JP2017219449A - Liquid level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid level sensor capable of improving a manufacturing property, and improving response speed of liquid level detection by being narrowed as far as possible.SOLUTION: A liquid level sensor 10 includes: a housing 11 which are formed with four through-holes 21-24 having an insulation property and liquid resistance and arranged in parallel with each other; a heating line 12 which has a heating portion 31a heated by energization, and is stored in a folded back state over the two through-holes 21 and 22; a thermocouple 13 which is stored in a folded back state over the other 2 through-holes 23 and 24; an insulation material 20 fitted in each through-hole 21-24; and sealing members 14 and 15 which have an insulation property and liquid resistance, and seal opening end portions of the through-holes 21-24.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a liquid level sensor that detects the height (liquid level) of a liquid stored in a container or the like using a heating element and a thermocouple.

  Conventionally, as a liquid level sensor that detects the height of the liquid level of a liquid stored in a container or the like, a heating element that generates heat by energization and a thermocouple in which a temperature measuring point is disposed adjacent to the heating element are provided. It is known to be composed of a metal cladding tube to be accommodated and to detect the liquid level by measuring the temperature at one temperature measuring point.

  This liquid level sensor detects the liquid level based on the temperature difference between these two states because the amount of heat released from the heating element differs depending on whether the heating element is in liquid or in gas. For example, when the heating element is in a liquid, the amount of heat released is larger than when it is in a gas, so the temperature of the heating element or its vicinity is lower than when the temperature is in the gas. Therefore, the liquid level sensor measures the temperature with a thermocouple, and determines that the liquid level sensor is in the liquid when the measured temperature is lower than a predetermined reference temperature. However, the liquid level sensor according to this configuration may detect the liquid level by mistake because the temperature at the temperature measuring point changes according to the temperature change of the surrounding liquid or gas.

  Therefore, a liquid level sensor that detects a water level based on a temperature difference between two temperature measuring points is known as a liquid level sensor that is hardly affected by changes in ambient temperature. For example, Patent Document 1 below discloses a water level sensor suitable for detecting the water level of a pressure suppression pool of a nuclear reactor plant. The water level sensor includes a cladding tube filled with an insulating material, and a heating wire (heating wire) and a thermocouple embedded in the insulating material in the cladding tube.

  The cladding tube is made of metal and has a bottomed cylindrical shape with one end closed and the other end open. The heating wire is inserted in a state of being folded into a U shape in the cladding tube. Moreover, the thermocouple is also inserted in the state folded in the U shape in the cladding tube. A thermocouple has two dissimilar metal junctions by alternately connecting two different metal wires, one first junction is located near the heating wire, and the other second junction is It is arranged at a position away from the heating wire. Further, the heating wire and the thermocouple are prevented from contacting each other by the insulating material filled in the cladding tube, and the insulation is maintained.

According to the configuration of this thermocouple, the potential difference generated between both ends of the thermocouple is the difference in the thermoelectromotive force between the first junction point and the second junction point. Therefore, by measuring this potential difference, both junction points You can see the temperature difference.
As described in Patent Document 1, when the first joint point and the second joint point are in water, the amount of heat radiation is larger than in the case of being in gas. The temperature of the first junction point and the second junction point arranged outside the heating region are both low, and the temperature difference between the junction points is small. On the other hand, when the first junction point and the second junction point are in the gas, the amount of heat radiation is less than in the case of being in water, so the first junction point arranged in the heating area by the heating wire is more The temperature is higher than the second junction point arranged outside the heating region, and the temperature difference between the junction points is large. Further, the temperature change around the water level sensor has the same effect on both the first junction point and the second junction point, and thus is substantially canceled out. Therefore, the water level sensor can detect the water level regardless of the ambient temperature change.

Japanese Patent Laid-Open No. 10-153681

  In the water level sensor described in Patent Document 1, since the heating wire and the thermocouple are both inserted in a state of being folded back in the cladding tube, four electric wires exist in parallel in the cladding tube. Therefore, when manufacturing the water level sensor, it is necessary to fill the insulating material while keeping the space between the heating wire and the thermocouple in a folded state while inserting them into the cladding tube. In order to perform such work reliably, it is necessary to make the inner diameter of the cladding tube large to some extent, and therefore it is difficult to reduce the diameter of the cladding tube.

  This problem consists of a metal cladding tube that contains a heating element that generates heat when energized and a thermocouple with a temperature measuring point adjacent to it, as described in the background art above. This also occurs in the liquid level sensor.

When the inner diameter of the cladding tube increases, the distance between the thermocouple inside the cladding tube and the external gas or liquid increases, and the influence of the external temperature hardly reaches the thermocouple. Therefore, the response of the thermocouple to an external temperature change may be reduced, and the response speed of water level detection may be deteriorated.
On the other hand, when the inner diameter of the cladding tube is reduced, it becomes difficult to prevent the contact between the heating wire and the thermocouple, and the manufacturability of the water level sensor is deteriorated. In other words, there is a trade-off relationship between the diameter reduction of the cladding tube and the manufacturability of the water level sensor.

  The present invention has been made in view of such circumstances, and a liquid level sensor that can improve manufacturability and can be formed as thin as possible to improve the response speed of liquid level detection. The purpose is to provide.

(1) The liquid level sensor of the present invention has an insulating and liquidproof property, and a housing in which four through holes are arranged in parallel with each other;
A heating wire that has a heating portion that generates heat when energized and is housed in a folded state across the two through holes;
A thermocouple housed in a folded state across the other two through holes;
An insulating material filled in each through hole;
It has insulation and liquid-proof property, and is provided with the sealing member which seals the opening end of the said through-hole.

  According to the above configuration, when the liquid level sensor is manufactured, the thermocouple and the heating wire are accommodated in the four through holes formed in the housing, respectively, so that the portions of the thermocouple and the heating wire that are parallel to each other can be obtained. Arranged so as not to touch. Therefore, it is not necessary to house the thermocouple and the heating wire while paying attention to mutual contact in one tube of the cladding tube as in the conventional case, and the manufacturability of the liquid level sensor can be improved.

  In addition, since the contact between the thermocouple and the heating wire at the time of manufacture does not become a problem, it becomes possible to form the casing as thin as possible. When the casing is formed thin, the heat capacity of the casing is reduced, The distance between the heating wire and the outside of the liquid level sensor is reduced. By reducing the heat capacity of the housing, the temperature drop of the housing when the liquid level sensor is submerged in the liquid and the temperature rise of the housing when exiting into the gas are accelerated, and in addition, By reducing the distance from the outside, heat dissipation when submerged in the liquid is increased, and the temperature drop of the housing is further accelerated. Thus, since the temperature change of the housing at the time of submerging in the liquid and exiting into the gas is accelerated, the response speed of the liquid level detection can be improved. In addition, since heat radiation in the gas is originally small, an increase in the heat radiation amount in the gas due to a reduction in the distance between the heating wire and the outside is slight, and this increase does not adversely affect the response speed.

(2) The thermocouple includes a first temperature measuring point and a second temperature measuring point accommodated in the through hole, and the first temperature measuring point and the second temperature measuring point are the through hole. It is preferable that the first temperature measuring point is arranged closer to the heat generating part than the second temperature measuring point.
According to this configuration, the first temperature measuring point is located close to the heat generating part, and the second temperature measuring point is arranged away from the heat generating part. As described above, the water level is detected regardless of the surrounding temperature change. Since the thermocouple in which the distance between the first temperature measuring point and the second temperature measuring point is determined in advance is inserted into the through hole, the mounting operation of the thermocouple can be facilitated.

(3) The casing is preferably made of ceramics.
As a result, it is possible to easily manufacture a casing in which four through holes are formed in advance, and it is also possible to make the casing thinner. In general, ceramics have a lower thermal conductivity than metal, so when a two-point temperature measurement type thermocouple is used as in (2) above, the heat of the heat generating part that heats the first temperature measurement point. Becomes difficult to be transmitted to the second temperature measuring point through the housing. Therefore, the distance between the two temperature measuring points can be reduced, and the liquid level sensor can be shortened in the axial center direction (hereinafter referred to as “long axis direction”) of the through hole of the housing.

(4) The four through holes are arranged side by side in the vertical and horizontal directions in a cross-sectional view, and the heating wire is accommodated in the two adjacent through holes, and the other two through holes adjacent to each other. It is preferable that the thermocouple is accommodated.
With such a configuration, the heating wire and the thermocouple are accommodated in each through hole so as not to cross each other at the portion folded back over the two through holes, so that the heating wire and the thermocouple are in contact with each other. There is no need to pay attention and manufacturing can be carried out efficiently.

(5) It is preferable that the said heat_generation | fever part is formed in the coil shape.
With such a configuration, the amount of heat generated per unit length of the heat generating portion (hereinafter referred to as “heat generation density”) can be increased, and the liquid level detection accuracy can be improved. In addition, since the heat generation density can be increased by forming the heat generating portion in a coil shape, when using the two-point temperature measurement type thermocouple as described in (2) above, the heat generating portion is formed to be shorter and two measurement results are obtained. The interval between the hot spots can be reduced, and the liquid level sensor can be shortened in the major axis direction of the casing.

  According to the liquid level sensor of the present invention, manufacturability can be improved and the response speed of liquid level detection can be improved by making the casing as thin as possible.

It is explanatory drawing which shows the usage condition of the liquid level sensor which concerns on one Embodiment of this invention. It is a perspective view of the liquid level sensor shown partially broken. It is a front view of a liquid level sensor. It is a figure which shows the AA line cross section of FIG. 3 in the state which looked at the insulating material transparently. It is a figure which shows the BB line cross section of FIG. 3 in the state which looked at the insulating material transparently. It is CC sectional view taken on the line of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory diagram showing a usage pattern of a liquid level sensor according to an embodiment of the present invention.
The liquid level sensor 10 of the present embodiment is a large container such as a pressure container used for a nuclear power plant, or a small liquid container used for home appliances, regardless of its use or the size of the container. It is used to detect the height (liquid level) of the liquid. The liquid level sensor 10 can be used to detect the liquid level in the container regardless of the type of liquid stored in the container, such as water or oil.

  In the example shown in FIG. 1, the liquid level sensor 10 is attached to a wall portion 72 of a liquid storage container 71 that stores a liquid L via a support member 73. Cables 18 and 19 with insulation coating are connected to the liquid level sensor 10, and power supply and transmission / reception of electric signals are performed via the cables 18 and 19. The liquid level sensor 10 is attached at a position corresponding to the lowest liquid level of the liquid storage container 71, for example, and detects that the liquid in the liquid storage container 71 has reached the lowest liquid level.

FIG. 2 is a perspective view (partially sectional view) of the liquid level sensor 10 shown with a part broken away, and FIG. 3 is a front view of the liquid level sensor 10. 4 is a cross-sectional view taken along line AA in FIG. 3, FIG. 5 is a cross-sectional view taken along line BB in FIG. 3, and FIG. 6 is a cross-sectional view taken along line CC in FIG. 4 and 5, the insulating material 20 is shown transparently so that the arrangement state of the thermocouple 13 and the coil portion 31a in the internal space of the through holes 21 to 24 can be understood.
As shown in FIGS. 2 and 3, the liquid level sensor 10 includes a housing 11, a heating wire 12, a thermocouple 13, sealing members 14 and 15, covering members 16 and 17, and cables 18 and 19. And an insulating material 20.

  The casing 11 is formed of a material having insulating properties (property that does not conduct electricity) and liquidproof properties (property that does not allow liquids to pass; waterproofness, oilproofness, etc.). For example, the housing 11 is formed of ceramics which is a sintered body made of alumina, magnesia, silica, or a mixture thereof. However, the casing 11 is not limited to these materials, and any other material (glass, synthetic resin, or the like) can be employed as long as it is a material having insulating properties and liquid-proof properties. Moreover, the housing | casing 11 has the rigidity which can hold | maintain own shape. The housing 11 of this embodiment is formed in a cylindrical shape. For example, the housing 11 is formed in an elongated cylindrical shape having an outer diameter of 1.2 mm and a length of 15 mm.

  In the housing 11, four through holes 21 to 24 are formed along the axial direction (longitudinal direction). The through holes 21 to 24 penetrate the housing 11 in the axial direction and open at both ends of the housing 11 in the axial direction. Each through-hole 21-24 is circular in cross section, and has a fixed internal diameter over the whole longitudinal direction. Further, the four through holes 21 to 24 are formed to have the same inner diameter. In the following description, one side of the casing 11 in the longitudinal direction is referred to as an upper side and the other side is referred to as a lower side.

  As shown in FIG. 4, the four through holes 21 to 24 are arranged in a quadrangular shape (square shape) in a cross-sectional view. That is, the four through holes 21 to 24 are arranged at equal intervals two by two vertically and horizontally. Further, the four through holes 21 to 24 are arranged at equal intervals from the center (axial center) X of the housing 11 and at equal intervals around the center X. In the following description, the two through holes 21 and 22 adjacent to each other are referred to as first and second through holes, and the other two through holes 23 and 24 adjacent to each other are referred to as third and fourth through holes. That's it.

  As shown in FIG. 5, the heating wire 12 is accommodated in the first through hole 21 and the second through hole 22. The heating wire 12 has a resistance wire 31 and a conducting wire 32. The resistance wire 31 has coil portions (heat generating portions) 31a wound in a coil shape at two locations in the length direction. Each coil part 31a is accommodated in the lower side of the first through hole 21 and the second through hole 22, respectively. Between the two coil parts 31a, it is made into the strand which is not formed in the coil shape, protrudes from the opening of the lower end of the 1st through-hole 21 and the 2nd through-hole 22, and both through-holes 21 and 22 are carried out. It is bridged between.

  As the resistance wire 31, a resistance wire having a nominal resistance value of 100Ω, specifically, an existing platinum resistance wire used for a resistance temperature detector incorporating Pt100 (conforming to JIS C1604-1997) is adopted. However, the resistance wire 31 of the present embodiment is stipulated in current or past domestic standards and international standards such as JIS C1604 (established in 2013), ASTM E1137 (established in 1995), IEC60751 (established in 2008), etc. A thing may be adopted. From the viewpoint of high versatility, it is preferable to employ a platinum resistance wire used for the resistance temperature detector defined in the currently established standard. In addition, as the platinum resistance thermometer wire employed for the resistance wire 31, for example, an ultrafine diameter of 50 μm or less is preferably used, and in this embodiment, a 25 μm wire is employed. The platinum used for this platinum resistance wire may be of any type as long as it conforms to the above standards, but in the present embodiment, it contains impurities that inevitably remain, but is substantially close to 100% purity. Things are used.

  The lower end of the conducting wire 32 of the heating wire 12 is connected to the upper end of the coil portion 31a accommodated in the first and second through holes 21 and 22, respectively. Further, the upper end portion of each conductive wire 32 protrudes from the opening at the upper end of the first and second through holes 21 and 22. The upper end of each conducting wire 32 is connected to the internal conducting wire 18 a of the power cable 18. A connection portion a between the coil portion 31 a and the conductive wire 32 is disposed at a substantially central portion in the longitudinal direction of the first and second through holes 21 and 22. Therefore, in the heating wire 12, one coil part 31a and the conducting wire 32 are accommodated in the first through hole 21, the other coil part 31a and the conducting wire 32 are accommodated in the second through hole 22, and the lower end is substantially U. It is in a folded state in a letter shape. In other words, the heating wire 12 is accommodated in a state of being folded back across the two through holes 21 and 22.

  An insulating material 20 is filled in the first and second through holes 21 and 22 in which the heating wires 12 are accommodated. The insulating material 20 mechanically holds the heating wire 12 and functions as a heat medium for increasing the thermal conductivity and improving the responsiveness. In the present embodiment, it is composed of an inorganic insulating material powder made of alumina, magnesia, silica, or a mixture thereof. As the inorganic insulating material powder of the insulating material 20, for example, it is preferable to use an alumina powder that has a relatively high thermal conductivity and is inexpensive.

  The lower ends and the upper ends of the first and second through holes 21 and 22 in which the heating wires 12 are accommodated are sealed by sealing members 14 and 15, respectively. The sealing members 14 and 15 are formed of a material having insulating properties and liquid-proof properties. For example, the sealing members 14 and 15 can use an adhesive mainly composed of alumina, magnesia, silica, zircon, or a mixture thereof. Further, enamel (glass bottle) such as epoxy resin may be used. The sealing members 14 and 15 prevent liquid from entering the first and second through holes 21 and 22 and prevent leakage of the insulating material 20 filled in the through holes 21 and 22.

  The lower sealing member 14 is provided so as to cover the resistance wire 31 protruding from the lower end openings of the first and second through holes 21 and 22. The upper sealing member 15 is provided so as to cover the lower side of the conducting wire 32 protruding from the upper end openings of the first and second through holes 21 and 22. The upper end portion of the conducting wire 32 protrudes upward from the sealing member 15.

  The two conducting wires 32 protruding from the sealing member 15 are connected to the pair of power cables 18. The power cable 18 is connected to a power supply for supplying power to the heating wire 12. The power cable 18 is formed by coating the outer surface of an internal conductor 18a such as a copper wire with a liquid-proof insulating coating 18b, and the lower end portion of the internal conducting wire 18a protruding from the insulating coating 18b is connected to the conductive wire 32. The conductive wire 32 and the internal conductive wire 18 a are covered with the covering member 16. The covering member 16 is formed in a rectangular parallelepiped shape, specifically, a thin plate shape.

  The covering member 16 is formed of a material having insulating properties and liquid-proof properties, for example, a synthetic resin material. More specifically, the covering member 16 is formed of a fluororesin (in particular, FEP). However, the covering member 16 is not limited to a fluororesin, and can be formed of a known synthetic resin material having insulating properties and liquid-proof properties such as silicon rubber and ethylene propylene rubber.

  The covering member 16 covers the conductor 32 protruding from the sealing member 15, the internal conductor 18 a of the power cable 18, the connection portion b thereof, and the lower end portion of the insulating coating 18 b of the power cable 18. . The lower end portion of the covering member 16 is inserted into the sealing member 15 and bonded thereto.

  As shown in FIG. 6, the thermocouple 13 has two types of thermocouple wires 41 and 42 made of different metals. Specifically, the thermocouple 13 includes one first thermocouple wire 41 and two second thermocouple wires 42, and a second thermocouple is connected to both ends of the first thermocouple wire 41. Line 42 is connected. One joining portion c between the first thermocouple wire 41 and the second thermocouple wire 42 is a first temperature measuring point, and the other joining portion d is a second temperature measuring point. And the thermocouple 13 detects temperature using the thermoelectromotive force which generate | occur | produces with the temperature difference of the 1st temperature measuring point c and the 2nd temperature measuring point d. As the thermocouple 13 of this embodiment, for example, a K-type thermocouple is adopted. Specifically, the first thermocouple wire 41 is an alumel wire, and the second thermocouple wire 42 is a chromel wire. However, the thermocouple 13 is not limited to a K-type thermocouple, and may be another type of thermocouple such as a T-type thermocouple.

  As the second thermocouple wire 42, the internal conductor 19a of the pair of thermocouple cables 19 is used. The thermocouple cable 19 is connected to an instrument that measures the thermoelectromotive force generated in the thermocouple 13. The thermocouple cable 19 is formed by coating the outer surface of the internal conductor 19a with a liquid-proof insulating coating 19b. On the lower side of the pair of thermocouple cables 19, the internal conducting wire 19 a protrudes from the insulating coating 19 b, and the lower end of the internal conducting wire 19 a is joined to both ends of the first thermocouple wire 41.

  The thermocouple 13 is accommodated in the third and fourth through holes 23 and 24. Specifically, the thermocouple 13 is accommodated across the third and fourth through holes 23 and 24 in a state where the thermocouple 13 is folded in a U shape below the housing 11. The first temperature measurement point c is disposed in the fourth through hole 24, and the second temperature measurement point d is disposed in the third through hole 23. More specifically, the first temperature measurement point c is disposed on the lower side of the fourth through hole 24, and the second temperature measurement point d is disposed on the upper side of the third through hole 23. Therefore, the first temperature measuring point c and the second temperature measuring point d are arranged with a space in the vertical direction (longitudinal direction of the housing 11).

  Further, since the first temperature measuring point c is disposed on the lower side of the fourth through hole 24, it is closer to the coil portion 31a of the heating wire 12 accommodated in the first and second through holes 21 and 22. Thus, since the second temperature measuring point d is arranged on the upper side of the third through hole 23, it is further away from the coil portion 31 a of the heating wire 12. Therefore, the heat of the coil part 31a is more easily transmitted to the first temperature measuring point c than the second temperature measuring point d.

An insulating material 20 is filled in the third and fourth through holes 23 and 24 in which the thermocouple 13 is accommodated. The insulating material 20 mechanically holds the thermocouple 13. The insulating material 20 is the same as that filled in the first and second through holes 21 and 22.
Further, the lower and upper ends of the third and fourth through holes 23 and 24 are sealed by the sealing members 14 and 15 described above, respectively.

The lower sealing member 14 also covers the first thermocouple wire 41 protruding from the lower end openings of the third and fourth through holes 23 and 24. The upper sealing member 15 also covers the second thermocouple wire 42 protruding from the upper end openings of the third and fourth through holes 23 and 24.
The second thermocouple wire 42 (19 a) protruding upward from the upper sealing member 15 and the lower end portion of the insulating coating 19 b covering the second thermocouple wire 42 (19 a) are covered with the covering member 17. The covering member 17 is made of the same material and shape as the covering member 16 described above. The lower side of the covering member 17 is inserted into the sealing member 15 and bonded thereto.

A liquid level detection method by the liquid level sensor 10 having the above configuration will be described.
In the liquid level sensor 10, the first temperature measuring point c of the thermocouple 13 is heated more than the second temperature measuring point d when the coil portion 31 a of the heating wire 12 generates heat by energization via the power cable 18. The thermocouple 13 generates a thermoelectromotive force according to the temperature difference between the first and second temperature measuring points c and d. The thermoelectromotive force generated in the thermocouple 13 is measured by a meter (not shown) via the thermocouple cable 19.

As shown in FIG. 1, when the liquid level sensor 10 is present in the liquid, the first temperature measuring point c and the second temperature measuring point d are both cooled by the liquid, so that there is almost no temperature difference between the two c and d. Absent. Therefore, no thermoelectromotive force is generated in the thermocouple 13.
On the other hand, when the liquid in the liquid storage container 71 decreases and the liquid level sensor 10 is exposed to the gas, the first temperature measuring point c is heated by the coil portion 31a of the heating wire 12, and therefore the second temperature measuring point. The temperature difference from d increases and a thermoelectromotive force is generated in the thermocouple 13. Therefore, it is possible to detect that the liquid in the liquid storage container 71 has decreased from the liquid level sensor 10 by detecting the thermoelectromotive force.

  In the liquid level sensor 10, the casing 11 is formed of a material having insulating properties and liquid-proof properties, and four through holes 21 to 24 are formed therein, and the heating wires 12 and 24 are formed in the through holes 21 to 24. A thermocouple 13 is accommodated. Therefore, the contact between the heating wire 12 and the thermocouple 13 is prevented only by housing the through holes 21 to 24 and the insulation is maintained. Therefore, when manufacturing the liquid level sensor 10, it is not necessary to house these in the housing 11 while paying attention to the contact between the heating wire 12 and the thermocouple 13, and the liquid level sensor 10 is easily manufactured.

  Further, since the contact between the heating wire 12 and the thermocouple 13 does not become a problem, the housing 11 can be formed as thin as possible (the outer diameter is reduced). If the housing 11 is formed thin, the housing 11 And the distance between the heating wire 12 and the outside of the liquid level sensor 10 is reduced. Since the heat capacity of the housing 11 is reduced, the temperature drop of the housing 11 when the liquid level sensor 10 is submerged in the liquid and the temperature rise of the housing 11 when the liquid level sensor 10 comes out into the gas are accelerated. By reducing the distance between the heating wire 12 and the outside, heat dissipation when immersed in the liquid is increased, and the temperature drop of the housing 11 is further accelerated. Thus, since the temperature change of the housing | casing 11 at the time of immersing in a liquid and coming out in gas becomes quick, the response speed of the liquid level detection by the liquid level sensor 10 can be improved. Since heat radiation in the gas is originally small, an increase in the heat radiation amount in the gas due to a reduction in the distance between the heating wire 12 and the outside is slight, and this increase does not adversely affect the response speed.

  The housing 11 is made of ceramics made of a sintered body such as alumina. This ceramic has a lower thermal conductivity than metal. For example, the housing 11 has a thermal conductivity of about 10% of stainless steel. Therefore, the heat of the coil portion 31 a of the heating wire 12 is difficult to be transmitted through the housing 11. Therefore, it becomes difficult for the heat of the coil part 31a to be transmitted to the second temperature measuring point d of the thermocouple 13 further away from the coil part 31a, and the first temperature measuring point c and the first temperature measuring point c when the liquid level sensor 10 is in the gas. A sufficient temperature difference between the two temperature measuring points d can be secured. Therefore, the interval between the first temperature measurement point c and the second temperature measurement point d can be shortened, and the length of the liquid level sensor 10 can also be shortened.

  Since the heating wire 12 includes a heating portion including the coil portion 31a, the heat generation density can be increased. Therefore, the temperature difference between the first temperature measurement point c and the second temperature measurement point d can be increased, and the liquid level detection accuracy can be increased. In addition, since the first temperature measuring point c can be sufficiently heated even if the coil portion 31a is made shorter, the interval between the first temperature measuring point c and the second temperature measuring point d is shortened, and the liquid level sensor This is effective for reducing the size of 10.

  Accordingly, the liquid level sensor 10 of the present embodiment can be reduced in length in addition to making the casing 11 thinner, so that the liquid level sensor 10 can be further downsized. Therefore, it can be suitably used for detecting the liquid level in the small liquid storage container 71.

The heat treatment apparatus of the present invention is not limited to the above embodiment, and can be appropriately changed within the scope of the invention described in the claims.
For example, the casing 11 of the above embodiment has a perfect cross-sectional outer shape, but is not limited thereto, and may be formed in an elliptical shape or the like. The housing 11 is not limited to a cylindrical shape, and may be formed in a prismatic shape. The through-holes 21 to 24 of the above embodiment have a perfect circular shape in cross section, but may be formed in an elliptical shape or the like, or may be formed in a polygonal shape. The four through holes 21 to 24 are not limited to be arranged (arranged) in a square shape in a cross-sectional view, but may be arranged in a rectangular shape or a rhombus shape. However, in order to make the casing 11 thinner and more easily, it is more preferable that the through holes 21 to 24 are arranged in a square shape in a cross-sectional view.

  The heating wire 12 and the thermocouple 13 may be accommodated in the through holes 21 to 24 positioned diagonally to each other. For example, the heating wire 12 may be accommodated in the first and third through holes 21 and 23, and the thermocouple 13 may be accommodated in the second and fourth through holes 22 and 24. However, in this case, since the heat generation wire 12 and the thermocouple 13 cross below the casing 11 and the possibility of contact with each other increases, the first and second through holes 21 adjacent to each other as in the above embodiment. More preferably, the heating wire 12 is accommodated in the second through holes 22, and the thermocouple 13 is accommodated in the third and fourth through holes 23, 24.

As for the thermocouple 13, both the 1st temperature measuring point c and the 2nd temperature measuring point d may be accommodated in the same through-hole.
The liquid level sensor 10 of the present invention may be a one-point temperature measuring type having a temperature measuring point only in the vicinity of the heat generating portion 31a of the heating wire 12. In this case, the liquid level can be detected by measuring the temperature change between when the temperature measuring point is in the liquid and when it is in the gas.
Further, the present invention does not preclude the provision of a covering member made of metal or the like on the outer surface of the housing 11 in order to further increase the strength and durability of the liquid level sensor 10.

10: Liquid level sensor 11: Housing 12: Heating wire 13: Thermocouple 14: Sealing member 15: Sealing member 20: Insulating material 21: First through hole 22: Second through hole 23: Third through hole 24 : 4th through-hole 31a: Coil part (heat generating part)
L: Liquid c: First temperature point d: Second temperature point

Claims (5)

A casing having four through-holes that are insulative and liquid-proof and arranged in parallel with each other;
A heating wire that has a heating portion that generates heat when energized and is housed in a folded state across the two through holes;
A thermocouple housed in a folded state across the other two through holes;
An insulating material filled in each through hole;
A liquid level sensor comprising: a sealing member that has an insulating property and a liquid-proof property and seals an opening end of the through hole.   The thermocouple includes a first temperature measuring point and a second temperature measuring point accommodated in the through hole, and the first temperature measuring point and the second temperature measuring point are the length of the through hole. 2. The liquid level sensor according to claim 1, wherein the liquid level sensor is arranged at intervals in a direction, and the first temperature measuring point is arranged closer to the heat generating portion than the second temperature measuring point.   The liquid level sensor according to claim 1 or 2, wherein the casing is made of ceramics.   The four through-holes are arranged two by two in a cross-sectional view, and the heating wires are accommodated in two adjacent through-holes, and the other two through-holes are adjacent to each other. The liquid level sensor according to any one of claims 1 to 3, wherein a pair is accommodated. The liquid level sensor according to claim 1, wherein the heat generating portion is formed in a coil shape.

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