JPH08114546A - Liquid concentration measuring device - Google Patents

Abstract

PURPOSE: To accurately measure the liquid concentration even in the case where a scattering light source is used or even in the case where the liquid at a little quantity is measured by providing a shading member in the measuring surface of the translucent medium except for an area, in which the total reflection of the incident light is generated in the case of the specified concentration of the liquid to be measured. CONSTITUTION: In the case where the liquid (f) to be measured at the specified concentration is dropped onto the measuring surface 24a, a part of the outgoing light from a light emitting diode 20 is reflected by the boundary surface and goes in nearly parallel with the boundary surface, and does not enter a photo diode 21 because almost of the optical component thereof is refracted and goes inside of the liquid (f) to be measured, and discharged outside or because the incident angle does not exceeds the maximum critical angle. The measuring surface 24a is provided with a shading film 32 in the area, in which total reflection of the incident light is to be generated, except for a transmitting hole 32a, and the light c4 , which enters the transmitting hole 32a, is reflected all in the condition that the light c4 exceeds the maximum critical angle, and all the optical component enters the diode 21. Light receiving quantity at this time is compared with the previously stored reference data showing the relation of the reflectance index with concentration, and concentration of the liquid to be measured can be thereby easily obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid concentration measuring device for measuring the concentration of a liquid to be measured.

[0002]

2. Description of the Related Art Conventionally, a liquid concentration sensor for measuring the concentration by utilizing the property of the liquid that there is a certain correlation between the concentration (volume ratio) of the liquid and the refractive index of the liquid. It has been known. This liquid concentration sensor is an LED
A light beam from a light-emitting element such as a light source is irradiated through an optical fiber into the liquid to be measured, a part of the light beam is reflected by a reflection film provided at the tip of the optical fiber, and the optical fiber is returned to the photodetector. And the concentration of the liquid to be measured is detected based on the incident light.

However, in this conventional liquid concentration sensor, when the luminous flux emitted from the light emitting element is a luminous flux which has no directivity and spreads radially, the luminous fluxes propagating in the optical fiber interfere with each other. Therefore, the reflected light reflected by the reflective film is not efficiently propagated to the photosensor in the photodetection section, and accurate density measurement becomes extremely difficult. Further, even when the amount of the liquid to be measured is small and the core portion at the tip of the optical fiber cannot be immersed, accurate measurement becomes difficult.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems associated with the conventional liquid concentration sensor, and can be applied to a liquid crystal even when a light source that emits divergent light is used for the light emitting element or when the liquid to be measured is small. An object of the present invention is to provide a liquid concentration measuring device capable of accurately measuring the concentration.

[0005]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a translucent medium having a refractive index higher than that of a liquid to be measured and having a measuring surface for contacting the liquid to be measured; A light-emitting element that transmits an optical medium and emits divergent light toward the measurement surface; is emitted from the light-emitting element and is reflected by the boundary surface between the measurement surface and the liquid to be measured on the measurement surface. A liquid concentration measuring device comprising: a light receiving element that receives reflected light;
Of the light emitted from the light emitting element and reflected on the measurement surface of the light-transmissive medium, at least a region where total reflection occurs on the measurement surface when the liquid to be measured has a specific concentration is shielded. It is characterized by the provision of.

On the front surface of the light receiving element, of the light emitted from the light emitting element and reflected by the measuring surface, the light reflected in the area where total reflection occurs at a specific density is incident on the second light receiving element. A light blocking member can be provided.

The present invention also provides a translucent medium having a refractive index higher than that of the liquid to be measured and having a measuring surface for contacting the liquid to be measured; A light emitting element for irradiating the measurement surface with divergent light; and a light receiving element for receiving reflected light emitted from the light emitting element and reflected at the boundary surface between the measurement surface and the liquid to be measured on the measurement surface. In a liquid concentration measuring device including;
Among the light emitted from the light-emitting element, a light-transmitting portion that receives reflected light at least in a region where total reflection occurs on the measurement surface when the liquid to be measured has a specific concentration; And a light-shielding member having; are provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. First, in order to facilitate understanding of the present invention, a liquid concentration measuring device 11 'devised by the present inventors will be described with reference to FIG. This liquid concentration measuring device 11 '
Is the basis of the liquid concentration measuring device 11 according to the invention.

The liquid concentration measuring device 11 'has a cylindrical casing 30. A circular measurement hole 30a and a ring fitting portion 30b concentric with the measurement hole 30a are formed at the center of the upper wall 30c of the casing 30. A prism holder 13 that holds the prism 24 is fixed inside the casing 30.

As shown in FIGS. 5, 6 and 8, the prism holder 13 forming a part of the inspection unit 10 'is formed into a substantially trapezoidal shape in a side view, and is opposed to and supported by a predetermined angle. It has surfaces 13a and 13e and a bottom portion 13d. Cylindrical supporting portions 18 and 19 are provided on these supporting surfaces 13a and 13e, respectively. The supporting portion 18 has a hollow portion 18a for mounting the light emitting diode (LED) 20, and the supporting portion 19 has a hollow portion 19a for mounting the photodiode 21. Fixing protrusions 13b for fixing the prism holder 13 to the casing 30 are provided at the four corners of the prism holder 13, and the four fixing protrusions 13b each have a bolt hole 13c. .

The prism 24 is made of a translucent medium such as glass having a refractive index higher than that of the liquid to be measured f, and has a measuring surface 24a with which the liquid to be measured f comes into contact and a supporting surface 13a of the prism holder 13. It has a light incident surface 24b inclined at the same angle, a light emitting surface 24d inclined at the same angle as the support surface 13e, and a notch 24c.

The prism holder 13 is fixed to the rear surface of the upper wall portion 30c via a fixing bolt 33 in a state where the measuring surface 24a of the prism 24 held inside faces the measuring hole 30a. Further, the upper wall portion 30c and the casing 30
An O-ring 31 fitted to the ring fitting portion 30b is contracted between the measurement surface 24a that contacts the back surface. As a result, the watertightness between the measurement hole 30a and the measurement surface 24a is maintained, and a concave portion for holding the liquid to be measured f is formed.

The light emitting diode 20 has a maximum critical angle at which the light c ₃ at the substantially central portion of the emitted light flux, which is divergent light, is obtained based on the refractive index of the prism 24 and the measured liquid f on the measurement surface 24a. The measurement surface 24a is provided with an angle of incidence of about θc. Photodiode 21
Is provided so that the reflected light reflected by the boundary surface I formed by the liquid to be measured f and the prism 24 can be focused as effectively as possible.

The terminals 20a, 21a of the light emitting diode 20 and the photodiode 21 are connected to the substrate 17, which is disposed in the inner space 15 of the casing 30, with lead wires 22,
They are connected to each other via 23. This board 17
A drive circuit 37 for driving the light emitting diode 20, an A / D conversion circuit 38 for converting the received light analog signal of the photodiode 21 into a digital signal, a ROM 39, a CPU 40 for performing various calculations, a liquid crystal display drive circuit 41, etc. Has been. The ROM 39 is a table showing the relationship between the received light amount of the measurement light received by the photodiode 21 and the concentration of the measured liquid f, which changes depending on the change in the reflectance on the boundary surface I according to the different concentrations of the measured liquid f. It is stored as data. The CPU 40 detects the concentration of the liquid to be measured f based on the received light amount of the photodiode 21 which changes depending on the concentration of the liquid to be measured f dropped on the measurement surface 24a and the table data of the ROM 39. The detection result of the CPU 40 is displayed on the liquid crystal display unit 25 (see FIG. 4) provided on the side surface of the casing 30. Reference numeral 16 in FIG.
Is the battery.

By the way, when a light beam traveling through a medium (medium) M ₁ having a constant refractive index is incident on a boundary surface with a medium (medium) M ₂ having a lower refractive index than the medium M ₁ ,
Assuming that the refractive indices of the medium M ₁ on the incident side and the medium M ₂ on the refractive side are n ₁ and n ₂ (n ₁ > n ₂ ), the incident angle of the light beam is a critical angle θ _c (= sin ⁻¹ (n ₂ / n ₁ )) is greater than total reflection. When the incident angle of the light beam is smaller than the critical angle θ _c , a part of the light beam has a refractive index ratio (n ₂ /
It transmits to the medium M ₂ side with a reflectance according to n ₁ ) and reflects the rest.

Therefore, in FIG. 5, when the boundary surface I is irradiated with a certain amount of light flux, the amount of reflected light is equal to that of the mediums M ₁ and M.
It changes according to the refractive index of ₂ . That is, the prism 2 made of a glass material or the like having a known refractive index n ₁ is used as the medium M _1.
4, and the medium M ₂ is the liquid to be measured f whose refractive index is unknown, the refractive index n ₂ of the liquid to be measured f can be detected by measuring the amount of reflected light by the photodiode 21. Based on this, the concentration of the liquid to be measured f can be detected.

In FIG. 5, when the liquid to be measured f having a specific concentration is dropped on the measurement surface 24, for example, the light c ₁ among the light emitted from the light emitting diode c ₁ , c ₂ , c ₃ is its light component. Since most of them are refracted in the liquid to be measured f and proceed to be released to the outside, they do not contribute to the measurement of the liquid to be measured f. Also light c
_In No. ₂ , since the incident angle is close to the maximum critical angle but does not exceed this angle, it is reflected by the boundary surface I, travels in a direction substantially parallel to the boundary surface I, and is not incident on the photodiode 21. Therefore, like the light c ₁ , it does not contribute to the measurement.

Further, the light c ₃ is in a state of exceeding the maximum critical angle and causes total reflection, so that all the light components are irradiated toward the photodiode 21. Since the amount of light received by the photodiode 21 at this time is the maximum, this amount of light received, the refractive index of the measured liquid f, and the calculated measured liquid f
The relationship with the density of is stored in the ROM 39 as reference data. Further, the relationship between the received light amount that gradually decreases from the reference data by a predetermined amount, the refractive index of the measured liquid f corresponding to the received light amount, and the concentration of the measured liquid f is stored as various data in the ROM 39. To remember. In this way, if the ROM 39 stores the table data defining the relation of each data for each received light amount of the photodiode 21, the CPU 40 corresponds to this table data at the time of measuring the liquid to be measured f. By calling, the concentration of the liquid to be measured f can be easily detected.
Further, the CPU 40 displays the detection result (numerical value) on the liquid crystal display unit 25.

The liquid concentration measuring device 11 'having the above structure operates as follows. First, an appropriate amount of the liquid to be measured f is dropped on the measurement surface 24a surrounded by the measurement hole 30a. In this state, a main switch (not shown) is turned on, the light emitting diode 20 is caused to emit light, and the light flux is irradiated toward the boundary surface I, so that the light c ₃ or the like is received by the photodiode 21. The light received by the photodiode 21 is
The received light amount is calculated by the CPU 40, and the CPU 40 further reads out the table data corresponding to the received light amount from the ROM 39 to detect the corresponding density,
The numerical value is displayed on the liquid crystal display unit 25.

The liquid concentration measuring device 11 'operates as described above, but as a result of research, it has been found that it has the following problems regarding the concentration measurement. That is, the measured liquid f
The light flux that contributes to the concentration measurement is extremely limited such as the light c ₃ , but the light that is refracted and emitted to the measured liquid f side is reflected by the wall surface of the measurement hole 30a, the water bubble b, and the like, and the prism 24 When the light returns to the side and enters the photodiode 21, this incident light is the disturbance light a from the outside of the liquid concentration measuring device 11 ′.
Along with this, it adversely affects the measurement. That is, the photodiode 21 receives not only the light that originally contributes to the concentration measurement but also the unnecessary light, so that it is difficult to reduce the measurement error.

The liquid concentration measuring device 11 according to the present invention has been completed in order to solve the above problems in the liquid concentration measuring device 11 'having the basic structure. The configuration will be described below with reference to FIGS. In the liquid concentration measuring device 11 shown in the figure, the same parts as those of the liquid concentration measuring device 11 'are designated by the same reference numerals.

The inspection unit 10 of the measurement device 11 is, like the inspection unit 10 'of the measurement device 11', a prism holder fixed to the back surface of the upper wall portion 30c of the casing 30 so as to face the measurement hole 30a. 13, a prism 24 housed in the prism holder 13, and the prism holder 1
3 has a light emitting diode 20 and a photodiode 21 mounted thereon. The light emitting diode 20 and the photodiode 21 are mounted on the prism holder 13 at the same angle as in the liquid concentration measuring device 11 '.

On the measurement surface 24a of the prism 24, a transmission hole 3 having a predetermined diameter is provided at a position where the divergent light from the light emitting diode 20 can be most effectively reflected by the photodiode 21.
2a is formed. That is, in the measurement surface 24a, of the light emitted from the light-emitting diode 20 and reflected by the measurement surface 24a, at least when the measured liquid f has a specific concentration, total reflection occurs on the measurement surface 24a (transmission hole 32a). )
The light-shielding film (light-shielding member) 32 is formed by silk-printing except the above. The transmission hole 32a has a predetermined diameter concentric with the measurement hole 30a, for example, φ3 mm. In Figure 1,
The light-shielding film 32 is drawn to be thick in order to facilitate understanding of the contents, but it is actually about 0.15 mm thick.

On the front surface of the photodiode 21,
A light blocking member 35 is provided which is located on the same plane as the support surface 13e. At the center of the light shielding member 35, the transmission hole 3
A light blocking member 35 having an entrance limiting hole 35a through which the measurement light c ₄ reflected by 2a and made into a substantially spot shape is made incident is provided. That is, the light shielding member 35 is configured to have substantially the same diameter as the hollow portion 19a of the supporting portion 19, and out of the light emitted from the light emitting diode 20 and reflected by the measurement surface 24a, total reflection occurs at a specific density. The entrance limiting hole 35a is provided at a position where the light reflected by the hole 32a enters. The light blocking member 35 has an entrance limiting hole (light transmitting portion) 35a and a light blocking portion 35b located at the periphery of the entrance limiting hole 35a.

The photodiode 21 has the above-mentioned light-shielding member 35 on the front surface, so that it cuts off the light which does not contribute to the measurement except the light reflected by the transmission hole 32a and contributes to the concentration measurement reflected by the transmission hole 32a. The measuring light c ₄ which is used is made to enter as much as possible.

The liquid concentration measuring device 11 having such an inspection section 10 operates as follows. That is, when an appropriate amount of the liquid to be measured f is dropped in the concave portion surrounded by the measurement hole 30a, the main switch (not shown) is turned on, and the light emitting diode 20 is caused to emit light, an extremely narrow range on the boundary surface I ( The measurement light c ₄ reflected by the transmission hole 32a of φd) is φ
As a spot of e, the light enters the photodiode 21 through the entrance limiting hole 35a of the light shielding member 35.

In this case, the reflectance at the boundary surface I corresponding to the transmission hole 32a changes depending on the concentration of the liquid to be measured f dropped on the concave portion. That is, if the measured liquid f has a relatively low concentration, the reflectance at the boundary surface I becomes high, and the amount of light received by the photodiode 21 becomes large. Further, when the concentration of the liquid to be measured f is relatively high, the reflectance at the boundary surface I becomes low, and the light component refracted toward the liquid to be measured f increases, so that the light received by the photodiode 21 is received. The amount of light decreases. Further, total reflection occurs depending on the concentration of the liquid to be measured f, and all the light components reaching the boundary surface I corresponding to the transmission hole 32a are received by the photodiode 21, so the amount of received light at this time becomes maximum.

Then, the measuring light c ₄ is emitted from the photodiode 2
When the light is received by 1, the amount of the received light is detected by the CPU 40, and the CPU 40 calls the table data corresponding to the received light amount from the ROM 39, detects the corresponding density, and displays the numerical value on the liquid crystal display unit 25. To do.

As described above, the liquid concentration measuring device 11 has the light emitting diode 20 and the photodiode 21 arranged at a predetermined emission angle and incidence angle, and the emission light from this light emitting diode 20 is used as the measurement light c _4. the transmission hole 32a to restrict provided, the received light, from the incident restriction hole 35a to limit the measuring beam c ₄ reflected by the transmission holes 32a corresponding interface I provided, such as a light emitting diode 20 as a light source divergence The liquid concentration can be accurately measured even when a light source that emits light is used as the light source or when the measured liquid f is small. Further, it is possible to suppress the variation of the measured value and to improve the accuracy of the concentration measurement.

Incidentally, in the liquid concentration measuring device 11 of the present invention, the light emitting diode 2 used at 3000 [mV], for example.
0 and the photodiode 21 are used, the photodiode 21 of the liquid concentration measuring device 11 'which is the basis of the present invention is used.
The sensor output is 2.059 depending on the amount of light received in the vicinity.
While it was [mV], the sensor output due to the amount of received light received through the entrance limiting hole 35a is 0.848 [mV]. Further, in the liquid concentration measuring device 11 of the present invention, the sensor output due to the light reflected by the measuring surface 24a of the liquid concentration measuring device 11 'which is the base is 20.341 [mV], while it is reflected by the transmission hole 32a. The sensor output by the emitted light is
It becomes 4.093 [mV].

In this embodiment, the ROM 39 stores the table data in which the relation of each data is defined in advance. However, the present invention is not limited to this, and the CPU 40 calculates a predetermined conditional expression based on the calculated received light amount. Alternatively, the concentration of the liquid to be measured may be calculated each time.

[0032]

As described above, according to the liquid concentration measuring apparatus of the present invention, it is possible to accurately measure the liquid concentration even when a light source that emits divergent light is used for the light emitting element or when the liquid to be measured is a small amount. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a front sectional view of essential parts showing a liquid concentration measuring device to which the present invention is applied.

FIG. 2 is a perspective view showing a prism holder used in the liquid concentration measuring apparatus.

FIG. 3 is a perspective view showing a prism used in the liquid concentration measuring apparatus.

FIG. 4 is a perspective external view showing the same liquid concentration measuring device.

FIG. 5 is a front sectional view showing a main part of a liquid concentration measuring device which is a basis of the liquid concentration measuring device according to the present invention.

FIG. 6 is a perspective view showing a prism holder used in the liquid concentration measuring device which is the basis of the present invention.

FIG. 7 is a perspective view showing a prism used in the liquid concentration measuring device which is the basis of the present invention.

FIG. 8 is a front cross-sectional view showing the entire liquid concentration measuring device which is the basis of the present invention.

[Explanation of symbols]

 11 Liquid Concentration Measuring Device 20 Light-Emitting Diode (Light-Emitting Element) 21 Photodiode (Light-Receiving Element) 24 Prism (Translucent Medium) 24a Measurement Surface 32 Light-Shielding Film (Light-shielding Member) 32a Transmission Hole (Light-transmitting Part) 35 Light-shielding Member (No. 1) 2 light blocking member) 35a entrance limiting hole 35b light blocking portion f measured liquid I boundary surface

Claims (3)

[Claims] 1. A translucent medium having a refractive index higher than that of a liquid to be measured and provided with a measurement surface for contacting the liquid to be measured; A light-emitting element that emits divergent light toward the light source; and a light-receiving element that receives the reflected light emitted from the light-emitting element and reflected by the boundary surface between the measurement surface and the liquid to be measured on the measurement surface. In the liquid concentration measuring device, the total reflection on the measurement surface of the transparent medium is at least when the liquid to be measured has a specific concentration among the light emitted from the light emitting element and reflected on the measurement surface. A liquid concentration measuring device, characterized in that a light-shielding member is provided while leaving a generated region. 2. The front surface of the light-receiving element according to claim 1, of the light emitted from the light-emitting element and reflected by the measurement surface, the light reflected in the region where total reflection occurs at a specific density. A liquid concentration measuring device, wherein a second light shielding member is provided at the position. 3. A translucent medium having a refractive index higher than that of the liquid to be measured and having a measurement surface for contacting the liquid to be measured; A light-emitting element that emits divergent light toward the light source; and a light-receiving element that receives the reflected light emitted from the light-emitting element and reflected by the boundary surface between the measurement surface and the liquid to be measured on the measurement surface. In the liquid concentration measuring apparatus, the front surface of the light receiving element receives, of the light emitted from the light emitting element, reflected light at least in a region where total reflection occurs on the measurement surface when the liquid to be measured has a specific concentration. A liquid concentration measuring device comprising: a light-transmitting portion; and a light-shielding member having a light-shielding portion on the periphery of the light-transmitting portion.