JP2005181165A - Liquid level sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid level sensor capable of measuring precisely a liquid level. <P>SOLUTION: This liquid level sensor has three sensor parts 2, 3, 4, and a measuring circuit 6, and the sensor parts 2, 3 are arranged on the first face 1a of a container 1 with a prescribed distance. The sensor part 4 is arranged on the second face 1b of the container 1, and is separated with prescribed distances respectively from the sensor parts 2, 3. An inclination angle of the container 1 is calculated on the basis of information from the liquid levels measured by the respective sensor parts 2, 3, 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a liquid level sensor that measures a liquid level.

Some containers that contain liquid include a liquid level sensor that measures the liquid level. As the liquid level sensor, for example, a float type sensor, a sensor using ultrasonic waves, a capacitance type sensor, and the like are known.
Here, when the container is small, for example, a height of 20 mm and a diameter of 20 mm, the float sensor has to reduce the float, so that the buoyancy of the float itself becomes too small. For this reason, there exists a problem that the position detection element linked with a float, such as a variable resistor, an optical element, and a magnetic element, cannot be supported. In addition, since the volume of the small container is small, the absolute value of the liquid level becomes small, and for example, high measurement accuracy of about plus or minus 0.5 mm in the height direction is required. If a sensor using ultrasonic waves is applied to a small container with such special characteristics, the distance for transmitting and receiving ultrasonic waves cannot be secured sufficiently, resulting in low measurement accuracy and accurate measurement of the liquid level. Can not do it.

On the other hand, the capacitance type sensor can be made smaller than the float type sensor, and can measure the liquid level with higher accuracy than a sensor using ultrasonic waves.
The capacitance type sensor has a configuration in which a pair of measurement electrodes partially immersed in a liquid is arranged along the vertical direction of the container. Here, since the dielectric constant in the liquid is larger than the dielectric constant in the air, the capacitance of the portion immersed in the liquid of the pair of measurement electrodes is increased. Therefore, the higher the liquid level, the larger the capacitance. Therefore, the liquid level can be measured by applying an AC signal to a set of measurement electrodes and measuring the capacitance. Here, some conventional liquid level sensors can measure the inclination of a container using a plurality of electrodes. As a specific configuration, there is a substrate having a long cylinder with a square cross section, and three measurement electrodes and one correction electrode provided on each surface of the substrate. And when there is a difference in the signal output from each measurement electrode, the tilt angle of the container is calculated from this difference (see, for example, Patent Document 1). As a technique for processing signals from a plurality of measurement electrodes, a method of sequentially selecting signals using a multiplexer is known (for example, see Patent Document 2).
Japanese Patent No. 3128930 Japanese Patent Laid-Open No. 6-34423

However, when the electrodes for measurement are provided on each surface of one substrate, the distance between the electrodes is short, so that the difference in capacitance due to the inclination of the container is small, and measurement errors are likely to occur. Furthermore, since a plurality of measurement electrodes are close to each other, electrostatic coupling occurs between the measurement electrodes, and the substrate having a long cylindrical shape is difficult to miniaturize, and the electrodes are accurately placed on each surface. It is difficult to place well.
If a multiplexer is used for signal processing, signals from a plurality of measurement electrodes cannot be detected simultaneously. For this reason, when the inclination angle of the container changes frequently, the liquid level cannot be detected correctly.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid level sensor capable of measuring the liquid level with high accuracy.

The present invention employs the following means in order to solve the above problems.
The liquid level sensor of the present invention includes a plurality of electrodes arranged in a container, and a sensor unit that detects a liquid level in the container based on a change in electrical characteristics between the electrodes is provided at a height of the container. It is characterized by being juxtaposed along a first surface parallel to the direction.
Since the liquid level sensor has two or more sensor units arranged along the surface of the container, the distance between the sensor units can be increased. For this reason, since the electrode which measures an electrical characteristic in one sensor part and the electrode which measures an electrical characteristic in another sensor part are separated, electrostatic coupling between the electrodes is prevented. Furthermore, the amount of change in electrical characteristics when the container is tilted increases.

In said liquid level sensor, it is preferable to provide a shield part between the said sensor parts arranged side by side.
In this liquid level sensor, since the shield part is disposed between the sensor parts arranged side by side, electrostatic coupling between electrodes belonging to different sensor parts is reliably prevented.

In the liquid level sensor, it is preferable that the plurality of sensor portions are integrally formed of an insulating film.
This liquid level sensor is easily manufactured because a plurality of sensor portions are integrally formed of an insulating film. In addition, it can be easily fixed to the container. Furthermore, it becomes easy to keep the distance between each sensor part constant.

In the liquid level sensor described above, it is preferable that at least one sensor unit is disposed on a second surface orthogonal to the first surface of the container.
In this liquid level sensor, since a plurality of sensor units are arranged in two orthogonal planes, it is possible to measure the liquid level and to measure the two axial inclinations of the container.

In the liquid level sensor, the plurality of sensor portions arranged on each of the first surface and the second surface are integrally formed of an insulating film, and the insulating film is It is preferable to bend along the first surface and the second surface.
This liquid level sensor is easily manufactured because a plurality of sensor portions are integrally formed of an insulating film. In addition, it can be easily fixed to the container. Furthermore, it becomes easy to keep the distance between each sensor part constant.

The liquid level sensor according to the present invention includes a plurality of electrodes arranged in a container, and has at least two sensor units for detecting a liquid level in the container based on a change in electrical characteristics between the electrodes. And the said sensor part is arrange | positioned along each of the two axis lines orthogonal to the height direction of the said container, It is characterized by the above-mentioned.
Since this liquid level sensor has arranged a plurality of sensor parts along each of two axes, the distance between sensor parts can be taken large. Furthermore, it is possible to measure the liquid level and to measure the inclination of the container in the two axial directions. In particular, the amount of change in electrical characteristics when the container is inclined increases.

Furthermore, the liquid level sensor according to the present invention includes a plurality of electrodes arranged in a container, and includes three sensor units that detect a liquid level in the container based on a change in electrical characteristics between the electrodes. The sensor unit is arranged in a triangular arrangement in a cross-sectional view orthogonal to the height direction of the container.
In this liquid level sensor, since the sensor parts are arranged in a triangular shape in a cross-sectional view, the distance between the sensor parts can be increased. Furthermore, the inclination angle of the container can be measured with high accuracy. In particular, the inclination angle can be measured even when the container has a complicated shape or has a circular cross section.

  According to the present invention, since the sensor unit including the electrode for measuring the change in the liquid level is arranged at a predetermined distance on the first surface of the container, the electrostatic capacitance between the electrodes of the other sensor units is arranged. Can be prevented. Therefore, the liquid level and inclination angle of the container can be measured with high accuracy. Furthermore, if a shield is provided between the sensor units having electrodes, electrostatic coupling between different sensor units can be effectively prevented, so that measurement accuracy is improved. In addition, when a plurality of sensor units are integrally formed, manufacturing and handling are facilitated.

The best mode for carrying out the invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the liquid level sensor in the first embodiment is electrically connected to the three sensor units 2, 3, 4 disposed in the container 1 and the sensor units 2, 3, 4. And a measurement circuit 6 to be connected.

  The three sensor parts 2, 3, and 4 are attached to the inner wall of the container 1 substantially parallel to the axis C1 in the height direction of the container. The sensor unit 2 and the sensor unit 3 are arranged at a predetermined distance on the first surface 1a along the axis C2 substantially orthogonal to the axis C1. In more detail, the sensor part 2 is arrange | positioned at the one side edge part of the 1st surface 1a, and the sensor part 3 is arrange | positioned at the other side edge part of the 1st surface 1a. The sensor part 4 is arrange | positioned at the 2nd surface 1b along the axis line C3 orthogonal to each of the axis line C1 and the axis line C2. The sensor part 4 is arrange | positioned in the 2nd surface 1b in the side edge part on the opposite side to the side edge part which contact | connects the 1st surface 1a. The sensor unit 4 is provided at a position at a predetermined distance from the sensor unit 2 and the sensor unit 3. In other words, the sensor units 2, 3, and 4 are triangularly arranged in a cross-sectional view orthogonal to the axis C1.

Next, the structure of each sensor part 2,3,4 is demonstrated. In addition, since the structure of each sensor part 2,3,4 is the same, it demonstrates below only the sensor part 2 as an example.
As shown in FIGS. 2 and 3, the sensor unit 2 has an elongated film shape, one base end 2 a side in the longitudinal direction is connected to the measurement circuit 6, and the distal end 2 b is located near the bottom surface of the container 1. To be fixed. Furthermore, the width of the sensor unit 2 is widened from the base end 2a toward the front end 2b. It is desirable that the end of the widened portion 21 is immersed in the liquid.
In the sensor unit 2, a cover film 7, a first insulating film 8, a second insulating film 9, and a cover film 10 are laminated in this order. Each of the films 7, 8, 9, and 10 is made of an insulating member having a low water absorption rate, such as polyethylene terephthalate (PET), polyester, nylon, or liquid crystal polymer.

On the cover film 7 corresponding to the outermost layer on one side, a shield layer 11 having a width about half that of the cover film 7 is provided in a sheet shape. The first insulating film 8 is in close contact with the cover film 7 so as to sandwich the shield layer 11 together with the cover film 7. The first insulating film 8 includes a linear measurement electrode 12, a drive electrode (measurement signal supply electrode) 13, a first shield electrode 14, a reference electrode 15, and a second shield electrode 16. Along the longitudinal direction of the one insulating film 8, the insulating films 8 are spaced apart from each other and arranged substantially in parallel. The second insulating film 9 is in close contact with the first insulating film 8 so as to sandwich the electrodes 12, 13, 14, 15 and 16 together with the first insulating film 8. On the second insulating film 9, a shield layer 17 having a width about half that of the second insulating film 9 is provided in a sheet shape. The cover film 10 is in close contact with the second insulating film 9 so as to sandwich the shield layer 17 together with the second insulating film 9.
As shown in FIG. 2, the second insulating film 9 and the cover film 10 are such that the base end 2 a side of the sensor unit 2 is shorter than the cover film 7 and the first insulating film 8, and On the corresponding base end 2a side, the respective electrodes 12, 13, 14, 15, 16 are exposed with a predetermined length.

As shown in FIGS. 2 and 3, the drive electrode 13 is provided on the surface 18 of the first insulating film 8 with a predetermined line width and thickness from the proximal end to the vicinity of the distal end. The upper end of the drive electrode 13 is connected to the measurement circuit 6 (see FIG. 1) on the base end 2a side of the sensor unit 2, and a predetermined drive AC signal is input thereto. Further, the lower end (tip) 13a of the drive electrode 13 is positioned above the tip 8a of the first insulating film 8 by a predetermined distance r1.
The measurement electrode 12 is provided on the surface 18 at a position spaced a predetermined distance from the drive electrode 13. The line width and thickness of the measurement electrode 12 are the same as those of the drive electrode 13. The upper end of the measurement electrode 12 is connected to the measurement circuit 6 on the base end 2 a side of the sensor unit 2. Further, the lower end (tip) 12a of the measurement electrode 12 is positioned above the tip 8a of the first insulating film 8 by a predetermined distance r1.
The measurement electrode 12 and the drive electrode 13 form a capacitive element. The capacitance is determined by the surface area of the measurement electrode 12 and the drive electrode 13, the distance between the electrodes, and the dielectric constant. As for the dielectric constant, the dielectric constant of the liquid is sufficiently larger than the dielectric constant of air. Therefore, the capacitance between the measurement electrode 12 and the drive electrode 13 is approximately the surface area immersed in the liquid surface, that is, the length from the lower end of the measurement electrode 12 and the drive electrode 13 to the liquid level described later. Proportional.

Further, the first shield electrode 14 is provided on the surface 18 at a position substantially symmetrical to the measurement electrode 12 with respect to the drive electrode 13. That is, the distance from the drive electrode 13 to the measurement electrode 12 and the distance from the drive electrode 13 to the first shield electrode 14 are substantially the same. The upper end of the first shield electrode 14 is grounded. Further, the lower end (tip) 14a of the first shield electrode 14 is positioned above the tip 8a of the first insulating film 8 by a predetermined distance r2. The distance r2 is larger than the distance r1.
The reference electrode 15 is disposed on the surface 18 at a position further away from the drive electrode 13. The width and thickness of the reference electrode 15 are equal to those of the drive electrode 13. The upper end of the reference electrode 15 is connected to the measurement circuit 6 on the base end 2 a side of the sensor unit 2. Further, the lower end (tip) 15a of the reference electrode 15 is located above the tip 8a of the first insulating film 8 by a predetermined distance r1.
The second shield electrode 16 is arranged on the surface 18 so as to sandwich the reference electrode 15 together with the first shield electrode 14. That is, the distance from the reference electrode 15 to the second shield electrode 16 is substantially equal to the distance from the reference electrode 15 to the first shield electrode 14. The upper end of the second shield electrode 16 is grounded. Further, the lower end (tip) 16a of the second shield electrode 16 is positioned above the tip 8a of the first insulating film 8 by a predetermined distance r2.

  Further, the shield layer 11 is provided at a position overlapping the shield electrodes 14 and 16 and the shield layer 17. Specifically, the width of the shield layer 11 is approximately equal to a value obtained by adding the width of each shield electrode 14, 16 to the distance between the electrodes of each shield electrode 14, 16. Further, the lower end (front end) of the shield layer 11 is positioned above the front ends of the first insulating film 8 and the second insulating film 9 by a predetermined distance r2 similarly to the shield electrodes 14 and 16. Here, the shield layer 11 is made of a conductive material. And it is electrically connected to the second shield electrode 16 through the conductive through-hole portion 20 formed in the first insulating film 8. The conductive through hole portion 20 is formed, for example, by plating a conductive material on the through hole formed in the first insulating film 8.

The shield layer 17 is made of a conductive material and has the same shape as the shield layer 11. The shield layer 17 is formed on the surface 19 opposite to the surface where the second insulating film 9 is in close contact with the surface 18 of the first insulating film 8. The lower end (tip) of the shield layer 17 is at the same position as the shield electrodes 14 and 16 and the shield layer 11. Further, the shield layer 17 is electrically connected to the first shield electrode 14 through a conductive through hole portion 23 formed in the second insulating film 9.
The shield layer 11 and the shield layer 17 are provided at positions sandwiching the reference electrode 15 and the shield electrodes 14 and 16 with the first insulating film 8 and the second insulating film 9 interposed therebetween. Therefore, the pair of shield electrodes 14 and 16 and the pair of shield layers 11 and 17 are disposed so as to surround the reference electrode 15 and are electrically connected. Since the shield electrodes 14 and 16 are grounded as described above, the pair of shield electrodes 14 and 16 and the pair of shield layers 11 and 17 serve as an electromagnetic shield for the reference electrode 15.

  A portion protruding from the shield in the vicinity of the lower end 15 a of the reference electrode 15 serves as a reference measurement unit 25, and a shielded portion serves as a signal conduction unit 26. The reference measurement unit 25 forms the drive electrode 13 and the capacitive element. The capacitance is determined by the surface area of the reference measurement unit 25 and the drive electrode 13, the distance between the electrodes, and the dielectric constant. The length of the reference measuring unit 25 is a length obtained by subtracting the predetermined distance r1 from the predetermined distance r2, and the value of the capacitance (dielectric constant) at this time is a reference when measuring the liquid level. Value. The signal conduction unit 26 has an upper end connected to the measurement circuit 6 and plays a role of inputting a predetermined signal generated by the reference measurement unit 25 to the measurement circuit 6.

  In addition, each electrode 12, 13, 14, 15, 16 and each shield layer 11, 17 are part of the conductive material in each film 7, 8, 9 to which a conductive material having a predetermined thickness is attached. It is formed by etching. Further, in the widened portion 21 of the sensor unit 2, the arrangement interval of the electrodes 12, 13, 14, 15, 16 is also long with the first shield electrode 14 as the center.

  As shown in FIG. 1, the measurement circuit 6 includes a first measurement circuit 27 connected to the sensor unit 2, a second measurement circuit 28 connected to the sensor unit 3, and a third measurement connected to the sensor unit 4. Circuit 29. Since each measurement circuit 27, 28, 29 has the same circuit configuration, only the configuration of the first measurement circuit 27 will be described below.

As shown in FIG. 4, the first measurement circuit 27 includes, for example, an oscillation circuit 31 that generates a square AC signal. The oscillation circuit 31 is connected to a series circuit composed of three inverters 32, 33, 34, a resistor 35 connected to the input terminal and the output terminal of the series circuit, and an input terminal of the inverter 32 and an output terminal of the inverter 33. The capacitor 36 is provided. The output terminal of the series circuit is connected to the drive electrode 13 of the sensor unit 2.
The first measurement circuit 27 includes a resistor 37 and an analog switch 38 that are connected to the measurement electrode 12 at one end. Furthermore, the first measurement circuit 27 includes a resistor 39 and an analog switch 40 having one end connected to the reference electrode 15. The other ends of the resistors 37 and 39 are grounded. Each analog switch 38, 40 is connected to a low pass filter 41. The control terminals of the analog switches 38 and 40 are connected to the oscillation circuit 31, and the switches are turned on or off according to the output waveform of the oscillation circuit 31.

  The low-pass filter 41 includes a capacitor 42 having one end connected to the analog switch 38 and a resistor 43, and a capacitor 44, a resistor 45, and a capacitor 46 are connected to the other end of the resistor 43. Further, the low-pass filter 41 includes a capacitor 47 having one end connected to the analog switch 40 and a resistor 48, and a capacitor 49, a resistor 50, and a capacitor 46 are connected to the other end of the resistor 48. . The output of the low pass filter 41 is connected to the differential amplifier circuit 51. The other ends of the capacitor 42 and the capacitor 47, the capacitor 44 and the capacitor 49, the resistor 45 and the resistor 50 are grounded. The capacitor 46 is interposed at the other end of each of the resistor 43 and the resistor 48.

The differential amplifier circuit 51 is mainly composed of three operational amplifiers 52, 53 and 54. The non-inverting input terminal of the operational amplifier 52 is connected to the output on the measurement electrode 12 side of the low-pass filter 41. The output terminal and the inverting input terminal of the operational amplifier 52 are connected via a resistor 55 to form a negative feedback loop. Further, the output terminal of the operational amplifier 52 is connected to the inverting input terminal of the operational amplifier 54 via the resistor 56. The inverting input terminal of the operational amplifier 52 is connected to the inverting input terminal of the operational amplifier 53 via the resistor 57 and the variable resistor 58.
An output on the reference electrode 15 side of the low-pass filter 41 is connected to a non-inverting input terminal of the operational amplifier 53. A resistor 59 is interposed between the output terminal and the inverting input terminal of the operational amplifier 53. Further, the output terminal of the operational amplifier 53 is connected to each of the resistor 60 and the resistor 61. The other end of the resistor 60 is grounded, and the resistor 61 is connected to the non-inverting input terminal of the operational amplifier 54.

  One end of a resistor 62 is connected to the output terminal of the operational amplifier 54. This resistor 62 is connected to another control circuit, from which a signal corresponding to the distance (liquid level) from the reference position h0 to the liquid level is output. A resistor 63 and a capacitor 64 are connected in parallel between the other end of the resistor 62 and the inverting input terminal of the operational amplifier 54.

Next, the operation of this liquid level sensor will be described. The container 1 is assumed to contain liquid at least up to a height (reference position h0) equal to the distance r2, as shown in FIG.
As shown in FIG. 4, the oscillation circuit 31 of the first measurement circuit 27 generates a driving AC signal. This AC signal is input to the drive electrode 13 and propagates to the measurement electrode 12, the reference measurement unit 25 of the reference electrode 15, and the shield using air and liquid as a medium. The measurement electrode 12 generates a reception signal corresponding to the capacitance based on the dielectric constant of the liquid, that is, the liquid level, by the propagation of the signal. This received signal is input to the analog switch 38 of the first measurement circuit 27. In addition, the reference measurement unit 25 (see FIG. 2) generates a reception signal corresponding to the capacitance based on the dielectric constant of the liquid by signal propagation. This received signal is input to the analog switch 40 of the first measurement circuit 27. Since the shield is grounded, no reception signal is generated.

  Since the analog switches 38 and 40 switch the switching of the switches according to the drive AC of the oscillation circuit 31, the reception voltage of the measurement electrode 12 and the reception voltage of the reference electrode 15 are synchronously detected. Receiving voltages synchronously detected by the analog switches 38 and 40 are input to the low-pass filter 41, an extra AC component is removed, and a DC component is extracted. Further, after being input to the differential amplifier circuit 51 and amplified, a signal proportional to the difference obtained by subtracting the reception voltage of the reference electrode 15 as a reference value from the reception voltage of the measurement electrode 12 is output.

  Here, the dielectric constant between the measurement electrode 12 and the portion of the drive electrode 13 immersed in the liquid and the dielectric constant between the measurement electrode 12 and the reference measurement unit 25 of the reference electrode 15 are the same value. It is. Therefore, when the amount of the liquid in the container 1 increases and the liquid level rises above the reference position h0, the capacitance between the drive electrode 13 and the measurement electrode 12 increases substantially in proportion to the liquid level. To do. On the other hand, the reference electrode 15 corresponds to the reference position h0 because the portion beyond the reference position h0 is shielded by the shield electrodes 14 and 16 and the shield layers 11 and 17 as shown in FIG. No change from capacitance. As described above, the sensor output is proportional to the difference between the signal based on the capacitance on the measurement electrode 12 side and the signal based on the capacitance on the reference electrode 15 side. Therefore, as the liquid level increases, it increases in proportion to this. Similarly, the sensor output decreases in proportion to the decrease in the liquid level. Thus, the sensor output of the sensor unit 2 is a signal having a magnitude approximately proportional to the liquid level with reference to the reception voltage of the reference measurement unit 25. Therefore, the absolute value of the liquid level is known from the magnitude of the signal.

Similarly, also in the sensor part 3 and the sensor part 4, the liquid level in each attachment position is detected based on an alternating current signal.
Here, as shown in FIG. 1, when the container 1 is in a horizontal state, the sensor outputs corresponding to the sensor units 2, 3, 4 have substantially the same value. On the other hand, when the container 1 is in an inclined posture, different sensor outputs are obtained for the sensor units 2, 3, and 4. In this case, the inclination angle of the container 1 can be calculated by performing a predetermined calculation based on each sensor output, that is, the value of each liquid level and the position of each sensor unit 2, 3, 4. Specifically, a tilt around a specific axis can be detected from sensor outputs of two sensor units selected from among the three sensor units 2, 3, and 4. For example, the sensor unit 2 and the sensor unit 3 can detect an inclination angle around the axis C3. From the sensor unit 2 and the sensor unit 4, an inclination angle around the axis C2 can be detected. The sensor unit 3 and the sensor unit 4 can detect an inclination angle around an axis connecting the sensor unit 3 and the sensor unit 4. Further, a three-dimensional inclination can be detected from the sensor outputs of the three sensor units 2, 3, and 4. The inclination angle in these cases can be calculated by the following formula 1.

  Here, θ represents the inclination angle of the liquid level with respect to the horizontal direction, and Δh is the difference in liquid level. The difference in the liquid level is obtained from the value of the liquid level in the sensor output of two sensor units arbitrarily selected from the three sensor units 2, 3, and 4. For example, it can be obtained by subtracting the value of the liquid level by the sensor output of the sensor unit 3 from the value of the liquid level by the sensor output of the sensor unit 2. De is a distance between the measurement electrodes, and corresponds to, for example, a linear distance from the measurement electrode 12 of the sensor unit 2 to the measurement electrode 12 of the sensor unit 3. In addition, the value preset for every container 1 is used for the distance between each measurement electrode 12. FIG. Further, the distances between the measurement electrodes 12 of the sensor unit 2 and the sensor unit 4 and between the sensor unit 3 and the sensor unit 4 are also set in advance for each container 1.

According to this embodiment, the plurality of sensor parts 2, 3, and 4 are distributed and arranged on the axis C2 and the axis C3, and the sensor parts 2, 3, and 4 are separated from each other by a sufficient distance. Therefore, electrostatic coupling between the electrodes 12, 13, 15 of the different sensor parts 2, 3, 4 can be suppressed. Therefore, the liquid level can be measured with high accuracy. In addition, since a part of the reference electrode 15 is electromagnetically shielded, the accuracy of the liquid level detected by each sensor unit 2, 3, 4 can be improved.
Furthermore, the inclination angle of the container 1 can be detected by performing a predetermined calculation based on the positions of the plurality of sensor units 2, 3, 4 and the respective sensor outputs. Here, since the three sensor units 2, 3, and 4 are arranged and arranged with a sufficient distance, the inclination angle can be measured with high accuracy.

And since the part which is not shielded, ie, the measurement part 25 for a reference, was arrange | positioned by the lower end of the reference electrode 15 and the bottom face of the container 1, it is easy to measure the electrostatic capacitance used as a reference. Therefore, the liquid level can be accurately measured even from a small amount of liquid. Here, the liquid level is obtained as a distance from the reference position h0. Since the reference position h0 is a known value when the mounting position of the liquid level sensor on the container 1 is determined, the liquid level is determined from the bottom surface of the container 1. The absolute value up to the liquid level can be easily obtained.
Further, since the measurement electrode 12 and the reference electrode 15 share the drive electrode 13 and measure the liquid level with three electrodes, the liquid level sensor can be downsized. Moreover, since each electrode 12,13,15 was covered with the some film 7, 8, 9, 10 with a small water absorption, contact with each electrode 12,13,15 and a liquid can be prevented.

  Here, as an application example of this liquid level sensor, fuel is stored in a fuel cell developed as a power source for a portable terminal device such as a PDA (electronic notebook), a computer, a cellular phone, or a driving source of a vehicle. The present invention can be applied to detect the storage amount (remaining amount) of a container or a container that stores waste liquid. Since the reference capacitance measured by the reference electrode 15 can be accurately measured, even if liquids with different dielectric constants, such as pure methanol or a mixture of formic acid and formaldehyde, are put in the container, it is ensured. The liquid level can be detected. Moreover, this liquid level sensor may be applied to a machine in which a liquid such as water is stored in a container, such as a washing machine, a dishwasher, an electric kettle, or a bathtub.

Next, a second embodiment will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component same as 1st Embodiment. In addition, overlapping explanation is omitted.
This embodiment is characterized in that a plurality of sensor portions are integrally formed of an insulating film.

  As shown in FIG. 5, an insulating film 70 is attached to the plane 1 a along the axis C <b> 2 of the container 1. On the insulating film 70, two sensor portions 2 and 3 are provided in parallel with the axis C1. The liquid level sensor in this embodiment includes two sensor units 2 and 3 on the insulating film 70, the sensor unit 4, and a measurement circuit 6 (see FIG. 1).

The width of the insulating film 70 is approximately equal to the length of the first surface 1a in the direction of the axis C2, and the height is approximately equal to the height of the sensor portions 2 and 3 in the direction of the axis C1. The sensor unit 2 is in close contact with one edge of the insulating film 70 in the width direction. In addition, the sensor unit 3 is in close contact with the other edge in the width direction of the insulating film 70. The insulating film 70 is manufactured from the same material as each of the films 7, 8, 9, and 10. The sensor unit 4 has a configuration similar to that shown in FIG.
Moreover, the sensor part 4 has the same structure as the sensor part 2 shown in FIG.

  In this liquid level sensor, since the two sensor parts 2 and 3 are integrally formed of the insulating film 70, the sensor parts 2 and 3 are easily fixed to the container 1. Furthermore, since the two sensor parts 2 and 3 are connected by the insulating film 70, the position of each sensor part 2 and 3 becomes difficult to shift, and the measurement accuracy can be improved.

Further, an insulating film 70 may be used in place of the cover films 7 of the sensor unit 2 and the sensor unit 3. That is, the shield layer 11 (see FIG. 3) is formed at each edge in the width direction of the insulating film 70, and this shield layer 11 is formed on the second shield electrode 16 on the first insulating film 8 by the conductive through-hole portion 20. Connecting.
Furthermore, the insulating film 70 may have a two-layer structure, and two insulating films 70 may be used instead of the cover film 7 and the first insulating film 8 of the sensor unit 2 and the sensor unit 3, respectively. In this case, the insulating film 70 in which the electrodes 12, 13, 14, 15, and 16 are arranged is brought into close contact with the insulating film 70 on which the shield layer 11 is formed. The shield layer 11 and the electrodes 12, 13, 14, 15, 16 are formed on both edges in the width direction of the two insulating films 70. And the 2nd insulating film 9 and the cover film 10 (both refer FIG. 3) are laminated | stacked on it.
Similarly, the cover film 7, the first insulating film 8, and the second insulating film 9 of the sensor unit 2 and the sensor unit 3 may be replaced with three insulating films 70. Further, all the films 7, 8, 9, 10 of the sensor unit 2 and the sensor unit 3 may be replaced with four insulating films 70. As described above, when each of the films 9 and 10 is replaced with the insulating film 70, a part of each of the electrodes 12, 13, 14, 15 and 16 is exposed for connection to the measurement circuit 6. The height in the direction of the axis C1 is adjusted.

  In such a case, the liquid level sensor can be easily manufactured. Here, since the electrodes 12, 13, 14, 15, 16 and the shield layers 11, 17 can use the conventional etching technique described above, the manufacturing cost can be kept low. In particular, if the insulating film 70 is used as the film on which the measurement electrodes 13 and the like are arranged, the electrodes 12, 13, 14, 15, 16 are formed on a large area film. The surface accuracy can be improved.

As shown in FIG. 6, all of the three sensor units 2, 3, 4 arranged in parallel with the axis C <b> 1 may be integrally formed with the insulating film 72. In this case, the insulating film 72 has a width substantially equal to the total length of the first surface 1a and the second surface 1b. Furthermore, it is bent at approximately 90 ° at the connecting portion of the first surface 1a and the second surface 1b along the respective surfaces 1a and 1b. For this reason, the insulating film 72 has a substantially L shape in plan view. And the sensor part 4 is provided in one edge part of the insulating film 72, and the sensor part 3 is provided in the other edge part. Further, the sensor unit 2 is provided in the vicinity of the bent portion 73 of the insulating film 72. The insulating film 72 is manufactured from the same material as the insulating film 70 described above. Each of the sensor units 2, 3, and 4 is provided on the insulating film 72 or is configured by using the insulating film 72 on at least one film.
In such a liquid level sensor, the same effect as described above can be obtained for the three sensor units 2, 3, and 4.

Next, a third embodiment will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the component same as each said embodiment. In addition, overlapping explanation is omitted.
This embodiment is characterized in that an electromagnetic shield is provided between a plurality of sensor units.
As shown in FIG. 7, the liquid level sensor includes three sensor units 2, 3, and 4 arranged in parallel with the axis C1, and a measurement circuit 6 (see FIG. 1). 3 is integrally formed of an insulating film 81. Furthermore, in the insulating film 81, a shield electrode 82 serving as a shield part is provided at a substantially intermediate position from the sensor part 2 to the sensor part 3. A shield part 83 is provided along the plane 1b at a substantially intermediate position from the sensor part 2 to the sensor part 4.

The insulating film 81 has the same shape as the insulating film 70 shown in FIG. 5 and is formed from the same material. The insulating film 81 is attached to the first surface 1a along the axis C2. Moreover, although the sensor part 2 and the sensor part 3 are provided in parallel on both the edge parts of the width direction of the insulating film 81, it is the several film which comprises each sensor part 2 and 3 similarly to the above. At least one of 7, 8, 9, 10 (see FIG. 3) may be the insulating film 81.
The shield electrode 82 is disposed in parallel with the height direction of the container 1, and the length in the height direction is the same as that of the other electrodes 12, 13, and 15. The shield electrode 82 is formed by partially etching the conductive material in the insulating film 81 to which the conductive material having a predetermined thickness is attached. It is preferable to cover the shield electrode 82 with a film so that the shield electrode 82 does not directly contact the liquid. For example, when the insulating film 81 has a two-layer structure, the insulating film 81 is laminated so as to sandwich the shield electrode 82.

  Moreover, the shield part 83 has the structure which covered the electroconductive shield electrode 84 with the insulating film 85, and the insulating film 85 is contact | adhered to the 2nd surface 1b. The shield electrode 84 is made of the same material as the shield electrode 82 and has the same shape. The insulating film 85 is manufactured from the same material as the insulating film 81.

This liquid level sensor is used in a state where the shield electrode 82 and the shield electrode 84 are grounded. For this reason, during the measurement of the liquid level, among the signals propagating from the drive electrode 13 of the sensor unit 2, signals directed to the sensor unit 3 and the sensor unit 4 are blocked by the shield electrode 82 and the shield electrode 84, respectively. For this reason, the electrostatic coupling between the sensor unit 2 and the sensor unit 3 or the sensor unit 4 is prevented. Similarly, the signal from the sensor unit 3 does not propagate to the sensor unit 2 because of the shield electrode 82. The signal from the sensor unit 4 does not propagate to the sensor unit 2 because of the shield electrode 84. In addition, since the distance of the sensor part 3 and the sensor part 4 is fully separated, the electrostatic coupling between both does not arise.
Therefore, in this liquid level sensor, the signals from the other sensor units 2, 3 and 4 are not received by the measurement electrode 12 or the reference electrode 15, so that the measurement accuracy of the liquid level is improved. Moreover, the measurement accuracy of the inclination angle of the container 1 calculated based on the liquid level and the arrangement of the sensor units 2, 3, 4 can be improved.

Here, as shown in FIG. 1, when the sensor unit 2 and the sensor unit 3 are arranged independently, a shield unit having the same configuration as the shield unit 83 is provided between the sensor unit 2 and the sensor unit 3. If the electrodes are arranged and the electrodes are grounded, electrostatic coupling between the sensor units 2 and 3 can be prevented.
Further, when the three sensor parts 2, 3, 4 are integrally formed with the insulating film 72 (see FIG. 6), the shield electrode 84 is bent from the position where the sensor part 4 is disposed on the insulating film 72. It is possible to prevent electrostatic coupling between the sensor unit 2 and the sensor unit 4 by disposing the portion 73 and connecting to the ground.

Note that the present invention is not limited to the above-described embodiment, and can be widely applied.
For example, using the fact that impedance is proportional to the area of an electrode immersed in a liquid, the impedance that is a higher concept of capacitance is measured, and the current detection circuit and the voltage detection circuit are detected so as to detect the liquid level. It may be a measurement circuit provided.
In addition, each measurement circuit 27, 28, 29 may be configured to input an AC signal having a different frequency for each sensor unit 2, 3, 4 to each drive electrode 13. Since crosstalk in each of the sensor units 2, 3, 4 and the measurement circuit 6 is prevented, measurement accuracy is improved.

In each embodiment, the number of sensor units may be four or more. The fourth and subsequent sensor portions may be arranged on the first surface 1a or on the second surface 1b. Moreover, you may arrange | position on the other surface of the container 1. FIG. Further, four or more sensor parts may be integrally formed of an insulating film, or a shield part similar to the shield electrode 82 or the shield part 83 may be disposed between the sensor parts.
Furthermore, the shape of the container 1 is not limited to a rectangular parallelepiped, and may be a cylindrical shape, a polygonal shape, or may have irregularities on the inner surface. Even in these cases, by arranging three or more sensor parts by dividing them into two axes orthogonal to the height direction of the container 1 or by arranging them in a triangular shape in a cross-sectional view, the liquid level or the inclination The angle can be measured with high accuracy.

In addition, each of the films 7, 8, 9, and 10 may be made of a material that does not absorb water or a material that hardly absorbs water, only the outermost cover films 7 and 10, and the outer surface of the film. Water absorption may be prevented by glass coating or further covering with a waterproof material.
Further, the sensor units 2, 3, and 4 may be configured without a shield. In this case, it is preferable to narrow the width of the signal conducting portion 26 with respect to the reference measuring portion 25 of the reference electrode 15.
In the measurement circuit 6, a phase shift circuit 100 (see FIG. 4) that shifts the phase of the signal by 90 ° may be interposed between the analog switches 38 and 40 and the oscillation circuit 31. Since it is possible to process data in the signal phase of the received voltage whose phase is shifted by 90 ° with respect to the drive waveform, it is possible to achieve higher sensitivity.

It is a whole lineblock diagram of a liquid level sensor in an embodiment of the invention. It is a figure which shows the sensor part of a liquid level sensor. It is a disassembled perspective view of the sensor part of a liquid level sensor. It is a figure which shows the structure of a part of measurement circuit. It is a block diagram of the liquid level sensor in embodiment of this invention. It is a block diagram of the liquid level sensor in embodiment of this invention. It is a block diagram of the liquid level sensor in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Container 1a 1st surface 1b 2nd surface 2, 3, 4 Sensor part 7, 10 Cover film (insulating film)
11, 17 Shield layer (shield)
12 Measurement electrode 13 Drive electrode 15 Reference electrode 70, 72, 81 Insulating film 82 Shield electrode (shield part)
83 Shield part C1, C2, C3 Axis h0 Reference position

Claims (7)

  A plurality of electrodes arranged in a container, and a sensor unit that detects a liquid level in the container based on a change in electrical characteristics between the electrodes, on a first surface parallel to the height direction of the container A liquid level sensor characterized by being juxtaposed along the surface.   The liquid level sensor according to claim 1, wherein a shield part is provided between the sensor parts arranged side by side.   The liquid level sensor according to claim 1, wherein the plurality of sensor units are integrally formed of an insulating film.   The liquid level sensor according to any one of claims 1 to 3, wherein at least one sensor unit is arranged on a second surface orthogonal to the first surface of the container.   The plurality of sensor portions disposed on each of the first surface and the second surface are integrally formed of an insulating film, and the insulating film includes the first surface and the second surface. The liquid level sensor according to claim 4, wherein the liquid level sensor is bent along the surface.   A plurality of electrodes arranged in a container, and having at least two sensor parts for detecting a liquid level in the container based on a change in electrical characteristics between the electrodes, the sensor part being a height of the container A liquid level sensor, wherein the liquid level sensor is arranged along each of two axes orthogonal to the direction. A plurality of electrodes arranged in a container, having three sensor parts for detecting a liquid level in the container based on a change in electrical characteristics between the electrodes, the sensor part being in the height direction of the container A liquid level sensor, wherein the liquid level sensor is arranged in a triangular arrangement in a cross-sectional view orthogonal to the horizontal axis.

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