JP2008298510A - Liquid level gauge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive liquid level gauge having high precision for liquid such as low temperature liquefied gas mainly stored in a very low temperature container. <P>SOLUTION: The liquid level gauge includes: a light source; a first optical fiber bundle 1 waveguiding measurement light from the light source; a light receiving element; a second optical fiber bundle 2 waveguiding reflected light onto the light receiving element; one or more sensor fiber bundles 13 in which the tip part is cut obliquely to form a reflective surface, while the measurement light is waveguided onto the reflective surface and the reflected light from the reflective surface is waveguided in order to bring the reflective surface into contact with the liquid; an interface part 10 in which the measurement light from the first optical fiber bundle is optically coupled to the sensor fiber bundle and the reflected light from the sensor fiber bundle is optically coupled to the second optical fiber bundle; and an arithmetic processing part determining the level of the liquid by processing an electric signal on the basis of the reflected light received by the light receiving element. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a level gauge that measures the level of a liquid using an optical fiber, and particularly suitable for the level of a low-temperature liquefied gas such as liquefied nitrogen, liquefied oxygen, liquefied carbon dioxide, liquefied argon, or liquefied hydrogen. It is intended for measurement.

  The low temperature liquefied gas is usually stored in a low temperature insulating container. The low temperature insulation container has a metal vacuum double structure, and the liquid level position of the low temperature liquefied gas cannot be confirmed from the outside. Therefore, a liquid level gauge is conventionally used in which a float (floating element) is used, a part of the float is disposed outside the container, and the liquid level is confirmed by the vertical movement of the float. This level gauge is a level gauge with a simple structure using a float and a spring.

  However, this liquid level gauge often does not display the correct liquid level due to the contact resistance of the float or the aging of the spring, and so on. The actual situation is that they are visually confirmed. As described above, the float type liquid level gauge has a problem in accuracy and responsiveness.

As another method of detecting the liquid level, a liquid level gauge using a diode or a resistor as a detection element is commercially available. Since this level gauge needs to energize the sensing element, it is necessary to prepare a power source, and since current flows through the sensing element, it cannot be used as a combustion-supporting gas.
As another method, Japanese Patent Laid-Open No. 8-184484 discloses “a liquid level measuring device and a liquid container with an optical liquid level gauge”. This prior invention includes a light-transmitting rod-shaped member, a light source portion that introduces light into the rod-shaped member, a light-receiving portion that measures the amount of light derived from the rod-shaped member, and an intensity difference between the introduced light and the derived light. And a calculating means for calculating the liquid level of the liquid container based on the above.

However, in this prior invention, since one optical cable is used for the light detection unit, the liquid level cannot be detected when it is broken or cracked by vibration or impact. Further, since the arrival time of the light reflected from the liquid surface is measured in order to detect the liquid surface, a high-performance arithmetic unit is required, resulting in an increase in cost.
Furthermore, the phase difference between the electrical signal and the electrical signal for modulation of the irradiation light is obtained and converted into the optical path distance. The liquid level is determined from the converted optical path distance, and the remaining amount is continuously measured. A mechanism for modulating light is also required, which increases costs. Since it is mainly to measure the remaining amount of liquid, there is a problem that the liquid level cannot be detected when the optical fiber is in liquid.

In addition, as a liquid level gauge using an optical waveguide, a liquid level measuring device is disclosed in Japanese Patent Laid-Open No. 6-167376.
JP-A-8-184484 JP-A-6-167376

  An object of the present invention is to provide an inexpensive and accurate liquid level gauge mainly for liquids such as low-temperature liquefied gas stored in a cryogenic container.

In order to solve the problem,
The invention according to claim 1 is a light source and a first optical fiber bundle that guides measurement light from the light source,
A light receiving element and a second optical fiber bundle for guiding reflected light to the light receiving element;
One or more end portions cut obliquely to form a reflecting surface, guide the measurement light to the reflecting surface, guide the reflected light from the reflecting surface, and the reflecting surface is in contact with the liquid A sensor fiber bundle,
An interface unit for optically coupling measurement light from the first optical fiber bundle to the sensor fiber bundle and optically coupling reflected light from the sensor fiber bundle to the second optical fiber bundle;
It is a liquid level gauge provided with the arithmetic processing part which processes the electric signal based on the reflected light received with the said light receiving element, and determines the liquid level of a liquid.

  The invention according to claim 2 is the liquid level gauge according to claim 1, wherein two or more sensor fiber bundles having different lengths are provided.

  According to a third aspect of the present invention, the measurement light from the light source is cut off at an end portion obliquely through the first optical fiber bundle and the interface portion to be a reflection surface, and the reflection surface is in contact with the liquid. Then, the light is guided to one or more sensor fiber bundles, and the reflected light reflected by the reflecting surface thereof is guided to the second optical fiber bundle through the sensor fiber bundle and the interface unit, and further sent to the light receiving element. The liquid level determination method is characterized in that the liquid level of the liquid is determined based on the output.

According to the present invention, a highly accurate liquid level gauge can be realized at low cost. That is, by using a flexible optical fiber bundle, it is not broken by vibration or impact. Since the optical fiber bundle has a small heat capacity and is only immersed in a low-temperature liquefied gas such as liquid nitrogen, there is no wasteful consumption of the low-temperature liquefied gas.
In addition, since the first optical fiber bundle and the second optical fiber bundle are separated from the sensor fiber bundle, even if one of them is damaged, only the damaged portion needs to be replaced.

Furthermore, since only light is irradiated inside the container, there is no heat generation, and safe and reliable measurement can be performed.
In addition, by changing the material of the optical fiber, it is possible to detect the liquid level of various types of liquids from room temperature to extremely low temperatures in multiple stages.

FIG. 1 shows an example of the main body of the liquid level gauge of the present invention. In FIG. 1, reference numeral 1 denotes a first optical fiber bundle, and reference numeral 2 denotes a second optical fiber bundle.
The first optical fiber bundle 1 guides measurement light from a light source such as a light-emitting diode or a laser diode (not shown) and sends it to the sensor fiber bundle via an interface section described later.

The first optical fiber bundle 1 uses, for example, 500 silica optical fibers having a diameter of 50 μm, and the incident end 3 of the measurement light is a bundle of 500 optical fibers bundled together. It is protected with a protective coating made of resin.
The second optical fiber bundle 2 guides the reflected light from the sensor fiber bundle through the interface unit and sends it to a light receiving element such as a photodiode (not shown) or an avalanche photodiode.

This second optical fiber bundle 2 uses, for example, 500 silica optical fibers having a diameter of 50 μm, and the reflected light exit end 4 is a bundle of 500 optical fibers bundled together. It is protected with a protective coating made of resin.
The portions of the first and second optical fiber bundles 1 and 2 other than the entrance end portion 3 and the exit end portion 4 are bundled into a single bundle of optical fiber groups constituting each of them. , And is housed in a protective tube 5 made of a metal flexible pipe.
The end of the protective tube 5 is housed in a sleeve 6a made of synthetic resin or the like.

  In the common bundle, the optical fibers forming the first optical fiber bundle 1 and the optical fibers forming the second optical fiber bundle 2 may be randomly bundled to form a bundle. As shown in FIG. They may be arranged and bundled to form a bundle. 2, reference numeral 7 indicates a common bundle, 8, 8,... Indicate optical fibers constituting the first optical fiber bundle 1, and 9, 9,... Indicate optical fibers that constitute the second optical fiber bundle 2. .

The interface unit 10 optically couples the measurement light from the first optical fiber bundle 1 to the sensor fiber bundle and simultaneously couples the reflected light from the sensor fiber bundle to the second optical fiber bundle 2. The interface unit 10 is composed of a substantially cylindrical tube portion 11, and a transparent partition plate 12 is provided at an intermediate portion in the longitudinal direction of the tube portion 11 so as to bisect the tube portion 11 in the longitudinal direction. ing.
The sleeve 6 a at the end of the common bundle is fitted into one of the cylindrical portions 11 so that the end of the common bundle faces the partition plate 12.

Reference numeral 13 in FIG. 1 denotes a sensor fiber bundle. For example, the sensor fiber bundle 13 is formed by bundling seven silica optical fibers having a diameter of 300 μm, and the tip portion thereof is protected by a metal pipe 14 as shown in FIG. The reflecting surface 15 is cut obliquely and polished.
Further, the base end portion of the sensor fiber bundle 13 is housed in a sleeve 6b made of synthetic resin or the like, and this sleeve 6b is fitted into the other inside of the tube portion 11 forming the interface portion 10, and the sensor fiber bundle 13 is inserted. Is opposed to the partition plate 12.

  Measurement light from the first optical fiber bundle 1 is optically coupled to the sensor fiber bundle 13 through the interface unit 10 and guided to the reflection surface 15. The measurement light is reflected by the reflecting surface 15, is again guided through the sensor fiber bundle 13 as reflected light, is transmitted to the second optical fiber bundle 2 through the interface unit 10, and is incident on a light receiving element (not shown). It has become.

When the reflection surface 15 of the sensor fiber bundle 13 comes into contact with the liquid, the refractive index of the medium in contact with the reflection surface 15 changes, so that the amount of light reflected on the reflection surface 15 changes (decreases), and this light amount change is detected by the light receiving element. Is detected, and it can be known that the tip portion of the sensor fiber bundle 13 is in contact with the liquid surface.
That is, when the reflecting surface 15 is immersed in the liquid, the measurement light is not reflected by the reflecting surface 15 but is refracted and proceeds into the liquid. On the other hand, when the reflecting surface 15 is not immersed in the liquid but in the gas phase, the light is reflected by the reflecting surface 15, and the measurement light is reflected by the reflecting surface 15 without going into the liquid, and is reflected as The data is transmitted to the second optical fiber bundle 2 through the sensor fiber bundle 13 and the interface unit 10.

Therefore, as shown in FIG. 1, by providing a plurality of sensor fiber bundles 13 having different lengths, the change in the liquid level can be known, and the function as a liquid level gauge is exhibited.
That is, when the liquid level of the liquid is high (the amount of liquid is large), many sensor fiber bundles 13 are immersed in the liquid. Conversely, when the liquid level is low (the amount of liquid is small), the sensor is immersed. The number of fiber bundles 13 is reduced. Depending on the height of the liquid surface, reflection or refraction occurs at each sensor fiber bundle 13, 13,..., And the amount of reflected light varies depending on the position of the liquid surface. By detecting this amount of light, the amount of liquid can be displayed.

  The angle θ of the reflection surface 15 of the sensor fiber bundle 13 is determined by the following equation (1), and the optimum angle varies depending on the liquid (medium) with which the reflection surface 15 is in contact.

  Table 1 shows suitable angles for various liquids (mediums). If the angle θ is set to 42 degrees from Table 1, it can be applied to almost all low-temperature liquefied gases, which is preferable for convenience.

FIG. 4 shows an example of the overall configuration of a liquid level gauge using the liquid level gauge main body shown in FIG.
The interface unit 10 of the level gauge main body 16 is attached so as to penetrate the upper wall of the heat insulating container 17, and the plurality of sensor fiber bundles 13, 13. The sensor fiber bundle 13 is soaked.

The incident end 3 of the first optical fiber bundle 1 and the emission end 4 of the second optical fiber bundle 2 are optically connected to the light emitting / receiving unit 18. The light receiving / emitting unit 18 is provided with a light source such as a light emitting diode or a laser diode and a light receiving element such as a photodiode or an avalanche photodiode, and measurement light having a wavelength of 640 nm from the light source is incident on the first optical fiber bundle 1. The reflected light from the two optical fiber bundles 2 is sent to the light receiving element, where it is converted into an electrical signal.
This electrical signal is sent to the arithmetic processing unit 19 where noise in the signal is removed and a moving averaging process is performed to obtain an output signal proportional to the reflected light.

  Since the low-temperature liquefied gas such as liquefied nitrogen is a cryogenic liquid, the liquid surface is shaken due to evaporation or the like, which causes noise in the amount of reflected light. In addition, when the light refracted from the sensor fiber bundle 13 and emitted into the liquid is reflected in the heat insulating container and re-enters the reflection surface 15 of the sensor fiber bundle 13, it becomes noise. Therefore, it is necessary to perform noise smoothing by performing a moving average operation in order to cut noise.

  By performing such arithmetic processing on the reflected light from each sensor fiber bundle 13, it is possible to know which sensor fiber bundle 13 has the reflecting surface 15 immersed in the liquid, and this information is displayed on the display unit 20. It can be sent to display the liquid level.

In this configuration example, the liquid level information obtained by the arithmetic processing unit 19 is sent to the RFID unit 21. The RFID unit 21 includes the liquid level information, room temperature information from a thermometer 22 that measures the temperature of the room in which the heat insulating container 17 is installed, and a thermometer 23 that measures the temperature of the heat insulating container 17 itself. And a transmitter for receiving the information from the memory and transmitting the information wirelessly.
By providing this RFID unit 21, liquid level centralized management becomes possible.

  FIG. 5 shows an example of the liquid level centralized management. A plurality of heat insulating containers 17, 17,... Are installed in the room, and a liquid level gauge is attached to each of the heat insulating containers 17. The RFID unit 21 is attached to the liquid level gauge, and liquid level information, room temperature information, and container temperature information about each heat insulating container 17 are transmitted wirelessly.

Antennas 24, 24 are installed on the ceiling of the room, receive radio waves transmitted from each RFID unit 21, receive the signal by the receiver 25, and take the signal into the personal computer 26 via the network for constant monitoring. Do.
In a system in which biological samples such as cells are cryopreserved in the heat insulating container 17, it is necessary to always store a certain amount of liquid nitrogen. Further, if there is an abnormality in the heat insulating container 17, the consumption amount of liquid nitrogen increases rapidly. Therefore, it is necessary to detect immediately and use a heat insulating container having a predetermined heat insulating performance.

As a function of the portion for displaying the liquid level, the liquid level is measured when the display switch is pressed. The interval of the liquid level measurement can be set arbitrarily for 1 second or more. The display is, for example, 5 seconds. The liquid level display is performed by a display unit using a light emitting diode, and an alarm sound is sounded for several seconds with a buzzer or the like in the case of Low as five levels of High, 75%, 50%, 25%, and Low.
Further, when the liquid amount is Low or more, the room temperature is simultaneously measured by the thermometer 22, the surface temperature of the heat insulating container 17 is measured by the thermometer 23, and the surface temperature of the heat insulating container 17 is a set value that is higher than the room temperature. When the temperature is lower than (for example, 5 ° C.), it is determined that the heat insulating performance of the heat insulating container 17 is deteriorated, and the container can be managed by making an alarm sound.

  In addition, it does not specifically limit as an optical fiber which comprises the 1st optical fiber bundle 1, the 2nd optical fiber bundle 2, and the sensor fiber bundle 13, Quartz fiber which has quartz as a main component, multicomponent glass An optical fiber, a plastic optical fiber, etc. can be used. Further, the thickness is not limited, and the number of optical fibers constituting the bundle is not limited.

  Increasing the number of optical fibers is preferable because the area for transmitting light is increased. Therefore, the thickness and number of optical fibers may be appropriately selected and determined from the required accuracy of the liquid level gauge, the mounting position with respect to the heat insulating container 17, the structure, and the like. Furthermore, the number of optical fibers of the first optical fiber bundle 1 and the second optical fiber bundle 2 is not necessarily the same.

Specific examples are shown below.
Ten sensor fiber bundles 13 are prepared using quartz for the core, quartz having a lower refractive index than the core for the clad, and an optical fiber coated with polyimide and acrylate, and an angle θ of the reflecting surface 15 of 42 degrees. The operation was confirmed using liquefied nitrogen and a light emitting diode as a light source.

  As shown in FIG. 6, the horizontal axis represents the number of sensor fiber bundles 13 immersed in liquid nitrogen, and the vertical axis represents the value obtained by changing the amount of reflected light from each sensor fiber bundle 13 to voltage. The relationship between the level and the amount of reflected light can be clearly shown, and it can be seen that the voltage changes almost in proportion to the number of sensor fiber bundles 13 immersed in liquid nitrogen.

  In order to use it as a liquid level gauge, for example, when the number of immersed liquids is 10 or 9, the liquid level is displayed as “HIGH”, and when 8, 7, or 6 are used, “75%”, 5 A liquid level gauge could be obtained by indicating “50%” in the case of four, “25%” in the case of 3, 2, 1, and “LOW” in the case of zero.

It is a schematic block diagram which shows an example of the main body of the liquid level gauge of this invention. It is a schematic sectional drawing which shows the arrangement | sequence state of the optical fiber in a common bundle. It is a schematic sectional drawing which shows the reflective surface vicinity of the sensor fiber bundle in this invention. It is a schematic block diagram which shows an example of the liquid level meter of this invention. It is drawing which shows the liquid level centralized management condition using the liquid level meter of this invention. It is a graph which shows the result of the specific example in this invention.

Explanation of symbols

1 ·· First optical fiber bundle 2 ·· Second optical fiber bundle 10 ·· Interface portion 13 ·· Sensor fiber bundle 19 ·· Operation processing portion

Claims (3)

A light source, and a first optical fiber bundle for guiding measurement light from the light source;
A light receiving element and a second optical fiber bundle for guiding reflected light to the light receiving element;
One or more end portions cut obliquely to form a reflecting surface, guide the measurement light to the reflecting surface, guide the reflected light from the reflecting surface, and the reflecting surface is in contact with the liquid A sensor fiber bundle,
An interface unit for optically coupling measurement light from the first optical fiber bundle to the sensor fiber bundle and optically coupling reflected light from the sensor fiber bundle to the second optical fiber bundle;
A liquid level gauge, comprising: an arithmetic processing unit that processes an electrical signal based on reflected light received by the light receiving element and determines a liquid level of the liquid.   The liquid level gauge according to claim 1, wherein two or more sensor fiber bundles having different lengths are provided.   One or more sensor fiber bundles, in which the measurement light from the light source is cut into a reflective surface by obliquely cutting the tip portion through the first optical fiber bundle and the interface unit, and the reflective surface comes into contact with the liquid The reflected light reflected by the reflection surface of the light is guided to the second optical fiber bundle through the sensor fiber bundle and the interface unit, and further sent to the light receiving element, and the liquid level of the liquid is determined based on the electrical output from the light receiving element A liquid level determination method characterized by determining a position.

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