JPH0868683A - Liquid level sensor - Google Patents

Abstract

PURPOSE: To obtain an optical liquid level sensor having no movable part and excellent in explosion resistance which is not damaged by rocking or vibration and can detect the liquid level easily. CONSTITUTION: A light pipe 11 comprising a transparent core part and a clad part having lower refractive index is provided, in the longitudinal direction thereof, with at least one constricted part 3. The liquid level sensor further comprises a light source 13 for introducing light into the light pipe 11, and a part 15 for receiving the light passed through the light pipe 11, wherein the light pipe 11 is disposed to intersect the liquid level 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical level sensor using a light pipe, which is used for measuring the liquid surface position of a liquid in a container.

[0002]

2. Description of the Related Art Conventionally, in order to detect the liquid level in a container, a float is floated on the liquid level, and the fluctuation of the liquid level is detected as a change in the resistance value of a sliding variable resistor due to the displacement of the float, which allows the movement It was designed to drive a magnet type or bimetal type meter.

However, such a conventional liquid level sensor, when used in an environment where there is great shaking such as at sea, or in a place subject to vibration, supports a float that is a movable part and its support. There is a problem that parts and shafts are damaged.

Further, since the sliding resistance portion is inside the container, electric sparks may be generated at the contacts of the sliding resistance, and when flammable gas or flammable liquid exists in the container, combustion or Explosion can occur and is extremely dangerous.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the problems of the conventional level sensor, is not damaged even if shaken or vibrated, is excellent in explosion proof, and has a simple mechanism. The challenge is to provide.

[0006]

Means for Solving the Problems As a result of various studies to solve the above problems, the present inventor has conceived to use a light pipe composed of a core component and a clad component having different refractive indexes, The present invention has been completed.

That is, according to the present invention, at least one constricted portion is provided in the length direction of a light pipe composed of a transparent core component and a clad component having a refractive index smaller than that, and light is applied to the light pipe. A liquid level sensor, wherein a light source for introducing the light and a light receiving section for receiving light passing through the light pipe are provided, and the light pipe is disposed so as to intersect the liquid level, In particular, the clad is made of a fluororesin having a thickness of 10 to 1,000 μm, and the core is a polysiloxane having a diameter of 1 to 100 mm,
It is preferably made of polymethylmethacrylate, polycarbonate or aromatic polyester.

As shown in FIG. 1, the light pipe used in the present invention comprises a transparent core component 1 and a clad component 2 having a refractive index smaller than that of the transparent core component 1 and at least one constricted portion 3 in the length direction thereof. Have

The core component 1 and the clad component 2 can be formed of a known material such as glass or synthetic resin. As the core component 1, polysiloxane, polymethylmethacrylate or polycarbonate which is transparent to transmitted light is used. Aromatic polyesters are preferred, and as the clad component 2, a fluororesin is preferably used because it has a lower refractive index than the core component 1 and is more excellent in chemical resistance, oil resistance and heat resistance. Preferred examples of the fluororesin include tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).

The core component 1 preferably has a diameter of 1 to 100 mm, and the clad component 2 preferably has a wall thickness of 10 to 1,000 μm.

The shape of the constricted portion 3 is shown in FIGS.
It can have any shape as shown in, and the number is 1
Any number may be used as long as it is equal to or larger than the number, but the larger the number, the finer the liquid surface can be detected. Usually 3-5
It is practical to provide about one piece.

FIG. 2 is a schematic side view showing an example of the liquid level sensor of the present invention. An optical fiber 12 is connected to one end of a light pipe 11 having a constricted portion 3 to form a light source 13.
To the optical sensor (light receiving portion) 15.

The light pipe 11 is a liquid 17 in a container 16.
The liquid level 18 is arranged so as to intersect with the liquid surface 18 in other words, in other words, it is arranged in the vertical direction.

The light introduced from the light source 13 through the optical fiber 12 into the light pipe 11 may be partially leaked to the outside at the constricted portion 3, but most of the light is transmitted through the pipe and the optical fiber The light is received by the optical sensor 15 via 14. Next, photoelectric conversion is performed, the signal comparator 19 compares the levels of the reference signal and the input signal, the variable resistor 20 is controlled, and the meter 21 is driven.

In this case, if the liquid 17 is present in the constricted portion 3, the amount of light leaked in the constricted portion 3 increases and the intensity of the light received by the optical sensor 15 decreases. Therefore, the intensity of this light is measured by the meter 21. By reading, the position of the liquid surface 18 can be known.

FIG. 5 is a view for explaining an example of a method for manufacturing a light pipe used in the liquid level sensor of the present invention, in which a plurality of fluororesin tubes 2, 2 ', 2 "are provided in the fluororesin shrink tube 4. Are placed at intervals (Fig.
(A)), the fluororesin shrink tube 4 is shrunk to form the constricted portions 3, 3'between the fluororesin tubes 2, 2 ', 2 "adjacent to each other (Fig. 5 (b)), and then the silicone The resin 1 is filled to obtain the light pipe 11 (see FIG. 5).
(C)).

Light pipe 11 obtained by this method
The fluororesin shrinkable tube 4 and the fluororesin tubes 2, 2 ', 2 "constitute a clad component, and the silicone resin 1 constitutes a core component.

FIG. 6 is a schematic side view showing another example of the liquid level sensor of the present invention. A light reflecting mirror 22 is provided at one end of a light pipe 11 having a constricted portion 3 and an optical fiber is provided at the other end. 12 and 14 are connected to guide light from the light source 13 to the light pipe 11 via the optical fiber 12 and guide light reflected by the reflecting mirror 22 to the optical sensor (light receiving unit) 15 via the optical fiber 14. It was done like this. Regarding the same parts as the liquid level sensor shown in FIG.
The same numbers are attached and the description is omitted.

[0019]

The principle of detecting the liquid surface by the light pipe used in the present invention is as follows.

That is, as shown in FIG. 3 (a), the light La introduced into the light pipe 11 is supplied to the core 1 and the cladding 2.
At the constricted portion 3, a part of the light La ′ is transmitted through the clad 2 and reflected at the boundary between the clad 2 and the external space. Further, some light La ″ may leak to the outside.

In this case, when the liquid 17 is present in the constricted portion 3, the difference in the refractive index between the liquid 17 and the cladding 2 is small,
The light transmittance at the boundary is increased, as shown in FIG.
As shown in FIG. 5, a certain proportion of the light Lb leaks toward the liquid 17, and the light Lb is reflected back to the core 1 by that much.
The proportion of a'is reduced. Therefore, if the intensity of the output light is detected, the relationship between the intensity of the output light and the liquid level becomes as shown by the solid line in FIG. 4 according to the number of the constricted portions 3, and the liquid level must be detected. You will be able to

The material of the core component 1, the light pipe 1
When the thickness of No. 1 and the shape of the constricted portion 3 change, the relationship between the intensity of the output light and the liquid level may become as shown by the dotted line in FIG.

[0023]

EXAMPLE 1 The present invention will be described in more detail below with reference to examples. FEP was extruded into a tubular shape having an outer diameter of 3.0 mm and a wall thickness of 0.2 mm, and constricted portions were formed at 5 places at 7 cm intervals. The shape of the constricted portion is a hyperboloid shape as shown in FIG. 1 (a), and the shortest outer diameter D of the constricted portion is 2.0 mm,
The maximum width L of the constricted portion was 5 mm.

Next, polysiloxane (KE-103 manufactured by Shin-Etsu Chemical Co., Ltd.) and a vulcanizing agent (CAT-10, the same).
3) was mixed, filled in this tube, and crosslinked and solidified to prepare a light pipe.

Using this light pipe, a liquid level sensor was assembled as shown in FIG.

This liquid level sensor can accurately detect the liquid level in the container, there is no risk of damage due to shaking or vibration, and no electric sparks are generated in the container. , There was no explosion.

[0027]

[Example 2] FEP having a wall thickness of 3.2 mm and an inner diameter of 3.0 mm
Inside the shrink tube, outer diameter 3.0 mm, wall thickness 0.2 mm,
As shown in FIG. 5 (a), six PFA tubes each having a length of 7 cm were inserted at an interval of 5 mm, filled with polymethylmethacrylate (14-7630 manufactured by Maris Co., Ltd.), and then solidified. A light pipe as shown in FIG. 5 (c) was created.

Using this light pipe, a liquid level sensor was assembled as shown in FIG.

Similar to the first embodiment, this liquid level sensor can accurately detect the liquid level in the container and is free from damage, combustion and explosion.

[0030]

Example 3 FEP was extruded into a tube having an outer diameter of 10 mm and a wall thickness of 0.2 mm, and constricted portions were formed at 5 places at 10 cm intervals. The shape of the constricted portion was the shape shown in FIG. 1C, and the shortest outer diameter D of the constricted portion was 7 mm and the maximum width L of the constricted portion was 5 mm.

Then, after filling with polycarbonate (Lexan manufactured by Engineering Plastics Co., Ltd.),
Solidified. A reflecting mirror was provided at one end of the tube, and two optical fibers were connected at the other end, to assemble a liquid level sensor as shown in FIG.

This liquid level sensor was able to accurately detect the liquid level in the container, as in Example 1, without causing damage, combustion, or explosion.

[0033]

This liquid level sensor can accurately detect the liquid level in the container, and since it has no moving parts, it will not be damaged even if shaken or vibrated, and an electric spark will be generated in the container. Since it did not occur, neither combustion nor explosion occurred.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of the shape of a constricted portion of a light pipe used in a liquid level sensor of the present invention.

FIG. 2 is a schematic side view showing an example of the liquid level sensor of the present invention.

FIG. 3 is a schematic diagram for explaining the operation of the liquid level sensor of the present invention.

FIG. 4 is a graph showing the relationship between the output light intensity and the liquid level in the liquid level sensor of the present invention.

FIG. 5 is a cross-sectional view for explaining an example of a method for manufacturing a light pipe used in the liquid level sensor of the present invention.

FIG. 6 is a schematic side view showing another example of the liquid level sensor of the present invention.

[Explanation of symbols]

 1 core component 2 clad component 3 constriction part 11 light pipe 13 light source 15 light receiving part 18 liquid level

Claims (2)

[Claims] 1. A light pipe comprising a transparent core component and a clad component having a refractive index smaller than that of the light pipe, and at least one constricted portion being provided in the length direction of the light pipe, and for introducing light into the light pipe. A liquid level sensor, comprising: a light source; and a light receiving section for receiving light that has passed through the light pipe, the light pipe being disposed so as to intersect the liquid surface. 2. The clad component has a wall thickness of 10 to 1,000.
Made of fluorocarbon resin with a diameter of 1-10
0mm polysiloxane, polymethylmethacrylate,
The liquid level sensor according to claim 1, which is made of polycarbonate or aromatic polyester.