JPH10122931A - Cryogenic liquid level gauge - Google Patents

Abstract

(57) [Problem] To provide an inexpensive and highly reliable liquid level meter for cryogenic use with a small amount of heat entering a cryogenic refrigerant. A measuring element fixed to a vacuum insulated container by a mounting flange and a measuring instrument connected to a measuring line, the measuring element is a metal low-temperature lead having high thermal conductivity and good electrical conductivity. 24a, an N-type thermoelectric element 22a and a P-type thermoelectric element 18 installed at one end and the other end thereof.
And a high-thermal-conductivity, good-conductivity metal room-temperature-side lead 20a installed on the opposite side of these thermoelectric elements, and a good-conductivity metal connection lead 19 for connecting these two room-temperature-side leads 20a. The temperature difference detected by the normal temperature element 21 and the low temperature element 23 installed at both ends of the thermoelectric element is converted into a liquid level by the measuring instrument 9b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryogenic liquid level for measuring the liquid level of a cryogenic refrigerant such as liquid helium injected into a liquid helium container or the like in a vacuum insulated container using a thermoelectric element and a thermometer. About the total.

[0002]

2. Description of the Related Art Generally, a superconducting coil is maintained in a superconducting state by being cooled by a cryogenic refrigerant such as liquid helium. Therefore, the superconducting coil is usually immersed and stored in the liquid helium injected into the liquid helium container in the vacuum insulated container. In order to excite the superconducting coil, it is necessary to incorporate a current lead into the vacuum insulated container and connect an external power supply to supply an exciting current. At this time,
Since the current lead connects the normal temperature part and the cryogenic part, if a large amount of heat enters the cryogenic part via the current lead, a large amount of expensive liquid helium will be consumed. Therefore, a method has been adopted in which Joule heat generated in the current lead is suppressed, and heat intrusion is suppressed by flowing vaporized low-temperature helium gas.

[0003] As described above, a cryogenic refrigerant such as liquid helium is generally used for cooling the superconducting coil. However, since the vacuum insulated container is usually made of stainless steel or the like, the cryogenic refrigerant injected into the inside is used. The position of the liquid level of the low-temperature refrigerant cannot be seen from outside. Therefore, conventionally, as a method of measuring the liquid level, a superconducting wire type, a semiconductor type, a capacitance type, a float type, a pressure type, an acoustic type, an optical type, a gauge type and the like have been devised. Among them, a superconducting wire type is generally used.

FIG. 5 is a schematic diagram of a superconducting device including a current lead connected to a superconducting coil and a superconducting wire type liquid level meter. In FIG. 5, a current lead 3 has a current lead room temperature terminal 1 at one end and a current lead low temperature terminal 4 at the other end, and is held in a vacuum insulated container 5 by a current lead mounting flange 2. A connection conductor from an external power supply (not shown) is connected to the current lead normal temperature terminal 1, and the current lead low temperature terminal 4 is connected to the liquid helium 7 inside the liquid helium container 6 built in the vacuum heat insulating container 5. It is connected to the immersed superconducting coil 8. Superconducting wire type liquid level meter
It comprises a tracing stylus 12 and a measuring instrument 9a, which are connected by a measuring line 10a. The measuring element 12 is fixed to the vacuum insulated container 5 or the liquid helium container 6 by the mounting flange 11a, and its measuring part is immersed in the liquid helium 7.

FIG. 6 is a basic configuration diagram of a conventional superconducting wire type liquid level meter. In FIG. 6, a probe 12 is a superconducting wire, and a liquid helium 7 injected into a liquid helium container 6.
, The optimum current is applied to the probe 12 using the measuring power source 14, the variable resistor 15, and the ammeter 16, and the resistance value of the probe 12 measured by the four-terminal method using the voltmeter 13 is The liquid level of the liquid helium 7 is measured.

[0006]

This superconducting wire type liquid level meter can measure continuously, is small and has a simple structure.
Since the amount of heat entering the liquid helium is large, the evaporation loss of the liquid helium is large, and the measurement error increases when a magnetic field is applied. Accordingly, an object of the present invention is to provide an inexpensive and highly reliable liquid level meter for cryogenic use with a small amount of heat entering a cryogenic refrigerant.

[0007]

According to the present invention, there is provided a cryogenic refrigerant for measuring a liquid level of a cryogenic refrigerant such as liquid helium injected into a liquid helium container or the like in a vacuum insulated container. A level gauge, comprising a measuring element fixed to a vacuum insulated container by a mounting flange and a measuring instrument connected to the measuring element by a measuring wire, wherein the measuring element has a high thermal conductivity and a good electrical conductivity. A U-shaped low-temperature lead made of metal such as copper, an N-type thermoelectric element installed at one end of the low-temperature lead, and a P-type thermoelectric element installed at the other end of the low-temperature lead. A normal-temperature-side lead made of a metal having high thermal conductivity and good electrical conductivity, for example, copper, and a good-conductive metal for connecting these two normal-temperature-side leads, for example, copper, installed on the opposite surface of the thermoelectric element. Closed by connecting lead And-loop configuration, a configuration having a thermometer temperature element or the like which is installed either at both ends of one or both of the thermoelectric element of the thermoelectric elements.

In this configuration, when liquid helium is injected into the liquid helium container, the liquid contact part of the low-temperature side lead is cooled. When the low-temperature side lead is cooled by conduction, a temperature difference is generated between the low-temperature side lead and the room-temperature side lead across the thermoelectric element. This temperature difference changes according to the distance from the thermoelectric element to the liquid level of liquid helium, and the temperature difference increases as liquid helium is injected. Therefore, the level of the liquid helium can be determined by measuring the temperature difference. Further, the thermoelectric element has a low thermal conductivity and does not generate heat due to measurement. As described above, by converting the temperature difference between both ends of the thermoelectric element into a liquid level, it is possible to provide a liquid level meter that is inexpensive, has high reliability, and has a small amount of heat entering the cryogenic refrigerant.

In addition, the present invention provides a liquid level gauge which is inexpensive, has high reliability, and has a small amount of heat penetrating into the cryogenic refrigerant by simplifying the structure by integrating the two normal temperature side leads and the connection lead. be able to. In addition, by integrating the two normal-temperature side leads, the connection lead, and the mounting flange to simplify the structure, a liquid level gauge is provided that is more inexpensive, has higher reliability, and has less heat penetration into the cryogenic refrigerant. can do.

In addition, a protective case for protecting the probe is provided on the outer periphery of the probe, which is made of a metal having a low thermal conductivity, for example, stainless steel, and has a through hole for liquid passage and gas release. A liquid level meter which improves the performance and suppresses disturbance generated at the time of injecting liquid helium, is inexpensive, has high reliability, and has a small amount of heat penetrating into the cryogenic refrigerant can be provided.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a tracing stylus according to a first embodiment of the present invention. The difference between the cryogenic liquid level meter of the present embodiment and the conventional liquid level meter lies in the measuring element composed of a thermoelectric element.
In the conventional example, the liquid level was obtained by applying a current to the superconducting wire and measuring the resistance value using a four-terminal method. On the other hand, in the present embodiment, a U-shaped low-temperature side lead 24a made of a metal having high thermal conductivity and good electrical conductivity, for example, copper,
An N-type thermoelectric element 22a is provided at one end of the low-temperature side lead 24a, and a P-type thermoelectric element 18 is provided at the other end, and a metal having high thermal conductivity and good conductivity, such as copper, is provided on the opposite side of these thermoelectric elements. A closed loop is formed by the normal temperature side lead 20a and the connection lead 19 made of a highly conductive metal such as copper for connecting the two normal temperature side leads 20a.
Then, using the room temperature element 21 installed on the room temperature side of one or both of the N-type thermoelectric element 22a and the P-type thermoelectric element 18 and the low temperature side element 23 installed on the low temperature side, the room temperature side is used. Temperature element 21 and low temperature element 2
3 is input to the measuring device 9b via the measuring line 10b, and converted into a liquid level by the measuring device 9b.

FIG. 2 is a longitudinal sectional view of a tracing stylus according to a second embodiment of the present invention. In FIG. 2, two normal-temperature-side leads and connection leads constituting a measuring element of the cryogenic liquid level meter and a mounting flange are integrated into a normal-temperature-side lead 20b to simplify the structure. FIG. 3 is a longitudinal sectional view of a tracing stylus according to a third embodiment of the present invention. In FIG. 3, the N-type thermoelectric element 22b, the P-type thermoelectric element 18, and the low-temperature side lead 24c are arranged concentrically,
Saves space. Also, the low temperature side lead 24c
Has a through hole 25 for liquid passage and gas release.

FIG. 4 is a longitudinal sectional view of a probe according to a fourth embodiment of the present invention. In FIG. 4, a protective case 26 for protecting the probe is provided on the outer periphery of the probe, which is made of a metal having a low thermal conductivity, such as stainless steel, and has a through hole 25 for liquid passage and gas release.

[0014]

As described above, according to the present invention, a normal temperature element and a low temperature element are used by using thermometers such as temperature elements installed at both ends of a thermoelectric element which is a part of a measuring element. Is measured and converted to the liquid level of liquid helium, so there is no heat generated by the probe, and since a thermoelectric element with low thermal conductivity is used, heat from the outside to the cryogenic refrigerant The amount of intrusion is reduced, and an inexpensive and highly reliable liquid level meter can be provided.

In addition, by integrating the two normal-temperature side leads and the connection leads constituting the tracing stylus to simplify the structure, it is inexpensive, highly reliable, and has a small amount of heat entering the cryogenic refrigerant. A level gauge can be provided. In addition, by integrating the two normal temperature side leads and the connection leads constituting the probe and the mounting flange to simplify the structure, the amount of heat infiltration into the cryogenic refrigerant, which is cheaper and more reliable, is improved. Level can be provided.

Further, by handling a protective case for protecting the probe, which is made of a metal having a low thermal conductivity, for example, stainless steel and has a through-hole for liquid passage and gas release, is provided around the probe. Performance is improved,
It is possible to provide an inexpensive and highly reliable liquid level meter with a small amount of heat penetrating into the cryogenic refrigerant, which suppresses disturbance generated when liquid helium is injected.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a tracing stylus showing a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a tracing stylus showing a second embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a tracing stylus showing a third embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a tracing stylus showing a fourth embodiment of the present invention.

FIG. 5 is a schematic view of a general superconducting device.

FIG. 6 is a basic configuration diagram of a conventional superconducting wire type liquid level meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Current lead normal temperature terminal, 2 ... Current lead mounting flange, 3 ... Current lead, 4 ... Current lead low temperature terminal, 5 ...
Vacuum insulated container, 6: liquid helium container, 7: liquid helium, 8: superconducting coil, 9a, 9b: measuring instrument, 10a,
10b: measurement line, 11a, 11b: mounting flange,
12: measuring element, 18: P-type thermoelectric element, 19: connection lead, 20a, 20b: normal temperature side lead, 21: normal temperature side temperature element, 22a, 22b: N-type thermoelectric element, 23: low temperature side temperature element, 24a, 24b, 24c: low-temperature side lead, 25
... through-hole, 26 ... protective case.

Claims (4)

[Claims] 1. A cryogenic liquid level meter for measuring the liquid level of a cryogenic refrigerant such as liquid helium injected into a liquid helium container or the like in a vacuum insulated container, which is fixed to the vacuum insulated container by a mounting flange. Measuring element, and a measuring instrument connected to the measuring element by a measuring wire, the measuring element has a U-shaped low-temperature side lead made of a metal having high thermal conductivity and good electrical conductivity, and the low-temperature side An N-type thermoelectric element installed at one end of the lead, a P-type thermoelectric element installed at the other end of the low-temperature side lead, and a high thermal conductivity installed on the opposite surface of these thermoelectric elements to provide high conductivity. A closed-loop configuration comprising a room-temperature-side lead made of a metal having a connection lead made of a highly conductive metal connecting these two room-temperature-side leads,
A cryogenic liquid level meter having a thermometer such as a temperature element installed at both ends of one or both of the thermoelectric elements. 2. The cryogenic liquid level meter according to claim 1, wherein two normal temperature side leads and a connection lead are integrated. 3. The cryogenic liquid level meter according to claim 1, wherein two normal temperature side leads, a connection lead, and a mounting flange are integrated. 4. A liquid level meter for cryogenic use according to claim 1, wherein a through hole made of a metal having a low thermal conductivity is provided on the outer periphery of the measuring element. A liquid level meter for cryogenic use, comprising a protective case for protecting a probe.