JP5685483B2 - Capacitive liquid level detector - Google Patents

Description

  The present invention relates to a capacitance type liquid level detection device.

  Conventionally, a capacitance type liquid level detection device that detects a liquid level based on a change in capacitance has been proposed. This apparatus includes a cylindrical first electrode and a cylindrical second electrode disposed in the cylinder of the first electrode. And this apparatus can detect a liquid level, since the amount of the liquid filled between both electrodes changes and a dielectric constant also changes by a liquid level changing (for example, refer patent document 1).

  As another electrostatic capacitance type liquid level detection device, a float having a through hole in the center, a long float shaft that penetrates the through hole of the float, and an electrode attached on the float shaft are provided. I have. This device includes an electrode inside the float through hole. Further, the electrode width of the electrode attached on the float axis changes along the float axis. For this reason, this apparatus can detect a liquid level, when the electrostatic capacitance between electrodes changes with respect to the change of a liquid level (for example, refer patent document 2).

JP 2008-26166 A Japanese Patent Application Laid-Open No. 11-281459

  Here, in the capacitance type liquid level detection device described in Patent Document 1, it is necessary to reduce the distance between both electrodes in order to increase the liquid level detection accuracy. However, when the distance between the electrodes is reduced, the liquid enters between the electrodes due to capillary action or the surface tension of the liquid, so that an appropriate liquid level cannot be detected.

  Moreover, in the electrostatic capacitance type liquid level detection device described in Patent Document 2, a liquid exists between an electrode attached on the float shaft and an electrode provided inside the float through-hole. The liquid level detection accuracy decreases due to the dielectric constant. Furthermore, the capacitance-type liquid level detection device described in Patent Document 2 must be provided with a temperature sensor or the like in order to perform temperature correction, and the configuration becomes complicated.

  The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to improve the liquid level detection accuracy by permitting dielectric constant correction and temperature correction, and having a configuration. An object of the present invention is to provide a capacitance type liquid level detection device capable of suppressing complication.

  The capacitance type liquid level detection device of the present invention is a capacitance type liquid level detection device that detects a liquid level based on a change in capacitance, and is displaced in accordance with the change in the liquid level and has a metal electrode. And 4 electrodes extending in the direction of change of the liquid level around the metal float, and an intervening member having dielectric properties interposed between the metal float and the 4 electrodes. The two electrodes have the same shape, and two of the four electrodes that are paired have a width that is wider at a constant rate with respect to the increasing direction of the liquid level. The other two electrodes of the pair are characterized in that the width of the electrodes is narrowed at a constant rate with respect to the increasing direction of the liquid level.

  According to this capacitance type liquid level detection device, the four electrodes have the same shape, and the two electrodes of the four electrodes are in a constant ratio with respect to the increasing direction of the liquid level. The width of the electrode is widened, and the other two electrodes in pairs among the four electrodes have a width of the electrode narrowed at a constant rate with respect to the increasing direction of the liquid level. For this reason, even when the temperature changes, the capacitance output based on the two electrodes and the capacitance output based on the other two electrodes change in the same manner, and the difference between the two is the same. The temperature characteristics are canceled by taking. Further, since the temperature characteristic is canceled, it is not necessary to separately provide a temperature sensor, and the configuration can be prevented from becoming complicated.

  Furthermore, when the liquid level rises, the capacitance of the two electrodes increases at a constant rate, and the capacitance of the other two electrodes decreases at a constant rate. In addition, since the four electrodes have the same shape, the increase and the decrease correspond to each other. Therefore, the average of the electrostatic capacity output based on the two electrodes and the electrostatic capacity output based on the other two electrodes is a constant value in consideration of the dielectric constant regardless of the liquid level. Thereby, the dielectric constant becomes clear and the dielectric constant can be corrected.

  Accordingly, the dielectric constant correction and the temperature correction can be performed to improve the liquid level detection accuracy, and the configuration can be prevented from becoming complicated.

  In the capacitance type liquid level detection device of the present invention, the interposition member is a cylinder extending in the direction of change of the liquid level, and the metal float is circular when viewed from the direction of change of the liquid level, The four electrodes are preferably provided in contact with the cylindrical outer wall.

  According to this capacitance type liquid level detection device, the interposition member is a cylinder extending in the direction of change of the liquid level, and the metal float is circular when viewed from the direction of change of the liquid level, and is disposed in the cylinder. The four electrodes are provided in contact with the cylindrical outer wall. For this reason, the metal float is guided by the cylinder, and the four electrodes are provided in contact with the outer wall of the cylinder, so that the positional relationship between the metal float and the four electrodes can be easily maintained. Can do. In addition, if a small hole is provided in the cylinder in order to allow liquid to enter the inside of the cylinder, the entry and exit of the liquid between the inside and outside of the cylinder will be restricted, and the liquid entering the inside of the cylinder will be in a semi-sealed state. be able to. Thereby, the swaying of the liquid level in the cylinder due to the vibration of the vehicle can be suppressed.

  According to the present invention, it is possible to provide a capacitance type liquid level detection device capable of performing dielectric constant correction and temperature correction to improve the liquid level detection accuracy and suppress the complication of the configuration. .

It is a partially broken figure of the electrostatic capacitance type liquid level detection apparatus which concerns on embodiment of this invention. It is sectional drawing of the metal float shown in FIG. 1, four electrodes, and an interposed member. FIG. 2 is a development view of four electrodes shown in FIG. 1. It is the schematic which shows the electrostatic capacitance of a metal float and four electrodes. It is the schematic which shows the electrostatic capacitance of two electrodes used as a metal float and a pair, and the electrostatic capacitance of two electrodes used as a metal float and another pair. It is the schematic which shows the difference of an electrostatic capacitance. It is the schematic which shows the average of an electrostatic capacitance.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is a partially broken view of a capacitive liquid level detection device according to an embodiment of the present invention. As shown in FIG. 1, the capacitance type liquid level detection device 1 detects the liquid level in a tank 10 containing a liquid (including liquefied gas) F based on the capacitance. 10, a metal float 20, four electrodes 30 a to 30 d, an interposition member 40, a detection circuit 50, and a flange 60.

  The tank 10 stores the liquid F therein. The tank 10 is made of, for example, a resin or a metal member. Examples of the metal member include iron, aluminum, and stainless steel.

  The metal float 20 is displaced up and down according to a change in the liquid level in the tank 10 and is formed in a hollow cylindrical shape. The metal float 20 is made entirely of metal to form a metal electrode. The metal float 20 may be formed of a metal only on the surface thereof to form a metal electrode, or the surface may be formed of a resin and only the center part may be formed of a metal to form a metal electrode. The metal electrode may be formed with a three-layer structure, such as a circular metal inside and a resin inside the circular metal.

  The four electrodes 30 a to 30 d are metal members that extend in the direction in which the liquid level changes around the metal float 20. The interposition member 40 is a member having a dielectric property interposed between the metal float 20 and the four electrodes 30 and is a member that extends in the direction in which the liquid level changes. These configurations will be described with reference to FIGS.

  FIG. 2 is a cross-sectional view of the metal float 20, the four electrodes 30 a to 30 d, and the interposition member 40 shown in FIG. 1. As described above, the metal float 20 has a cylindrical shape. For this reason, as shown in FIG. 2, the metal float 20 has a circular shape as seen from the direction of change of the liquid level. Further, the interposition member 40 is a cylinder, and the metal float 20 is disposed in the cylinder. For this reason, the metal float 20 is guided by the cylinder. The interposition member 40 has a liquid intrusion opening formed at the lower end surface and the lower end side surface so that the liquid F enters the cylinder, and an air vent opening formed at the upper end surface and the upper end side surface. .

  The four electrodes 30a to 30d are attached to the outer wall of the interposed member 40, that is, the cylindrical outer wall. Moreover, since the metal float 20 is guided by the cylinder, the positional relationship between the metal float 20 and the four electrodes 30a to 30d is difficult to change. The four electrodes 30a to 30d may not be attached to the interposition member 40, and metal plating may be applied to the interposition member 40 or a film may be formed by sputtering. That is, the four electrodes 30a to 30d only need to be provided in contact with each other on the interposed member 40.

  FIG. 3 is a development view of the four electrodes 30a to 30d shown in FIG. As shown in FIG. 3, the four electrodes 30a to 30d have, for example, a trapezoidal shape, and each has the same shape. Among these, the first and third electrodes 30a and 30c are paired, and the widths of the electrodes 30a and 30c are increased at a constant rate with respect to the increasing direction of the liquid level. On the other hand, the second and fourth electrodes 30b and 30d are paired, and the widths of the electrodes 30b and 30d are narrowed at a constant rate with respect to the increasing direction of the liquid level.

  Reference is again made to FIG. The detection circuit 50 detects the liquid level based on the capacitance generated between the metal float 20 and the four electrodes 30a to 30d. The flange 60 is a member that integrally connects the interposition member 40 and the detection circuit 50. Further, the flange 60 is disposed so as to close the opening R of the tank 10.

  FIG. 4 is a schematic diagram showing the capacitance of the metal float 20 and the four electrodes 30a to 30d. The electrostatic capacitance between the metal float 20 and the first and third electrodes 30a and 30c, and the electrostatic capacitance between the metal float 20 and the second and fourth electrodes 30b and 30d are as shown in FIG.

  That is, the capacitance between the metal float 20 and the first electrode 30a is Ca, the capacitance between the metal float 20 and the second electrode 30b is Cb, and the capacitance between the metal float 20 and the third electrode 30c is Let Cc be the electrostatic capacitance between the metal float 20 and the fourth electrode 30d. In this case, the capacitance Cac between the first electrode 30a and the third electrode 30c is Cac = 1 / (1 / Ca + 1 / Cc). Further, the electrostatic capacitance Cbd between the second electrode 30b and the fourth electrode 30d is Cbd = 1 / (1 / Cb + 1 / Cd).

  Next, an outline of liquid level detection by the capacitive liquid level detection device 1 according to the present embodiment will be described. FIG. 5 shows the capacitance of the two electrodes 30a and 30c paired with the metal float 20, and the capacitance of the metal float 20 and the two pairs of electrodes 30b and 30d. FIG.

  As shown in FIGS. 1 and 3, the first and third electrodes 30a and 30c have the width of the electrodes 30a and 30c increased at a constant rate with respect to the increasing direction of the liquid level. In the electrodes 30b and 30d, the widths of the electrodes 30b and 30d are narrowed at a constant rate with respect to the increasing direction of the liquid level. For this reason, the electrostatic capacitance Cac increases monotonously as the liquid level increases, and the electrostatic capacitance Cbd decreases monotonously as the liquid level increases.

  FIG. 6 is a schematic diagram showing the difference in capacitance. As described above, the capacitance Cac monotonously increases as the liquid level increases, and the capacitance Cbd monotonously decreases as the liquid level increases. For this reason, by taking the difference (Cac−Cbd) between the two, the capacitance increases monotonously with the increase in the liquid level as shown in FIG. The detection circuit 50 shown in FIG. 1 detects the liquid level from the capacitance that monotonously increases as shown in FIG. That is, the detection circuit 50 stores data indicating the relationship between the liquid level and the capacitance as shown in FIG. 6, for example, and detects the liquid level based on the obtained difference.

  Next, the operation of the capacitive liquid level detection device 1 according to this embodiment will be described. For example, it is assumed that the tank 10 is filled up to an arbitrary liquid level (for example, the position shown in FIG. 1) from the state where the liquid F is not contained in the tank 10. In this case, the liquid F enters the inside of the interposition member 40 through the opening of the interposition member 40, and the metal float 20 is displaced according to the liquid level.

  The detection circuit 50 detects the capacitance in the state as described above. And the detection circuit 50 will take the difference (Cac-Cbd) of the detected electrostatic capacitance, and will detect a liquid level based on the data memorize | stored beforehand. Note that since the detection circuit 50 takes the difference in capacitance, even if the temperature changes, both capacitances change in the same way, so that the temperature characteristic can be canceled.

  Further, from the relationship between the shape and arrangement of the four electrodes 30a to 30d, as shown in FIG. 5, the increase in the capacitance of the first and third electrodes 30a and 30c, the second and fourth electrodes 30b, The amount of decrease in the capacitance of 30d matches. For this reason, the average of both electrostatic capacitances becomes a constant value.

  FIG. 7 is a schematic diagram showing an average of capacitance. As shown in FIG. 7, the average capacitance ((Cac + Cbd) / 2) is a constant value regardless of the liquid level. This constant value depends on the dielectric constant of the liquid F, and is different when liquids F having different dielectric constants are accommodated in the tank 10. As shown in FIG. 7, the detection circuit 50 can obtain the dielectric constant by taking the average of the capacitance, and can perform the dielectric constant correction.

  Thus, according to the capacitive liquid level detection device 1 according to the present embodiment, the four electrodes 30a to 30d have the same shape, and two of the four electrodes 30a to 30d are paired. The electrodes 30a and 30c are widened at a constant rate with respect to the increasing direction of the liquid level, and the other two electrodes 30b and 30d that are paired out of the four electrodes 30a to 30d are The width of the electrode is reduced at a constant rate with respect to the increasing direction of the liquid level. For this reason, even when a temperature change occurs, the capacitance output based on the two electrodes 30a and 30c and the capacitance output based on the other two electrodes 30b and 30d change in the same manner. Therefore, temperature correction is possible by taking the difference between the two. Further, since temperature correction is possible, it is not necessary to separately provide a temperature sensor, and the configuration can be prevented from becoming complicated.

  Furthermore, when the liquid level rises, the capacitances of the two electrodes 30a and 30c increase at a constant rate, and the capacitances of the other two electrodes 30b and 30d decrease at a constant rate. In addition, since the four electrodes 30a to 30d have the same shape, the increase and the decrease correspond to each other. Therefore, the average of the capacitance output based on the two electrodes 30a and 30c and the capacitance output based on the other two electrodes 30b and 30d is a constant value that takes into account the dielectric constant regardless of the liquid level. . Thereby, the dielectric constant becomes clear and the dielectric constant can be corrected.

  Accordingly, the dielectric constant correction and the temperature correction can be performed to improve the liquid level detection accuracy, and the configuration can be prevented from becoming complicated.

  Further, the interposition member 40 is a cylinder extending in the change direction of the liquid level, and the metal float 20 is circular when viewed from the change direction of the liquid level, and is disposed in the cylinder, and the four electrodes 30a to 30d. Is provided in contact with the cylindrical outer wall. For this reason, the metal float 20 is guided by the cylinder, and the four electrodes 30a to 30d are provided in contact with the cylindrical outer wall, so that the metal float 20 and the four electrodes 30a to 30d are in contact with each other. The positional relationship can be easily maintained.

  As shown in FIG. 2, the metal float 20 is disposed inside a cylindrical interposed member 40. Therefore, by designing the metal float 20 as close as possible to the interposition member 40, the amount of the liquid F that enters the gap between the metal float 20 and the interposition member 40 can be reduced, and capillary action and surface tension can be reduced. Thus, even if the liquid F enters between the metal float 20 and the interposition member 40, it can be made less susceptible to influence.

  In addition, in the liquid level detection device described in Patent Document 2, high accuracy is required for the float shaft and the float, which increases the manufacturing cost. However, this embodiment is advantageous in terms of cost. That is, in this embodiment, even if the size of the metal float 20 and the size of the interposition member 40 are slightly different, only the size of the capacitance is slightly changed, and the difference or average is not affected. Therefore, the manufacturing cost can be suppressed.

  In particular, in the present embodiment, the gap between the metal float 20 and the interposition member 40 becomes large due to the influence of the dimensional error, and even if the metal float 20 moves in the lateral direction (direction perpendicular to the liquid level change direction) Not affected. For example, as shown in FIG. 4, it is assumed that the metal float 20 has moved in the direction of the first electrode 30a. In this case, the capacitance Ca is increased, but the capacitance Cc is decreased and balanced, and the change in the capacitance Cac is suppressed. Therefore, even if the metal float 20 moves in the lateral direction, there is no problem in the liquid level detection accuracy, and the metal float 20 and the interposition member 40 are not required to have strict dimensions, so that the manufacturing cost can be suppressed.

  As described above, the present invention has been described based on the embodiment, but the present invention is not limited to the above embodiment, and may be modified without departing from the gist of the present invention.

  For example, the capacitance type liquid level detection device 1 according to the present embodiment has the metal float 20 that is displaced according to the liquid level at the center of the tank 10, but is not limited to this, and is provided on the tank wall side. You may do it. Furthermore, although the interposition member 40 is a cylinder extending in the liquid level change direction, the present invention is not limited to this and may be a cylinder, or may extend in a direction slightly inclined with respect to the liquid level change direction.

  In the present embodiment, the four electrodes 30a to 30d have a trapezoidal shape, but the shape is not limited to this and may be other shapes such as a right triangle. In addition, in this embodiment, it is only necessary to have four electrodes 30a to 30d, and other electrodes may be additionally provided. That is, it is only necessary to include at least four electrodes 30a to 30d.

  Moreover, although the metal float 20 which concerns on this embodiment is a column shape, not only this but a spherical shape may be sufficient. When the metal float 20 has a cylindrical shape, the distance between the upper and lower portions of the cylinder and the four electrodes 30a to 30d is equal, and the opposing area between the metal float 20 and the four electrodes 30a to 30d is large and short. Since they can be arranged at a distance, it is advantageous in terms of liquid level detection accuracy. On the other hand, when the metal float 20 has a spherical shape, it is advantageous when used in a high-pressure liquefied gas tank because of its excellent pressure resistance.

DESCRIPTION OF SYMBOLS 1 ... Capacitance type liquid level detection apparatus 10 ... Tank 20 ... Metal float 30a-30d ... Electrode 40 ... Interposition member 50 ... Detection circuit 60 ... Flange

Claims (2)

A capacitance type liquid level detection device that detects a liquid level based on a change in capacitance,
A metal float that displaces according to the change in liquid level and has a metal electrode;
Four electrodes extending in the direction of change in liquid level around the metal float;
A dielectric intervening member interposed between the metal float and the four electrodes,
The four electrodes have the same shape,
Of the four electrodes, the two electrodes paired with each other have a wide width at a constant rate with respect to the increasing direction of the liquid level,
The other two electrodes paired out of the four electrodes have an electrode width narrowed at a constant rate with respect to the increasing direction of the liquid level. . The interposition member is a cylinder extending in the direction of change of the liquid level,
The metal float is circular when viewed from the direction of change of the liquid level, and is disposed in the cylinder.
The capacitance type liquid level detection device according to claim 1, wherein the four electrodes are provided in contact with the cylindrical outer wall.

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