JPS60222727A - Superconducting type liquid level sensor - Google Patents

Abstract

PURPOSE:To obtain a superconducting liquid level sensor characterized by a small amount of evaporation of liquid helium, by shorting the lower connecting parts of two pieces of superconducting wires, which are provided in parallel in the inside of a protecting tube. CONSTITUTION:A returning superconducting wire 2A is provided in parallel with an incoming superconducting wire 2 in a superconducting type liquid level sensor 20. Lower connecting parts 2c and 2Ac of the respective wires are connected. An incoming current lead wire 5a and an incoming voltage lead wire 6a are extracted from an upper connecting part 2a of the incoming superconducting wire 2 and connected to one terminal of a DC power source 8 and one terminal of an indicator 7. A returning current lead wire 5Aa and a returning voltage lead wire 6Aa are extracted from an upper connecting part 2Aa of the returning superconducting wire 2A and connected to the other terminals of the DC power source 8 and the indicator 7, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a superconducting liquid level sensor used, for example, in a helium level gauge.

[Prior art]

Figure 1 shows the cross-sectional structure of a conventional superconducting liquid level sensor.
Further, FIG. 2 shows an electrical equivalent circuit of a helium level meter that measures the level of liquid helium in a container using the superconducting liquid level sensor shown in FIG. 7. In Figures 1 and 2, 10 is a superconducting liquid level sensor, l is a protection tube, C is a superconducting wire, C is an upper end connection of the superconducting wire, and C is a liquid helium l/L in the superconducting wire. Liquid level height position, 2C is the lower end connection of the superconducting wire, 3 is the ventilation hole, DA is the end fixing plate, ja is the upper current lead wire, 3C is the lower current lead wire,
6a is an upper voltage lead wire, 6C is a lower voltage lead wire, RI is an indicator, t is a DC power supply, t is a container, and 1/ is liquid helium.

Next, the operation will be explained. The liquid level sensor 10 is for measuring the liquid level of, for example, liquid helium l/, which is stored in a container.
It utilizes the superconductivity phenomenon in liquid helium of a superconducting wire made of a metal that transitions to a superconducting state at a slightly higher temperature than JK). Superconducting wire 2 is a protective tube/
The upper current lead ta and the upper voltage lead 6a come out directly from the upper end connecting part core a, and From the lower end connection part C, connect the lower current lead wire I.
C and the lower voltage lead wire 6c pass through the inside of the protective tube 1, pass through the end fixing plate located at the upper part, and are taken out to the outside. Also, the ventilation holes 3 are multiple holes drilled at appropriate positions in the protective tube l.

Liquid helium and gas helium enter and exit through these holes.

Is this liquid level sensor 10 in a container as shown in Fig. 2? The upper current lead wire ja and the lower current lead wire 3 are fixed inside the
Connect c to a DC power supply and let a constant current flow through it. Further, the upper voltage lead wire 6a and the lower voltage lead wire 6c are connected to an indicator 7. In the helium level gauge constructed in this way, the height of liquid helium // is at position 2b, which is in the middle of superconducting wire λ.
In this case, the helium between the upper end connection part 2a and the middle position B is in a gas state and is poorly cooled, and the superconducting wire through which a constant current is flowing breaks the superconducting state and enters the normal conductive state, decreasing electrical resistance. It is occurring. Further, since the helium between the middle position b and the lower end connection part 2c is in a liquid state and well cooled, it becomes a superconductor and its electrical resistance is zero. That is, by reading the voltage generated at both ends of the superconducting wire λ through which a constant current is flowing with the indicator 7, the level of the liquid helium can be measured.

In addition, in a normally used superconducting liquid level sensor, the current value flowing through the superconducting wire 2 is about 200 rlLk, and the voltage generated in the normal conducting part is approximately /Sv per 10 va of the length of the superconducting wire λ, which is generated in this part. Joule heat generation 1 is 1
It is about 03-W per 0 cm.

Therefore, the degree of helium gas in the surrounding area increases.・In addition, this liquid level sensor has a structure in which the superconducting wire λ, the lower current lead wire left C, and the lower voltage IJ-dead bag 6C coexist inside the protection tube, and these lead wires are coated with Teflon or the like. It is a copper wire with a diameter of about 0.3 ms.

In the structure described above, most of the Joule heat generated in the normal current inside the protection tube and the conductive part is transferred to the liquid helium at the bottom due to heat conduction between the surrounding helium gas and the two copper lead wires. move towards. The heat transfer tQ at this time can be calculated using the following formula, where λ is the thermal conductivity of the material, S is the conduction cross section, t is the conduction length, TI is the temperature on the high side, and TJ is the temperature on the low temperature side. .

Q=λ・−(TI−TJ) Here, the thermal conductivity of helium gas λHe == 0.000/<W/cm@K) The conduction cross section of helium gas SHθ =0. /coro (d) Helium gas conduction length tHe = t (b) Lead wire thermal conductivity λcu = to ('W/cIrL*K) Lead wire conduction cross section S (u = o, ootp(ctl) Using the temperature on the high side TI = to (K) and the temperature on the low temperature side TJ = Kuko (K), and calculating the amount of heat transferred via helium gas and the lead wire, the amount of heat transferred via helium gas QHe
= 7.3 x 10' (W), the amount of heat transferred via the IJ lead wire Qcu = l/xiO'' (5), and the amount of heat transferred via the lead wire is more than i,ooo times larger. Also, these amounts of heat transfer are a factor in the evaporation of liquid helium.

Recently, Mankyun magnetic field superconducting magnets such as NMR (nuclear magnetic resonance) imaging devices and NMR analyzers are being planned. These low-occupancy containers for superconducting magnets do not supplement liquid helium for a long time, and have so-called low heat loss. However, since the conventional liquid level sensor has the above-mentioned structure, when it is used to measure the liquid level height of °C helium, a large amount of heat is transferred via the two lead wires. In other words, there was a drawback that a large amount of liquid helium evaporated, making the device uneconomical.

[・Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. Two superconducting wires are stretched in parallel inside a protective tube, and each upper end connection of these military superconducting wires is connected to the conventional one. Similarly to The purpose of the present invention is to provide a superconducting liquid level sensor in which the connection is made at the upper part, and the amount of heat transferred through these lower lead wires is eliminated, thereby reducing the evaporation of liquid helium.

[Embodiments of the invention]

That is, FIG. 3 shows a cross-sectional structure of an embodiment of the superconducting liquid level sensor according to the present invention, and FIG. This figure shows the electrical circuit of a helium level gauge that measures the level of water. In the superconducting liquid level sensor 20 shown in FIG. 3, an incoming superconducting wire λA is stretched in parallel with an outgoing superconducting wire λ, which corresponds to a conventional superconducting wire, and the lower end connecting portions 2c and 2kc of each are connected. In addition, from the upper end connection part 2a of the outgoing superconducting wire, pull out the outgoing current lead wire (ra) and the outgoing voltage lead wire Aa, which correspond to the conventional upper current lead wire and upper voltage lead wire, respectively, and connect them to the DC power source. At the same time, a return current lead wire 5Aa and a return voltage lead wire AAa are drawn out from the upper end connection core Aa of the two return superconducting wires and connected to the DC power source and the other end of the indicator 7, respectively.

Since the superconducting liquid level sensor of the present invention is configured as described above, the output voltage displayed on the indicator 7 and the Joule heat value generated in the normal conducting part are approximately - times that of conventional liquid level sensors. . However, since there is no material with high thermal conductivity such as copper inside the protective tube 1, the amount of heat in the normal current and conductive part is difficult to transfer to the liquid helium at the bottom, and it is protected by natural convection through the ventilation hole 3 at the top. It will diverge upwards outside the tube l.

〔Effect of the invention〕

As described above, according to the present invention, multiple superconducting wires are stretched in parallel inside the protective tube, their lower end connections are connected to each other, and current lead wires are connected from each upper end connection point as in the conventional case. The structure allows the lead wire to be pulled out from the inside of the protection tube, eliminating the amount of heat transferred through the lead wire and creating an economical superconducting liquid level sensor with less evaporation of liquid helium. There is an effect that can be provided.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional structural diagram of a conventional superconducting liquid level sensor, Figure 2
The figure is an electrical circuit diagram of a helium level gauge using a conventional superconducting liquid level sensor, the second drawing is a cross-sectional structural diagram showing an embodiment of the present invention, and the fourth figure is a helium level gauge using an embodiment of the present invention. It is an electric circuit diagram of a liquid level gauge. /...Protective tube, Co...Outbound superconducting wire 1.2 people...Return superconducting wire 1.2a, 2Aa...Top end connection part, 2c and 2k
c...Lower end connection part, 5a...Outgoing current lead wire, left Aa
...Return current lead wire, 6a...Outbound voltage lead wire, 6
Aa...Return voltage lead wire, 7 pairs.In addition, in the diagram, the same reference numerals indicate the same or equivalent parts.Agent: Dosho Soga Proceedings Amendment "Voluntary" June 15, 1980 To the Commissioner of the Patent Office 1.Display of the incident Showa era! Patent application No. 7 in 2017? ! f417 No. 2, Name of the invention Superconducting liquid level sensor 3, Relationship to the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name Name
(601) Mitsubishi Electric Co., Ltd. Representative Jin Katayama Hachibu 4, Agent address 4th floor, Marunouchi Building, 2-4-1 Marunouchi, Chiyoda-ku, Tokyo (1) Detailed explanation of the invention in the specification 9 Sections of amendments The statement of contents is amended as follows.

Claims (1)

[Claims] A protective tube, two superconducting wires stretched in parallel inside the protective tube, and lead wires for current supply and voltage measurement connected to the upper end connections of these two superconducting wires, respectively. , A superconducting liquid level sensor characterized in that the lower end connecting portions of the single superconducting wire are short-circuited.