JP2021177125A - Capacitance type liquid-level sensor - Google Patents

Abstract

To provide a capacitance type liquid-level sensor that can be affixed in close contact along on a three-dimensional curved surface of a container even with the curved surface, and can accurately measure the level of a liquid in the container.SOLUTION: A capacitance type liquid-level sensor 10, in which a detection electrode 40 is affixed to an outer wall of a container, measures the level of a liquid accommodated in the container based on the change of capacitance between the detection electrode 40 and a counter electrode. The detection electrode 40 comprises at least one of shaft sections 11 and a plurality of arm sections 12 connected to the shaft section 11. Notch sections 13 are arranged between the adjacent arm sections of the plurality of arm sections 12. With the notch sections 13 suitably arranged along on the three-dimensional curved surface of the container, the detection electrode 40 can be affixed in close contact along on the three-dimensional curved surface of the container.SELECTED DRAWING: Figure 1A

Description

The present invention relates to a capacitance type liquid level sensor for detecting the liquid level inside a container, for example, by attaching it to an outer wall of a container or the like containing a liquid.

There are various types of liquid level sensors for measuring the liquid level in the container, that is, the amount of liquid, such as a float method, a capacitance method, and an ultrasonic method.
A donut-shaped float is attached to the float-type liquid level sensor so as to penetrate the center, and the float moves up and down in conjunction with the top and bottom of the liquid level. However, if solid impurities or deposits are present in the liquid, there arises a problem that the solid impurities or deposits are caught between the central pipe and the float and the float becomes immobile.

Since the capacitance type liquid level sensor does not have a moving part or a sliding part unlike the float type, there is an advantage that sticking cannot occur. There are two types of liquid level sensors of this type: an electrode immersion type in which the electrode portion is immersed in the liquid in the container, and an electrode outer wall attachment type in which the electrode portion is attached to the outer wall inside the container. In the electrode outer wall affixing method, the electrode part is attached to the outer wall of the container, so the electrode part does not come into contact with the liquid inside the container. It is often used for measuring. It is also used for measuring the amount of a liquid having strong acidity and alkalinity that causes the electrode portion to corrode. In this way, the electrode outer wall sticking method has the advantage that the amount of liquid in the container can be measured without immersing the electrode part in the liquid, but on the other hand, it is made of a conductive material such as metal. It cannot be used in the container that is used.

Here, the operating principle of the capacitance type liquid level sensor will be described by taking the electrode outer wall sticking type as an example. The capacitance type liquid level sensor measures the capacitance of the electrode and estimates the liquid level from the value.

Considering a parallel plate capacitor in which two electrodes face each other in parallel, the area of the two electrodes facing each other is S, the distance between the two electrodes is d, and the relative permittivity of the insulator sandwiched between the two electrodes is ε _r. Assuming that the permittivity of the vacuum is ε ₀ , the capacitance C of the parallel plate capacitor can be expressed _{by C = S × ε r} × ε _{0 / d.} Therefore, if the distance d between the two electrodes of the parallel plate capacitor is constant, the capacitance C of the parallel plate capacitor is proportional to the relative permittivity εr of the insulator sandwiched between the two electrodes. For example, a rectangular + side electrode is attached to one surface of a liquid container having parallel planes facing each other, and the same shape as the + side electrode is attached to the surface facing the + side electrode at a position parallel to and facing the + side electrode. And when the-side electrodes of the same area are attached, those opposing electrodes form a parallel plate capacitor.
Next, when water is poured into the entire container, the counter electrode can be regarded as a parallel plate capacitor in which water is filled between both electrodes. Since the relative permittivity of air is approximately 1 and the relative permittivity of water is approximately 80, it is static when no water is added, that is, when it is filled with air and when it is filled with water. The capacitance will be 80 times different.

A predetermined capacitance threshold value, for example, a capacitance value 40 times the capacitance when filled with air is set as a threshold value in advance, and when the capacitance is smaller than the capacitance threshold value, it is determined that water is not contained. If the capacitance is larger than the capacitance threshold, it can be determined that water is contained. In this way, the presence or absence of liquid can be determined by 0 and 1 depending on whether the capacitance of the counter electrode exceeds or does not exceed a certain threshold value, and is called an on / off type capacitance type liquid level sensor. ing.

Further, by providing a plurality of + electrodes, it is possible to measure the liquid level in a plurality of stages. For example, it is assumed that three + electrodes are attached to the side surface of the container from the bottom surface upward every 1 cm. Each electrode behaves as the on / off type electrode described above. When water is poured into the container, the capacity exceeds the threshold value in order from the lower electrode, that is, the number of electrodes turned on increases. When all electrodes are off, the liquid level is determined to be 1 cm or less. When only the bottom electrode is on and the other two electrodes are off, the liquid level is determined to be 1 cm or more and less than 2 cm. Similarly, when all the electrodes are on, the level of the liquid level is determined to be 3 cm or more. By increasing the number of + electrodes in this way, multiple levels can be specified. Such a method is called a multi-point type.

Further, there is a method called a linear type as a method capable of finely detecting the liquid level. The longitudinal direction of the rectangular + side electrode having a substantially total length of the container is attached to the side surface so as to be the vertical direction of the container. The lower end of the + side electrode should be in contact with the bottom surface of the container, and the upper end should be equal to the full position of the container. The capacity value of the + side electrode when no liquid is put in this container is measured, and it is recorded as C0. Next, the volume when the liquid is injected to the position where the liquid comes into contact with the upper end of the electrode, that is, the position where the liquid is full is recorded as CF. The difference in capacity between full and empty is CF-C0. Assuming that the distance from the bottom to the full is 10 cm, the volume increases by 1/10 × (CF-C0) for every 1 cm increase in the liquid level. Assuming that the measured volume is C, it can be obtained by the liquid level level (C-C0) / (CF-C0) x 10 from the bottom surface. Using this method, the liquid level can be obtained linearly.

The electrode part of the capacitive liquid level sensor used by attaching it to the outer wall of the container currently on the market uses a rectangular flexible substrate, and the liquid level level inside the cylindrical or conical container. It enables detection. For example, Non-Patent Document 1 discloses a liquid level sensor in which the electrode portion is made of a flexible material. In this capacitive liquid level sensor, the electrode portion can be wound around a thin resin gauge tube or the like to measure the amount of liquid in the tank.

Liquid level sensor CLA series manufactured by Kameoka Electronics Co., Ltd. (https://www.kameokadennsi.co.jp/levelsensor)

In the capacitance type and electrode outer wall sticking type liquid level sensor, it is necessary to stick the electrode part on the outer wall of the container and obtain the change in the capacitance of the liquid in contact with the inner wall of the container. It is necessary to make it adhere to the outer wall. However, if this adhesion is poor, an air layer is formed between the outer wall of the container and the electrode portion, the capacitance detected by the capacitance sensor decreases from the original capacitance value, and the liquid level becomes lower than the original liquid level. It will be judged low. When the container has a flat outer wall such as a cube or a rectangular parallelepiped, the electrode part may be brought into close contact with the entire length of the container along the flat surface, so that the electrode part is made of a hard material such as a metal plate or a printed substrate. It can be configured and may have a square or rectangular shape. The electrode portion can be brought into close contact with the outer wall of the container by attaching it to the outer wall of the container using double-sided adhesive tape or an adhesive.

However, if the container is cylindrical and the electrode portion is made of a hard metal plate or a printed circuit board, the electrode portion cannot be brought into close contact with the outer wall of the container. In this case, by forming the electrode portion with a thin metal plate or a flexible substrate, the square or rectangular electrode portion can be brought into close contact with the outer wall of the container.

However, there are various shapes of liquid containers in circulation. For example, considering a spherical container, its outer wall surface becomes a three-dimensional curved surface that is convex in the vertical, horizontal, and radial directions. Therefore, if the electrode shape is square or rectangular, it adheres not only to a thin metal plate but also to a flexible substrate. This cannot be done, and the outer periphery of the electrode portion is slackened. On the contrary, when the outer wall of the container has a three-dimensional curved surface having a concave shape like a horse saddle, the outer peripheral portion of the electrode portion cannot be extended with a flexible substrate having a constant length and width, so that the electrode portion is used. There is a problem that they cannot be brought into close contact with each other.

In view of the above problems, the present invention allows a container having various three-dimensional curved surfaces to be closely attached along the various curved surfaces and is not easily peeled off, so that the liquid level of the container can be accurately adjusted. It is an object of the present invention to provide an extremely excellent capacitance type liquid level sensor capable of measuring.

According to the above object, according to the present invention, a capacitance type liquid level sensor is provided by attaching a detection electrode to the outer wall of a container and measuring the liquid level contained in the container by changing the capacitance between the detection electrode and the counter electrode. The detection electrode includes at least one shaft portion and a plurality of arm portions connected to the shaft portion, and a notch portion is arranged between the adjacent arm portions of the plurality of arm portions. The detection electrode is achieved by a capacitive liquid level sensor that can be attached to the surface of the three-dimensional curved surface of the outer wall of the container by providing a notch on the surface of the three-dimensional curved surface of the container.

According to the present invention, the above object is the first flexible layer, the detection electrode and the ground electrode formed on the surface side of the first flexible layer, and the second one formed on the surface of the detection electrode and the ground electrode. A flexible layer is provided, the detection electrode is provided with at least one shaft portion and a plurality of arms connected to the shaft portion, and a notch is provided between the adjacent arms of the plurality of arms. The detection electrode is provided by a capacitive liquid level sensor that can be attached to the surface of the three-dimensional curved surface of the container by disposing a notch on the surface of the three-dimensional curved surface of the outer wall of the container. NS.
According to the present invention, the above object is the first flexible layer, the detection electrode and the ground electrode formed on the surface side of the first flexible layer, and the second one formed on the surface of the detection electrode and the ground electrode. A flexible layer, a third flexible layer formed on the upper part of the second flexible layer, a shield electrode formed on the surface side of the third flexible layer, and a fourth flexible layer formed on the upper part of the shield electrode. And, the detection electrode comprises at least one shaft and a plurality of arms connected at an angle to the shaft, and between the adjacent arms of the plurality of arms. Is provided with a notch, and the detection electrode is achieved by a capacitive liquid level sensor that can be attached to the surface of the three-dimensional curved surface of the container by arranging the notch on the surface of the three-dimensional curved surface of the container. ..

In the above configuration, the detection electrode is preferably arranged on a flexible substrate. Preferably, the detection electrode, the ground electrode and the shield electrode are made of a metal plate or a metal foil, which are arranged on a conductive film.
The detection electrode preferably consists of a metal layer disposed on the non-woven fabric. The capacitance type liquid level sensor is preferably a linear type sensor that is converted into a liquid level by the capacitance value generated in the detection electrode. The detection electrode preferably includes a plurality of notches, and a change in the liquid level of the container is determined by a change in the capacity of the detection electrode.

According to the present invention, even a container having various three-dimensional curved surfaces can be closely attached along the curved surface, and the liquid level of the container can be accurately measured. It is possible to provide an extremely excellent capacitance type liquid level sensor.

It is a top view which shows the 1st Embodiment of the capacitance type liquid level sensor of this invention. FIG. 3 is a cross-sectional view taken along the line II of FIG. 1A. It is a top view which shows the 1st modification in 1st Embodiment. It is an enlarged view of FIG. 2A. It is a top view which shows the 2nd modification in 1st Embodiment. It is an enlarged view of FIG. 3A. It is a top view which shows the 3rd modification in 1st Embodiment. It is a top view which shows the 4th modification in 1st Embodiment. It is a top view which shows the 5th modification in 1st Embodiment. It is an enlarged view of FIG. 6A. It is a top view which shows the detection electrode of the 6th modification in 1st Embodiment. It is a top view which shows the 2nd Embodiment of the capacitance type liquid level sensor by this invention. It is an enlarged view of FIG. 8A. FIG. 8 is a cross-sectional view taken along the line II-II of FIG. 8A. It is a top view of the detection electrode and the ground electrode arranged on the container side which show the 3rd Embodiment of the capacitance type liquid level sensor by this invention. It is a top view of the shield electrode which shows the 3rd Embodiment. 9 is a cross-sectional view taken along the line III-III of FIG. 9A. It is a figure which shows the state which attached the detection electrode of the capacitance type liquid level sensor of this invention to the glass which has a three-dimensional curved surface for example. It is a circuit diagram explaining the capacitance measurement of a capacitance type liquid level sensor. It is a figure which shows the electrode waveform of the capacitance measurement using the circuit shown in FIG. 11A. It is a graph which shows the relationship between the count value of the counter and the liquid level when the capacitance type liquid level sensor is attached to the glass of FIG. 10 and water is poured.

Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.
1A and 1B show the first embodiment of the capacitive liquid level sensor according to the present invention, FIG. 1A is a plan view, and FIG. 1B is a cross section taken along the line I-I of FIG. 1A. The detection electrode 40 of the capacitance type liquid level sensor 10 according to the present embodiment includes a shaft portion 11, an arm portion 12, and a concave notch portion 13. The capacitance type liquid level sensor 10 includes, for example, a first flexible layer 21, a detection electrode 40 formed on the surface side of the first flexible layer 21, and a second detection electrode 40 formed on the surface of the detection electrode 40. It is composed of a flexible layer 22 and.

The detection electrode 40 is made of a conductive material, and is made of a thin metal plate, a metal foil, a flexible substrate made of a polyimide resin or the like, a conductive film, a cloth knitted with a conductive thread, a non-woven metal plated, or the like. A conductive material having a certain degree of flexibility can be used. As the conductive material, for example, copper can be used. The detection electrode 40 can be manufactured by a subtractive method, for example, by patterning a copper foil formed on the first flexible layer 21 by electroplating or the like by etching with a resist. The thickness of the detection electrode 40 can be, for example, 10 μm to 100 μm.

The first flexible layer 21 and the second flexible layer 22 are so-called flexible films, which are layers made of a resin such as polyimide. The first and second flexible layers 21 and 22 can be appropriately selected according to the application of the capacitance type liquid level sensor 10, and preferably have a thickness of, for example, 10 μm to 100 μm.

The detection electrode 40 is formed of a flake-shaped, strip-shaped, elongated thin layered electrode in which cut portions 13 are formed at arbitrary intervals. In the figure, the overall shape of the detection electrode 40 shown in FIG. 1A is a so-called one shaft portion 11 in the vertical direction and a plurality of arm portions 12 arranged in parallel in the left-right and horizontal directions at intervals above and below the shaft portion 11. It has a fish-bone shape. In other words, the detection electrode 40 forms a cut portion 13 from the left and right toward the center portion at regular intervals along a vertically long rectangle having a constant length and width, and forms a shaft portion 11 perpendicular to the center. A plurality of arm portions 12 are provided from the shaft portion 11 at an angle so that the entire arm portion 12 can be flexibly bent in the vertical direction or the horizontal direction. Here, to give an angle means that the shaft portion 11 is orthogonal to the shaft portion 11, is bent in a direction at a right angle, or is connected at a predetermined angle, for example, a shaft. The portion may be angled in the range of about 10 to 170 degrees.

(First modification of the detection electrode)
2A and 2B show the first modification 10A in the first embodiment. The detection electrode 40A of the first modification 10A is composed of a shaft portion 11, a plurality of arm portions 12a protruding to the left from the shaft portion 11, and a concave cut portion 13 formed between each arm portion 12a. It is a so-called comb-shaped electrode, and as shown in FIG. 2B, in the basic configuration, the first arm portion 12a1 and the second arm portion 12a2 are connected via the shaft portion 11, and the first arm portion 12a1 and the shaft portion are connected. A recess, that is, a notch portion 13, is formed from the 11 and the second arm portion 12a2.

(Second modification of the detection electrode)
3A and 3B show a second modification 10B of the capacitive liquid level sensor. The detection electrode 40B has a shaft portion 11b, an arm portion 12b, and a concave cut portion 13b formed in a so-called zigzag shape. Connected via the first shaft portion 13b1, from the first arm portion 12b1, the first shaft portion 11b1 and the second arm portion 12b2, the first recess, that is, the first notch portion 13b1 is on the left side in the drawing. It is formed.
Further, the second arm portion 12b2, the second shaft portion 11b2, and the third arm portion 12b3 to the second recess, that is, the second notch portion 13b2 are formed on the right side in the drawing. The detection electrode 40B has a shape like approximately 2 Arabic numerals by arranging two concave electrodes of the detection electrode 40A of the first modification alternately. The number of concave electrodes is not limited to two, and a plurality of concave electrodes may be arranged side by side to form a serpentine shape as shown in FIG. 3A.

(Third modification of the detection electrode)
FIG. 4 shows the detection electrode 40C of the third modification 10C of the capacitance type liquid level sensor. The detection electrode 40C has a configuration in which the comb tooth electrodes of the first modification 10A are arranged in a ladder shape so as to face each other, and has a shape in which the arm portion is hung between the shaft portions on both the left and right sides. Therefore, a notch portion 13e is formed in the detection electrode 40C by these voids.

(Fourth modification of the detection electrode)
FIG. 5 shows the detection electrode 40D of the modified example 10D of the capacitance type liquid level sensor. The detection electrode 40D has a configuration in which the comb tooth electrodes of the two detection electrodes 40A of the first modification 10A shown in FIG. 2A are arranged back to back.

(Fifth modification of the detection electrode)
6A and 6B show a fifth modification 10E of the capacitive liquid level sensor. The detection electrode 40E has a configuration in which the tips of the first and second arm portions 12a1, 12a1 of the detection electrode 40A of the first modification 10A shown in FIG. 2B are bulged into circular and pentagonal shapes 12e1, 12e2, respectively. It consists of. The tip shapes of the first and second arm portions 12e1 and 12e2 are not limited to this, and any shape may be used, and a recess, that is, a notch portion is formed between the first and second arm portions. In this way, the distance between the tips of the first and second arms 12e1 and 12e2 can be widened or narrowed so that the entire electrode can be aligned with the three-dimensional curved surface.

(Sixth modification of the detection electrode)
FIG. 7 shows the detection electrode 40F of the sixth modification 10F of the capacitance type liquid level sensor. The detection electrode 40F has two detection electrodes 40A of the first modification 10A arranged back to back, and in a symmetrical shape with the detection electrodes 40A back to back, a shape in which an elongated arm portion is connected in the axial direction from the central arm portion. have. The detection electrode 40F has a so-called fractal structure in which thinner branches extend from thick branches of a tree. In this modification, the fractal structure is described as two layers, but it may be formed in any number of layers.
Here, in the capacitance type liquid level sensor 10, when the container is placed on a metallic base, the detection electrode 40F is attached to the container, and the electrode is connected to the metallic base to connect the counter electrode. And it is sufficient. As a result, a volume is generated between the detection electrode 40F and the counter electrode, and this volume changes depending on the liquid level of the liquid injected into the container. The potential of the counter electrode may be a predetermined potential, or may be 0 V (ground potential). When the capacitance measuring circuit generated by the capacitance type liquid level sensor 10 is grounded to, for example, a metal case or the ground of the measuring circuit, the metal case or the ground may be used as a counter electrode.

(Second Embodiment of Capacitive Liquid Level Sensor)
8A and 8B show a second embodiment of the capacitive liquid level sensor according to the present invention. In this capacitance type liquid level sensor 30, the first flexible layer 21, the outer detection electrode 40G formed on the surface side of the first flexible layer 21, and the detection electrode 40G are arranged with a gap 45 open. It is composed of a ground electrode 50 to be provided, a detection electrode 40G, and a second flexible layer 22 coated on the ground electrode 50. The capacitance type liquid level sensor 30 includes a shaft portion 41, an arm portion 42, and a concave notch portion 43, similarly to the capacitance type liquid level sensor 10 according to the first embodiment. The capacitance type liquid level sensor 30 can be manufactured by using a commercially available flexible printed circuit board (also referred to as Flexible Printed Circuits, FCB). In this case, the ground electrode 50 can also be formed at the same time by patterning a copper foil or the like in the same manner as the detection electrode 40G. Further, the second flexible layer 22 may be a layer having the same thickness as the first flexible layer 21.

As shown in FIGS. 8A to 8C, the detection electrode 40G is a fish-bone-shaped electrode arranged on the outside, the ground electrode 50 is an electrode arranged inside the detection electrode 40G, and the detection electrode 40G and the ground are arranged. The electrodes 50 are insulated by gaps 45 at predetermined intervals, that is, insulating regions. The detection electrode 40G has a width W1 and a length L1. The ground electrode 50 may be arranged on the inside of the detection electrode 40G and on the outside of the detection electrode 40G.

The capacitance type liquid level sensor 30 is different from the capacitance type liquid level sensor 10 and the modified example in that it further has a ground electrode 50. In the capacitance type liquid level sensor 10 and the modified example, a metal plate or ground around the container is used as a counter electrode, but the capacitance type liquid level sensor 30 includes a ground electrode 50 together with a detection electrode 40G. Therefore, it can be easily mounted on the container, and there is an advantage that the capacitance generated in the detection electrode 40G and the ground electrode 50 is stable.

(Third Embodiment of Capacitive Liquid Level Sensor)
9A-9C show the capacitance type liquid level sensor 80 according to the third embodiment of the present invention, and FIG. 9A is a plan view and a view of the detection electrode 40G and the ground electrode 50 arranged on the container side. 9B is a plan view of the shield electrode 60, and FIG. 9C is a cross-sectional view taken along the line III-III of FIG. 9A. The capacitance type liquid level sensor 80 includes a first flexible layer 21, a detection electrode 40G and a ground electrode 50 formed on the surface side of the first flexible layer 21, and a surface of the detection electrode 40G and the ground electrode 50. A second flexible layer 22 formed on the surface of the second flexible layer 22, a third flexible layer 23 formed on the upper portion of the second flexible layer 22, and a shield electrode 60 formed on the surface side of the third flexible layer 23. A fourth flexible layer 24 formed on the upper part of the shield electrode 60 is provided.

The capacitance type liquid level sensor 80 of the third embodiment has a configuration in which a shield electrode 60 is further provided on the capacitance type liquid level sensor 30 of the second embodiment. The shield electrode 60 is arranged between the third flexible layer 23 and the fourth flexible layer 24. In the case of the figure, the detection electrode 40G and the ground electrode 50 attached to the container side and the shield electrode 60 arranged at a position opposite to the detection electrode 40G and the ground electrode 50 are bonded by the adhesive 70. The capacitance type liquid level sensor 80 according to the third embodiment can be manufactured by using a commercially available two-layer flexible printed substrate.
As shown in FIG. 9B, the shield electrode 60 has a fish-bone shape and has a plurality of notches, and has a similar area so as to cover the detection electrode 40G, the shield electrode 50, and the void 45, and is made of copper foil. Etc. can be formed by patterning. Further, the third and fourth flexible layers 23 and 24 may be made of the same material as the first flexible layer 21.

Similar to the detection electrode 40G shown in FIG. 8, the detection electrode 40G includes a shaft portion 41 and a plurality of arm portions 42 connected to the shaft portion 41, and is between adjacent arm portions 42 of the plurality of arm portions 42. A notch 43 is formed in the. The detection electrode 40G is attached to the surface of the three-dimensional curved surface of the container so as to arrange the notch 43.

Here, the first flexible layer 21 is provided with a through hole (not shown) for connecting the detection electrode 40G and the ground electrode 50 with a conducting wire, and the detection electrode 40G and the ground electrode 50 are connected to the first flexible layer 21 through the through hole. The conducting wire for connection may be connected by soldering or the like. Further, the fourth flexible layer 24 is also provided with a through hole (not shown) for connecting the shield electrode 60 with a conducting wire, and the conducting wire for connecting to the shield electrode 60 via the through hole is soldered or the like. May be connected by.

The capacitance type liquid level sensor 80 is different from the capacitance type liquid level sensor 30 in that it further has a shield electrode 60. Although the capacitance type liquid level sensor 80 has more layers than the above embodiment, since it is provided with the shield electrode 60, the capacitance type liquid level sensor 80 is less affected by ambient noise than the capacitance type liquid level sensor 30. Can be measured.

FIG. 10 is a diagram showing a state in which the capacitance type liquid level sensor 80 of the present invention is attached to a glass 90 having a three-dimensional curved surface.
As shown in FIG. 10, when the detection electrode 40G is pressed against the spherical surface of the glass 90, the tip side of the first arm and the tip side of the second arm come close to each other by the plurality of notches 43 formed between the arms 42. The entire electrode can be aligned with the spherical surface. Alternatively, when the detection electrode 40G is pressed against the saddle-shaped surface of the horse, the tip end side of the first arm portion and the tip end side of the second arm portion are far apart, and the entire electrode can be aligned with the spherical surface.

According to the detection electrodes 40 of the capacitance type liquid level sensor of the present invention and the detection electrodes 40A to 40G of the first to sixth modified examples, the notches 13, 43, that is, the recesses are provided, so that the surface looks like a spherical surface. It is possible to bring the electrodes into close contact with each other along a convex surface or a concave surface such as a saddle-shaped surface. In this example, a plurality of cut portions 13 and 43 are provided, but a plurality of cut portions 13 and 43 can be arranged in an arbitrary shape such as a comb shape or a zigzag shape according to the shape of the container. That is, by forming at least one notch portions 13, 43, the distance between the tip portions of the arm portions is narrowed, so that the three-dimensional curved surface having a substantially convex shape to the outside, that is, a spherical curved surface can be followed. Moreover, by widening the distance between the tips of the two arms sandwiched between the notches 13, even if a substantially convex three-dimensional curved surface, for example, a saddle-shaped curved surface of a horse is formed inside the container. , You can follow this curved surface. The arm may have a fractal shape, that is, a dendritic shape. As a result, the detection electrodes 40, 40A to 40G can be provided by providing the notches 13, 43 even for a three-dimensional curved surface in which the electrodes cannot be brought into close contact with each other in the conventional electrode shape such as a circle or a polygon. It can be brought into close contact with a three-dimensional curved surface.

(Capacitance measurement using a capacitance type liquid level sensor)
The capacitance type liquid level sensors 10, 30, 80 according to the first to third embodiments have detection electrodes 40, 40A to F on the outside of a non-conductive container, for example, a container made of resin, glass, ceramic, or the like. Alternatively, the lower layer side of the detection electrode 40G and the ground electrode 50 is attached to the outer wall of the container, the change in volume that occurs according to the liquid level in the container is measured, and the liquid in the container is measured from the calibration curve between the change in volume and the liquid level. The position can be measured. Double-sided adhesive tape or adhesive can be used for adhesion. As a method of measuring the capacitance using the capacitance type liquid level sensors 10, 10A to 10F, 30, 80, various methods such as a bridge circuit, a method of measuring the CR time constant, and a method of comparing with the reference capacitance by a comparator are used. be able to.

11A and 11B are diagrams for explaining the capacitance measurement of the capacitance type liquid level sensor 80, FIG. 11A shows a circuit diagram 100, and FIG. 11B shows an electrode waveform 120.
As shown in FIG. 11A, the first switch 101 and the second switch 102 connected to the detection electrode 40G, the first pulse circuit 103 that applies a pulse to the detection electrode 40G and the shield electrode 60, and the first. The comparator 105 connected to the switch 101 and the reference capacitance 104, the third switch 106 connected to the first switch 101, the steady current source 107 connected to the third switch 106, and the comparator 105 are connected. It includes a reference power supply (V _REF ) 108, a second pulse circuit connected to the output of the comparator 105, a counter 109, and a timer 110 that generates a counter reset signal in the counter 109. A buffer 115 may be inserted between the shield electrode 60 and the first pulse circuit 103.

The ground electrode 50 is connected to the ground potential (0 V). The detection electrode 40G is connected to the reference capacitance 104 via the first switch 101, and is connected to the ground potential (0V) via the second switch 102. The first pulse generation circuit controls the on (ON) and off (OFF) of the first switch 101 and the second switch 102.
First, the second switch 102 is turned on, the detection electrode 40G is connected to the ground potential, and the battery is completely discharged. Next, the second switch 102 is turned off to disconnect the detection electrode 40G from the ground potential. Then, when the first switch 101 is turned on and the detection electrode 40G is connected to the reference capacitance 104, the detection electrode 40G receives an electric charge from the reference capacitance 104.
Next, the first switch 101 is turned off to disconnect the detection electrode 40G from the reference capacitance 104. Here, the first switch 101 and the second switch 102 are driven by signals that do not overlap each other so that they do not turn on at the same time.

Since the reference capacitance 104 is always _{maintained at V REF} = 1.2V, the waveform of the detection electrode 40G is such that 0V and V _REF = 1.2V are alternately repeated as in the waveform of the detection electrode 40G shown in FIG. 11B. It becomes a waveform.

Assuming that the frequency of this waveform is f (Hz) and the capacitance of the detection electrode 40G is C (F), the detection electrode 40G _{draws the current of f × C × V REF} from the reference capacitance 104. If this is left as it is, the electric charge is steadily extracted from the reference capacitance 104, and the voltage of the reference capacitance 104 drops from 1.2V and approaches 0V.

One terminal of the comparator 105 is connected to the reference capacitance 104, and the other terminal is connected to the _{steady-state voltage source V REF = 1.2V.} The comparator 105 constantly compares the voltage of the reference capacitance 104 with the voltage of V _REF = 1.2V, and when the voltage of the reference capacitance 104 _{becomes lower than V REF} = 1.2V, sends a command to the second pulse generation circuit to send a command to the second pulse generation circuit. The pulse generation circuit of the above generates a pulse having a certain pulse width to turn on the third switch 106, and the count value of the counter 109 is incremented by one.

When the counter 109 receives the count reset signal from the timer 110, the count value is reset to 0. A steady-state current source 107 is connected to the reference capacitance 104 via a third switch 106, and when the third switch 106 is turned on, a predetermined steady-state current is supplied to the reference capacitance 104.
Here, the comparator 105, the second pulse generation circuit, the third switch 106, and the steady current source 107 form a feedback loop, and the voltage of the reference capacitance 104 is always V _REF = 1.2V due to this feedback loop. It is kept at 1.2V, which is equal to.

When the capacitance of the detection electrode 40G is small, the current drawn from the reference capacitance 104 is small, so that the count value of the pulse for turning on the third switch 106 required to keep the reference capacitance 104 at 1.2V is small. ..
On the contrary, when the capacitance of the detection electrode 40G is large, the current drawn from the reference capacitance 104 becomes large, so the count value of the pulse for turning on the third switch 106 required to keep the reference capacitance 104 at 1.2V. Becomes larger.
That is, with the above configuration, the count value of the counter 109 is a value proportional to the capacity of the detection electrode 40G. The capacity of the detection electrode 40G can be estimated by reading the count value of the counter 109.
The above-mentioned capacitance measurement can also be applied to the capacitance type liquid level sensor 30 of the second embodiment. Further, in the case of the capacitance type liquid level sensor 10 of the first embodiment, since there is no ground electrode, the above-mentioned counter electrode is used instead, and between the detection electrodes 40, 40A to 40F and the counter electrode. It is sufficient to measure the capacity generated in.

(How to use the shield electrode)
The shield electrode 60 is driven by a signal from the first pulse generation circuit 103 via the buffer 115. As shown in FIG. 11B, the signal applied from the first pulse generation circuit 103 to the shield electrode 60 is a signal that is always equal to the waveform of the detection electrode 40G.
In this way, since the detection electrode 40G and the shield electrode 60 always have the same voltage, no capacitance is generated between the detection electrode 40G and the shield electrode 60. The presence of the shield electrode 60 makes it difficult for noise from the outside to propagate to the detection electrode 40G, and the capacitance detection accuracy of the detection electrode 40G can be improved. Hereinafter, examples of the capacitive liquid level sensor 80 of the present invention will be described in more detail.

The capacitance type liquid level sensor 80 shown in FIGS. 9A to 9C was manufactured. Specifically, the detection electrode 40G and the ground electrode 50 of FIG. 9A and the shield electrode 60 of FIG. 9B were manufactured from a commercially available two-layer flexible printed substrate. The thickness of the copper foil is about 12 μm, and the thickness of the first to fourth polyimide layers is about 12.5 μm to 25 μm. The thickness of the two-layer flexible printed circuit board was about 104 μm. The detection electrode 40G has seven arm portions 42 on the left and right, and has a width (W) of about 2 cm and a length (L) of about 8 cm. The manufactured capacitance type liquid level sensor 80 is attached to a glass 90 having a cubic curved surface using an adhesive, and the relationship between the capacity and the water level when water is used as the liquid is shown in FIGS. 11A and 11B. It was measured by the capacitance measurement circuit shown.

FIG. 12 is a graph showing the relationship between the count value of the counter 109 and the liquid level when the capacitance type liquid level sensor 80 is attached to the glass 90 of FIG. 10 and water is poured. The horizontal axis of FIG. 12 is the water level from the bottom of the glass 90, and the vertical axis is the count value corresponding to the capacity value.
As shown in FIG. 12, the water level ranges from when the water level reaches the lower end of the detection electrode 40G (water level of 1 on the horizontal axis) to when the water level reaches the upper end of the detection electrode 40G (water level of 9 on the horizontal axis). It was found that the count value increased as the water level increased, and it was found that the water level could be measured, that is, the water level, that is, the liquid level of the glass 90 operating as a liquid level sensor and having a cubic curved surface could be accurately measured.

The present invention can be implemented in various forms without departing from the spirit of the present invention.
For example, in the above-described embodiment, as shown in FIG. 10, the detection electrode 40G is attached so that the shaft portion 41 faces up and down along the liquid level direction (Z direction) of the container, but the upper part of the container is attached. The detection electrode 40G may be attached to the side in the XY direction, that is, in the direction orthogonal to the liquid level direction. According to this configuration, not only the liquid level can be detected, but also that the liquid level has reached the upper part of the container can be detected.

In the above-described embodiment, the method of determining the number of pulse counts required to equalize the amount of charge drawn from the reference capacitance 104 and the amount of charge injected into the reference capacitance 104 is used for the capacitance of the detection electrode 40G. Of course, other methods may be used as long as the capacity of 40 G can be measured.

10,10A-10E,30,80 Capacitive liquid level sensor 40,40A-40G Detection electrode 11,41 Shaft 12,42 Arm 13,43 Notch 21 First flexible layer 22 Second flexible layer 23 Third flexible layer 24 Fourth flexible layer 50 Ground electrode 60 Shield electrode 90 Glass 100 Capacitance measurement circuit diagram 101 First switch 102 Second switch 103 First pulse circuit 104 Reference capacitance 105 Comparator 106 Third Switch 107 Steady current source 108 Reference power supply (V _REF )
109 Second pulse circuit and counter 110 Timer 115 Buffer 120 Electrode waveform

Claims (9)

A capacitance type liquid level sensor in which a detection electrode is attached to the outer wall of a container and the liquid level contained in the container is measured by the capacitance change between the detection electrode and the counter electrode.
The detection electrode includes at least one shaft portion and a plurality of arm portions connected to the shaft portion.
A notch is formed between the adjacent arms of the plurality of arms.
A capacitance type liquid level sensor capable of attaching the detection electrode to the surface of the three-dimensional curved surface of the container by arranging the notch on the surface of the three-dimensional curved surface of the container. The first flexible layer and
The detection electrode and the ground electrode formed on the first flexible layer,
A second flexible layer overlaid on the detection electrode and the ground electrode,
With
The detection electrode has at least one shaft portion and a plurality of arm portions connected to the shaft portion.
A notch is formed between the adjacent arms of the plurality of arms.
The detection electrode is a capacitance type liquid level sensor that can be attached to the surface of the three-dimensional curved surface of the container by arranging the notch on the surface of the three-dimensional curved surface of the container. The first flexible layer and
A detection electrode and a ground electrode formed on the surface side of the first flexible layer,
A second flexible layer overlaid on the surfaces of the detection electrode and the ground electrode,
A third flexible layer overlaid on top of the second flexible layer,
A shield electrode formed on the surface side of the third flexible layer and
A fourth flexible layer overlaid on the shield electrode and
With
The detection electrode includes at least one shaft portion and a plurality of arm portions connected at an angle to the shaft portion.
To prepare
A notch is provided between the adjacent arms of the plurality of arms.
The detection electrode is a capacitance type liquid level sensor that can be attached to the surface of the three-dimensional curved surface of the container by providing the notch on the surface of the three-dimensional curved surface of the container. The capacitance type liquid level sensor according to claim 1, wherein the detection electrode is arranged on a flexible substrate. The capacitance type liquid level sensor according to claim 3, wherein the detection electrode, the ground electrode, and the shield electrode are made of a metal plate or a metal foil. The capacitance according to claim 3, wherein the first to fourth flexible layers are each made of a conductive film, and the detection electrode, the ground electrode, and the shield electrode are arranged on each conductive film. Mold level sensor. The capacitance type liquid level sensor according to any one of claims 1 to 3, wherein the detection electrode is made of a metal layer arranged on a non-woven fabric. The capacitance type liquid level sensor according to any one of claims 1 to 3, wherein the capacitance type liquid level sensor is a linear type sensor that is converted into a liquid level by a capacitance value generated in the detection electrode. The capacitance type liquid level according to any one of claims 1 to 3, wherein the detection electrode is provided with a plurality of cut portions, and a change in the liquid level of the container is determined by a change in the volume of the detection electrode. Sensor.

Images