JPH11311561A - Water level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a water level by a simple structure. SOLUTION: A pair of electrodes 11 and 12 for measuring being arranged at a specific interval of (d) are installed in a water measurement range in a water tank. A pair of electrodes 21 and 22 for upper-part reference being arranged at a specific interval of (d) is installed above the water tank so that they are continuously positioned in the air. A pair of electrodes 31 and 32 for lower-part reference being arranged at a specific interval of (d) is installed at the bottom part of the water tank so that they are continuously dipped into liquid. The dielectric constant is obtained based on the capacitance between the electrodes 21 and 22, and the dielectric constant of the liquid is obtained based on the capacitance between the electrodes 31 and 32. According to the dielectric constants and the capacitance between the electrodes 11 and 12, a water level (h) is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water level sensor,
In particular, it relates to a water level sensor that can detect an arbitrary water level from a predetermined reference position to a liquid level.

[0002]

2. Description of the Related Art A water level sensor is used to measure the amount of water stored in a water tank or a dam. Conventionally, as a water level sensor generally used, a type using a mechanical float and a type using a pressure sensor are mainly used. In the former type using a mechanical float, the float is floated on the liquid surface, and the water level is determined by detecting the vertical movement of the float.
On the other hand, in the latter type in which the pressure sensor is diverted, the water pressure is detected by a pressure sensor submerged in the liquid, and the water level is obtained indirectly from the water pressure value. As the pressure sensor, for example, a sensor that detects the water pressure received by the metal diaphragm as a change in the resistance value of the piezoresistive element is used.

[0003]

However, the above-mentioned type using a mechanical float has a problem that the structure is complicated due to having a mechanical drive unit. In addition, there is a possibility that the floating operation such as dust may hinder the operation of the float, and there is a problem that reliability is lacking. On the other hand, the type in which the pressure sensor is diverted also requires a device to prevent water from entering the pressure detecting section, and thus the structure must be complicated. Further, since the water level is obtained indirectly from the water pressure value, if the specific gravity of the liquid changes due to factors such as temperature fluctuation, there is a problem that an accurate water level cannot be obtained.

[0004] In order to solve such a problem, Japanese Patent Application No. 9-287889 discloses a liquid crystal device using a capacitance element composed of a pair of measurement electrodes and a capacitance element composed of a pair of reference electrodes. There is disclosed a water level sensor capable of removing an error component based on a change in specific gravity or the like and performing accurate water level measurement. However, in this water level sensor,
Since an error component based on a change in the state of the atmosphere cannot be removed, there is a problem that a measurement value with sufficient accuracy cannot always be obtained.

Accordingly, an object of the present invention is to provide a water level sensor capable of performing water level measurement with sufficient accuracy with a simple structure.

[0006]

According to a first aspect of the present invention, there is provided a water level sensor for measuring a water level from a predetermined reference position to a liquid level. A measurement electrode, a pair of upper reference electrodes arranged at a predetermined interval, a pair of lower reference electrodes arranged at a predetermined interval, fixing means for fixing these electrodes, and each of these electrodes And a measuring circuit for measuring the water level by using the above, the length of the measuring electrode in the predetermined reference axis direction is set to be longer than the required water level measuring range, and the upper reference electrode is used for measuring the water level. Each electrode is fixed so that the lower reference electrode is located below the water level measurement range, and the measurement circuit determines the capacitance between the pair of measurement electrodes and the pair of upper reference electrodes. Capacitance between the pair of lower reference electrodes The water level is measured based on the three values of the capacitance between them.

(2) The second aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the aspect, based on the capacitance between the pair of upper reference electrodes, information about the dielectric constant εα of the atmosphere under the measurement environment is determined, and the capacitance between the pair of lower reference electrodes. , Information on the dielectric constant εβ of the measurement object in the measurement environment is obtained, and the water level is determined based on the information and the capacitance between the pair of measurement electrodes.

(3) A third aspect of the present invention is the above-described first aspect.
In the water level sensor according to the aspect, the pair of measurement electrodes, the pair of upper reference electrodes, and the pair of lower reference electrodes are each formed of a flat plate electrode having the same width W, and The electrode pairs are also arranged in parallel with the same electrode spacing d.

(4) The fourth aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the aspect, in the measurement circuit, the output value indicating the value of the capacitance between the pair of measurement electrodes, so as to show a linear relationship to the rise of the water level, between the measurement electrodes The electrode spacing is different for each part.

(5) The fifth aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the aspect, in the measurement circuit, the output value indicating the value of the capacitance between the pair of measurement electrodes, the width of the measurement electrode so as to show a linear relationship to the rise in water level Is different for each part.

(6) The sixth aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the first to fifth aspects, a tubular structure capable of introducing a liquid therein is used as a fixing means,
Each electrode is formed on the inner surface or outer surface of the tube wall of this tubular structure.

(7) A seventh aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the fifth to fifth aspects, the pair of measurement electrodes, the pair of upper reference electrodes, and the pair of lower reference electrodes are each formed of a pair of conductive wires, and the pair of conductive wires are parallel to each other. Alternatively, they are fixed by fixing means so as to form a stranded wire with each other.

(8) The eighth aspect of the present invention is the above-mentioned first aspect.
In the water level sensors according to the fifth to fifth aspects, the fixing means is constituted by a flat support substrate, and each measurement electrode and each reference electrode is constituted by a conductive layer formed on the support substrate.

(9) The ninth aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the first to fifth aspects, one measurement electrode, one upper reference electrode, one lower reference electrode,
The other measurement electrode, the other upper reference electrode, and the other lower reference electrode are each formed of a cylindrical conductor having an inner circumference larger than the outer circumference of the columnar conductor. In addition, a columnar conductor is inserted inside a cylindrical conductor, and is fixed by a fixing means in a state where a space through which a liquid can penetrate is secured between the two.

(10) A tenth aspect of the present invention is the water level sensor according to the first to fifth aspects, wherein one of the measuring electrode, one of the upper reference electrode, and one of the lower reference electrode are A single conductor is used, and this single conductor is shared by the electrodes.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

§1. The basic principle beginning of the present invention, illustrating the basic principle of the water level sensor according to the present invention. Now, as shown in FIG.
And 12 are prepared. Here, the measuring electrodes 11, 1
Numeral 2 is a rectangular flat plate electrode (made of a conductive material) having a width W and a height L, which are arranged in parallel so as to face each other at a predetermined interval d. I do. When a pair of electrodes are arranged facing each other in this manner, a capacitance element is formed by both electrodes, and the capacitance value C thereof is expressed as ε, the area of the electrodes as S, and the distance between the electrodes as d. Then, C = εS / d (1) is given. If the measuring electrodes 11 and 12 are rectangular flat plates, the area S is S = W · L, so the above equation is C = ε · W · L / d (2)

The basic principle of the water level sensor according to the present invention is that, as shown in FIG. 1, a pair of measuring electrodes 11 and 12 arranged at a predetermined interval d and a fixing for fixing the pair of measuring electrodes. The sensor (not shown in FIG. 1) and a measuring circuit 15 for measuring the water level based on the capacitance between the pair of measuring electrodes 11 and 12 constitute a sensor. Now, this water level sensor is connected to the measuring electrodes 11,
Consider a case in which the flat plate 12 is placed in a water tank such that the flat plate surface is in the vertical direction. FIG. 2 is a front view showing a state in which the apparatus is installed as described above. Here, as shown in the figure, the lower end positions of the measuring electrodes 11 and 12 are θ0, and the liquid surface position of the water tank is θ.
1. The principle of measuring the water level h up to the liquid level when the position θ0 is set as the reference position by using this water level sensor with the upper end positions of the measurement electrodes 11 and 12 being θ2 will be described.

When the water level sensor is in such a state,
The capacitance C of the capacitance element composed of the measurement electrodes 11 and 12 is higher than the liquid level (the height k between the positions θ1 and θ2).
) And the capacitance Ch of the portion below the liquid surface (the portion corresponding to the height h from the positions θ0 to θ1). Here, assuming that the dielectric constant of the atmosphere is εα (when using this sensor in a chamber filled with a special gas, the capacitance Ck of the portion above the liquid level is expressed by the dielectric constant of the gas. However, in the present specification, the atmosphere above the water level to be measured, including the gas in the atmosphere, is referred to as the atmosphere.), Ck = εα · W · k / d (3 ), The capacitance Ch of the portion below the liquid level is given by the dielectric constant of the liquid as εβ (the application of the water level sensor according to the present invention is not necessarily limited to the liquid level measurement. Any material having a certain degree of fluidity, such as a viscous material or a powder, may be used.
Ch = εβ · W · h / d (4). Therefore, the total capacity C is represented by C = (εα · k + εβ · h) · W / d (5) If a circuit for detecting the total capacitance C of the pair of measurement electrodes 11 and 12 is provided in the measurement circuit 15, k = L−h, and L, W, and d are known dimension values. And εα and εβ are known values (actually,
Although it fluctuates due to environmental conditions such as temperature, measures for this fluctuation will be described later).
If applied to (5), the water level h can be obtained.

As described above, when the water level sensor shown in FIG. 1 is used, the water level can be measured within the range of the length L of the measuring electrodes 11 and 12 in the longitudinal direction (within the range of the positions θ0 to θ2 in FIG. 2). Will be possible. In other words, when the longitudinal direction of the measurement electrodes 11 and 12 is used as a reference axis, the length of the measurement electrode in the reference axis direction is set to be longer than a necessary water level measurement range, and What is necessary is just to install a sensor so that a direction may turn to a perpendicular direction. In practice, it is preferable to adopt a configuration in which the surface area of the submerged portions of the measuring electrodes 11 and 12 monotonically increases as the water level rises. With such a configuration, the value of the capacitance detected by the measurement circuit 15 monotonically increases with the rise of the water level, and the increase in the capacitance value is directly used as a measurement value indicating the increase in the water level. It becomes possible to present. In particular, as in the rectangular flat plate shown in FIG. 1, a cut surface (same as the upper end surface in the illustrated example) obtained by cutting along a plane perpendicular to the reference axis (the direction of the length L) is obtained. If the shape is the same regardless of the cutting position on the reference axis, the capacitance value and the water level show a substantially linear relationship (actually, a perfect linear output cannot be obtained, The correction will be described in §5), and the handling of measured values becomes convenient.

§2. Use of Reference Electrode In the above-described water level sensor, the water level h is calculated based on Expression (5).
In order to obtain the values, the values of the dielectric constant εα of the atmosphere and the dielectric constant εβ of the liquid are required. For this reason, in practice, the values of the standard dielectric constant εα of the atmosphere and the standard dielectric constant εβ of the liquid whose water level is to be measured are set in advance, and using the set values, the equation (5) Is calculated. However, these dielectric constants are not always constant. For example, the dielectric constant εβ of a liquid will naturally differ if the liquid to be measured is different, and even the same liquid will differ depending on temperature conditions and the like. That is, if the liquid to be measured itself becomes different, such as water, benzene, heavy oil, alcohol,.
Will be different from each other. Further, even when the liquid itself is the same, for example, when measuring the water level in a bathtub, the dielectric constant εβ varies depending on the temperature of the water put in the bathtub. Alternatively, in the case of measuring the water level in the water tank of the washing machine, since the water contamination state before and after washing is different, the dielectric constant εβ also differs. On the other hand, the dielectric constant εα of the atmosphere also changes with temperature and humidity. When the water level sensor is used in a special chamber, the dielectric constant εα changes when the atmospheric gas in the chamber changes.

In the water level sensor according to the present invention, accurate measurement can be performed in response to such a change in the dielectric constant. FIG.
1 is a perspective view showing a basic configuration of a water level sensor according to the present invention. This water level sensor further includes a pair of upper reference electrodes 21 and 22 and a pair of lower reference electrodes 31 and 32 in addition to the water level sensor shown in FIG. A pair of upper reference electrodes 21 and 22 and lower reference electrodes 31 and 32
Is a pair of plate-like plate electrodes (width W, length M in this example) arranged at a predetermined interval from each other (in this example, the predetermined interval is d), like the pair of measurement electrodes 11 and 12. And
The capacitive element is formed by being fixed by fixing means (not shown). The measurement circuit 40 of the water level sensor includes a capacitance between the pair of measurement electrodes 11 and 12, a capacitance between the pair of upper reference electrodes 21 and 22, and a pair of lower reference electrodes 31 and 12. It has a function of measuring the water level based on the capacitance between 32 and the three.

Now, the measuring electrode 11 of this water level sensor,
12 is installed in the water tank such that the flat surface thereof is vertical, and the upper reference electrodes 21 and 22 and the lower reference electrodes 31 and 32 are also formed such that the flat surfaces thereof are vertical. Consider the case where it is installed inside. In addition,
The pair of measurement electrodes 11 and 12 are preferably installed so that the longitudinal direction is as vertical as possible in order to improve the measurement sensitivity.
The installation directions of 1 and 32 may be arbitrary, and may be set in the horizontal direction as in the embodiment described later. However, the upper reference electrodes 21 and 22 are always placed in the atmosphere during the measurement, and are set at positions where some of them are not immersed in the liquid. ,
During the measurement, it should always be completely immersed in the liquid, and it should be installed in such a position that any part of it is not exposed to the atmosphere. FIG. 4 is a front view showing a state in which the apparatus is installed as described above. In FIG. 4, as in FIG.
The lower end position of the water tanks 1 and 12 is θ0, the liquid surface position of the water tank is θ1, the upper end position of the measuring electrodes 11 and 12 is θ2, and the bottom surface position of the water tank is θ3. The principle of measuring the water level h up to the liquid level when the above is set forth will be described.

As described above, the capacitance value C of the capacitance element
Is determined by the following equation (1), where ε is the dielectric constant between the electrodes, S is the area of the electrodes, and d is the distance between the electrodes.

C = εS / d (1) Upper reference electrodes 21 and 2 in the water level sensor shown in FIG.
Since the electrode area S and the electrode interval d of the second and lower reference electrodes 31 and 32 are known, if the capacitance value of the capacitance element constituted by each electrode can be measured, the dielectric constant between the electrodes ε will be obtained. Moreover, since the upper reference electrodes 21 and 22 are always placed in the atmosphere, the dielectric constant ε between the electrodes is equivalent to the dielectric constant εα of the atmosphere, and the lower reference electrodes 31 and 32 are always liquid. Since it is placed inside, the dielectric constant ε between the electrodes corresponds to the dielectric constant εβ of the liquid.

On the other hand, the capacitance C of the capacitive element composed of the pair of measuring electrodes 11 and 12 is obtained by the following equation (5) as described above.

C = (εα · k + εβ · h) · W / d (5) Here, since the electrode width W, electrode length L (= h + k), and electrode interval d are known, the capacitance C Can be measured, the dielectric constants εα and ε obtained using the respective reference electrodes can be measured.
The water level h can be obtained using β. Since the dielectric constants εα and εβ used here correspond to the actually measured values in the measurement environment, no matter what kind of environment the type of liquid, the type of atmosphere, the temperature and the humidity are, The value will be accurate according to the environment. Thus, according to this water level sensor, it is possible to measure the water level with sufficient accuracy while having a simple structure.

In short, the basic principle of water level measurement by the water level sensor according to the present invention is as follows. Information on the dielectric constant εα of the atmosphere under the measurement environment is obtained based on the capacitance between a pair of upper reference electrodes. Based on the capacitance between the lower reference electrodes, information on the dielectric constant εβ of the measurement object under the measurement environment is obtained, and based on the information and the capacitance between the pair of measurement electrodes. The point is to determine the water level. In order to perform measurement based on such a principle, first, a length L of a measurement electrode in a predetermined reference axis direction (vertical direction in the illustrated example) is set to be longer than a necessary water level measurement range. There is a need. Conversely, in the case of the illustrated example, the maximum range in which the water level can be measured is the length L of the measurement electrode. On the other hand, it is necessary that the upper reference electrode be fixed above the water level measurement range, and the lower reference electrode be fixed below the water level measurement range. In other words, as described above, the upper reference electrodes 21 and 22 are always placed in the atmosphere during the measurement, and the upper reference electrodes 21 and 22 are placed in such a position that some of them are not immersed in the liquid. The lower reference electrodes 31 and 32 need to be installed at a position where they are always completely immersed in the liquid during the measurement and some of them are not exposed to the atmosphere.

As a basic principle, as described above, the dielectric constant εα of the atmosphere and the dielectric constant εβ of the liquid are obtained using the reference electrode, and these values are substituted into the equation (5) to determine the water level. Although it is obtained, in order to simplify the calculation for obtaining the water level, in the sensor according to the present embodiment, a pair of measurement electrodes, a pair of upper reference electrodes, and a pair of lower reference electrodes, A configuration is adopted in which the electrodes are constituted by plate electrodes having the same width W, and both electrode pairs are arranged in parallel with the same electrode spacing d. That is, as shown in FIG. 3, the measurement electrodes 11, 1
2 is a width W and a height L, and the distance between the two is d.
Similarly, the dimensions of each of the reference electrodes 21, 22, 31, 32 are defined as a width W and a height M, and the interval between them is defined as d. FIG. 5 is a front view showing only the respective electrodes extracted under the measurement environment as shown in FIG.

Here, as shown in FIG. 5, the capacitance value of a portion (length k) above the liquid surface of the capacitance element composed of the pair of measurement electrodes 11 and 12 is represented by C1α. The capacitance value of the portion below the liquid surface (the portion of length h) is C1β
And the total capacitance value of both is C1. In other words, the capacitance value C1α is a capacitance value determined depending on the dielectric constant εα of the atmosphere, and the capacitance value C1β is the dielectric constant εβ of the liquid.
Is a capacitance value determined depending on Then, the following equation can be defined: C1 = C1α + C1β (6) C1α = εα · W · k / d (7) C1β = εβ · W · h / d (8)

On the other hand, the capacitance value of the capacitance element composed of the pair of upper reference electrodes 21 and 22 is C2, and the capacitance value of the capacitance element composed of the pair of lower reference electrodes 31 and 32 is C2.
3 is assumed. Here, the former is a capacitance value determined depending on the dielectric constant εα of the atmosphere, and the latter is a capacitance value determined depending on the dielectric constant εβ of the liquid. Therefore, C2 = εα · W · M / d ( 9) The equation of C3 = εβ · W · M / d (10) can be defined. By transforming these equations, the following equation is obtained: C2 / M = εα · W / d (11) C3 / M = εβ · W / d (12), and the right-hand side of these equations (11) and (12) is obtained. Are substituted into the right sides of the equations (7) and (8), respectively, to obtain C1α = C2 / M · k = C2 / M (L−h) (13) C1β = C3 / M · h (14) The left side of these equations (13) and (14) is expressed by equation (6)
By substituting into the right side of the following equation, the following expression is obtained: C1 = C2 / M (L−h) + C3 / M · h = (C2 · L− (C2−C3) · h) / M (15) By solving this equation (15) for h, the following equation is obtained: h = (C2 · L−C1 · M) / (C2−C3) (16) Here, since L and M are known values as the dimension values of each electrode, if the capacitance values C1, C2, and C3 of the three capacitance elements are measured, FIG.
The water level h up to the liquid level when the position θ0 is set as the reference position can be obtained. When the water level from the position θ3 on the bottom of the water tank is required, it can be obtained as h + m.

FIG. 6 is a block diagram showing a specific configuration example of the measuring circuit 40. Here, C shown at the left end of the figure
1, C2 and C3 are a pair of measurement electrodes 11, 1 respectively.
2, a capacitive element constituted by a pair of upper reference electrodes 21 and 22 and a pair of lower reference electrodes 31 and 32 is shown. The capacitance detection units 41, 42, and 43 are circuits that output the capacitance values C1, C2, and C3 of the respective capacitance elements as signals, and the C / V conversion units 44, 45, and 46 convert these signals into voltage values. V1, V2, and V3. The calculation unit 47 calculates the value h by performing the calculation of the above equation (16) using the respective voltage values V1, V2, V3 (the values corresponding to the respective capacitance values C1, C2, C3). , And a circuit for adding a depth m to the bottom of the water tank and outputting a value of h + m as a final water level value.

§3. Basic Embodiments Next, some basic embodiments of the water level sensor according to the present invention will be described. The feature of the embodiment shown here is that a tubular structure into which a liquid can be introduced is used as a fixing means, and each electrode is formed on the inner surface or outer surface of the tube wall of the tubular structure. For example, as shown in a perspective view of FIG. 7, a prismatic tubular structure 50 is prepared. A prismatic through-hole is formed inside the tubular structure 50, and a liquid can be introduced into the through-hole. For example, if such a tubular structure 50 is installed in a water tank as shown in FIG. 4 so that the longitudinal direction thereof is oriented vertically, the tubular structure 50 is introduced into the tubular structure 50 based on the water level in the water tank. The water level of the liquid also rises and falls, and by measuring the water level of the liquid in the tubular structure 50, the water level in the water tank can be known. When realizing the water level sensor according to the present invention, a pair of measurement electrodes, a pair of upper reference electrodes,
What is necessary is just to form a pair of lower reference electrode.

FIG. 8 is a cross-sectional view showing an embodiment in which each electrode is formed on the inner surface of the tube wall of the tubular structure 50 (a sectional view of the tubular structure 50 shown in FIG. 7 cut along a horizontal plane).
A state is shown in which a pair of measurement electrodes 51 and 52 are arranged on the inner surface of the tube wall so as to face each other. FIG. 9A is a side sectional view of the tubular structure 50 shown in FIG. 8 taken along a cutting line AA in the figure, and FIG. 9A is a side sectional view taken along a cutting line BB in the figure. FIG. 9B shows each of them. As shown in the side sectional view of FIG. 9A, the inner surface of the tube wall of the tubular structure 50 has
A pair of measurement electrodes 51 and 52 having a length L are arranged so as to form a capacitive element. In addition, a pair of upper reference electrodes 53 and 54 are arranged on the upper part to form a capacitive element, and a pair of lower reference electrodes 55 and
56 are arranged so as to form a capacitive element. FIG.
(b) shows one of the electrodes 51, 53, and 55 among these electrodes.

If a water level sensor having such a structure is used, it is possible to make a measurement in which the length L of the measuring electrodes 51 and 52 is within a water level measurement range. That is, as long as the water level is within the range of the length L, the upper reference electrodes 53 and 54 are always located in the air, and the lower reference electrodes 55 and 56 are always located in the liquid. The measurement based on the set principle becomes possible. That is, the water level can be obtained by measuring the capacitance values of the three capacitance elements formed by the respective electrodes. In this example, in the tubular structure 5
0 is made of an insulating material, each electrode is formed directly on the inner surface of the tube wall. However, when the tubular structure 50 is made of a conductive material, each electrode is formed via an insulating layer. What is necessary is just to form it. Hereinafter, some modified examples of the basic embodiment will be described.

FIG. 10 is a side sectional view of a modification using a tubular structure 60 having a U-shaped cross section whose upper end and lower end are bent in the horizontal direction. The point that a pair of measurement electrodes 61 and 62 having a length L are arranged on the inner surface of the tube wall of the tubular structure 60 so as to form a capacitive element is the same as in the above-described embodiment. A pair of upper reference electrodes 63 and 64 are arranged on the upper part so as to form a capacitive element.
The lower part is the same in that a pair of lower reference electrodes 65 and 66 are arranged so as to form a capacitive element. However, since each of the reference electrodes 63 to 66 is oriented in the horizontal direction, the space required for these reference electrodes in the vertical direction is saved, and the water level measurement range L is made longer. It becomes possible.

FIG. 11 is a cross-sectional view showing an embodiment in which each electrode is formed on the outer surface of the tube wall of the tubular structure 70. A state is shown in which a pair of measurement electrodes 71 and 72 are arranged on the outer surface of the tube wall so as to face each other. FIG. 12 (a) is a side sectional view of the tubular structure 70 shown in FIG. 11 taken along the cutting line AA in the figure, and FIG. 12 (b) is a side view seen from the left side of the figure.
Shown respectively. As shown in the side sectional view of FIG. 12A, a pair of measuring electrodes 71 and 72 having a length L are arranged on the outer surface of the tube wall of the tubular structure 70 so as to form a capacitive element. Have been. A pair of upper reference electrodes 73 and 74 are arranged on the upper part to form a capacitive element.
Below, a pair of lower reference electrodes 75 and 76 are arranged so as to form a capacitive element. FIG. 12B shows one of the electrodes 71, 73,
75 is shown.

As described above, even when each electrode is formed on the outer surface of the tube wall of the tubular structure 70, three capacitance elements are still formed, and measurement based on the basic principle of the present invention is possible. become. When the electrodes are formed on the outer surface, not only the liquid to be measured but also the tube wall of the tubular structure 70 is interposed between the capacitance elements. Therefore,
The dielectric constant between the pair of electrodes constituting the capacitive element depends not only on the dielectric constant of the air or liquid but also on the dielectric constant of the tube wall material. Atmospheric permittivity ε based on the capacitance value of the capacitive element
The information about α can be obtained, and the lower reference electrode 7
The basic principle that information on the dielectric constant εβ of the liquid can be obtained based on the capacitance value of the capacitance element composed of 5,76 is the same. However, in order to increase the detection sensitivity, it is preferable to reduce the thickness of the tube wall of the tubular structure 70 as much as possible. In addition, although there is a restriction that a conductive material cannot be used for the tube wall of the tubular structure 70, it is only necessary to form the electrodes on the outer surface, so that there is an advantage that the manufacturing cost can be reduced.

FIG. 13A shows a modified example using a tubular structure 80 having a U-shaped cross section whose upper end and lower end are bent in the horizontal direction, instead of the tubular structure 70 in the above example. It is a side sectional view. A pair of measuring electrodes 81 having a length L,
82, a pair of upper reference electrodes 83 and 84, and a pair of lower reference electrodes 85 and 86 are all formed on the outer surface of the tube wall of the tubular structure 80. FIG. 13B shows a modification of the modified example shown in FIG. 13A in which one measuring electrode 81, one upper reference electrode 83, and one lower reference electrode 85 are connected to a common electrode made of a single conductor. It is a sectional side view which shows the modified example comprised by 87. In the measurement circuit 40 shown in FIG. 6, one of the electrodes constituting the three capacitive elements C1, C2, and C3 can be connected to a common ground level. Therefore, these electrodes are formed of a single conductor. No problem occurs. Therefore, as shown in FIG.
The electrodes 81, 83, 85 can be shared. By using such a common electrode 87, the manufacturing cost can be further reduced.

FIGS. 14 (a) to 14 (f) are cross-sectional views showing further modifications in which each electrode is formed on the outer surface of a tubular structure. In the modified example shown in FIG. 14A, a pair of electrodes 91 and 92 forming a capacitive element are arranged at positions orthogonal to each other (two orthogonally adjacent surfaces), and the modified example shown in FIG. In this example, a pair of electrodes 93 and 94 forming a capacitive element are adjacently arranged on the same plane. As described above, the pair of electrodes forming the capacitive element do not necessarily need to be arranged at opposing positions, and may be arranged in any positional relationship as long as an element capable of detecting a change in dielectric constant based on the water level can be formed. Absent. That is, in principle, it suffices that the configuration is such that the liquid can enter the path of the electric flux lines formed between the pair of electrodes. Even if the arrangement as shown in FIG. 14A or the arrangement as shown in FIG. 14B is adopted, the lines of electric force between the pair of electrodes enter the inside of the tubular structure 90, so that the measurement becomes possible.

FIG. 14C shows a cylindrical tubular structure 100.
2 shows an example in which a pair of electrodes 101 and 102 are arranged on the opposing surfaces. As described above, the electrode shape does not necessarily have to be a flat plate shape, but may be a shape along the tube wall. FIG.
(d) shows an example in which a pair of electrodes 103 and 104 are arranged adjacent to the outer surface of a cylindrical tubular structure 100.

FIG. 14E shows a prismatic tubular structure 110.
A groove 115 is formed on one side surface along the longitudinal direction, and a pair of electrodes 111 and 1 are formed on the outer surface of the tube wall where the groove 115 is formed.
An example in which No. 12 is formed is shown. FIG. 14 (f) shows a groove 1 along one side of the cylindrical tubular structure 120 along the longitudinal direction.
25 shows an example in which a pair of electrodes 121 and 122 are formed on the outer surface of the tube wall where the groove 125 is formed. In general,
The capacitance value increases as the electrode distance d decreases. Therefore, as shown in FIG. 14E or FIG. 14F, when the grooves 115 and 125 are formed and the capacitance value of this portion is obtained, a larger capacitance value is measured. As a result, the measurement sensitivity can be improved.

The examples shown in FIGS. 14 (a) to 14 (f) are examples in which the electrodes are formed on the outer surface of the tube wall. Of course, the electrodes may be formed on the inner surface of the tube wall. .

In the examples described above, a tubular structure is used as a fixing means for fixing each electrode at a predetermined position. However, the fixing means does not necessarily need to be a tubular structure. Any structure may be used as long as it can be fixed at a predetermined position. For example, FIG. 15 is a longitudinal sectional view of an example in which four electrode plates 131, 132, 133, and 134 are directly fixed to the wall surface of the water tank 130. Each electrode plate is directly adhered to the rear wall of the water tank 130. The electrode plate 131 is one measuring electrode, the electrode plate 132 is one upper reference electrode, and the electrode plate 13.
Reference numeral 3 functions as one lower reference electrode, and the electrode plate 134 functions as a common electrode opposed thereto.
In this example, the length L of the measurement electrode 131 is a measurable range.

§4. Further Embodiments Next, some further embodiments of the present invention will be described.
In the water level sensor shown in FIG. 16A, a pair of electrodes forming a capacitive element are constituted by a pair of conductive wires, and the pair of conductive wires are fixed by fixing means so as to be parallel. That is, on the insulating support substrate 140, a pair of conductive wires 141 and 142 constituting a measurement electrode are attached in parallel at a predetermined interval. A pair of conductive lines 143 and 144 constituting the upper reference electrode are similarly mounted in parallel at a predetermined interval, and a pair of conductive lines 145 constituting the lower reference electrode are provided below. ,
146 are also mounted in parallel at a predetermined interval. Each of the conductive wires 141 to 146 and the terminals T141 to T1
46 is connected by a wire, the terminal T
C1, the capacitance between terminals 141 and T142, and terminal T143,
The capacitance between T144 is C2, the terminals T145, T146
The water level can be measured by applying the measurement circuit 40 shown in FIG.
Each electrode will constitute a thin columnar electrode,
As described above, the lines of electric force between the two electrodes pass through the region around the two electrodes. Therefore, when the liquid enters the surrounding region, a change in the dielectric constant occurs and measurement becomes possible.

On the other hand, in the water level sensor shown in FIG. 16B, a pair of electrodes forming a capacitive element is constituted by a pair of conductive wires,
As a stranded wire is constituted by this pair of conductive wires,
It is fixed by fixing means. That is, on the insulating support substrate 150, a pair of conductive wires 151 and 152 constituting a measurement electrode are attached in a state of forming a stranded wire, and an upper reference electrode is formed beside the pair of conductive wires 151 and 152. A pair of conductive wires 153 and 154 are attached in a state of similarly forming a stranded wire, and beside the pair of conductive wires 155 and 156 forming a lower reference electrode similarly form a stranded wire. Installed in state. However, the twisted wire portions of the conductive wires 151 and 152 are formed near the center to be the water level measurement range, whereas the twisted wire portions of the conductive wires 153 and 154 are only the upper portion thereof, and The stranded portion of 155,156 is only the lower portion.

Each conductive wire is covered with an insulating layer, and a portion constituting a substantial capacitive element is a stranded wire portion. The other parts function simply as wiring. Therefore, the capacitance element (conductive lines 153, 15) composed of the upper reference electrode pair is located substantially above the capacitance element (the stranded portion of the conductive lines 151, 152) composed of the measurement electrode pair.
No. 4 stranded wire portions), and a capacitive element (a stranded wire portion of the conductive wires 155 and 156) composed of the lower reference electrode pair is disposed below the capacitive element composed of the measurement electrode pair. Will be. As long as the liquid level is within the measurable range, the capacitive element consisting of the upper reference electrode pair is completely located in the atmosphere, and the capacitive element consisting of the lower reference electrode pair is completely immersed in the liquid. It has become.

Each of the conductive lines 151 to 156 and a terminal T151
To T156, the terminal T15
C1, the capacitance between terminals T152 and T152, and terminals T153 and T1.
With the capacitance between the terminals 54 as C2 and the capacitance between the terminals T155 and T156 as C3, the water level can be measured by applying the measurement circuit 40 shown in FIG. When the stranded wire is used as the electrode as described above, the length of the electrode immersed in the liquid is increased, and thus the merit of improving the sensitivity can be obtained.

In the water level sensor shown in FIG. 17A, the fixing means is constituted by a flat support substrate, and each electrode is constituted by a conductive layer formed on the support substrate. That is, on the insulating support substrate 160, a pair of conductive layers 161 and 162 forming the measurement electrode are juxtaposed on the same plane, and above the pair of conductive layers forming the upper reference electrode. The layers 163 and 164 are juxtaposed on the same plane, and a pair of conductive layers 165 and 166 constituting the lower reference electrode are juxtaposed on the same plane below the layers. Each of the conductive layers 161 to 166 and the terminals T161 to T161
166 is connected by wiring, the capacitance between the terminals T161 and T162 becomes C1, the terminal T16
C2, the capacitance between terminals T165 and T1
The measurement circuit 4 shown in FIG.
By applying 0, the water level can be measured. In the illustrated example, the wiring is formed between each conductive layer and each terminal. However, since the distance between the wirings is large, the measured value is not significantly affected. In this embodiment, each electrode is a conductive layer formed on the same plane. However, as described above, the lines of electric force between the electrodes are not limited to this plane, and pass through the vicinity area on the front and back sides. Therefore, the support substrate 1
By immersing the front and back of 60 in the liquid, a change in the dielectric constant occurs, and measurement becomes possible.

The water level sensor shown in FIG.
(a) The supporting substrate 160 of the water level sensor shown in (a) is bent from the center to form an L-shaped supporting substrate 170 when viewed from above.
Which has been processed so as to obtain Since a pair of electrodes on which a capacitor is to be formed are formed separately on two planes intersecting with each other, FIG.
The measurement with higher sensitivity is possible as compared with the water level sensor shown in FIG.

In the embodiment shown in FIGS. 17A and 17B, insulating films such as polyimide are used as the support substrates 160 and 170, and electrodes and wiring such as copper formed by patterning on the insulating films are used. It can be composed of metal foil. The water level sensor having such a configuration is suitable for mass production and can keep the manufacturing cost low.

In the water level sensor shown in FIG. 18A, one of the measuring electrode and each of the reference electrodes is connected to a common cylindrical conductor 18.
0, and the other measuring electrode and each reference electrode are constituted by cylindrical conductors 181, 182, 183 having an inner circumference larger than the outer circumference of the columnar conductor 180. As shown, the cylindrical conductors 181, 1
The cylindrical conductor 180 is inserted into the insides of 82 and 183, and a gap is secured between both to allow a liquid to penetrate.
It is fixed by fixing means. This is shown in FIG.
This is clearly shown in the cross-sectional view of FIG. A filling fixing portion 181A made of an insulator is formed between the columnar conductor 180 and the cylindrical conductor 181 and both are fixed. The filling and fixing portion 181A has a semicircular cross section, and in FIG.
Only the upper half of the interior is filled. A gap 181B is provided in the lower half of the inside of the cylindrical conductor 181.
Is formed, and the structure is such that the liquid can penetrate there. Similarly, the columnar conductor 180 and the cylindrical conductor 182
A filling fixing portion 182A made of an insulator is formed between the two, and both are fixed. Again, the filling and fixing portion 182A has a semicircular cross section, and a semicircular void portion 182B through which liquid can penetrate is formed on the other side. Further, the columnar conductor 180 and the cylindrical conductor 183
A filling fixing portion 183A made of an insulator is also formed between them, and both are fixed. Again, the filling and fixing part 183A has a semicircular cross section, and a semicircular void 183B through which liquid can penetrate is formed on the other side.

After all, in FIG. 18 (a), about a half of the columnar conductor 180 near the center functions as one of the measuring electrodes, and the upper quarter is the upper reference electrode. , And about a quarter of the lower part functions as one of the lower reference electrodes. If the conductors 180 to 183 and the terminals T180 to T183 are connected by wiring, the terminals T180, T18
The capacitance between the terminals T180 and T182 is represented by C1, the capacitance between the terminals T180 and T182 is represented by C2, and the capacitance between the terminals T180 and T183 is represented by C3. It can be performed. If one measuring electrode and one reference electrode are formed of a single conductor as in this example, the single conductor can be shared, and the structure can be further simplified. Can be. Of course, in the water level sensor shown in FIGS. 16 (a) and (b) or FIGS. 17 (a) and (b), one measuring electrode and one reference electrode are formed of a single conductor. , It is possible to share this single conductor.

§5. Device for Obtaining Linear Output As already described in §1, when a pair of measurement electrodes 11 and 12 as shown in FIG. 1 are prepared and immersed in a liquid as shown in FIG. The capacitance value between the two electrodes gradually increases with the rise. Here, a linear relationship should be established in principle between the change in the water level and the change in the capacitance value. That is, in the measurement circuit 40 shown in FIG. 6, the output value C1 of the capacitance detection unit 41 increases linearly with the rise of the water level, and if the C / V conversion unit 44 performs linear conversion, this C / V V conversion unit 3
3 should also increase linearly with increasing water level.

However, according to an experiment using the water level sensor according to the present invention, it was found that the relation between the water level and the capacitance value was not completely linear. That is, even if a conversion circuit that outputs a voltage proportional to the capacitance value is used for the C / V conversion unit 44, the output value V1 of the C / V conversion unit 44 is linear with respect to a change in water level. It doesn't. Specifically, for example, a solid line graph G1 in FIG.
The relationship shown by is obtained. In principle, a linear relationship as shown by the broken line graph G0 should be obtained,
In practice, a linear relationship is obtained until the water level reaches the predetermined value LL, but after that, the output value tends to gradually deviate from the linear graph G0. The detailed reason why this phenomenon occurs is unknown at this stage, and is an issue that is left for future research.

However, if the output value does not show a linear characteristic as described above, some correction is required to present the final water level as a measured value, which is not preferable in practical use. In general, when a linear signal system is handled, a relatively simple analog circuit can be used as the measurement circuit 40, so that the manufacturing cost can be reduced.
However, in order to convert a nonlinear signal into a linear signal,
A complicated arithmetic circuit such as a microprocessor is required, and the manufacturing cost must increase.

Here, a method for solving such a problem will be described. Now, for example, FIG.
(b), a water level sensor having a structure as shown in FIG. 1 was prototyped, and the capacitance value C1 between the measurement electrodes 51 and 52 (actually, the voltage value V
Assume that a non-linear relationship as shown in a graph G1 in FIG. 19 is obtained between the water level and the output value when measuring 1). When reproducibility is recognized in such a non-linear relationship, such non-linearity can be corrected by changing the physical structure of the measurement electrodes 51 and 52. Hereinafter, two specific methods will be described.

In the first method, the electrode interval between the measurement electrodes 51 and 52 may be made different for each part. For example, in the example shown in FIG.
Is formed as a conductive layer having a uniform thickness, which is formed by measuring electrodes 51A and 52A shown in FIG.
It changes like this. Measurement electrodes 51A, 52A
Is uniform up to the position of the water level LL,
In the section from L to water level L, the thickness gradually increases. In other words, the electrode spacing d gradually decreases as it goes upward. In the graph shown in FIG. 19, the ratio of decreasing the electrode interval d is determined as appropriate by examining how much the graph G1 deviates from the linear graph G0 in the section from the water level LL to the water level L in the graph shown in FIG. What should I do? In other words, the output value indicating the value of the capacitance may be adjusted so as to indicate a linear relationship with the rise in the water level. Of course, the electrode spacing may be adjusted by changing only the thickness of one of the pair of measurement electrodes, or the wall spacing of the tubular structure 50 may be inclined to adjust the electrode spacing. You may.

In the second method, the width of the electrode between the measurement electrodes 51 and 52 may be different for each part. For example, in the example shown in FIG. 9 (b), the measuring electrode 51 is formed as a conductive layer having a uniform width, but this is formed like a measuring electrode 51B shown in FIG. 20 (b). Change it. The width of the measurement electrode 51B is uniform up to the position of the water level LL, but gradually increases in the section from the water level LL to the water level L. The ratio of increasing the width of the electrode is determined as appropriate by examining how much the graph G1 deviates from the linear graph G0 in the section from the water level LL to the water level L in the graph shown in FIG. What should I do? In other words, the output value indicating the value of the capacitance may be adjusted so as to indicate a linear relationship with the rise in the water level. Such adjustment by the electrode width may be performed for only one of the pair of measurement electrodes, or may be performed for both. Of course, adjustment using both the above-described first method and second method is also possible.

As described above, in the method of correcting the non-linear characteristic of the water level sensor according to the present invention by changing the physical structure of the measurement electrode, the operation of determining the optimum physical structure of the measurement electrode for correction is performed. Although a little complicated, the mass production cost is almost the same as when no such correction is performed. Therefore, a reduction in manufacturing cost can be expected as compared with a method of performing a linear correction operation in a measurement circuit.

As described above, the present invention has been described based on several embodiments. However, the present invention is not limited to these embodiments, and can be implemented in various other forms. In particular, the shapes and forms of the respective electrodes in the individual embodiments described above are merely examples, and the present invention is not limited to these forms and forms. In particular, in the above-described embodiment, an example has been described in which a liquid is used as the measurement target of the water level.However, the water level sensor according to the present invention is not limited to use in measuring the level of the liquid, and may be a viscous body or a liquid. The present invention is also applicable to the field of measuring the amount of an object having a certain degree of fluidity such as powder. For example, if you use it in a warehouse that stores grains such as rice and wheat,
It is possible to measure the amount of grain. It is also applicable to many solids that are collectively considered fluids. For example, it is also possible to measure the amount of small electronic components such as chip-shaped resistance elements and capacitors (storage height in a storage). For convenience of description, in the specification of the present application, the term "water level sensor" is used, but the "water level" here is not only a liquid level, but also a viscous substance,
It also broadly includes levels for powders, many solids that are collectively considered fluids.

[0062]

As described above, according to the water level sensor according to the present invention, since the water level is measured by using the capacitance values of the three capacitance elements, the water level measurement with a simple structure and sufficient accuracy is achieved. Will be able to do.

[Brief description of the drawings]

FIG. 1 is a perspective view (partially a block diagram) for explaining a basic principle of a water level sensor according to the present invention.

FIG. 2 is a front view showing a state in which a water level measurement is performed using the water level sensor shown in FIG.

FIG. 3 is a perspective view (partially a block diagram) showing basic components of a water level sensor according to the present invention.

FIG. 4 is a front view showing a state where a water level measurement is being performed using the water level sensor shown in FIG. 3;

FIG. 5 is a front view showing only each electrode extracted in the measurement environment shown in FIG. 4;

FIG. 6 is a block diagram showing a detailed configuration of a measurement circuit of the water level sensor shown in FIG.

FIG. 7 is a perspective view of a tubular structure used in a basic embodiment of a water level sensor according to the present invention.

FIG. 8 is a cross-sectional view of an embodiment in which each electrode is formed on the inner surface of the tube wall of the tubular structure.

FIG. 9 is a side sectional view of an embodiment in which each electrode is formed on the inner surface of the tube wall of the tubular structure.

FIG. 10 is a side sectional view of an embodiment using a tubular structure having a U-shaped cross section whose upper end and lower end are bent in the horizontal direction.

FIG. 11 is a cross-sectional view of an embodiment in which each electrode is formed on an outer surface of a tube wall of a tubular structure.

FIG. 12 is a side sectional view and a side view of an embodiment in which each electrode is formed on the outer surface of the tube wall of the tubular structure.

FIG. 13 is a side cross-sectional view of two embodiments using a tubular structure having a U-shaped cross section whose upper end and lower end are bent in the horizontal direction.

FIG. 14 is a cross-sectional view showing various embodiments in which each electrode is formed on the outer surface of the tubular structure.

FIG. 15 is a longitudinal sectional view of an embodiment in which four electrode plates are directly fixed to a wall surface of a water tank.

FIG. 16 is a perspective view of an embodiment in which electrodes forming a capacitive element are formed of conductive lines.

FIGS. 17A and 17B are a front view and a perspective view of an embodiment in which an electrode forming a capacitor is formed by a conductive layer on a supporting substrate.

18A and 18B are a perspective view and a cross-sectional view of an embodiment in which electrodes forming a capacitive element are formed of columnar and cylindrical conductors.

FIG. 19 is a graph showing a relationship between a water level and a capacitance value in the water level sensor according to the present invention.

FIG. 20 is a side sectional view showing an embodiment in which linear correction is performed based on the physical structure of an electrode.

[Explanation of symbols]

11, 12 ... Measurement electrode 15 ... Measurement circuit 21, 22 ... Top reference electrode 31, 32 ... Lower reference electrode 40 ... Measurement circuit 41-43 ... Capacity detector 44-46 ... C / V converter 47 ... Calculation Part 50: tubular structure 51, 51A, 51B, 52, 52A: measuring electrode 53, 54: upper reference electrode 55, 56: lower reference electrode 60: tubular structure 61, 62: measuring electrode 63, 64 ... upper reference electrode 65, 66 ... lower reference electrode 70 ... tubular structure 71, 72 ... measurement electrode 73, 74 ... upper reference electrode 75, 76 ... lower reference electrode 80 ... tubular structure 81, 82 ... Measurement electrodes 83 and 84 Upper reference electrodes 85 and 86 Lower reference electrodes 87 Common electrodes 90 Tubular structures 91 to 94 Electrodes for forming capacitor elements 100 Tubular structures 101 to 104 Capacitance elements Electrode for forming 110 ... tubular structure 111, 112 ... electrode for forming capacitor element 115 ... groove 120 ... tubular structure 121, 122 ... electrode for forming capacitor element 125 ... groove 130 ... water tank 131-134 ... electrode plate 140 ... Support substrates 141, 142 ... Conductive wires (measuring electrodes) 143, 144 ... Conductive wires (upper reference electrodes) 145, 146 ... Conductive wires (lower reference electrodes) 159 ... Support substrates 151, 152 ... Twisted wire Conductive wires (measurement electrodes) 153, 154 stranded conductive wires (upper reference electrode) 155, 156 stranded conductive wires (lower reference electrode) 160 support substrate 161, 162 conductive layer ( Measurement electrodes) 163, 164: conductive layer (upper reference electrode) 165, 166: conductive layer (lower reference electrode) 170: folded support substrate 180: columnar conductive Body 181 to 183 Cylindrical conductor 181A to 183A Filling and fixing part 181B to 183B Gap C1, C1α, C1β, C2, C3 Capacitance / capacitance element d Electrode spacing h, k, m Length / Water level L, M: length of electrode LL: specific water level T141 to T183: terminal W: width of electrode εα, εβ: dielectric constant θ0 to θ3: position of water level

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobumitsu Taniguchi 4-73, Sugaya, Ageo City, Saitama Prefecture Inside Wako Co., Ltd. (72) Inventor Hideo Morimoto 172 Ikezawacho, Yamatokoriyama City, Nara Prefecture Nita Factory

Claims (10)

[Claims] 1. A water level sensor for measuring a water level from a predetermined reference position to a liquid level, comprising: a pair of measuring electrodes arranged at a predetermined interval; and a pair of upper electrodes arranged at a predetermined interval. A reference electrode, a pair of lower reference electrodes arranged at a predetermined interval, fixing means for fixing the respective electrodes, and a measurement circuit for measuring a water level using the respective electrodes, comprising: The length of the measurement electrode with respect to the reference axis direction is set longer than the required water level measurement range, the upper reference electrode is located above the water level measurement range, and the lower reference electrode is Each electrode is fixed so as to be located below the water level measurement range, the measurement circuit, the capacitance between the pair of measurement electrodes, the capacitance between the pair of upper reference electrodes, Of the pair of lower reference electrodes Water level sensor, characterized in that to measure the water level on the basis of the tripartite capacitance. 2. The water level sensor according to claim 1, wherein information on the dielectric constant εα of the atmosphere under the measurement environment is obtained based on a capacitance between the pair of upper reference electrodes. Based on the capacitance between the electrodes, information on the dielectric constant εβ of the measurement object under the measurement environment is obtained, and the water level is determined based on the information and the capacitance between the pair of measurement electrodes. A water level sensor, comprising: 3. The water level sensor according to claim 1, wherein the pair of measurement electrodes, the pair of upper reference electrodes, and the pair of lower reference electrodes are each formed of a flat electrode having the same width W. A water level sensor comprising: a plurality of electrode pairs arranged in parallel to each other with the same electrode spacing d. 4. The water level sensor according to claim 1, wherein an output value indicating a capacitance value between the pair of measurement electrodes in the measurement circuit has a linear relationship with a rise in the water level. A water level sensor, wherein an electrode interval between measurement electrodes is different for each part. 5. The water level sensor according to claim 1, wherein in the measurement circuit, an output value indicating a value of a capacitance between the pair of measurement electrodes has a linear relationship with a rise in the water level. A water level sensor, wherein the width of the measuring electrode is different for each part. 6. The water level sensor according to claim 1, wherein a tubular structure capable of introducing a liquid therein is used as a fixing means, and each of the tubular structures is provided on an inner surface or an outer surface of a tube wall of the tubular structure. A water level sensor having electrodes formed thereon. 7. The water level sensor according to claim 1, wherein each of the pair of measurement electrodes, the pair of upper reference electrodes, and the pair of lower reference electrodes includes a pair of conductive wires, A water level sensor, wherein a pair of conductive wires are fixed by fixing means so as to be parallel or to form a stranded wire with each other. 8. The water level sensor according to claim 1, wherein the fixing means is constituted by a flat support substrate, and each measurement electrode and each reference electrode are formed on the support substrate. A water level sensor comprising a conductive layer. 9. The water level sensor according to claim 1, wherein one of the measurement electrodes, one of the upper reference electrodes, and one of the lower reference electrodes are each formed of a columnar conductor, The other measurement electrode, the other upper reference electrode, and the other lower reference electrode are each formed of a cylindrical conductor having an inner circumference larger than the outer circumference of the columnar conductor, and are formed inside the cylindrical conductor. A water level sensor, wherein the columnar conductor is inserted into the gap and fixed by a fixing means in a state where a gap is provided between the two conductors so that a liquid can penetrate. 10. The water level sensor according to claim 1, wherein one of the measurement electrodes, one of the upper reference electrodes, and one of the lower reference electrodes are formed of a single conductor, A water level sensor wherein the single conductor is shared by the electrodes.