JPH11108735A - Water level sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure a water level by a simple structure. SOLUTION: A pair of measuring electrodes 11, 12 (width: W, length: L1) disposed at a fixed distance (d) therebetween are installed in a water level measuring area in a water tank, and a pair of reference electrodes 21, 22 (width: W, length: L0) disposed similarly at a fixed distance d therebetween are installed on the bottom of the water tank. As to capacitance between the electrodes 21, 22, a difference ΔC0 is found between a value when the water tank is empty and a value when the water tank is filled up to a position θ0. As to capacitance between the electrodes 11, 12, a difference ΔC1 is found between a value when the water tank is empty and a value when the water tank is filled up to a position θ1. A water level (h) to be measured is found by a calculation, h=(ΔC1/δC0).L0.

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.

Accordingly, an object of the present invention is to provide a water level sensor capable of accurately measuring a water level with a simple structure.

[0005]

[Means for Solving the Problems]

(1) A first aspect of the present invention relates to a water level sensor for measuring a water level from a predetermined reference position to a liquid level, wherein a pair of measurement electrodes arranged at a predetermined interval, and the pair of measurement electrodes And a measuring circuit for measuring the water level based on the capacitance between the pair of measuring electrodes.

(2) The second aspect of the present invention relates to the above-described first aspect.
In the water level sensor according to the aspect, the length of each measurement electrode in the predetermined reference axis direction is set longer than the required water level measurement range, and the entire sensor is set so that the reference axis direction is oriented in the vertical direction. When installed, the surface area of the submerged portion of each measurement electrode monotonically increases as the water level rises.

(3) The third aspect of the present invention is the above-described second aspect.
In the water level sensor according to the aspect, the pair of measurement electrodes is constituted by a pair of conductive wires, and the pair of conductive wires is fixed by fixing means such that the pair of conductive wires are parallel or form a stranded wire. Things.

(4) The fourth aspect of the present invention is the above-mentioned second aspect.
In the water level sensor according to the aspect, the fixing means is constituted by a flat support substrate, and each measurement electrode is constituted by a conductive layer formed on the support substrate.

(5) The fifth aspect of the present invention is the above-mentioned second aspect.
In the water level sensor according to the aspect, one of the measurement electrodes is constituted by a cylindrical conductor, and the other measurement electrode is constituted by a cylindrical conductor having an inner periphery larger than the outer periphery of the columnar conductor. A cylindrical 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.

(6) A sixth aspect of the present invention is the above-mentioned first aspect.
In the water level sensor according to the fifth to fifth aspects, a pair of reference electrodes arranged at a predetermined interval is further provided, and the pair of measurement electrodes and the pair of reference electrodes are fixed by fixing means, and the measurement is performed. The circuit measures the water level based on both the capacitance between the pair of measurement electrodes and the capacitance between the pair of reference electrodes.

(7) A seventh aspect of the present invention is the above-mentioned sixth aspect.
In the water level sensor according to the aspect, the pair of reference electrodes is fixed at a lower position than the pair of measurement electrodes.

(8) The eighth aspect of the present invention is the above-mentioned sixth aspect.
Alternatively, in the water level sensor according to the seventh aspect, the shape of the pair of measuring electrodes is the same regardless of the cutting position on the reference axis, which is obtained by cutting a plane perpendicular to the predetermined reference axis. The shape of the pair of reference electrodes is the same as that of the pair of measurement electrodes, or the shape of the pair of measurement electrodes is expanded and contracted along the reference axis.

(9) The ninth aspect of the present invention is the above-mentioned eighth aspect.
In the water level sensor according to the aspect, the difference ΔC0 between the capacitance value of the pair of reference electrodes when not in contact with the liquid at all and the capacitance value when completely immersed in the liquid, For a pair of measurement electrodes, the difference ΔC1 between the capacitance value in a state where it is not in contact with the liquid at all and the capacitance value in a state where a portion corresponding to the water level to be measured is immersed in the liquid, Using the length L0 of the reference electrode in the reference axis direction, the measurement circuit calculates the water level h with the lowermost position of the measurement electrode as the reference position by the calculation of h = (ΔC1 / ΔC0) · L0. It was made.

(10) According to a tenth aspect of the present invention, in the water level sensor according to the sixth to ninth aspects, one of the measuring electrode and one of the reference electrodes is formed of a single conductor. The single conductor is used in common for the measurement electrode and the reference electrode.

(11) According to an eleventh aspect of the present invention, in the water level sensor according to the first aspect, the effective surface area related to the capacitance is periodically changed along a predetermined reference axis. A pair of measuring electrodes having various shapes are prepared, and a measuring circuit measures a water level based on a periodic change in capacitance between the pair of measuring electrodes.

(12) According to a twelfth aspect of the present invention, in the water level sensor according to the eleventh aspect described above, the water level sensor is arranged at a predetermined interval from each other along the reference axis, and is sufficient to be involved in capacitance. The measurement electrode is constituted by a plurality of effective electrode portions having a large effective surface area and a wiring portion connecting these effective electrode portions to each other.

(13) According to a thirteenth aspect of the present invention, in the water level sensor according to the eleventh or twelfth aspect, the measuring circuit differentiates a signal indicating a capacitance value of the pair of measuring electrodes. The counted value n is obtained by counting the pulse components included in the differential signal, and the water level is obtained based on the product (n · P) of the shape period P of the measuring electrode and the counted value n. .

(14) According to a fourteenth aspect of the present invention, in the water level sensor according to the first to thirteenth aspects, each electrode is covered with an insulating layer so that the water level of the conductive solution can be measured. It was made.

[0019]

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)

As shown in FIG. 1, the water level sensor according to the present invention comprises a pair of measuring electrodes 11 and 12 arranged at a predetermined distance d and fixing means (FIG. 1) for fixing the pair of measuring electrodes. 1) and a measuring circuit 15 that measures the water level based on the capacitance between the pair of measuring electrodes 11 and 12. Now, consider a case where the water level sensor is installed in a water tank such that the flat surfaces of the measurement electrodes 11 and 12 are vertical. FIG.
FIG. 4 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 position of the measuring electrodes 11 and 12 is θ0, the liquid surface position of the water tank is θ1, and the measuring electrodes 11 and 12 are.
The principle of measuring the water level h up to the liquid level when the position θ0 is set as the reference position with the water level sensor 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, the capacitance Ck of the portion above the liquid surface is represented by Ck = εα · W · k / d (3) where the dielectric constant of air is εα, and the capacitance of the portion below the liquid surface is static. The capacitance Ch is represented by Ch = εβ · W · h / d (4), where εβ is the dielectric constant of the liquid. 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, and the handling of the measured values becomes convenient.

§2. Embodiment Using Reference Electrode In the water level sensor described above, the water level h is calculated based on the equation (5).
In order to obtain the values, the values of the dielectric constant of air εα and the dielectric constant of liquid εβ are required. For this reason, in practice, the values of the standard dielectric constant εα of air and the standard dielectric constant εβ of the liquid whose water level is to be measured are set in advance, and the set value is used to calculate the equation (5). Is calculated. However, these dielectric constants are not always constant. In particular, the dielectric constant εβ of a liquid is naturally different if the liquid to be measured is different, and even if the same liquid, the dielectric constant differs depending on temperature conditions and the like. come. For example, if the liquid to be measured is different, such as water, benzene, heavy oil, alcohol,..., The dielectric constant εβ will naturally be different. Also, 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.

Here, an embodiment capable of coping with such a change in the dielectric constant will be described. The water level sensor shown in FIG. 3 is the same as the water level sensor shown in FIG.
22 are provided. This pair of reference electrodes 21,
Reference numeral 22 denotes a pair of plate-like plate electrodes arranged at a predetermined interval from each other, like the pair of measurement electrodes 11 and 12.
The capacitive element is formed by being fixed by fixing means (not shown). The measurement circuit 30 in this embodiment measures the water level based on both the capacitance between the pair of measurement electrodes 11 and 12 and the capacitance between the pair of reference electrodes 21 and 22. Having.

Now, the measuring electrode 11 of this water level sensor,
12 is installed in a water tank such that its flat surface is in a vertical direction, and the reference electrodes 21 and 22 are installed in the water bath such that its flat surface is in a horizontal direction. 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.

Here, first, as shown in FIG. 3, the dimensions of the measuring electrodes 11 and 12 are defined as width W1 and height L1.
And the interval between them is d1. Similarly, the reference electrode 2
The dimensions 1 and 22 are defined as width W0 and height L0, and the interval between them is defined as d0. The dielectric constant of air is εα, and the dielectric constant of the liquid to be measured is εβ. First, under the condition that no liquid is contained in the water tank (in other words, the state where each electrode is not in contact with the liquid at all), the capacitance C1 of the capacitance element including the pair of measurement electrodes 11 and 12 is used. (em
p) and the capacitance C0 (emp) of the capacitive element composed of the pair of reference electrodes 21 and 22, C1 (emp) = εα · W1 · L1 / d1 (6) C0 (emp) = εα · W0 L0 / d0 (7) On the other hand, under the condition that the liquid is contained in the water tank up to the state shown in FIG. 4 (up to the position θ1), the capacitance C1 (i) of the capacitance element including the pair of measurement electrodes 11 and 12 is provided.
n) and the capacitance C0 (in) of the capacitance element composed of the pair of reference electrodes 21 and 22: C1 (in) = εα · W1 · k / d1 + εβ · W1 · h / d1 (8) C0 ( in) = εβ · W0 · L0 / d0 (9)

Therefore, the capacitance differences ΔC1 and ΔC0 between when the liquid is not contained and when the liquid is contained are defined as follows.

ΔC1 = C1 (in) −C1 (emp) (10) ΔC0 = C0 (in) −C0 (emp) (11) Equations (6) to (9) are added to the right side of equations (10) and (11). Is substituted, ΔC1 = Δε · h · W1 / d1 (12) ΔC0 = Δε · L0 · W0 / d0 (13) where Δε = εβ−εα (14) is obtained. Here, W1, W0, L0, d1, d0
Are both known values, so that if the measurement circuit 30 can measure the values of ΔC1 and ΔC0, the unknowns are only Δε and h, and the simultaneous equations (12) and (13) , The water level h.

However, practically, W1 = W0 = W, d
If 1 = d0 = d, ΔC1 = Δε · h · W / d (15) ΔC0 = Δε · L0 · W / d (16), and both sides of the equation (15) are replaced by both sides of the equation (16). If divided, ΔC1 / ΔC0 = h / L0 (17), and eventually, the water level h can be obtained by a simple arithmetic expression of h = (ΔC1 / ΔC0) · L0 (18). In order to be able to use a simple arithmetic expression such as Expression (18), generally, the shape of a pair of measurement electrodes is set on a plane perpendicular to a predetermined reference axis (vertical axis at the time of installation). The cut surface obtained by cutting was set to have the same shape regardless of the cutting position on the reference axis, and the shape of the pair of reference electrodes was expanded and contracted along the reference axis. What is necessary is just to make it into a shape. For example, in the case of the example shown in FIG. 3, the cut surface obtained by cutting the pair of measurement electrodes 11 and 12 on a plane (horizontal plane) perpendicular to the reference axis along the direction of the length L1 is as follows: The shape of the pair of reference electrodes 21 and 22 is the same regardless of the cutting position on the reference axis.
12 is reduced along the reference axis. Of course, the reference electrodes 21 and 22 are used as the measurement electrodes 11 and 12.
May be extended along the reference axis, or may have exactly the same dimensions as the measurement electrodes 11 and 12, but in practice, the size was reduced in order to reduce the size of the whole water level sensor. Preferably, it is shaped.

In order to perform the measurement based on the above-described principle, the reference electrodes 21 and 22 need to be completely immersed (over the entire length L0) in the liquid at the start of the measurement. . In other words, the capacitance C0 (in) used when obtaining ΔC0 by the equation (11) is the capacitance when the reference electrodes 21 and 22 are completely immersed in a liquid having a dielectric constant εβ. Must be capacity. For this reason, in actual measurement, it is preferable to dispose the pair of reference electrodes 21 and 22 at a lower position than the pair of measurement electrodes 11 and 12. Then, even when the empty water tank is filled with liquid and the water level gradually increases, when the water level reaches the measurable range (in FIG. 4, the water reaches the position θ0). ), The reference electrodes 21 and 22 are already completely immersed in the liquid. It is preferable that the pair of measurement electrodes 11 and 12 be installed so that the longitudinal direction is as vertical as possible in order to improve the measurement sensitivity. However, the installation direction of the pair of reference electrodes 21 and 22 is arbitrary. It doesn't matter. In the example shown in FIG.
22 is placed sideways.

FIG. 5 is a block diagram showing a specific configuration example of the measuring circuit 30. Here, C shown at the left end of the figure
Reference numeral 1 denotes a capacitive element constituted by a pair of measurement electrodes 11 and 12, and C0 denotes a pair of reference electrodes 2
1 shows a capacitive element constituted by 1 and 22. The capacitance change amount detection units 31 and 32 are circuits that output the change amounts ΔC1 and ΔC0 of the capacitance of each capacitance element as signals, and the C / V conversion units 33 and 34 convert these signals into voltage values V1 and V2. This is a circuit for converting to V0. The division unit 35
Is a circuit that divides both voltage values and outputs a signal corresponding to V1 / V0. The water level calculator 36 performs a calculation based on Expression (18) (the input V1 / V0 value is ΔC1 / ΔC
This is a circuit for calculating a water level h by performing an operation of multiplying this value by a value corresponding to L0. In this embodiment, the adder 37 further adds the distance m between the positions θ3 to θ0 shown in FIG.
(A water level with the position θ3 at the bottom of the water tank as a reference position) is output.

§3. Next , a more specific example of the embodiment using the reference electrode described in §2 will be described. In the embodiments described so far, the capacitor is formed with a pair of flat electrodes facing each other so as to be convenient for explaining the principle of the present invention. However, when a pair of flat plates having an area S are opposed to each other with a distance d therebetween and the dielectric constant of a region sandwiched between the two flat plates is ε, a capacitance C represented by C = εS / d is obtained. The theory that this is true holds true for an infinite plane where the area S is infinite. Actually, since the area S is finite, not only the region sandwiched between the two flat plates but also the dielectric constant of the surrounding region has an effect. In fact, it is present not only in the rectangular parallelepiped region sandwiched between the plate electrodes, but also in the surrounding region). Therefore, in practice, the measurement electrode and the reference electrode used in the present invention do not necessarily have to be plate-shaped electrodes, and may be, for example, columnar electrodes. Further, even when a pair of plate-shaped electrodes is used, it is not always necessary to oppose both, and a configuration in which they are juxtaposed on the same plane may be adopted.

In the water level sensor 40 shown in FIG. 6A, a pair of measuring electrodes 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, a pair of conductive wires 42 and 43 constituting a measurement electrode are attached in parallel at a predetermined interval on an insulating support substrate 41, and a pair of conductive wires 42 and 43 constituting a reference electrode are provided below the pair. The conductive wires 44 and 45 are similarly attached in parallel at a predetermined interval. Each conductive wire 42, 4
3, 44, 45 and terminals T42, T43, T44, T4
5 is connected by wiring, the terminal T4
Assuming that the capacitance between the terminals T2 and T43 is C1 and the capacitance between the terminals T44 and T45 is C0, the water level can be measured by applying the measurement circuit 30 shown in FIG. Each electrode forms a thin columnar electrode, but as described above, the lines of electric force between the two electrodes pass through the area around both electrodes, so that liquid enters the area around this electrode. Causes a change in the dielectric constant, and enables measurement.

On the other hand, the water level sensor 50 shown in FIG.
The pair of measurement electrodes are formed of a pair of conductive wires, and are fixed by fixing means such that the pair of conductive wires form a stranded wire. That is, a pair of conductive wires 5 constituting the measurement electrode
2 and 53 are attached in a state of forming a stranded wire, and a pair of conductive wires 5 forming a reference electrode are provided beside the stranded wire.
4, 55 are attached in a state where the stranded wires are similarly formed. However, the stranded portions of the conductive wires 54 and 55 are only lower portions than the conductive wires 52 and 53, and the portions above the stranded wires function simply as wiring. Each conductive wire is covered with an insulating layer, and a portion constituting a substantial capacitive element is a stranded wire portion. Thus, in effect,
The capacitive element (the stranded wire portion of the conductive wires 54 and 55) composed of the reference electrode pair is disposed below the capacitive element (the stranded wire portion of the conductive wires 52 and 53) composed of the measurement electrode pair. In other words, when the liquid level reaches the measurable range, the capacitance element composed of the reference electrode pair is completely immersed in the liquid. Each of the conductive lines 52, 53,
If the terminals 54 and 55 are connected to the terminals T52, T53, T54 and T55, the capacitance between the terminals T52 and T53 is C1, and the capacitance between the terminals T54 and T55 is C1.
By setting the value to 0 and applying the measurement circuit 30 shown in FIG. 5, the water level can be measured. 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 60 shown in FIG. 7A, 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, a pair of conductive layers 62 and 63 constituting a measuring electrode are juxtaposed on the same plane on an insulating support substrate 61, and a pair of conductive layers 62 and 63 constituting a reference electrode are provided below the pair. 64 and 65 are juxtaposed on the same plane.
Each of the conductive layers 62, 63, 64, 65 and terminals T62, T6
3, the capacitance between the terminals T62 and T63 is C1, and the capacitance between the terminals T64 and T65 is C0, and the measurement shown in FIG. By applying the circuit 30, the water level can be measured. In the illustrated example, the conductive layers 64 and 65 are used.
Although the wiring layers 66 and 67 are formed between the wiring and the terminals T64 and T65, the distance between the wirings is large, so that the measured values are not significantly affected. In this embodiment, each electrode is a conductive layer formed on the same plane, but as described above, the lines of electric force between the electrodes are not limited to this plane,
Since the liquid crystal passes through the area near the front and back, the front and back of the support substrate 61 are immersed in the liquid, causing a change in the dielectric constant, thereby enabling measurement.

The water level sensor 70 shown in FIG.
(a) The support substrate 60 of the water level sensor 60 shown in (a) is bent from the center, and processed to be L-shaped when viewed from above. Since a pair of electrodes on which a capacitance element is to be formed are separately formed on two planes intersecting with each other, measurement with higher sensitivity than the water level sensor 60 can be performed.

In the embodiment shown in FIGS. 7A and 7B,
By using an insulating film such as polyimide as the support substrate 61, the conductive layers 62 to 67 used as electrodes and wirings can be formed of a metal foil such as copper formed by patterning on the insulating film. 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 80 shown in FIG. 8A, one of a measurement electrode and a reference electrode is connected to a common cylindrical conductor 81.
And the other measurement electrode and reference electrode are constituted by cylindrical conductors 82 and 83 having an inner periphery larger than the outer periphery of the columnar conductor 81. As shown in the drawing, the columnar conductor 81 is inserted inside the cylindrical conductors 82 and 83, and the fixing is performed by the fixing means in a state in which a gap for allowing liquid to penetrate therebetween is secured. This is clearly shown in the cross-sectional view of FIG. A filling fixing portion 82A made of an insulator is formed between the columnar conductor 81 and the cylindrical conductor 82, and both are fixed. The filling and fixing portion 82A
8 (b), only the upper half of the inside of the cylindrical conductor 82 is filled. A cavity 82B is formed in the lower half of the inside of the cylindrical conductor 82, and has a structure in which liquid can penetrate there. Similarly, the columnar conductor 81 and the cylindrical conductor 8
A filling fixing portion 83A made of an insulator is formed between the first fixing member 3 and the second fixing member 3, and both are fixed. Again, the filling and fixing portion 83A has a semicircular cross section, and a semicircular void portion 83B through which liquid can penetrate is formed on the other side.

After all, as shown in FIG.
The upper 3/4 portion of 1 functions as one of the measurement electrodes, and the lower 1/4 portion functions as one of the reference electrodes. If the conductors 81, 82, 83 and the terminals T81, T82, T83 are connected by wiring, the capacitance between the terminals T81, T82 is C
1. With the capacitance between the terminals T81 and T83 being C0, the water level can be measured by applying the measurement circuit 30 shown in FIG. 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. it can. Of course, also in the water level sensor shown in FIG. 6 or FIG. 7, it is possible to configure one measuring electrode and one reference electrode with a single conductor and share this single conductor. .

§4. Embodiment in which effective surface area is periodically changed In §2 described above, by using a reference electrode,
Although the method for dealing with the change in the dielectric constant has been described, another method for dealing with the change in the dielectric constant will be described here. FIG. 9 is a plan view of a water level sensor 90 using this other method. This water level sensor 90 is formed by forming a pair of measuring electrodes 92 and 93 having a shape as shown on a supporting substrate 91 made of a polyimide film. Measuring electrode 92,
Reference numeral 93 denotes a conductive layer made of a metal foil, which has a symmetrical shape as shown in the figure.

The measuring electrode 92 includes a plurality of effective electrode portions 92.
A and a wiring portion 92B connecting these effective electrode portions 92A to each other. When a reference axis is defined in the vertical direction in the drawing, the effective electrode portions 92A are electrodes arranged at a predetermined interval along the reference axis. Similarly, the measurement electrode 93 includes a plurality of effective electrode portions 9.
3A and a wiring portion 93B connecting these effective electrode portions 93A to each other. Although the measurement electrode 92 and the measurement electrode 93 are juxtaposed on the same plane, a capacitance is formed between the two electrodes as described above. Here, the effective electrode portions 92A and 93A are electrodes having an effective surface area sufficient to contribute to the capacitance. On the other hand, the wiring portions 92B, 92B only need to have at least a sufficient surface area to function as a wiring, and an area for participating in capacitance is not necessarily required. In the example shown in FIG. 9, the capacitance formed between the electrodes 92 and 93 is predominantly based on the effective electrode portions 92A and 93A, and the capacitance based on the wiring portions 92B and 93B is very small. is there.

Eventually, the water level sensor 90 shown in FIG. 9 has a shape such that the effective surface area related to the capacitance changes periodically along a predetermined reference axis (vertical direction in FIG. 9). Thus, a pair of measurement electrodes 92 and 93 are formed. In the illustrated example, the effective electrode portions 92A, 93
The vertical width of A is hA, and the wiring portions 92B, 93B
Is hB in the vertical direction, and the shape changes at a period P. As described above, when the measurement electrodes 92 and 93 whose shapes change periodically are used, the change in the water level can be detected based on the periodic change in the capacitance between the measurement electrodes 92 and 93. .

For example, as shown on the left side of FIG.
Let us define h2, h3, h4, h5,. here,
Each odd-numbered section is a section in which the effective electrode portions 92A and 93A are arranged, and each even-numbered section is a wiring section 9.
This is a section where 2B and 93B are arranged. Then, the support substrate 91 is placed in a water tank such that the reference axis (vertical direction in FIG. 9) is oriented vertically, and between the measurement electrodes 92 and 93 when the water tank is gradually filled with liquid. Consider what happens to the change in capacitance of FIG. 10 is a graph showing a change in the capacitance value C under such a condition.
On the horizontal axis of the graph, the water level is indicated by the scale of the section,
The vertical axis of the graph indicates the capacitance value C corresponding to each water level. As shown in the figure, it can be seen that the graph is a periodic function that increases stepwise from the initial value Cφ. That is,
While the water level belongs to the odd-numbered section, the capacitance value C increases with the increase of the water level, but the water level hardly increases while the water level belongs to the even-numbered section. . The reason is, as described above, the effective electrode section 9
2A and 93A have a sufficient effective area to affect the capacitance, whereas the wiring portions 92B and 93B
Does not have such a sufficient effective area, and
This is because the electrodes are formed at the left and right ends, so that the distance between the electrodes is large and the capacitance cannot be sufficiently affected.

Now, in the graph shown in FIG.
Although the absolute value of the capacitance value C changes depending on the change in the dielectric constant εβ of the liquid, it can be seen that the periodic characteristic of the graph is constant regardless of the dielectric constant of the liquid. That is, on the graph, a periodic change of increase / stagnation / increase / stagnation / increase / stagnation /... Is repeated from the initial value Cφ, for example, a feature that “the third increase occurs in the section h5”. Is invariant regardless of the dielectric constant of the liquid. Therefore, by counting the number of times of increase or stagnation of the capacity value C after the water tank is filled with the liquid, it is possible to recognize in which section the current water level is in accordance with the count value. .

In order to detect the water level based on such a basic principle, a measuring circuit as shown in FIG. 11 may be prepared. C shown at the left end of the measurement circuit indicates a capacitive element including the measurement electrodes 92 and 93 in the water level sensor 90 shown in FIG. The C / V converter 94 is a circuit that converts the capacitance value C of the capacitance element into a voltage V.
Actually, the terminals T92 and T93 shown in FIG. 9 are connected to the input terminals of the C / V converter 94. As the water tank is filled with the liquid, the C / V converter 94 outputs a periodically increasing voltage value as shown in the graph of FIG. Therefore, if this voltage value is differentiated in the differential operation unit 95, a pulse signal corresponding to the repetition cycle of increase / stagnation / increase / stagnation / ... can be obtained. The pulse signal is counted by a counter 96 to obtain a count value n indicating the number of pulses, and a multiplier 97 multiplies the count value n by the shape period P of the measuring electrodes 92 and 93 (n · P). ), A water level with the lower end position of the section h1 as the reference position can be obtained. The measurement circuit shown in FIG. 11 further includes an adder 98, and as shown in FIG. 9, adds the height h0 of the lower margin of the support substrate 91, thereby setting the lower end position of the support substrate 91 as the reference position. Water level (n · P) + h0 is obtained.

According to the above-described measurement principle, only information on "in which section the current water level is" can be obtained. However, the shape period P of the measurement electrodes 92 and 93 can be reduced according to the required measurement accuracy. If set, measurement with the required accuracy is possible. Alternatively, it is also possible to adopt a method of obtaining an accurate water level in each section by linear interpolation based on the slope of the graph of the “increase” obtained in the past and the actually obtained capacity value C. is there.

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. For example, in the embodiment shown in FIG. 9 in which the effective surface area is periodically changed, each of the measurement electrodes 92 and 93 is a plate-like electrode formed on the support substrate 91, but is used for three-dimensional measurement. It is also possible to use electrodes. Specifically, it is basically cylindrical, but with respect to the central axis direction,
Two electrodes having a shape whose diameter changes periodically may be prepared, arranged in parallel, and used as a measurement electrode. Even in this case, the measuring electrode is "the effective surface area related to the capacitance periodically changes along the reference axis."
Condition can be satisfied.

Although not particularly described in the above embodiments, when measuring the water level of a conductive solution, the electrodes are insulated so that the electrodes are not short-circuited when immersed in the solution. It must be in a form coated with a layer.

[0050]

As described above, according to the water level sensor according to the present invention, the water level is measured by using the change in the capacitance value of the capacitance element. Therefore, the accurate water level can be measured with a simple structure. become able to.

[Brief description of the drawings]

FIG. 1 is a perspective view (partially a block diagram) showing components of a basic 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 components of a water level sensor using a reference electrode 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 block diagram showing a detailed configuration of a measurement circuit of the water level sensor shown in FIG.

FIG. 6 is a perspective view showing a specific configuration example of the water level sensor shown in FIG.

FIG. 7 is a perspective view showing another specific configuration example of the water level sensor shown in FIG.

8 is a perspective view and a cross-sectional view showing still another specific configuration example of the water level sensor shown in FIG.

FIG. 9 is a front view of a water level sensor having periodic electrodes according to the present invention.

FIG. 10 is a graph showing a measurement principle of the water level sensor shown in FIG.

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

[Explanation of symbols]

 11, 12 ... Measurement electrode 15 ... Measurement circuit 21, 22 ... Reference electrode 30 ... Measurement circuit 31, 32 ... Capacity change amount detection unit 33, 34 ... C / V conversion unit 35 ... Division unit 36 ... Water level calculation unit 37 ... Addition unit 40 ... Water level sensor 41 ... Support substrate 42, 43 ... Conductive wire (measuring electrode) 44, 45 ... Conductive wire (reference electrode) 50 ... Water level sensor 51 ... Support substrate 52, 53 ... Twisted wire conductive Wires (measurement electrodes) 54, 55 stranded conductive wires (reference electrodes) 60 water level sensor 61 support substrates 62, 63 conductive layers (measurement electrodes) 64, 65 conductive layers (reference electrodes) 66, 67: Wiring layer 70: Water level sensor 80: Water level sensor 81: Cylindrical conductor 82, 83 ... Cylindrical conductor 82A, 83A: Filling fixed part 82B, 83B ... Gap part 90: Water level sensor 91: Support substrate 92,93 Measurement electrodes 92A, 93A: Effective electrode portions 92B, 93B: Wiring portion 94: C / V conversion portion 95: Differential operation portion 96: Counter 97: Multiplication portion 98: Addition portion C, C0, C1: Capacitance / capacitance Element d, d0, d1 ... electrode interval h, k, m ... length / water level h1-h19 ... section hA, hB, h0 ... length of each part L, L0, L1 ... electrode length T42-T93 ... terminal W , W0, W1... Electrode width εα, εβ .dielectric constant θ0 to θ3... Water level position

Claims (14)

[Claims] 1. A water level sensor for measuring a water level from a predetermined reference position to a liquid level, comprising: a pair of measurement electrodes arranged at a predetermined interval; and fixing means for fixing the pair of measurement electrodes. And a measurement circuit for measuring a water level based on a capacitance between the pair of measurement electrodes. 2. The water level sensor according to claim 1, wherein a length of each measurement electrode in a predetermined reference axis direction is set longer than a required water level measurement range, and the reference axis direction is a vertical direction. A water level sensor characterized in that the surface area of the submerged portion of each measurement electrode monotonically increases as the water level rises when the entire sensor is installed facing the water. 3. The water level sensor according to claim 2, wherein the pair of measurement electrodes are formed of a pair of conductive wires, and the pair of conductive wires are configured to be parallel to each other or to form a stranded wire. A water level sensor fixed by fixing means. 4. The water level sensor according to claim 2, wherein the fixing means is constituted by a flat support substrate, and each measuring electrode is constituted by a conductive layer formed on the support substrate. Water level sensor. 5. The water level sensor according to claim 2, wherein one of the measuring electrodes is formed of a columnar conductor, and the other of the measuring electrodes is a cylinder having an inner circumference larger than the outer circumference of the columnar conductor. A water level, wherein the column-shaped conductor is inserted inside the cylindrical conductor, and is fixed by a fixing means in a state where a space through which a liquid can permeate is secured between the two. Sensor. 6. The water level sensor according to claim 1, further comprising a pair of reference electrodes arranged at a predetermined interval, and a pair of measurement electrodes and a pair of reference electrodes provided by fixing means. The electrodes are fixed, and the measurement circuit measures a water level based on both the capacitance between the pair of measurement electrodes and the capacitance between the pair of reference electrodes. Water level sensor. 7. The water level sensor according to claim 6, wherein the pair of reference electrodes is fixed at a lower position than the pair of measurement electrodes. 8. The water level sensor according to claim 6, wherein a cut surface obtained by cutting the shape of the pair of measurement electrodes by a plane perpendicular to a predetermined reference axis is on the reference axis. The shape of the pair of reference electrodes is the same as that of the pair of measurement electrodes, or the pair of measurement electrodes is expanded or contracted along the reference axis. A water level sensor having a shape. 9. The water level sensor according to claim 8, wherein a capacitance value of the pair of reference electrodes when no liquid is touched and a capacitance value when completely immersed in the liquid. ΔC0 from the measured value, the capacitance value of the pair of measurement electrodes when not in contact with the liquid, and the capacitance when the portion corresponding to the water level to be measured is immersed in the liquid. Using the difference ΔC1 from the value and the length L0 of the reference electrode in the reference axis direction, the measurement circuit calculates the h = (ΔC1 / ΔC0) · L0 to determine the lowermost position of the measurement electrode as the reference position. A water level sensor for determining a water level h. 10. The water level sensor according to claim 6, wherein one of the measurement electrodes and one of the reference electrodes are formed of a single conductor, and the single conductor is measured. A water level sensor characterized in that the water level sensor is used commonly for a reference electrode and a reference electrode. 11. The water level sensor according to claim 1, wherein a pair of measurement electrodes having a shape such that an effective surface area related to the capacitance changes periodically along a predetermined reference axis. A water level sensor, wherein the measurement circuit measures a water level based on a periodic change in capacitance between the pair of measurement electrodes. 12. The water level sensor according to claim 11, further comprising: a plurality of effective electrode units arranged at a predetermined distance from each other along a reference axis and having an effective surface area sufficient to contribute to capacitance. And a wiring section for connecting these effective electrode sections to each other to form a measurement electrode. 13. The water level sensor according to claim 11, wherein the measuring circuit differentiates a signal indicating a capacitance value of the pair of measuring electrodes, and counts a pulse component included in the differentiated signal. A water level sensor for obtaining a count value n and obtaining a water level based on a product (n · P) of the shape period P of the measurement electrode and the count value n. 14. The water level sensor according to claim 1, wherein each electrode is covered with an insulating layer so that the water level of the conductive solution can be measured.