JP2009294138A - Inline flammable gas sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inline flammable gas sensor with easy implementation to external piping, capable of measuring the flammable gas with high precision regardless of improvement of measurement sensitivity and responsiveness and changes in ambient temperaturem by increasing the contact surface area between a gas to be measured and the thermally-sensitive portion of a thermometric element and improving gas replaceability. <P>SOLUTION: The flammable gas sensor includes a cross sectional projection cavity 3 and a sensor 20 mounted on the upper part in the cross conventional projection cavity 3 of a block 2, having a temperature adjustment unit to maintain a temperature in the cavity 3 at a constant, which has a measuring thermopile 8, with a hot junction to carry Pt particles and a comparing thermopile 9 for not to carry Pt particles that are closely juxtaposed; joints 18A, 18B connectable to external piping systems 17A, 17B arranged on the lower both sides of the cross sectional projection cavity 3 in the block 2; and a gas flow guide 19 for flow-guiding to contact the introduced measuring gas to the hot junctions of the thermopiles 8, 9 in the cross sectional convex cavity 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention measures, for example, oxygen (O ₂ ) supply and exhaust lines of fuel cells in order to prevent disasters such as explosion of flammable gases such as CO, HC, formaldehyde, and hydrogen in petrochemical plants. Used to measure the concentration of combustible gas, mainly hydrogen, contained in the measurement target gas by installing it in the pipe where the target gas is transported and measuring the calorific value of the measurement target gas The in-line type combustible gas sensor.

  As described above, as an in-line type gas sensor that is installed and used in a transportation pipe for a gas to be measured, conventionally, an opening is formed in the peripheral wall of the transportation pipe, and a recess that communicates with the gas flow path inside the pipe through this opening. A micro-flow sensor that has a shape pocket part and a plurality of thermopile temperature measuring elements is attached to the pocket part, and the temperature detection signals output from the plurality of temperature measuring elements are processed and measured. What was comprised so that the density of gas might be measured is known (for example, refer patent document 1). Further, it can be easily applied to measure the concentration of combustible gas using the microflow sensor having such a structure.

Japanese Patent Application Laid-Open No. 2004-125685

  However, the in-line type gas sensor using the microflow sensor shown in Patent Document 1 and the like has a sufficiently large diameter so as not to be affected by the flow of the measurement target gas flowing in the internal gas flow path on the peripheral wall of the pipe. It is necessary to form a small opening or to form a concave pocket that communicates with the gas flow path inside the pipe through this opening, and the structure and construction for mounting the gas sensor are complicated. In addition, the gas to be measured flowing in the pipe must be introduced into the pocket through a narrow and small opening, and after measurement, it must be discharged from the pocket through the narrow opening and returned to the pipe. The contact area between the gas and the thermosensitive part of the temperature measuring element cannot be made large, and not only the amount of heat generated by the contact between the two is small, but also the replaceability between the gas molecules after reaction and the measurement target gas is poor. Therefore, the in-line measuring the concentration of the combustible gas such as hydrogen contained in the measurement target gas by measuring the calorific value of the measurement target gas flowing in the pipe using the microflow sensor having the structure as described above. Even if it is applied to a type flammable gas sensor, sufficient measurement sensitivity and responsiveness cannot be obtained, and flammability with a concentration from a low level (for example, on the order of 1 ppm for hydrogen concentration) to a high level (near 100%) There is a problem that the measurement of gas cannot be put to practical use.

  In addition, the microflow sensor is installed in a recessed pocket and exposed to the outside of the pipe, so it is easily affected by ambient temperature such as outside air, and drifts due to changes in ambient temperature. There is also a problem that measurement errors are likely to occur.

  The present invention has been made in view of the above circumstances, and its purpose is that in-line mounting is simple and easy, and that the contact area between the gas to be measured and the thermosensitive part of the temperature measuring element is increased and the object to be measured with respect to the thermosensitive part. In-line flammability that improves measurement sensitivity and responsiveness even with low-concentration flammable gas by improving gas substitution, and can obtain highly accurate measurement results regardless of changes in ambient temperature It is in providing a sex gas sensor.

  The in-line flammable gas sensor according to the present invention devised to achieve the above object has a cavity having a convex cross section and is provided with a non-corrosive means provided with temperature adjusting means for keeping the temperature in the cavity constant. Temperature measuring device having a heat sensitive part carrying an oxidation catalyst for generating heat of oxidation reaction upon contact with a gas to be measured on the lower surface of the circuit board on the upper surface part in the convex cavity of the block made of a conductive material A sensor unit for measuring the concentration of the combustible gas in the measurement target gas is mounted by arranging the element and a comparative temperature measuring element having a heat sensitive part not supporting the oxidation catalyst in close proximity, and by the output difference between these two temperature measuring elements. In addition, on both sides of the lower part of the convex cavity in the block, there are provided joint portions that can be connected to an external piping system in order to introduce and discharge the gas to be measured in the cavity. Inside mold cavity It is characterized in that the gas flow guide for the flow guide so as to contact with the heat-sensitive part of the two temperature measuring elements the measurement target gas introduced into the air sinuses are installed.

  The in-line flammable gas sensor according to the present invention having the above-described characteristic configuration is provided on both sides of the lower portion of the block without the need to form an opening portion having a small diameter or a pocket portion connected to the existing transportation piping system. Since it is only necessary to directly connect (directly connect) the joint portion to the external piping system, the gas sensor can be used by in-line mounting simply and easily from the structural and construction aspects.

Moreover, in the mounted state, a large amount of measurement target gas is introduced into the large convex cavity of the block from the external piping system through the joint, and the introduced measurement target gas is introduced into the upper surface of the convex cavity by the flow guide. Flow-guided toward the mounted sensor unit and brought into contact with the measurement and comparison temperature measuring elements of the sensor unit, and in accordance with this contact, the combustible gas in the measurement target gas is transferred to the heat-sensitive part of the measurement temperature measurement element. It is oxidized by the oxidation catalyst supported on the catalyst to generate heat of reaction. For example, when the combustible gas is hydrogen gas (H ₂ ),
2H ₂ + O ₂ → H ₂ O + Q (1)
As shown by the following reaction formula, hydrogen gas (H ₂ ) molecules react with oxygen gas (O ₂ ) molecules to generate water molecules (H ₂ O). At this time, reaction heat Q is generated, and the gas to be measured The temperature sensing element of the measurement temperature sensor rapidly rises due to the amount of heat, including the amount of heat held, and a voltage corresponding to the temperature is output. No reaction heat is generated by the reaction, and the temperature is raised only by the amount of heat held by the measurement target gas, and a voltage corresponding to the temperature is output. By calculating the difference between these two output voltages, the amount of heat held by the gas to be measured that contacts the two temperature measuring elements while the convex cavity is maintained at a constant temperature by the temperature adjusting means is the same. Only the resulting voltage is obtained, and by determining the concentration of combustible gas such as hydrogen in the measurement target gas from that voltage, the predetermined combustible gas concentration is not affected at all by changes in ambient temperature such as outside air, It can be measured with high accuracy.

  In addition, the gas to be measured is introduced into a convex cavity that is sufficiently large in volume, and the flow of the introduced gas to be measured is guided to the sensor part by a guide. The measurement target gas can be quickly replaced to improve measurement sensitivity and responsiveness, and both temperature measuring elements are maintained at a constant temperature by the temperature control means, so the concentration of combustible gas in the measurement target gas Can be efficiently measured continuously from a low level to a high level.

  In the in-line flammable gas sensor according to the present invention, as described in claim 2, the measuring temperature measuring element on the heat-sensitive part side carrying the oxidation catalyst of the sensor part and the heat-sensitive part side not carrying the oxidation catalyst are provided. When adopting a configuration in which the reference temperature measuring elements are connected so that their polarities are opposite to each other in series, temperature drift caused by changes in ambient temperature can be achieved by simply connecting the wires using bonding wires. It is possible to compensate and improve the measurement accuracy.

  Moreover, in the in-line type combustible gas sensor according to the present invention, as described in claim 3, the measuring temperature measuring element on the heat sensitive part side carrying the oxidation catalyst of the sensor part and the heat sensitive part not carrying the oxidation catalyst. The comparison temperature measuring element on the side is connected so that their polarities are opposite to each other in series, and an amplifier for amplifying the output difference signal of both the temperature measuring elements is provided, and the output signal from this amplifier is You may employ | adopt the structure which provides the measurement circuit which calculates a combustible gas density | concentration by calculating. In this case, the output signal from the amplifier can be easily sampled, and the temperature adjustment means can be controlled appropriately and quickly using the sampling data.

Further, in the in-line flammable gas sensor according to the present invention, as described in claim 4, the measurement temperature measuring element of the sensor unit includes a carbon nanotube (Carbon Nano Tube) carrying an oxidation catalyst in its heat sensitive part. The temperature sensor for comparison is represented by a carbon nanotube that does not carry an oxidation catalyst in its heat-sensitive part. It is preferable that the carbon clusters are connected to each other.
In this case, the carbon cluster represented by CNT connected to the heat sensitive part of the temperature measuring element for measurement has a very large thermal conductivity (the thermal conductivity of CNT is about 6000 W / m · K), In addition, since the contact area with the combustible gas in the gas to be measured can be very large, the reaction heat according to the above reaction formula (1) can be increased, and the large reaction heat can be rapidly and efficiently obtained. It can be transmitted to the heat sensitive part of the temperature measuring element for measurement, and the temperature rise degree of the heat sensitive part can be remarkably increased. Therefore, by using the oxidation catalyst-supported carbon cluster, the gas sensor as a whole is reduced in size, and the temperature rise efficiency in the heat sensitive part of the temperature measuring element is increased to increase the measurement sensitivity of the combustible gas concentration such as hydrogen in the measurement target gas and A significant improvement in measurement accuracy can be realized.

  Further, as both temperature measuring elements of the sensor unit in the in-line type combustible gas sensor according to the present invention, it is most preferable to use a thermopile as described in claim 5, and as the oxidation catalyst, platinum, palladium, Any selected from noble metals including rhodium, iridium, and nickel may be used.

  Further, the block in the in-line flammable gas sensor according to the present invention is divided into a lower block having a convex cavity and an upper block for closing an upper end opening of the convex cavity, as described in claim 6. And the circuit board is sandwiched and fixed between the lower and upper blocks in an airtight state, so that both the temperature measurement of the sensor unit can be performed even in the recessed convex cavity formed in the block. The elements can be easily mounted, the assembly of the gas sensor as a whole is easy, and the maintainability such as inspection and repair of the temperature measuring elements is also excellent.

  Furthermore, in the in-line type combustible gas sensor according to the present invention, as described in claim 7, it is preferable that the entire outer periphery of the block is surrounded by a cover for heat insulation and electromagnetic shielding. In this case, the temperature inside the convex cavity can be easily maintained regardless of a large external temperature change, and is less susceptible to external noise such as electromagnetic waves, so that the predetermined measurement sensitivity and measurement accuracy can be further improved. Improvements can be made.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view of the entire inline-type combustible gas sensor according to the first embodiment of the present invention, and FIG. 2 is a transverse sectional view taken along line XX of FIG. The in-line flammable gas sensor 1 includes a non-corrosive material having a rectangular shape in plan view, for example, a metal block 2. The metal block 2 is divided into a lower block 2B having a cavity 3 having a convex cross section and an upper block 2A for closing the upper end opening of the convex cavity 3, and the upper block 2A and the lower block 2B In the state where the peripheral portion of the circuit board 4 made of a high temperature resistant semiconductor material, for example, alumina, is sandwiched between them, and the O-ring 5 is arranged around the entire contact portion between the lower block 2B and the peripheral portion of the circuit board 4. By inserting a plurality of set screws 6 from the upper surface side of the upper block 2A to the lower block 2B side, a circuit is formed between the upper and lower blocks 2A and 2B so that the inside of the convex cavity 3 is kept airtight. The substrate 4 is sandwiched and fixed.

A heater 7A is embedded in the upper block 2A of the block 2 and a heater 7B is embedded in the lower block 2B, and on the lower surface of the circuit board 4 positioned at the upper end in the convex cavity 3 As an example of a temperature measuring element for measurement and comparison, for example, two thermopiles 8 and 9 are formed by joining dissimilar metals such as polycyan and aluminum, and generate and output thermoelectromotive force by the Seebeck effect according to the amount of heat received. Are formed in close proximity to each other, and a diaphragm-like insulating film 10 such as a SiO ₂ or SiN thin film is formed over the entire upper surface of the circuit board 4 including the surfaces of the thermopiles 8 and 9 (see FIG. 3). Is formed.

  As clearly shown in FIG. 3, platinum (Pt) particles, which are an example of an oxidation catalyst, are preliminarily supported on the hot junction part, which is the heat sensitive part of one of the two thermopiles 8 and 9. A plurality of CNTs 11 as typical examples of carbon clusters are arranged in parallel so as to be parallel to each other in a vertical orientation perpendicular to the insulating film 10 (hereinafter referred to as a thermopile for measurement), and the other A plurality of CNTs 12 that do not carry Pt particles are arranged in parallel so as to be parallel to each other in a vertical orientation perpendicular to the insulating film 10 as described above. (Hereinafter referred to as a thermopile for comparison). These CNTs 11 carrying Pt particles and CNTs 12 not carrying Pt particles are composed of a sulfur atom S of a thiol group attached to one end thereof and Au atoms of gold (Au) thin films 13 and 14 formed on the insulating film 10 part. By forming the CNT-R-S-Au structure into a film by bonding, the measurement thermopile 8 and the comparative thermopile 9 are connected to the hot junctions, and the measurement thermopile 8 and the comparative thermopile 9 thus configured A sensor unit 20 for measuring the combustible gas concentration is mounted in the convex cavity 3 in the block 2. Note that R in the chemical formula CNT-RS-Au is a carbon chain.

  A temperature sensor 15 is attached to the circuit board 4 adjacent to the measurement and comparison thermopiles 8 and 9, and the temperature detected by the temperature sensor 15 is fed back to the temperature adjustment circuit 16 (see FIG. 4). The temperature adjusting means is configured to keep the temperature in the convex cavity 3 constant by applying a control voltage corresponding to the difference between the detected temperature fed back and the set temperature to the heaters 7A and 7B. . The temperature adjustment range by this temperature adjustment means is 60 to 200 ° C., preferably 80 to 150 ° C. In this embodiment, it is set to 80 ° C. As the temperature sensor 15, a thermocouple, a thermistor, or the like is used.

In addition, on both sides of the lower block 2B that linearly opposes the lower portion of the convex cavity 3 in the block 2, an outside in which the measurement target gas flows to introduce and discharge the measurement target gas into the convex cavity 3 Joint portions 18A and 18B connectable to the piping system, that is, the upstream side piping 17A and the downstream side piping 17B are attached, and the lower block 2B corresponding to the intermediate portion in the convex cavity 3 has an upstream side The gas to be measured introduced into the cavity 3 from the pipe 17A through the joint 18A is flow-guided in an upward flow so as to come into contact with the CNTs 11 and 12 of both the thermopiles 8 and 9, as indicated by the stripe arrows in FIG. A fin-plate-shaped gas flow guide 19 is fixedly installed.
The two thermopiles 8 and 9 in the sensor unit 20 are shown juxtaposed in the gas flow direction in the drawing, but actually they are juxtaposed at right angles to the gas flow direction.

  FIG. 4 is an example of the measurement circuit of the inline-type combustible gas sensor 1 according to the first embodiment, and the thermopile 8 and 9 are connected so that their polarities are opposite to each other in series. At the same time, the thermopile 8 and 9 are connected to a preamplifier 21 for impedance conversion and voltage amplification of the difference between their outputs (electromotive forces). Since the preamplifier 21 generally has a small electropile of the thermopile, it amplifies the electromotive force by (1 + R2 / R1) times so that the electromotive force has a gain of several thousand times or more and can be handled easily. The output of the preamplifier 21 is input to the analog input terminal AIN0 of the AD converter 22 and the digital signal obtained by AD conversion is taken into the MPU 23 to calculate the temperature of the measurement target gas, thereby calculating the concentration of the combustible gas in the measurement target gas. It is configured to measure. In addition, the temperature detected by the temperature sensor 15 is fed back to the temperature adjustment circuit 16, and a control signal output from the MPU 23 according to a difference between the detected temperature fed back and a preset temperature input in advance via the MPU 23. Based on this, a control voltage is applied to the heaters 17A and 17B via the heater driver 24, and temperature adjusting means for holding the temperature in the convex cavity 3 constant (80 ° C. in this embodiment) is incorporated in the measurement circuit. It is.

  The preamplifier 21 is installed on the upper surface of the upper block 2A in the block 2, and the preamplifier 21 is shielded by a cover 25 so as not to be affected by external noise and external temperature change. Further, the entire outer periphery of the block 2 has a structure surrounded by a heat insulating and electromagnetic shielding cover 26. By grounding the cover 26, a concentration signal having a high S / N ratio is sent to the outside. It can be sent out. The concentration value of the combustible gas calculated by the MPU 23 may be displayed as it is, transferred to a host device such as a host computer, for example, printed, or recorded and stored in a memory. May be.

  In the in-line type combustible gas sensor 1 configured as described above, the joint portions 18A and 18B attached to both sides of the block 2 are directly connected (directly connected) to the upstream piping 17A and the downstream piping 17B of the external piping system. ), It is possible to introduce a gas to be measured at a flow rate equivalent to the flow rate flowing in the external piping system into the convex cavity 3 of the gas sensor 1, and the influence of the gas flow on the external piping system Since there is no need to form a small-diameter opening or a concave pocket connected to the small-diameter opening to prevent the gas sensor 1 from being subjected to construction, It can also be used simply and easily in-line.

In a mounted and used state, a large amount of measurement target gas introduced into the convex cavity 3 of the block 2 from the upstream pipe 17A through the joint portion 18A is transferred to the upper surface of the convex cavity 3 by the fin plate-like gas flow guide 19. It is guided to flow toward the sensor unit 20 mounted on the unit and is brought into contact with the measurement thermopile 8 and the comparison thermopile 9 of the sensor unit. Here, when a measurement target gas containing a flammable gas such as hydrogen comes into contact with the CNT 11 supporting the Pt particles of the measurement thermopile 8, a flammable gas in the measurement target gas, for example, a hydrogen gas (H ₂ ) molecule, becomes CNT 11. Under the Pt particles supported on the catalyst, as shown in the above formula (1), it reacts with oxygen gas (O ₂ ) molecules to generate water molecules (H ₂ O). appear. This reaction heat Q is quickly and efficiently transmitted from the surface of the Pt particles to the hot junction of the thermopile 8 for measurement through the CNT 11 having a very high thermal conductivity of about 6000 W / m · K. The contact portion is rapidly and greatly heated to output a large voltage.

  On the other hand, in the non-supporting CNT 12 of the thermopile 9 for comparison, no reaction heat is generated due to the chemical reaction as described above. Will be. The difference between these two output voltages is input to the measurement circuit shown in FIG. 3, and a predetermined combustible gas concentration is measured by obtaining the combustible gas concentration such as hydrogen in the measurement target gas from the difference voltage.

  At the time of this measurement, the temperature in the convex cavity 3 into which the measurement target gas is introduced is maintained at a constant temperature by the above-described temperature adjusting means, so that the measurement thermopile 8 and the comparison thermopile 9 of the sensor unit 20 are maintained. Therefore, even if the ambient temperature such as the outside air changes, only the voltage caused by the reaction heat by the CNTs 11 carrying the Pt particles of the thermopile 8 for measurement changes. The predetermined combustible gas concentration can be accurately measured regardless of changes in ambient temperature such as outside air.

  In addition, after the gas to be measured is introduced into the convex cavity 3 that is sufficiently large in volume, the flow is guided toward the sensor unit 20 by the guide 19, so that the gas molecules after the generation of reaction heat and the measurement object are generated. The replacement with the gas is performed quickly, so that the measurement sensitivity and the response can be improved, and the combustible gas concentration from the low level to the high level can be measured continuously and efficiently.

Incidentally, FIG. 5 shows the result of an experiment conducted by the inventors on the relationship between the concentration of hydrogen gas (H ₂ ) contained in the measurement target gas and the sensor output using the above-described inline-type combustible gas sensor 1. It is an H ₂ gas calibration curve. As is clear from the figure, the in-line flammable gas sensor 1 allows the H ₂ gas concentration to be continuously reduced from a low level (on the order of 1 ppm) to a high level (around 100%). Thus, it was confirmed that the measurement can be performed efficiently.

  In the first embodiment, both the measurement thermopile 8 and the comparative thermopile 9 of the sensor unit 20 are connected with the CNTs 11 carrying Pt particles and the CNTs 12 not carrying Pt at their heat sensitive parts (hot contact parts). As shown above, a fibrous porous layer such as carbon fiber is bonded and formed on the hot contact portion of each thermopile 8 and 9 with a silane coupling agent or the like, and Pt particles or the like are formed on the fibrous porous layer on the measurement thermopile 8 side. A configuration may be adopted in which the oxidation catalyst is supported, while the fibrous porous layer on the side of the comparative thermopile 9 does not support the oxidation catalyst.

  Further, a dehumidifier such as an electronic cooling type or a hollow fiber membrane differential pressure drying type is provided on the upstream side pipe 17A connecting the in-line type combustible gas sensor 1 shown in the first embodiment via the joint 18A. By attaching and lowering the humidity of the gas to be measured, it is possible to remove the influence of the output drop due to the humidity and improve the measurement sensitivity.

  As the temperature sensor 15, as shown in the above embodiment, the temperature of the upper block 2 </ b> A or the lower block 2 </ b> B is uniformly transmitted in addition to being attached to the surface side of the circuit board 4 adjacent to the thermopile 8, 9. It may be inserted at the position, or a thin platinum film or aluminum wiring may be provided on the thermopile chip.

  Furthermore, in the above embodiment, the thermopile is used as the temperature measuring element. However, even if the thermistor bolometer is used in addition to the above, the entire sensor is reduced in size as described above. The effect of improving the measurement sensitivity and measurement accuracy of the combustible gas is exhibited.

It is a longitudinal section of the whole in-line type combustible gas sensor concerning a 1st embodiment of the present invention. It is a cross-sectional view along the XX line of FIG. It is an expanded secondary sectional view of the principal part of the in-line type combustible gas sensor concerning a 1st embodiment. It is an example of the measurement circuit of the in-line type combustible gas sensor which concerns on 1st Embodiment. A H ₂ gas calibration curve showing experimental results conducted by the present inventors using an in-line type combustible gas sensor according to the first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 In-line type combustible gas sensor 2 Block 2A Upper block 2B Lower block 3 Convex cavity 4 Circuit board 7A, 7B Heater 8 Thermopile for measurement 9 Thermopile for comparison 11 CNT carrying Pt particles
12 Pt particle non-supported CNT
15 Temperature sensor (component of temperature control means)
16 Temperature control circuit (component of temperature control means)
17A Upstream piping 17B Downstream piping 18A, 18B Joint 19 Fin plate-shaped gas flow guide 20 Sensor 21 Preamplifier

Claims (7)

    The lower surface of the circuit board is formed on the upper surface of the non-corrosive material block in the block made of a non-corrosive material having a cavity having a convex cross section and having a temperature adjusting means for keeping the temperature in the cavity constant. A measuring temperature measuring element having a thermosensitive part carrying an oxidation catalyst that generates an oxidation reaction heat upon contact with the measurement target gas and a comparative temperature measuring element having a thermosensitive part not carrying an oxidation catalyst are arranged close to each other. In addition, a sensor unit for measuring the concentration of combustible gas in the gas to be measured based on the output difference between these two temperature measuring elements is mounted, and on both sides of the lower portion of the convex cavity in the block, the object to be measured is placed in the cavity. A joint that can be connected to an external piping system for introducing and discharging gas is provided, and in the convex cavity, the gas to be measured introduced into the cavity is connected to the two temperature measuring elements. To contact the heat sensitive part of Inline combustible gas sensor, wherein a gas flow guide for moving the guide is installed.   The measuring temperature measuring element on the heat sensitive part side carrying the oxidation catalyst of the sensor part and the comparative temperature measuring element on the heat sensitive part side not carrying the oxidation catalyst are such that their polarities are opposite to each other in series. The in-line combustible gas sensor according to claim 1 connected.   The measurement temperature measuring element on the heat sensitive part side carrying the oxidation catalyst of the sensor part and the comparison temperature measurement element on the heat sensitive part side not carrying the oxidation catalyst so that their polarities are opposite to each other in series. A measurement circuit is provided that has an amplifier for connecting and amplifying an output difference signal of both the temperature measuring elements, and for calculating a combustible gas concentration by calculating the output signal from the amplifier. The in-line flammable gas sensor described in 1.   The temperature measuring element for measurement of the sensor unit is configured by connecting carbon clusters represented by carbon nanotubes carrying an oxidation catalyst to the heat sensitive part, and the temperature measuring element for comparison is a thermosensitive element for comparison. The in-line flammable gas sensor according to any one of claims 1 to 3, wherein a carbon cluster represented by a carbon nanotube that does not carry an oxidation catalyst is connected to the part.   The in-line type combustible gas sensor according to any one of claims 1 to 4, wherein a thermopile is used as both temperature measuring elements of the sensor unit.   The block is divided into a lower block having a convex cavity and an upper block for closing an upper end opening of the convex cavity, and the circuit board is sandwiched and fixed between the lower and upper blocks in an airtight state. The in-line combustible gas sensor according to any one of claims 1 to 5. The in-line type combustible gas sensor according to any one of claims 1 to 6, wherein the entire outer periphery of the block is surrounded by a cover for heat insulation and electromagnetic shielding.

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