JPS5854514B2 - Ekimenkei - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid level gauge using a superconducting material that makes it possible to continuously detect the level of liquid helium even under adverse environments with large temperature gradients.

Conventionally, in order to continuously detect the liquid helium level,
A liquid level gauge was used in which a fine wire made of vanadium (Vanadium) or Ta (Tantalum) was stretched vertically into a container and the position of the liquid level was detected from the change in resistance of the wire.

In other words, the critical temperatures of V and Ta are approximately 4.3 and 5.3, respectively, so liquid helium (at 1 atm.
．． The part immersed in the gas (2 K) shows a superconducting state with zero electrical resistance, and the part in the gas shows a normal conducting state with electrical resistance.Using this fact, the position of the liquid level can be determined from the value of the electrical resistance of the element. This is a method of detecting

The critical temperature of these materials is the temperature of liquid helium 4.2
Therefore, when the temperature gradient inside the container fluctuates constantly, such as when injecting liquid helium, moving the container, or operating a superconducting Maguit, the superconducting temperature reaches a point well above the liquid level. become a state.

In addition, since the liquid temperature rises to about 5.5 degrees due to pressure increase, it is limited to use in places where such pressure fluctuations are large.

Furthermore, since the critical magnetic field of these materials is several hundred to several thousand Gauss, they cannot be used in superconducting equipment that generates high magnetic fields.

As a method to solve these drawbacks, there is a liquid level gauge using an alloy superconducting wire with a high critical temperature and high critical magnetic field.

As this type of material, an Nb-Zr alloy having a critical magnetic field of 70 to 90 KG and a critical temperature of about 10 was used.

Since the critical temperature of this material is high, it becomes superconducting well above the liquid level and does not indicate the correct liquid level.

In order to avoid this, a method is used in which a suitable current is passed through the element and the self-heating of the element causes the normally conductive portion generated at the upper end of the liquid level gauge to propagate to the liquid surface.

In other words, it takes advantage of the fact that cooling with liquid is several tens to hundreds of times faster than cooling with gas.

Considering the design, manufacturing, calibration, and measurement of this continuous liquid level gauge, it is required that there is a direct relationship between the height of the liquid level and the resistance. must exhibit a constant value regardless of temperature.

However, the specific electrical resistance of the material actually used varies depending on the temperature.

FIG. 1 shows the temperature dependence of the specific electrical resistance of the Nb-25atSZr wire (0,25φ).

In the figure, ρ. , ρsoo are the critical temperature and 30
It represents the specific electrical resistance at 0K.

As is clear from the figure, the temperature dependence of specific electrical resistance is large, and when used in a liquid level gauge, the relationship between the liquid level and resistance is no longer a linear relationship, and it is necessary to calibrate each container before use. (because the temperature gradient varies from container to container).

These drawbacks are exacerbated as the level gauge becomes longer.

The Nb-Ti alloy wire according to the present invention makes it possible to eliminate these drawbacks.

Conventionally, Nb-Ti alloys have been used as wire materials for superconducting maguits, and are required to stably flow as large a current as possible.

In order to increase the current density, it is necessary to perform a suitable combination of processing and heat treatment, and it has been known that heat treatment plays an especially important role.

However, when used as a liquid level gauge, a large current density is not required and the residual resistance value ρ is low.

It is required that the temperature dependence be large and the temperature dependence be small.

The present invention has made it possible to obtain such a wire.

That is, oxygen at 800p, p-m to 3000p,
It has been found that by strongly working the Nb-Ti alloy, the residual resistance increases and the temperature dependence becomes significantly smaller.

Figure 2 shows Nb-55a containing oxygen at 1250 p, p.
The temperature dependence of the specific electrical resistance of a wire obtained by subjecting a t% Ti alloy to 99.995 cold working is shown.

The degree of cold work is a value defined by the following formula. (Written by Kaipo d
Analysis Section after processing) - (Area S Cold working degree - X 100) (Cross-sectional area S before processing.

) 6 compared to the value ρ300 at 300 even near the critical temperature.
The number of employees will decrease.

Normally, the temperature difference between the top and bottom of the container where the level gauge is placed is several tens of degrees.

Resistance changes due to temperature gradients are less than a few.

The relationship between the liquid level and the resistance of the level gauge does not deviate from a linear relationship.

In order to avoid the above-mentioned disadvantages as a liquid level gauge,
The smaller the resistance change, i.e. ρ.

The closer the value of /ρaOO is to 1, the better. Considering the stacking required for measurement, tolerance, etc., the value of ρlρ300 is 0.
．． Requires 90 or above.

Nb-55a t %Ti with processing degree of 99.995%
The amount of oxygen added to the alloy and the resistance ratio ρ.

/ρ300 is shown in Figure 3 □.

As the amount of oxygen increases, the resistance change becomes sharper and smaller,
The value of ρ0/ρ300 approaches 0.94.

FIG. 4 shows the resistance ratio when the same sample shown in FIG. 3 was annealed.

Figure 5 shows Nb-55 containing oxygen at 2150 p, p, rr6.
The relationship between the working degree and resistance ratio of at%Ti alloy is shown.

For these reasons, N that has been extremely strongly processed by adding oxygen
It can be seen how small the temperature dependence of the resistance of the b-Ti alloy is.

Other superconducting alloys, such as Nb 25 as shown in FIG.
For at% Zr alloy, the value of ρ0/ρ300 is 0.66
, becomes 0.11 when annealed, and the Nb-T according to the present invention
It is extremely low compared to i-alloy.

The material according to the present invention with low temperature dependence of resistance is Ti
These three amounts can be obtained in the range of 30 at% to 75 at%.

In addition, Zr or Ta is used as a third element in the range of 3at% to 30a.
It was found that a similar effect could be obtained with a material added at 1%.

The new discovery that the temperature dependence of electrical resistance is extremely small has made it possible to manufacture highly reliable and precise liquid level gauges.

Next, the present invention will be explained based on examples.

Residual specific electrical resistance ρ of a Nb-55a t%Ti superconducting wire with an oxygen content of 1250 p-p-m cold-worked (processing rate 99.995%) from a diameter of 25 mm to 0.14 iiφ.

is 85μΩα, resistance ratio ρ. /ρ300 is 0.94.

A liquid level gauge with a measurement length of 40 m was manufactured using this wire.

As shown in FIG. 6, current terminals 21, 22 and voltage terminals 31, 32 are provided at both ends of the superconducting wire 10 stretched vertically, and a measuring current of 200 mA is applied.

At the upper end of the superconducting wire 1, a heater 4 for generating a normal electric part is attached.

The relationship between the output voltage (■) of the liquid level gauge and the liquid level height H was H=-9.09V+40, as shown in FIG. 7, showing an extremely good linear relationship.

Next, another example will be described.

A superconducting wire of Nb-60a t'%T 1-5a t%Ta was cold-worked from 20 mm to 0.14 mm as in the previous example.

Residual resistance ρ of the obtained wire. is 90 .mu..OMEGA., and the resistance ratio is 0.95.

A liquid level gauge for a measurement range of 60 CIrL was manufactured using this wire and operated at a measurement current of 200 mA.

The relationship between the output voltage and the liquid level H is H = -8,55V.
It became a straight line of +60.

[Brief explanation of the drawing]

Figure 1 shows Nb-25at%Zr alloy wire (0.25mmφ
) is a characteristic diagram showing the temperature dependence of specific electrical resistance. Figure 2 shows Nb containing oxygen at 1250 p, p, m.
A characteristic diagram showing the temperature dependence of specific electrical resistance of a wire (O114imφ) obtained by cold-working 99.995% of -55 at% Ti alloy.
a t % Ti alloy added oxygen amount and resistance ratio ρ0/ρ3
FIG. 4 is a characteristic diagram showing the relationship between 0.00 and 1.0% of Nb-55at, which was annealed for 1 hour at 900° C. after processing. Figure 5 is a characteristic diagram showing the relationship between ρsoo and ρsoo.
A characteristic diagram showing the relationship between the processing degree and the resistance ratio ρ0/ρ300 of the Nb-55at%Ti alloy including 50 p, p, m3, and FIG. 6 is a schematic diagram showing the circuit configuration of a liquid level gauge according to an embodiment of the present invention. ,
FIG. 7 is a characteristic diagram of the liquid level gauge according to the present invention. In the figure, 1 is a superconducting wire, 21.22 is a current terminal, and 3
1 and 32 are voltage terminals, and 4 is a heater.

Claims (1)

[Scope of Claims] 1. In a device in which a part of a superconducting wire is immersed in a liquid to be measured and the level of the liquid to be measured is measured from its electrical resistance value, the superconducting wire is Oxygen is added to a superconducting alloy made of titanium and niobium at 8o. ppm to 3000 ppm added,
Critical temperature iT obtained by further severe processing
Specific electrical resistance ρ at c. and the specific electrical resistance ρ300 at 300, the ratio ρ0/p
A liquid level gauge characterized in that the superconducting wire has a value larger than 0.9.