JPH0244213A - Liquid level sensor - Google Patents

Abstract

PURPOSE:To achieve a higher sensitivity with a higher photo detection rate of a photo detector by packing a transparent material with a refractive index thereof close to a prism into a space between the prism and a light emitting element. CONSTITUTION:A conical prism 2 with a top angle of 90 deg. is formed integral at the top end of a cylindrical case 1 comprising a transparent polycarbonate resin and a silicon resin 7 with a refractive index thereof of 1.4 close to 1.586 of the polycarbonate resin is packed and solidified at a clearance between a photo coupler 5 having a light emitting element 3 and a photo detector 4 arranged in parallel and a prism 2. When the prism 2 contacts air, light from the light emitting element 3 is reflected with the prism 2 to be received with the photo detector 4 while the light is refracted outside the system at a point (a) of the prism and is not received with the photo detector 4 when the prism 2 contacts a liquid. With such an arrangement, a high sensitivity is obtained with a higher photo detection rate while it is possible to fix the photo coupler 5 stably in the case 1 by the silicon resin 7.

Description

[Detailed description of the invention] The zero invention in the industrial application field is that a light emitting element and a light receiving element are arranged side by side on the back surface of a prism, and when the outer surface of the prism is in contact with air, the light emitted from the light emitting element is is reflected by the other two surfaces of the prism and received by the light receiving element, and when the outer surface of the prism is in contact with the liquid, the light emitted from the light emitting element is refracted out of the prism and is received by the light receiving element. The present invention relates to a liquid level sensor that detects whether the liquid level has reached the outer surface of a prism by not receiving light.

Conventionally, in this type of liquid level sensor, the light-emitting element and the light-receiving element are arranged as close as possible to the back surface of the prism, but they cannot be brought into complete contact with each other. It is difficult to do this, and some gaps are created.

On the other hand, according to Fresnel's law, the reflectance R when light is perpendicularly incident on a substance with a refractive index of Ng from a substance with a refractive index of Na is expressed by the following equation.

n= (Ng-Na)/(Ng+Na)" Here, if the material of the prism is polycarbonate resin, its refractive index N is 1.586, and the refractive index Na of air is 1.0.
Therefore, the reflectance was 0.0513, and about 5% of the light was reflected by the prism, resulting in a decrease in the light receiving rate and a decrease in sensitivity.

Means for Solving the Problems As a means for solving these problems, the present invention adopts a structure in which the space between the prism and the light emitting element is filled with a transparent substance whose refractive index is close to that of the prism.

Functions and Effects of the Invention The present invention has the above configuration, and in the Moeki Fresnel equation, N
a#Ng, the reflectance R decreases, the light-receiving rate of the light-receiving element improves, the current consumption of the light-emitting element decreases, and the durability improves, and the light-receiving area decreases due to the inclination of the light-emitting element. Furthermore, by using a solidified material such as silicone resin as the filling material, it is possible to firmly fix the light emitting element within the case.

Example An embodiment of the present invention will be described below with reference to the accompanying drawings.

In the figure, l is a cylindrical case made of transparent polycarbonate resin, and a conical prism 2 with an apex angle of 90° is integrally formed at the lower end. At the bottom of the case l, as shown in an enlarged view in FIG. The lead wire 6 of .4 is connected to a signal processing circuit (not shown) installed in the upper part of the case l, and the gap between the photocoupler 5 and the prism 2 is filled with silicone resin 7 and solidified.

In this embodiment, when the prism 2 is in contact with the air, the light emitted from the light emitting element 3 passes through the silicone resin 7, is reflected at two points 1 and b of the prism 2, and returns to the silicone resin 7. As shown in FIG. 2, when the light is received by the light receiving element 4 and a liquid level non-detection signal is inputted to the signal processing circuit, and the prism 2 is in contact with the liquid, the light emitting element 3 is detected as shown by the chain line in FIG.
The light emitted from the light emitting element 3 is refracted at point a of the prism and goes out, and is not received by the light receiving element 4, so that a liquid level detection signal is generated. The reflectance when entering the prism 2 perpendicularly from the polycarbonate resin is 1.
．． 586, the refractive index of the silicone resin 7 is 1.4, so according to the Fresnel equation mentioned above, R = 0.00388, which is extremely small and close to O, so almost all of the light emitted from the light emitting element 3 is received. The light is received by the element 4 and extremely high sensitivity can be obtained.

Furthermore, the silicone resin 7 has the advantage of stably fixing the photocoupler 5 inside the case l.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of the main part thereof. ! 2 cases 2 Nibrism 3: Light emitting element 4: Light receiving element 7: Silicone resin first surface

Claims (1)

[Claims] A prism is integrally fixed to the tip of a cylindrical case, and a light emitting element and a light receiving element are arranged side by side with a space left on the back side of the prism, and when the outer surface of the prism is in contact with air, the light emitting element is removed from the prism. The emitted light is reflected by the other two surfaces of the prism and received by the light receiving element, and when the outer surface of the prism is in contact with the liquid, the light emitted from the light emitting element is refracted out of the prism. The liquid level sensor detects whether or not the liquid level has reached the outer surface of the prism by emitting light and not being received by the light receiving element, the liquid level sensor detecting whether or not the liquid level has reached the outer surface of the prism. A liquid level sensor characterized in that it is filled with a transparent substance whose ratio is similar to that of the prism.