gas sensor

Abstract

The objective is to provide a gas sensor capable of detecting a wide range of flammable gases while suppressing the decrease in sensitivity of the gas detection element due to toxic substances. [Solution] A gas sensor 100 comprises a casing 110 having a gas introduction opening 111, a gas detection element 120 disposed inside the casing 110 that causes a change in resistance value upon contact with the gas to be detected, and a filter mechanism 130 that filters the gas to be detected introduced into the casing 110 through the gas introduction opening 111. The filter mechanism 130 is configured to block the gas introduction opening 111 and consists of a photocatalytic filter 131 supporting a photocatalyst, and an ultraviolet light source 135 disposed inside the casing 110 that irradiates ultraviolet light to activate the photocatalyst.

Description

Technical Field

[0001] The present invention relates to, for example, a gas sensor for detecting flammable gases, which has excellent silicone poisoning durability.

Background Art

[0002] For example, some types of catalytic combustion type gas sensors used for detecting flammable gases have a configuration in which a gas sensitive part formed by supporting an oxidation catalyst on a carrier made of a metal oxide sintered body is fixed to the surface of a temperature measuring resistor that generates heat by energization, and include a gas detection element. The catalytic combustion type gas sensor has high detection versatility in that it can detect hydrocarbon gases, VOCs (volatile organic compounds), etc. regardless of the type. However, when silicone compounds such as hexamethyldisiloxane and silicone oil, which are poisoning substances, are present in the atmosphere of the measurement target space, the silicone compound is adsorbed and accumulated on the surface of the oxidation catalyst (poisoning), resulting in a problem that the performance (activity) of the oxidation catalyst deteriorates and the detection sensitivity gradually decreases.

[0003] In response to such a problem, for example, it is conceivable to prevent poisoning of the gas detection element by arranging a silicone removal filter. A gas sensor provided with such a silicone removal filter is disclosed in, for example, Patent Document 1.

Prior Art Documents

Patent Documents

[0006] The present invention has been made based on the circumstances described above, and aims to provide a gas sensor capable of detecting a wide range of flammable gases while suppressing the decrease in sensitivity of the gas detection element due to toxic substances. [Means for solving the problem]

[0007] The gas sensor of the present invention comprises a casing having a gas introduction opening, a gas detection element disposed within the casing that produces a change in resistance value upon contact with a gas to be detected, and a filter mechanism that filters the gas to be detected introduced into the casing through the gas introduction opening, wherein the filter mechanism is configured to block the gas introduction opening and supports a photocatalyst, and an ultraviolet light source disposed within the casing that irradiates ultraviolet light to activate the photocatalyst. [Effects of the Invention]

[0008] According to the invention of claim 1, even when used in an environment where a toxic substance, such as a silicone compound, is present, the toxic substance can be decomposed and removed by the action of a photocatalyst without reducing the permeability of the target gas to be detected. Therefore, a decrease in the sensitivity of the gas detection element due to the toxic substance can be suppressed, and highly reliable gas detection can be performed stably over a long period of time.

[0009] According to the invention of claim 2, high silicone poisoning resistance can be obtained, and various flammable gases that are the target gases can be detected with high reliability. According to the invention of claim 3, toxic substances can be reliably removed without reducing the gas permeability of the photocatalytic filter. According to the invention of claim 4, the gas detection element is not affected by thermal effects due to the heat generated by the ultraviolet light source, thus providing high reliability in the detection results. According to the invention of claim 5, even if the gas detection element is equipped with a silicone compound that is poisoned by the silicone compound, it becomes possible to detect the target gas, which is a flammable gas, in an environment where the silicone compound is present. [Brief explanation of the drawing]

[0010] [Figure 1] This figure schematically shows the configuration of an example of a gas sensor according to the present invention. [Figure 2] This figure schematically shows the configuration of an example of a detection circuit for a gas sensor according to the present invention. [Figure 3] This figure shows an example of the gas permeability characteristics of a filter mechanism. [Figure 4] This figure shows the change in sensor output over time for a mixed gas of siloxane and methane. [Modes for carrying out the invention]

[0011] The gas sensor of the present invention is, for example, a gas that detects hydrocarbon gases such as methane, isobutane, pentane, and hexane, hydrogen gas, and other flammable gases; and, For example, alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone and butyl ketone; and volatile organic compounds (VOCs) such as benzene, toluene, and xylene. This is the gas to be detected.

[0012] As shown in Figure 1, the gas sensor 100 according to this embodiment includes a casing 110 having a gas introduction opening 111 that opens on one side, a gas detection element 120 disposed inside the casing 110, and a filter mechanism 130 that filters the gas to be tested introduced into the casing 110 through the gas introduction opening 111.

[0013] As shown in Figure 2, the gas detection element 120 consists of a catalytic combustion type gas detection element, a hot-wire type semiconductor type gas detection element, or a thermal conduction type gas detection element that produces a change in resistance value upon contact with the gas to be detected, and the gas sensing part 121 is formed around a resistance heating element 122 that generates heat when an electric current is applied.

[0014] When the gas detection element 120 is a catalytic combustion type gas detection element, the gas sensing part 121 is constructed by supporting an oxidation catalyst on a support made of a metal oxide sintered body. Examples of metal oxides that can be used to make up the support include ZrO2 (zirconia), Al2O3 (alumina), SiO2 (silica), and zeolite. As the oxidation catalyst, for example, at least one selected from the group consisting of Pt, Pd, PtO, PtO2, and PdO can be used. Furthermore, if the gas detection element 120 is a hot-wire semiconductor type gas detection element, the gas sensing part 121 is made of a sintered metal oxide semiconductor. Moreover, if the gas detection element 120 is a thermal conduction type gas detection element, the gas sensing part 121 is made of, for example, a sintered mixture of glass and an alumina support. The thermal conduction type gas detection element may consist only of a resistance heating element 122. The resistance heating element 122 in the gas detection element 120 is composed of a heater having a coil portion in which metal wires made of, for example, platinum or an alloy thereof are wound in a coil shape.

[0015] This gas sensor 100 is driven, for example, by constant voltage control, and a voltage controlled to a constant magnitude from a power source 125 is applied to a resistance heating element 122, so that the gas sensitive part 121 is heated to a predetermined temperature. At this time, a constant resistance value is maintained in the gas detection element 120. Reference numeral 126 in FIG. 2 is voltage detection means. In the case of a catalytic combustion type gas detection element, when the detected gas contacts the surface of the gas sensitive part 121, the temperature of the surface of the gas sensitive part 121 rises, and the change amount of the resistance value of the resistance heating element 122 generated accordingly is detected by measuring the current value flowing through the current detection resistor 127 by the current detection means 128. In the case of a hot wire type semiconductor gas detection element, when the detected gas contacts the surface of the gas sensitive part 121, the oxygen adsorbed on the surface of the metal oxide semiconductor is desorbed, and the change amount of the resistance value of the metal oxide semiconductor generated accordingly is detected by measuring the current value flowing through the current detection resistor 127 by the current detection means 128. Also, in the case of a thermal conductivity type gas detection element, when the detected gas contacts the surface of the gas sensitive part 121, the state of heat dissipation changes due to the thermal conductivity unique to the gas, and the temperature of the surface of the gas sensitive part 121 changes. The change amount of the resistance value of the resistance heating element 122 generated accordingly is detected by measuring the current value flowing through the current detection resistor 127 by the current detection means 128. The gas sensor 100 may be driven by constant current control. In this case, a current controlled to a constant magnitude from the power source 125 is supplied to the resistance heating element 122, and the change amount of the resistance value of the gas detection element may be detected by measuring the change in voltage.

[0016] The filter mechanism 130 is composed of a photocatalyst filter 131 carrying a photocatalyst and an ultraviolet light source 135 that irradiates ultraviolet light for activating the photocatalyst. The photocatalyst filter 131 is arranged so as to block the gas introduction opening 111. The ultraviolet light source 135 is arranged at a position facing the gas introduction opening 111 in the casing 110.

[0017] The photocatalyst filter 131 is composed of a photocatalyst adhered to the surface of a sheet-like support having air permeability.

[0018] The support is made of, for example, a non-woven fabric. As the non-woven fabric, for example, one that is not easily affected by deterioration such as a decrease in strength due to ultraviolet exposure, such as a glass fiber sheet, can be used. The porosity of the support is preferably, for example, 60 to 95%. The amount of the photocatalyst supported per unit volume of the support is 0.1 g / cm 3 ~0.6 g / cm 3 and is preferably set within the range.

[0019] As the photocatalyst, for example, one mainly composed of titanium oxide (TiO2) particles is used. The photocatalyst preferably contains either or both of noble metal fine particles such as platinum (Pt) and palladium (Pd) and high specific surface area materials such as silica (SiO2) and alumina (Al2O3). When using a photocatalyst containing noble metal fine particles, the content ratio of the noble metal fine particles is preferably, for example, 0.1 to 5.0 wt% based on the weight of the main component, and more preferably 0.1 to 3.0 wt%. Also, when using a photocatalyst containing a high specific surface area material, the content ratio of the high specific surface area material is preferably, for example, 1 to 50 wt% based on the weight of the main component, and more preferably 5 to 15 wt%. By using such a photocatalyst, a toxic substance contained in the test gas, such as a silicone compound, can be surely decomposed and removed. The thickness of the photocatalyst filter 131 is preferably, for example, 0.1 to 5.0 mm, and more preferably 0.4 to 0.8 mm.

[0020] The ultraviolet light source 135 can be any light source that emits ultraviolet light of a wavelength capable of activating the photocatalyst, such as an ultraviolet lamp, an ultraviolet LED, or a laser light source.

[0021] In this embodiment, the ultraviolet light source 135 is arranged thermally separated from the gas detection element 120, and is configured so that the heat generated by the ultraviolet light source 135 is not transferred to the gas detection element 120. Specifically, the gas detection element 120 and the ultraviolet light source 135 are thermally separated by ensuring a sufficient distance between them. Alternatively, the gas detection element 120 and the ultraviolet light source 135 may be thermally separated by, for example, providing a thermal shielding member between them.

[0022] In this configuration, the filter mechanism 130 is configured to allow flammable gases and volatile organic compounds (VOCs) to pass through while removing silicone compounds. As the photocatalytic filter 131, a photocatalyst containing 90 wt% titanium dioxide, 0.2 wt% platinum, and 9.8 wt% silica is applied to the surface of a nonwoven fabric with a porosity of approximately 90% at a concentration of 0.35 g / cm³. 3 Figure 3 shows the gas permeability of methane gas and isopropanol, respectively, when a material is attached with a supported amount and an ultraviolet LED irradiating with ultraviolet light at a wavelength of 365 nm is used as the ultraviolet light source 135. The solid lines in Figure 3 represent the sensor output when no filter is provided, and the dashed line represents the sensor output when a silicone removal filter configured to adsorb and remove silicone compounds is used instead of the photocatalytic filter 131. Also, t1 represents the time when methane gas is introduced, and t2 represents the time when isopropanol gas is introduced.

[0023] As shown in Figure 4, when a catalytic combustion type gas detection element is used as the gas detection element 120 and the above-mentioned photocatalytic filter 131 is used, the degree of decrease in sensor sensitivity (the curve shown by the solid line in Figure 4) when detecting a mixed gas of siloxane gas (cyclotetrasiloxane (D4) and cyclopentasiloxane (D5)) and methane gas is smaller than the degree of decrease in sensor sensitivity (shown by the dashed line in Figure 4) when a silicone removal filter configured to adsorb and remove silicone compounds is used instead of the photocatalytic filter 131. This indicates that the filter mechanism 130 has sufficiently high removal performance for siloxane gas, which is the poisoning substance. Therefore, the gas sensor 100 equipped with the above-described filter mechanism 130 has silicone poisoning resistance and can detect methane gas as the target gas with high reliability. The curve shown by the dashed line in Figure 4 shows the change in sensor sensitivity over time when the filter is not provided.

[0024] As described above, the gas sensor 100 according to this embodiment can selectively decompose and remove silicone compounds by the action of a photocatalyst without reducing the permeability of the target gas, such as flammable gases or volatile organic compounds, even when used in an environment where silicone compounds, which are toxic substances, are present. Therefore, it is possible to suppress the decrease in sensitivity of the gas detection element 120 due to silicone compounds and to stably perform highly reliable gas detection over a long period of time.

[0025] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications can be made. For example, the specific configuration of the gas sensor, such as the positional relationship between the gas detection element and the ultraviolet light source, and the position of the gas introduction opening in the casing (position of the photocatalytic filter), is not limited to that of the above embodiment. [Explanation of symbols]

[0026] 100 Gas Sensors 110 Casing 111 Gas inlet opening 120 gas detection elements 121 Gas-sensitive section 122 Resistive heating element 125 Power supply 126 Voltage detection means 127 Resistor for current detection 128 Current detection means 130 Filter mechanism 131 Photocatalytic filter 135 Ultraviolet light source

Claims

1. A gas sensor comprising a casing having a gas introduction opening, a gas detection element disposed within the casing that produces a change in resistance value upon contact with the gas to be detected, and a filter mechanism that filters the gas to be detected introduced into the casing through the gas introduction opening, The gas sensor is characterized in that the filter mechanism comprises a photocatalytic filter provided to block the gas introduction opening and supporting a photocatalyst, and an ultraviolet light source disposed inside the casing and irradiating ultraviolet light to activate the photocatalyst.

2. The gas sensor according to claim 1, characterized in that the filter mechanism is configured to allow flammable gases and volatile organic compounds to pass through and remove silicone compounds.

3. The gas sensor according to claim 1, characterized in that the photocatalytic filter is formed by attaching a photocatalyst to the surface of a breathable support.

4. The gas sensor according to claim 1, characterized in that the ultraviolet light source is arranged thermally separated from the gas detection element, and the heat generated by the ultraviolet light source is not transmitted to the gas detection element.

5. The gas sensor according to claim 1, characterized in that the gas detection element is a catalytic combustion type gas detection element, a hot-wire type semiconductor type gas detection element, or a thermal conduction type gas detection element.

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