JPH04305123A - Liquid level detector - Google Patents

Abstract

PURPOSE:To enable accurate and correct detection of a specified liquid level without being affected even by the pollution of a light emission surface or the like of a light emitting body and the adhesion of a liquid drop or a liquid film. CONSTITUTION:A photodetecting body 3 is arranged on a light emission body 1 which emits light L from a projector 2 from a horizontal emission surface 1a and an inclined emission surface 1b with a gap G therebetween. The photodetecting body 3 is provided with a first photo detector 4 which receives light regardless of whether the gap is in a liquid or not, a second photo detector 5 which receives light only when the gap G is in the liquid and a third photo detector 6 which receives light only when the gap G is in the air. When a output ratio between the second photo detector 5 and the first photo detector 4 is larger than that between the third photo detector 6 and the first photo detector 4, a liquid level is determined as specified one.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detection device for optically detecting liquid levels such as water and oil levels in various tanks.

0002

2. Description of the Related Art Conventionally, as shown in FIG. 3, a light emitting body 3 is used as a detection device of this type, and has a pair of total reflection surfaces 31a and 31b made of glass or the like and inclined with respect to a liquid surface M.
1 is disposed between the light emitter 32, the photodetector 33, and the liquid level M, and the total reflection surface 31a is used as the measurement surface to measure the liquid level M.
does not reach the measurement surface 31b, the projector 32
The light L from the measurement surface 31a and the other total reflection surface 31b
At a predetermined liquid level (the level indicated by the chain line H) at which the liquid level M reaches the measurement surface 31a, the light L from the projector 32 is reflected by the photodetector 33 and received by the photodetector 33.
It is known that the light is directed directly into the liquid as shown by the dotted line without being reflected at point a. That is, this is
It is determined whether the liquid level is below a predetermined level based on whether the photodetector 33 detects light or not.

0003

[Problems to be Solved by the Invention] However, in the above conventional liquid level detection device, the liquid level is determined based on the absolute amount of light received by the photodetector 33, which is the amount of light reflected from the measurement surface 31a. If the surface 31a becomes dirty or has droplets or a liquid film attached thereto, the amount of light changes due to light scattering on the measurement surface 31a, which may lead to malfunction.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to reliably and accurately detect the liquid level by preventing malfunctions, regardless of changes in the amount of light caused by dirt on the measurement surface of the light emitting body. The purpose of the present invention is to provide a liquid level detection device that can perform

[0005]

[Means for Solving the Problems] In order to achieve the above object, a liquid level detection device according to the present invention comprises a light projector disposed facing the liquid surface and a translucent material. a light emitting body that separates and emits the light into two parts, a horizontal light emitting surface and an inclined light emitting surface, and a light receiving body disposed opposite to the light emitting surface of the light emitting body with a predetermined gap therebetween; a first photodetector set at a position on the photoreceptor side to receive light from the horizontal light exit surface regardless of whether or not the gap is in the liquid; a second photodetector set at a position to receive light from the inclined light emitting surface only at certain times; and a second photodetector set at a position to receive light from the inclined light emitting surface only when the gap is in the air on the side of the photoreceptor; a third photodetector set at a position to It is configured to determine a predetermined liquid level by comparing the output ratio.

According to the present invention, the gap between the light emitting body and the light receiving body is determined based on the output of the first photodetector that receives light from the projector regardless of whether or not the gap is in the liquid. The output ratio between the second photodetector and the first photodetector that receives light only when the gap is in the liquid, and the third photodetector that receives light only when the gap is in the air.
Since the output ratio between the photodetector and the first photodetector is compared, even if the light emitting surface of the light emitting body is contaminated and causes light scattering, it will be affected by the change in the light amount. A predetermined liquid level is detected without any problem.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the main parts of a liquid level detection device according to an embodiment of the present invention. In the figure, 1 is a light emitting body made of a translucent material, such as glass or transparent synthetic resin. A light projector 2 such as a light emitting diode is held facing the liquid surface M, and a measuring device is provided at the lower end of the light projector 2 in order to divide the light L from the projector 2 into two toward the liquid surface M. A horizontal light exit surface 1a along the liquid surface as a surface,
A tilted light exit surface 1b tilted with respect to the liquid level M is formed.

3 is a predetermined gap G at the lower end of the light emitting body 2;
They are photoreceptors facing each other with a distance between them, and are equipped with first, second, and third photodetectors 4, 5, and 6, such as phototransistors. The first photodetector 4 is set at a position that receives light from the horizontal light exit surface 1a regardless of whether or not the gap G is in the liquid, and the second photodetector 5 is set at a position that receives light from the horizontal light exit surface 1a regardless of whether the gap G It is set at a position where it receives light from the inclined light emitting surface 1b only when it is in the liquid. Further, the third photodetector 6 is set at a position where it receives light from the inclined light exit surface 1b only when the gap G is in the air.

The first, second and third photodetectors 4,
The liquid level is determined by the liquid level determining section shown in FIG. 2 using the outputs 5 and 6. That is, in FIG. 2, 21 is a first arithmetic circuit that calculates the ratio between the output B of the second photodetector 5 and the output A of the first photodetector 4, and 22 is a third photodetector. 6 and the output A of the first photodetector 4. A comparison circuit 23 compares the magnitude of the output B/A from the first arithmetic circuit 21 and the output C/A from the second arithmetic circuit 22 to determine the liquid level.

Next, the operation of the above configuration will be explained. Now, when the liquid level M is at the position shown by the solid line in FIG. 1, the gap G is in the air, so the light L from the projector 2 that passes through the horizontal light exit surface 1a goes straight to the first The light received by the photodetector 4 and passed through the inclined light exit surface 1b is bent as shown by the solid line and is not received by the second photodetector 5, but is received by the third photodetector 6. First arithmetic circuit 2
1, the ratio B/A between the output B of the second photodetector 5 and the output A of the first photodetector 4 is calculated, and the second calculation circuit 22 calculates the ratio B/A of the output B of the second photodetector 5 and the output A of the first photodetector 4, and the second calculation circuit 22 calculates the ratio B/A of the output B of the second photodetector 5 and the output A of the first photodetector 4, and The ratio C/A between the output C of the detector 6 and the output A of the first photodetector 4 is calculated. Next, the comparison circuit 23 compares the output ratio B/A from the first arithmetic circuit 21 and the output ratio C/A from the second arithmetic circuit 22, but here, B/A<C /A, so it is determined that the upper air/liquid level M has not reached the predetermined liquid level H shown by the chain line.

Furthermore, when the liquid level M reaches a predetermined liquid level H,
Gap G will be submerged in the liquid. In this case, the floodlight 2
Of the light L from the horizontal light exit surface 1a, the light also travels straight and is received by the first photodetector 4. Furthermore, since the light that has passed through the inclined light exit surface 1b travels straight as shown by the dotted line, it is not received by the third photodetector 6 but is received by the second photodetector 5. The first arithmetic circuit 21 calculates the ratio B/A between the output B of the second photodetector 5 and the output A of the first photodetector 4 in the same manner as described above, and the second arithmetic circuit 22 calculates the ratio B/A of the output B of the second photodetector 5 and the output A of the first photodetector 4. , the ratio C/A between the output C of the third photodetector 6 and the output A of the first photodetector 4 is calculated. Next, the comparison circuit 23
Now, compare the output ratio B/A from the first arithmetic circuit 21 and the output ratio C/A from the second arithmetic circuit 22, and get B/A.
If A>C/A, it is determined that the liquid level M has reached the predetermined liquid level H.

Here, even if the light exit surfaces 1a, 1b are dirty or have droplets attached to them, causing light scattering, the first, second and third photodetectors 4, 5, 6 only changes the amount of light equally, it is possible to accurately detect a predetermined liquid level without being influenced by the above-mentioned dirt or the like.

[0014]

As described above, according to the present invention, a translucent light emitting body having a horizontal light emitting surface and an inclined light emitting surface for light from a projector is provided with a gap between the light emitting surfaces. A first photodetector is provided with a photoreceptor and receives light regardless of whether or not the gap is in the liquid; a second photodetector is provided with a photodetector that receives light only when the gap is in the liquid; A third photodetector that receives light only when it is in the air is arranged on the photoreceptor, and whether the ratio of the output of the second photodetector and the output of the first photodetector is constant. Therefore, even if the light exit surface is dirty or has droplets or liquid film attached to it, the comparison value will not change, only the same amount of light will change for each photodetector. Therefore, the risk of malfunction in liquid level detection is eliminated, and liquid level detection can always be performed reliably and accurately.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing main parts of a liquid level detection device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a liquid level determination section of the liquid level detection device.

FIG. 3 is a configuration diagram showing main parts of a conventional liquid level detection device.

[Explanation of symbols]

1 Light emitting body 1a Horizontal light exit surface 1b Inclined light exit surface 2 Floodlight 3 Photoreceptor 4 First photodetector 5 Second photodetector 6 Third photodetector 23 Comparison circuit G Gap

Claims (1)

[Claims] [Claim 1] A floodlight disposed facing the liquid surface;
A light emitting body made of a translucent material and emitting light from the light projector by dividing it into two parts, a horizontal light emitting surface and an inclined light emitting surface, and a predetermined gap between the light emitting surface of the light emitting body. a first photodetector set on the side of the photoreceptor to receive light from the horizontal light exit surface regardless of whether or not the gap is in the liquid; , a second photodetector set at a position to receive light from the inclined light exit surface only when the gap is in liquid on the side of the photoreceptor; and when the gap is in air on the side of the photoreceptor. a third photodetector that receives light from the inclined light exit surface; A liquid level detection device characterized in that it is configured to determine a predetermined liquid level by comparing the output ratio of a photodetector.