JPH023938B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a measuring device for measuring the density, concentration, specific gravity, etc. of a liquid, and more specifically, to a measuring device for measuring the density, concentration, specific gravity, etc. of a liquid using an optical system. The present invention relates to a measuring device for measuring.

2. Description of the Related Art Measuring devices that use optical systems to measure the density, concentration, specific gravity, etc. of liquids have been known. In this device, a transmitting body is immersed in the liquid to be measured, the measurement light is projected toward the interface wall that forms the interface with the liquid to be measured, and the light reflected from this interface wall is received by the light receiving element. Based on the amount of this reflected light, the density, concentration, specific gravity, etc. of the liquid to be measured are measured.

By the way, the light-receiving element receives reflected light and external light other than the reflected light, and when the amount of reflected light is small, the light-receiving element is greatly affected by the external light. The conventional measuring device has the disadvantage that it is difficult to accurately measure the density, concentration, specific gravity, etc. of a liquid.

In order to improve this drawback, Japanese Patent Application Laid-Open No. 53-139560
As disclosed in the above publication, it has been proposed that a reflecting mirror is provided on the interface wall to totally reflect the incident light so that the amount of reflected light does not decrease as much as possible.
In the device disclosed in JP-A No. 53-139560, it is difficult to attach the reflecting mirror itself, and since the angle of incidence of the incident light is fixed, total reflection occurs only under certain specified conditions. Therefore, there are problems such as a small change in the amount of light during measurement, and the disturbance light greatly affects the measurement results, lowering the measurement accuracy.In addition, it has the disadvantage that it is difficult to manufacture at a low cost.

The present invention has been made in view of the above-mentioned drawbacks of the conventional art, and an object of the present invention is to provide a measuring device that can prevent the attenuation of the amount of reflected light as much as possible and that can be easily manufactured. There is a feature of the present invention, in order to effectively utilize the law of total internal reflection of light,
This is due to the improved shape of the interface wall.

Embodiments of the present invention will be described below with reference to the drawings.

In FIGS. 1 and 2, 1 is a liquid to be measured having a refractive index n ₁ , and 2 is a light transmitting body 2 having a refractive index n ₂ .
, and the refractive index n ₂ is said to be larger than the refractive index n ₁ . As shown in FIG. 2, this light transmitting body 2 is made of a plate-like body made of glass, plastic, etc. and has an appropriate thickness. A light source 6 faces the light entrance 3 via a lens 7, and a light receiving element 8 faces the light receiving aperture 4. The light inlet 3 has light inlet guide walls 9 and 10 having a predetermined width t, and the light receiving aperture 4 has light inlet guide walls 11 and 12.

The light transmitting body 2 serves as an optical path for measurement light having a reflection region and a transmission region, and the light emitted from the light source 6 is converted into parallel light by the presence of a lens 7, and the light is passed through the light entrance as measurement light. Light enters from 3, interface wall 5
The light is reflected at the light receiving port 4 and taken out as reflected light from the light receiving port 4.

Reference numeral 13 denotes a portion not directly involved in measurement, which is usually flat. The interface wall 5 is
As shown in the figure, the shape is a cylindrical curved circular arc surface that follows an imaginary circle with a radius R centered on point O, and the light entrance guide wall 10 and the light reception opening guide wall 12 are tangent to this imaginary circle. exists on the line.

The shape of the interface wall 5 is selected so that all straight measurement light entering from the light entrance 3 is effectively reflected under predetermined conditions.
The straight measurement light L incident along the point P on the interface wall 5
If it is reflected at
are the refractive index n 1 of the liquid to be measured ₁ and the refractive index of the light transmitting body 2
When it is larger than the critical angle determined by n ₂ (critical angle α=Sin−1n ₁ /n ₂ where n ₂ > n ₁ ) and smaller than the right angle, the straight measurement light L will move in this range. Since the light is totally reflected, the shape of the arcuate surface of the interface wall 5 must satisfy this condition.

If this condition, in which the incident angle β of the straight measurement light L at point P on the interface wall 5 is larger than the critical angle and smaller than the right angle, is applied to the case where the liquid to be measured is an aqueous sugar solution, for example, the sugar concentration is 0. % (pure water) liquid, the incident angle β is larger than the critical angle of total reflection determined by the refractive index of pure water and the refractive index of the light transmitting material, and smaller than the right angle. This corresponds to the measurement lower limit when a sugar solution is used as the liquid to be measured (hereinafter referred to as the measurement lower limit).On the other hand, the straight measurement light L' incident along the guide wall 10 is Assuming that it is reflected at point Q of interface wall 5, the line connecting point OQ becomes normal N,
The angle between this normal N and the straight measurement light L' is the angle of incidence β', and this angle of incidence β' is the critical angle determined by the refractive index of the liquid to be measured 1 and the refractive index of the light transmitting body 2. When the angle is larger than , and less than or equal to the right angle, the straight measurement light L' is totally reflected at the point Q, so the shape of the interface wall 5 must also satisfy this condition.

This condition, in which the incident angle β' of the straight measuring beam L' at point Q on the interface wall 5 is larger than the critical angle and smaller than the right angle, can be applied to the case where the liquid to be measured is an aqueous sugar solution, for example. When the interface wall 5 is immersed in a liquid with the maximum sugar concentration, the incident angle β' is larger than the critical angle of total reflection determined by the refractive index of the sugar aqueous solution with the maximum sugar concentration and the refractive index of the light transmitting material, and is less than the right angle. This means that P, which is the lower limit of measurement, corresponds to the upper limit of measurement when an aqueous sugar solution is used as the liquid to be measured (hereinafter referred to as the upper limit of measurement).
For example, when it comes to concentration measurement, when it is an arcuate surface along a virtual circle passing through point and point Q, which is the measurement upper limit,
Over the entire range from pure water to supersaturated water, total reflection occurs in relation to the critical angle corresponding to the refractive index n ₁ of the liquid to be measured at that time.

Next, the radius R of the virtual circle that satisfies the above conditions is determined as follows. That is, the normal N and the straight measurement light
When the angle with L' is a right angle and the light entrance guide walls 9 and 10 are parallel, the angle between the normal N and the straight measurement light L is a right angle, so the normal N and the straight measurement Let S be the intersection with light L, and the distance OS between the points OS is
Since the distance OS obtained by Rsinβ and the width t of the guide walls 9 and 10 added is the radius R of the virtual circle, it will be explained below (1),
It is determined based on formula (2).

R=Rsinβ+t...(1) R=t/(1-sinβ)...(2) Also, the distance l between points QP is the angle (π/2 -β), it can be obtained as l=R・(π/2−β)...(3).

Next, a specific design example of this light transmitting body 2 will be explained.

Here, the sucrose concentration ranges from 0% (lower measurement limit) to approx.
A design example for measuring the concentration of sucrose solution up to 65% (measurement upper limit) will be explained, and glass will be used as the material of the light transmitting body 2.

In that case, the refractive index n ₂ of the light transmitting body 2 used is 1.520 at 20 degrees Celsius. Furthermore, assuming that the refractive index n ₁ of a sucrose solution (water) with a sucrose concentration of 0% is 1.330 at 20 degrees C, then when the incident angle β of the rectilinear measurement light L at point P is equal to the critical angle, Assuming that the width t of the light aperture guide wall is 3 mm, the critical angle α is determined by the formula α=sin ^-1 1.330/1.520, and α=61.05 (degrees).

Also, the radius R is R=3/1-sin61.05 It is obtained from the formula, R=24.01 (mm) becomes.

Also, the distance l between points PQ is l=(90−61.05)・24.01・2π/360 It is obtained from the formula, l=12.13mm becomes.

The distance l between the points PQ obtained above satisfies the conditions of the incident angles β and β' required by the straight measurement beams L and L', respectively, and in the case of an actual device, the distance l between the points PQ and In order to include these conditions in the interface wall 5 at the starting point (lower measurement limit side), the incident angle β is set to be equal to or close to the critical angle and to be small.

Next, the measuring method of the lateral measuring device in this specific example will be explained.

The interface wall 5 of the light transmitting body 2 is immersed in the liquid 1 to be measured.

When the concentration of the sucrose solution as the liquid to be measured 1 is 0%, all the straight measurement light emitted from the light source 6 and entering from the light entrance 3 is totally reflected between points QP on the interface wall 5. , taken out from the light receiving port 4. The amount of reflected light received by the light receiving element 8 is
It is maximum when the concentration of the liquid to be measured 1 is 0%.

When the concentration of the sucrose solution as the liquid to be measured 1 increases, the critical angle α determined by the refractive index n ₂ of the light transmitting body 2 and the refractive index n ₁ of the liquid to be measured 1 changes.
That is, as the concentration of the sucrose solution increases, the critical angle α increases, and at the QP portion of the interface wall 5,
The range where the incident angle is close to the interfacial angle, that is, the total reflection area, gradually narrows from point P to point Q, and the total reflection side is no longer filled sequentially from the measurement light closest to the straight measurement light L, so that the light receiving element 8 The amount of light received at this point decreases.

In this case, the interface wall 5 is an arcuate surface on a virtual circle with radius R, and the measurement light is irradiated onto this arcuate surface as parallel light along the light entrance guide wall 9, so the measurement light is reflected only on this arcuate surface. The decrease in the amount of light received toward the light receiving element is caused only by the change in the total reflection region corresponding to the critical angle determined by the change in the concentration of the sucrose solution.

The refractive index n ₂ of the light transmitting body 2 and the refractive index of the liquid to be measured 1
When n is equal to ₁ , total reflection occurs at the point Q of the interface wall 5
The amount of reflected light received by the light receiving element 8 is the minimum.

Therefore, by determining the electromotive force generated by the light receiving element 8 for each concentration, unknown concentrations can be measured using this measuring device.

As explained above, in the present invention, the shape of the interface wall is an arcuate surface, and all straight measurement light that is collimated by passing through a lens and enters the light entrance is totally reflected under predetermined conditions. With this configuration, attenuation of the measuring light is prevented as much as possible and changes in the amount of light reaching the light receiving element are increased, so that a measuring device that can perform accurate measurements and is easy to manufacture can be provided.

[Brief explanation of drawings]

FIG. 1 is a side view showing the configuration of the main parts of a measuring device according to the present invention, and FIG. 2 is a sectional view taken along the line - in FIG. 1. DESCRIPTION OF SYMBOLS 1... Liquid to be measured, 2... Light transmitting body, 3... Light entrance, 4... Light receiving port, 5... Interface wall, 8... Light receiving element, 9, 10... Light entrance guide wall, 11,12...
... Light receiving port guide wall, R ... Radius, M, N ... Normal line,
l...Distance between points PQ, α...Critical angle, β, β'...
…Angle of incidence.

Claims (1)

[Claims] 1. A measuring light transmitting body 2 having a light entrance 3, an interface wall 5, and a light receiving opening 4 and having a refractive index n ₂ larger than the refractive index n ₁ of the liquid 1 to be measured is attached to the liquid 1 to be measured.
The liquid to be measured 1 is immersed in water, and the measurement light is projected toward the interface wall 5, and the reflected light reflected at the interface wall 5 is received by the light receiving element 8. The measuring device is configured to measure at least one of the density, concentration, specific gravity, etc. of This arcuate surface is such that the incident angle β of the straight measurement light L that enters the interface wall 5 along one of the light entrance guide walls 9 of the light entrance 3 reaches the measurement lower limit concentration of the liquid 1 to be measured. It is larger than the critical angle of total reflection determined by the corresponding refractive index and the refractive index of the light transmitting body 2 and smaller than the right angle, and the interface along the other light entrance guide wall 10 of the light entrance 3 The angle of incidence β' of the straight measurement light L' entering the wall 5 is determined by the critical angle of total reflection determined by the refractive index corresponding to the upper limit measurement concentration of the liquid 1 to be measured and the refractive index of the light transmitting body 2. is a cylindrical curved circular arc surface along a virtual circle with a radius R selected such that R is large and smaller than a right angle, and the light entrance guide wall 10 exists on a tangent to the circular arc surface, and the light entrance A measuring device for measuring the density, concentration, specific gravity, etc. of a liquid, characterized in that a guide wall 9 is parallel to a light entrance guide wall 10 with a width t.