KR20070080816A - Manufacturing method of the sensor for liquid concentration measurement and sensor thereof - Google Patents

Abstract

A method for manufacturing a sensor to minutely measure the concentration of liquid and the sensor manufactured by the same are provided to prevent the effect of an electric field generated from the outside of an insulator tube by a shielding layer made of a metal film. A sensor(100) manufactured by a method for manufacturing the sensor to minutely measure the concentration of liquid includes a sensor tube(10), a high electrode(20), and a low electrode(30). The sensor tube is a cylindrical insulator tube having a constant length to measure the concentration of the liquid by measuring the electric capacity of the liquid filled inside of the sensor tube. More than two high and low electrodes in a shape of a ring are positioned on an external side surface of the sensor tube as the insulator tube. The low electrode in the shape of the ring is positioned on both sides from the center of the high electrode in the shape of the ring when the increment of output electric capacity is needed.

Description

TECHNICAL MANUFACTURING METHOD OF MANUFACTURING A SENSOR FOR MEASURING PRECISION OF A LIQUID AND A SENSOR MADE BY THE SAME

1 is a schematic cross-sectional view illustrating the electrode structure to measure the conventional liquid dielectric constant,

2 is an exemplary embodiment for showing a sensor equipped with an electrode according to the present invention;

Figure 3 is an exemplary cross-sectional view showing an electric field simulation form for measuring the capacitance by increasing the output capacitance using a sensor implemented by the present invention,

4 is an exemplary cross-sectional view showing an electric field simulation form for measuring capacitance by adding a guard electrode to a sensor implemented by the present invention;

5 is a schematic view showing to explain the measuring principle according to the electrode structure,

Figure 6 is a graph showing the results of measuring the change in capacitance for the aqueous solution for each concentration using a sensor constituting the structure of the present invention at various frequencies,

Figure 7 is a graph showing the measurement of the influence state on the material of the insulator tube during capacitive measurement according to the present invention.

<Description of the code | symbol about the principal part of drawing>

10: insulator tube (sensor tube)

20: High electrode

30: Low electrode

40: Guard electrode

50: shield

60: Screen

100: sensor

The present invention relates to a method for manufacturing a sensor for precisely measuring the concentration of a liquid and a sensor produced thereby

More specifically, a high electrode and a low electrode having a ring shape are positioned on the outer surface of the sensor tube, which is an insulator tube having a cylindrical shape, and when the output capacitance needs to be increased, the low electrode is positioned on both sides of the high electrode. By arranging the electrodes spaced apart from each other, it is possible to precisely measure the concentration of the liquid regardless of the length of the sensor tube, the insulator tube, and the overall size of the sensor, and allow the user to directly indicate the concentration of the liquid. Manufacture of sensors to improve the convenience of measurement, etc., and to maximize the satisfaction and reliability of use by applying to the tester or user due to the simple structure of the sensor for measuring the concentration of liquid A method and a sensor produced thereby.

In general, the dielectric constant is one of the important electrical properties of various insulators or dielectric materials.

Therefore, the conventional method for measuring the liquid dielectric constant (dielectric constant) as shown in the accompanying drawings, as shown in Figure 1, the capacitance measured after filling the liquid (Liquid) in the electrode structure (1) (C _liq) ) And the electric capacity (C _air ) measured in the liquid-free air is calculated by Equation 1 below.

[Equation 1]

ε _r = (C _liq / C _air ) × 1.0005

Here, the number 1.0005 described above is for compensating for an error caused by measuring in air as the dielectric constant of air.

However, the measurement of the dielectric constant by the electrode structure has the following problems.

In other words, if an acid is placed between the first two electrodes (2,3), a chemical reaction occurs, and thus the measurement liquid cannot be measured, and there is a problem in that the liquid to be measured is limited, and the second inner electrode (2) In order to coaxially install inside the cylinder (outer electrode) 3, an insulator (4) must be inserted so that the characteristics of the liquid as well as the insulator (4) can be measured during capacitance measurement. There is a problem that the cause of error occurs by measuring together the characteristic. Third, after measuring one liquid, the electrode must be separated, washed, dried and reassembled in order to measure the other liquid. Finding assembly conditions equal to capacity is extremely difficult and has the cumbersome problem of having to repeat the process of measuring dielectric constants from scratch.

In addition, since the container is operated by one electrode, it is directly affected by an external electric field, and there is an inconvenience in that a separate ground power source must be installed inside the shielded container to prevent this.

In addition, in order to solve the above problems, when the sensor with a large number of electrodes is manufactured to increase the output capacitance, or the width of the high electrode and the low electrode is increased, and the width of the guard electrode is designed to be small, the liquid Although there is an advantage in measuring the concentration of, the measurement of the liquid concentration of the sensor tube should be made of at least 130mm or more, there is a problem that it is difficult to apply directly when it is necessary to minimize the size of the overall sensor.

Therefore, due to the problems described above, the method of measuring the dielectric constant and the electrode structure of the related art have limited limitations in efficiency such as the inability to accurately measure the concentration of the liquid. Problems such as satisfactory use and deterioration of reliability are implied, and measurement accuracy is not limited to several percent.

The present invention was created to solve various problems of the prior art as described above, and has the following object.

The present invention enables precise measurement of the concentration of liquid irrespective of the length of the sensor tube as the insulator tube and the overall size of the sensor, and according to what concentration of liquid is filled inside the sensor tube as the insulator tube. The manufacturing method of the sensor for precisely measuring the concentration of the liquid to change the capacity can be easily analyzed the relationship with the concentration, and to improve the convenience for measurement, such as the user can directly indicate the concentration. And a sensor manufactured thereby.

Another object of the present invention is a manufacturing method of a sensor for precisely measuring the concentration of the liquid to maximize the satisfaction and reliability of using the applied to the tester or the user due to the simple structure for the sensor for measuring the concentration of the liquid and It is to provide a sensor manufactured thereby.

Another object of the present invention is to derive the correlation of the change characteristics of the capacitance according to the change in concentration, and to accurately store the concentration of the liquid to be automatically converted and directed by storing the relation according to the memory of the electronic circuit The present invention provides a method for manufacturing a sensor for measuring and a sensor manufactured thereby.

In order to achieve the above object, the present invention has a ring shape on the outer surface of the sensor tube which is a cylindrical insulator tube having a constant length for measuring the capacitance of the liquid filled inside the tube to measure the concentration of the liquid. At least two high electrodes and a low electrode are provided, and when it is necessary to increase the output capacitance, the ring-shaped low electrodes are disposed on both sides of the ring-shaped high electrode, and are spaced apart more precisely. When it is necessary to perform stable measurement, a guard electrode having a ground potential is formed between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode, and the sensor tube is the insulator tube. In order to prevent the electric field effect generated from the outside of the insulator tube, a shielding film made of a metal film is formed on the outside of the insulator tube. Between the outer surface of the sensor tube, which is an insulator tube, and the shielding film, a screen is formed to improve the measurement sensitivity in measuring the capacitance. The dielectric constant of the material of the insulator tube and the dielectric constant of the liquid to be measured are described above. The dielectric constant for the material of the insulator tube is formed to be greater than or equal to the dielectric constant of the liquid.

Hereinafter, the present invention will be described in detail.

In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted, and the following terms will consider functions in the present invention. The terms are set according to the definition of the terminology, which may vary depending on the intention or convention of the user, the experimenter, and the producer.

First, the manufacturing method of the sensor for precisely measuring the concentration of the liquid of the present invention has a high electrode and a low electrode to measure the concentration of the liquid by measuring the capacitance of the liquid filled inside the sensor tube which is an insulator tube, respectively And forming two or more ring electrodes on the outer surface of the sensor tube, which is an insulator tube, wherein the materials of the insulator tube are quartz, sapphire, and alumina. In the step of placing any one of the high electrode and the low electrode having a ring shape in the sensor tube which is the insulator tube, the ring-shaped low electrode on both sides of the ring-shaped high electrode This is done by placing them spaced apart.

And, in order to prevent the electric field effect generated from the outside of the sensor tube which is the insulator tube, forming a shielding film made of a metal film on the outside of the sensor tube which is an insulator tube, In the measurement, the step of forming a screen for improving the measurement sensitivity is further performed.

The screen is implemented by forming a metal material.

The method may further include forming a guard electrode having a ground potential between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode.

Accordingly, the insulator tube of the sensor dielectric constant of the material of the tube (ε _tube) and the dielectric constant of the liquid to be measured (ε _liq) is the dielectric constant (ε _tube) has a dielectric constant (ε _liq of the liquid of the insulator tube Greater than or equal to (ε _tube ≥ ε _liq ) to form and execute.

In addition, the configuration of the sensor manufactured by the above-described manufacturing method, in the sensor using a sensor tube which is a cylindrical insulator tube having a constant length in order to measure the capacitance of the liquid filled inside the tube to measure the concentration of the liquid At least two high and low electrodes having a ring shape are disposed on the outer surface of the sensor tube, which is the insulator tube, and when there is a need to increase the output capacitance, The low electrode of the ring shape is arranged in a spaced apart state.

In this case, when it is necessary to perform a more accurate and stable measurement, a guard electrode having a ground potential is formed between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode. In order to prevent the electric field effect generated from the outside of the sensor tube which is an insulator tube, a shielding film made of a metal film is formed on the outside of the sensor tube which is an insulator tube.

In addition, a screen is formed between the outer surface of the sensor tube which is the insulator tube and the shielding film to remove the electric field distributed to the rear surface of the sensor so as to improve the measurement sensitivity for the measurement of the capacitance at the front of the sensor. The screen is made of metal.

And, in the sensor tube which is the insulator tube, the capacitive output in the air to be measured is filled with the liquid which is filled in the sensor tube which is the insulator tube or passes through the sensor tube which is the insulator tube, regardless of the length of the sensor tube which is the insulator tube. The concentration can be measured precisely by the capacitance measurement value.

In the case of measuring capacitance using a sensor having the above configuration, if the width of the ring-shaped electrode formed above is greater than or equal to a certain size, the width of the electrode is irrelevant in the measurement, so there is no problem in principle. will be.

EXAMPLE

First, it is possible to precisely measure the concentration of the liquid by using the sensor of the present invention, which changes the capacitance according to what concentration of the liquid is filled inside the sensor tube, and analyzes the relationship with the concentration It is to be able to directly indicate the concentration by measuring the capacitance.

In this way, by measuring the capacitance when the liquid in the sensor tube is filled with a liquid of various concentrations, and derives and derives the functional relationship between the concentration and the capacitance from the result and input it into the memory of the electronic circuit You can automatically display the unknown concentration every time you measure it.

To this end, it will be described in detail with reference to the accompanying drawings.

That is, as shown in Figures 2 to 4, the sensor 100 to measure the capacitance of the liquid (liquid) filled in the interior of the sensor tube 10, which is an insulator tube to measure the concentration of the liquid After forming a ring shape having a high electrode 20 and a low electrode 30, respectively, the ring-shaped electrodes 20, 30 are placed on the outer surface of the sensor tube 10, which is an insulator tube, respectively. will be.

This is to use the sensor tube 10, which is a cylindrical insulator tube having a certain length, in order to measure the capacitance of the liquid filled therein to measure the concentration of the liquid, wherein the insulator tube of the sensor tube 10 Two or more High electrodes 20 and Low electrodes 30 having a ring shape are located on the outer surface.

In the above configuration, when it is necessary to increase the output capacitance, the ring-shaped Low electrodes 30 are disposed on both sides of the ring-shaped High electrodes 20, but the High electrodes 20 and the Low electrodes are disposed. 30 are arranged to be spaced apart from each other.

When a more accurate and stable measurement needs to be performed, a guard having a ground potential between the ring-shaped high electrode 20 and the low electrode 30 and outside the ring-shaped low electrode 30 Guard) electrode 40 is formed, which is to make a more stable measurement.

In addition, the shielding film 50 made of a metal film is formed on the outside of the sensor tube 10 that is the insulator tube, which is to prevent the electric field effect generated from the outside of the sensor tube 10 that is the insulator tube.

In addition, the screen 60 is formed between the outer surface of the sensor tube 10, which is the insulator tube, and the shielding film 50, which removes an electric field distributed to the rear surface of the sensor 100 as a whole. This is to improve the measurement sensitivity for the measurement of capacitance in front of.

The material of the sensor tube 10, which is the insulator tube, is preferably made of one of quartz, sapphire, and alumina in order to improve the efficiency of the measurement on the concentration of the liquid.

The material for the screen 60 may be any material as long as it is a metal material, because the use of a specific material does not improve the measurement sensitivity.

That is, the high electrode 20 and the low electrode 30 adhere to the outer surface of the sensor tube 10, which is an insulator tube made of alumina, quartz, sapphire, etc., by attaching them using a gold film forming technology. The liquid to be measured flows inside the integrated sensor tube 10 (although not shown in the drawing, there are small holes at the left and right ends of the shielding film so that the liquid can pass).

At this time, since the space between the integrated sensor tube 10 and the shielding film 50 is wide, even if the concentration of the liquid is constant, the magnitude of the measured capacitance changes according to the position where the sensor tube 10 is fixed. This is because the electric field generated between the electric field is generated not only inside the tube but also outside, and is greatly influenced by the distance to the shielding film 50.

Accordingly, when the screen 60 is installed on the outside of the sensor tube 10 in which the electrode is formed, the above-described problem can be solved, so that accurate capacitance measurement is always performed regardless of the installation position of the sensor tube 10. It is possible to block the electric field exposed to the outside to improve the overall measurement sensitivity.

The principle of measuring the capacitance at the electrode is applied to a completely different principle from the capacitor (capacitor) by a conventional parallel plate, which is shown in Figure 5 attached to the capacitor when measuring the capacitor (C1) If the electrode corresponding to (C2) is grounded and the electrode corresponding to the capacitor C1 is grounded when measuring the capacitor C2, the output capacitance is determined by Equation 2 below.

[Equation 2]

C = (C1 + C2) / 2 = (ε _o ε _r ln2 / π) L = 1.95354904 (pF / m)

Where ε _o is the dielectric constant of vacuum and ε _r is the dielectric constant of the measurement object.

Following this, the capacitance is determined only by the length of the sensor tube, which is an insulator tube, and the size, spacing, structure, shape, material, and surface conditions of the electrode have no influence.

As can be seen in Equation 2, the output capacitance in vacuum has a value as small as about 0.0019 pF / mm, and when applied as a sensor using such a small capacitance change has a problem that the sensitivity of the sensor is insufficient. .

In addition, in order to increase the output capacitance, first, the sensor with the large number of electrodes should be manufactured. Second, the width of the high and low electrodes should be increased, and the width of the guard electrode should be made small. It can be measured very accurately when applied, but when it is applied to measure the concentration of liquid, the length of sensor tube, which is an insulator tube, should be at least 130mm. Therefore, when it is necessary to minimize the size of the overall sensor, accurate measurement There is a problem that can not be achieved.

Thus, in order to solve the above problem, in the sensor tube 10 which is the insulator tube, the capacitive output of air measured is irrespective of the length of the sensor tube 10 that is the insulator tube. The concentration of the liquid filled in the sensor tube 10 which is an insulator tube or passing through the sensor tube which is an insulator tube can be precisely measured by the capacitance measurement value.

Accordingly, Figure 6 is a graph showing the results of measuring the change in capacitance for the aqueous solution for each concentration using a sensor constituting the structure of the present invention at various frequencies, which is a ring in the sensor tube (10) which is an insulator tube In the state in which the high electrode 20 and the ring-shaped low electrode 30 are formed, the interval between the high electrode 20 and the low electrode 30 is set to 5 mm, and the high electrode 20 and The capacitance of the aqueous solution for each concentration is varied by using a sensor R1 having a width of the low electrode 30 each having a width of 10 mm and a sensor R2 having a width of the electrode having a width of 30 mm regardless of the distance between the electrodes. As a result of measuring each branch frequency, it can be seen that the slopes of all the measurement results performed by the sensors R1 and R2 are the same.

According to this, if the sensor 100 having a ring-shaped electrode structure implemented by the present invention is used, the length of the sensor tube 10 which is the insulator tube, that is, the overall length (size) of the sensor is made small. And even if formed, the measurement sensitivity of the sensor can be seen that almost the same results can be obtained while minimizing the influence of the width or the measurement frequency of the electrode.

In addition, accurate measurement is possible according to the material of the electrode support insulator tube, which is formed in the state where the ring-shaped high electrode 20 and the low electrode 30 are formed on the outer surface of the sensor tube 10 which is the insulator tube. When measuring the capacitance change of the liquid filled inside the sensor tube 10, which is an insulator tube, the thinner the thickness of the wall surface of the sensor tube 10, which is the insulator tube, the more accurate measurement becomes possible.

That is, larger than the dielectric constant (ε _liq ) for the material of the sensor tube 10, which is the insulator tube (ε _tube > ε _liq ) In the case of ε _liq , the measurement error is minimized theoretically and experimentally through the research based on the present invention, and the material of insulator tube is selected by considering the dielectric constant (ε _liq ) of the liquid to be measured. This will allow more accurate measurements in capacitive measurements.

Therefore, as shown in FIG. 7, a graph showing a state of influence on the material of the sensor tube 10, which is an insulator tube, during measurement of capacitance, is a graph showing both sides of a sensor electrode made of a flexible material. The measurement results are shown for the case of attaching a sensor insulated with a kapton having a dielectric constant (ε _r ) of 3.5 to the outer wall of two kinds of insulator tubes.

Based on this, it can be seen that the use of a sapphire insulator tube with a dielectric constant of 9.4 shows a much greater inclination than that of a fused silica insulator tube with a dielectric constant of about 3.8. It means to be good.

On the other hand, it can be seen that the inclination difference between the diameter of the insulator tube is 50mm and the case of 48mm is not very large, and the appropriate insulator tube is made small while reducing the size of the insulator tube in the concentration measurement of the aqueous solution having a dielectric constant of about 60 to 80. Selecting a material will allow for more accurate measurements.

The measurement experiment described above is a measurement experiment carried out for the sake of understanding, and it is understood that the present invention is not limited thereto.

In addition, the present invention may be variously modified and may take various forms in the manufacturing method of the sensor for precisely measuring the concentration of the liquid and the configuration of the sensor 100 manufactured thereby. It is to be understood, however, that the present invention is not limited to the specific forms referred to in the above description, but rather includes all modifications, equivalents and substitutions within the spirit and scope of the invention as defined by the appended claims. It should be understood that.

As described above, the present invention is provided with a high electrode and a low electrode having a ring shape on the outer surface of the sensor tube which is an insulator tube, the low electrode is disposed on both sides of the high electrode spaced apart from each other It is possible for the user to conveniently measure the precise concentration of the liquid by a sensor having a simple structure and an effect capable of accurately measuring the concentration of the liquid regardless of the length of the insulator tube and the overall size of the sensor tube. The effect of providing the property and the effect of the electric field generated from the outside of the insulator tube by the shielding film made of a metal film is prevented.

In addition, according to the present invention, the capacitance changes depending on which concentration of liquid is filled in the inside of the sensor tube, and the relationship with the concentration can be analyzed so that the user can directly indicate the concentration. By applying this, various effects such as maximizing satisfaction and reliability of the sensor for measuring the concentration of the liquid used can be simultaneously achieved.

Claims (17)

Forming a ring shape having a high electrode and a low electrode to measure the concentration of the liquid by measuring the capacitance of the liquid filled inside the sensor tube, the insulator tube; And Placing at least two ring-shaped electrodes on an outer surface of the sensor tube as an insulator tube; Method of manufacturing a sensor for precisely measuring the concentration of the liquid, characterized in that the execution. The method of claim 1, The material of the sensor tube, which is the insulator tube, is selected from quartz, sapphire and alumina. The method of claim 1, In the step of placing a high electrode and a low electrode having a ring shape in the sensor tube which is the insulator tube, And a ring-shaped low electrode disposed on both sides of the ring-shaped high electrode in a state of being spaced apart from each other. The method of claim 3, In order to prevent the electric field effect generated from the outside of the sensor tube, which is the insulator tube, forming a shielding film on the outside of the sensor tube, which is an insulator tube, and improving the measurement sensitivity in measuring the capacitance on the outside of the sensor tube, which is the insulator tube. A method of manufacturing a sensor for precisely measuring the concentration of a liquid, further comprising the step of forming a screen for making a screen. The method of claim 4, wherein The shielding film is a method of manufacturing a sensor for precisely measuring the concentration of the liquid, characterized in that formed by a metal film. The method of claim 4, wherein The screen is a method of manufacturing a sensor for precisely measuring the concentration of the liquid, characterized in that formed by a metal material. The method of claim 3, Accurately measuring the concentration of the liquid, characterized in that the step of forming a guard electrode having a ground potential between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode Method for producing a sensor for The method of claim 1, The dielectric constant (ε _tube) and dielectric constant (ε _liq) are the same or have a dielectric constant (ε _tube) of the greater than the dielectric constant (ε _liq) of the liquid of the liquid to be measured for the material of the insulator tube of the sensor tube Ε _tube ≧ ε _liq ) forming and executing the sensor for precisely measuring the concentration of the liquid. Dielectric constant (ε _tube ) for the material of the sensor tube, the insulator tube, and the dielectric constant (ε) of the liquid to be measured to measure the concentration of the liquid by measuring the capacitance of the liquid filled inside the sensor tube, the insulator tube. _liq ) is such that the dielectric constant (ε _tube ) is greater than or equal to the dielectric constant (ε _liq ) of the liquid (ε _tube ≧ ε _liq ) forming; Forming a ring shape each having a high electrode and a low electrode to attach to the sensor tube which is the insulator tube; Placing at least two ring shapes on an outer surface of the sensor tube, which is an insulator tube, and disposing ring-shaped low electrodes on both sides of the ring-shaped high electrode, spaced apart from each other; Forming a shielding film made of a metal film on the outside of the sensor tube which is an insulator tube to prevent an electric field effect generated from the outside of the sensor tube which is the insulator tube; Forming a screen made of a metal material on the outside of the sensor tube, which is the insulator tube, in order to improve measurement sensitivity; And Forming a guard electrode having a ground potential between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode; Method of manufacturing a sensor for precisely measuring the concentration of the liquid, characterized in that for further executing. In the sensor using a sensor tube which is a cylindrical insulator tube having a constant length to measure the concentration of the liquid by measuring the capacitance of the liquid filled therein, And at least two high and low electrodes having a ring shape are positioned on an outer surface of the sensor tube which is the insulator tube. The method of claim 10, Sensors for precisely measuring the concentration of the liquid, characterized in that the ring-shaped Low electrodes are arranged on both sides of the ring-shaped high electrode spaced apart from each other. The method according to claim 10 or 11, wherein And a guard electrode having a ground potential between the ring-shaped high electrode and the low electrode and outside the ring-shaped low electrode. The method of claim 10, In order to prevent the electric field effect generated from the outside of the sensor tube, which is the insulator tube, a shielding film made of a metal film is formed on the outside of the sensor tube, which is an insulator tube, and the capacitance between the outer surface of the sensor tube, which is the insulator tube, and the shielding film. Sensor for measuring the concentration of the liquid, characterized in that to form a screen for improving the measurement sensitivity in the measurement of. The method of claim 13, The screen is a sensor for accurately measuring the concentration of the liquid, characterized in that made of a metallic material. The method of claim 10, The dielectric constant (ε _tube ) for the material of the insulator tube and the dielectric constant (ε _liq ) of the liquid to be measured are such that the dielectric constant (ε _tube ) is greater than or equal to the dielectric constant (ε _liq ) of the liquid (ε _tube ≥ ε _liq ) sensor for precisely measuring the concentration of the liquid, characterized in that formed. The method of claim 10, In the sensor tube which is the insulator tube, the capacitive output of the air to be measured is the concentration of the liquid which is filled in or passes through the sensor tube which is the insulator tube, regardless of the length of the sensor tube which is the insulator tube. Sensor for precise measurement by capacitive measurement. In the sensor using a sensor tube which is a cylindrical insulator tube having a constant length to measure the concentration of the liquid by measuring the capacitance of the liquid filled therein, Two or more high electrodes having a ring shape and a low electrode are disposed on an outer surface of the sensor tube which is the insulator tube, and ring low electrodes are disposed on both sides of the ring shaped high electrode, spaced apart from each other. A guard electrode having a ground potential is formed between the ring-shaped high electrode and the low electrode and outside of the ring-shaped low electrode, and influences an electric field generated from the outside of the sensor tube as the insulator tube. A shielding film made of a metal film is formed on the outside of the sensor tube, which is an insulator tube, and is made of a metal material between the outer surface of the sensor tube, which is an insulator tube, and a shielding film, to improve measurement sensitivity in measuring capacitance. the screen is formed, and the dielectric constant (ε _liq) of the liquid to be measured and the dielectric constant (ε _tube) for the material of the insulator tube of the Dielectric constant (ε _tube) is (ε _tube to be greater than or equal to the dielectric constant (ε _liq) of the liquid ≥ ε _liq ) Sensors for precisely measuring the concentration of the liquid, characterized in that formed.

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