Liquid level sensor

Abstract

To provide a liquid level sensor of which detection accuracy is prevented from dropping by suppressing accumulation of ice on a spacer.SOLUTION: The present invention includes: a transmitting electrode 4 (outer electrode) and a receiving electrode 5 (inner electrode) formed in a cylindrical shape to detect the liquid level of cryogenic liquefied gas stored in a freezing preservation container by a change in capacitance. An insulator spacer 7 is disposed between the transmitting electrode 4 and the receiving electrode 5. The spacer 7 includes a communication hole 8 connecting the upper side and the lower side of the spacer 7 to each other and a surface 7c inclined so that the communication hole 8 gradually decreases in size toward the lower side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a liquid level sensor, and more particularly to a capacitance type liquid level sensor that detects the liquid level of a low-temperature liquefied gas. [Background technology]

[0002] Conventionally, capacitance-type liquid level sensors have been known for detecting the liquid level of low-temperature liquefied gas stored in a cryopreservation container, etc. This liquid level sensor has a sensor unit formed by inserting a cylindrical inner electrode (receiving electrode) into an elongated cylindrical outer electrode (transmitting electrode) that is open at the bottom, and is configured to be able to measure the capacitance between the outer electrode and the inner electrode.

[0003] Furthermore, there has been a technique in which a spacer made of an insulator is placed between the outer electrode and the inner electrode to maintain a constant distance between the outer electrode and the inner electrode (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-60398 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the liquid level sensor of Patent Document 1 mentioned above, when the liquid level sensor is inserted into a cryopreservation container filled with low-temperature liquid gas, the moisture in the air contained within the liquid level sensor, etc., freezes due to the low-temperature liquefied gas, and the resulting ice accumulates at the top of the spacer, which could reduce detection accuracy.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a liquid level sensor that can prevent ice from accumulating on the spacer and prevent a decrease in detection accuracy. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the liquid level sensor of the present invention is a capacitance-type liquid level sensor that detects the height of the liquid level of a liquid stored in a container, and is characterized in that it comprises a cylindrically formed outer electrode and an inner electrode that is provided inside the outer electrode with a gap between them, one of the inner electrode and the outer electrode being a transmitting electrode and the other being a receiving electrode, and it has a spacer made of an insulator to maintain a constant distance between the outer electrode and the inner electrode, and the spacer has an inclined surface that slopes so that the communication hole that connects the upper and lower sides of the spacer gradually becomes smaller toward the downward side.

[0008] The communication hole is a space between the inner peripheral surface of the outer electrode and the outer peripheral surface of the spacer.

[0009] Furthermore, the communication hole is formed penetrating from the upper surface to the lower surface of the spacer.

[0010] It is also preferable that a plurality of the spacers are arranged along the axial direction of the transmitting electrode and the receiving electrode.

[0011] Furthermore, the liquid level sensor of the present invention is a capacitance-type liquid level sensor that detects the liquid level of a liquid stored in a container, and is characterized in that it comprises a cylindrical inner electrode with an open lower end, a cylindrical outer electrode with an open lower end that is arranged on the outer periphery of the inner electrode via a gap, and a cylindrical ground electrode with an open lower end that is arranged on the outer periphery of the outer electrode via a gap, and has spacers that separate and insulate the lower ends of the inner electrode, the outer electrode, and the ground electrode, respectively, and the space between the inner surface of the ground electrode and the outer surface of the spacer is formed as a communicating hole, and the spacer has an inclined surface that slopes toward the communicating hole.

[0012] Furthermore, it is preferable that the spacer has a convex portion inserted into a first gap formed between the inner electrode and the outer electrode and a second gap formed in the gap between the outer electrode and the ground electrode, and that at least a portion of the convex portion has an inclined portion.

[0013] Furthermore, it is preferable to dispose a filling tube for filling the container with low-temperature liquefied gas on the inner periphery side of the inner electrode. [Effects of the Invention]

[0014] According to the liquid level sensor of the present invention, ice that reaches the top of the spacer flows down the inclined surface through the communication hole to the bottom of the spacer and can be discharged to the outside. This makes it difficult for ice to accumulate between the outer electrode and the inner electrode, preventing problems caused by ice and a decrease in detection accuracy. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view of a liquid level sensor showing a first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II of FIG. [Figure 3] 1 is a front view of a spacer used in a liquid level sensor according to a first embodiment of the present invention. [Figure 4] FIG. [Figure 5] FIG. 10 is a schematic cross-sectional view of a liquid level sensor showing a second embodiment of the present invention. [Figure 6] FIG. 10 is a plan view of a spacer used in a liquid level sensor according to a second embodiment of the present invention. [Figure 7] FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6. [Figure 8] FIG. 10 is a plan view of a liquid level sensor showing a third embodiment of the present invention. [Figure 9] FIG. [Figure 10] XX cross-sectional view of FIG. 8. [Figure 11]10 is a cross-sectional view taken along the line XI-XI in FIG. 8. [Figure 12] FIG. 10 is a perspective view of a spacer used in a liquid level sensor according to a third embodiment of the present invention. [Figure 13] FIG. 10 is a perspective view of a spacer showing a fourth embodiment of the present invention. [Figure 14] FIG. 10 is a cross-sectional view of a liquid level sensor showing a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] 1 to 4 are diagrams showing a first embodiment of a liquid level sensor of the present invention. Note that the arrows shown in Fig. 1 indicate the up and down directions, and the left side of the drawing will be referred to as the top in the description.

[0017] The liquid level sensor 1 detects the liquid level of a low-temperature liquefied gas, such as liquid nitrogen, stored in a container such as a cryopreservation container (not shown), and is equipped with a sensor unit 2 inserted into the cryopreservation container, a base unit 3 attached to the top of the sensor unit 2, and a calculation unit (not shown) connected to the base unit 3 for calculating the liquid level.

[0018] The sensor unit 2 includes a long, thin cylindrical transmitting electrode 4 (outer electrode of the present invention) that is open at the bottom and extends in the vertical direction, and a cylindrical receiving electrode 5 (inner electrode of the present invention) that is inserted into the transmitting electrode 4 along the central axis of the transmitting electrode 4, and the outside of the transmitting electrode 4 is covered with a protective cover 6. A plurality of through holes 4a are provided in the side surface of the transmitting electrode 4. Furthermore, a plurality of through holes (not shown) are also provided in the side surface of the protective cover 6.

[0019] In addition, between the transmitting electrode 4 and the receiving electrode 5, a plurality of spacers 7 made of an insulating material such as synthetic resin are arranged along the axial direction of the transmitting electrode 4 and the receiving electrode 5 to keep the distance between the transmitting electrode 4 and the receiving electrode 5 constant.

[0020] 2, the spacer 7 has an oval (elliptical) shape in plan view, and has an insertion hole 7a in the center through which the receiving electrode 5 is inserted. The spacer 7 also has a pair of mounting portions 7b, 7b on its side surface that fit into the inner circumferential surface 4b of the transmitting electrode 4. Furthermore, the space between the inner circumferential surface 4b of the transmitting electrode 4 and the side surface of the spacer 7 other than the mounting portions 7b, 7b forms a communication hole 8 that connects the upper and lower sides of the spacer 7.

[0021] The side surfaces of the spacer 7 other than the mounting portions 7b have inclined surfaces 7c at the upper position and vertical flat surfaces 7d at the lower side. The inclined surfaces 7c are inclined from the central upper end portion 7e of the spacer 7 so that the communication holes 8 become gradually smaller downward.

[0022] When the sensor unit 2 of the liquid level sensor 1 formed as described above is inserted vertically into a cryopreservation container filled with low-temperature liquefied gas, liquid enters the space between the transmitting electrode 4 and the receiving electrode 5 up to the height of the liquid level through the opening at the bottom end, the through-holes on the side of the protective cover 6, and the multiple through-holes 4a in the transmitting electrode 4, creating a region filled with liquid and a region filled with gas in the space between the transmitting electrode 4 and the receiving electrode 5. The region filled with liquid has a higher dielectric constant than the region filled with gas, resulting in a larger capacitance, and therefore the capacitance increases as the liquid level rises. In other words, the capacitance detected by the sensor unit 2 is proportional to the height of the liquid filling the space between the transmitting electrode 4 and the receiving electrode 5, and the liquid level is calculated by the calculation unit based on the capacitance measured by the sensor unit 2.

[0023] When the sensor unit 2 is inserted into a freezing container filled with low-temperature liquid gas, the moisture in the air contained in the sensor unit 2 etc. freezes due to the low-temperature liquefied gas, generating ice, but when the generated ice reaches the top of the spacer 7, it falls along the inclined surface 7c, flows out to the bottom side of the spacer 7 through the communication hole 8, and is finally discharged from the bottom end of the transmitting electrode 4 to the outside of the sensor unit 2. This makes it difficult for ice to accumulate between the transmitting electrode 4 and the receiving electrode 5, making it possible to prevent problems caused by ice when detecting the liquid level and a decrease in detection accuracy.

[0024] 5 to 7 show a second embodiment of the present invention, and the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. Note that the arrows shown in Fig. 5 indicate the up and down directions, and the left side of the drawing will be considered as the top in the description.

[0025] The spacer 12 used in the liquid level sensor 11 of this embodiment is formed in a cylindrical shape and has an insertion hole 12a formed in the center, through which the receiving electrode 5 is inserted. The spacer 12 has an outer diameter that fits closely to the inner circumferential surface 4b of the transmitting electrode 4, and the outer circumferential surface 12b serves as a mounting portion for mounting the spacer 12 between the transmitting electrode 4 and the receiving electrode 5.

[0026] Four communication holes 13 are formed at equal intervals around the periphery of the insertion hole 12a, penetrating from the upper surface 12c to the lower surface 12d of the spacer 12. Furthermore, the inner periphery of each communication hole 13 gradually becomes smaller from the upper surface 12c to the lower surface 12d, forming an inclined surface 12e.

[0027] In the case of the liquid level sensor 11 of the second embodiment, moisture in the air contained in the sensor unit 2 etc. freezes due to the low-temperature liquefied gas, generating ice, but when the generated ice reaches the upper surface 12c of the spacer 12, it falls along the inclined surfaces 12e of each communication hole 13, flows out to the lower side of the spacer 12, and is finally discharged from the lower end of the transmitting electrode 4 to the outside of the sensor unit 2. This makes it difficult for ice to accumulate between the transmitting electrode 4 and the receiving electrode 5, making it possible to prevent malfunctions caused by ice when detecting the liquid level and a decrease in detection accuracy.

[0028] 8 to 12 show a third embodiment of the present invention. A liquid level sensor 21 of this embodiment includes a cylindrical receiving electrode 22 (inner electrode of the present invention) with an open lower end, a cylindrical transmitting electrode 23 (outer electrode of the present invention) that is arranged on the outer periphery of the receiving electrode 22 and has an open lower end, and a cylindrical ground electrode 24 that is arranged on the outer periphery of the transmitting electrode 23 and has an open lower end.

[0029] A plurality of air vents 22a, 23a, 24a for discharging air and vaporized low-temperature liquefied gas are formed above the receiving electrode 22, the transmitting electrode 23, and the ground electrode 24, respectively. A plurality of liquid vents 23b, 24b for introducing low-temperature liquefied gas are formed below the transmitting electrode 23 and the ground electrode 24, respectively. The ground electrode 24 protrudes vertically further than the receiving electrode 22 and the transmitting electrode 23, and the receiving electrode 22 protrudes upward further than the transmitting electrode 23.

[0030] A blocking member 25a that blocks the upper opening of the ground electrode 24 is provided above the ground electrode 24, and a first upper insulator 25b that blocks the upper opening of the receiving electrode 22 is provided above the receiving electrode 22. Furthermore, a second upper insulator 25c that blocks the upper opening is provided between the upper part of the receiving electrode 22 and the upper part of the transmitting electrode 23, and a third upper insulator 25d that blocks the upper opening is provided between the upper part of the transmitting electrode 23 and the upper part of the ground electrode 24. Furthermore, the blocking member 25a is provided with a cable insertion portion 21a through which a cable (not shown) connected to each electrode is inserted.

[0031] Furthermore, in order to maintain a constant distance between the ground electrode 24, the transmitting electrode 23, and the receiving electrode 22, a spacer 26 made of an insulating material such as synthetic resin is provided across the lower part of the ground electrode 24, the lower part of the transmitting electrode 23, and the lower part of the receiving electrode 22.

[0032] The spacer 26 includes a through hole 26a having the same diameter as the inner diameter of the receiving electrode 22, a receiving electrode mounting portion 26b formed on the outer periphery of the through hole 26a and on which the lower end of the receiving electrode 22 is mounted, four support portions 26c provided at equal intervals in the circumferential direction on the outer periphery of the receiving electrode mounting portion 26b, and inclined surfaces 26d provided between adjacent support portions 26c, 26c. The space between the outer periphery 26e of the inclined surface 26d and the inner periphery 24c of the ground electrode 24 forms a communication hole 27 for communicating the low-temperature liquefied gas.

[0033] Each support portion 26c includes an attachment portion 26f that protrudes from the receiving electrode mounting portion 26b toward the ground electrode 24 and is bolted to the inner circumferential surface 24c of the ground electrode 24, a first convex portion 26g that protrudes into a first gap E1 formed between the transmitting electrode 23 and the receiving electrode 22, a second convex portion 26h that protrudes into a second gap E2 formed between the transmitting electrode 23 and the ground electrode 24, and a concave transmitting electrode mounting portion 26i on which the lower end of the transmitting electrode 23 is placed between the first convex portion 26g and the second convex portion 26h. The inclined surface 26d has an outer diameter substantially the same as the outer diameter of the transmitting electrode 23 and is inclined from the receiving electrode mounting portion 26b side toward the communication hole 27.

[0034] When the liquid level sensor 21 described above is inserted into a cryopreservation container filled with low-temperature liquefied gas, the low-temperature liquefied gas is supplied to the inside of the receiving electrode 22, the first gap E1, and the second gap E2 through the through-hole 26a, the communication hole 27, and the inclined surface 26d of the spacer 26, the liquid through-hole 23b of the transmitting electrode 23, and the liquid through-hole 24b of the ground electrode 24. Also, air and vaporized low-temperature liquefied gas inside the liquid level sensor 21 are discharged to the outside of the liquid level sensor 21 through the air vents 22a, 23a, and 24a. Then, the liquid level of the low-temperature liquefied gas is detected by the electrostatic capacitance between the electrodes, which changes with the change in the liquid level as the low-temperature liquefied gas enters the first gap E1.

[0035] Furthermore, the moisture in the air contained within the liquid level sensor 21 freezes due to the low-temperature liquefied gas, generating ice. When the generated ice reaches the top of the spacer 26, it falls along the inclined surface 26d and is discharged to the outside of the liquid level sensor 21 through the communication hole 27. This makes it difficult for ice to accumulate in the first gap E1, preventing problems caused by ice when detecting the liquid level and reducing detection accuracy.

[0036] Figure 13 shows a fourth embodiment in which the spacer 26 of the third embodiment is improved. Components similar to those of the third embodiment are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0037] In the spacer 28 of this embodiment, the first convex portion 28a (inclined portion of the present invention) protruding into the first gap E1 and the second convex portion 28b (inclined portion of the present invention) protruding into the second gap E2 are formed in an arc shape (inclined shape) that convex upward. As a result, when ice formed in the first gap E1 reaches the first convex portion 28a, the ice is guided along the first convex portion 28a to the inclined surface 26d and discharged to the outside of the liquid level sensor through the communication hole 27. Furthermore, when ice formed in the second gap reaches the second convex portion 28b, the ice is guided along the second convex portion 28b to the communication hole 27 and discharged to the outside of the liquid level sensor. As a result, compared to the third embodiment, ice is less likely to accumulate in the first gap E1, preventing problems caused by ice during liquid level detection and reduced detection accuracy.

[0038] In addition, the first convex portion and the second convex portion are not limited to being formed in an arc shape that convex upward, and the upper surfaces of the first convex portion and the second convex portion may be formed as surfaces that slope linearly toward the communicating hole.

[0039] FIG. 14 shows a fifth embodiment of the present invention, in which the same components as those in the third embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0040] The liquid level sensor 31 of this embodiment is integrally connected to a fill tube 32 for filling the cryopreservation container with low-temperature liquefied gas. Insertion holes 33a, 33b for the fill tube 32 are formed coaxially in the center of the closure member 25a and the first upper insulator 25b, and the insertion hole 33b has an inner diameter slightly larger than that of the insertion hole 33a. The fill tube 32 is press-fitted into the insertion hole 33a from above toward the inside of the receiving electrode 22, and the tip side of the fill tube 32 passes through the insertion hole 33b, thereby being integrally connected to the liquid level sensor 31.

[0041] In this embodiment, the liquid level sensor 31 is disposed at a predetermined position in the cryopreservation container, and when low-temperature liquefied gas is supplied from the filling tube 32, the low-temperature liquefied gas is supplied into the cryopreservation container through the opening at the lower end of the receiving electrode 22 and the through-hole 26a of the spacer 26. Furthermore, as the liquid level rises, the low-temperature liquefied gas is introduced into the first gap E1 and the second gap E2 through the liquid through-holes 23b, 24b and the communication hole 27 of the transmitting electrode 23 and the ground electrode 24. Then, as in the third embodiment, the low-temperature liquefied gas enters the first gap E1, and the electrostatic capacitance between the electrodes changes with the change in the liquid level, thereby detecting the liquid level of the low-temperature liquefied gas.

[0042] In the above-described embodiments, the receiving electrode is the inner electrode and the transmitting electrode is the outer electrode, but the present invention is not limited to this, and the receiving electrode may be the outer electrode and the transmitting electrode may be the inner electrode.

[0043] Furthermore, in the above embodiment, liquid nitrogen is used as an example of low-temperature liquefied gas, but the present invention is also applicable to a liquid level sensor that detects the liquid level of low-temperature liquefied gas such as helium, argon, or other inert gas. [Explanation of symbols]

[0044] 1...liquid level sensor, 2...sensor portion, 3...base portion, 4...transmitting electrode, 4a...through hole, 4b...inner peripheral surface, 5...receiving electrode, 6...protective cover, 7...spacer, 7a...insertion hole, 7b...mounting portion, 7c...inclined surface, 7d...flat portion, 7e...central upper end portion, 8...communication hole, 11...liquid level sensor, 12...spacer, 12a...insertion hole, 12b...outer peripheral surface, 12c...upper surface, 12d...lower surface, 12e...inclined surface, 13...communication hole, 21...liquid level sensor, 21a...cable insertion portion, 22...receiving electrode, 22a...air vent, 23...transmitting electrode, 23a...air vent, 23b...liquid vent, 24...ground electrode, 24a...air vent, 24b...liquid vent, 24c...inner circumferential surface, 25a...blocking member, 25b...first upper insulator, 25c...second upper insulator, 25d...third upper insulator, 26...spacer, 26a...through hole, 26b...receiving electrode mounting portion, 26c...support portion, 26d...inclined surface, 26e...outer circumferential surface, 26f...mounting portion, 26g...first convex portion, 26h...second convex portion, 26i...transmitting electrode mounting portion, 27...communication hole, 28...spacer, 28a...first convex portion, 28b...second convex portion, 31...liquid level sensor, 32...filling tube, 33a, 33b...insertion hole

Claims

1. A capacitance-type liquid level sensor that detects the height of a liquid level stored in a container, The magnetron includes an outer electrode formed in a cylindrical shape and an inner electrode provided inside the outer electrode via a gap, one of the inner electrode and the outer electrode is a transmitting electrode, and the other is a receiving electrode; a spacer made of an insulator for maintaining a constant distance between the outer electrode and the inner electrode; The liquid level sensor is characterized in that the spacer has an inclined surface inclined so that a communication hole connecting the upper side and the lower side of the spacer becomes gradually smaller toward the downward side.

2. 2. The liquid level sensor according to claim 1, wherein the communication hole is a space between an inner peripheral surface of the outer electrode and an outer peripheral surface of the spacer.

3. 2. The liquid level sensor according to claim 1, wherein the communication hole is formed so as to penetrate from the upper surface to the lower surface of the spacer.

4. 4. The liquid level sensor according to claim 1, wherein a plurality of the spacers are arranged along the axial direction of the transmitting electrode and the receiving electrode.

5. A capacitance type liquid level sensor that detects the liquid level of a liquid stored in a container, a cylindrical inner electrode having an open bottom end; a cylindrical outer electrode having an open lower end and disposed on the outer circumferential side of the inner electrode via a gap; a cylindrical ground electrode having an open lower end and disposed on the outer circumferential side of the outer electrode via a gap, a spacer that separates and insulates the lower end of the inner electrode, the lower end of the outer electrode, and the lower end of the ground electrode from each other; a space between an inner peripheral surface of the ground electrode and an outer peripheral surface of the spacer is formed as a communication hole, The spacer has an inclined surface that is inclined toward the communication hole.

6. the spacer includes a protrusion that is inserted into a first gap formed between the inner electrode and the outer electrode and a second gap formed in a gap between the outer electrode and the ground electrode, 6. The liquid level sensor according to claim 5, wherein at least a part of the convex portion has an inclined portion.

7. 7. The liquid level sensor according to claim 5, wherein a filling tube for filling the container with low-temperature liquefied gas is disposed on the inner circumferential side of the inner electrode.

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