JPH02280015A - Superconducting liquid level sensor - Google Patents

Abstract

PURPOSE:To obtain the liquid level sensor which is suitable especially for a low temperature and can be handled easily by selecting the critical temperature of a superconductive line to the boiling point or above of a liquid to be measured, and allowing the electric resistance value of the superconductive line exposed on the liquid face to correspond to a liquid level. CONSTITUTION:A superconductive body in which the critical temperature of a superconductive line 1 is a little higher than the boiling point of the liquid is selected, measuring points 2 (21, 22, 23) are connected thereto in series at a prescribed interval, and a constant-current source 3 is connected to both its ends. Also, in order to measure a voltage generated in each measuring point 2, both ends of each measuring point 2 and a terminal 5 for measuring a voltage are connected by a wiring 6, and the electric resistance value of the superconductive line 1 exposed on the liquid face is allowed to correspond to a liquid level. According to this constitution, only the measuring point 2 being above the liquid face 7 has an electric resistance, and a resistance in the liquid becomes '0', therefore, by measuring this potential difference with a potentiometer 4, the liquid face 7 can be measured easily without providing a movable part.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a superconducting liquid level sensor that detects the liquid level of a liquid in a container, particularly a liquid with a low boiling point.

<Prior Art> Conventionally, float-type, buoyancy-type, electrostatic-type, radiation-type, ultrasonic-type, pressure-type, and other sensors have been used to detect liquid level.

As mentioned above, the float type is based on the position of the float floating on the liquid surface, and the buoyancy type is based on the displacement 1 of a spring balanced with the buoyancy of the float.
The electrostatic type is based on the change in capacitance due to the change in the area of the dielectric liquid immersed between the container and the opposing electrode, the radiation type is based on the attenuation due to the liquid layer of R-rays, which have strong penetrating power, and the ultrasonic type is based on the amount of attenuation caused by the liquid layer, and the ultrasonic type is based on the amount of ultrasonic waves. The liquid level was detected by measuring the liquid pressure using a Bourdon tube or U-shaped tube, using the pressure method based on the round trip time of reflection on the liquid surface.

FIG. 5 shows an example of a pressure type liquid level needle, in which the pressure in the pipe 16 disposed above the liquid level 7 in the container 8 and the pressure at the bottom of the container 8 are adjusted. The height of the liquid level is measured by a differential pressure gauge 11 that detects the difference between the pressure in the pipe 17 whose pressure is controlled by the generator 18 and the control valve 12.

<Problems to be Solved by the Invention> The float-type and buoyancy-type liquid level sensors described above require mechanical adjustment because they use a movable part for detection, and cannot be expected to operate accurately at low temperatures. In an electrostatic type, if the container is used as a conductor and the distance between the opposite electrode and the counter electrode is not narrowed, the capacitance will be small and the sensitivity will be low.If the distance between the electrodes is narrowed, errors due to foreign matter adhesion and short circuits are likely to occur.

Those using radiation are difficult to handle due to the strong penetrating power of Ir1r rays.

The ultrasonic method has the advantage of non-contact detection, but it can cause errors due to dirt adhering to the vibrator, and no product has been developed that can be used practically in extremely low-temperature environments.

The pressure type equalizes the pressure of the liquid at the bottom of the liquid container with the pressure of the fluid coming from the pipe, and requires a device to pressurize the liquid or gas in the pipe, and a device to measure the pressure. It becomes necessary.

In addition, with the pressure method, when measuring the liquid level of cryogenic liquid,
There is a possibility of condensation on parts exposed to the outside air or freezing of attached moisture, so countermeasures are required.

Furthermore, there is a drawback that as the viscosity of the liquid increases, errors in measuring the pressure of the liquid increase.

An object of the present invention is to solve the problems of conventional liquid level sensors, especially those for low temperatures, and to provide a superconducting liquid level sensor that is easy to handle and can perform stable measurements.

Means for Solving the Problems> The present invention is a liquid level sensor that utilizes the characteristic of a superconductor that its electrical resistance becomes zero at a temperature below the critical temperature Tc.

Superconductors have a Tc of about 20 for conventional alloys,
In recent years, the Tc has been developed one after the other.

La-5r-Cu-0 series 40, Y-Ba-Cu-0
90 of the system, 110K of B1-5r-Ca-Cu-0 system
(high Tc phase) and 80K (low Tc phase), T no Ba-Ca
-Cu-0 series 125KC high Tc phase) etc. have been reported.

On the other hand, TC gases include those such as propane and butane that have a relatively low pressure even at room temperature, and others that have a low boiling point and have a very high pressure at room temperature. The boiling point of this gas at 1 atmosphere and the critical temperature of the gas are shown in Table 1.

Table 1 Characteristics of liquefied gases Gases whose critical temperature is lower than room temperature as shown in Table 1 are:
It cannot be liquefied unless it is cooled to a critical temperature.

When the gas liquefied as described above is used at normal pressure of 1 atmosphere, it is maintained at its boiling point temperature.

In the superconductor and cooling gas explained above, when the superconductor and the cooling gas have a boiling point lower than the Tc of the superconductor, the superconductor below the liquid surface has zero resistance and is cooled. Since a superconductor on a surface has electrical resistance in its normal conduction state, the liquid level can be detected by detecting that electrical resistance.

Superconductors have relatively low resistivity even in the normal conduction state, so
By forming the superconductor into a thin wire-shaped bend or winding configuration, the resistance value can be increased, and this superconductor wire can be formed into an electrically insulating substrate or a protective film with a similar coefficient of thermal expansion. It is desirable to fix and protect it with a low heat 8-way configuration.

In the present invention, the superconducting wire described above.

A method in which a constant current is applied and the entire liquid level is detected by the output from a voltage detection terminal appropriately arranged on a superconducting wire.In the present invention, the Tc of the superconductor is selected to be higher than the boiling point of the liquid whose liquid level is to be detected. , the superconducting wiring is constructed so that as the liquid in the container increases or decreases, the portion in the liquid increases or decreases, and the electrical resistance value increases or decreases. Therefore, thermal equilibrium is reached after a certain delay time even after the liquid increases or decreases, and the liquid level can be measured only by measuring electrical resistance.It is also compact and easy to handle, with no moving parts or complicated attachments required. It can be made into a superconducting liquid level sensor.

<Example> Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a basic embodiment of the superconducting liquid level sensor of the present invention. In Figure 1, 8 is a liquid container, 7 is the liquid level, and the superconducting wire 1 is shown by a thick line perpendicular to the liquid level 7.
is provided. The superconducting wire 1 has measurement points 2 (21, 22, 28) formed at regular intervals with a long wire length in a folded or zigzag shape that has a large resistance value when in a normal conduction state, and each measurement point 2 is connected in series. A constant current source 3 is connected to both ends of the constant current source 3, and in order to measure the voltage generated at each measurement point 2, a wiring 6 is connected between both ends of each measurement point 2 and the terminal 5 for voltage measurement. Connected. terminal 5
A potentiometer 4 is connected to measure the potential difference at each measurement point.

With the configuration shown in FIG. 1 above, when a current is passed through the superconducting wire 1 using the constant current source 3, only the measurement point 2 above the liquid level 7 has electrical resistance, so the potential difference is measured using the potentiometer 4. By measuring, the liquid level 7 can be measured. Note that the number of measuring points 2 can be increased as necessary to improve the accuracy of measuring the liquid level.

First Embodiment FIG. 2 shows a first embodiment of the present invention, in which the superconducting wire 1 is wired on an electrically insulating substrate 14.

This first embodiment is the same as the basic configuration diagram of the liquid level sensor shown in FIG. 1, except that the superconducting wire l having the measurement point 2 is formed on the substrate 14. will be explained without illustration. The substrate 14 in this figure is made of glass,
A material made of ceramics or a polymeric material such as polyimide, which has good electrical insulation and a low coefficient of thermal expansion, was used.

The superconducting wire 1 is made into a folded shape to increase the wire length at each measurement point 2, and a cutout hole 9 is provided in the substrate 14 in the middle of the measurement point 2, thereby increasing the resistance value generated at the measurement point. Second, the influence of heat conduction between measurement points is reduced, increasing the accuracy of liquid level measurement.

Note that in this embodiment, the voltmeter 4 with high input impedance is used.
Therefore, a conventional metal wire 611'i for measuring the potential difference at the measurement point was used by welding or ultrasonic bonding to the superconducting wire 1.

Like the substrate 14, the film that protects the superconducting wire 1 formed on the substrate 14 from outside air and liquid must have electrical insulation properties and a low coefficient of thermal expansion, and is made of molten glass.

A protective film was formed by dipping the entire substrate 14 into a polymer solution such as polyimide or a ceramic alcokind solution (sol-gel method).

The power source of this superconducting liquid level sensor does not necessarily have to be a constant current power source; as shown in Figure 2, the bias current circuit includes a resistor R and a voltmeter 4' that measures the voltage generated at R. If current fluctuations are monitored, the measured value will not change even if the bias current slightly fluctuates, so a normal DC power supply 10 can be used.

Furthermore, to measure the potential difference at each measurement point 2, the potential difference between adjacent terminals 50 is sequentially measured using a scanner voltmeter as shown in Figure 1, but as shown in Figure 2, the potential difference between the adjacent terminals 50 is measured at approximately the ground level of one liquid level sensor. When the potential difference at each measurement point 2 is sequentially integrated in a table using the lowest potential as a reference, a potential difference is generated only at the measurement point (not shown) above the liquid level, and the measured values shown in FIG. 8 are obtained.

The horizontal axis in FIG. 8 is the position of terminal 5, where 0 is the ground terminal, and the terminal position where the number of measurement points is increased sequentially is shown, and the vertical axis shows the potential difference between the ground and each terminal. From FIG. 3, the relationship between the measurement point and the potential difference can be seen, and the liquid level can be measured at the point where the potential difference rises.

Second Embodiment A second embodiment of the present invention is shown in FIG. The second example is
The parts other than the parts shown in FIG. 4 related to the superconducting wire 1 can be the same as the basic configuration shown in FIG. 1 and the first embodiment shown in FIG. 2, so the explanation of the parts other than those shown in FIG. Omitted.

In this figure, reference numeral 15 denotes a cylindrical substrate, around the outer periphery of which the superconducting wire 1 is wound along a spiral groove formed in the substrate 15. This superconducting wire 1 is wound densely at each measurement point 2, and between each measurement point 20, it is connected to a terminal 5 by a voltage measurement conductor 6 with an insulating coating through a through hole made close to each other. There is.

The cylindrical substrate shown in FIG. 4, the superconducting wire, the conductive wire for voltage measurement, etc. were made in the same manner as in the first example.

The cylinder of this second embodiment can have a large mechanical strength even if its diameter is reduced, and can be used by being inserted into a container containing a liquid to be measured through a small hole made at the top.

The following configuration can be considered as an improvement or modification of the first embodiment described above. When forming a liquid level sensor having the shape shown in FIG. 2, the Suhanota method, MBE method,
Alternatively, a superconducting thin film can be created by physical or chemical means such as CVD, or a superconducting thick film can be created by a spray pyrolysis method or a sol-gel method using a compound of elements constituting a superconductor. Then, by photolithography and l-etching, the superconducting wire 1 and the conductive wire for potential difference measurement are simultaneously manufactured from the same superconducting film.

Therefore, the process of later connecting a large number of potential difference measurement conductors 6 to the middle of the superconducting wire 1 explained in the example in @ is no longer necessary, and this improves the reliability of the superconducting liquid level sensor. can be done.

The superconducting liquid level sensor formed as in the above example does not malfunction and is easy to handle, even if there is dirt or foreign matter attached to it, the heat transfer may be delayed and the detection speed may be slightly degraded. It's safe.

The superconducting liquid level sensor of the present invention is difficult to maintain.

Alternatively, there is no need for large-scale accessory equipment, and it is suitable for miniaturization, and can be used for small liquid containers, and by combining the sensor, it can also be used for large containers.

The output of this liquid level sensor is a digital output that corresponds to the presence or absence of resistance of the superconducting wire at each measurement point, so it is easy to connect to digital equipment such as a microcomputer and perform automatic measurement or control. It is.

Furthermore, the superconducting liquid level sensor of the present invention can be used at extremely low temperatures, such as liquid nitrogen temperatures, where conventional liquid level sensors have not performed well, although the Tc of current superconductors may be low. It can be effectively used as a liquid level sensor. However, from now on,
As the development of superconductor materials progresses and +Tc increases, it becomes possible to create liquid level sensors that can be used for liquids with higher boiling points.

As explained in the above embodiments, the superconducting liquid level sensor of the present invention uses a superconductor whose Tc is slightly higher than the boiling point of the liquid to be measured, has a highly sensitive configuration, has no moving parts, and has a digital output. It has the characteristics of being easy to handle.

<Effects of the Invention> The present invention uses a superconducting wire whose Tc is slightly higher than the boiling point of the liquid to be measured, and utilizes the fact that the resistance of the part of the superconducting wire immersed in the liquid becomes zero. It is a suitable liquid level sensor.

Furthermore, the superconducting liquid level sensor of the present invention does not require any moving parts;
It can be shaped to match the structure of the liquid container, prevents malfunctions due to adhesion of foreign objects, and is easy to handle and highly safe. Furthermore, the attached equipment can be made smaller, the output is digital, and the processing circuitry can be made at a lower cost, so it can be applied to small-sized manufacturing equipment, measuring equipment, etc., and can be used to automatically measure and control liquid levels.

[Brief explanation of drawings]

FIG. 1 is a basic connection configuration diagram of the liquid level sensor of the present invention, FIG. 2 is a partially omitted perspective view of the first embodiment of the present invention, and FIG. 3 is a diagram of the first embodiment of the present invention.
FIG. 4 is a diagram showing the output characteristics of the embodiment, FIG. 4 is a configuration diagram of a second embodiment of the present invention, and FIG. 5 is a configuration diagram of a conventional pressure type liquid level needle. DESCRIPTION OF SYMBOLS 1... Superconducting wire, 2... Measuring point, 4 and 4'... Potentiometer, 5... Terminal, 6... Leading wire for measuring potential difference, 7... Liquid level, 8...・Container, 9 ・Cut hole, 10
- DC power supply, 11... Differential pressure gauge, 12... Control valve, 13... Pressure generator, 14... Board, 15...
・Cylindrical board. 16.17...-Pipe. Agent Patent attorney Takeshi Sugiyama (and 1 other person) σ Figure 5 Illustration of the Heisei case Patent application No. 1-102972 2. Name of the invention Relationship to the superconducting liquid level sensor correction case Patent applicant Address 22-22 Nagaike-cho, Abeno-ku, Osaka 8545 Name (504) Sharp Corporation Representative Haruo Tsuji

Claims (1)

[Scope of Claims] 1. A superconductor having a critical temperature higher than the boiling point of the liquid stored in a liquid container and mounted linearly with a small heat capacity is immersed for a length corresponding to the amount of the liquid. A superconducting liquid level sensor, characterized in that the superconducting wire is installed so that the height of the superconducting wire changes, and the electric resistance value of the superconducting wire exposed above the surface of the liquid corresponds to the level of the liquid. 2. The superconducting wire according to claim 1, wherein the superconducting wire is supported or protected by a material made of an inorganic oxide, polyimide, epoxy resin, etc., which is electrically insulating and has approximately the same coefficient of thermal expansion. Conductive liquid level sensor.