JPH0943027A - Liquid-surface-level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid-surface-level sensor by which the liquid-surface level of a liquid injected into a container can be measured precisely. SOLUTION: In a liquid-surface-level sensor 1, the liquid-surface level of liquid nitrogen injected into a container 2 is detected. The liquid-surface-level sensor is constituted of a float 6 which is supported in a state that it is inserted into the liquid nitrogen from the upper part and in which the volume of a part immersed in the liquid nitrogen is changed by a liquid surface which is moved up and down clue to a change in the liquid nitrogen inside the container 2 and of a load detector 7 which is connected to the float 6 and which detects a change in buoyancy due to a change in the volume of the part immersed in the liquid nitrogen out of the float 6. The float 6 is constituted of a rod- shaped body or the like whose specific gravity is higher than that of the liquid nitrogen and which is arranged and installed so as to be suspended from the upper part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid surface level sensor for detecting the liquid surface level of a liquid injected into a container, and particularly to the detection of the liquid surface level in a container into which a cryogenic liquid such as liquid nitrogen is injected. The present invention relates to a suitable liquid level sensor.

[0002]

2. Description of the Related Art As conventional liquid level sensors, there are known photodetection type, float type (magnetostriction type), capacitance type and superconducting type sensors.

The optical detection type sensor uses an optical fiber. The optical fiber is attached to the inner wall of the container, and its tip is provided at the level to be measured. As a result, when the liquid reaches a certain level, the tip of the optical fiber comes into contact with the liquid, and the refractive index at this tip changes. As a result, the light reflected and returned at the tip of the optical fiber is not scattered and returned, and it can be detected that the liquid level is at a height higher than a predetermined position.

In the float type sensor, the float floating on the liquid surface moves up and down in accordance with the change of the liquid surface, and by detecting this movement, the level of the liquid surface is detected. In this case, there is also a magnetostrictive sensor that detects a change in float by magnetic distortion.

The capacitance type sensor uses a material whose capacitance changes when immersed in a liquid. The material whose capacitance changes is provided at a desired height, and when the liquid reaches this height, the capacitance changes and the liquid level is detected.

The superconducting sensor uses a substance that becomes superconducting by an extremely low temperature liquid such as liquid nitrogen. This substance is provided at the height to be detected, and when the liquid reaches this height, the capacitance changes to detect the liquid level.

[0007]

However, when the above-mentioned sensors are used as sensors for detecting the liquid level of a cryogenic liquid such as liquid nitrogen, there are the following problems.

(1) When a photo-detection type sensor is used, frost may be attached to the emission part of the detection light to cause malfunction. Further, when the liquid boils or the liquid surface is disturbed, the emitting portion of the detection light may come into contact with or separate from the liquid, which may cause a malfunction. Further, since the sensor is provided on the inner wall surface of the container or the like, the detection is performed at one point (emission point of the detection light) of the specific height. For this reason, when the liquid level exceeds that point, it is not possible to measure how high it is after that. The same cannot be measured when the wall level is below the specific point.

(2) In the case of a float type or capacitance type sensor, malfunction may occur due to frost on the movable part or the like, or malfunction may occur due to liquid surface disturbance.

(3) In the case of a superconducting sensor, there are cases where the superconducting state does not occur due to a slight difference in temperature. However, the temperature of the liquid inside the container may change when a part of the liquid is taken out to the outside, and this temperature change may cause the sensor to malfunction. Further, since this sensor is also provided on the inner wall surface of the container, detection is performed at one specified point, and accurate level measurement of the entire liquid surface cannot be performed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid level sensor capable of accurately and reliably measuring the level of a liquid surface.

[0012]

A liquid level sensor according to the present invention is a liquid level sensor for detecting the liquid level of a liquid injected into a container, and is supported in a state of being inserted into the liquid from above. And a liquid insert body in which the volume of a portion immersed in the liquid changes due to a liquid level that rises and falls with a change in the amount of liquid in the container, and is connected to the liquid insert body, And a load detecting means for detecting a change in buoyancy due to a change in volume of a portion of the liquid insert immersed in the liquid.

In the liquid insert, the buoyancy acting on the liquid insert changes due to the change in the volume of the portion immersed in the liquid. If the load detecting means measures in advance the magnitude of the buoyancy acting on the liquid insert when the liquid in the container is at a specific level, the liquid level can be measured from the amount of change in the buoyancy.

Further, it is preferable that the liquid inserter has a specific gravity higher than that of the liquid and is constituted by a rod-shaped body or a long plate-shaped body suspended from above.

As a result, the weight of the liquid insert changes subtly with changes in the liquid level. This change is a change in buoyancy, and the liquid level can be measured from the amount of change in buoyancy.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a liquid level sensor according to the present invention will be described below with reference to the drawings.

[Structure] FIG. 1 is a front sectional view showing a state in which the liquid level sensor 1 according to the present embodiment is mounted in a container 2, and FIG. 2 shows the liquid level sensor 1 according to the present embodiment. It is a principal part enlarged view shown in the state which the part was fractured | ruptured.

The container 2 has a closed structure, and a cryogenic liquid such as liquid nitrogen is poured into the container 2. The wall surface of the container 2 is formed thick so as to enhance heat insulation. An upper part of the container 2 serves as an inlet, and a lid 3 is provided.

A liquid take-out device 4 for taking out the liquid injected into the container 2 and a liquid level sensor 1 for measuring the liquid level of the liquid are attached to the lid 3. The liquid removal device 4 is configured to include a heater that hangs from the lid 3 to the bottom of the container 2.

The liquid level sensor 1 detects a change in the weight of the float 6 which is connected to the float 6 as a liquid inserter which is supported in a state of being inserted into the liquid from above and which is connected to the float 6. The load detector 7 is generally configured.

The float 6 is made of a material having a specific gravity higher than that of the liquid and is formed in a long plate shape. The float 6 is arranged so as to be suspended in the liquid from above. When the liquid in the container 2 is liquid nitrogen, Teflon (polytetrafluoroethylene, [Teflon]) is used as a material having a higher specific gravity than the liquid nitrogen.
Is a trademark of DuPont, acetal resin (for example, so-called “Duracon”, etc.), or a resin similar to these.

The float 6 has its lower end hanging down to the vicinity of the bottom of the container 2 and its upper end constantly protruding upward from the liquid surface (even if the liquid level fluctuates up and down, the upper end is always above the liquid surface). It is set to a length of (approaching upward). this is,
This is because if the float 6 is completely immersed in the liquid, the change of the liquid surface up and down cannot be seen. That is, the buoyancy of the surrounding liquid acts on the portion (immersed portion) of the float 6 inserted in the liquid, and the weight of the float 6 changes by the amount of the buoyancy. If the amount of the portion of the float 6 immersed in the liquid (volume of the immersed portion) changes, the weight of the float 6 also changes correspondingly, but the float 6 is completely immersed in the liquid and the liquid surface There is no change in buoyancy if there is no part protruding from above. For this reason, the upper end of the float 6 is set so as to always protrude upward from the liquid surface regardless of the change in the liquid surface level. The load detector 7 detects a change in the weight of the float 6 due to a change in buoyancy. The float 6 is connected to a load detector 7 via a suspending wire 8.

The load detector 7 detects a change in buoyancy caused by a change in the weight of the float 6, and as shown in FIG. 2, it is roughly composed of a fixed cylinder portion 10 and a measuring portion 11. The fixed tubular portion 10 is formed of a tubular body into which the suspending wire 8 is inserted, and is provided with a screw 12 for fixing the lid body 3 on the outside.

The measuring section 11 is a section for directly measuring the change in the weight of the float 6 (change in buoyancy), and the case 14 constituting the outer shell, and the weight of the float 6 mounted in the case 14. Of the load cell 15 for electrically detecting the change of the load cell, the hanging wire 16 for transmitting the load between the hanging wire 8 and the load cell 15, and the liquid level by the electric signal from the load cell 15 which is connected to the load cell 15. The control unit (not shown) for calculating is roughly configured.

The case 14 is composed of a cylindrical body 18 whose upper part is closed and whose lower part is open, and a lid 19 which is attached to an opening below the cylindrical body 18. An O-ring 20 is provided on the lid body 19 to seal the inside of the cylindrical body 18. A wire insertion hole 21 is provided in the central portion of the lid body 19, and the upper end portion of the fixed cylindrical portion 10 is fixed to the wire insertion hole 21. A suspension wire 8 supporting the float 6 is provided in the fixed cylinder portion 10 and the wire insertion hole 21.
Has been passed through. The upper end of the hanging wire 8 is connected to the hanging metal fitting 16. The suspending metal member 16 is formed in a U shape so as to surround the load cell 15, and the suspending wire 8 is connected to the lower end portion thereof, and the contact terminal 22 that directly contacts the load cell 15 is provided at the upper end portion thereof. .

The load cell 15 changes its electric resistance due to the strain generated inside, and changes the current value accordingly. This load cell 15 has a hanging metal fitting 1
6, the weight of the float 6 acts, and as the weight of the float 6 changes due to the change in buoyancy, the strain in the load cell 15 changes and the electrical resistance (current value) changes. It is like this. The lid 19 is provided with a connector 23 for extracting a change in current from the load cell 15.

The control unit is connected to the load cell 15 via a connector 23. A change in current value generated in the load cell 15 is input as a signal to the control unit. The change in the current value from the load cell 15 is proportional to the change in the buoyancy acting on the float 6, that is, the change in the liquid level. Therefore, the container 2
A plurality of values, such as the current value at the position where the liquid level of the liquid inside is the highest and the current value at the position where the liquid level is the lowest, are input to the control unit in advance and the relationship between the liquid level and the change amount of the current value I ask for it. Then, based on the relationship between the liquid level and the amount of change in current value, the liquid level is calculated from the input current value.

[Operation] In the liquid level sensor 1 constructed as described above, the liquid level of the liquid injected into the container 2 is detected as follows.

The float 6 of the liquid level sensor 1 is immersed in a state where the upper end of the float 6 is left on the liquid surface and the lower portion is inserted into the liquid. Since buoyancy acts on the submerged portion of the float 6, the float 6 is lighter than its original weight by the amount of buoyancy. The load of the float 6 acts on the load cell 15 via the suspension wire 8 and the suspension fitting 16. In this load cell 15,
The current value changes due to the load of the float 6, and the controller detects the amount of change in the current value. The change amount of the current value is detected by the current value from the load cell 15 and the reference current value (for example, the current value from the load cell 15 at the position where the liquid level is the lowest).
By comparing with. Then, the control unit calculates the liquid level from the amount of change in the current value of the load cell 15 based on the relationship between the liquid level and the amount of change in current value that are input in advance.

At this time, even when the liquid boils or the liquid surface vibrates violently, the inside of the liquid does not change so much, and the float 6 immersed in the liquid hardly shakes the liquid surface. It is stable without being affected.

[Effect] In the liquid level sensor 1 constructed as described above, since the float 6 is inserted from the surface of the liquid (liquid level) to the vicinity of the bottom of the container 2, the liquid level is caused by boiling of the liquid or the like. Even if the liquid is disturbed, there is almost no effect and there is no adverse effect such as frost due to low temperature, and the liquid level can be stably and accurately measured. As a result, it is possible to provide a highly reliable liquid level sensor 1 with few failures.

Further, since the liquid surface level is measured by the change in the buoyancy acting on the float 6, the liquid surface level can be continuously measured not only at one point but also from the highest level to the lowest level. .

[Modification] In the above embodiment, the load cell 15 is used as a means for measuring the weight of the float 6, but the present invention is not limited to this, and the weight of the float 6 such as a mass meter can be measured. You may use the means of.

In the above embodiment, liquid nitrogen was used as an example of the low temperature liquid, but the liquid level sensor 1 of the present invention can be used for other low temperature liquids.

In the above embodiment, the float 6 as the liquid insert body is made of a material such as Teflon having a higher specific gravity than the liquid, but a material having a lower specific gravity than the liquid may be used. In this case, since the float 6 is pushed upward by the buoyancy of the liquid, the load cell 15 is attached in the opposite manner to the above embodiment, and the amount of change in the force with which the float 6 is pushed up by buoyancy is measured.

In the above-mentioned embodiment, the float 6 is constituted by a long plate-shaped body, but if the float 6 has a height (length) from the liquid surface to the bottom of the container 2, it is the same as in the above-mentioned embodiment. The action and effect of can be exhibited. For this reason, other shapes such as a rod-shaped body or a flat plate-shaped body may be used.

In the above-described embodiment, the float 6 is composed of one long plate-shaped body, but as shown in FIG. 3, a plurality of rod-shaped bodies or long plate-shaped bodies are integrally molded to form the float. You may. As a result, more stable measurement can be performed with respect to fluctuations in the liquid surface, fluctuations in liquid convection, and the like, as compared with the case of being constituted by one long plate.

[0038]

As described above in detail, the liquid level sensor according to the present invention has the following effects.

(1) Since the liquid inserter is supported in a state of being inserted into the liquid from above, even if the liquid surface is disturbed due to boiling of the liquid or the like, there is almost no effect, and the liquid level is stable and accurate. Will be able to measure.

(2) Even if frost is generated due to low temperature,
It is possible to provide a liquid level sensor that is not adversely affected by this, has few failures, and is highly reliable.

(3) Since the liquid level is measured by the change in the buoyancy acting on the liquid inserter, it is possible to measure the liquid level not only at one point but continuously from the highest level to the lowest level. become.

[Brief description of drawings]

FIG. 1 is a front cross-sectional view showing a state in which a liquid level sensor according to this embodiment is mounted in a container.

FIG. 2 is an enlarged view of a main part of the liquid level sensor according to the present embodiment with a part thereof broken away.

FIG. 3 is a schematic front view showing a modified example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid level sensor, 2 ... Container, 3 ... Lid, 4 ... Liquid extraction device, 6 ... Float, 7 ... Load detector, 8 ... Suspension wire.

Claims (2)

[Claims] 1. A liquid level sensor for detecting a liquid level of a liquid injected into a container, the liquid level sensor being supported by being inserted into the liquid from above.
A liquid inserter in which the volume of the portion immersed in the liquid changes due to the liquid level that rises and falls according to the change in the amount of liquid in the container; and a liquid inserter connected to the liquid inserter. And a load detecting means for detecting a change in buoyancy due to a change in volume of a portion immersed in the liquid, wherein the liquid level is detected from the change in buoyancy detected by the load detecting means. Liquid level sensor that does. 2. The liquid level sensor according to claim 1, wherein the liquid insert body has a specific gravity higher than that of the liquid, and is a rod-shaped body or a long plate-shaped body suspended from above. A liquid level sensor configured to measure the change in the weight of the liquid inserter by the load detecting means to detect the change in the buoyancy, and to detect the liquid level from the change in the buoyancy.