JP2007298362A - Capacitive liquid level sensor - Google Patents

Abstract

A capacitive liquid level sensor capable of detecting a stable liquid level even for liquids having different dielectric constants.
A capacitance type liquid level sensor has a capacitance that changes in accordance with the liquid level, and a ratio of the capacitance also changes in accordance with the liquid level. And second sensor elements 12 and 13. Accordingly, it is possible to perform stable liquid level detection without being influenced by the dielectric constant even for liquids having different dielectric constants based on the capacitance ratio.
[Selection] Figure 1

Description

  The present invention relates to a capacitance type liquid level sensor.

FIG. 13 is a perspective view showing a configuration example of a conventional capacitance type liquid level sensor. The capacitive liquid level sensor 1 includes an insulating substrate 2 and a pair of electrodes 3 a and 3 b disposed on the main surface of the substrate 2. Each of the pair of electrodes 3a and 3b has a terminal portion 4 and a detection portion 5. The detection unit 5 includes a main body 6 extending from the terminal unit 4 and a plurality of orthogonal parts 7 provided on the main body 6 at equal intervals and orthogonally. As the liquid level rises, the capacitance between the electrodes increases, and the liquid level is output by detecting the value from the terminal unit 4. A characteristic of this sensor is that the electrodes 3a and 3b have a plurality of orthogonal portions 7. When the liquid level reaches each orthogonal part 7, the electrostatic capacity between the electrodes 3a and 3b changes greatly, so that the liquid level can be easily detected (see Patent Document 1).
JP 05-118894 A

  The capacitive liquid level sensor having the above-described configuration is a sensor that detects the capacitance between patterns arranged on the same plane, and the electrode plate area that is substantially opposed is small, and the sensor capacitance changes with respect to the liquid level. Is also small. Therefore, it is difficult to detect the liquid level of a solution having a low dielectric constant. Therefore, when liquid level detection of liquids having different dielectric constants is taken into consideration, correction at the detection circuit portion to which the sensor is connected is required when detecting the liquid level of liquids having low dielectric constants.

  Moreover, since this electrostatic capacitance type liquid level sensor does not have a reference sensor part, there is a problem that the detected value becomes the liquid level. In this case, since the measured value varies depending on external factors such as the dielectric constant of the solution and the state of the electrode, it is difficult to always reliably detect the capacitance.

  In view of the above problems, an object of the present invention is to provide a capacitance type liquid level sensor capable of stable liquid level detection even for liquids having different dielectric constants.

  The invention according to claim 1, which has been made to solve the above-mentioned problems, is a capacitance type liquid level sensor that detects the liquid level of the liquid by capacitance, each of which corresponds to the liquid level. A capacitance-type liquid surface comprising: first and second sensor elements having a capacitance that varies depending on the liquid level; It exists in the level sensor.

  In the first aspect of the present invention, each of the capacitance type liquid level sensors has a capacitance that changes corresponding to the liquid level, and the ratio of the capacitance also corresponds to the liquid level. First and second sensor elements that change are provided. Accordingly, it is possible to perform stable liquid level detection without being influenced by the dielectric constant even for liquids having different dielectric constants based on the capacitance ratio.

  According to a second aspect of the present invention, there is provided a capacitive liquid level sensor according to the first aspect, wherein each of the first and second sensor elements is at the liquid level. Correspondingly, the capacitance level sensor has a capacitance that increases at different rates of change and has a matching capacitance at the maximum detectable liquid level.

  In the invention described in claim 2, the first and second sensor elements increase at different rates corresponding to the liquid level, and have the same capacitance at the maximum detectable liquid level. Have. Thereby, the capacitance ratio changes corresponding to the liquid level up to the maximum detectable liquid level, and the liquid level can be detected with high sensitivity.

  In order to solve the above-mentioned problem, the invention according to claim 3 is the capacitance type liquid level sensor according to claim 1 or 2, wherein the capacitance type liquid level sensor is a support substrate; The first sensor element disposed on one surface of the support substrate and the second sensor element disposed on the other surface of the support substrate, wherein the first and second sensor elements are The signal electrode and the ground electrode each formed in a flat plate shape, and the gap between the electrode plates of the signal electrode and the ground electrode are formed so that a gap gradually narrows in the direction from one end to the other end in the longitudinal direction of the sensor. And the gap of the second sensor element is gradually narrowed in the opposite direction to the gap of the first sensor element. For capacitive liquid level sensor To.

  According to a third aspect of the present invention, the capacitive liquid level sensor is disposed on the support substrate, the first sensor element disposed on one surface of the support substrate, and the other surface of the support substrate. Each of the first and second sensor elements includes a signal electrode and a ground electrode formed in a flat plate shape, and one end in the sensor longitudinal direction between the electrode plates of the signal electrode and the ground electrode. And a dielectric layer disposed so as to generate a gap whose width gradually decreases in the direction from the other end to the other end, and the gap of the second sensor element is the same as the gap of the first sensor element. The width gradually decreases in the opposite direction. Thereby, the capacitance ratio of the first and second sensor elements can be increased, and the detection accuracy of the liquid level can be increased.

  According to a fourth aspect of the present invention, there is provided a capacitive liquid level sensor according to the third aspect, wherein the dielectric has an angle other than 90 ° with respect to the sensor longitudinal direction. Are arranged so that a plurality of gaps having a constant width across the sensor width are formed at intervals, and the plurality of gaps are set so that the constant width gradually becomes narrower in a direction from one end to the other end in the sensor longitudinal direction. It exists in the electrostatic capacitance type liquid level sensor characterized by the above-mentioned.

  In the invention according to claim 4, the dielectric is disposed such that a plurality of gaps having a constant width across the sensor width are formed at an interval with an angle other than 90 ° with respect to the sensor longitudinal direction. The gap is set such that the constant width gradually becomes narrower in the direction from one end to the other end in the sensor longitudinal direction. Thereby, the first and second capacitance changes and the capacitance ratio can be made a function of the liquid level.

  In order to solve the above-mentioned problem, the invention according to claim 5 is the capacitance type liquid level sensor according to claim 3, wherein the dielectric has a diagonal line extending from one end to the other end in the sensor longitudinal direction. The electrostatic capacity type liquid level sensor is characterized in that it is arranged so as to generate a gap that gradually becomes narrower.

  In the invention described in claim 5, the dielectric is arranged so as to generate a gap that gradually narrows so as to draw a diagonal line from one end to the other end in the longitudinal direction of the sensor. Thereby, the first and second capacitance changes and the capacitance ratio can be made a function of the liquid level.

  In order to solve the above-mentioned problem, the invention according to claim 6 is the capacitance type liquid level sensor according to any one of claims 1 to 5, wherein the first and second sensor elements are The capacitive liquid level sensor is disposed on the front and back surfaces of the support substrate.

  In the invention described in claim 6, the first and second sensor elements are respectively disposed on the front and back of the support substrate. Thereby, the entire width of the capacitive liquid level sensor is reduced, and a space-saving and compact sensor can be realized.

  In order to solve the above-mentioned problem, the invention according to claim 7 is the capacitance type liquid level sensor according to any one of claims 1 to 5, wherein the first and second sensor elements are The capacitive liquid level sensor is arranged on the same surface of the support substrate.

  In the invention according to claim 7, the first and second sensor elements are respectively disposed on the same surface of the support substrate. Thereby, the thickness of the capacitance type liquid level sensor is reduced, and a sensor suitable for an installation environment where the thickness of the sensor is a problem can be realized.

  According to the first aspect of the present invention, there is provided a capacitance type liquid level sensor that detects the liquid level of the liquid based on the capacitance, each having a capacitance that changes in accordance with the liquid level. In addition, since the capacitance ratio is provided with the first and second sensor elements that change in accordance with the liquid surface level, based on the capacitance ratio, even for liquids having different dielectric constants, Stable liquid level detection can be performed without being affected by the dielectric constant.

  According to a second aspect of the present invention, each of the first and second sensor elements increases at a different rate of change corresponding to the liquid level, and is static at the maximum detectable liquid level. Since it has electric capacity, the ratio of the electrostatic capacity changes corresponding to the liquid level up to the maximum detectable liquid level, and the liquid level can be detected with high sensitivity.

  According to the third aspect of the present invention, the capacitance type liquid level sensor is disposed on the support substrate, the first sensor element disposed on one surface of the support substrate, and the other surface of the support substrate. The first sensor element and the second sensor element have a signal electrode and a ground electrode formed in a flat plate shape, and a sensor longitudinal direction between electrode plates of the signal electrode and the ground electrode, respectively. A gap between the first sensor element and the first sensor element. The gap between the first sensor element and the first sensor element is a gap between the first sensor element and the first sensor element. Since the width is gradually narrowed in the reverse direction, the ratio of the capacitances of the first and second sensor elements can be increased, and the detection accuracy of the liquid level can be increased.

  According to the fourth aspect of the present invention, the dielectric is arranged such that a plurality of gaps having a constant width across the width of the sensor are formed with an angle other than 90 ° with respect to the sensor longitudinal direction. The gap is set so that the constant width gradually becomes narrower in the direction from one end of the sensor in the longitudinal direction to the other end, so that the ratio between the first and second capacitance changes and the capacitance can be determined. It can be a surface level function.

  According to the fifth aspect of the present invention, the dielectric is arranged so as to generate a gap that gradually narrows so as to draw a diagonal line from one end to the other end in the longitudinal direction of the sensor. Capacitance change and capacitance ratio can be a function of liquid level.

  According to the sixth aspect of the present invention, since the first and second sensor elements are respectively disposed on the front and back of the support substrate, the entire capacitance type liquid level sensor is reduced in size and space-saving and compact. Sensor can be realized.

  According to the seventh aspect of the present invention, since the first and second sensor elements are arranged on the same surface of the support substrate, the thickness of the capacitive liquid level sensor is reduced, and the sensor A sensor suitable for an installation environment where thickness is a problem can be realized.

  Hereinafter, a capacitance type liquid level sensor according to an embodiment of the present invention will be described with reference to the drawings.

  (First Embodiment) FIG. 1 shows a first embodiment of a capacitive liquid level sensor according to the present invention, (A) is a perspective view, (B) is a perspective view of a main sensor, C) is a perspective view of a reference sensor.

  The capacitive liquid level sensor 10 includes a support substrate 11 made of an insulator, a main sensor 12 disposed on one surface of the support substrate 11, and a reference sensor 13 disposed on the other surface. The main sensor 12 corresponds to the first sensor element in the claims, and the reference sensor 13 corresponds to the second sensor element in the claims.

The main sensor 12 has a laminated structure in which a dielectric 122 is disposed between the signal electrode 121 and the ground electrode 123. That is, the main sensor 12 is disposed between the signal electrode 121 made of an elongated plate-shaped conductor, the ground electrode 123 made of a conductor having the same shape and the same size as the signal electrode 121, and the signal electrode 121 and the ground electrode 123. In addition, a dielectric 122 made of a plurality of dielectric pieces 122 _{1 to} 122 _n (in FIG. 1, for example, n = 8) is laminated. The dielectric 122 uses a material whose dielectric constant is relatively smaller than that of the liquid whose liquid level is measured (preferably, a sufficiently small material). In FIG. 1B, the signal electrode 121 is omitted.

A plurality of dielectric pieces 122 ₁ to 122 _n is the general shape of a parallelogram with the exception of the dielectric strip 122 ₁ and 122 _n at both ends (as viewed from the top), between each of the sensor The gaps 124 _{1 to} 124 _n-1 having a certain width (excluding 90 °) with respect to the longitudinal direction and crossing the sensor width are arranged to be generated. Further, the plurality of gaps 124 _{1 to} 124 _n-1 have a constant width gradually in a direction from one end (left end portion in FIG. 1B) to the other end (right end portion in FIG. 1B) in the sensor longitudinal direction. It is set to be wide. Further, the plurality of dielectric pieces 122 _{1 to} 122 _n have an overall outer shape after their arrangement substantially the same as the outer shape of the signal electrode 121 and the ground electrode 123.

The reference sensor 13 has a stacked structure similar to that of the main sensor 12. That is, the reference sensor 13 has a laminated structure in which the dielectric 132 is disposed between the signal electrode 131 and the ground electrode 133. The reference sensor 13 includes a signal electrode 131 made of an elongated plate-shaped conductor, a ground electrode 133 made of a conductor having the same shape and the same size as the signal electrode 131, and a plurality of signals disposed between the signal electrode 131 and the ground electrode 133. The dielectric pieces 132 _{1 to} 132 _n are stacked on each other. The dielectric 132 uses the same material as the dielectric 122. In FIG. 1C, the signal electrode 131 is omitted.

A plurality of dielectric pieces 132 ₁ to 132 _n is the general shape of a parallelogram with the exception of the dielectric strip 132 ₁ and 132 _n at both ends (as viewed from the top), between each of the sensor It is arranged so that the gap 134 ₁ ~134 _n-1 with a constant width across the sensor width has the same angle as gap 124 ₁ ~124 _n-1 of the above results with respect to the longitudinal direction. Further, the plurality of gaps 134 _{1 to} 134 _n-1 has a constant width gradually in a direction from one end (left end portion in FIG. 1C) to the other end (right end portion in FIG. 1C) in the sensor longitudinal direction. It is set to be wide. Furthermore, the plurality of dielectric pieces 132 _{1 to} 132 _n have substantially the same outer shape after arrangement as the signal electrodes 131 and the ground electrode 133.

In the main sensor 12 and the reference sensor 13, the dielectric piece 122 ₁ in the main sensor 12 and the dielectric piece 132 _{1 in the} reference sensor 13 are in the same position on the front side and the back side of one end of the support substrate 11, and the dielectric piece 122 _n and the dielectric piece 132 _n are arranged on the support substrate 11 so as to be in the same position on the other front side and back side of the support substrate 11. Further, the gap 134 ₁ ~134 _n-1 of the gap 124 ₁ ~124 _n-1 and the reference sensor 13 of the main sensor 12, respectively, become identical in exactly inverse relationship gradually narrows degree progressively widens degree Yes.

  1 has a laminated structure having seven layers 121, 122, 123, 11, 133, 132 and 131 from the top, and processes the shape of the conductor and dielectric, The conductors 121, 123, 131, and 133 are formed as a four-layer substrate having four conductor layers, or the conductors and dielectrics are similarly processed to form the conductors 123 and 133 and the dielectric 11. 3 substrates of a double-sided printed board having a dielectric 122 and a conductor 121 and a single-sided printed board having a dielectric 132 and a conductor 131 are bonded together with an adhesive or the like. Can do.

When the main sensor 12 and the reference sensor 13 are used in the liquid level detection circuit due to the above-described structure, for example, a capacitive liquid level sensor in a tank filled with a liquid whose liquid level is to be detected. one end of the 10 (end on the side of the dielectric piece 122 ₁ is disposed) is in contact with the tank bottom, is erected to be substantially perpendicular. The main sensor 12 functions as a sensor in which the capacitance Cp varies depending on the liquid level due to the liquid filled between the electrode plates, that is, the gaps 124 _{1 to} 124 _n−1 . Similarly, the reference sensor 13 functions as a sensor in which the capacitance Cr changes depending on the liquid level by the liquid filled between the plates, that is, the gaps 134 _{1 to} 134 _n−1 .

  FIG. 2 is a characteristic diagram showing the relationship between the output voltages V12 and V13 corresponding to the capacitances Cp and Cr of the main sensor 12 and the reference sensor 13 with respect to the liquid level. As can be seen from FIG. 2, the output voltage V12 of the main sensor 12 has a characteristic that increases rapidly as the liquid level increases and gradually changes. Further, the output voltage V13 of the reference sensor 13 has a characteristic that increases gradually as the liquid level increases and gradually changes rapidly. That is, the main sensor 12 and the reference sensor 13 are sensors having characteristics in which changes in the output voltage with respect to changes in the liquid level (in other words, changes in capacitance) are inverse functions of each other. The ratio between the output voltage V12 of the main sensor 12 and the output voltage V13 of the reference sensor 13 with respect to the same liquid level (that is, the ratio between the capacitance Cp and Cr) is also a value that is a function of the liquid level.

  As can be seen from FIG. 2, each of the main sensor 12 and the reference sensor 13 increases at different rates of change corresponding to the liquid level, and has a capacitance that coincides with the maximum detectable liquid level. Thereby, the capacitance ratio changes corresponding to the liquid level up to the maximum detectable liquid level, and the liquid level can be detected with high sensitivity.

  Next, FIG. 3 is a diagram showing a configuration example of a liquid level detection circuit using the capacitance type liquid level sensor 10 of FIG. In this example, the change in the liquid level is detected as a change in the oscillation frequency of the oscillator based on the change in the capacitance of the main sensor 12 and the reference sensor 13.

  In FIG. 3, the liquid level detection circuit 20 includes oscillators 21 and 22, integration circuits 23 and 24, diodes 25 and 26, an arithmetic processing unit 27, a memory 28, and a display unit 29. The oscillator 21 is a CR oscillator whose oscillation frequency changes with a change in the capacitance Cp of the main sensor 12. The oscillator 22 is a CR oscillator whose oscillation frequency changes due to a change in the capacitance Cr of the reference sensor 13. The arithmetic processing unit 27 is composed of, for example, a microcomputer.

  Next, the operation of the liquid level detection circuit of FIG. 3 will be described with reference to the flowchart of FIG. First, measurement of the capacitances Cp and Cr corresponding to the liquid level of the main sensor 12 and the reference sensor 13 is started (step S1). That is, the oscillators 21 and 22 oscillate at an oscillation frequency corresponding to the capacitances Cp and Cr of the main sensor 12 and the reference sensor 13, and perform capacitance-frequency conversion.

  Next, the integration circuits 23 and 24 integrate the oscillation outputs of the oscillators 21 and 22 and convert them into DC voltages (frequency-voltage conversion) corresponding to the respective oscillation frequencies (step S2). The converted DC voltage is supplied to the arithmetic processing unit 27 via the diodes 25 and 26, respectively.

  Next, the arithmetic processing unit 27 converts the supplied DC voltage into a liquid level value and outputs it (step S3). The process of step S3 is performed in the following steps S31 to S33. First, the supplied DC voltage is measured, and the difference between the sensor voltage values of the main sensor 12 and the reference sensor 13 in the air is output from the measured voltage (step S31). That is, the main sensor 12 and the reference sensor 13 have capacitance values that are not immersed in the liquid. Therefore, in order to detect the liquid level from the amount of change in capacitance, the difference between the voltage value based on the capacitance value of the sensor itself and the measurement voltage stored in advance in the memory 28 is obtained, and the amount of change in capacitance of the sensor. Only the voltage by is calculated.

  Next, the ratio of the differential voltage in the main sensor 12 and the differential voltage in the reference sensor 13 obtained in step S31 is calculated (step S32). The calculated ratio is a value that varies according to the actual liquid level. Since this value is a ratio, even if the dielectric constant of the liquid whose liquid level is to be detected changes, the value represents the liquid level without being affected by the dielectric constant.

  Next, the liquid level is calculated and output using the ratio calculated in step S32 and the conversion formula between the ratio and the liquid level stored in advance in the memory 28 (step S33).

  Next, the liquid level value calculated in step S3 is displayed on the display unit 29 (step S4). The above steps S1 to S4 are repeated, and display corresponding to the change in the liquid level is performed.

The characteristics of the first embodiment of the present invention described above are as follows.
(1) The gaps between the main sensor 12 and the reference sensor 13 are characterized in that the width of each sensor is reversed from small to large and from large to small. The capacitance to be detected varies depending on the size of the gap between the main sensor 12 and the reference sensor 13. By changing the gap shape of the dielectrics 122 and 132, the capacity ratio between the small gap and the large gap is increased, and the liquid level can be easily detected by the ratio. Since the liquid level is detected by the ratio, there is an advantage that it does not depend on the dielectric constant of the solution for detecting the liquid level. The capacitance ratio between the main sensor 12 and the reference sensor 13 is determined by the gap width between the electrode plates. If the relationship between the capacitance ratio and the liquid level is clear, the liquid level detection of liquids of any dielectric constant can be performed. Is possible.
(2) Since the main sensor 12 is arranged on the front side of the support substrate 11 and the reference sensor 13 is arranged on the back side, and the main sensor 12 and the reference sensor 13 are integrated, the size of the main sensor 12 is maintained and the reference sensor 13 is included. It is a sensor, a small and space-saving sensor.

  Next, a specific design example of the air gap in the main sensor 12 and the reference sensor 13 will be described.

The above-mentioned ratio is K, the capacitance of the main sensor 12 is Cp, the capacitance of the reference sensor 13 is Cr, the detection voltage of the main sensor 12 (calculated from the integration circuit 23 in the detection circuit of FIG. The voltage input to the processing unit 27) is Vp, and the detection voltage of the reference sensor 13 (the voltage input to the arithmetic processing unit 27 from the integration circuit 24 in the detection circuit of FIG. 3 via the diode 26) is Vr.
K = Vp / Vr = Cp / Cr (1)
It is represented by

  The state of change in capacitance varies depending on parameters such as the parallelogram angle, spacing (gap), and base length of the dielectric pieces in the space filled with the solution, including the shape of the capacitive liquid level sensor 10 itself. It is difficult to formulate unless it is actually measured. Therefore, the relationship between the sensor liquid level position and the ratio K is recorded by actual measurement using some test solution (liquid). A conversion formula for the specific liquid level is formulated from the recorded actual measurement values and stored in the memory 28.

For example, as shown in FIG. 5, the gaps 134 _{1 to} 132 _n-1 of the reference sensor 13 have an angle that rises to the right, and the right end of the lower gap (for example, 134 ₁ ) when viewed from the horizontal direction in the figure. Matches the left edge of the next void above (eg, 134 ₂ ) or overlaps the right edge of the lower void (eg, 134 ₁ ) with the vicinity of the left edge of the next void above (eg, 134 ₂ ) to make it in, also the width of the gap 134 ₁ as the reference 1, 134 2 × 134 _{1 2} width, three times 134 ₁ the width of 134 _3, 134 _n-1 width 134 ₁ of the (n -1) Set as double.

Similarly, the air gaps 124 _{1 to} 122 _n-1 of the main sensor 12 are raised to the right at the same angle as the reference sensor 13, and the right end of the lower air gap (for example, 124 ₁ ) when viewed from the horizontal direction in FIG. Coincides with the left end of the next gap (eg, 124 ₂ ), or the vicinity of the right end of the lower gap (eg, 124 ₁ ) overlaps with the vicinity of the left end of the next upper gap (eg, 124 ₂ ) In addition, the width of the gap 124 ₁ is set as the reference ₁ having the same width as the gap 134 ₁ , the width of 124 ₂ is 1/2 times 124 ₁ , the width of 124 ₃ is 1/3 times 124 ₁ , and 124 _n− set _first width 124 ₁ of 1 / (n-1) as multiplication.

In this case, when the liquid is filled in the gap of the reference sensor 13 in the order of 134 ₁ and 134 ₂ , the change in the capacitance Cr is represented by a straight line (a thick solid line) in FIG. ), The change due to the gaps 134 ₂ and 134 ₃ is twice or three times as much as the change due to the gap 134 ₁ . For example, when the change amount y of the capacitance Cr due to the gap 134 ₁ is expressed as a function of the liquid level x, y = x / 2, the change amount due to the gap 134 ₂ is expressed as y = x, and the gap 134 _3. The amount of change due to is represented by y = 3x / 2.

Similarly, the width of the gap 134 ₁ as a reference 1 of the same width as the gap 124 _1, 134 2 × 134 _{1 2} width, so that four times the 134 ₁ the width of 134 _3, the gap of the upper width If the set to be twice the gap below, changes in the capacitance Cr of the reference sensor 13, as shown in FIG. 6 (B), relative to the amount of change due to gap 134 _1, the gap 134 change by _2, 134 _3, respectively, twice, four times the amount of change. That is, when the change amount y of the capacitance Cr due to the gap 134 ₁ is expressed as a function of the liquid level x, y = x / 2, the change amount due to the gap 134 ₂ is expressed as y = x, and the gap 134 ₃ The amount of change due to is represented by y = 2x.

On the other hand, the amount of change in the capacitance Cp of the main sensor 12 is expressed by an inverse function of the functional expression of the reference sensor 13. For example, in the case of FIG. 6 (A), the variation of the electrostatic capacitance Cp by the gap 124 ₁ is represented by y = 2x, the amount varies according to the air gap 124 ₂ is expressed by y = x, the amount of change due to gap 134 ₃ Is represented by y = 2x / 3.

  Accordingly, the gap dimension is designed based on a function in which the amount of change in the capacitance of the reference sensor 13 changes gradually, such as the graph of y = x / 2 at the beginning, and vice versa. If the main sensor 12 is designed to be expressed by a function, the ratio K becomes a large value, and the detection accuracy can be improved.

Further, the change in the capacitance Cr shown in the straight lines (represented by three thick solid lines) in FIGS. 6A and 6B is represented by, for example, the curves in FIGS. 6A and 6B (thin solid lines). ), It can be formulated by approximating it with a high-order function expression of y = ax ⁿ . In this case, change of the capacitance Cp of the main sensor 12 is formulated to approximate the inverse function of the high-order function equation of y = ax ^n.

When the height h of one air gap is smaller than the total length L of the sensor, one air gap can be roughly regarded as one point in measurement in the change in measurement capacity, and the bottom line size of the air gap is adjusted to the required area. Change. For example, when the change in the capacitance Cr of the reference sensor 13 can be approximated by a functional expression of y = x ² through the gaps 134 ₁ , 134 _2, and 134 ₃ , as shown in FIG. If the angle is θ, the capacitance Cr of the reference sensor 13 is
Cr = y = x ² tan θ × h (2)
It is represented by

When the height h of one gap is larger than the total length L of the sensor (as shown in FIG. 6B), as shown in FIG. 8, the respective gaps 134 ₁ , 134 ₂ and 134 _{3 are used.} If the heights at h are h1, h2, and h3, respectively, the electrostatic capacity Cr of the reference sensor 13 captures a linear capacitance change in each gap. In this case, the gap base is matched to y = x ² to the inclination change of the differentiating the y '= 2x.

Then, the capacitance Cr of the reference sensor 13 when the height x of the solution is in the gap 134 ₁ in each of the air gap (x <h1), the
Cr = t × tan θ × x = C1 (3)
It becomes. Here, t is the width of the gap 134 ₁ .

Further, the capacitance Cr of the height x of the solution is in the gap _{134 2 (h1 <x <h1} + h2) Reference sensor 13 when the
Cr = 2t × tan θ × (x−h1) + C1 = C2 (4)
It becomes.

Further, the capacitance Cr of the reference sensor 13 when the height x of the solution is in the gap _{134 3 (h1 + h2 <x} ) is
Cr = 4t × tan θ × (x−h1−h2) + C1 + C2 = C3 (5)
It becomes.

(Second Embodiment)
Next, FIG. 9 shows a second embodiment of a capacitive liquid level sensor according to the present invention, wherein (A) is a front perspective view and (B) is a rear perspective view. The capacitive liquid level sensor 10 has substantially the same configuration as that of the first embodiment shown in FIG. 1 and is different in the shapes of the dielectrics 122 and 132. In FIG. 9A, the signal electrode 121 is omitted, and in FIG. 9B, the signal electrode 131 is omitted.

  The dielectric 122 of the main sensor 12 has a shape in which the width gradually decreases linearly from one end (the left end in the drawing) in the longitudinal direction of the sensor to the other end (the right end in the drawing). Accordingly, the width gradually increases so as to draw a diagonal line from one end (right end portion in the drawing) to the other end (left end portion in the drawing) in the sensor longitudinal direction between the electrode plate of the ground electrode 123 and the signal electrode 121 (not shown). The gap 124 becomes narrow.

  The dielectric 132 of the reference sensor 13 gradually decreases in width linearly from one end (the right end in the figure) to the other end (the left end in the figure) in the longitudinal direction of the sensor. The sensor 12 has the same proportion as the dielectric 122 but has a shape whose width decreases in the opposite direction. Accordingly, the width gradually increases so that a diagonal line is drawn from one end (left end portion in the drawing) to the other end (right end portion in the drawing) in the sensor longitudinal direction between the electrode plates of the ground electrode 133 and the signal electrode 131 (not shown). The gap 134 becomes narrow.

  When the main sensor 12 and the reference sensor 13 are used in the liquid level detection circuit 20 due to the above-described structure, for example, a capacitance type liquid level in a tank filled with a liquid whose liquid level is to be detected. One end of the sensor 10 (the lower end in FIG. 9) is in contact with the bottom of the tank so as to be substantially vertical. The main sensor 12 functions as a sensor whose capacitance Cp varies depending on the liquid level due to the liquid filled in the gap 124 between the electrode plates of the ground electrode 123 and the signal electrode 121. Similarly, the reference sensor 13 functions as a sensor whose capacitance Cr changes depending on the liquid level by the liquid filled in the gap 134 between the electrode plates of the ground electrode 133 and the signal electrode 131.

  The capacitive liquid level sensor 1 of the second embodiment shown in FIG. 9 is processed in the same manner as in the first embodiment shown in FIG. 1 and formed as a four-layer substrate, or one double-sided surface. It can be created by bonding three substrates of a printed circuit board and two single-sided printed circuit boards with an adhesive or the like.

  FIG. 10 is a characteristic diagram showing the relationship of the output voltage corresponding to the electrostatic capacities of the main sensor 12 and the reference sensor 13 with respect to the liquid level.

  As can be seen by comparing FIG. 10 and FIG. 2, the capacitive level sensor 10 according to the second embodiment is less sensitive than the sensor of the first embodiment shown in FIG. Is suitable for detecting the liquid level of a liquid having a high dielectric constant.

  Next, an example of deriving the capacitances Cp and Cr and the ratio K of the capacitance type liquid level sensor of the second embodiment will be described.

As shown in FIG. 11, the width of the main sensor 12 is a, the length is b, the liquid level is x, and the dielectrics 122 and 132 draw a diagonal line from one end of the sensor to the other end. When the width is reduced, the measurement capacity C ₁₂ of the main sensor ₁₂ is
C ₁₂ = ε ₀ ε _r × (1 / d) × {a + (a−ax / b)} x / 2) + C ₀ (6)
It is represented by Here, d is the distance between the electrode plates of the signal electrode 121 and the ground electrode 123, ε ₀ is the capacitance in the air (portion not immersed in the liquid) in the main sensor 12, and ε _r is the relative dielectric constant of the liquid. . Similarly, the measurement capacitance C ₁₃ of the reference sensor ₁₃ is
C ₁₃ = ε ₀ ε _r × (1 / d) × (ax ² / 2b) + C ₀ (7)
It is represented by

Therefore, the electrostatic capacity Cp of the main sensor 12 and the electrostatic capacity Cr of the reference sensor 13 are expressed by Cp = C ₁₂ −C ₀ (8) from the above expressions (6) and (7).
Cr = C ₁₃ −C ₀ (9)
It is required as follows.

  Therefore, the ratio K can be obtained by substituting the above equations (8) and (9) into the above equation (1).

  (Third Embodiment) FIG. 12 is a perspective view showing a third embodiment of the capacitive liquid level sensor according to the present invention. In the first embodiment shown in FIG. 1, the main sensor 12 and the reference sensor 13 are arranged on both sides of the support substrate 11, but the capacitive liquid level sensor 10 of the third embodiment is supported. The main sensor 12 and the reference sensor 13 are arranged on one surface of the substrate 11. In FIG. 12, the signal electrodes 121 and 131 are omitted.

  A capacitive liquid level sensor 10 according to the third embodiment shown in FIG. 12 includes a support substrate 11, a single-sided printed board constituting the main sensor 12, and a single-sided printed board constituting the reference sensor 13. The substrate can be formed by bonding with an adhesive or the like.

  Since the capacitance type level sensor 10 according to the third embodiment has the main sensor 12 and the reference sensor 13 on the same surface of the support substrate 11, the support substrate 11 as in the first and second embodiments. This is suitable when the entire thickness is thinner than the configuration having the reference sensor 13 on the back surface, and the back surface of the support substrate 11 may not be used depending on the mounting position.

As described above, the present invention has the following advantages.
(1) Since the liquid level is detected by the capacitance ratio of the main sensor 12 and the reference sensor 13, it is not affected by the dielectric constant of the liquid. Therefore, stable liquid level detection is possible even for liquids having different dielectric constants or external factors related to capacitance changes such as temperature and deterioration.
(2) Compared to the conventional example of FIG. 13, the area of the opposing electrodes can be substantially increased, and the amount of change in capacitance with respect to the liquid level can be increased. Suitable for liquid level detection.
(3) Since the change amount of the electrostatic capacitance with respect to the liquid level is large, the slight influence of the capacitance detection value due to the sensor deterioration or the individual difference of the sensor can be ignored.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various deformation | transformation and application are possible.

  For example, in the above-described first embodiment, the plurality of dielectric pieces are arranged so as to generate a gap between them, but instead, the same plate-like dielectric as the electrode has the same gap as the gap. Alternatively, the groove may be formed.

  Further, in the above-described embodiment, the gap width is configured to change linearly, but instead, it may be configured to change in a curved manner.

1 shows a first embodiment of a capacitive liquid level sensor according to the present invention, in which (A) is a perspective view, (B) is a perspective view of a main sensor, and (C) is a perspective view of a reference sensor. FIG. (First embodiment) FIG. 2 is a characteristic diagram showing a relationship of output voltages corresponding to the capacitances of the main sensor and the reference sensor with respect to the liquid level in the capacitance type liquid level sensor of FIG. 1. (First embodiment) It is a figure which shows the structural example of the liquid level detection circuit using the electrostatic capacitance type liquid level sensor of FIG. (First embodiment) 6 is a flowchart for explaining the operation of the liquid level detection circuit of FIG. (First embodiment) It is a figure for demonstrating the example of a setting of the space | gap in the electrostatic capacitance type liquid level sensor of FIG. (First embodiment) (A) And (B) is a figure for demonstrating the variation | change_quantity of the electrostatic capacitance corresponding to the example of a setting of the space | gap of FIG. 5, respectively. (First embodiment) It is a figure for demonstrating calculation of the electrostatic capacitance in the electrostatic capacitance type liquid level sensor of FIG. (First embodiment) It is a figure for demonstrating calculation of the electrostatic capacitance in the electrostatic capacitance type liquid level sensor of FIG. (First embodiment) 2nd Embodiment of the electrostatic capacitance type liquid level sensor which concerns on this invention is shown, (A) is a perspective view of the front side, (B) is a perspective view of the back side. (Second Embodiment) FIG. 10 is a characteristic diagram showing the relationship of the output voltage corresponding to the capacitance of the main sensor and the reference sensor with respect to the liquid level in the capacitance type liquid level sensor of FIG. 9. (Second Embodiment) It is a figure for demonstrating the derivation | leading-out example of the electrostatic capacitance of the main sensor and the reference sensor in the electrostatic capacitance type liquid level sensor of FIG. 9, and these ratios. (Second Embodiment) It is a perspective view which shows 3rd Embodiment of the electrostatic capacitance type liquid level sensor which concerns on this invention. (Third embodiment) It is a perspective view which shows the structural example of the conventional electrostatic capacitance type liquid level sensor.

Explanation of symbols

10 Capacitance type level sensor 11 Support substrate 12 Main sensor (first sensor element)
121 signal electrodes 122 dielectric 122 ₁ to 122 _n dielectric piece 123 ground electrode 124 ₁ to 124 _n void 13 Reference sensor (second sensor element)
131 Signal electrode 132 Dielectric body 132 _{1 to} 132 _n Dielectric piece 133 Ground electrode 134 _{1 to} 134 _n Air gap

Claims (7)

A capacitance type liquid level sensor that detects a liquid level by a capacitance,
Each has an electrostatic capacity that changes in accordance with the liquid level, and the ratio of the electrostatic capacity includes first and second sensor elements that change in accordance with the liquid level. Capacitance type liquid level sensor. The capacitance type liquid level sensor according to claim 1,
Each of the first and second sensor elements increases at different rates corresponding to the liquid level, and has a capacitance that matches the maximum detectable liquid level. Capacitive liquid level sensor. The capacitance type liquid level sensor according to claim 2,
The capacitive liquid level sensor includes a support substrate, the first sensor element disposed on one surface of the support substrate, and the second sensor disposed on the other surface of the support substrate. Having an element,
The first and second sensor elements are gradually formed in a direction from one end of the sensor longitudinal direction to the other end between the signal electrode and the ground electrode formed in a flat plate shape, and the electrode plates of the signal electrode and the ground electrode, respectively. It has a laminated structure composed of dielectrics arranged so as to generate gaps whose width becomes narrower,
The capacitance type liquid level sensor, wherein the gap of the second sensor element is gradually narrowed in a direction opposite to the gap of the first sensor element. The capacitive liquid level sensor according to claim 3,
The dielectric is arranged such that a plurality of gaps having a constant width across the width of the sensor having an angle other than 90 ° with respect to the sensor longitudinal direction are generated at intervals.
The capacitance type liquid level sensor, wherein the plurality of gaps are set so that a constant width thereof gradually decreases in a direction from one end to the other end in the sensor longitudinal direction. The capacitive liquid level sensor according to claim 3,
The capacitance type liquid level sensor, wherein the dielectric is disposed so as to generate a gap that gradually decreases in width so as to draw a diagonal line from one end to the other end in the sensor longitudinal direction. The capacitance type liquid level sensor according to any one of claims 1 to 5,
The capacitance type liquid level sensor, wherein the first and second sensor elements are respectively disposed on the front and back sides of a support substrate. The capacitance type liquid level sensor according to any one of claims 1 to 5,
The capacitance type liquid level sensor, wherein the first and second sensor elements are respectively disposed on the same surface of the support substrate.

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