JPH1151744A - Level meter and underground-permeation-face level measuring apparatus using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a level meter which does not comprise a moving part and in which a failure is hard to generate. SOLUTION: A level meter is provided with a float 1 which is long in the up-and-down direction, with a fixed case 3 which houses the float 1 and into which a liquid can creep, with a tension-resistant body 13 which connects the float 1 to the fixed case 3 in such a way that the float 1 does not rise relatively with reference to the fixed case 3 when buoyancy acts on the float 1 and with a sensor 15 which detects the elongation and the strain of the tension-resistant body 13. An optical-fiber Bragg diffraction grating is used as the sensor 15. A change in the buoyancy of the float 1 is converted into a change in the tension of the tension-resistant body 13, and a level is measured on the basis of the elongation and the strain of the tension-resistant body 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level gauge for measuring the height of a liquid surface, and to a device for measuring the level of a submerged surface using the same.

[0002]

2. Description of the Related Art A conventional liquid level meter generally floats a float on the surface of a liquid and measures the liquid level from the height of the float.

[0003]

However, since the conventional liquid level meter has a float and a movable part attached to the float, a failure due to the movable part, such as the float being caught, is likely to occur, and the reliability is low. There was a problem.

In order to check the strength of the embankment when the river rises, it is important to detect how much the soil constituting the embankment is infiltrated by water seepage. There was no suitable means to measure the infiltration surface level in the ground.

[0005] It is an object of the present invention to provide a liquid level gauge having substantially no movable parts, and an underground infiltration surface level measuring apparatus using the same.

[0006]

According to the liquid level meter of the present invention which achieves this object, a float which is long in the vertical direction, a fixed case in which the liquid containing the float can enter, and buoyancy acted on the float. A strength member that connects the float and the fixed case so that the float does not rise relatively to the fixed case, and a sensor that detects an extension strain of the strength member is provided. .

With this configuration, even if the liquid level rises, the float does not rise because it is retained by the strength member, and the rise in the liquid level increases the buoyancy of the float and increases the tension of the strength member. Will be. Since an increase in the tension of the tensile strength member appears as elongational strain of the tensile strength member, the liquid level can be measured by detecting the elongational strain with a sensor.

As the sensor, an optical fiber Bragg grating (hereinafter, referred to as FBG), an optical fiber Brillouin OTDR, an electric load cell, or the like can be used. FGB detects a change in elongation strain of an optical fiber as a wavelength shift amount of Bragg reflected light, and because it is electrically insulating, does not suffer from lightning strikes, sparks, etc., has excellent corrosion resistance, and transmits a signal through an optical fiber. Remote monitoring, no battery (power supply) required, large wavelength shift, multiple FBs
G is connected in series on one optical fiber to enable simultaneous measurement at multiple points, and has advantages such as easy production and high reproducibility.

An optical fiber Brillouin OTDR detects a change in elongation strain of an optical fiber as a wavelength shift amount of Brillouin scattered light in the optical fiber, and has the above-mentioned advantages of the FBG. Is not provided. Although the electric load cell can be used, it has not only the above advantages of the FBG, but also is not suitable for outdoor use because the sensor output is affected by moisture. Therefore, it is particularly preferable to use FBG as the sensor.

Although the liquid level meter of the present invention is suitable as a water level meter, it can also be used to measure the amount of liquid other than water, for example, oil (surface level).

Further, the liquid level meter of the present invention can be used as an underground infiltration surface level measuring device by using a fixed case for accommodating the float as a container having a water-permeable peripheral wall and capable of being buried underground. it can. When such an underground infiltration surface level measuring device is buried in the ground, water in the infiltrated soil penetrates through the water-permeable peripheral wall into the container, and the surface of the water that accumulates in the container is removed. Since the height is almost the same level as the infiltrated surface in the ground, the level of the infiltrated surface in the ground can be measured by measuring the water level in the container. If the level of the infiltration surface in the ground can be measured, it is extremely effective for predicting the break of a bank when the river is flooded and for predicting the occurrence of landslide in a landslide zone.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. [Embodiment 1] FIG. 1 shows an embodiment of a liquid level meter according to the present invention. In the figure, reference numeral 1 denotes a hollow sealed float that is long in the vertical direction, and 3 denotes a fixed case that accommodates the float 1. A buoyancy transmission rod 5 is vertically fixed to the center of the upper end surface of the float 1, and a flat plate 7 is horizontally fixed to the upper end of the buoyancy transmission rod 5.

The fixed case 3 has a horizontal cover plate 9 at its upper end.
And has a structure in which the lower end is opened (the lower end may have a bottom plate with a hole). A guide pipe 11 through which the buoyancy transmitting rod 5 penetrates is fixed to a central portion of the cover plate 9. The cover plate 9 of the fixed case 3 and the flat plate 7 above the float 1 are connected by a tensile member 13. Three or more, preferably six to ten, strength members 13 are provided around the guide pipe 11 at equal intervals in the circumferential direction. An FBG 15 is fixed to one of the strength members 13 in the longitudinal direction by an adhesive 17. FB
G15 is formed on a part of the optical fiber 16.

Reference numeral 19 denotes a bracket for vertically fixing the fixed case 3 to the fixed structure, and reference numeral 21 denotes a fixed case 3.
A guide 23 for keeping the float 1 vertical within the cap 23 is a cap that covers a portion protruding from the upper end of the fixed case 3. The optical fiber 16 is pulled out of the cap 23,
One end is connected to a measuring instrument 25 installed in a monitoring station or the like, and the other end is connected to, for example, the FBG of the next liquid level meter (it may be terminated as it is). As shown in FIG. 2, the measuring device 25 includes a light source 27, a coupler 29, a tunable bandpass filter 31, a photodetector 33, and the like.

Next, the operation of the liquid level meter configured as described above will be described. When this liquid level gauge is used, for example, as a river water level gauge, the fixed case 3 is vertically fixed to a pier or the like by the bracket 19. The water W of the river enters the fixed case 3 from the lower end opening of the fixed case 3. When the water W enters the fixed case 3, the float 1 receives buoyancy proportional to the water level and tries to rise, but is prevented from rising by the tensile strength member 13.

As a result, the buoyancy acting on the float 1 is converted into the tension of the strength member 13. Multiple tensile members 13
Are arranged at equal intervals around the guide pipe 11, substantially equal tension is applied to each strength member 13. As a result, an elongation strain is generated in each tensile member 13 in proportion to the tension. Since the FBG 15 is integrally fixed to one tensile member 13, when the tensile member 13 undergoes elongation distortion, the same amount of elongation distortion also occurs in the FBG 15.

Light enters the optical fiber 16 including the FBG 15 from the light source 21 of the measuring instrument 25 through the coupler 29. In the FBG 15, when the Bragg condition of the FBG is satisfied, Bragg reflected light of a specific wavelength is generated.
The wavelength of the Bragg reflected light changes as shown in FIG. 3, for example, depending on the magnitude of the elongation distortion of the FBG 15. Therefore, if the wavelength of the Bragg reflected light is detected by the tunable bandpass filter 31 and the photodetector 33 in the measuring device 25, the amount of elongation distortion of the FBG 15 can be measured.
Since the amount of elongation strain is an amount proportional to the water level, the water level can be measured.

In the water level meter having the above configuration, when the materials and dimensions of the components are set as follows, the relationship between the water level and the amount of elongation strain of the tensile strength member is as shown in FIG. Fixed case: Hard PVC pipe with outer diameter of 267 mm and length of 2500 mm. The top lid is a 5mm thick rigid polyvinyl chloride plate. Float: Made of hard polyvinyl chloride, outer diameter 216m
m, inner diameter 195mm, length 1900mm, upper and lower plate thickness 5
mm. Buoyancy transmission rod: Hard polyvinyl chloride, outer diameter 60m
m, length 250 mm. Flat plate at the upper end of buoyancy transmission rod: stainless steel, outer diameter 18
0 mm, plate thickness 10 mm. Tensile strength body: Eight single steel wires with an outer diameter of 5.5 mm and a length of 200 mm. Therefore, the water level can be accurately measured by detecting the elongation strain of the tensile strength member by the FBG.

In this embodiment, an example was described in which the FBG was attached to one of a number of tensile members, but the FBG was attached to a plurality of tensile members, and measurement was performed with each FBG. It is also possible to average the obtained data. This enables more accurate measurement.

[Embodiment 2] FIG. 5 shows an embodiment of an underground infiltration surface level measuring apparatus according to the present invention. The underground infiltration surface level measuring device measures the level H of infiltration by water W that has infiltrated the soil S. In FIG. 5, FIG.
The same reference numerals are given to the same parts as. This device is a fixed case for housing the float 1 and has a container 35 having a strength enough not to be deformed or damaged by earth pressure even when buried in the ground.
You are using The container 35 has a bottom plate 37.

A number of small holes 39 are formed in the peripheral wall of the container 35 and the bottom plate 37. Further, the container 35 is provided integrally with a filter layer 41 that allows water to pass through but substantially does not allow soil to pass outside the peripheral wall and the bottom plate 37. The filter layer 41 can be composed of, for example, an open-cell foamed plastic sheet or the like. The container 35 is made longer than the float 1 so that a space G is formed between the bottom plate 37 and the bottom surface of the float 1. The configuration other than the above is the same as that of the first embodiment.

The underground infiltration surface level measuring device constructed as described above is used for a container 3 with a filter layer 41 as shown in the figure.
5 is used in a state of being buried vertically in the soil S. Sat
When the infiltration surface level H in the filter rises, the filter layer 4
The water W enters the container 35 through the holes 1 and the holes 39.
The soil S is blocked by the filter layer 41 and does not enter. As a result, the water level in the container 35 is substantially the same as the infiltration surface level in the soil S. Therefore, if the water level in the container 35 is measured in the same manner as in the first embodiment, the infiltration surface level H can be measured. .

Although the filter layer 41 prevents the soil from entering the container 35, fine particles of the soil may still pass through the filter layer 41 and enter the container 35. The soil particles that have entered the container 35 settle at the bottom of the container 35. The space G between the bottom plate 37 and the bottom surface of the float 1 is for depositing soil that has entered the container 35. Since the amount of the soil fine particles entering the container 35 through the filter layer 41 is very small, by making the space G sufficiently large, it is possible to prevent the measurement operation from being hindered by the infiltrated soil.

FIG. 6 shows an example of the state of use of the underground infiltration surface level measuring device. An underground infiltration surface level measuring device 47 is buried at an appropriate interval in the dike 45 of the river 43 and the optical fiber 1
6 is connected in series. One end of the optical fiber 16 is connected to a measuring instrument 25 installed at a monitoring station, and the measured values are processed by a computer 49. By doing so, it is possible to intensively monitor the infiltration level at various points of the embankment 45, to grasp the state of the embankment 45 at the time of increasing the water level, and to predict the collapse,
Repair work can be performed accurately.

[0025]

As described above, according to the present invention, a change in the buoyancy of the float is converted into a change in the tension of the tensile strength member, and the liquid level is measured from the elongation strain of the tensile strength member. A highly reliable liquid level meter having no movable parts can be obtained. Also, by using this liquid level meter, it is possible to configure a device for measuring the level of the infiltrated surface in the ground, and it is possible to monitor the strength of the embankment and predict the landslide in the landslide zone.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a liquid level meter according to the present invention.

FIG. 2 is a block diagram showing a configuration of a measuring instrument used for the liquid level meter of FIG.

FIG. 3 is a graph showing a change in Bragg reflection wavelength with respect to a change in elongation strain of FBG.

FIG. 4 is a graph showing the relationship between the water level and the elongation strain of the tensile strength member in the liquid level meter of FIG.

FIG. 5 is a cross-sectional view showing an embodiment of an underground infiltration surface level measuring device according to the present invention.

FIG. 6 is an explanatory diagram showing an example of a use state of the underground infiltration surface level measuring device of FIG. 5;

[Explanation of symbols]

 1: float 3: fixed case 5: buoyancy transmission rod 7: flat plate 9: cover plate 11: guide pipe 13: tensile strength member 15: FBG (optical fiber Bragg diffraction grating) 16: optical fiber 17: adhesive 25: measuring instrument 35 : Container 39: Hole 41: Filter layer W: Water S: Soil H: Infiltration surface level

Claims (3)

[Claims] A float that is long in the vertical direction, a fixed case into which a liquid containing the float can enter, and a float that prevents the float from rising relative to the fixed case when buoyancy acts on the float. A liquid level meter comprising: a tensile strength member that connects the tension strength member and a fixed case; and a sensor that detects an extension strain of the tensile strength body. 2. The liquid level meter according to claim 1, wherein the sensor is a fiber Bragg grating attached to a tensile member. 3. The liquid level gauge according to claim 1, wherein the fixed case is a container that can withstand burial in the ground, and has a peripheral wall that allows water to pass through but does not allow soil to pass through. Underground infiltration surface level measurement device.