resistor 110 (described later) of the gas detection element 100 is energized. It prevents the ignition from the measurement chamber 21s to the outside of the combustible gas detection device 1, and has an explosion-proof function.

Furthermore, in this embodiment, a dew condensation prevention heater 60 made of a heating resistor is placed on the upper surface of the element holder back plate 22 (the surface facing the circuit board 2), and the dew condensation prevention heater 60 faces the circuit board 2 side. Two pin-like terminals 61 and 62 protrude. The dew condensation prevention heater 60 is mounted on the circuit board 2 by inserting the terminals 61 and 62 into the through holes of the circuit board 2 and soldering them.
The dew condensation prevention heater 60 heats the vicinity of the heating resistor 110 (in this example, in the measurement chamber 21 s) to prevent condensation of the heating resistor 110. In particular, when detecting a hydrogen leak in a fuel cell, the atmosphere to be detected is saturated or close to water vapor, and the heating resistor 110 exposed to the atmosphere to be detected is likely to condense, resulting in a decrease in detection accuracy. Therefore, the dew condensation prevention heater 60 is effective.

Next, the configuration of the gas detection element 100 will be described with reference to FIGS. 2 and 3.
FIG. 2 shows a plan view of the gas detection element 100. The gas detection element 100 has a rectangular shape in plan view, and includes a base 101 made of a silicon substrate. A spiral heating resistor 110 is disposed at the center of the surface of the substrate 101, and two leads 110 a and 110 b extend from the heating resistor 110. Rectangular electrode pads 112 and 114 are exposed at both corners on the lower side of the base 101, the lead 110 a is connected to the electrode pad 112, and the lead 110 b is connected to the electrode pad 114.
On the other hand, on the surface of the base 101 above the heating resistor 110, a second temperature sensor (second temperature detecting means) 130 made of a thin film resistor and having an elongated rectangular shape along the upper side of the base 101 is disposed. Two leads (not shown) extend from the second temperature sensor 130. Rectangular electrode pads 132 and 134 are exposed at both corners on the upper side of the substrate 101, and the leads of the second temperature sensor 130 are connected to the electrode pads 132 and 134, respectively.
The electrode pads 112 and 132 are electrically connected to the terminals 41 and 42, for example, by wire bonding. The electrode pads 114 and 134 are electrically connected to the common terminal 43 by wire bonding, for example.
The heating resistor 110 and the second temperature sensor 130 are embedded in an inner protective layer 107 (not shown) formed on the surface of the base 101.

3 is a cross-sectional view taken along line III-III in FIG. An upper insulating layer 105 and a lower insulating layer 103 are formed on the upper and lower surfaces of the substrate 101, respectively. The upper insulating layer 105 includes a silicon oxide film 105a formed on the upper surface of the base 101 and a silicon nitride film 105b stacked on the upper surface of the silicon oxide film 105a. Similarly, the lower insulating layer 103 includes a silicon oxide film 103a formed on the lower surface of the base 101 and a silicon nitride film 103b stacked on the lower surface of the silicon oxide film 103a.
On the other hand, the central portion of the lower surface of the substrate 101 is removed in a trapezoidal shape when viewed in a cross section along the thickness direction to form an opening 101a, and the upper insulating layer 105 is exposed from the opening 101a. That is, the base 101 forms a diaphragm structure by the opening 101 a and the upper insulating layer 105. By disposing the heating resistor 110 on the upper surface of the upper insulating layer 105 located on the opening 101a, the heating resistor 110 is thermally isolated from the surroundings, and the heating resistor 110 is heated and lowered. This can be done in a short time, and the power consumption of the heating resistor 110 can be reduced.

An insulating inner protective layer 107 is formed on the upper surface of the upper insulating layer 105. Inside the inner protective layer 107, a heating resistor 110, lead parts 110a and 110b (not shown), and lead parts 110a are provided. , 110b, contact portions 112a, 114a connected to the tips of the electrodes 110b are embedded. After these constituent parts are formed on the inner protective layer 107, the constituent parts of the inner protective layer 107 are further deposited to embed each constituent part in the inner protective layer 107. Further, an outer protective layer 109 is laminated on the surface of the inner protective layer 107.
Of the inner protective layer 107 and the outer protective layer 109, the upper portions of the contact portions 112a and 114a are removed by etching or the like, and electrode pads 112 and 114 are deposited on the removed portions, respectively. Thereby, the contact portions 112a and 114a and the electrode pads 112 and 114 are electrically connected to each other, and the heating resistor 110 can be energized through the electrode pads 112 and 114.

The heating resistor 110, the second temperature sensor 130, the main temperature sensor 50, the lead portions thereof, and the electrode pads 112, 114, 132, and 134 can be formed of a conductive material such as platinum (Pt) or a Pt alloy. .
The base 101 is not limited to a silicon substrate, and may be made of alumina (Al ₂ O ₃ ) or a semiconductor material.
The inner protective layer 107 and the outer protective layer 109 can be formed from silicon oxide, silicon nitride, or the like.

Next, the configuration of the control unit 3 will be described with reference to FIG. The control unit 3 includes a gas detection element circuit (corresponding to a “gas detection unit” in the claims) 310, a second temperature measurement circuit 320, a main temperature measurement circuit 330, and a microcomputer to which signals from these circuits are input. 3a. The microcomputer 3a includes a known CPU (central processing unit) and a memory (ROM, RAM), and a program stored in advance in the ROM or the like is executed by the CPU and output to the outside as a gas concentration signal. The microcomputer 3a (CPU) corresponds to “concentration calculation means”, “main temperature detection means”, and “correction means” in the claims.
The control unit 3 is connected to the heating resistor 110, the second temperature sensor 130, and the main temperature sensor 50 through the terminals 41 to 43, 51, 52, 61, and 62 described above.

The gas detection element circuit 310 includes a Wheatstone bridge circuit 311 including a heating resistor 110 and fixed resistors a1 to a3, an operational amplifier 312 that amplifies a potential difference obtained from the Wheatstone bridge circuit 311, and a transistor. And a constant temperature control circuit 314. In the Wheatstone bridge circuit 311, one end of the fixed resistor a2 and one end of the fixed resistor a3 are connected, and one end of the fixed resistor a1 and one end of the heating resistor 110 are connected. The other end of the fixed resistor a3 and the other end of the heating resistor 110 are connected to the ground, and the other end of the fixed resistor a2 and the other end of the fixed resistor a1 are connected to the collector of the constant temperature control circuit 314 (transistor). Has been.
The potential between the fixed resistor a2 and the fixed resistor a3 is input to the inverting input terminal (−) of the operational amplifier 312 via a predetermined resistor. The potential between the heating resistor 110 and the fixed resistor a1 is input to the non-inverting input terminal (+) of the operational amplifier 312 via a predetermined resistor and input to the microcomputer 3a via an A / D converter (not shown). Is done. The output of the operational amplifier 312 is negatively fed back and input to the base of the constant temperature control circuit 314. A constant voltage Vcc is applied to the emitter of the constant temperature control circuit 314.
As described above, the constant temperature control circuit 314 controls the voltage so that the heating resistor 110 is maintained at a constant temperature according to the output of the operational amplifier 312. Further, the control voltage at this time is output to the microcomputer 3a, and the voltage across the terminals of the heating resistor 110 (corresponding to the hydrogen concentration in the atmosphere to be detected) is detected. In this embodiment, the gas detection element circuit 310 is set so that the heating resistor 110 is maintained at 200 ° C.

The second temperature measurement circuit 320 includes a Wheatstone bridge circuit 321 composed of a second temperature sensor 130 made of resistors and fixed resistors b1 to b3, and an operational amplifier that amplifies the potential difference obtained from the Wheatstone bridge circuit 321. 322. In the Wheatstone bridge circuit 321, one end of the second temperature sensor 130 and one end of the fixed resistor b3 are connected, and one end of the fixed resistor b1 and one end of the fixed resistor b2 are connected. The other end of the second temperature sensor 130 and the other end of the fixed resistor b2 are connected to the ground, and a constant voltage Vcc is applied to the other end of the fixed resistor b3 and the other end of the fixed resistor b1.
The potential between the second temperature sensor 130 and the fixed resistor b3 is input to the inverting input terminal (−) of the operational amplifier 322 via a predetermined resistor. The potential between the fixed resistor b1 and the fixed resistor b2 is input to the non-inverting input terminal (+) of the operational amplifier 322 via a predetermined resistor. The output of the operational amplifier 322 is negatively fed back and input to the microcomputer 3a via an A / D converter (not shown).
In this way, a voltage change due to the temperature change of the second temperature sensor 130 is output from the operational amplifier 322, and the temperature around the second temperature sensor 130 (the temperature in the measurement chamber 21s) is measured.

The main temperature measurement circuit 330 includes a Wheatstone bridge circuit 331 including a main temperature sensor 50 made of resistors and fixed resistors c1 to c3, and an operational amplifier 332 that amplifies a potential difference obtained from the Wheatstone bridge circuit 331. Is provided. In the Wheatstone bridge circuit 331, one end of the main temperature sensor 50 and one end of the fixed resistor c3 are connected, and one end of the fixed resistor c1 and one end of the fixed resistor c2 are connected. The other end of the main temperature sensor 50 and the other end of the fixed resistor c2 are connected to the ground, and a constant voltage Vcc is applied to the other end of the fixed resistor c3 and the other end of the fixed resistor c1.
The potential between the main temperature sensor 50 and the fixed resistor c3 is input to the inverting input terminal (−) of the operational amplifier 332 via a predetermined resistor. The potential between the fixed resistor c1 and the fixed resistor c2 is input to the non-inverting input terminal (+) of the operational amplifier 332 via a predetermined resistor. The output of the operational amplifier 332 is negatively fed back and input to the microcomputer 3a via an A / D converter (not shown).
In this manner, a voltage change due to the temperature change of the main temperature sensor 50 is output from the operational amplifier 332, and the temperature around the main temperature sensor 50 (the temperature of the detected atmosphere, that is, the temperature around the casing member 11) is measured.

Next, the influence of the absolute humidity of the atmosphere to be detected on the output of the combustible gas detection device 1 will be described with reference to FIGS. In addition, since absolute humidity can be taken as synonymous with the amount of water vapor (vol.%), The description of the amount of water vapor is also used below.
FIG. 5 shows the relationship between the temperature of the atmosphere to be detected and the amount of water vapor at 90% RH. In this embodiment, since it is assumed that the combustible gas detection device 1 is applied to a fuel cell with generation of water, the amount of water vapor at 90% RH is used as a state where the relative humidity is high. Yes.
FIG. 6 shows the relationship between the influence on the output of the combustible gas detector 1 (specifically, the hydrogen gas concentration calculated from the voltage across the terminals of the heating resistor 110) and the amount of water vapor. This relationship is created by measuring the error of the output of the combustible gas detection device 1 with respect to the ideal output when the amount of water vapor is changed. Here, the error with respect to the ideal output is, for example, when measurement is performed in an environment where the hydrogen concentration is 0%, while the ideal output is the hydrogen concentration 0%, whereas the actual output of the combustible gas detection device 1 is hydrogen. If the density is 1%, the error with respect to the ideal output (that is, the influence on the output) is a value that is defined as 1%.
It can be seen from FIG. 6 that the error in the output of the combustible gas detection device 1 varies when the amount of water vapor varies.

FIG. 7 shows a graph in which the relationship between the influence on the output of the combustible gas detection device 1 and the temperature is obtained from the relationship of FIG. 5 (temperature and water vapor amount) and the relationship of FIG. 6 (output and water vapor amount). . From FIG. 7, by measuring the temperature of the atmosphere to be detected by the main temperature sensor 50, it is possible to estimate the output fluctuation of the combustible gas detection device 1 due to the amount of water vapor.
Here, the relationship between the temperature of the atmosphere to be detected and the output fluctuation of the combustible gas detection device 1 (more precisely, the amount of water vapor (absolute humidity) in the atmosphere to be detected and the output fluctuation of the combustible gas detection device 1). The relationship expressed by temperature) corresponds to the “second relationship” in the claims.
And, when measuring the hydrogen gas (combustible gas) concentration in the actual detected atmosphere from the relationship of FIG. 7, that is, the relationship between the temperature of the detected atmosphere and the output fluctuation of the combustible gas detection device 1, The influence on the output due to the temperature (absolute humidity) of the atmosphere to be detected can be corrected. In this embodiment, the relationship between the temperature of the atmosphere to be detected and the amount of water vapor at 90% RH and the output of the combustible gas detector 1 (specifically, the hydrogen calculated from the voltage across the terminals of the heating resistor 110). Based on the relationship between the gas concentration and the amount of water vapor, the second relationship that is the relationship between the temperature of the detected atmosphere and the output fluctuation of the combustible gas detection device 1 was obtained. It is good also considering what calculated | required the relationship with the output fluctuation | variation of the gas detection apparatus 1 directly as a 2nd relationship.

FIG. 8 shows the relationship between the voltage between the terminals of the heating resistor 110 and the hydrogen concentration in the atmosphere to be detected (corresponding to the “first relationship” in the claims). The first relationship is, for example, a calibration curve obtained using a model gas with a known hydrogen concentration in advance as the detected atmosphere.
Here, the first relationship changes depending on the ambient temperature of the heating resistor 110 (specifically, the temperature in the measurement chamber 21s measured by the second temperature sensor 130), and the higher the temperature in the measurement chamber 21s, the higher the temperature in the measurement chamber 21s. Since the voltage for keeping the temperature of the heating resistor 110 constant is small, the first relationship also changes.
In this way, by changing the first relationship based on the temperature of the second temperature sensor 130 close to the heating resistor 110, an appropriate first relationship according to the ambient temperature of the heating resistor 110 can be used. And detection accuracy of hydrogen (combustible gas) is improved.
In particular, when heating the vicinity of the heating resistor 110 (in this example, in the measurement chamber 21 s) using the dew condensation prevention heater 60, the temperature near the heating resistor 110 is different from the temperature of the main temperature sensor 50. For this reason, it is effective to change the first relationship based on the temperature of the second temperature sensor 130 reflecting the temperature in the measurement chamber 21s.

  On the other hand, in this case, the temperature near the heating resistor 110 (in the measurement chamber 21s) does not necessarily reflect the temperature of the atmosphere to be detected. Therefore, when performing output correction according to the second relationship, it is preferable to be based on the temperature of the main temperature sensor 50 that is disposed outside the measurement chamber 21s and reflects the temperature of the detected atmosphere.

FIG. 9 shows a flow of a process for calculating and correcting the hydrogen gas (combustible gas) concentration in the atmosphere to be detected by the microcomputer (CPU; hereinafter referred to simply as “CPU”) 3a.
The CPU acquires the temperature in the measurement chamber 21s from the second temperature sensor 130 (step S2), and further acquires the voltage between the terminals of the heating resistor 110 (step 4). Next, the CPU refers to the first relationship according to the temperature in the measurement chamber 21 s from the first relationship table 3 a stored in the ROM (hereinafter simply referred to as “ROM”) of the microcomputer 3 a, and the terminal A hydrogen gas concentration is calculated based on the inter-voltage (step S6). Based on the first relationship table 3a, the hydrogen gas concentration calculated in step S6 corresponds to the “gas concentration calculation value” in the claims.
In this embodiment, the first relationship between the terminal voltage of the heating resistor 110 and the hydrogen gas concentration at several temperatures (for example, 30 ° C. and 80 ° C.) is stored in the first relationship table 3a. ing. The first relationship may be a table in which the inter-terminal voltage and the hydrogen gas concentration are associated with each other for several temperatures, or may be a predetermined mathematical expression having the temperature and the inter-terminal voltage as variables, for example. .

Next, the CPU acquires the temperature of the detected atmosphere from the main temperature sensor 50 (step S8). Next, the CPU refers to the second relation table 3a stored in the ROM, and corrects the calculated gas concentration based on the temperature of the detected atmosphere (step S10).
In this embodiment, the second relation is a table in which the change rate of the gas concentration calculated value with respect to the reference temperature (−10 ° C.) is associated with each temperature, and this change rate is calculated in step S6. A correction value is obtained by multiplying the calculated gas concentration value. For example, the second relationship may be a predetermined mathematical formula using temperature as a variable.
Further, the CPU outputs the calculated gas concentration value corrected in step S10 to the outside as a gas concentration signal (step S12).

  In this embodiment, the relationship between the temperature of the atmosphere to be detected and the output of the combustible gas detector 1 (the value obtained by converting the voltage between the terminals into the hydrogen gas concentration) is the second relationship. The relationship between the temperature and the voltage between the terminals of the heating resistor 110 may be the second relationship. In this case, when the CPU acquires the inter-terminal voltage in step S4, the CPU refers to the second relation table 3a (however, a table of the rate of change of the inter-terminal voltage with respect to the temperature) based on the temperature of the atmosphere to be detected. Correct the voltage between terminals. Then, referring to the first relation table 3a based on the corrected inter-terminal voltage, a gas concentration calculation value is calculated as in step S6, and this value is output to the outside as it is as a gas concentration signal.

It goes without saying that the present invention is not limited to the above-described embodiment, and extends to various modifications and equivalents included in the spirit and scope of the present invention.
For example, in the above embodiment, the two temperature sensors (temperature detection means) of the main temperature sensor 50 and the second temperature sensor 130 are provided, but only one of the temperature sensors is provided, and the temperature of this temperature sensor is adjusted. Based on this, the correction may be performed from the second relationship. However, as described above, when the temperature in the vicinity of the heating resistor 110 and the temperature of the detected atmosphere are different in order to prevent condensation, two temperature sensors, the main temperature sensor 50 and the second temperature sensor 130, are provided. And the detection accuracy of combustible gas improves.

  EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.

The combustible gas detection device 1 shown in FIGS. 1 to 4 was manufactured. Using this combustible gas detector 1, several model gases with known hydrogen gas concentrations were measured under the following measurement conditions.
Measurement conditions Gas composition: H ₂ = 0,2,4%, Air = bal.
Gas Temperature and humidity: 25 ℃ -0% RH, 20 ℃ -90% RH (2.1% H 2 O), 52 ℃ -90% RH (12.1% H 2 O), 66 ℃ -90% RH (23.2% H ₂ O)
Gas flow rate: 5L / min

FIG. 10 shows the relationship between the output (gas concentration calculation value) of the combustible gas detection device 1 and the hydrogen concentration (known value) in the model gas when the correction process in step S10 is not performed. It can be seen that when the temperature of the model gas (that is, absolute humidity) changes, the sensor output (gas concentration calculation value) fluctuates even when the hydrogen concentration is the same, and is affected by the absolute humidity.
On the other hand, FIG. 11 shows the relationship between the output (gas concentration calculation value) of the combustible gas detection device 1 and the hydrogen concentration (known value) in the model gas when the correction process of step S10 is performed. It can be seen that even if the temperature of the model gas (that is, absolute humidity) changes, the sensor output (gas concentration calculation value) is almost the same if the hydrogen concentration is the same, and the influence of absolute humidity can be corrected.

1 Combustible gas detection device 3 Control unit (gas detection unit)
3a Microcomputer (concentration calculation means, main temperature detection means, correction means)
11 Casing member 21s Measurement chamber 50 Main temperature sensor (main temperature detection means)
60 Condensation prevention heater 110 Heating resistor 130 Second temperature sensor (second temperature detection means)

Claims (4)

One heating resistor that is exposed to the atmosphere to be detected in a stable relative humidity environment and whose temperature changes in accordance with the concentration of the combustible gas in the atmosphere to be detected;
A gas detection unit that controls energization of the heating resistor so that the heating resistor is maintained at a predetermined temperature, and detects a voltage between terminals of the heating resistor at this time;
Based on a first relationship between the concentration of the combustible gas and the voltage between the terminals, concentration calculating means for calculating the concentration of the combustible gas in the detected atmosphere as a gas concentration calculated value from the voltage between the terminals; ,
Main temperature detecting means for detecting the temperature of the detected atmosphere;
Based on the second relationship between the gas concentration calculated value or the inter-terminal voltage and the temperature of the detected atmosphere, the gas concentration calculated value or the inter-terminal voltage is calculated from the temperature detected by the main temperature detecting means. Correction means for correcting;
A combustible gas detection device.   The combustible gas detection device according to claim 1, further comprising a dew condensation prevention heater for preventing dew condensation on the heating resistor. The heating resistor is installed in a measurement chamber that is formed in the combustible gas detection device and communicates with the detected atmosphere, and the main temperature detection means is arranged outside the measurement chamber,
A second temperature detecting means disposed in the measurement chamber for detecting the temperature in the measurement chamber;
The combustible gas detection device according to claim 1, wherein the concentration calculation unit changes the first relationship based on a temperature detected by the second temperature detection unit.   The combustible gas according to claim 3, further comprising a casing member that forms the measurement chamber and integrally forms a main temperature detection means attachment portion for attaching the main temperature detection means to the outside of the measurement chamber. Detection device.

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