JP2010096692A - Liquid level sensor of liquefied gas and cryopreservation container - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor of a liquefied gas, preventing heat from transmitting to a cryogenic liquefied gas in a container to reduce an amount of evaporation of the gas. <P>SOLUTION: A cable of a plastic optic fiber 21 having a liquid level detecting part for detecting a liquid level of the cryogenic liquefied gas is accommodated in a sleeve 20. The sleeve 20 has: a lower sleeve 20a inserted into a liquid phase of the cryogenic liquefied gas; an upper sleeve 20b provided in a gaseous phase of the gas; and a bent tube 20c provided between an upper part of the upper sleeve 20b and a lower part of the lower sleeve 20a in a gaseous phase above the highest point of the liquid level of the cryogenic liquefied gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquefied gas level detecting device and a cryopreservation container, and more particularly, to a liquid level detecting device for detecting a liquid level of a low-temperature liquefied gas stored in a heat insulating container and the liquid level detecting device. It relates to the cryopreservation container used.

In the fields of medicine, culture, food, and the like, various samples are cryopreserved by cooling with a low-temperature liquefied gas such as liquefied nitrogen. As a heat-insulated container for cryopreservation, a special cryopreservation container equipped with a liquid supply line, a temperature sensor, and a liquid level sensor is used to automatically control the temperature in the container. (For example, refer to Patent Document 1). In addition, various types of liquid level sensors (liquid level detection devices) are used depending on the application, but in recent years, liquid level detection devices using optical fiber sensors are widely used as what can be provided at low cost. (For example, see Patent Document 2).
Japanese Patent Laying-Open No. 2005-249309 JP 2002-131115 A

  The cryopreservation container described in Patent Document 1 is effective for a large-scale stationary facility because piping and wiring are connected to the container itself, but there is a problem in cost in a small-scale facility. It was difficult to carry around. For this reason, a sample is frozen and stored using a bottle-shaped insulated container having a volume of several liters to several tens of liters so that it can be carried. When such a portable container is used, since the liquid level sensor as described in Patent Document 1 cannot be mounted, the liquid amount can be calculated by measuring the total weight of the container, An appropriate liquid level detector, for example, an optical fiber sensor as disclosed in Patent Document 1, is inserted to check the liquid amount.

  Although the method of measuring the weight of the container has an advantage that the amount of liquid can be continuously monitored, those capable of performing precise measurement are generally expensive and problematic in terms of cost. On the other hand, the optical fiber sensor can be configured relatively inexpensively. However, since the liquid level detector at the bottom of the sensor must be inserted into the low-temperature liquefied gas, the low-temperature liquefied gas is introduced by heat penetration from the optical fiber sensor. There was a problem that the amount of evaporation increased.

  Accordingly, the present invention provides a liquid level detector for a liquefied gas that can suppress heat from being transmitted to the low-temperature liquefied gas in the container and can suppress the evaporation amount of the liquefied gas, and a cryopreservation container using the liquid level detector. It is intended to provide.

  In order to achieve the above object, the liquid level detection device of the present invention stores the cable of the liquid level detection means having a liquid level detection unit for detecting the liquid level of the low-temperature liquefied gas stored in the heat insulating container in the sheath tube, In the liquid level detection device for detecting the liquid level by inserting the sheath tube into the heat insulation container, the sheath tube includes a lower sheath tube inserted into the liquid phase of the low-temperature liquefied gas, and the heat insulation container. An upper sheath tube disposed in the gas phase, and a bent tube provided between the upper portion of the upper sheath tube and the lower portion of the lower sheath tube in the gas phase above the highest level of the liquid level of the low-temperature liquefied gas It has the part.

  The heat insulating container has a heat insulating tank between an outer tank and an inner tank, and the inner tank is connected to a cylindrical container body through a conical portion whose upper diameter is reduced at the upper part of the container body. A neck portion formed in a cylindrical shape having a smaller diameter than the container body, an opening portion provided at an upper end of the neck portion, and a lid member attached to the opening portion, and the lower sheath tube is It may be disposed in the container body, the upper sheath tube may be disposed in the neck portion, and the bent tube portion may be bent along the inner peripheral wall of the conical portion. Preferably, the lower sheath tube is provided in parallel with the axis of the heat insulating container, and the distance between the inner surface of the upper sheath tube and the outer surface of the lower sheath tube is smaller than the inner diameter of the neck portion. The upper end of the sheath tube is locked to the upper end of the opening. It can also be held in the serial insulated container.

  The lid member has a plug portion to be inserted into the neck portion, and an outer periphery of the plug portion is between the inner peripheral surface of the neck portion when the plug portion is inserted into the neck portion. It is preferable that a plurality of concave grooves into which the sheath tube can be inserted are provided in the axial direction.

  Further, the liquid level detection means may be formed of a plastic optical fiber, and seals a gap between the outer periphery of the cable and the inner periphery of the sheath tube above the highest level of the liquid level. You can also.

  The sheath tube may have a through hole in a peripheral wall at a position corresponding to the liquid level detection unit, and includes a temperature sensor that detects the temperature of the gas phase part above the highest level of the liquid level. The lower sheath tube and the bent tube portion may be made of metal, and the upper sheath tube may be made of nonmetal. Further, it is preferable that the heat insulating container is a cryopreservation container and the liquefied gas is liquefied nitrogen.

  Further, the cryopreservation container of the present invention is a cryopreservation container using the above-described liquid level detection device for liquefied gas, and is engaged with the upper end of the opening at the upper part of the sheath tube, and the outside of the lid member. And a main body part of a liquid level detecting device having a liquid level display part outside the heat insulating container, and the cable drawn from the outer end of the locking pipe part. It is connected to the main body.

  The liquid level detection device of the present invention provides the entire sheath tube by providing a bent tube portion in the gas phase between the lower sheath tube inserted into the liquid phase and the upper sheath tube disposed in the gas phase. Compared to the case of forming with a straight pipe, the sheath pipe of the gas phase portion can be lengthened and the heat transport amount can be reduced, so that the evaporation amount of the low-temperature liquefied gas due to heat penetration can be suppressed. In addition, by bending the bent tube portion along the conical portion of the container, it is possible to prevent the object to be frozen such as the cryopreserved sample from getting in and out of the heat insulating container.

  Furthermore, by using a plastic optical fiber as the liquid level sensor, the plastic optical fiber can be easily accommodated in the sheath tube along the bent shape of the sheath tube without damaging it, and the cost required for processing can be reduced. it can. In addition, by sealing the gap between the outer periphery of the cable and the inner periphery of the sheath tube with an adhesive or the like above the highest level of the liquid level, heat can be transmitted through the gap between the cable and the sheath tube. Can be prevented. Furthermore, the state of a liquid level detection part can be easily confirmed by providing a through-hole in the position corresponding to the liquid level detection part of a sheath pipe surrounding wall. Further, by providing a temperature sensor capable of detecting the temperature of the gas phase part, the state in the container can be known more reliably. Furthermore, the heat insulation of a sheath pipe can be improved by making an upper sheath pipe nonmetallic.

  In addition, by applying the above-described liquid level detection apparatus to a cryopreservation container for cryopreserving various samples, the amount of liquefied nitrogen evaporated can be suppressed as much as possible, and the sample can be cryopreserved satisfactorily. Furthermore, when the cryopreserved sample is taken in and out, it is possible to take out the sheath tube while leaving it in the container, so that an increase in the temperature of the sheath tube can be avoided.

  1 to 5 show an example of a cryopreservation container equipped with the liquid level detection device of the present invention. FIG. 1 is a sectional front view of the cryopreservation container, and FIG. 2 is a sectional view taken along line II-II in FIG. 3 is a cross-sectional view of the main part of the liquid level detection device, FIG. 4 is an explanatory view of the main part of the liquid level sensor, and FIG. 5 is a front view of the cryopreservation container.

  The cryopreservation container 10 is a heat insulating container in which a heat insulating layer is formed between an outer tank 11 and an inner tank 12, and the inner tank 12 is formed in a cylindrical container body 13 and an upper portion of the container body 13. Is integrally formed with a neck portion 15 provided continuously through a conical portion 14 having a reduced diameter. The outer tub 11 is integrally formed with a cylindrical portion 11a that accommodates the container main body 13 via a heat insulating material and a reduced diameter portion 11b whose upper diameter is reduced to accommodate the neck portion 15, and a reduced diameter portion. The upper end portion of 11b and the upper end portion of the neck portion 15 are welded to connect the outer tub 11 and the inner tub 12. Further, a pair of grips 11c and 11c are projected from the upper surface of the reduced diameter portion 11b.

  An upper end opening 15 a of the neck portion 15 where the upper end portion of the outer tub 11 is welded is detachably fitted with a lid member 16, and the lid member 16 is attached to a cap 17 detachably provided on the upper portion of the outer tub 11. Covered. In addition, a liquid level detection device 18 for detecting the liquid level of liquid nitrogen stored in the container main body 13 is inserted into the cryopreservation container 10.

  The lid member 16 includes a plug portion 16a made of a heat insulating material that is inserted into the neck portion 15 having a smaller diameter than the container body 13, and a lid portion that is provided above the plug portion 16a and closes the upper end opening 15a of the neck portion 15. 16b. The plug portion 16a is formed in a substantially cylindrical shape having a diameter slightly smaller than the inner diameter of the neck portion 15, and is provided at equal intervals in the circumferential direction with six concave grooves 16c continuous in the container axial direction opened to the outer peripheral side. It has been. The liquid level detection device 18 is inserted into one of the concave grooves 16c, and holding members 19 for holding the object to be frozen in the container body 13 are inserted into the other five, respectively. Is formed with an opening 16d through which the liquid level detection device 18 is inserted.

  The cap 17 includes a circular fixing portion 17a provided surrounding the upper opening of the outer tub 11, and a cap portion 17b detachably fitted to the upper portion of the fixing portion 17a. Is formed with an opening 17c through which the liquid level detection device 18 is inserted.

  The liquid level detection device 18 accommodates four sets of U-type liquid level detection means having different lengths in the sheath tube 20 and a thermocouple (not shown) as one temperature sensor. Configured. The sheath tube 20 includes a lower sheath tube 20a inserted into the liquid phase of the liquefied nitrogen, an upper sheath tube 20b disposed in the gas phase in the inner tank 12, and the highest level of the liquid level of the liquefied nitrogen. It has a bent tube portion 20c provided between the upper portion of the upper sheath tube 20b and the lower portion of the lower sheath tube 20a in the upper gas phase.

  The lower sheath tube 20a is disposed in the container body 13, the upper sheath tube 20b is disposed in the concave groove 16c of the plug portion 16a disposed in the neck portion 15, and the bent tube portion 20c is disposed in the conical portion 14. It is bent along the inner peripheral wall. Further, the upper sheath tube 20b has a heat insulation performance higher than that of metal and is formed of a non-metallic material that can be used even at a low temperature, for example, epoxy resin or glass fiber, and the lower sheath tube 20a and the bent tube portion 20c are bent. It is formed integrally by bending a metal tube, such as a stainless steel tube, which is easy to process and drill.

  In this embodiment, the upper sheath tube 20b and the lower sheath tube 20a are provided in parallel to the axis L1 of the container body 13, and the container inner surface of the upper sheath tube 20b and the container outer surface of the lower sheath tube 20a. The distance D1 with the side surface is made smaller than the inner diameter D2 of the neck portion 15, and the sheath tube 20 can be inserted into the container main body 13 through the neck portion 15 having a smaller diameter.

  Further, a locking portion 20d bent in the horizontal direction is connected to the upper end of the upper sheath tube 20b, and the locking portion 20d is locked to the upper end opening 15a of the neck portion 15 so that the sheath tube 20 is While being held by the heat insulating container 10, the front end side of the locking portion 20 d protrudes outside the heat insulating container 10 through the opening 16 d of the lid member 16 and the opening 17 c of the cap 17, and is provided separately. Connected to the detection device main body 22.

  At the upper end of the bent tube portion 20c, a vent hole 20e is formed, and the lower sheath tube 20a has four detection holes 20f and 20g in the vertical direction so that the liquid level can be detected in five stages. , 20h, 20i are formed.

  The plastic optical fiber 21 is folded in a U shape, and the U-shaped portion 21a is used as a liquid level detecting portion, and is configured by partially removing the clad of the U-shaped portion 21a. The four sets of plastic optical fibers 21 are arranged at positions corresponding to the detection through holes 20f, 20g, 20h, and 20i, respectively, with U-shaped portions 21a formed in the lower sheath tube 20a of the sheath tube 20. The U-shaped portion 21a of the long plastic optical fiber 21 is at the position of the detection through hole 20i arranged at the lowermost position, and the U-shaped portion 21a that is shortened in order at the positions of the detection through holes 20h and 20g is the shortest U-shaped. The portions 21a are respectively arranged at the positions of the detection through holes 20f at the uppermost position. The thermocouple housed in the sheath tube 20 is provided with a temperature measuring contact at the tip at a position near the through hole 20e formed in the bent tube portion 20c.

  Further, as shown in FIG. 3, the inner periphery of the upper sheath tube 20b of the sheath tube 20 and the outer periphery of the cable portion of each plastic optical fiber 21 inserted into the upper sheath tube 20b or the cable portion of the thermocouple. In between, the adhesive A1 is filled and sealed.

  The holding member 19 is inserted into the concave groove 16c of the plug portion 16a, a support portion 19a protruding into the container body 13 from the concave groove 16c, and a knob protruding from the base end of the support portion 19a toward the outer peripheral side of the neck portion. It includes a portion 19b and a net-like canister 19c connected to the tip of the support portion 19a and containing a material to be frozen. The canister 19c has a shape and size that can be removed from the neck portion 15 with the lid member 16 removed from the upper end opening 15a, the plug portion 16a removed from the neck portion 15, and the upper sheath tube 20b of the sheath tube 20 remaining. Formed.

  The liquid level detection device main body 22 contains a light emitting part, a light receiving part, a control circuit, etc. corresponding to the plastic optical fiber 21 and the thermocouple, respectively. As shown in FIG. Is connected to the upper sheath tube 20b through the connecting portion 24, suspended from the cryopreservation container 10 by the attachment strap 25, and connected to the power cable 26 and the signal cable 27. . In the liquid level detection device main body 22, the liquid level detected by the liquid level detection device 18 is displayed on the liquid crystal portion, and the temperature measured by the thermocouple is displayed on the temperature display portion 22a.

  The liquid level of liquefied nitrogen detected by the four sets of plastic optical fibers 21 is a region below the detection through hole 20i, a region between the detection through holes 20i and 20h, and a region between the detection through holes 20h and 20g. The LED 22b in the rectangle arranged in five stages indicating the region between the detection through holes 20g and 20f and the region above the detection through hole 20f is turned on corresponding to the liquid level position. Is displayed. In addition, four small LEDs 22c are turned on according to liquid level drop, temperature abnormality, liquid level sensor disconnection, temperature sensor disconnection, and the like. Further, these pieces of information are transmitted to an external control device or the like via the signal cable 27.

  In the cryopreservation container 10 formed as described above, a predetermined amount of liquefied nitrogen is introduced into the container body 13, and the lower sheath tube 20 a and the bent tube portion 20 c of the liquid level detection device 18 and the cryopreserved material of the holding member 19 are stored. Are inserted into the container body 13 respectively. At this time, the sheath tube 20 and the holding member 19 can be disposed at predetermined positions by providing circumferential grooves corresponding to the respective concave grooves 16c of the plug portion 16a on the upper surface of the upper end opening 15a.

  Then, the plug portion 16 a is attached to the neck portion 15 while the upper sheath tube 20 b of the sheath tube 18 of the liquid level detection device 18 and the support portion 19 a of each holding member 19 are inserted into each concave groove 16 c of the plug portion 16 a. The lid portion 16b of the lid member 16 is mounted on the upper surface of the plug portion 16a, the locking portion 20d is protruded from the opening portion 16d of the lid portion 16b, and the locking portion 20d is locked to the upper end opening 15a. 20 is held in the heat insulating container 10. Further, the cap portion 17b is fitted to the fixing portion 17a in a state where the locking portion 20d of the liquid level detection device 18 is projected from the opening 17c of the cap 17. The liquid level detection device main body 22 is provided on the front surface of the frozen storage container 10 by hanging the mounting strap 25 on the reduced diameter portion 11b of the outer tub 11.

  The liquefied nitrogen contained in the cryopreservation container 10 naturally evaporates as the cryopreservation time becomes longer, so that the liquid level is lowered. The change in the liquid level of the liquefied nitrogen is detected using the change in the return light between when the U-shaped portion 21a of each plastic optical fiber 21 is in the liquid phase and when it is in the gas phase. That is, when the U-shaped portion 21a of the optical fiber 21 is in the liquid phase, light diffuses from here, and the amount of light detected by the light receiving portion changes, so that the liquid level can be detected. Thereby, with respect to the detection through holes 20f, 20g, 20h, 20i corresponding to the U-shaped portions 21a, the liquid level of the liquefied nitrogen is a region below the detection through holes 20i, the detection through holes 20i, The liquid level detection device main body is located in any of the region between 20h, the region between the detection through holes 20h and 20g, the region between the detection through holes 20g and 20f, and the region above the detection through hole 20f. 22 LEDs 22b.

  Further, the temperature of the gas phase region is detected by the thermocouple and displayed on the temperature display portion 22 a of the liquid level detection device main body 22. By monitoring the gas phase temperature in the container, the temperature in the cryopreservation container 10 has risen and it has become difficult to properly preserve the object to be cryopreserved, for example, in the heat insulation layer of the cryopreservation container 10. It is possible to detect that an abnormality has occurred and heat intrusion has occurred, and it is possible to quickly respond to an abnormal temperature rise.

  When taking out the object to be frozen from the cryopreservation container 10, the cap part 17 b and the lid member 16 are sequentially removed from the fixing part 17 a and the neck part 15, respectively, and the plug part 16 a is removed from the neck part 15. Next, holding the knob 19b, the support 19a of the holding member 19 is moved and rotated, the positions of the canister 19c and the neck 15 are aligned, and the canister 19c is pulled out of the neck 15 to take out the object to be frozen.

  In the liquid level detection device 18 described above, the bent pipe portion 20c is provided in the gas phase between the lower sheath tube 20a inserted into the liquid phase of liquefied nitrogen and the upper sheath tube 20b disposed in the gas phase. Compared with the case where the entire sheath tube is formed as a straight tube, the sheath tube in the gas phase can be lengthened and the amount of heat transport can be reduced, so that the amount of liquefied nitrogen evaporation due to heat penetration can be suppressed. Therefore, the sample can be cryopreserved satisfactorily. Further, by bending the bent tube portion 20c along the conical portion 14 of the container main body 13, there is no hindrance when the object to be frozen such as a cryopreserved sample is taken in and out of the heat insulating container.

  Furthermore, by adopting the plastic optical fiber 21 as the liquid level sensor, the plastic optical fiber 21 can be easily inserted along the bent shape of the sheath tube 20 without being damaged and accommodated in the sheath tube. The cost required can be reduced.

  Further, the gap between the cable and the sheath tube 20 is formed by sealing the space between the outer periphery of the cable of the plastic optical fiber 21 and the inner periphery of the sheath tube 20 with the adhesive A1 above the highest level of the liquid surface. Heat can be prevented from passing through. Furthermore, by providing a through hole at a position corresponding to each U-shaped portion 21a, which is a liquid level detection portion, on the peripheral wall of the sheath tube, it functions as a gas vent hole and can prevent erroneous detection. In addition, the presence or absence of disconnection of the plastic optical fiber 21 can be easily confirmed. Furthermore, it is possible to easily confirm the state of the liquid level detection unit, that is, whether or not the U-shaped portion 21a is in a proper position. Further, by providing a temperature sensor for detecting the temperature of the gas phase portion, the state in the container body 13 can be known more reliably.

  Further, the lower sheath tube 20a and the bent tube portion 20c for performing bending and drilling are made of metal, and the upper sheath tube 20b is made of a non-metallic heat insulating material such as epoxy resin or glass fiber, thereby The processing can be easily performed and the heat insulation can be further improved. Furthermore, when the cryopreserved sample is taken in and out, the sheath tube 20 can be taken out while remaining in the container, so that an increase in the temperature of the sheath tube 20 can be avoided.

  In the above-described embodiment, the upper sheath tube is formed of epoxy resin, glass fiber, or the like. However, since the heat transport amount can be reduced by the bent tube portion, the entire sheath tube may be a stainless steel tube. . Further, the object to be frozen may be arranged in either the liquid phase region or the gas phase region.

  Furthermore, the liquid level detection device of the present invention is not limited to detecting the liquid level of liquefied nitrogen in a cryopreservation container as described above, but various low-temperature liquefied gas such as liquefied nitrogen, liquefied argon, liquefied helium, liquefied oxygen, etc. It can be applied to a storage container, and the bent tube portion of the sheath tube is not limited to the inner wall of the container, but can be formed in a spiral shape or a zigzag shape according to the shape of the container. The liquid level sensor stored in the sheath tube is not limited to the optical fiber type, but may be a capacitance type, a diode type, or a thermocouple type using the Seebeck effect. Further, the optical fiber sensor unit is not limited to the U-shaped one as in the above-described embodiment, and the optical fiber sensor unit has a prism at the end of two optical fibers, or the optical fiber end has a wedge shape. What is to be processed, one in which grooves (V-shaped, U-shaped, etc.) are cut at predetermined intervals in the length direction of the optical fiber, and the diameter of the optical fiber is gradually reduced toward the end. It may be processed. The optical fiber may be made of quartz. Further, the present invention is not limited to the liquid level detection of a non-pressure container such as a cryopreservation container, but can be used for a high pressure container or the like by appropriately devising the opening of the container and the structure of the liquid level gauge.

It is a cross-sectional front view which shows one example of the cryopreservation container to which the liquid level detection apparatus of this invention is applied. It is II-II sectional drawing of FIG. It is a principal part sectional drawing of a liquid level detection apparatus similarly. It is a principal part explanatory drawing of a liquid level sensor similarly. It is a front view of a cryopreservation container similarly.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Cryopreservation container, 11 ... Outer tank, 11a ... Cylindrical part, 11b ... Reduced diameter part, 11c ... Handle, 12 ... Inner tank, 13 ... Container main body, 14 ... Conical part, 15 ... Neck part, 15a ... Upper end opening 16 ... Lid member, 16a ... Plug part, 16b ... Lid part, 16c ... Groove, 16d ... Opening part, 17 ... Cap, 17a ... Fixing part, 17b ... Cap part, 17c ... Opening, 18 ... Liquid level detection device , 19 ... Holding member, 19a ... Supporting part, 19b ... Picking part, 19c ... Canister, 20 ... Sheath pipe, 20a ... Lower sheath pipe, 20b ... Upper sheath pipe, 20c ... Bent pipe part, 20d ... Locking part, 20e ... Through hole, 21 ... Plastic optical fiber, 21a ... U-shaped part, 22 ... Liquid level detecting device main body part, 22a ... Temperature display part, 22b, 22c ... LED, 23 ... Connecting pipe, 24 ... Connecting part, 25 ... Installation Strap, 26 ... Power cable 27 ... signal cable, A1 ... adhesive

Claims (12)

The cable of the liquid level detecting means having a liquid level detecting unit for detecting the liquid level of the low-temperature liquefied gas stored in the heat insulating container is housed in the sheath tube, and the liquid level is detected by inserting the sheath tube into the heat insulating container. In the liquid level detecting device, the sheath tube includes a lower sheath tube inserted into a liquid phase of the low-temperature liquefied gas, an upper sheath tube disposed in a gas phase in the heat insulating container, and the low-temperature liquefied gas. A liquefied gas liquid characterized by having a bent pipe portion provided between an upper part of the upper sheath tube and a lower part of the lower sheath tube in a gas phase above the highest level of the liquid surface Surface detection device. The heat insulating container has a heat insulating tank between an outer tank and an inner tank, and the inner tank is connected to a cylindrical container body through a conical portion whose upper diameter is reduced at the upper part of the container body. A neck portion formed in a cylindrical shape having a smaller diameter than the container body, an opening portion provided at an upper end of the neck portion, and a lid member attached to the opening portion, and the lower sheath tube is 2. The device according to claim 1, wherein the tube body is disposed in the container body, the upper sheath tube is disposed in the neck portion, and the bent tube portion is bent along an inner peripheral wall of the conical portion. Liquid level detector for liquefied gas. The upper sheath tube and the lower sheath tube are provided in parallel to the axis of the heat insulating container, and the distance between the container inner surface of the upper sheath tube and the container outer surface of the lower sheath tube is set to the neck portion. The liquefied gas level detecting device according to claim 2, wherein the level is smaller than the inner diameter. The liquid level detection device for a liquefied gas according to claim 2 or 3, wherein an upper end portion of the sheath tube is held by the heat insulating container while being engaged with an upper end of the opening. The lid member has a plug portion that is inserted into the neck portion, and the outer periphery of the plug portion is located between the inner peripheral surface of the neck portion when the plug portion is inserted into the neck portion. The liquid level detection device for a liquefied gas according to any one of claims 2 to 4, wherein a plurality of concave grooves into which the sheath tube can be inserted are provided in the axial direction. 6. The liquid level detecting device for a liquefied gas according to claim 1, wherein the liquid level detecting means is formed of a plastic optical fiber. The liquid of the liquefied gas according to any one of claims 1 to 6, wherein a gap between the outer periphery of the cable and the inner periphery of the sheath tube is sealed above the highest level of the liquid surface. Surface detection device. The liquid level detection device for a liquefied gas according to any one of claims 1 to 7, wherein the sheath tube has a through hole in a peripheral wall at a position corresponding to the liquid level detection unit. The liquid level detection of a liquefied gas according to any one of claims 1 to 8, wherein the sheath tube includes a temperature sensor that detects a temperature of a gas phase portion above a highest level of the liquid level. apparatus. The liquid level detection device for a liquefied gas according to any one of claims 1 to 9, wherein the lower sheath tube and the bent tube portion are made of metal, and the upper sheath tube is made of nonmetal. The liquefied gas level detecting device according to any one of claims 1 to 10, wherein the heat insulating container is a cryopreservation container, and the liquefied gas is liquefied nitrogen. A cryopreservation container using the liquefied gas level detection device according to any one of claims 2 to 11, wherein the container is engaged with an upper end of the opening at the upper end of the sheath tube, and the outside of the lid member. And a main body part of a liquid level detecting device having a liquid level display part outside the heat insulating container, and the cable drawn from the outer end of the locking pipe part. A cryopreservation container connected to the main body.

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