JPH0367579B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is an optical liquid level leveling system that utilizes the property that light propagating in an optical transmission line leaks in response to the difference in refractive index between the gas phase and the liquid phase. Regarding sensors.

(Prior Art) In recent years, various measurement sensors using optical transmission paths such as optical fibers have been proposed for liquid level measurement in the industrial measurement field. For example, a sensor that detects the presence or absence of liquid or the liquid level by peeling off a part of the cladding part of an optical fiber to expose the core part and detecting the presence or absence of liquid or the liquid level based on changes in the amount of light transmitted through the optical fiber, or
Publication No. 18126 discloses a liquid level sensor in which a first optical path for transmitting incident light and a second optical path for transmitting reflected light are formed by optical fibers, and a prism is attached to one end of the optical fiber that becomes the open end of the optical fiber. etc. are disclosed.

(Problems to be solved by the invention) In the former of the above conventional liquid level measurement sensors,
The optical fiber cladding section, in the latter case the prism section, functions as a sensor. For this reason, the measurement area of the liquid level is a point;
It has been impossible to measure continuous changes in liquid level with one sensor. In order to measure continuous changes in liquid level, it would be necessary to line up a large number of similar sensors, resulting in high cost and insufficient resolution.

Therefore, the present invention provides an optical liquid level sensor using a simple and inexpensive optical transmission line that can measure continuous changes in liquid level by bending one optical transmission line with a certain radius of curvature. This is a technical problem to be solved.

(Means for solving the problem) The technical means for solving the above problem is to arrange the middle part of the optical fiber in the liquid level change range, and to reduce the amount of light incident from one end of the optical fiber to a predetermined amount of light. In an optical liquid level sensor that detects the liquid level based on the amount of light received at the other end, a middle part of the optical fiber is wound so that the central axis direction is the liquid level change direction. In addition to forming the coil into a single-layer coil with multiple turns to match the above, it suppresses light leakage when the liquid level is low, while increasing the amount of light leakage when the liquid level is high. The present invention is to adopt a structure in which the winding pitch or winding diameter of the coiled portion is gradually changed so that the amount of light received changes linearly in response to changes in the liquid level.

(Operation, Principle) Next, the principle of liquid level measurement in the optical liquid level sensor of the present invention will be explained with reference to FIGS. 1 to 3.

First, with reference to FIG. 1, consider the propagation of light 3 in air 2 through optical transmission line 1 having a refractive index nf. When light 3 is incident on the interface between optical transmission line 1 and air 2 at an angle θ, the propagation angle of light 3 with respect to the incident angle θ is θa = sin ^-1 (na/nf) (however, na is refractive index of air). That is, when the incident angle θ is in the range θa<θ≦90°, the light 3 is repeatedly totally reflected at the left and right interfaces and propagates within the optical transmission path 1.

Next, as shown in FIG. 2, consider a case where a part of the optical transmission line 1 is in contact with a liquid phase 4 having a refractive index nl. In liquid phase 4, the propagation angle of light 3 is θl=sin ^-1
It is given by (nl/nf), and the light 3 propagates without attenuation in the range where the incident angle θ is θl<θ≦90°.
However, the light 3 whose incident angle θ is in the range θa<θ<θl becomes a radiation mode and rapidly attenuates. In other words,
Once a certain range of the optical transmission path 1 is immersed in the liquid and the light 3 in the radiation mode leaks out as leaked light 6, a constant amount of light is propagated irrespective of the liquid level 5. Therefore, it is not possible to measure changes in the liquid level 5 over a desired height using transmitted light intensity.

Next, consider a case where the optical transmission line 1 is bent with a radius R as shown in FIG. The light 7 propagating without reflection from the straight portion of the optical transmission line 1 is reflected at the outer surface of the R portion of the optical transmission line 1. Similarly, the light 8 that has propagated while being reflected in the liquid phase 4 is also reflected at the outer and inner R portions of the optical transmission line 1 and propagates. At this time, since the optical transmission line 1 is curved with a radius R, the reflection angle of the propagating light changes. Therefore, the reflection angle converted to the range θa < θ < θl becomes a new liquid phase radiation mode, and as the liquid level 5 rises,
The amount of transmitted light will decrease.

By applying this principle and bending the optical transmission line 1 from a large radius to a gradually smaller radius, it is possible to reduce the amount of transmitted light according to the liquid level 5, and by measuring this amount of transmitted light. The liquid level 5 can be measured continuously.

(Example) Next, an example of an optical liquid level sensor using an optical transmission line according to the present invention will be described with reference to the drawings.

4a and 4b show a liquid level sensor formed by winding an optical fiber 13 around a cylinder 14 and continuously giving it an arbitrary radius of curvature. This liquid level sensor transmits light from a light source such as a light emitting diode (not shown) to one end 11 of an optical fiber 13.
For example, a phototransistor is provided on the other end 12 side of the optical fiber 13 to receive light that has entered the optical fiber 13 and has passed through the optical fiber 13. FIG. 4a shows a liquid level sensor in which the winding pitch of the optical fiber 13 is constant. The output of this liquid level sensor has the characteristics shown in Figure 5a, where the lower part of the liquid level sensor leaks a large amount of light when immersed in the liquid phase, and the liquid level is higher than the upper part. The change in the amount of transmitted light decreases as it reaches this point. Therefore, as shown in Figure 4b, by making the winding pitch of the optical fiber large at the beginning and gradually decreasing it towards the top, we can prevent the sudden leakage of light when the liquid level is low and Increases the amount of light leakage when the surface is high,
As a whole, a linear output characteristic as shown in FIG. 5b is obtained.

In addition, the shape of the support around which the optical fiber 13 is wound is changed to the sixth shape.
Linear output characteristics can also be obtained by forming the pillars 14a and 14b in a shape in which the radius of curvature gradually decreases toward the top as shown in the figure. FIGS. 6a and 6c are a plan view and a front view of the conical support 14a, and FIGS. 6b and d are a plan view and a front view of the quadrangular pillar 14b.

In Fig. 6b, the corners of a rectangular prism are rounded, and the radius of curvature decreases as it goes upward. The optical fiber wound around this support is connected to the straight part and R
will have a department. By configuring the sensor section by combining the straight section and the R section in this way, the amount of light leakage can be easily controlled and the liquid level can be measured over a wider range.

FIG. 7 shows a liquid level sensor in which an optical fiber 13 is twisted in a meandering manner to continuously give an arbitrary radius of curvature. There is.

Further, when a plastic fiber is used as the optical fiber, the support 14 may be removed after being wound around the cylinder 14 and thermally deformed. Incidentally, the support 14 may be composed of several thin rods instead of one rod. This improves the drainage of the optical fiber and shortens the response time. However, this is not necessary for measuring the level of gasoline in an automobile, as it is generally better to have a slower response time.

FIG. 8 shows a ridge-shaped optical transmission line 9 bent at an arbitrary radius of curvature on an optically transparent dielectric substrate 10.
This is a liquid level sensor with a Light from a light source such as a light emitting diode is incident on one end 11 of the rigid optical transmission line 9, and a phototransistor, for example, for receiving transmitted light is provided at the other end 12 of the rigid optical transmission line 9. Further, the radius of curvature of the rod-shaped optical transmission line 9 is large at the bottom of the tank, and gradually decreases as it goes upward. This reduces the amount of light leakage at locations where the liquid level is low, and provides output characteristics that are linear with respect to the liquid level.
The amount of light leakage is determined by the radius of curvature, width, and refractive index of the ridge-shaped optical transmission line 9 and the refractive index of the liquid to be measured.

Also, the rigid optical transmission line 9 (refractive index nf) in Fig. 8
When a cladding layer is provided with an optically transparent material with a refractive index nc (nc<nf) on Changes can be measured.

(Effects of the Invention) As described above, according to the present invention, the middle part of the optical fiber is disposed in the liquid level change range, and a predetermined amount of light incident from one end of the optical fiber is transmitted to the other end. In an optical liquid level sensor that detects the liquid level based on the amount of light received when the light is received, the intermediate part of the optical fiber is
The coil is formed into a single-layer coil with multiple turns so that the direction of the winding center axis coincides with the direction of the liquid level change, and it suppresses light leakage when the liquid level is low, while suppressing light leakage when the liquid level is high. Since the winding pitch or the winding diameter of the coiled portion is configured to be gradually changed so as to increase the amount of leakage, the liquid level can be detected linearly at low cost with a simple configuration. .

[Brief explanation of drawings]

Fig. 1 is a principle explanatory diagram showing the light propagation characteristics of an optical transmission line, Fig. 2 is a principle explanatory diagram showing the light propagation characteristics when a part of the optical transmission line is in contact with a liquid phase, and Fig. 3 1 is a principle explanatory diagram showing light propagation characteristics when a part of an optical transmission line bent with a radius R is immersed in a liquid phase. The following drawings relate to embodiments: Fig. 4a is an external view of a liquid level sensor in which an optical fiber is wound on a cylindrical surface with a constant pitch, and Fig. 4b is an external view of a liquid level sensor in which an optical fiber is wound on a cylindrical surface with a gradually changing pitch. An external view of the rolled liquid level sensor, Fig. 5a shows the output characteristics of the liquid level sensor shown in Fig. 4a, and Fig. 5b shows the output characteristics of the liquid level sensor shown in Fig. 4b. Figure 6a is a plan view of a conical column for providing linear output characteristics to the liquid level sensor, Figure 6c is a front view of Figure 6a, and Figure 6b is a square columnar column. The plan view, FIG. 6d, is a front view of FIG. 6b. Fig. 7 is an external view of a liquid level sensor with optical fibers formed in a meandering shape, Fig. 8a is an external view of a liquid level sensor with a ridge-shaped optical transmission path formed on a substrate, Fig. 8 b is a sectional view taken along the line A-A' in FIG. 8a. 9...Rigid optical transmission line, 10...Substrate, 11...Light incident position, 12...Phototransistor mounting position,
13... Optical fiber, 14... Cylindrical column, 14a... Conical support, 14b... Square columnar support.

Claims (1)

[Claims] 1. An optical liquid that detects the liquid level based on the amount of light received after a predetermined amount of light incident from one end of an optical fiber leaks according to the refractive index difference between the gas phase and the liquid phase. In the surface level sensor, the optical fiber is wound in a cylindrical shape or in a single-layer coil around a cylindrical core in a shape that gradually changes the winding pitch so that the amount of received light changes linearly with changes in the liquid level. An optical liquid level sensor characterized by a coiled surface. 2. In an optical liquid level sensor that detects the liquid level based on the amount of light received after a predetermined amount of light incident from one end of an optical fiber leaks according to the refractive index difference between the gas phase and the liquid phase, the above-mentioned An optical liquid level sensor characterized in that the optical fiber is wound in a single-layer coil around a conical or pyramidal core so that the amount of received light changes linearly with changes in the liquid level.