Sensor

Abstract

Provided is a sensor for use in a vaporizer, the sensor comprising: one or more sensor elements; a first flow path for delivering a fluid from the outside of the sensor to the positions of the sensor elements; and a second flow path for returning, to the outside of the sensor, the fluid delivered through the first flow path to the positions of the sensor elements. As the fluid, a non-gaseous fluid obtained by vaporizing a precursor using the vaporizer is used. The thus provided sensor is usable continuously for a long period of time at temperatures greater than the maximum operating temperature of the sensor elements included in the sensor. A portion of inert gas for purging the interior of a housing of the vaporizer may be used as the fluid. The sensor may further comprise a protective tube that is closed at one end and open at the other end, and the sensor elements may be disposed in the protective tube. In this case, the sensor elements are disposed in at least one of the first flow path or the second flow path. Preferably, at least one of a member composing the first flow path and a member composing the second flow path is composed of a material having a lower thermal conductivity than a member composing the protective tube.

Description

Sensor

[0001] The present invention relates to a sensor for use under high temperatures.

[0002] In the manufacturing process of semiconductor devices such as integrated circuits, various types of semiconductor source gases (hereinafter referred to as "source gases") are used depending on the purpose of the process. For source gases in which the precursor is stored in a liquid or solid state, the precursor is converted into a source gas in a gaseous state using a vaporizer, and then supplied to the semiconductor manufacturing equipment via piping. One example of a method for generating source gas from a precursor in a vaporizer is to heat a precursor stored in a tank to generate vapor.

[0003] Furthermore, with advances in integrated circuit manufacturing technology, there has been an increase in the use of novel material gases that have lower equilibrium vapor pressures and are therefore less likely to vaporize than conventional material gases (see, for example, Patent Document 1). When using such novel material gases, if the temperature of the material gas drops during the process of supplying it from a vaporizer to a semiconductor manufacturing apparatus, the material gas may condense or sublimate, returning to a liquid or solid precursor state, or the precursor adhering to the inner wall of the material gas flow path may dry and solidify, subsequently peeling off from the inner wall and causing particles. Therefore, in order to prevent the material gas from condensing and solidifying within the flow path, attempts have been made to heat the flow path by providing a heater around the material gas flow path.

[0004] As mentioned above, there is a recent trend toward increasing temperatures of precursor and / or material gases in vaporizers.

[0005] On the other hand, vaporizers generally incorporate a valve for starting or stopping the supply of the generated material gas, a flow rate control device for controlling the flow rate of the material gas, and various sensors for detecting the amount of precursor and the properties of the material gas (e.g., temperature, pressure, etc.). For example, a liquid level sensor for detecting the amount of precursor in a liquid state uses a sensor element such as a Hall IC or a reed switch so as to be able to detect the liquid level of the precursor. Many sensor elements, including Hall ICs and reed switches, have a maximum operating temperature, which is the upper limit of the operating temperature at which they can be used over a long period of time while maintaining normal operation.

[0006] For example, semiconductor elements having a pn junction, which is a junction between a p-type semiconductor and an n-type semiconductor, have a property in which their electrical conductivity changes significantly depending on the surrounding environment, and are therefore widely used as sensors. Sensors using semiconductor elements are called semiconductor sensors. There are a wide variety of semiconductor sensors, including, but not limited to, temperature sensors, optical sensors, magnetic field sensors, pressure sensors, and acceleration sensors.

[0007] Patent Document 2, filed by the same applicant, discloses a liquid level sensor for detecting the level of a liquid. This liquid level sensor includes a vertically disposed sleeve, a float configured to move along the sleeve in response to fluctuations in the liquid level, a resistor array, and multiple grounding means configured with Hall ICs, a type of semiconductor sensor. The Hall IC functions as a magnetic field sensor, detecting the magnetic field generated by a magnet provided in the float and grounding the resistor array at the position where the float is located. In this configuration, an electrical signal generated in the resistor array changes in response to fluctuations in the liquid level, and the liquid level can be detected by extracting the electrical signal.

[0008] The temperature of the pn junction of a semiconductor element is called the "junction temperature." If the junction temperature exceeds a certain limit, a large number of electron-hole pairs are generated, preventing the semiconductor element from operating normally. This limit is called the "maximum junction temperature." The maximum junction temperature of a typical semiconductor element is approximately 170°C when heated temporarily. However, to ensure the long-term reliability of a semiconductor sensor, it is recommended that the temperature of the pn junction (junction temperature) be maintained at a predetermined temperature (e.g., 100°C) that is sufficiently lower than the maximum junction temperature. If a semiconductor sensor is used for a long period of time in an environment where the junction temperature exceeds this predetermined temperature, it is necessary to replace the semiconductor sensor with an unused one at short intervals to prevent malfunction.

[0009] Furthermore, the multiple grounding means provided in the liquid level sensor may be configured with reed switches instead of Hall ICs, which are a type of semiconductor sensor, as described above. As is well known to those skilled in the art, a reed switch is configured with two magnetic reeds whose free ends are held at a predetermined distance inside a glass tube or the like. When an external magnetic field is applied, the reeds are magnetized, causing the free ends to attract each other and come into contact, closing the circuit, and when the magnetic field disappears, the elasticity of the reeds causes the free ends to separate and open the circuit.

[0010] Therefore, for example, if the temperature of the reed switch exceeds the Curie temperature of the material that makes up the reed, the magnetic properties of the reed may change, causing the reed switch to malfunction.Furthermore, the elastic modulus of the material that makes up the reed may change depending on the temperature, which may also cause the reed switch to malfunction.

[0011] As described above, not only semiconductor sensors but also many other sensor elements, including reed switches, have a maximum operating temperature, which is the upper limit of the operating temperature at which they can be used over a long period of time while maintaining normal operation. Therefore, in order to continue using the sensor over a long period of time without replacing it, it is preferable to maintain the operating temperature of the sensor so that it does not exceed the maximum operating temperature of the sensor element.

[0012] JP 2009-74108 A International Publication No. 2022 / 004739

[0013] As described above, in order to continue using a sensor for a long period of time without replacing it, it is preferable to maintain the sensor's operating temperature so as not to exceed the maximum operating temperature of the sensor element. However, depending on the sensor's application, there is a need to continuously use the sensor at temperatures higher than the maximum operating temperature. As an example, a liquid level sensor equipped with the Hall IC or reed switch described above may be provided in the tank of a vaporizer. As described above, a vaporizer is a device used to supply material gas to semiconductor manufacturing equipment and the like. The vaporizer's tank stores a liquid material as a precursor to the material gas, and the liquid level is measured by a liquid level sensor.

[0014] When a method of heating a liquid material stored in a tank is adopted as a method of vaporizing a material gas, the liquid level sensor in contact with the liquid material in the tank is typically heated to the same temperature as the liquid material. Some liquid materials require heating to a temperature exceeding the maximum operating temperature of the sensor element in order to achieve the vapor pressure required to supply the material gas. However, as described above, in order to ensure the long-term reliability of the sensor, it is necessary to maintain the operating temperature of the sensor so as not to exceed the maximum operating temperature of the sensor element. For example, in a vaporizer equipped with a liquid level sensor formed by a semiconductor element having a pn junction, there is a problem in that the liquid material cannot be heated and vaporized at a temperature exceeding a predetermined temperature (e.g., 100°C) sufficiently lower than the maximum junction temperature in order to ensure long-term reliability.

[0015] The present invention has been made in consideration of the above-mentioned problems, and one object of the present invention is to provide a sensor that can be used continuously for a long period of time at temperatures that exceed the maximum operating temperature of the sensor element that constitutes the sensor.

[0016] The sensor according to the present invention is a sensor for use in a vaporizer, and includes one or more sensor elements, a first flow path that delivers a fluid from the outside of the sensor to the position of the sensor element, and a second flow path that returns the fluid delivered to the position of the sensor element by the first flow path to the outside of the sensor. Note that the fluid is not a gas obtained by vaporizing a precursor using a vaporizer.

[0017] In this configuration, the sensor element is cooled by the fluid flowing through the first and second flow paths, and the temperature of the sensor element can be maintained lower than the temperature outside the sensor even if the temperature outside the sensor rises to a temperature exceeding the maximum operating temperature of the sensor element.

[0018] In a preferred embodiment, the sensor according to the present invention further includes a protective tube having one closed end and the other open end, and the sensor element is disposed inside the protective tube. In this case, at least one of the members constituting the first flow path and the member constituting the second flow path may be made of a material having a lower thermal conductivity than the member constituting the protective tube. In this configuration, heat is less likely to be transmitted from the outside to the inside of the protective tube, so that the temperature rise of the sensor element can be more reliably suppressed. Furthermore, the sensor according to the present invention can be configured as a liquid level sensor used in a vaporizer.

[0019] As described above, in the present invention, the sensor element is cooled by the fluid flowing through the first and second flow paths. This allows the temperature of the sensor element to be maintained lower than the temperature outside the sensor, even if the temperature outside the sensor rises to a temperature exceeding the maximum operating temperature of the sensor element. Therefore, the temperature at which a sensor including a sensor element is continuously used over a long period of time can be set higher than in the past. This allows the operating temperature of a carburetor using a liquid level sensor including a sensor element to be set higher than the maximum operating temperature of the sensor element.

[0020] FIG. 1 is a schematic diagram illustrating an example of the configuration of a sensor according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the configuration of a sensor according to a first preferred embodiment of the present invention. FIG. 3 is a schematic diagram illustrating the configuration of a sensor according to a second embodiment of the present invention. FIG. 4 is a partial cross-sectional view illustrating an example of a liquid level sensor according to the present invention. FIG. 5 is an assembly view illustrating an example of a liquid level sensor according to the present invention. FIG. 6 is a front view illustrating an example of a main part of a liquid level sensor according to the present invention. FIG. 7 is a partial cross-sectional view illustrating an example of a liquid level sensor according to prior art.

[0021] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description and drawings are merely examples of the preferred embodiments of the present invention, and the preferred embodiments of the present invention are not limited to the preferred embodiments shown in the following description and drawings.

[0022] First Embodiment In a first embodiment, the present invention is an invention of a sensor used in a vaporizer, the sensor comprising one or more sensor elements, a first flow path that delivers a fluid from outside the sensor to the position of the sensor element, and a second flow path that returns the fluid delivered to the position of the sensor element by the first flow path to the outside of the sensor, and in which a non-gaseous fluid obtained by vaporizing a precursor with the vaporizer is used as the fluid.

[0023] The sensor element included in the sensor according to the present invention is an element for detecting, for example, the amount of precursor of a material gas stored in a tank or the like installed inside a vaporizer, or the properties of the material gas (e.g., temperature, pressure, etc.). As described above, many sensor elements have a maximum operating temperature, which is the upper limit of the operating temperature at which the sensor can be used over a long period of time while maintaining normal operation. Therefore, in order to continue using the sensor over a long period of time at temperatures higher than the maximum operating temperature of the sensor element without replacing it, it is necessary to maintain the operating temperature of the sensor element so as not to exceed the maximum operating temperature.

[0024] Specific examples of the sensor element include semiconductor elements such as Hall ICs and reed switches. The semiconductor element included in the sensor according to the present invention is a semiconductor element having a pn junction. As described above, semiconductor elements having a pn junction have the property that their electrical conductivity changes significantly depending on the surrounding environment, and therefore can function as sensors. Examples of the semiconductor element according to the present invention include optical sensors, magnetic field sensors, pressure sensors, and acceleration sensors, but the semiconductor element according to the present invention is not limited to these sensors.

[0025] Furthermore, the semiconductor element included in the sensor according to the present invention is not limited to an element in which only the portion that functions as a sensor is made of a semiconductor having a pn junction. For example, the sensor element itself may not be a semiconductor, but an amplifier or other peripheral circuitry associated with the sensor may be made of a semiconductor, or both the sensor portion and the peripheral circuitry may be made of a semiconductor.

[0026] The number of sensor elements included in the sensor according to the present invention may be one, two, or more. When the sensor according to the present invention includes two or more sensor elements, all the sensor elements may be of the same type, or different types of sensor elements may be mixed.

[0027] FIG. 1 is a schematic diagram showing an example of the configuration of a sensor according to the first embodiment of the present invention. As illustrated in FIG. 1 , the sensor 2s according to the present invention includes a first flow path 3, which is a flow path that delivers a fluid from the outside of the sensor 2s to the position of the sensor element 2, and a second flow path 4, which is a flow path that returns the fluid delivered by the first flow path 3 to the position of the sensor element 2 to the outside of the sensor 2s. The first flow path 3 and the second flow path 4 only need to be configured as continuous spaces, and the shapes of these spaces are not limited. The shapes of the spaces that define the first flow path 3 and the second flow path 4 are preferably shapes that provide low fluid resistance and are unlikely to impede the flow of fluid. The first flow path 3 and the second flow path 4 may be directly connected to each other at the position of the sensor element 2, or may be indirectly connected via a transition portion that is neither the first flow path 3 nor the second flow path 4, as illustrated in FIG. 1 . The first flow path 3 and the second flow path 4 may each be a single system, or each may branch into multiple systems or merge again.

[0028] The first flow path 3 is a flow path that delivers fluid from the outside of the sensor 2s to the position of the sensor element 2. However, the first flow path 3 itself does not necessarily need to reach the position of the sensor element 2 from the outside of the sensor 2s. For example, if there is another flow path that guides the fluid to be delivered to the position of the sensor element 2 from the outside to the inside of the sensor 2s, the fluid may be delivered from the outside of the sensor 2s to the position of the sensor element 2 via that other flow path and the first flow path 3. Furthermore, even if the end of the first flow path 3 on the sensor element 2 side does not reach the position of the sensor element 2, it is sufficient that the flow of fluid released from the first flow path 3 reaches the sensor element 2 and a cooling effect is produced.

[0029] On the other hand, the second flow path 4 is a flow path that returns the fluid delivered to the position of the sensor element 2 by the first flow path 3 to the outside of the sensor 2s. However, the second flow path 4 itself does not necessarily need to reach from the position of the sensor element 2 to the outside of the sensor 2s. For example, if there is another flow path that guides the fluid delivered to the position of the sensor element 2 from the inside to the outside of the sensor 2s, the fluid delivered to the position of the sensor element 2 by the first flow path 3 may be returned to the outside of the sensor 2s via that other flow path and the second flow path 4. Furthermore, even if the end of the second flow path 4 on the sensor element 2 side does not reach the position of the sensor element 2, it is sufficient that the flow of the fluid that has been delivered to the position of the sensor element 2 by the first flow path 3 and warmed by cooling the sensor element 2 leaves the position of the sensor element 2 and is guided to the outside of the sensor 2s via the second flow path 4.

[0030] Due to the action of the first flow path 3 and the second flow path 4 described above, the fluid acting as a heat transfer medium removes heat from the sensor element 2 and releases the heat to the outside of the sensor 2s. Note that either or both of the first flow path 3 and the second flow path 4 according to the present invention may be formed by independent tubular members, or the first flow path 3 and the second flow path 4 may be integrally formed by a single member.

[0031] When operating the sensor 2s according to the present invention to perform sensing, a fluid is supplied to the first flow path 3 as indicated by the open arrows in FIG. 1 , while simultaneously discharging or recovering the fluid from the second flow path 4 as indicated by the filled arrows in FIG. 1 . As described above, the fluid used when using the sensor 2s according to the present invention is a fluid other than a gas obtained by vaporizing a precursor using a vaporizer to which the sensor 2s according to the present invention is applied. Any fluid that has the effect of cooling the sensor element 2 may be used, including any fluid commonly used as a refrigerant. The fluid used in the present invention is preferably a stable substance that has a large heat capacity, is easy to handle, and is unlikely to chemically react with the walls of the first flow path 3 and the second flow path 4. Specifically, an inert gas such as water, air, or nitrogen gas is preferred as the fluid used in the present invention. To achieve the cooling effect of the sensor element 2 according to the present invention, the temperature of the fluid supplied to the sensor 2s must be lower than the temperature around the sensor element 2.

[0032] In the sensor 2s according to the present invention having the above configuration, the sensor element 2 comes into contact with the fluid delivered to the position of the sensor element 2 by the first flow path 3. A portion of the heat transferred from the periphery of the sensor element 2 toward the sensor element 2 is carried away from the position of the sensor element 2 to the outside by the flow of the fluid. Furthermore, the sensor element 2 generally consumes very little power and generates only a small amount of heat. Therefore, the temperature of the sensor element 2 roughly matches the temperature of the fluid, which is the ambient temperature. As a result, even if the ambient temperature of the sensor 2s exceeds the maximum operating temperature of the sensor element 2, the temperature of the sensor element 2 can be maintained lower than the ambient temperature of the sensor 2s. This prevents malfunctions and / or accelerated deterioration of the sensor element due to temperature increases. Therefore, according to the present invention, a sensor 2s can be provided that can be used continuously for a long period of time at temperatures exceeding the maximum operating temperature of the sensor element 2 constituting the sensor 2s.

[0033] 1, the sensor 2s having the sensor element 2 is disposed inside the tank 6 that contains the precursor of the material gas supplied by a vaporizer (not shown). However, the location of the sensor 2s in the vaporizer is not limited to the example shown in Fig. 1, and the sensor 2s can be disposed in a suitable position, such as on the surface or inside of a component of the vaporizer, depending on the physical quantity to be detected by the sensor 2s.

[0034] In the technical field, for example, in a vaporizer for supplying a flammable material gas, there is known a vaporizer that is housed inside a housing and that is configured to purge the inside of the housing by flowing an inert gas into the housing for the purpose of explosion prevention, etc. In such a vaporizer, if the inert gas for purging can also be used to cool the sensor element, this would be desirable because it would be possible to prevent the vaporizer from becoming complicated in configuration and / or the manufacturing costs from increasing.

[0035] Therefore, in a preferred first embodiment, the sensor of the present invention is the sensor described above, in which at least the component constituting the vaporizer on which the sensor is arranged is housed inside a housing, the vaporizer is configured so that the inside of the housing is purged by flowing an inert gas into the inside of the housing, and at least a portion of the inert gas flows into the first flow path and the second flow path as the above-mentioned fluid.

[0036] In this embodiment, specific examples of the inert gas used as a fluid for cooling the sensor element include argon and nitrogen gas, but nitrogen gas is preferred from the viewpoint of reducing operating costs. Furthermore, in this embodiment, the vaporizer already includes a mechanism for supplying the inert gas from the outside to the inside of the housing and discharging the inert gas from the inside to the outside of the housing. Therefore, by supplying the inert gas for purging from the supply flow path for the inert gas for purging to the first flow path and discharging the inert gas from the second flow path through the discharge flow path for the inert gas for purging, a flow path for the fluid for cooling the sensor element can be easily constructed.

[0037] 2A is a schematic diagram illustrating the configuration of a sensor according to a first preferred embodiment of the present invention. In the example shown in FIG. 2A, a sensor 2s is disposed inside a tank 6 constituting a vaporizer (not shown), and the tank 6 is housed inside a housing 10. A first flow path 3 branches off from a supply flow path 11 for supplying a purging inert gas into the housing 10, and a second flow path 4 merges with an exhaust flow path 12 for exhausting the purging inert gas. This allows a portion of the inert gas to flow through the first flow path 3 and the second flow path 4 as a fluid for cooling the sensor element 2.

[0038] 2(b), the sensor 2s is disposed inside the tank 6, and the tank 6 is housed inside the housing 10, similar to the example shown in FIG. 2(a). However, in the example shown in FIG. 2(b), a supply flow path 11 for supplying a purging inert gas to the inside of the housing 10 is directly connected to the first flow path 3, and all of the inert gas is supplied to the first flow path 3. Furthermore, the fluid that has passed the position of the sensor 2 is discharged into the inside of the housing 10 from the second flow path 4, passes through the space inside the housing 10, and is then discharged to the outside of the housing 10 from the discharge flow path 12 for discharging the purging inert gas. This allows all of the inert gas to flow through the first flow path 3 and the second flow path 4 as a fluid for cooling the sensor element 2.

[0039] As a result of the above, this embodiment makes it possible to use the sensor continuously for a long period of time at temperatures exceeding the maximum operating temperature of the sensor element that constitutes the sensor, while suppressing the complexity of the vaporizer configuration and / or increase in manufacturing costs.

[0040] In a first preferred embodiment, the sensor according to the present invention further includes a means for supplying fluid to the first flow path. For example, if the fluid is a compressed gas stored in a cylinder, the means for supplying fluid to the first flow path can be configured with a pressure reducing valve connected to the cylinder for adjusting the gas pressure to an appropriate value, and a pipe or other component for continuously supplying gas to the first flow path maintained at a low pressure. Alternatively, if the fluid is a liquid or a low-pressure gas, the means for supplying fluid to the first flow path can be configured with a pump or other component for forcibly feeding fluid into the first flow path.

[0041] The fluid supplied to the first flow path is delivered to the position of the sensor element and then discharged to the outside from the outlet of the second flow path. The discharged fluid may be discharged directly into the atmosphere or may be recovered using components such as piping and a vacuum pump. The recovered fluid may be discarded as is or may be reused after cooling.

[0042] In a first preferred embodiment, the semiconductor sensor according to the present invention includes a temperature sensor at or near the sensor element. In this configuration, by monitoring the temperature of the sensor element with the temperature sensor, it is possible to monitor whether the temperature of the sensor element exceeds a target value.

[0043] Second Embodiment In a second embodiment, the present invention relates to the sensor according to the first embodiment described above, further comprising a protective tube having one end closed and the other end open, with the sensor element disposed inside the protective tube. The first flow path is configured to deliver fluid from the other end of the protective tube to the endmost sensor element, which is the sensor element closest to one end of the protective tube. The second flow path is configured to return the fluid delivered by the first flow path to the endmost sensor element to the other end. Additionally, the sensor element is disposed in at least one of the first flow path or the second flow path.

[0044] FIG. 3 is a schematic diagram illustrating the configuration of a sensor according to a second embodiment of the present invention. The protective tube 1 included in the sensor 2s illustrated in FIG. 3(a) is a straight tubular member, and a sensor element 2 is disposed therein. In the example illustrated in FIG. 3(a), multiple sensor elements 2 are fixed to the surface of a holding member 2h. The protective tube 1 preferably has sufficient space therein to accommodate the sensor elements 2 and other components. The protective tube 1 serves to protect the sensor element 2 by isolating it from the external environment. One end of the protective tube 1 (the lower end in FIG. 3) is closed, thereby preventing the external environment from entering the interior of the protective tube 1. The other end of the protective tube 1 (the upper end in FIG. 3) is open, allowing electrical signals to be exchanged with the sensor element 2 and for fluid to be supplied to the sensor element for cooling the sensor element 2.

[0045] The protective tube 1 according to the second embodiment is preferably made of stainless steel or another metal or alloy. The thickness of the wall of the protective tube 1 should not be too thin to ensure the strength to maintain the shape of the protective tube 1, and should not be too thick to interfere with the collection of information about the external environment. The protective tube 1 preferably has a sufficient length to allow the sensor element 2 to reach the position where sensing is to be performed.

[0046] 3(a), the first flow path 3 is configured to deliver fluid from the open end (the other end) of the protective tube 1 to the endmost sensor element, which is the sensor element 2 that is closest to the closed end (the one end) of the protective tube 1. On the other hand, the second flow path 4 is configured to return the fluid delivered to the endmost sensor element by the first flow path 3 to the open end (the other end) of the protective tube 1.

[0047] The first flow path 3 shown in Fig. 3(a) delivers fluid from the open end of the protective tube 1 to the position of the endmost sensor element 2 of the sensor elements 2 that is closest to the closed end of the protective tube 1. Here, the endmost sensor element closest to the closed end of the protective tube 1 refers to the sensor element that is located farthest from the open end of the protective tube 1. By delivering fluid to the position of the endmost sensor element using the first flow path 3, it is possible to cool all of the sensor elements 2. The sensor 2s shown in Fig. 3(a) includes multiple sensor elements 2, but if there is only one sensor element 2, it is sufficient for the first flow path 3 to deliver the fluid to the position of that one sensor element.

[0048] As described above, the first flow path 3 does not need to reach the position of the sensor element 2; it is sufficient that the flow of fluid released from the first flow path 3 reaches the sensor element 2 and produces a cooling effect. In the second embodiment, the sensor element is disposed in at least one of the first flow path or the second flow path. When the endmost sensor element is disposed in the second flow path 4, the fluid delivered through the first flow path 3 to a position close to the closed end of the protective tube 1 may then enter the second flow path 4, and the fluid may reach the endmost sensor element inside the second flow path and perform cooling. In this way, the case where the entire first flow path and a part of the second flow path work together to deliver the fluid to the endmost sensor element is also included in the embodiment of the first flow path in the present invention.

[0049] As described above, the second flow path according to the present invention is a flow path that returns the fluid delivered to the position of the sensor element by the first flow path to the outside of the sensor. The second flow path according to the second embodiment returns the fluid delivered to the position of the endmost sensor element by the first flow path to the open end of the protective tube. Because one end of the protective tube is closed, the fluid delivered to the position of the endmost sensor element by the first flow path needs to be returned to the outside of the protective tube again. The second flow path functions as a path for returning the fluid to the outside of the protective tube. Due to the action of the first and second flow paths, heat is removed from the sensor element by the fluid as a heat medium and released to the outside of the protective tube.

[0050] As described above, either or both of the first flow path and the second flow path according to the present invention may be formed by independent tubular members, or the first flow path and the second flow path may be integrally formed by a single member. Alternatively, either the first flow path or the second flow path may be formed by the inner wall of a protective tube.

[0051] In the sensor 2s illustrated in FIG. 3A, a cylindrical second flow path 4 with a closed end and an open end is housed inside the protective tube 1 with its closed end facing the closed end of the protective tube 1. Furthermore, a plurality of sensor elements 2 fixed to a holding member 2h and a cylindrical first flow path 3 are housed inside the second flow path 4, and the endmost sensor element 2 and the downstream end of the first flow path 3 are close to each other near the bottom of the protective tube 1. Therefore, in the sensor 2s illustrated in FIG. 3A, as shown by the outline arrow, the fluid supplied to the upstream end of the first flow path 3 flows from the downstream end of the first flow path 3 to the bottom of the second flow path 4. Of the plurality of sensor elements 2, the endmost sensor element 2 located near the bottom of the second flow path 4 (i.e., near the closed end of the protective tube 1) is first cooled by the fluid. Thereafter, as the fluid flows downstream (upper side in Figure 3) along the second flow path 4, the other sensor elements 2 also come into contact with the fluid and are cooled, and the fluid is discharged to the outside of the sensor 2s from the downstream end of the second flow path 4 (upper end in Figure 3) as shown by the black arrow.

[0052] On the other hand, the sensor 2s illustrated in FIG. 3B has a different configuration from the sensor 2s illustrated in FIG. 3A in that the second flow path 4 is not housed inside the protective tube 1 as an independent component, and does not include the second flow path 4 as an independent component. In the sensor 2s illustrated in FIG. 3B, the fluid supplied to the upstream end of the first flow path 3 flows out from the downstream end of the first flow path 3 to the bottom of the protective tube 1, as indicated by the hollow arrows. Then, of the multiple sensor elements 2, the endmost sensor element 2 located near the bottom of the protective tube 1 (i.e., near the closed end of the protective tube 1) is first cooled by the fluid. Then, as the fluid flows downstream (upper side in FIG. 3 ) along the internal space of the protective tube 1, the other sensor elements 2 also come into contact with the fluid and are cooled. Finally, the fluid is discharged from the open end of the protective tube 1 (upper end in FIG. 3 ) to the outside of the sensor 2s, as indicated by the solid arrows. That is, in the example shown in FIG. 3( b ), the space inside the protective tube 1 functions as the second flow path 4 .

[0053] In the example shown in FIG. 3 , all the sensor elements are arranged in the second flow path. However, as described above, in the sensor according to the second embodiment, the sensor elements are arranged in at least one of the first flow path or the second flow path. Here, "sensor elements arranged in the first flow path or the second flow path" means that all the sensor elements, including the endmost sensor element, are present inside the first flow path or the second flow path, and the surfaces of the sensor elements or their housings are in contact with the fluid flowing through the first flow path or the second flow path, thereby removing heat. In the second embodiment, all the sensor elements are arranged in at least one of the first flow path or the second flow path, and there is no sensor element that is not arranged in either the first flow path or the second flow path. When two or more sensor elements are present, all the sensor elements may be arranged in only one of the first flow path or the second flow path, or they may be arranged distributedly in both the first flow path and the second flow path.

[0054] In a preferred sensor according to the second embodiment, at least one of the components constituting the first flow path and the second flow path is made of a material having a lower thermal conductivity than the material constituting the protective tube. As described above, the fluid flowing through the first flow path and the second flow path functions as a heat medium that suppresses the temperature rise of the sensor element. However, because the temperature outside the protective tube is higher than the temperature of the fluid, the fluid may be heated by heat from outside the protective tube, causing the temperature of the fluid to rise before it is delivered to the position of the sensor element. If at least one of the components constituting the first flow path and the second flow path is made of a material having a lower thermal conductivity than the material constituting the protective tube, heat from outside the protective tube is less likely to be transferred to the fluid, preventing the temperature rise of the fluid and allowing the original cooling function to be exerted.

[0055] In this preferred second embodiment, the material constituting at least one of the components constituting the first flow path and the second flow path may be any material as long as it has a lower thermal conductivity than the material constituting the protective tube. For example, if the protective tube is made of a metal or alloy as described above, by constituting at least one of the first flow path and the second flow path with polytetrafluoroethylene or another fluororesin having a lower thermal conductivity than the protective tube, the increase in the temperature of the fluid can be suppressed. In at least one of the first flow path and the second flow path, the entire flow path may be made of a material having a lower thermal conductivity than the protective tube, or only a portion of the flow path may be made of a material having a lower thermal conductivity than the protective tube. For example, if the flow path is made of multiple components, even if some of the components have a higher thermal conductivity than the material constituting the protective tube, the increase in the temperature of the fluid throughout the flow path can be suppressed as long as the remaining portions have a lower thermal conductivity.

[0056] In this preferred second embodiment, the first flow path and the second flow path themselves may be made of a material having low thermal conductivity. Alternatively, the flow path may have a structure in which multiple tubes are stacked in layers, and a material having low thermal conductivity may be used in some of the layers. Alternatively, the protective tube may have a double structure consisting of an outer tube and an inner tube, and the gap between the two may be a vacuum. This vacuum-maintained space is one embodiment of the "material having a lower thermal conductivity than the components constituting the protective tube" in the present invention. Furthermore, the protective tube may have a double structure consisting of an outer tube and an inner tube, and at least one of the components constituting the first flow path and the second flow path may be made of a material having a lower thermal conductivity than the components constituting the protective tube.

[0057] In a preferred second embodiment, the sensor according to the present invention has a first flow path disposed inside the second flow path. Here, "the first flow path disposed inside the second flow path" means that the component constituting the first flow path is located inside the component constituting the second flow path in a position where it contacts the fluid flowing through the second flow path in the cross section of the protective tube. In this configuration, the fluid first passes through the first flow path disposed inside the second flow path to the position of the endmost sensor element, and then returns through the second flow path to the open end of the protective tube. All sensor elements, including the endmost sensor element, are disposed in at least one of the first flow path or the second flow path and therefore come into contact with the fluid flowing through these flow paths. In this configuration, the outside of the first flow path is surrounded by the fluid flowing through the second flow path, so heat from the outside of the protective tube is not directly transferred to the fluid flowing through the first flow path. This suppresses the temperature rise of the fluid flowing through the first flow path, thereby enhancing the cooling effect of the fluid on the sensor element. As mentioned above, in the sensor 2s illustrated in FIG. 3A, the first flow path 3 is disposed inside the second flow path 4. That is, the sensor 2s illustrated in FIG. 3(a) satisfies the requirements for the sensor according to this preferred embodiment.

[0058] Third Embodiment In a third embodiment, the present invention provides a liquid level sensor for use in a vaporizer, the liquid level sensor comprising: a protective tube having one closed end and the other open end and extending in a vertical direction; one or more sensor elements disposed inside the protective tube; a first flow path that is a flow path configured to deliver a fluid from the other end (open end) of the protective tube to a position of an endmost sensor element that is the sensor element closest to the one end (closed end) of the protective tube among the sensor elements; a second flow path that is a flow path configured to return the fluid delivered to the position of the endmost sensor element by the first flow path to the position of the other end (open end) of the protective tube; and a float that has a magnet and is configured to move along the protective tube in accordance with fluctuations in the liquid level of a precursor that is vaporized into a gas by the vaporizer, the sensor element being disposed in at least one of the first flow path or the second flow path; and the fluid is not a fluid obtained by vaporizing the precursor by the vaporizer.

[0059] In this embodiment, the protective tube is installed vertically and positioned so that its length is aligned with a direction perpendicular to the liquid surface of the liquid (precursor of the material gas to be supplied by the vaporizer) whose liquid level is to be known. A float equipped with a magnet moves along the protective tube as the liquid level changes. The sensor element turns on and off in response to the magnetic field generated by the magnet. By detecting this as an electrical signal, the liquid level at which the float is located can be determined. Specific examples of such a sensor element include a Hall IC and a reed switch. However, the sensor element used in this embodiment is not particularly limited as long as it can output a signal corresponding to the magnetic field generated by the magnet to determine the liquid level at which the float is located.

[0060] In this embodiment, when a fluid is passed through the first and second flow paths, the temperature of all the sensor elements, including the endmost sensor element, is maintained lower than the temperature outside the protective tube, thereby preventing malfunction and deterioration over time due to temperature rise of the sensor elements, as in the first and second embodiments. Since the preferred embodiments of the protective tube, first flow path, second flow path, etc. in the third embodiment are the same as those in the second embodiment, a description thereof will be omitted here.

[0061] The liquid level sensor according to the third embodiment can be used as a liquid level sensor for a tank included in a vaporizer. As described above, when a vaporizer employs a method of heating a liquid material (precursor) stored in a tank to vaporize a material gas, the liquid level sensor in contact with the liquid material in the tank is generally heated to the same temperature as the liquid material. Some liquid materials cannot obtain the vapor pressure required to supply the material gas unless they are heated to a temperature exceeding the maximum operating temperature of the sensor element (e.g., 100°C). By using the liquid level sensor according to the third embodiment, the temperature of the sensor element can be maintained lower than the temperature of the liquid material, even when the liquid material is heated to a temperature exceeding the maximum operating temperature of the sensor element. This allows the vapor pressure of the material gas to be increased while ensuring the long-term reliability of the sensor.

[0062] Although the third embodiment described above is limited to a liquid level sensor, the present invention is not limited to liquid level sensors. The effects of the present invention can be obtained even when the semiconductor sensor in the first embodiment is replaced with an optical sensor, a magnetic field sensor, a pressure sensor, an acceleration sensor, or the like, without departing from the gist of the present invention.

[0063] The following description of an embodiment of the present invention will be given with reference to the drawings, taking a liquid level sensor used in a vaporizer as an example. Note that the following description is merely an example of an embodiment of the present invention, and the present invention is not limited to the scope of the following embodiment.

[0064] FIG. 7 is a partial cross-sectional view showing an example of the structure of a vaporizer equipped with a liquid level sensor according to the prior art disclosed in Patent Document 1. This liquid level sensor is entirely installed inside a tank 6, and includes a protective tube 1 that is closed at one end and open at the other and extends vertically; two or more Hall ICs (semiconductor elements) 2 having a pn junction and disposed inside the protective tube 1; and a float 5 that includes a magnet 5a and is configured to move along the protective tube in response to fluctuations in the liquid level. The tank 6 is filled with a liquid material, and the liquid material is heated by a heater (not shown), vaporizing the liquid material to generate gas. In other words, the liquid material is a precursor of the material gas to be supplied by the vaporizer. The temperature of the liquid material is measured by a temperature sensor 7. However, FIG. 7 shows only the port for inserting the tip of the temperature sensor 7 into the tank 6. The generated gas accumulates in the space above the liquid level inside the tank 6. The gas stored inside the tank 6 can be extracted to the outside of the tank 6 using piping (not shown) and used for various purposes.

[0065] The Hall IC (semiconductor element) 2 is configured to ground the connection point of a resistor string consisting of multiple resistors connected in series. The Hall IC (semiconductor element) 2 is activated by the magnetic field generated by the magnet 5a, changing the resistance value of the resistor string. The level of the liquid material can be detected by extracting an electrical signal corresponding to this resistance value.

[0066] In the vaporizer having the structure shown in Figure 7, the protective tube 1 is made of stainless steel. Air is present around the Hall IC (semiconductor element) 2 inside the protective tube 1. The liquid material stored in the tank 6 is heated to generate gas. When the temperature of the liquid material rises, the temperature of the outer wall of the protective tube 1 in contact with the liquid material first rises, and the heat is transferred to the inner wall of the protective tube 1 by conduction. Next, heat is transferred from the inner wall of the protective tube 1 to the Hall IC (semiconductor element) 2 by conduction, air convection, and electromagnetic radiation.

[0067] The closed end of the protective tube 1 is inserted deep below the liquid surface in the tank 6, and the area around the protective tube 1 is filled with heated liquid material. Since the cross-sectional area of ​​the protective tube 1 is small compared to the area of ​​its outer surface, the amount of heat released from the Hall IC (semiconductor element) 2 arranged inside the protective tube 1 to the outside through the space on the inner diameter side of the protective tube 1 is small compared to the amount of heat transferred from the outside to the inside of the protective tube 1. Therefore, when thermal equilibrium is reached, the temperature of the Hall IC (semiconductor element) 2 rises to a temperature nearly equal to the temperature of the liquid material. For this reason, in the conventional vaporizer shown in Figure 7, in order to avoid damage to the Hall IC (semiconductor element) 2 and / or accelerated aging, it was not possible to raise the temperature of the liquid material to a temperature exceeding the maximum operating temperature (100°C) of the Hall IC (semiconductor element) 2.

[0068] Fig. 4 is a partial cross-sectional view showing an example of the structure of a vaporizer equipped with a liquid level sensor according to the present invention. The basic configuration of this liquid level sensor is the same as that of the conventional vaporizer shown in Fig. 7. Specifically, the liquid level sensor shown in Fig. 4 includes a stainless steel protective tube 1 that is entirely disposed inside a tank 6, has one closed end and the other open end, and extends vertically; two or more Hall ICs (semiconductor elements) 2 that have pn junctions and are disposed inside the protective tube 1; and a float 5 that includes a magnet 5a and is configured to move along the protective tube in response to fluctuations in the liquid level. In addition to the above configuration, the liquid level sensor according to the present invention further includes a first flow path 3 that delivers fluid from the open end of the protective tube 1 to the position of the endmost Hall IC (endmost sensor element) 2b of the Hall ICs (semiconductor elements) 2 that is closest to the closed end of the protective tube 1, and a second flow path 4 that returns the fluid delivered by the first flow path 3 to the endmost Hall IC (endmost semiconductor element) 2b to the open end of the protective tube 1. As in the case of FIG. 7, in FIG. 4, only the port portion of the temperature sensor 7 that measures the temperature of the liquid material is shown.

[0069] 4, the first flow path 3 is disposed inside the second flow path 4. That is, in FIG. 4, the first flow path 3 is configured by a thin tube having an outer diameter sufficiently smaller than the inner diameter of the protective tube 1, and is disposed so as to extend vertically from the open end to the closed end of the protective tube 1. The position of the end of the first flow path 3, which is on the fluid outlet side, on the lower side, is located below the position of the endmost Hall IC (endmost sensor element) 2b, which is closest to the closed end of the protective tube 1, among the multiple Hall ICs (semiconductor elements) 2. No Hall IC (semiconductor element) 2 is disposed inside the first flow path 3.

[0070] In Fig. 4, the space inside the protective tube 1 from the position of the lower tip of the first flow path 3 to the position of the open end of the protective tube 1, excluding the portion of the first flow path 3, constitutes the second flow path 4. All of the Hall ICs (semiconductor elements) 2 are arranged in the second flow path 4. Although omitted in Fig. 4, the liquid level sensor shown in Fig. 4 is equipped with a means for supplying fluid to the first flow path 3.

[0071] 4, a fluid is first supplied from the upper end of the first flow path 3 using a supply means (not shown). The supplied fluid flows downward through the interior of the first flow path 3 and then flows out from the lower end into the second flow path 4 inside the protective tube 1. Next, the fluid flows upward through the second flow path 4 while coming into contact with the row of Hall ICs (semiconductor elements) 2, and is released to the outside from the open end of the protective tube 1.

[0072] In the liquid level sensor according to the present invention shown in FIG. 4 , as described above, a fluid flows inside the protective tube 1. Because the fluid flowing inside the protective tube 1 never stops in one place but is constantly flowing, even if the heat of the liquid material reaches the inner wall of the protective tube 1, there is no heat transfer path for that heat to be transmitted further to the Hall IC (semiconductor element) 2. Furthermore, because the fluid flowing through the first flow path 3 is surrounded by the fluid returning through the second flow path 4, the temperature of the fluid flowing through the first flow path 3 does not increase due to the heat of the heated liquid material. Furthermore, because of the movement of the fluid, a substance, the system does not reach a thermal equilibrium state indefinitely. Due to these effects, the liquid level sensor according to the present invention shown in FIG. 4 can maintain the temperature of the Hall IC (semiconductor element) 2 at a temperature lower than the temperature of the liquid material.

[0073] FIG. 5 is an assembly diagram of the vaporizer equipped with the liquid level sensor illustrated in FIG. 4. In FIG. 5, a sleeve 4a with an outer diameter of 10.0 mm and an inner diameter of 9.0 mm, and a plug 4b with an outer diameter of 9.0 mm that closes the tip of the sleeve 4a, are shown above a stainless steel protective tube 1 with an inner diameter of 10.8 mm. During assembly, the plug 4b is first inserted into the lower end of the sleeve 4a, and then the sleeve 4a is inserted until its lower end contacts the closed end of the protective tube 1. The inner diameter of this sleeve 4a corresponds to the outer diameter of the second flow path 4. Next, the printed wiring board 2a on which the Hall IC (semiconductor element) 2 and a resistor array are arranged, and the elongated thin tube 3a that constitutes the first flow path 3 are fixed together are inserted into the sleeve 4a of the protective tube 1 and fixed in place with a fixing jig.

[0074] FIG. 6 is a front view illustrating the assembled state of the sleeve 4a, plug 4b, printed wiring board 2a, and capillary tube 3a that constitutes the first flow path 3. In FIG. 6(a), a plug 4b is inserted into the lower end of the sleeve 4a. This is to prevent fluid supplied to the lower end of the sleeve 4a through the first flow path 3 from entering the gap between the inner diameter of the protective tube 1 and the outer diameter of the sleeve 4a. The capillary tube 3a that constitutes the first flow path 3 and the sleeve 4a that constitutes the second flow path are both made of fluororesin with low thermal conductivity. The plug 4b is made of a silicone resin sponge. In FIG. 6(b), the lower end of the printed wiring board 2a is inserted into the sleeve 4a, and the capillary tube 3a that constitutes the first flow path 3 is also inserted.

[0075] In the assembled state shown in Figure 6(b), the fluid that has descended through the first flow path 3 is released from the tip of the capillary tube 3a into the inside of the sleeve 4a, and is prevented from descending by the plug 4b, so that it rises toward the top of the sleeve 4a. As shown in Figure 6(a), the lower end of the capillary tube 3a that constitutes the first flow path 3 is cut at an angle, so that even if the tip comes into contact with the plug 4b, the plug 4b does not prevent the fluid from being released. The fluid ascending through the sleeve 4a is first delivered to the position of the endmost Hall IC (endmost sensor element) 2b, then comes into contact with other Hall ICs 2 one after another, and finally reaches the open end of the protective tube 1 where it is released to the outside.

[0076] In this configuration, the sleeve 4a that forms the outer wall of the second flow path 4 is made of a fluororesin with low thermal conductivity, so heat from the inner wall of the protective tube 1 is not easily transferred to the fluid flowing through the second flow path 4. Furthermore, the thin tube 3a of the first flow path 3 disposed inside the second flow path 4 is also made of a fluororesin, and the plug 4b that closes the tip of the sleeve 4a is made of a silicone resin, so almost no heat from the protective tube 1 is transferred to the fluid flowing through the first flow path 3. Therefore, the temperature of the fluid delivered to the endmost Hall IC 2b is almost the same as the temperature of the fluid supplied to the first flow path 3.

[0077]

[0078] Table 1 shows data showing the relationship between the flow rate of nitrogen gas and the temperature of each part when the tank 6 of the vaporizer shown in Figure 4 was empty, the bottom of the tank 6 was heated by a heater (not shown), and nitrogen gas at room temperature was supplied to the first flow path 3 while controlling the temperature detected by the temperature sensor 7 provided in the tank to be 110°C. The temperatures were measured at two locations: on the inner diameter side near the open end of the protective tube 1, and at the position of the Hall IC (semiconductor element) 2 in the row of Hall ICs (semiconductor elements) 2 that was closest to the open end of the protective tube 1. The temperature measurements were taken approximately 10 minutes after the flow rate of nitrogen gas had stabilized, when the temperatures of each part had stabilized.

[0079] The left column of Table 1 shows temperature data for the case where the sleeve 4a and plug 4b shown in Figures 5 and 6 are present. According to this, when the nitrogen gas flow rate was zero, the temperatures of the protective tube 1 and the Hall IC (semiconductor element) 2 were nearly equal, both exceeding 90°C. When nitrogen gas was flowing, the temperature of each part decreased as the flow rate increased, and the temperature difference between the two locations increased. These results show that by using the liquid level sensor of the present invention, the temperature of the Hall IC (semiconductor element) 2 can be maintained at a temperature lower than the tank 6 temperature, even when it exceeds 100°C. It is also clear that flowing nitrogen gas reduces the temperature of not only the Hall IC (semiconductor element) 2 but also the protective tube 1.

[0080] The right column of Table 1 shows the temperature data when the sleeve 4a and plug 4b shown in Figures 5 and 6 are not present. When compared at the same nitrogen gas flow rate, the temperature drop at each part was smaller when the sleeve 4a and plug 4b were not present than when they were present, and the temperature difference was also smaller. This shows that the cooling effect of the Hall IC 2 according to the present invention is greater when the outer wall of the second flow path 4 is formed by the inner wall of the sleeve 4a, which has a low thermal conductivity, than when the outer wall of the second flow path 4 is formed by the inner wall of the protective tube 1.

[0081]

[0082] Table 2 shows data showing the relationship between the flow rate of nitrogen gas and the temperature of each part when the tank temperature detected by the temperature sensor 7 was controlled to 140°C in the same device configuration as Table 1. The left column of Table 2 shows temperature data for the case with the sleeve 4a and plug 4b shown in Figures 5 and 6. This shows that even when the tank temperature is 140°C, the temperature of the Hall IC (semiconductor element) 2 can be cooled to less than 100°C by flowing nitrogen gas at a flow rate of 3.7 slm (standard liters per minute) or more. On the other hand, in the case of the configuration with the sleeve but without the plug shown on the right side of Table 2, it was found that the cooling effect of the nitrogen gas is greater than when the sleeve 4a and plug 4b are used. This is thought to be because the absence of plug 4b allows some of the nitrogen gas supplied to the tip of the first flow path 3 to penetrate into the gap between the protective tube 1 and the outer wall of the sleeve 4a, and the remaining nitrogen gas rises inside the sleeve 4a to cool the Hall IC (semiconductor element) 2, thereby more reliably blocking heat transfer from the outside to the inside of the protective tube 1. That is, in this case, the second flow path 4 branches into two systems.

[0083] In the above-described embodiment, as the flow rate of nitrogen gas supplied to the first flow path increases, the amount of heat released from inside the tank 6 to the outside through the protective tube 1 increases, and so it was necessary to increase the heater output in order to maintain the temperature inside the tank 6. However, according to the data in Tables 1 and 2, the temperature of the tank 6 is maintained at the set temperature even when the flow rate of nitrogen gas is at its maximum. This shows that even when the liquid level sensor according to the present invention is applied to a vaporizer according to the prior art, there is no need to replace the heater with one with a higher heating capacity, and the conventional heater can be used as is.

[0084] According to the embodiment of the present invention described above, the applicable temperature range of the liquid level sensor can be expanded to higher temperatures simply by adding the first flow path, the second flow path, and a fluid supply means, without substantially changing the structure of the liquid level sensor according to the prior art shown in FIG.

[0085] REFERENCE SIGNS LIST 1 Protective tube 2 Sensor element (Hall IC) 2a Printed wiring board 2b Endmost sensor element (endmost Hall IC) 2h Holding member 2s Sensor 3 First flow path 3a Thin tube 4 Second flow path 4a Sleeve 4b Plug 5 Float 5a Magnet 6 Tank 7 Temperature sensor 10 Housing 11 Supply path 12 Discharge path

Claims

1. 1. A sensor for use in a carburetor, comprising: One or more sensor elements; a first flow path that delivers a fluid from the outside of the sensor to the position of the sensor element; a second flow path that returns the fluid delivered to the position of the sensor element by the first flow path to the outside of the sensor; Equipped with At least a member on which the sensor is disposed among members constituting the carburetor is accommodated inside a housing, The vaporizer is configured to flow an inert gas into the interior of the housing to purge the interior of the housing; The sensor is configured such that at least a portion of the inert gas flows as the fluid through the first flow path and the second flow path. Sensor.

2. 1. A sensor for use in a carburetor, comprising: One or more sensor elements; a first flow path that delivers a fluid from the outside of the sensor to the position of the sensor element; a second flow path that returns the fluid delivered to the position of the sensor element by the first flow path to the outside of the sensor; Equipped with the fluid is not a gas obtained by vaporizing a precursor with the vaporizer, A protective tube having one end closed and the other end open, the sensor element is disposed inside the protective tube, the first flow path is configured to deliver the fluid from the other end of the protective tube to an endmost sensor element, which is the sensor element closest to the one end of the protective tube, among the sensor elements; the second flow path is configured to return the fluid delivered to the position of the endmost sensor element by the first flow path to the position of the other end, the sensor element is disposed in at least one of the first flow path and the second flow path, a member constituting the first flow path and a member constituting the second flow path are both made of a material having a lower thermal conductivity than a material constituting the protective tube, The first flow path is disposed inside the second flow path, The protective tube does not constitute a flow path for the fluid. Sensor.

3. The sensor according to claim 1 or 2, The sensor element is a semiconductor element having a pn junction. Sensor.

4. 4. The sensor according to claim 3, The semiconductor element is a Hall IC. Sensor.

5. The sensor according to claim 1 or 2, The sensor element is a reed switch. Sensor.

6. 1. A liquid level sensor for use in a carburetor, comprising: a protective tube having one end closed and the other end open and extending in a vertical direction; One or more sensor elements disposed inside the protective tube; a first flow path configured to deliver the fluid from the other end of the protective tube to a position of an endmost sensor element that is the sensor element closest to the one end of the protective tube among the sensor elements; a second flow path configured to return the fluid delivered to the position of the endmost sensor element by the first flow path to the position of the other end of the protective tube; a float including a magnet and configured to move along the protective tube in accordance with a change in a liquid level of the precursor that is vaporized by the vaporizer to become a gas; Equipped with the sensor element is disposed in at least one of the first flow path and the second flow path, At least a member on which the liquid level sensor is disposed among the members constituting the vaporizer is accommodated inside a housing, The vaporizer is configured to flow an inert gas into the interior of the housing to purge the interior of the housing; The liquid level sensor is configured so that at least a portion of the inert gas flows as the fluid through the first flow path and the second flow path. Liquid level sensor.

7. 1. A liquid level sensor for use in a carburetor, comprising: a protective tube having one end closed and the other end open and extending in a vertical direction; One or more sensor elements disposed inside the protective tube; a first flow path configured to deliver the fluid from the other end of the protective tube to a position of an endmost sensor element that is the sensor element closest to the one end of the protective tube among the sensor elements; a second flow path configured to return the fluid delivered to the position of the endmost sensor element by the first flow path to the position of the other end of the protective tube; a float including a magnet and configured to move along the protective tube in accordance with a change in a liquid level of the precursor that is vaporized by the vaporizer to become a gas; Equipped with the sensor element is disposed in at least one of the first flow path and the second flow path, the fluid is not a fluid obtained by vaporizing the precursor with the vaporizer, a member constituting the first flow path and a member constituting the second flow path are both made of a material having a lower thermal conductivity than a material constituting the protective tube, The first flow path is disposed inside the second flow path, The protective tube does not constitute a flow path for the fluid. Liquid level sensor.

8. The liquid level sensor according to claim 6 or 7, The sensor element is a Hall IC. Liquid level sensor.

9. The liquid level sensor according to claim 6 or 7, The sensor element is a reed switch. Liquid level sensor.

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