JP5923350B2 - Liquid level detector - Google Patents

Description

  The present invention relates to a sensor unit that outputs a change in capacitance according to a liquid level of a container, and a liquid level detection device that detects a liquid level based on an output result of the sensor.

  In the conventional capacitive liquid level sensor, in order to accurately measure the liquid level (liquid level) corresponding to various liquids, an electrode (liquid level sensor) for measuring the liquid level, A dielectric constant correction electrode (dielectric constant correction sensor) for measuring the dielectric constant change of the liquid is provided, and it is necessary to always monitor the dielectric constant change of the liquid and correct the liquid level.

  The dielectric constant correction sensor is generally installed at the bottom of a container containing a liquid to be measured, and the capacitance of the dielectric constant correction electrode is prevented from changing due to a change in liquid level by using, for example, a shield structure (for example, a patent) Reference 1).

JP 2005-181165 A

  In the liquid level detection device using the above-described conventional capacitive liquid level sensor, in order to perform the dielectric constant correction, the characteristics of the liquid level sensor and the dielectric constant correction sensor are measured in advance, and the characteristics are measured. There has been a problem that it is necessary to store in an arithmetic control circuit or the like that detects the liquid level of a microcomputer or the like. In particular, since there is an individual difference (error) in each sensor electrode, it is necessary to write characteristics for each sensor, which is troublesome.

  In addition, there is a problem in that the liquid level correction is shifted due to the dimensional error of the electrodes constituting the dielectric constant correction sensor.

  Therefore, an object of the present invention is to provide a liquid level detecting device that does not require measurement of sensor characteristics in advance and can easily detect a liquid level without being affected by the dielectric constant.

The invention according to claim 1, which has been made in order to solve the above problem, is a sensor that is arranged in a container and measures a capacitance between electrodes, and is based on a change in capacitance measured by the sensor. Detecting means for detecting a liquid level in the container , wherein the plurality of sensors are arranged in the vertical direction of the container, and the plurality of sensors are the plurality of sensor electrodes. Are arranged in a straight line, and the plurality of sensor electrodes and the one ground electrode are overlapped with the first substrate and the first substrate arranged at a predetermined interval from each other. And a second substrate in which a second ground electrode different from the one ground electrode is provided on the entire surface on the side that does not overlap the first substrate, and the first substrate and the So as to be sandwiched between second substrates Wherein the plurality of sensor electrodes, wherein one of the ground electrode and the second ground electrode, each wiring layer to terminals electrically connected for connecting with outside is provided, said detecting means, for a plurality of said sensors each And measuring the liquid level in the container based on the capacitance measured by the other sensors with reference to the capacitance of the sensor disposed at the lowermost end. This is a liquid level detecting device.

  According to a second aspect of the present invention, in the first aspect of the present invention, the liquid level is positioned depending on whether or not the detection means matches the capacitance of the sensor disposed at the lowermost end. Identifying the sensor, and detecting a liquid level in the identified sensor based on a ratio between a capacitance of the identified sensor and a capacitance of the sensor disposed at the lowest end. It is a feature.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the detection unit is exposed from the liquid surface based on a result of measuring the capacitance of each of the plurality of sensors. An exposure specifying means for specifying the sensor, a capacitance of the sensor specified by the exposure specifying means, a capacitance of the sensor specified by the detecting means that the liquid level is positioned, and a lowermost end. And correcting means for detecting the liquid surface level by correcting the electrostatic capacity due to condensation based on the electrostatic capacity of the sensor arranged.

As described above, according to the first aspect of the present invention, the sensor unit includes a plurality of sensors arranged side by side in the vertical direction of the container, and the detection unit measures the capacitance for each of the plurality of sensors. The level of the liquid in the container is detected based on the capacitance measured by the other sensors on the basis of the capacitance of the sensor arranged at the bottom end. By sequentially comparing the capacitances as a reference, it is possible to detect the position of the liquid level among a plurality of sensors arranged in the vertical direction in the container, and the sensor in which the liquid level is positioned It is possible to detect an accurate liquid level from the electrostatic capacity. Therefore, it is not necessary to measure the sensor characteristics in advance, and the liquid level can be easily detected without being affected by the dielectric constant. The plurality of sensors are configured by providing a plurality of sensor electrodes and one ground electrode on the same substrate, and the plurality of sensor electrodes are arranged in a straight line on the substrate. In addition, since the plurality of sensor electrodes and one ground electrode are arranged at a certain distance from each other, a plurality of sensors can be arranged side by side on the same substrate, and can be easily installed in a container. Become. Further, the sensor unit has a first substrate having a plurality of sensor electrodes and one ground electrode provided on the surface thereof, and is superposed on the first substrate and has a surface on a side not overlapping the first substrate. A second substrate having a second ground electrode different from one ground electrode on the entire surface, and a plurality of sensor electrodes and one ground electrode so as to be sandwiched between the first substrate and the second substrate. And a wiring layer for electrically connecting each of the second ground electrodes to a terminal for connecting to the outside, each sensor electrode detects a capacitance on the first substrate, and the detected capacitance Can be output to the outside through the wiring layer. Since the wiring layer is shielded by the first substrate and the ground electrode of the third substrate, the change in the wiring capacitance due to the change in the liquid level can be prevented.

  According to the second aspect of the present invention, the detection unit specifies the sensor on which the liquid level is located according to whether or not the detection unit matches the capacitance of the sensor arranged at the lowermost end, and the specified sensor Since the liquid level in the specified sensor is detected based on the ratio of the capacitance of the sensor and the capacitance of the sensor disposed at the lowermost end, the liquid level is determined based on the sensor disposed at the lowermost end. By specifying the surface position, the liquid level can be detected.

  According to the third aspect of the present invention, the exposure means for identifying the sensor exposed from the liquid surface based on the result of the capacitance measured by each of the plurality of sensors, and the exposure Due to condensation based on the capacitance of the sensor specified by the specifying means, the capacitance of the sensor specified as the liquid level is positioned by the detecting means, and the capacitance of the sensor arranged at the lowest end Correction means for correcting the capacitance and detecting the liquid level, so that the correction due to condensation can be calculated from the capacitance of the sensor that is completely exposed from the liquid level. The detection accuracy can be increased by reducing the influence of the.

It is a block diagram of the liquid level detection apparatus concerning one Embodiment of this invention. It is a block diagram of the sensor electrode part shown by FIG. It is sectional drawing which follows the II line | wire of FIG. 3 is a flowchart showing a liquid level detection operation of the liquid level detection device shown in FIG. 1. 5 is a flowchart showing an operation of liquid level calculation shown in FIG. It is a figure of the sensor electrode part for operation | movement description of the flowchart of FIG. 4 and FIG. It is the graph which showed the specific example of the liquid level detection operation. It is the graph which showed the specific example of the liquid level detection operation in consideration of dew condensation.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of a liquid level detecting device 1 according to an embodiment of the present invention. FIG. 2 is a block diagram of the sensor electrode unit shown in FIG. FIG. 3 is a cross-sectional view taken along the line II of FIG. As shown in FIGS. 1 to 3, the liquid level detection device 1 includes a sensor electrode unit 2 and a sensor measurement unit 3.

  The sensor electrode unit 2 includes eight sensors 2a to 2h arranged in the vertical direction in the drawing, and the vertical direction is a vertical direction in the container. That is, when the sensor electrode unit 2 is installed in the container, the sensor 2a is on the lowermost end (bottom) side of the container, and the sensor 2h is on the uppermost end side of the container. Although the present embodiment will be described with eight sensors, the number of sensors is not limited to this, and the number of sensors may be determined as appropriate according to the size of the container to be installed, detection accuracy, and the like.

  As shown in FIG. 2 and FIG. 3, the sensor electrode unit 2 has three layers in which three conductor layers each including a substrate 4 as a first substrate and a substrate 5 as a second substrate are formed. It consists of a printed circuit board.

  The board | substrate 4 is formed in a substantially rectangular shape, and the electrodes 4a-4i and the terminal 4j are formed. The electrodes 4a to 4h as the plurality of sensor electrodes are formed in an isosceles triangle shape, and the electrodes 4a, 4b, 4c, 4d, 4e, 4f, 4g, and 4h are formed along one side in the longitudinal direction of the substrate 4. They are arranged in a straight line. That is, the electrodes 4a to 4h do not have to be arranged so that the sides face each other as long as they are arranged linearly along the reference line. That is, the sensor electrode unit 2 is installed so that the longitudinal direction of the substrate 4 is the vertical direction of the container. Of course, the electrodes 4a to 4h are not in contact with each other and are spaced apart from each other.

  The electrode 4i as one ground electrode is formed on a portion other than the electrodes 4a to 4h of the substrate 4 formed thereon. The electrode 4i is arranged so as to leave a certain distance (a in FIG. 2) from the inclined surface portion of the electrodes 4a to 4h without contacting the electrodes 4a to 4h.

  The terminal 4j has terminals 4j1 to 4j9 formed at one end in the longitudinal direction of the substrate 4 and functions as an output terminal and a ground terminal for measurement values from each sensor. The terminal 4j is electrically connected to wirings 5a to 5i described later through through holes. Note that the terminals 4j are not in contact with each other and with the electrodes 4a to 4i on the same plane of the substrate 4.

  The substrate 5 is formed in a substantially rectangular shape that is the same shape as the substrate 4, and wirings 5 a to 5 i are formed on one surface (hereinafter referred to as the front surface) 51, and the other surface (hereinafter referred to as the back surface in the following description). An electrode 5k is formed at 52.

  Wirings 5a to 5h as wiring layers extend at the same length from one end portion in the longitudinal direction of the substrate 5 to the other end portion with a space therebetween. With this configuration, even if a slight change occurs in the wiring capacity, all the wiring capacity can be canceled. The wiring 5i is shorter than the other wirings 5a to 5h. However, since the wiring 5i is a wiring for the ground electrode, it may be long enough to connect the terminal and the ground electrode. In addition, although the wiring 5i is arrange | positioned away from the other wirings 5a-5h, you may arrange | position not only that but the space | interval similar to the wiring 5a-5h.

  Each of the wirings 5a to 5i has a through hole 5j formed at two locations on the wiring, and electrically connects a corresponding electrode on the substrate 4 and the terminal 4j through the through hole 5j. That is, the wiring 5a electrically connects the electrode 4a and the terminal 4j1, the wiring 5b electrically connects the electrode 4b and the terminal 4j2, the wiring 5c electrically connects the electrode 4c and the terminal 4j3, The wiring 5d electrically connects the electrode 4d and the terminal 4j4, the wiring 5e electrically connects the electrode 4e and the terminal 4j5, the wiring 5f electrically connects the electrode 4f and the terminal 4j6, and the wiring 5g. Electrically connects the electrode 4g and the terminal 4j7, the wiring 5h electrically connects the electrode 4h and the terminal 4j8, and the wiring 5i electrically connects the electrode 4i and the electrode 5k to the terminal 4j9. .

  The electrode 5k as the second ground electrode is formed on the entire back surface 52 of the substrate 5 and is electrically connected to the terminal 4j9 through the through hole and the wiring 5i as described above.

  As shown in FIG. 3, the substrate 4 and the substrate 5 constitute a three-layer printed circuit board so that the substrate 4 is superposed on the surface 51 side of the substrate 5. Therefore, the electrodes 4 a to 4 i are formed on one side of the sensor electrode unit 2, and the electrode 5 k is formed on the other side of the sensor electrode unit 2. The surface on which the electrodes 4a to 4i are formed is coated with an insulating material 4k so that even a conductive liquid can be measured as shown in FIG.

  In the sensor electrode unit 2 configured as described above, the electrodes 4a to 4h function as a plurality of sensor electrodes, and the electrode 4i functions as one ground electrode. That is, the electrode 4a and the electrode 4i are the sensor 2a of FIG. 1, and the terminal 4j1 is connected to the sensor measurement unit 3 as an output of the sensor 2a. The electrode 4b and the electrode 4i are the sensor 2b of FIG. 1, and the terminal 4j2 is connected to the sensor measurement unit 3 as an output of the sensor 2b. The electrode 4c and the electrode 4i are the sensor 2c of FIG. 1, and the terminal 4j3 is connected to the sensor measurement unit 3 as an output of the sensor 2c. The electrode 4d and the electrode 4i are the sensor 2d of FIG. 1, and the terminal 4j4 is connected to the sensor measurement unit 3 as an output of the sensor 2d. The electrode 4e and the electrode 4i are the sensor 2e of FIG. 1, and the terminal 4j5 is connected to the sensor measurement unit 3 as an output of the sensor 2e. The electrode 4f and the electrode 4i are the sensor 2f of FIG. 1, and the terminal 4j6 is connected to the sensor measurement unit 3 as an output of the sensor 2f. The electrode 4g and the electrode 4i are the sensor 2g of FIG. 1, and the terminal 4j7 is connected to the sensor measurement unit 3 as an output of the sensor 2g. The electrode 4h and the electrode 4i are the sensor 2h in FIG. 1, and the terminal 4j8 is connected to the sensor measurement unit 3 as an output of the sensor 2h. A terminal 4j9 to which the electrode 4i is connected corresponds to a terminal for grounding each sensor in FIG.

  The wirings 5a to 5i may be formed not on the substrate 5, but on the surface on the back side of the surface on which the electrodes 4a to 4i of the substrate 4 are provided. In short, a plurality of sensor electrodes, one ground electrode and each of the second ground electrodes are electrically connected to terminals so as to be sandwiched between intermediate layers of the three-layer printed circuit board, that is, the first substrate and the second substrate. What is necessary is just to be able to comprise a wiring layer.

  The sensor measuring unit 3 serving as a detecting unit, an exposure specifying unit, and a correcting unit includes a signal switching circuit such as a multiplexer for switching each sensor and CV conversion for converting a capacitance value detected from the sensor into a voltage value or the like. An arithmetic control circuit such as a microcomputer for detecting a liquid level (liquid level) from the voltage value or frequency converted by the circuit, the CF conversion circuit, and the conversion circuit is provided.

  Next, the operation when measuring the liquid level in the liquid level detecting device 1 having the above-described configuration will be described with reference to the flowcharts of FIGS. The flowcharts shown in FIGS. 4 and 5 are executed by the microcomputer (arithmetic control circuit) of the sensor measurement unit 3.

In the description of the flowcharts of FIGS. 4 and 5, as shown in FIG. 6, the sensors 2 a to 2 h are described as sensors 1 to 8, and H is the liquid level in the entire sensor electrode unit 2 (the liquid level in the container). ), H is the liquid level per sensor, and C _n is the capacitance value of sensor n (n = 1 to 8).

  First, in step S101 in FIG. 4, the sensors 1 to 8 are measured and the process proceeds to step S102. In this step, the signal switching circuit is switched, and the sensors 1 to 8, that is, the electrodes 4a to 4h and the electrodes 4i are switched. The capacitance value of the capacitor formed between them is measured and converted into a voltage value by a CV conversion circuit or the like. Note that the order of measurement may be the order of sensors 1 to 8 or vice versa. Further, a plurality of CV conversion circuits and the like may be provided without the signal switching circuit, and measurement may be performed at a time. That is, the detection unit measures the capacitance for each of the plurality of sensors.

Next, in step S102, it is determined whether the amount of change from the initial value of the measured C ₁ value is the capacitance value of the sensor 1 at step S101 is 0, if it is 0 (YES ) Proceeds to step S103, and if not 0 (NO), the process proceeds to step S104. In step S103, the liquid level is set to 0 (H = 0) and the process returns to step S101. Since each sensor has an initial value such as a wiring capacity, when the amount of change from the initial value of the capacitance of the sensor 1 is 0, it can be determined that the sensor 1 is not in contact with the liquid. Since the sensor is arranged at the lowermost end of the container, it can be said that the liquid level is zero. Then, the liquid level information is output from the sensor measurement unit 3 to a display device (not shown) or the like, and for example, the liquid level is displayed.

Step In S104, the value of C ₁ is the capacitance value of the sensor 1 which has been measured is determined whether a C ₂ or higher is the capacitance value of the sensor 2 in step S101, in C ₂ or more If there (YES), the processing goes to step S106, (the case of nO) when not C ₂ or more, the process proceeds to step S105. In step S105, the liquid level is set to 0 (H = 0) and the process returns to step S101. In the case of this step, the capacitance (change amount) is not 0, but the capacitance of the sensor 2 is larger than that of the sensor 1, so that the liquid for measuring the liquid level is not touched to the sensor, but dew condensation occurs. The liquid level is regarded as 0 on the assumption that the liquid by is attached to the sensor. In step S104, had been compared to C _2, it may be compared with the average value of C ₂ -C _8. By doing so, it is possible to detect a state in which condensation has adhered more accurately.

In step S106, whether C ₂ is C ₁ and the capacitance value of the sensor 2 is the capacitance value of the sensor 1 is storing the value of C ₁ when it becomes the same value as the C ₁ reference value If NO in step S107, the flow advances to step S107. If not, the flow advances to step S109. In the present embodiment, as described later, the liquid level is detected based on the capacitance value of the sensor 1 located at the lowermost end. However, if the sensor 1 itself has a liquid level, there is no reference value as it is. Can not. Therefore, the capacitance value when the sensor 1 and the sensor 2 become the same value is stored as the reference value, and the value is detected as the C ₁ reference value. That is, if the sensor 1 and the sensor 2 have the same value, it can be said that the liquid level is completely immersed up to the sensor 2, so that the sensor 1 as the reference value (reference value) is completely immersed. It is possible to obtain the capacitance value in the state of being.

In step S107, it is determined whether or not the C ₁ reference value is the same value as the value of C ₁ that is the capacitance value of sensor 1 measured in step S101. In the case), the process proceeds to step S109, and if not the same value (in the case of NO), the process proceeds to step S108. In step S108, since the liquid level is determined to be on the sensor 1 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (1), and the process returns to step S101. The description of the flowchart in FIG. 5 will be described later.

In step S109, it is determined whether or not the value of C ₁ that is the capacitance value of sensor 1 measured in step S101 and the value of C ₂ that is the capacitance value of sensor 2 are the same. If it is a value (in the case of YES), the value of sensor 1 at this time is stored as a C ₁ reference value, and the process proceeds to step S111. If it is not the same value (in the case of NO), the process proceeds to step S110. In step S110, since the liquid level is determined to be on the sensor 2 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (2), and the process returns to step S101.

Here, the operation of calculating (detecting) the liquid level will be described along the flowchart shown in FIG. First, in step S201, the average value _Cave of the capacitance of the exposed electrode is calculated, and the process proceeds to step S202. In this step, the average value C _{ave of the} capacitance of the sensors n + 1 to 8 positioned higher (upper side) than the sensor n having the liquid level, that is, the electrode completely exposed from the liquid surface is shown as follows (1). It is calculated by the formula.

Next, in step S202, a condensation correction value C _calib is calculated, and the process proceeds to step S203. If there is adherence capacity due to condensation on the sensor n with liquid level, when the average value C _ave of the capacity of the exposed electrode adhesion capacity, the electrostatic capacitance C _n of sensor n that the liquid level, following (2 ) Expression.

Therefore, the following expression (3) is derived from the expression (2). In other words, the average value of the capacitance of the capacitance C _n capacitances C ₁ and an exposed electrode of the difference of the mean value C _ave of the capacitance of the exposed electrode sensor 1 from the sensor n in this step there is a liquid level The dew condensation correction value C _calib is calculated by the equation (3) divided by a value based on the ratio with C _ave . The dew condensation adhering to the sensor n having the liquid level is corrected by the equation (3). That is, the static due to condensation on the basis of the capacitance of the sensor identified to be exposed from the liquid surface, the capacitance C _n of sensor n that the liquid level, the capacitance C ₁ of the sensor 1, the The capacity is corrected.

Next, in step S203, the liquid level (H) is calculated and the process returns. In this step, the liquid level is calculated by the following equation (4) based on C ₁ which is the capacitance value of the sensor 1.

Equation (4) calculates the liquid level in the sensor with the liquid level by using the ratio of the capacitance value of the sensor with the liquid level as a reference based on the capacitance value C ₁ of the sensor 1, The liquid level for the sensor located on the lower side (lower side) of the sensor with the surface is added. That is, the liquid level in the container is detected based on the capacitance measured by the other sensors with reference to the capacitance of the sensor arranged at the lowermost end. Note that equation (4), when executed in step S108 is calculated by substituting the values of C ₁ to C ₁ reference value.

Returning to the flowchart of FIG. 4, in step S <b> 111, is the value of C ₂ that is the capacitance value of sensor 2 measured in step S <b> 101 and the value of C ₃ that is the capacitance value of sensor 3 equal? If it is the same value (in the case of YES), the process proceeds to step S113, and if it is not the same value (in the case of NO), the process proceeds to step S112. In step S112, since it is determined that the liquid level is on the sensor 3 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (3), and the process returns to step S101.

In step S113, the value of C ₄ is the capacitance value of C ₃ values and the sensor 4 is the capacitance value of the sensor 3 measured in step S101 it is determined whether the same value, the same If it is a value (in the case of YES), the process proceeds to step S115, and if it is not the same value (in the case of NO), the process proceeds to step S114. In step S114, since it is determined that the liquid level is on the sensor 4 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (4), and the process returns to step S101.

In step S115, it is determined whether or not the value of C ₄ that is the capacitance value of sensor 4 measured in step S101 and the value of C ₅ that is the capacitance value of sensor 5 are the same. If it is a value (in the case of YES), the process proceeds to step S117, and if it is not the same value (in the case of NO), the process proceeds to step S116. In step S116, since the liquid level is determined to be on the sensor 5 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (5), and the process returns to step S101.

In step S117, the and the value of C ₆ is the capacitance value of the values and the sensor 6 of the C ₅ is the capacitance value of the sensor 5, which is measured in step S101 it is determined whether the same value, the same If it is a value (in the case of YES), the process proceeds to step S119, and if it is not the same value (in the case of NO), the process proceeds to step S118. In step S118, since it is determined that the liquid level is on the sensor 6 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (6), and the process returns to step S101.

In step S119, it is determined whether or not the value and the same value of C ₇ is the capacitance value of the values and the sensor 7 of the C ₆ is the capacitance value of the sensor 6 measured in step S101, the same When it is a value (in the case of YES), it progresses to step S121, and when it is not the same value (in the case of NO), it progresses to step S120. In step S120, since it is determined from the determination result before this step that the liquid level is on the sensor 7, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (7), and the process returns to step S101.

In step S121, it is determined whether or not the value and the same value of C ₈ is the capacitance value of the values and the sensor 8 of the C ₇ is the capacitance value of the sensor 7 measured in step S101, the same If it is a value (in the case of YES), the process proceeds to step S123, and if it is not the same value (in the case of NO), the process proceeds to step S122. In step S122, since the liquid level is determined to be on the sensor 8 from the determination result before this step, the liquid level is calculated by the flowchart of FIG. 5 as liquid level calculation (8), and the process returns to step S101.

In step S123, since the value of C ₈ is the capacitance value of the values and the sensor 8 of the C ₇ is the capacitance value of the sensor 7 is determined to be the same value, until the sensor 1 to the sensor 8 And the liquid level is determined to be in the full state, and the process returns to step S101.

  In the flowchart of FIG. 4, steps S107, S109, S111, S113, S115, S117, S119, and S121 specify a sensor having a capacitance value smaller than that of the sensor 1, and substantially each of the plurality of sensors. The sensor exposed from the liquid surface is specified based on the result of measuring the capacitance.

  Here, a specific example of the above-described operation will be described with reference to FIGS.

  7 and 8 are graphs showing the capacitance detected for each sensor in the order in which the sensors are arranged. FIG. 7 shows a case where the liquid level is in the center of the sensor 3. In this case, since the liquid 1 is filled in the positions of the sensors 1 and 2, the electrostatic capacity becomes the same value, and the sensor 3 has a liquid surface near the center, so that the electrostatic capacity is half that of the sensor 1. Become. Therefore, when the capacitance of the sensor 1 is used as a reference, it can be seen that the sensor 2 is completely immersed in the liquid 1 because the sensor 2 has the same value, and the sensor 1 has the liquid 1 up to the center because it is half the value of the sensor 1. The liquid level of the liquid 1 can be detected because it is understood that the liquid 1 is immersed in the liquid. In the flowchart of FIG. 4, the process proceeds to steps S101, S102, S104, S106, (S107), S109, S111, and S112.

  In FIG. 7, even in the case of the liquid 2 having a dielectric constant different from that of the liquid 1, the liquid level can be detected in the same manner. In the present embodiment, since the liquid level is detected with reference to the sensor 1 arranged at the lowest end (lowest level), it is not necessary to perform operations such as dielectric constant correction even if the dielectric constants are different.

  Next, FIG. 8 shows an example in which condensation is attached to the sensor and the additional capacitance is detected. As shown in FIG. 8, since dew condensation is attached to the sensor 3, a value larger by the additional capacity than the electrostatic capacity due to the original liquid level is detected. Therefore, it is possible to correct the capacitance based on the original liquid level by correcting the amount of additional condensation due to the above-described equation (3). In addition, since the actual liquid level is detected by the capacitance of the sensor 3 at the liquid level, the fluctuation of the capacitance due to condensation that has adhered to the sensors 4 to 8 does not become an error in the liquid level.

  According to the above embodiment, the liquid level is calculated from the sensor electrode unit 2 in which the sensors 2a to 2b installed in the container are arranged in the vertical direction and the capacitance values measured by the sensors 2a to 2b. The sensor measurement unit 3 includes a sensor measurement unit 3 that detects the capacitance value measured by the sensors 2a to 2b with reference to the capacitance value of the sensor 2a located at the lowermost end among the capacitance values measured by the sensors 2a to 2b. The sensor on which the liquid level is located is identified according to whether or not it coincides with the capacitance of 2a, and based on the ratio between the capacitance of the identified sensor and the capacitance of the sensor arranged at the lowest end. Since the liquid level of the specified sensor is detected, the liquid level is detected at which sensor position among the sensors 2b to 2h by sequentially comparing with the capacitance of the sensor 2a arranged at the lowermost end. That can be detected Position can be accurately detected liquid level from the capacitance of the electrostatic capacitance sensor 2a of sensors located. Therefore, it is not necessary to measure the sensor characteristics in advance, and the liquid level can be easily detected without being affected by the dielectric constant.

  In addition, the sensor measuring unit 3 identifies a sensor that is completely exposed from the liquid surface, and identifies the capacitance due to condensation that has adhered to the sensor from the capacitance of the identified sensor and the position of the liquid surface. By detecting the liquid level by correcting the capacitance due to condensation based on the capacitance of the sensor that has been placed and the capacitance of the sensor located at the lowest end, the effect of condensation is reduced. And the detection accuracy can be increased.

  In the sensor electrode unit 2, electrodes 4a to 4h serving as measurement electrodes of a plurality of sensors and electrodes 4i serving as ground electrodes are formed on a substrate 4, and the electrodes 4a to 4h are arranged in a straight line. In both cases, since the electrodes 4a to 4h and the electrode 4i are arranged at a predetermined interval, a plurality of sensors can be arranged side by side on one substrate, and can be easily installed in a container.

  The sensor electrode unit 2 includes electrodes 4 a to 4 i formed on the substrate 4, and wirings 5 a to 5 i that electrically connect the electrodes 4 a to 4 i and the terminals 4 j to the surface 51 of the substrate 5. The capacitance (voltage) detected by the electrodes 4a to 4h is output to the terminal 4j through the wirings 5a to 5i because the electrode 5k to be the ground electrode is formed on the back surface 52. Since these wirings are sandwiched between the installation electrodes, a change in wiring capacity due to a change in liquid level can be prevented.

  In the above-described embodiment, the liquid level is detected by sequentially comparing the value of the lowest sensor and the value of the lower sensor, but conversely, the value of the lowest sensor and the value of the higher sensor are sequentially detected. The liquid level may be detected by comparison. For example, in the case of FIG. 7 and FIG. 8, when the sensor 1 is compared with the value of the sensor 1 in order from the sensor 8, and the sensor having the same value as the sensor 1 is detected (sensor 2), The liquid level may be detected by determining that there is a liquid level.

  In the above-described embodiment, the sensor electrodes 4a to 4h of the sensor electrode unit 2 are formed in an isosceles triangular shape, but are not limited thereto, and may be in other shapes such as a rectangle or a fan shape. However, each of the sensor electrodes 4a to 4h has the same shape (the same area), and needs to be arranged at a certain distance from the electrode 4i that is the opposing ground electrode. In addition, since the change in capacitance with respect to the change in the liquid level increases as the length of the facing of the sensor electrodes 4a to 4h and the electrode 4i increases, a triangle or a curve including a slope as illustrated is included. A fan shape or the like is preferred.

  In addition, embodiment mentioned above only showed the typical form of this invention, and this invention is not limited to embodiment. That is, various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Liquid level detection apparatus 2 Sensor electrode part (multiple sensors)
3 Sensor measurement unit (detection means, exposure specifying means, correction means)
3a-3h Sensor electrode 3i Ground electrode (one ground electrode)
4 Substrate (first substrate)
4k ground electrode (second ground electrode)
5 Substrate (second substrate)

Claims (3)

A liquid level provided with a sensor arranged in the container for measuring the capacitance between the electrodes, and a detecting means for detecting a liquid level in the container based on a change in the capacitance measured by the sensor. In the level detection device,
A plurality of the sensors are arranged in the vertical direction of the container ,
The plurality of sensors includes a first substrate in which the plurality of sensor electrodes are arranged in a straight line, and the plurality of sensor electrodes and the one ground electrode are arranged at a predetermined interval from each other. And a second substrate overlaid on the first substrate and provided with a second ground electrode different from the one ground electrode on the entire surface on the side not overlapping the first substrate; And electrically connecting a terminal for connecting each of the plurality of sensor electrodes, the one ground electrode, and the second ground electrode to the outside so as to be sandwiched between the first substrate and the second substrate. A wiring layer to be connected is provided,
The detection means causes each of the plurality of sensors to measure the capacitance, and based on the capacitance measured by the other sensors on the basis of the capacitance of the sensor arranged at the lowermost end. A liquid level detection apparatus for detecting a liquid level in the container.   The detection means identifies the sensor on which the liquid level is located according to whether or not it matches the capacitance of the sensor arranged at the lowest end, and the capacitance of the identified sensor and the lowest end The liquid level detection apparatus according to claim 1, wherein a liquid level in the specified sensor is detected based on a ratio with a capacitance of the sensor arranged in the sensor. The detection means is
An exposure specifying means for specifying the sensor exposed from the liquid surface based on the result of measuring the capacitance with respect to each of the plurality of sensors;
The capacitance of the sensor specified by the exposure specifying means, the capacitance of the sensor specified by the detection means that the liquid level is located, and the capacitance of the sensor arranged at the lowest end , A correction means for correcting the electrostatic capacity due to condensation based on the above and detecting the liquid level,
The liquid level detecting device according to claim 2, comprising:

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