Thermal conduction gas sensors and gas detectors

Abstract

To provide a heat conduction type gas sensor and gas detector that can highly accurately detect density of detection object gas even if a direction of the heat conduction type gas sensor, or a pressure of an ambient environment changes.SOLUTION: A heat conduction type gas sensor comprises: a casing that has a gas introduction inlet introducing examined gas inside; a heat conduction element that has a coil-like functional part arranged within the casing; and a heat conduction element storage member that stores the heat conduction element within the casing. The heat conduction element storage member has a storage chamber in which the heat conduction element is stored; and a ventilation hole that introduces examined gas to the storage chamber. In the storage chamber, the functional part in the heat conduction element is surrounded by a wall face blocking airflow except the ventilation hole.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat conduction type gas sensor and a gas detector provided with the same.

Background Art

[0002] For example, as a gas sensor for detecting a flammable gas or the like, a heat conduction type gas sensor is known. This heat conduction type gas sensor utilizes the fact that the thermal conductivity of the ambient atmosphere varies depending on the type and concentration of the gas, and detects the change in the thermal conductivity in the test gas as the concentration of the target gas to be detected. Specifically, the heat conduction type gas sensor has, for example, a heat conduction element made of a metal coil. When the target gas to be detected comes into contact with the heat conduction element while the heat conduction element is energized, the state of heat dissipation changes due to the thermal conductivity unique to the target gas to be detected, and thereby the temperature of the heat conduction element changes. Then, as the temperature of the heat conduction element changes, the resistance value of the metal coil constituting the heat conduction element changes, and the concentration of the target gas to be detected is measured based on the amount of change in this resistance value.

[0003] As such a heat conduction type gas sensor, there is known one having a casing (cap) having a gas inlet and a heat conduction element arranged inside the casing, and the heat conduction element has a structure in which a coating film made of gold is formed on the surface of a core wire made of platinum (see Patent Document 1). In this heat conduction type gas sensor, when a test gas containing a flammable gas such as butane or propane as the target gas to be detected flows into the casing from the gas inlet, the target gas to be detected comes into contact with the heat conduction element, so that the temperature of the heat conduction element that has generated heat changes according to the concentration of the target gas to be detected. Therefore, the resistance value of the heat conduction element changes, and the concentration of the target gas to be detected is calculated and output based on the amount of change in this resistance value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, gas detectors equipped with such thermal conduction gas sensors have problems such as directional dependence, where the concentration reading fluctuates when the orientation of the thermal conduction gas sensor changes, and pressure dependence, where the concentration reading fluctuates when the pressure of the surrounding environment changes. The reasons for these problems are presumed to be as follows. When a thermal conduction gas sensor is energized, the thermal conduction element heats up to a high temperature, for example, around 400°C. This heat generated by the thermal conduction element creates an airflow around it. When the orientation of the thermal conduction gas sensor changes, or when the pressure of the surrounding environment changes, the airflow changes, resulting in differences in heat conduction and thus a fluctuation in the concentration reading.

[0006] The present invention was made based on the circumstances described above, and its purpose is to provide a heat conduction gas sensor and a gas detector that can detect the concentration of the target gas with high accuracy even when the orientation of the heat conduction gas sensor or the pressure of the surrounding environment changes. [Means for solving the problem]

[0007] The heat conduction gas sensor of the present invention comprises a casing having a gas inlet for introducing the gas to be tested, A heat conduction element having a coil-shaped functional part is disposed within the casing, A heat conduction element housing member that houses the heat conduction element within the casing, It is equipped with, The heat conduction element housing member has a housing chamber in which the heat conduction element is housed, and a vent for introducing the gas to be tested into the housing chamber. The aforementioned storage chamber is formed by a recess formed on the surface of the heat conduction element housing member, In the aforementioned storage chamber, the functional part of the heat conduction element is surrounded by a wall surface that blocks airflow, except for the ventilation opening.Occasionally, The distance between the functional part and the wall surface surrounding the functional part is 0.2 to 2.0 mm, and the distance between the functional part and the ventilation opening is 0.8 to 2.2 mm. It is characterized by the following: Furthermore, the heat conduction gas sensor of the present invention comprises a casing having a gas inlet for introducing the gas to be tested, A heat conduction element having a coil-shaped functional part is disposed within the casing, A heat conduction element housing member that houses the heat conduction element within the casing, It is equipped with, The heat conduction element housing member has a housing chamber in which the heat conduction element is housed, and a vent for introducing the gas to be tested into the housing chamber. The aforementioned storage chamber is formed by a recess formed on the surface of the heat conduction element housing member, In the aforementioned storage chamber, the functional part of the heat conduction element is surrounded by a wall surface that blocks airflow, except for the ventilation opening. A breathable airflow restricting member, which restricts the airflow passing through the vent, is arranged to cover the vent.

[0008] In the heat conduction type gas sensor of the present invention, it is preferable that the distance between the functional part and the wall surface surrounding the functional part is 0.2 to 2.0 mm, and the distance between the functional part and the vent is 0.8 to 2.2 mm. Furthermore, it is preferable that the diameter of the functional part is 0.2 to 0.4 mm.

[0009] Furthermore, in the heat conduction type gas sensor of the present invention, it is preferable that a breathable airflow restricting member, which restricts the airflow passing through the vent, is arranged to cover the vent. Furthermore, it is preferable that the airflow restricting member be made of glass wool.

[0010] The gas detector of the present invention is characterized by comprising the above-described thermal conduction type gas sensor. [Effects of the Invention]

[0011] According to the present invention, in a storage chamber in which a heat conduction element is housed, formed by a recess formed on the surface of a heat conduction element housing member, the functional part of the heat conduction element is surrounded by a wall surface that blocks airflow, except for a ventilation opening. Furthermore, the distance between the functional part and the wall surrounding it is 0.2 to 2.0 mm, and the distance between the functional part and the ventilation opening is 0.8 to 2.2 mm. Therefore, even if the orientation of the thermal conduction gas sensor or the pressure of the surrounding environment changes, the concentration of the target gas can be detected with high accuracy. Furthermore, by positioning the airflow restricting member, which regulates the airflow passing through the vent, so as to cover the vent, the concentration of the target gas can be detected with even greater accuracy.

Brief Description of the Drawings

[0012] [Figure 1] It is an explanatory cross-sectional view showing the configuration in an example of the thermal conduction type gas sensor of the present invention. [Figure 2] It is an explanatory view showing the thermal conduction type gas sensor shown in FIG. 1 disassembled. [Figure 3] It is an explanatory view showing the configuration of the thermal conduction element in the thermal conduction type gas sensor shown in FIG. 2, (a) is a perspective view, (b) is a cross-sectional view cut in the longitudinal direction, and (c) is a cross-sectional view cut in a direction perpendicular to the longitudinal direction. [Figure 4] It is a plan view showing an enlarged recess in the thermal conduction element housing member. [Figure 5] It is an explanatory cross-sectional view showing the recess and its peripheral portion in the thermal conduction element housing member cut along the longitudinal direction of the thermal conduction element. [Figure 6] It is an explanatory cross-sectional view showing the recess and its peripheral portion in the thermal conduction element housing member cut along a direction perpendicular to the longitudinal direction of the thermal conduction element. [Figure 7] It is a block diagram showing an outline of the configuration in an example of the gas detector of the present invention. [Figure 8] It is an explanatory view showing the orientation of the thermal conduction element housing member in the thermal conduction type sensor in the direction dependence test of the example. [Figure 9] It is a graph showing the result of the direction dependence test of the example. [Figure 10] It is a graph showing the result of the pressure dependence test of the example.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the gas detector of the present invention will be described. Figure 1 is an explanatory cross-sectional view showing the configuration of an example of the thermal conduction gas sensor of the present invention. Figure 2 is an explanatory diagram showing the thermal conduction gas sensor 10 shown in Figure 1 in an exploded view. This thermal conduction gas sensor 10 has a cylindrical casing 11. In this casing 11, an opening at one end (the upper end in Figure 1) is a gas inlet 11a for introducing the gas to be tested into the casing 11. Inside the casing 11, a substantially circular substrate 15 is arranged along a plane perpendicular to the axial direction of the casing 11. A temperature and humidity sensing element 16 for measuring the temperature and humidity of the gas to be tested, and a plurality of studs 17 are mounted on this substrate 15. In addition, the substrate 15 has two through holes 18 that penetrate in the thickness direction of the substrate 15, through which conductive pins 24, which will be described later, are inserted.

[0014] A disc-shaped heat conduction element housing member 20, which houses the heat conduction element 25, is arranged on the substrate 15 inside the casing 11. This heat conduction element housing member 20 is made of a resin material having insulating and heat-resistant properties, such as polyphenylene sulfide (PPS) resin containing fibers such as glass fibers. A recess 26 is formed on the surface (upper surface in Figure 2) of the heat conduction element housing member 20, forming a housing chamber S in which the heat conduction element 25 is housed. In addition, a ventilation passage 21 for introducing the gas to be tested into the temperature and humidity sensing element 16 is formed in the heat conduction element housing member 20, extending from the surface to the back surface of the heat conduction element housing member 20.

[0015] As shown in Figure 3(a), the heat conduction element 25 is composed of a coil-shaped functional part 25a and lead parts 25b integrally connected to each end of the functional part 25a. Furthermore, as shown in Figures 3(b) and (c), the heat conduction element 25 is composed of a core wire 25c and a coating film 25d formed on the surface of the core wire 25c. The core wire 25 is made of a metal such as platinum, which has a high coefficient of thermal resistance and good corrosion resistance at high temperatures. The coating film 25b is made of a metal that is inert to the gas to be detected, such as gold. The thickness of the coating film 25b is, for example, 0.1 μm. As a method for forming the coating film 25b, an appropriate thin film formation method such as sputtering can be used.

[0016] The diameter (coil diameter) of the functional part 25a in the heat conduction element 25 is preferably 0.2 to 0.4 mm. Furthermore, the length (coil length) of the functional part 25a in the heat conduction element 25 is, for example, 0.3 to 1.2 mm. Furthermore, the number of turns of the coil constituting the functional unit 25a is, for example, 8 to 12 turns. As an example of the dimensions of the heat conduction element 25, the wire diameter is 20 μm, the diameter of the functional part 25a is 0.3 mm, the length of the functional part 25a is 1.0 mm, and the number of turns of the coil constituting the functional part 25a is 11 turns.

[0017] In this example, the recess 26 of the heat conduction element housing member 20 has a long planar shape that extends in the same direction as the longitudinal direction of the heat conduction element 25 (the axial direction of the coil constituting the functional part 25), as shown in Figure 4, and a housing chamber S is formed in the central region of the recess 26. The opening of this recess 26 is a vent 27 for introducing the test gas into the housing chamber S. This vent 27 is formed to face the gas inlet 11a of the casing 11.

[0018] In the recess 26 of the heat conduction element housing member 20, support regions R for supporting the heat conduction element 25 are formed on both sides of the housing chamber S. A step is formed at the boundary between the bottom surface of the housing chamber S and the bottom surface of each support region R, so that the bottom surface of each support region R protrudes from the bottom surface of the housing chamber S. Two conductive pins 24 are provided in the heat conduction element housing member 20 so as to extend from the back surface of the heat conduction element housing member 20 in the thickness direction of the heat conduction element housing member 20 and reach the support regions R. The outer ends of each lead portion 25b of the heat conduction element 25 are fixedly supported in an electrically connected state to the respective end faces of the conductive pins 24, and the respective end faces of the conductive pins 24 are covered with a spot coat 23 made of epoxy resin. In addition, each of the support regions R is filled with a resin encapsulant 28 so as to cover the spot coat 23.

[0019] In the storage chamber S of the heat conduction element housing member 20, the functional part 25a of the heat conduction element 25 is surrounded by walls that block airflow, except for the ventilation opening 27. In this example, as shown in Figure 6, the functional part 25a of the heat conduction element 25 is surrounded by two side walls W1 and W2 and a bottom wall W3 in the storage chamber S of the heat conduction element housing member 20.

[0020] In the storage space S, the distance between the functional part 25a of the heat conduction element 25 and the wall surface surrounding the functional part 25a (in the illustrated example, each of the side wall surfaces W1, W2 and the bottom wall surface W3) is preferably 0.2 to 2.0 mm. Furthermore, the distance between the wall surface surrounding the functional part 25a that does not face the ventilation opening 27 (in the illustrated example, the side wall surfaces W1, W2) and the functional part 25a is preferably 0.2 to 1.2 mm, and more preferably 0.4 to 1.0 mm. If the distance between the functional unit 25a and the wall surface is too small, the heat conduction element 25 may dissipate too much heat, making it difficult for the heat conduction element 25 to reach the required temperature. On the other hand, if the distance between the functional unit 25a and the wall surface is too large, the upward airflow from the heat conduction element 25 becomes larger when the vent 27 is facing upward. This results in a significantly different heat dissipation state compared to when the vent 27 is facing downward. Therefore, if the direction of the vent 27 changes from upward to another direction, such as downward, or if the pressure of the surrounding environment changes, the concentration indicator may easily fluctuate.

[0021] Furthermore, in the storage space S, the distance between the functional part 25a of the heat conduction element 25 and the vent 27 is preferably 0.8 to 2.2 mm, and more preferably 1.2 to 1.8 mm. If the distance between the functional unit 25a and the vent 27 is too small, the upward airflow from the heat conduction element 25 will be greater when the vent 27 is facing upward. This results in a significantly different heat dissipation state of the heat conduction element 25 compared to when the vent 27 is facing downward. Therefore, if the direction of the vent 27 changes from upward to another direction, such as downward, or if the pressure of the surrounding environment changes, the concentration reading may fluctuate easily. On the other hand, if the distance between the functional unit 25a and the vent 27 is too large, the output when the target gas is detected may decrease.

[0022] On the surface of the heat conduction element housing member 20, a circular, sheet-like airflow restricting member 12 is positioned to cover the openings of the vents 27 and the ventilation passage 21, thereby restricting the airflow passing through the vents 27. The material used to constitute this airflow restricting member 12 is one that is breathable, and specific examples include glass wool, quartz wool, and alumina wool. Furthermore, the thickness of the airflow restricting member 12 is, for example, 0.2 to 0.8 mm.

[0023] A circular sintered wire mesh 13, made of, for example, stainless steel (SUS316), is positioned on the airflow restricting member 12, with its peripheral edge fixed to the inner wall surface of the casing 11. The airflow restricting member 12 is sandwiched between the sintered wire mesh 13 and the heat conduction element housing member 20. Furthermore, below the substrate 15 inside the casing 11, a sealant 14, which is made of a cured adhesive such as epoxy resin adhesive, is provided to close the opening on the lower side of the casing 11.

[0024] Figure 7 is a block diagram illustrating the schematic configuration of an example of a gas detector equipped with a thermal conduction gas sensor according to the present invention. This gas detector comprises a thermal conduction gas sensor 10 shown in Figure 1 and a control unit 30 that controls the operation of the thermal conduction gas sensor 10. The control unit 30 includes a power supply 31 for the heat conduction element, a power supply 32 for the temperature and humidity sensing element, an ammeter 35 for measuring the current of the heat conduction element 25, a voltmeter 36 for measuring humidity, and a voltmeter 37 for measuring temperature. The power supply 31 and ammeter 35 for the heat conduction element are electrically connected to the heat conduction element 25 via conductive pins 24 (see Figure 2). The power supply 32 for the temperature and humidity sensing element, the voltmeter 36 for measuring humidity, and the voltmeter 37 for measuring temperature are electrically connected to the temperature and humidity sensing element 16 via studs 17 (see Figure 2).

[0025] In such a gas detector, when a voltage of, for example, 0.2 to 2.0V is applied to the heat conductive element 25, and the target gas, such as a flammable gas like butane or propane, flows into the storage chamber S of the heat conductive element housing member 20 via the sintered wire mesh 13 and the airflow restricting member 12, the target gas comes into contact with the heat conductive element 25. As a result, the temperature of the heated heat conductive element 25 changes according to the concentration of the target gas, causing the resistance value of the heat conductive element 25 to change. Based on this change in resistance value, the concentration of the target gas is calculated and output.

[0026] According to the above-described thermal conduction gas sensor 10, in the storage chamber S in which the thermal conduction element 25 is housed, the functional part 25a of the thermal conduction element 25 is surrounded by walls W1, W2, and W3 that block airflow, except for the ventilation opening 27. Therefore, even if the orientation of the thermal conduction gas sensor 10 or the pressure of the surrounding environment changes, changes in the state of airflow inside the storage chamber S are suppressed, and as a result, the concentration of the target gas can be detected with high accuracy. Furthermore, since the airflow restricting member 12, which restricts the airflow passing through the vent 27, is positioned to cover the vent 27, changes in the state of the airflow passing through the vent 27 are suppressed, allowing for detection of the concentration of the target gas with even greater accuracy.

[0027] Although embodiments of the gas detector of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. For example, the storage chamber S of the heat conduction element housing member 20 is not limited to those shown in Figures 4 and 5, but can be of various shapes, as long as the functional part 25a of the heat conduction element 25 is surrounded by a wall surface that blocks airflow, except for the ventilation opening 27. Furthermore, the resin encapsulant 28 in the heat conduction element housing member 20 is not essential, and the spot coat 23 may be left exposed. [Examples]

[0028] <Example 1> A thermal conduction sensor with the following specifications was fabricated according to the configurations shown in Figures 1 to 6, and a gas detector with the configuration shown in Figure 7 was fabricated using this thermal conduction sensor. [Casing (11)] Material: Polybutylene terephthalate (PBT) resin Dimensions: Overall length = 16.6 mm, Diameter of gas inlet (11a) = 11.0 mm [Airflow restricting member (12)] Material: Glass wool Dimensions: Diameter = 12.8 mm, Thickness = 0.40 mm [Thermal conductive element housing member (20)] Material: Polyphenylene sulfide (PPS) resin containing glass fibers Dimensions: Diameter = 16.0 mm, Thickness = 6.7 mm Dimensions of storage compartment (S): Length (length of the heat conduction element) = 2.5 mm, Width = 2.2 mm, Height = 4 mm [Thermal conduction element (25)] The structure consists of a platinum core wire (25c) with a gold coating (25d) formed on its surface, and the functional part (25a) has 11 turns. Dimensions: Wire strand = 20 μm, diameter of functional part (25a) = 0.3 mm, length of functional part (25a) = 1.0 mm. In the above, the distance between the functional part (25a) of the heat conduction element (25) and the side walls (W1, W2) of the storage chamber (S) is 0.95 mm, and the distance between the functional part (25a) of the heat conduction element (25) and the bottom wall (W3) of the storage chamber (S) is 1.75 mm. Furthermore, the distance between the functional part (25a) of the heat conduction element (25) and the vent (27) is 1.95 mm.

[0029] [Direction-dependent testing] The above gas detector was operated in an isobutane gas (100 vol%) atmosphere, and the output value was measured while changing the orientation of the thermal conductive element housing member (20) to the orientation shown in Figure 8, from position 1 to position 6. The relative output value was determined with the output value of position 1 set to 100%. Here, the output value for each position was measured after holding that position for 30 seconds. The results are shown in Figure 9.

[0030] [Pressure-dependent testing] The above gas detector was operated in an isobutane gas (100 vol%) atmosphere, and the relative output value was investigated when the ambient pressure was varied, with the output value at the reference pressure (atmospheric pressure) set to 100%. The results are shown in Figure 10. In Figure 10, the ambient pressure values ​​represent gauge pressure.

[0031] <Comparative Example 1> A thermal conduction type gas sensor and gas detector were fabricated with the same configuration as in Example 1, except that a thermal conduction element housing member was not used. Directional dependence and pressure dependence tests were performed on this gas detector in the same manner as in Example 1. The results are shown in Figures 9 and 10.

[0032] As is clear from the results in Figures 9 and 10, it was confirmed that the gas detector according to Example 1 can detect the concentration of the target gas with high accuracy even when the orientation of the thermal conduction gas sensor or the pressure of the surrounding environment changes. [Explanation of Symbols]

[0033] 10. Thermal Conduction Gas Sensor 11 Casing 12 Airflow regulating member 13 Sintered wire mesh 14. Sealing material 15 circuit boards 16 Temperature and humidity sensing elements 17 Stud 18 Through holes 20 Heat conduction element housing member 21 Ventilation channel 23 Spot Court 24 conductive pins 25 Heat Conducting Elements 25a Functional part 25b Lead section 25c core wire 25d coating film 26 recess 27 Ventilation holes 28 Resin encapsulants 30 Control Unit 31 Power supply for thermal conductive elements 32 Power supply for temperature and humidity sensing element 35 Ammeter 36. Voltmeter for measuring humidity 37. Voltmeter for temperature measurement R support area S Storage Room W1, W2 side wall W3 Bottom wall

Claims

1. A casing having a gas inlet for introducing the test gas inside, A heat conduction element having a coil-shaped functional part is disposed within the casing, A heat conduction element housing member that houses the heat conduction element within the casing, It is equipped with, The heat conduction element housing member has a housing chamber in which the heat conduction element is housed, and a vent for introducing the gas to be tested into the housing chamber. The aforementioned storage chamber is formed by a recess formed on the surface of the heat conduction element housing member, In the aforementioned storage chamber, the functional part of the heat conduction element is surrounded by a wall surface that blocks airflow, except for the ventilation opening. A heat conduction type gas sensor characterized in that the distance between the functional part and the wall surface surrounding the functional part is 0.2 to 2.0 mm, and the distance between the functional part and the vent is 0.8 to 2.2 mm.

2. The heat conduction type gas sensor according to claim 1, characterized in that the diameter of the functional part is 0.2 to 0.4 mm.

3. A casing having a gas inlet for introducing the test gas inside, A heat conduction element having a coil-shaped functional part is disposed within the casing, A heat conduction element housing member that houses the heat conduction element within the casing, It is equipped with, The heat conduction element housing member has a housing chamber in which the heat conduction element is housed, and a vent for introducing the gas to be tested into the housing chamber. The aforementioned storage chamber is formed by a recess formed on the surface of the heat conduction element housing member, In the aforementioned storage chamber, the functional part of the heat conduction element is surrounded by a wall surface that blocks airflow, except for the ventilation opening. A heat conduction type gas sensor characterized in that a breathable airflow restricting member, which restricts the airflow passing through the vent, is arranged to cover the vent.

4. The heat conduction type gas sensor according to claim 3, characterized in that the airflow restricting member is made of glass wool.

5. A gas detector characterized by comprising a heat conduction type gas sensor according to any one of Claims 1 to 4.

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