JPS6111633A - Liquid sensor - Google Patents

Abstract

PURPOSE:To obtain an optical prism with few foreign noises and high discriminating ability by providing a wave length selecting reflection surface to the inside of the prism. CONSTITUTION:A beam 13 generates light with the light length lambda1, lambda2 and is made incident to the prism 11 through a means 18 such as ordinary lens or the like paralleling luminous flux. The incident beam is separated to the lights with wave length lambda1, lambda2 which are made incident to light detectors, 14, 15 respectively, converted into electric signals and amplified with amplifiers 16, 17, and outputted as output signals V1, V2. The existence discrimination of a liquid is usually made by comparing variation amounts with reference levels of the V1, V2 at the time of full reflection when the surface (a) of the prism 11 contacts the air.

Description

[Detailed Description of the Invention] [Technical Field] The present invention utilizes the fact that the angle of total reflection changes due to the difference in the refractive index of liquid substances in contact with the reflective surface of an optical prism to determine the presence or absence, type, concentration, etc. of liquid. Related to optical liquid sensors for detection and identification.

"Prior Art" As an example of the configuration of a sensor that detects or identifies liquid by utilizing total reflection of light, there is a Utility Application No. 12-12-1983.The configuration of this device will be explained with reference to FIG. The signal light emitted from the prism is converted into a parallel light flux by the lens 3 and enters the prism 5. When the prism is in the air, the signal light has an incident angle θ such that it is totally reflected by the detection reflection surface a. The totally reflected signal light is focused by a lens 4 and coupled to an optical fiber 2.

Next, when a liquid having a refractive index n is in contact with the outside of the detection reflection surface a, if the incident angle θ is selected within an appropriate range, the incident light changes from a total reflection state to a partial reflection state. Therefore, if the optical output level is monitored at the detection end of the optical fiber/<2 on the light receiving side, if liquid is in contact with the outside of the detection reflective surface a, the received light level will drop, so the presence or absence of liquid can be detected. be able to.

Figure 2 shows the above consideration through calculations, which is a graph of the calculated values of reflection loss at the prism's detection reflection surface for the incident angle θ.In the figure, the solid line represents the refraction of the prism. When the index πO = 1.51 and the light θ = 62°, if the liquid in contact with the detection reflection surface a of the prism is water (with a refractive index of 1.333), the light is totally reflected and refracted more than the water. This shows that the reflection loss of the sensor increases significantly in the case of oils with a high refractive index (1.4 to 1.5).If this configuration is used, it is possible to detect a small amount of oil without being affected by water. It can be seen that it is possible to detect an oil liquid, or in other words, it is possible to distinguish between two types of liquids.Such a sensor can be used to distinguish between liquids with similar refractive indexes, for example, water and ethyl ether ( u = 1.354) and ethyl alcohol (n
= 1.362), the problem arises that the reliability of identification decreases due to various factors such as manufacturing variations in the sensor, changes in the refractive index of the liquid due to temperature, and variations in the light source level. . As a way to avoid this, as illustrated by the broken line in Figure 2, two or three sensors using different wavelength inputs can be used in parallel so that the refractive index of the prism is different. , and if we compare its output, we get
The accuracy of identification can be improved. However, with this configuration, it is clear that the entire sensor including the light source, optical prism, and photodetector will be larger and more expensive, and furthermore, each sensor will require a different light source and optical transmission system. Since this method uses the following methods, it has the disadvantage that errors inevitably occur due to differences in the characteristics of each of these elements due to temperature changes, changes over time, and the like.

[Object of the Invention] The object of the present invention is to provide a light source that emits two or more different lights, a means for collimating the light flux from the light source, an optical prism,
An optical liquid sensor comprising a signal photodetector for detecting light of each wavelength, wherein the optical prism has a wavelength-selective reflecting surface therein, and a light source and a means for collimating the light beam. Since either or both of the optical prism and the signal photodetector are coupled by optical fibers, it is possible to use a common light source and prism part.
We offer an optical liquid sensor that is low cost, has high discrimination ability, and has low external noise.

It is about providing.

[Configuration of the Invention] Next, the configuration of the present invention will be described. FIG. 3 shows a cross-sectional structure of a liquid detection prism which is the principle of the present invention. In the figure, the signal light consisting of two different wavelengths, 1 and 2, enters the liquid detection surface a (hereinafter referred to as a surface) of the detection optical prism composed of the prism 11 and the second prism 12 at an incident angle θ. incident and reflected. The reflected light passes through prism 11
The light is incident on a second reflecting surface b (hereinafter referred to as "surface") parallel to the a-plane.

Here, if the b-plane has the characteristic of reflecting light with a wavelength of 1 and transmitting light with a wavelength of Z, the signal light will be divided into the solid line corresponding to the input 1 and the solid line corresponding to the input 1 in FIG. The signal light is propagated as shown by the broken line corresponding to 2, and the signal light is separated into input and input. The pre-incident Z that has passed through the b-plane is reflected by the reflective surface C (hereinafter referred to as C-plane) that is parallel to the b-plane of the second prism, and is transmitted through the b-plane again, reaching the a-plane, where it is reflected. Then, it becomes signal light S□, which is reflected at the other wavelength or a-plane and becomes signal light S1. Therefore, if the separated signal lights are detected by two photodetectors or a set of photodetectors with two photodetection surfaces and compared with each other, it is possible to detect a difference in refractive index between liquids, especially between liquids with no difference in refractive index. In the example above, it is possible to identify liquids whose refractive index is to the right of the solid line and near the range where the broken line indicates relatively low loss.

According to this method, the optical prism part for detection can be made smaller, and the propagation part on the light source side, where variations in coupling loss itself and temperature changes are likely to be large, is common for input 1 and input 2. It has the advantage of good stability in terms of characteristics.

[Embodiment] Fig. 1 illustrates one of the specific embodiments of the present invention, in which a light beam 13 emits light of wavelengths 1 and 2, and a means 18 for collimating the light beam using a lens or the like is usually used. After that, Prism 11
incident on . The incident light beam is separated into light beams with wavelengths 1 and 2 according to the process explained in FIG.
6.17, the output signal v1. It is output as v2. The presence or absence of liquid is normally determined by Vi during total reflection, such as when the a-plane of the prism 11 is in contact with air.
What is necessary is to compare the variation value with respect to the reference level of v2.

FIG. 4 shows another embodiment of the present invention, in which optical fibers are coupled between the light source 13 and the optical prism 11, and between the optical prism 11 or 12 and the photodetector 14.15. According to this example, there are excellent practical advantages such as being able to downsize the liquid sensor portion, reducing the wrap-around of electrical signals from the light source side to the photodetector side, and other external electrical noises.

In the above description, lenses and the like that are not directly related to the essence of the present invention are omitted. Further, although the wavelengths of light are set to two, input 1 and input 2, for simplicity, more wavelengths can be used if necessary.

[Effects of the Invention] According to the present invention, by using an optical prism having an internal wavelength-selective reflecting surface, light from a light source that emits light of two or more different wavelengths can be simultaneously reflected by one set of prisms. ,
By being able to obtain light with two or more wavelengths, and by coupling optical fibers between the light source and the means for collimating the light flux, and between the optical prism and the signal photodetector, it is possible to achieve low cost and high performance. Accordingly, it is possible to provide an optical liquid sensor that has a high degree of discrimination ability and has little external noise.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing one embodiment of the present invention, Fig. 2 is a diagram illustrating calculated values showing the reflection loss of a luminous flux due to different wavelengths, and Fig. 3 is a diagram showing a liquid detection principle according to the present invention. FIG. 4 is a cross-sectional view of the prism for use in the liquid sensor, FIG. 4 is a diagram showing another embodiment of the present invention, and FIG. 5 is a diagram showing the structure of a conventional liquid sensor. 1-Sea human radiation 2-m-outgoing light 3--lens 4--lens 5-m-prism
11-m-Optical prism 12--Second prism 1
3-m-light source 14.15-m-detector 18.1
7--Amplifier 18--Lens 21--Optical fiber. 22.23-Sea optical fiber a--one sensing surface b-=
-Reflection and transmission surface c--Reflection surface θ--Incidence angle 1, Input 2--Light wavelength Sl, 52--Isshin. Signal light V,,V2-m-output signal

Claims (1)

[Scope of Claims] 1) A light source that emits light of two or more different wavelengths, means for collimating the light flux from this light source, an optical prism, and a signal photodetector for detecting light of each wavelength. An optical liquid sensor comprising: an optical liquid sensor, wherein the optical prism has a wavelength-selective reflective surface therein. 2) A claim characterized in that either or both of the light source and the means for collimating the light beam and the optical prism and the signal photodetector are coupled by an optical fiber. The liquid sensor according to item 1.