Liquid level gauge

Abstract

The present invention comprises: a sensor unit 30 equipped with a ground conductor 40 extending in a liquid level detection direction and a plurality of electrodes 31 arrayed in the liquid level detection direction and forming an electrostatic capacitance between themselves and the ground conductor 40; an adjustment unit 70; a switch means 80; an identification means 90; and a liquid level determination means 100. The electrodes 31 are divided into n groups. An i-th group (i = 1, 2, ..., n) is formed of electrodes 31 at the 2i -1 (2k - 1)th position from the last in the liquid level detection direction (where k is a natural number from 1 to 2n - i). The electrodes 31 belonging to the same group are connected in parallel and connected to the switch means 80. The identification means identifies the magnitude of the electrostatic capacitance of the i-th group and a group combining the (i +1)-th group through the n-th group for when i = 1, 2, ..., n -1, and identifies the magnitude of the electrostatic capacitance of the n-th group and the adjustment unit 70. The switch means 80 sequentially switches the connection of each group with the identification means 90 to enable identification. The liquid level is determined on the basis of the identification by the identification means 90.

Description

[Technical Field]

[0001] This disclosure ,liquid Regarding position meters. [Background technology]

[0002] FIG. 1 is a copy of FIG. 1 of Patent Document 1, and shows the principle of a prior art water level sensor. The prior art water level sensor measures the water level from a predetermined reference position (for example, the bottom of the tank) in the tank 1 to the liquid level L. The reference line 10 is an imaginary line, and Z observation points Q are positioned on the reference line 10. z (z=1, 2, ..., Z) is set in advance. In the example shown in Fig. 1, Z=7, and seven observation points Q1 to Q7 are shown.

[0003] Electrode pairs P1 to P7 are arranged in a one-to-one relationship at the levels of observation points Q1 to Q7. Determination means 11 to 17 are connected to the electrode pairs P1 to P7 in a one-to-one relationship. Each of the determination means 11 to 17 has a function of determining whether the capacitance value of a corresponding electrode pair among the electrode pairs P1 to P7 exceeds a predetermined reference value. For example, if the determination means 13 determines that the capacitance value of the electrode pair P3 arranged at the level of observation point Q3 exceeds the predetermined reference value, liquid is present at the level of observation point Q3. If the determination means 13 determines that the capacitance value of the electrode pair P3 arranged at the level of observation point Q3 does not exceed the predetermined reference value, no liquid is present at the level of observation point Q3.

[0004] When i determination means, from the first to the ith (i∈{1, 2, ..., Z}) among the Z determination means, output a determination result indicating that the reference value has been exceeded, the water level output means 20 outputs information indicating the level of the ith observation point. In the example shown in Fig. 1, determination means 11-14 corresponding to electrode pairs P1-P4 below the liquid level L (i.e., immersed in the liquid) output a determination result indicating that the reference value has been exceeded, and determination means 15-17 corresponding to electrode pairs P5-P7 above the liquid level L (i.e., not immersed in the liquid) output a determination result indicating that the reference value has not been exceeded, so the water level output means 20 outputs information indicating the level of the fourth observation point Q4. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-311562 Summary of the Invention [Problem to be solved by the invention]

[0006] The water level sensor of the above-mentioned prior art determines the water level by determining the presence or absence of liquid at each level of two or more observation points set in the direction in which the water level changes (hereinafter referred to as the level change direction) based on the capacitance values ​​of each of two or more electrode pairs arranged in a one-to-one correspondence at the levels of the two or more observation points. The water level sensor of the above-mentioned prior art determines the water level approximately using discrete values. Therefore, the water level sensor of the above-mentioned prior art requires a large number of electrode pairs to determine the water level with high resolution, and as a result, a large number of conductors corresponding to the large number of electrode pairs are also required.

[0007] For example, if Z observation points are set in the direction of level change to identify the water level with high resolution, the water level sensor of the prior art described above requires not only Z electrode pairs but also Z+1 conductors, because one electrode of each of the Z electrode pairs is connected to a common conductor and the other electrode of each of the Z electrode pairs is connected to Z different conductors in a one-to-one relationship.

[0008] In view of the above background art, liquid level gauge The total number of conductors drawn from Observe the numbers Total number of stations the number plus 1 It has a configuration that can be reduced Glue Disclose the position. [Means for solving the problem]

[0009] The technical matters described herein are not intended to explicitly or implicitly limit the invention described in the claims, nor to enable anyone other than those who benefit from the invention (e.g., the applicant and the right holder) to limit the invention described in the claims, but are provided simply to facilitate understanding of the gist of the invention. The outline of the invention from other perspectives can be understood, for example, from the claims at the time of filing of this patent application.

[0010] of the present disclosure The liquid level meter comprises a ground conductor extending in the liquid level detection direction, a sensor unit having a plurality of electrodes arranged in the liquid level detection direction to form capacitance with the ground conductor, an adjustment unit, a switching means, a discrimination means, and a liquid level determination means. The plurality of electrodes are divided into n groups, and the i-th group (i=1, 2, ..., n) is the second lowest group in the liquid level detection direction. i-1 (2k-1)th (k is 1 to 2 n-i the plurality of electrodes are connected in parallel with each other when they belong to the same group and are connected to a switching means; the discrimination means discriminates the magnitude relationship between the capacitance of the ith group and the capacitance of the combined group of the (i+1)th group to the nth group for each of i=1, 2, ..., n-1, and further discriminates the magnitude relationship between the capacitance of the nth group and the capacitance of the adjustment unit; the switching means sequentially switches the connection between the groups and the discrimination means to enable discrimination by the discrimination means; and the liquid level determination means determines the liquid level based on the discrimination by the discrimination means. [Effects of the Invention]

[0011] According to this invention, liquid level gauge The total number of conductors drawn from Observe the numbers Total number of stations the number plus 1 It can be done for less than that. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a water level sensor according to a prior art; [Figure 2] 1 is a diagram for explaining the configuration of a water level meter according to a first embodiment of the present invention; [Figure 3] FIG. 3(a) is a diagram for explaining the operation of the water level meter shown in FIG. 2, and FIG. 3(b) is a diagram for explaining the operation of the water level meter shown in FIG. 2. [Figure 4] 3 is a flowchart showing the flow of water level measurement by the water level meter shown in FIG. 2. [Figure 5] 3 is a table showing the operation of the switches when measuring the water level using the water level meter shown in FIG. 2. [Figure 6] FIG. 10 is a diagram for explaining the configuration of a water level meter according to a second embodiment of the present invention. [Figure 7] 7 is a flowchart showing the flow of water level measurement by the water level meter shown in FIG. 6. [Figure 8] 7 is a table showing the operation of the switches when measuring the water level using the water level meter shown in FIG. 6. [Figure 9]FIG. 10 is a diagram for explaining the configuration of a water level meter according to a third embodiment of the present invention. [Figure 10] 10(a) is a diagram for explaining the operation of the water level meter shown in FIG. 9, and FIG. 10(b) is a diagram for explaining the operation of the water level meter shown in FIG. [Figure 11] 10 is a table showing the operation of the switches when measuring the water level using the water level meter shown in FIG. 9. [Figure 12] FIG. 10 is a diagram for explaining the configuration of a water level meter according to a fourth embodiment of the present invention. [Figure 13] 13 is a table showing the operation of the switches when measuring the water level using the water level meter shown in FIG. 12 . [Figure 14] FIG. 10 is a diagram for explaining the configuration of a water level meter according to a fifth embodiment of the present invention. [Figure 15] 10A-10C are examples of interface sensor configurations related to the interface sensor of the present disclosure but not protected by the claims of this application. [Figure 16] 1 shows an example of the configuration of an interface sensor according to the present disclosure. [Figure 17] 1 shows an example of the configuration of an interface sensor according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0013] A liquid level meter according to an embodiment of the present invention will be described by way of example with reference to the drawings. In the following description of Figures 2 to 14, water will be used as an example of the liquid. [Example]

[0014] FIG. 2 shows the configuration of a first embodiment of a water level meter according to the present invention, which comprises a sensor unit 30, a ground conductor 40, a carrier wave generating circuit 50, two resistors 61 and 62, an adjustment unit 70, a switching means 80, a discrimination means 90, a water level determination means 100, and a control means 110.

[0015] The sensor unit 30 has a plurality of electrodes 31 (15 in this example) arranged in the water level detection direction, and the electrodes 31 form electrostatic capacitance with a ground conductor 40 extending in the water level detection direction. Although the substrate for these electrodes 31 is not shown, they are provided as a pattern formed on a substrate, and the pattern is waterproof coated. The ground conductor 40 is formed, for example, by a metal pipe surrounding the sensor unit 30, and the metal pipe is made of, for example, stainless steel. As shown in Figure 2, the 15 electrodes 31 are numbered C1 to C15, starting from the bottom one in the water level detection direction.

[0016] The 15 electrodes 31 are divided into four groups. Here, when the number of groups is n and the n groups are referred to as the first group to the nth group, the electrodes 31 constituting the i-th group (i=1, 2, ..., n) are arranged in the second to nth groups from the bottom in the water level detection direction. i-1 (2k-1)th (k is 1 to 2 n-i In this example, since n=4, the electrodes 31 constituting each group are designated as C1 to C15 as follows:

[0017] 1st group...C1,C3,C5,C7,C9,C11,C13,C15 2nd group...C2, C6, C10, C14 3rd group…C4,C12 4th group…C8 All the electrodes 31 belonging to the same group are connected in parallel to the switching means 80 .

[0018] As shown by the symbols S1 to S7, the switching means 80 in this example has seven switches 81, and by switching the paths by turning these switches 81 ON / OFF, the detection values ​​(capacitance of each group) obtained by each group of the sensor unit 30 can be input (connected) to either of the two inputs a, b of the discrimination means 90.

[0019] A carrier wave generating circuit 50 is connected to two wires extending from the switching means 80 to two inputs a and b of the discriminating means 90 via resistors 61 and 62. The carrier wave generating circuit 50 generates and outputs a carrier wave.

[0020] The adjustment unit 70 is a capacitor having a capacitance as described below, one end of which is connected to a wiring extending from the switching means 80 to the input b of the discrimination means 90, and the other end of which is grounded.

[0021] The determination means 90 determines the magnitude relationship between the capacitances connected to the inputs a and b. Here, the capacitance connected to the input a is C a and the capacitance connected to input b is C b Then, C a and C b The circuit operation of the determining means 90 for determining the magnitude relationship between the values ​​of the two signals will be described with reference to the timing chart shown in FIG.

[0022] C a >C b The timing chart shown in FIG. 3(a) is obtained when the carrier wave generating circuit 50 and the resistance of the resistor 61 and the capacitance C a Since a CR delay circuit is formed by the above, the waveform at point a is a waveform that is delayed with respect to the carrier wave (rectangular wave) output by the carrier wave generating circuit 50. The waveform at point b is also a waveform that is delayed in the same way, but C a >C b Therefore, the delay of the waveform at point b is smaller. In this example, the discrimination means 90 is equipped with a circuit that digitizes each waveform using voltage s as a threshold, and a logic circuit that sets Hi at the rising edge of the digitized waveform at point a and Lo at the rising edge of the digitized waveform at point b, and the waveform of the discrimination process (output waveform of the logic circuit) is as shown in Figure 3(a). a >C b In this case, the waveform for the discrimination process becomes Hi for a time exceeding half a cycle, so the Hi time is longer than the Lo time.

[0023] C a <C bWhen it is, the timing chart shown in Fig. 3(b) is obtained. In this case, the delay of the waveform at point a is smaller, and the waveform of the discrimination process becomes as shown in Fig. 3(b) due to the above circuit configuration. Since it becomes Lo in a time exceeding half a cycle, the time of Lo becomes longer than the time of Hi. Therefore, by comparing the Hi time and the Lo time of the discrimination process waveform, C a and C b can be discriminated as to which is larger or smaller, and the discrimination means 90 outputs 1 when C a >C b and outputs 0 when C a <C b .

[0024] The water level determination means 100 determines the water level based on the determination of the discrimination means 90 operating as described above and outputs it to the outside. The ON / OFF of the seven switches 81 of the switching means 80 is controlled by a control signal from the control means 110, and a signal synchronized with this control is also input from the control means 110 to the water level determination means 100.

[0025] Next, the flow until the water level output by the water level gauge having such a configuration is obtained will be described with reference to the flowchart shown in Fig. 4. In Fig. 4, the number of groups is set as n, G i represents the i-th group, and G i+1 , G i+2 , G n represent the (i + 1)-th group, the (i + 2)-th group, and the n-th group, respectively.

[0026] First, set i = 1 (step M1), and turn off all the switches 81 of the switching means 80 (step M2). Then, turn on the switch 81 that connects the input a of the discrimination means 90 and G i , and further turn on the switches 81 that connect the input b of the discrimination means 90 and G i+1 , G i+2 , …, G n (steps M3, M4). The discrimination means 90 discriminates the magnitude relationship between the inputs a and b (step M5), and outputs 1 to the water level determination means 100 if a > b, and outputs 0 to the water level determination means 100 if a < b. The water level determination means 100 stores this as a 2 i-1 -bit value (steps M6, M7).

[0027] Next, set i = i + 1 (step M8), determine whether i = n (step M9), and if i ≠ n, return to step M2 and repeat steps M2 to M9 until i = n.

[0028] When i = n, after turning off all switches 81 of the switching means 80 (step M10), turn on the switch 81 that connects the input a of the discrimination means 90 and G n (step M11). The discrimination means 90 discriminates the magnitude relationship between the inputs a and b (step M12), and if a > b, outputs 1 to the water level determination means 100, and if a < b, outputs 0 to the water level determination means 100. The water level determination means 100 stores this as the value of 2 n-1 bits (steps M13, M14), and the water level determination means 100 converts the 2 0 bits to 2 n-1 bits of value, that is, converts the binary number to the water level by referring to the memory and outputs it (step M15).

[0029] In this way, in this example, the discrimination means 90 discriminates the magnitude relationship between the detection value obtained by the i-th group and the detection value obtained by the group combining the (i + 1)-th group to the n-th group for i = 1, 2,..., n - 1 respectively, and further discriminates the magnitude relationship between the detection value obtained by the n-th group and the detection value obtained by the adjustment unit 70 to measure the water level. The switching means 80 sequentially switches the connection between the group of the sensor unit 30 and the discrimination means 90 to enable such discrimination by the discrimination means 90.

[0030] Table 1 shown in FIG. 5 shows the water level gauge shown in FIG. 2, that is, in the water level gauge where the number n of the group of the sensor unit 30 is 4 and i ranges from 1 to 4 in the flowchart shown in FIG. The ON / OFF of the seven switches 81 of the switching means 80, that is, S1 to S7, at i = 1 to 4. In the water level gauge shown in FIG. 2, when the first group to the fourth group are represented by G1 to G4, the connection of the groups to the two inputs a and b of the discrimination means 90 is as follows at i = 1 to 4.

[0031] [[ID=2,6]] Input a Input b i=1:2 0 Bit judgement G1G2+G3+G4 i=2:2 1 Bit determination G2G3+G4 i=3:2 2 Bit judgement G3G4 i=4:2 3 Bit decision G4N / A(=not applicable) Below, we will explain in detail the capacitance connected to inputs a and b of the discrimination means 90, using the example when the water level W is at the position indicated by the two-dot chain line in Figure 2 and the ninth electrode C9 from the bottom is submerged in water.

[0032] The capacitance when the electrode 31 is in the air is C air and the capacitance when it is in water is C water The capacitor of the adjustment unit 70 is hereinafter referred to as C99, and its capacitance is 0.5 C. water The relative dielectric constant of water is 80 at 20°C, water =80C air For i=1 to 4, the capacitances connected to inputs a and b are as follows: <i=1:2 0 Bit Determination> ·Input a:G1=C1+C3+C5+C7+C9+C11+C13+C15 =5C water +3C air =403C air ·Input b:G2+G3+G4=C2+C4+C6+C8+C10+C12+C14+C99 =4.5C water +3C air =363C air <i=2:2 1 Bit Determination> Input a: G2=C2+C6+C10+C14 =2C water +2C air =162C air Input b: G3+G4=C4+C8+C12+C99 =2.5C water +C air =201C air <i=3:2 2 Bit Determination> Input a: G3=C4+C12 =C water +C air =81C air Input b: G4=C8+C99 =1.5C water =120C air <i=4:2 3 Bit Determination> Input a: G4=C8 =C water =80C air Input b: N / A=C99 =0.5C water =40C air From the above, at i=1, a>b, so 2 0 The bit becomes 1, and at i=2, a <bより2 1 The bit is 0. Also, at i=3, a <bより2 2 The bit becomes 0, and at i=4, a>b, so 2 3 The bit is 1. So adding these together gives us 1001 in binary, which is 9 in decimal.

[0033] In this way, the water level meter shown in Figure 2 treats the water level as a binary number, and at low water levels where none of the electrodes 31 are submerged, the binary number is 0000, and at high water levels where all of the electrodes 31 are submerged, the binary number is 1111 (15 in decimal).

[0034] In this example, the adjustment unit 70 is 0.5C water It is a capacitor having a capacitance of i=4, 2 3The adjustment unit 70 functions to compare with G4 when determining the bit, but it also functions to ensure that the two detected values ​​(capacitances) whose magnitude relationship is determined by the determination means 90 are always different from each other, that is, to prevent the magnitude relationship from being reversed due to an error factor or the like, resulting in erroneous detection. The sensitivity can be adjusted by adjusting the resistance values ​​of the resistors 61 and 62.

[0035] The following describes Examples 2 to 5. Note that parts corresponding to the configuration of Example 1 shown in Fig. 2 are given the same reference numerals, and detailed description thereof will be omitted. [Example]

[0036] As described above, the adjustment unit 70 functions to change the detection value appropriately according to the water level and to prevent erroneous detections. However, if, for example, the capacitance error of the electrodes 31 is not uniform, a situation may arise in which the detection value does not change appropriately according to the water level with just the capacitance of one adjustment unit 70 when the combination of the electrode groups changes.

[0037] For example, in the water level gauge shown in FIG. 2, only the electrode 31 to which C4 is attached is +0.5C. water Consider the case where there is an error of . That is, when the water level is W, C4' = 1.5C water At this time, for i=1 to 4, the capacitances connected to the inputs a and b of the discrimination means 90 are as follows: <i=1:2 0 Bit Determination> ·Input a:G1=C1+C3+C5+C7+C9+C11+C13+C15 =5C water +3 Cair =403C air ·Input b:G2+G3+G4=C2+C4'+C6+C8+C10+C12+C14+C99 =4.5C water +3C air +C99=363C air +C99 <i=2:2 1 Bit Determination> Input a: G2=C2+C6+C10+C14 =2C water +2C air =162C air Input b: G3+G4=C4'+C8+C12+C99 =2.5C water +C air +C99=201C air +C99 <i=3:2 2 Bit Determination> Input a: G3 = C4' + C12 =1.5C water +C air =121C air Input b: G4=C8+C99 =C water +C99=80C air +C99 <i=4:2 3 Bit Determination> Input a: G4=C8 =C water =80C air Input b: N / A=C99 Since the true value of the binary number is 1001, a>b at i=1 and a>b at i=2. <b、i=3ではa<b、i=4ではa> b. Therefore, for i=1, it is 403C. air >363C air +C99 to C99<40C air must be 121C for i=3. air <80C air +C99>41C air However, there is no C99 that satisfies both of these requirements. i There is no single C99, ie, adjustment unit 70, that satisfies all bit determinations.

[0038] 6, the second embodiment is configured to provide a plurality of adjustment units 70 (four in this example, labeled C101 to C104), and further to provide switching means 120 for switching the connection of these adjustment units 70 to input b of the determination means 90. The switching means 120 includes four switches 121 labeled S11 to S14 for turning on / off the connection of each adjustment unit 70, i.e., C101 to C104, to input b.

[0039] In this example, multiple adjustment units 70 are provided, and by switching using the switching means 120, it is possible to select the adjustment unit 70 to function according to the group (combination of groups) connected to the discrimination means 90.

[0040] The flowchart shown in Figure 7 shows the process leading up to the water level output by the water level meter of this embodiment 2. Compared to the flowchart shown in Figure 4 above, step M4' has been added between steps M4 and M5, in which "the switch that connects the adjustment unit corresponding to i to b is turned on," and step M11' has been added between steps M11 and M12, in which "the switch that connects the adjustment unit corresponding to n to b is turned on."

[0041] Table 2 shown in Fig. 8 adds the ON / OFF of four switches 121 of the switching means 120, i.e., S11 to S14, for i=1 to 4 to the contents of Table 1 shown in Fig. 5. In this example, C101 is selected from the four adjustment units 70, i.e., C101 to C104, for i=1, C102 for i=2, C103 for i=3, and C104 for i=4, and is connected to input b of the discrimination means 90. The ON / OFF of the four switches 121 of the switching means 120 is controlled by a control signal from the control means 110 that is synchronized with the control signal that controls the switching means 80. The capacitance values ​​of the four adjustment units 70 are determined by a prior test. [Example]

[0042] 9 shows the configuration of a third embodiment of a water level meter according to the present invention. In this example, a charging circuit 130 is provided as the input circuit instead of a carrier wave generating circuit 50, and capacitance detection is performed using a switched capacitor. Switches S11 to S14 are provided between the charging circuit 130 and four groups G1 to G4 formed by electrodes 31 of the sensor unit 30, respectively, and switching means 80 having seven switches 81, i.e., S1 to S7, is located between the four groups G1 to G4 and discrimination means 90'. Furthermore, a switch S21 is provided between the adjustment unit 70 and the charging circuit 130, and a switch S22 is provided between the adjustment unit 70 and discrimination means 90'.

[0043] This water level meter also basically detects the water level according to the flowchart shown in FIG. 4, and for each i=1 to 4, switches S1 to S7, S11 to S14, and S21 to S22 are controlled as shown in Table 3 in FIG.

[0044] Although the discrimination means 90' determines the magnitude relationship of the capacitance and outputs 1 or 0, its configuration (circuit configuration) and operation are different from those of the discrimination means 90. As an example, let us consider the case where i=3, and consider the C connected to inputs a and b respectively. a and C b The circuit operation of the determining means 90' for determining the magnitude relationship between the two will be described with reference to the timing chart shown in FIG.

[0045] When the switches S13, S14, and S21 are ON and the switches S4, S7, and S22 are OFF, the third group G3 and the fourth group G4 of the sensor unit 30 and the adjustment unit 70 are charged with the voltage E0 generated by the charging circuit 130. a and C b Each has an integrating circuit and a sample-and-hold circuit (S / H circuit). When switches S13, S14, and S21 are OFF and switches S4, S7, and S22 are ON, C a and C b The charges of C move to the integrating circuit. a and C b The amplitude voltage V of each integrator circuit a ,V bis the integral capacitance, C s This gives us the following:

[0046]

number

[0047] V a ,V b can be obtained as a DC voltage by the sample-and-hold circuit located after the integrator circuit, and C a >C b When C a <C b Therefore, by comparing the voltage values, C a and C b The discrimination means 90' can discriminate between the magnitude of C a >C b When , it outputs 1, and C a <C b When , the water level determining means 100 converts the output of the discriminating means 90' into a water level and outputs it, similar to the water level determining means 100 in FIG. [Example]

[0048] Fig. 12 shows a water level meter of Example 4. This water level meter is a modified example of the water level meter of Example 3, and is equipped with two charging circuits, so that the voltage charged to each of the groups G1 to G4 of the sensor unit 30 can be changed by the two charging circuits 130, 140. Switches S15 to S17 are provided between the groups G2 to G4 and the charging circuit 140, respectively. In this example, for each i=1 to 4, switches S1 to S7, S11 to S17, and S21 to S22 are controlled, for example, as shown in Table 4 in Fig. 13.

[0049] According to this configuration, for example, if it is desired to adjust the sensitivity of electrode 31 to water, such sensitivity adjustment can be performed by adjusting the voltage of charging circuits 130, 140, since the voltages of the two integrating circuits provided in discrimination means 90' are proportional to the voltage of the charging circuit. [Example]

[0050] FIG. 14 shows a water level meter according to a fifth embodiment. In this example, an A / D converter 150 is provided between the switching means 80 and the discrimination means 90, and an adjustment value storage unit 160 is also provided to store a pre-determined adjustment value (capacitance adjustment voltage value) as a digital value. Comparing voltages using an analog circuit requires the use of an IC and multiple resistors. This has the disadvantage of increasing the circuit size as the number of adjustment values ​​increases, as in the configuration with four adjustment units 70 shown in the second embodiment. The method of sequentially switching the connections between the sensor units 30 and the A / D converter 150 by the switching means 80 is the same as in the first embodiment. In this example, the waveforms at points a and b in FIG. 3 are acquired as digital data, enabling subsequent processing to be performed digitally. Using the adjustment value as an offset for the waveform at point b achieves the same effect as the adjustment units in the first and second embodiments. The A / D converter 150 may also measure the differential voltage between input a and input b. In this case, the adjustment value is used as an offset for the differential voltage.

[0051] Various embodiments of the water level meter according to the present invention have been described above. In the water level meter according to the present invention, a plurality of electrodes that are arranged in the water level detection direction and form capacitance with the ground conductor are divided into n groups, and the i-th group (i=1, 2, ..., n) is the second lowest group in the water level detection direction. i-1 (2k-1)th (k is 1 to 2 n-i It is composed of electrodes positioned at positions (a natural number up to 100), and by repeatedly comparing the magnitude of the capacitance while changing the combination of groups, it is possible to obtain a resolution equal to the number of electrodes.

[0052] Therefore, the number of wires (detection side wires) connecting each electrode of the sensor section to the discrimination means only needs to be the number of groups, and only one discrimination means is required.

[0053] Furthermore, for example, if one considers detecting the water level in 1000 steps (a resolution of 1 / 1000 of the measurement range), in the case of a configuration like the conventional example shown in Figure 1, the number of discrimination means and electrode pairs would each be 1000, and the number of wires on the detection side leading to the discrimination means would be 1000.

[0054] On the other hand, in the water level meter of this invention, the above-mentioned group configuration allows for 2 n -1 electrode measurement is possible, that is, 1 / (2 n -1), so to obtain a resolution of 1 / 1000, the number of groups is 10, and therefore only 10 wires are required on the detection side.

[0055] The water level meter described above can be used to measure the water level of a river, for example, and when measuring the water level of a river, if the grounding conductor 40 is a metal pipe, the metal pipe is driven into the ground at the bottom of the river. The water level meter described above can also be used as a liquid level meter to detect the level of liquid in a tank, for example.

[0056] Hereinafter, the interface sensor 200 of the present disclosure and a liquid level meter including the interface sensor 200 will be described from another perspective with reference to FIGS. 16 and 17, which show non-limiting examples. Prior to this description, in order to facilitate understanding of the interface sensor 200 of the present disclosure, an interface sensor 2 related to the interface sensor 200 of the present disclosure will be described with reference to FIG. 15. Note that although the interface sensor 2 is not protected by the scope of the claims of the present application, the description of the interface sensor 2 is useful for understanding the interface sensor 200, and therefore the description of the interface sensor 2 will be incorporated into the description of the interface sensor 200 as necessary. Note that the incorporation of the description is not necessarily explicit.

[0057] The interface sensor 2 is a sensor for determining the position of an interface between two types of materials (i.e., a first material and a second material that are different from each other). However, for accurate determination of the position, the number of interfaces must be either 1 or 0 within the range from plane P(1) to plane P(M(1)), which will be described later. As will be described later, the interface sensor 2 includes a first electrical conductor 5a and E second electrical conductors 5b (E is shown in Equation (4)). E electrode pairs are formed between the first electrical conductor 5a and the E second electrical conductors 5b. The position of the interface between the first and second materials is determined by utilizing physical quantities that occur at each of the E electrode pairs depending on the properties of the first or second material present between them. An "interface" is the contact boundary between a first material as a homogeneous phase and a second material as a homogeneous phase. A "homogeneous phase" is an entity of a material system that is uniform in chemical composition and physical state. In other words, if the physical and chemical properties of any part V of a substance system entity are the same as those of any part W that is different from part V of the substance system entity, the substance system entity is a "homogeneous phase." A typical example of the interface sensor 2 is a sensor for identifying the position of the interface between a liquid (e.g., water) as a first substance and a gas (e.g., air) as a second substance.

[0058] The configuration of the interface sensor 2 will now be described. The symbols used in the following description are unrelated to the symbols used in the description of the above-mentioned embodiment. Furthermore, if the electrical capacitance between two conductors having equal positive and negative charges is C, the electrical resistance between the two conductors is R, the dielectric constant of the medium between the two conductors is ε, and the electrical resistivity of the medium between the two conductors is ρ, then the relationship RC = ερ holds. Therefore, hereinafter, only the electrostatic capacitance of the electrode pair will be described, and a description of the electrical resistance of the electrode pair will be omitted.

[0059] The interface sensor 2 includes a first electrical conductor 5a and K sensor blocks 3, where K is a predetermined integer satisfying 2≦K.

[0060] The K sensor blocks 3 are formed on F substrates 9 each having a flat plate shape without being limited to the following example. F is a predetermined integer satisfying 1 ≦ F ≦ K. When F < K, there are substrates 9 having two or more sensor blocks 3. In the example shown in FIG. 15, F = 1. When F ≧ 2, the F substrates 9 may be arranged on one plane, may be arranged like angle steel or channel steel, or may be arranged like triangular pipes or square pipes without being limited to the following example.

[0061] The first electric conductor 5a is, for example, a metal. The first electric conductor 5a may be one electric conductor or may include two or more electric conductors.

[0062] When the first electric conductor 5a is one electric conductor, the shape of the first electric conductor 5a may be a flat plate or a cylinder without being limited to the following example. When the first electric conductor 5a has a cylindrical shape, the cross-sectional shape of the cylinder in a cross-section perpendicular to the longitudinal direction of the cylinder is, for example, a circle or a rectangle. When the first electric conductor 5a has a cylindrical shape, the K sensor blocks 3 are usually arranged inside the first electric conductor 5a, but this is not the limit.

[0063] When the first electric conductor 5a includes two or more electric conductors, the shape of each of the electric conductors included in the first electric conductor 5a may be a flat plate or the shape of each of the components for forming the above-described cylinder (for example, the shape of an object obtained by cutting the above-described cylinder in a direction perpendicular to its longitudinal direction (that is, a cylinder shorter than the above-described cylinder), the shape of an object obtained by cutting the above-described cylinder in its longitudinal direction (for example, in the case of a cylindrical cylinder, a 1 / 4 cylindrical shape)) without being limited to the following example. When the first electric conductor 5a includes two or more electric conductors, the two or more electric conductors may be independent of each other. That is, the two or more electric conductors included in the first electric conductor 5a may not be in contact with each other or may not have the same potential.

[0064] 15, the first electrical conductor 5a is a single electrical conductor, in order to facilitate understanding of the interface sensor 2. In FIG. 15, in consideration of ease of viewing the figure, the edges of the first electrical conductor 5a are explicitly illustrated, and the first electrical conductor 5a is depicted as if it were transparent.

[0065] The kth sensor block 3 among the K sensor blocks 3 includes M(k) second electrical conductors 5b and n(k) conducting wires 7. The second electrical conductors 5b will be described later. The n(k) conducting wires 7 are conducting wires drawn from the sensor block 3 and connected to the M(k) second electrical conductors 5b as described later. The n(k) conducting wires 7 are connected to a detection circuit as described later. In FIG. 15, for ease of viewing, only some of the second electrical conductors and some conducting wires are labeled. k is a parameter representing an integer satisfying 1≦k≦K, that is, k∈{x∈N:1≦x≦K}. N is the set of all positive integers. For each k∈{x∈N:1≦x≦K}, n(k) is a predetermined integer satisfying 2≦n(k). For each k∈{x∈N:1≦x≦K}, M(k) is expressed by Equation (1). "×" represents multiplication. M(1), i.e., the number of second electrical conductors 5b included in the first sensor block 3, determines the resolution of the interface sensor 2. In other words, M(1) corresponds to the total number of "observation points" described above (this total number was represented by the symbol Z in the explanation of the prior art). More specifically, as will become clear from equations (4) and (5) below, in order to make the total number L of conducting wires 7 drawn from the interface sensor 2 smaller than the sum of the total number M(1) of observation points and 1, M(1) must be 4, M(1) = 6, or M(1) ≧ 8.

number

[0066] In the design of the interface sensor 2, the value of M(1) related to the resolution of the interface sensor 2 will usually be determined first. From this perspective, n(k) is a positive divisor of M(1) (excluding 1 and M(1)). Therefore, for each k ∈ {x ∈ N: 1 ≤ x ≤ K}, n(k) < M(1). Furthermore, note that the representation of M(1) is not unique. For example, when M(1) = 60, M(1) can be M(1) = 2 × 30 (i.e., K = 2, n(1) = 30, n(2) = 2), M(1) = 3 × 20 (i.e., K = 2, n(1) = 20, n(2) = 3), M(1) = 12 × 5 (i.e., K = 2, n(1) = 5, n(2) = 12), M(1) = 4 × 3 × 5 (i.e., K = 3, n(1) = 5, n(2) = 3, n(3) = 4), M(1) = 5 × 6 × 2 (i.e., K = 3, n(1) = 2, n(2) = 6, n(3) = 5), M(1) = 2 × 3 × 2 × 5 (i.e., K = 4, n(1) = 5, n(2) = 2, n(3) = 3, n(4) = 2), and so on, having more than two representations (i.e., more than two factorizations). When M(1) has more than two representations, the person implementing the interface sensor 2 can arbitrarily select one representation considering the ease of implementation of the interface sensor 2, the manufacturing cost of the interface sensor 2, the usage environment of the interface sensor 2, etc. That is, the more than two representations of M(1) mean the design freedom of the interface sensor 2.

[0067] The second electrical conductor 5b is, for example, a metal. The shape of the second electrical conductor 5b is not limited to the following examples and may be a rectangular flat plate or a circular flat plate. In the k-th (k ∈ {x ∈ N: 1 ≤ x ≤ K}) sensor block 3, M(k) electrode pairs are formed between the first electrical conductor 5a and M(k) second electrical conductors 5b. The M(k) electrode pairs have the same capacitance C with each other when, for example, each space between the M(k) electrode pairs is filled with a first substance. k Stated from another perspective, 'the M(k) electrode pairs have the same capacitance C with each other when, for example, each space between the M(k) electrode pairs is filled with a first substance.k In order to satisfy the condition that "has m (k) second electrical conductors 5b" among M(k) second electrical conductors 5b included in the k-th (k∈{x∈N: 1≦x≦K}) sensor block 3, k the area of ​​the second electrical conductor 5b, and m k The distance between the second electrical conductor 5b and the first electrical conductor 5a is appropriately set. k is 1≦m k ≦M(k), that is, m k ∈{x∈N:1≦x≦M(k)}. For example, if the M(k) second electrical conductors 5b included in the kth (k∈{x∈N:1≦x≦K}) sensor block 3 have the same area, the above condition is met if the distances between the first electrical conductor 5a and the M(k) second electrical conductors 5b are equal to each other. In the example shown in FIG. 15, the shape of the first electrical conductor 5a is a rectangular flat plate with an area larger than the area of ​​one substrate 9 having K sensor blocks 3. In the example shown in FIG. 15, the K sensor blocks 3 are located on one surface of one substrate 9, and the first electrical conductor 5a is located parallel to and faces one surface of the substrate 9. In FIG. 15, for ease of viewing, the first electrical conductor 5a is regarded as a transparent object, and only the outline of the first electrical conductor 5a is shown. When the interface sensor 2 is viewed from the front (i.e., when viewed from the front of the paper of FIG. 15), the first electrical conductor 5a overlaps with all of the second electrical conductors 5b included in the K sensor blocks 3, and the distance between the edge of the first electrical conductor 5a and each of the second electrical conductors 5b is sufficiently large. In the example shown in FIG. 15, if the M(k) second electrical conductors 5b included in the k-th (k∈{x∈N:1≦x≦K}) sensor block 3 have the same area, the above condition is easily achieved. The capacitance C of each of the M(k) electrode pairs included in the k-th sensor block 3 is k is the capacitance C of each of the M(j) electrode pairs included in the jth (j≠k) sensor block 3. j It may be the same as or different from.

[0068] m of the M(k) second electrical conductors 5b included in the k-th (k∈{x∈N: 1≦x≦K}) sensor block 3 k The second electrical conductor 5b is located in the r(k,m) plane among the M(1) planes. k )th plane P(r(k,m k It is located in k As mentioned above, 1≦m k ≦M(k), that is, m k ∈{x∈N:1≦x≦M(k)}. For each k∈{x∈N:1≦x≦K} and for each m k For ∈{x∈N:1≦x≦M(k)}, r(k,m k ) is expressed by equation (2). The M(1) planes P(1), ..., P(M(1)) are mutually disjoint and parallel. The M(1) planes P(1), ..., P(M(1)) are arranged in space in an order according to the magnitude relationship of the elements of the set {x∈N: 1≦x≦M(1)} (i.e., the magnitude relationship of natural numbers). Specifically, between the first plane P(1) and the pth (p∈{x∈N: 3≦x≦M(1)}) plane P(p), the qth (q∈{x∈N: 2≦x≦p-1}) plane P(q) exists. More simply, if the normal direction of the M(1) parallel planes P(1), ..., P(M(1)) is called the first direction, the M(1) planes P(1), ..., P(M(1)) are arranged in this order in the first direction. For any g∈{x∈N:1≦x≦M(1)-2}, h∈{x∈N:g+1≦x≦M(1)-1}, the distance between the gth plane P(g) and the g+1th plane P(g+1) may or may not be equal to the distance between the hth plane P(h) and the h+1th plane P(h+1). For example, it is advisable to narrow the spacing between adjacent planes in a measurement range where the position of the interface is desired to be more accurately identified. In the kth (k∈{x∈N:1≦x≦K}) sensor block 3, the M(k) second electrical conductors 5b are typically arranged linearly, but this is not limited thereto. For example, they may be arranged in the shape of walking footprints.

number

[0069] From the viewpoints of easiness of design and manufacturing of the interface sensor 2, etc., the K sensor blocks 3 are generally arranged in a second direction orthogonal to the first direction. The total number of possible arrangement patterns of the K sensor blocks 3 in the second direction is K!, that is, Π k=1 K k. When the first direction is the vertical direction, "plane" may be rephrased as, for example, "level".

[0070] Of the M(k) second electrical conductors 5b included in the k-th (k ∈ {x ∈ N: 1 ≤ x ≤ K}) sensor block 3, the m k -th (m k ∈ {x ∈ N: 1 ≤ x ≤ M(k)}) second electrical conductor �b is connected to the s(m k )-th conductor 7 among the n(k) conductors 7. The m k -th (m k ∈ {x ∈ N: 1 ≤ x ≤ M(k)}) second electrical conductor 5b and the s(m k )-th conductor 7 are connected to each other via the branch line 7x in this example. s(m k ) is an integer satisfying 1 ≤ s(m k ) ≤ n(k), that is, s(m k ) ∈ {x ∈ N: 1 ≤ x ≤ n(k)}. For each k ∈ {x ∈ N: 1 ≤ x ≤ K} and each m k ∈ {x ∈ N: 1 ≤ x ≤ M(k)}, Equation (3) holds. In Equation (3), the symbol mod represents the remainder operation, and m k mod n(k) is the remainder obtained by Euclidean division of the dividend m k by the divisor n(k).

Number

[0071] As is clear from the above description, the number E of the second electrical conductors 5b included in the interface sensor 2 is given by Equation (4), and the number L of the conductors 7 drawn from the interface sensor 2 is given by Equation (5). Under the above conditions, L < M(1) + 1 can be achieved.

Number

[0072] Next, an example of a method for identifying the position of an interface using the interface sensor 2 will be described. In the k-th (k∈{x∈N: 1≦x≦K}) sensor block 3, a detection circuit (not shown) detects t k The th electrode pair (i.e., t k The sum of the physical quantities (for example, the sum of the capacitances) generated in each of the electrodes (the electrode pair formed by the second electrical conductor 5b and the first electrical conductor 5a connected to the second conductor 7) and t k +1st electrode pair (i.e., t k + the difference D(t k ) is compared with a predetermined threshold δ. k is 1≦t k ≦n(k)−1, that is, t k ∈{x∈N:1≦x≦n(k)−1}. k ∈{x∈N:1≦x≦n(k)-1}, D(T k )>δ, the candidate positions of the interface are given by b(k)+1 intervals determined by a pair of two planes expressed by equation (6). However, when k=K, we define y=0. One "interval" is the region between the two planes expressed by equation (6). For all t k For D(t k )≦δ, either the interface has not reached the plane P(1) or the interface has exceeded the plane P(M(1)). The detection circuit may be a component of the interface sensor 2 or may be a physical entity independent of the interface sensor 2. In the latter case, the detection circuit may be a component of a level meter including the interface sensor 2. The detection circuit may be, without limitation, a detection circuit of the prior art, or may comprise an AC signal generator for generating AC signals to be applied to n(k) conductors 7 for each k∈{x∈N:1≦x≦K}), and a voltage generator for each t k ∈{x∈N:1≦x≦n(k)-1}, the difference D(t kIt may be a detection circuit including a comparator that compares with a threshold value δ, or it may be the detection circuits shown in FIGS. 2 and 6 (including a carrier wave generation circuit 50 and a discrimination means 90), or it may be the detection circuit shown in FIG. 9 (including a charging circuit 130, a plurality of switches controlled by a control means 110, and a discrimination means 90'), or it may be the detection circuit shown in FIG. 12 (including charging circuits 130 and 140, a plurality of switches controlled by a control means 110, and a discrimination means 90'), or it may be a detection circuit including a PLD (programmable logic device). Examples of PLDs include FPGAs (field-programmable gate arrays).

Number

[0073] As an example, the position of the interface can be specified by the algorithm shown in Table 1. That is, except when the interface has not reached the plane P(1) and when the interface exceeds the plane P(M(1)), the section common to each sensor block 3 is specified as the section where the interface exists. In the algorithm shown in Table 1, it is assumed that there exists a T K ∈{x∈N: 1≦x≦n(K)-1} that satisfies D(T K )>δ in the K-th sensor block 3. For example, assuming K' is an integer that satisfies 1 < K' < K, if there does not exist a T K’+1 ∈{x∈N: 1≦x≦n(K'+1)-1} that satisfies D(T K’+1 )>δ in the (K'+1)-th sensor block 3 and there exists a T K’ ∈{x∈N: 1≦x≦n(K')-1} that satisfies D(T K’ )>δ in the K'-th sensor block 3, then K may be rewritten as K' in the algorithm shown in Table 1. When K' = 1, the interface exists in the section corresponding to y = 0 among the b(1)+1 sections determined by the pair of two planes represented by Equation (6).<XXX <XXX

Table 1

[0074] <XXX The interface sensor 2 may include a second electrical conductor 5b for determining whether the interface has not reached the plane P(1) and / or a second electrical conductor 5b for determining whether the interface has exceeded the plane P(M(1)). k For D(t k )≦δ, it can be seen that the interface does not reach the plane P(1), and therefore the former second electrical conductor 5b is not essential.

[0075] A specific configuration example of the interface sensor 2 is shown in FIG. 15. The configuration example shown in FIG. 15 is an example where M(1) = 30 and K = 3. In the example shown in FIG. 15, M(1) = 2 × 5 × 3 is used as the factorization based on the three factors of M(1). That is, n(1) = 3, n(2) = 5, and n(3) = 2. Therefore, from equation (1), M(1) = 30, M(2) = 10, and M(3) = 2.

[0076] Of the 30 second electrical conductors 5b included in the first sensor block 3, the m1-th (m1∈{x∈N:1≦x≦30}) second electrical conductor 5b is located on the r(1,m1)-th plane P(r(1,m1)) of the 30 planes. Here, from equation (2), r(1,m1)=m1. In other words, the p-th (p∈{x∈N:1≦x≦30}) second electrical conductor 5b included in the first sensor block 3 is located on the p-th plane P(p).

[0077] Of the ten second electrical conductors 5b included in the second sensor block 3, the m2-th (m2∈{x∈N:1≦x≦10}) second electrical conductor 5b is located on the r(2,m2)-th plane P(r(2,m2)) of the 30 planes. Here, from equation (2), r(2,m2)=3×m2. In other words, the p-th (p∈{x∈N:1≦x≦10}) second electrical conductor 5b included in the second sensor block 3 is located on the (3×p)-th plane P(3×p). For example, the seventh (p=7∈{x∈N:1≦x≦10}) second electrical conductor 5b included in the second sensor block 3 is located on the 21st plane P(21).

[0078] Of the two second electrical conductors 5b included in the third sensor block 3, the m3-th (m3∈{x∈N:1≦x≦2}) second electrical conductor 5b is located on the r(3,m3)-th plane P(r(3,m3)) of the 30 planes. Here, from equation (2), r(3,m3)=15×m3. In other words, the p-th (p∈{x∈N:1≦x≦2}) second electrical conductor 5b included in the third sensor block 3 is located on the (15×p)-th plane P(15×p). For example, the first (p=1∈{x∈N:1≦x≦2}) second electrical conductor 5b included in the third sensor block 3 is located on the 15-th plane P(15).

[0079] Of the 30 second electrical conductors 5b included in the first sensor block 3, the m1-th (m1∈{x∈N:1≦x≦30}) second electrical conductor 5b is connected to the s(m1)-th conductor 7 of the three conductors 7. From equation (3), for example, the seventh second electrical conductor 5b is connected to the first conductor 7 (7 mod 3 = 1), the 17th second electrical conductor 5b is connected to the second conductor 7 (17 mod 3 = 2), and the 24th second electrical conductor 5b is connected to the third conductor 7 (24 mod 3 = 0).

[0080] The m2th (m2∈{x∈N:1≦x≦10}) second electrical conductor 5b among the ten second electrical conductors 5b included in the second sensor block 3 is connected to the s(m2)th conductor 7 among the five conductors 7. From equation (3), the first and sixth second electrical conductors 5b are connected to the first conductor 7 (1 mod 5 = 6 mod 5 = 1), the second and seventh second electrical conductors 5b are connected to the second conductor 7 (2 mod 5 = 7 mod 5 = 2), the third and eighth second electrical conductors 5b are connected to the third conductor 7 (3 mod 5 = 8 mod 5 = 3), the fourth and ninth second electrical conductors 5b are connected to the fourth conductor 7 (4 mod 5 = 9 mod 5 = 4), and the fifth and tenth second electrical conductors 5b are connected to the fifth conductor 7 (5 mod 5 = 10 mod 5 = 0).

[0081] Of the two second electrical conductors 5b included in the third sensor block 3, the m3-th second electrical conductor 5b (m3 ∈ {x ∈ N: 1 ≤ x ≤ 2}) is connected to the s(m3)-th conductor 7 out of the two conductors 7. From Equation (3), the first second electrical conductor 5b is connected to the first conductor 7 (1 mod 2 = 1), and the second second electrical conductor 5b is connected to the second conductor 7 (2 mod 2 = 0).

[0082] The number E of the second electrical conductors 5b included in the configuration example of the interface sensor 2 shown in FIG. 15 is 42 from Equation (4), and the number L of the conductors 7 is 10 from Equation (5). Since the total number M(1) of the observation points is 30, L < M(1) + 1 holds. According to the prior art water level gauge shown in FIG. 1, the number of the conductors is 31 (= M(1) + 1). Further, for example, although not shown, when M(1) = 1440, K = 5, n(1) = 5, n(2) = 3, n(3) = 2, n(4) = 8, n(5) = 6, the number L of the conductors 7 in the interface sensor 2 is 24, and according to the prior art water level gauge shown in FIG. 1, the number of the conductors is 1441 (= M(1) + 1).

[0083] In the example shown in FIG. 15, the number F of the substrates 9 is 1, but F may be 2 or F may be 3. In the case of F = 2, for example, the first sensor block 3 and the second sensor block 3 are formed on the first substrate, and the third sensor block 3 is formed on the second substrate.

[0084] Next, the interface sensor 200 of the present disclosure will be described. While the interface sensor 2 includes K sensor blocks 3, the interface sensor 200 includes one sensor block 300 and has a configuration equivalent to the configuration of the interface sensor 2.

[0085] The interface sensor 200 is a sensor for determining the position of an interface between two types of materials (i.e., a first material and a second material that are different from each other). However, to accurately determine the position, the number of interfaces must be one or zero within the range from plane P(1) to plane P(E), which will be described later. As will be described later, the interface sensor 200 includes a first electrical conductor 500a and E second electrical conductors 500b (E is shown in Equation (7)). E electrode pairs are formed between the first electrical conductor 500a and the E second electrical conductors 500b. The position of the interface between the first material and the second material is determined by utilizing physical quantities that appear at each of the E electrode pairs depending on the properties of the first material or the second material present between the E electrode pairs. The terms "interface" and "homogeneous phase" are as defined above. A typical example of the interface sensor 200 is a sensor for determining the position of an interface between a liquid (e.g., water) as a first material and a gas (e.g., air) as a second material.

[0086] The configuration of interface sensor 200 will now be described. The symbols used in the following description are unrelated to the symbols used in the description of the previous embodiment or the description of interface sensor 2. Furthermore, if the electrical capacitance between two conductors having equal positive and negative charges is C, the electrical resistance between the two conductors is R, the dielectric constant of the medium between the two conductors is ε, and the electrical resistivity of the medium between the two conductors is ρ, then the relationship RC = ερ holds. Therefore, hereinafter, only the electrostatic capacitance of the electrode pair will be described, and a description of the electrical resistance of the electrode pair will be omitted.

[0087] The interface sensor 200 includes a first electrical conductor 500a, E second electrical conductors 500b, L electrical leads 700 extending from the sensor block 300, and a lead selector 800. Typically, the E second electrical conductors 500b and the L electrical leads 700 are formed on a flat substrate 900. The substrate 900, except for the E second electrical conductors 500b, is waterproof coated. The lead selector 800 may be formed on the substrate 900 or on another substrate, without being limited to the following example. When the first substance is a liquid, the lead selector 800 is preferably located in a position that is not immersed in the liquid, and is waterproof if located in a position that is immersed in the liquid.

[0088] The first electrical conductor 500a may be, for example, a metal, and may include one electrical conductor or two or more electrical conductors.

[0089] When the first electrical conductor 500a is a single electrical conductor, the shape of the first electrical conductor 500a is not limited to the following examples and may be a flat plate or a cylinder. When the first electrical conductor 500a has a cylindrical shape, the cross-sectional shape of the cylinder in a cross section perpendicular to the longitudinal direction of the cylinder is, for example, a circle or a rectangle. When the first electrical conductor 500a has a cylindrical shape, the sensor block 300 is usually disposed inside the first electrical conductor 500a, but this is not limited to this.

[0090] When the first electrical conductor 500a includes two or more electrical conductors, the shape of each of the electrical conductors included in the first electrical conductor 500a is not limited to the following examples and may be a flat plate or the shape of each of the components constituting the above-mentioned tube (for example, the shape of an object obtained by cutting the above-mentioned tube in a direction perpendicular to its longitudinal direction (in other words, a tube shorter than the above-mentioned tube), or the shape of an object obtained by cutting the above-mentioned tube in its longitudinal direction (for example, in the case of a cylinder, it is a quarter-cylindrical shape)). When the first electrical conductor 500a includes two or more electrical conductors, the two or more electrical conductors may be independent of each other. However, it is desirable that the two or more electrical conductors included in the first electrical conductor 500a have the same potential, for example, by contacting each other.

[0091] Hereinafter, from the viewpoint of ease of understanding of the interface sensor 200, the first electrical conductor 500a is a single electrical conductor in the first example shown in Fig. 16 and the second example shown in Fig. 17. In Fig. 16 and Fig. 17, in consideration of ease of viewing the figures, the edge of the first electrical conductor 500a is explicitly illustrated, and the first electrical conductor 500a is depicted as if it were transparent.

[0092] The sensor block 300 includes E second electrical conductors 500b and L conductors 700. The second electrical conductors 500b will be described later. The L conductors 700 are conductors extending from the sensor block 300 and connected to a conductor selector 800 (described later). In FIGS. 16 and 17, for clarity, only some of the second electrical conductors and some conductors are labeled. E is expressed by Equation (7). L is expressed by Equation (8). K is a predetermined integer satisfying 2≦K. j is a parameter representing an integer satisfying 1≦j≦K, i.e., j∈{x∈N:1≦x≦K}. For each j∈{x∈N:1≦x≦K}, n(j) is a predetermined integer satisfying 2≦n(j). N is the set of all positive integers. E, i.e., the number of second electrical conductors 500b included in the sensor block 300, determines the resolution of the interface sensor 200. That is, E corresponds to the total number of "observation points" mentioned above (this total number was represented by the symbol Z in the description of the prior art). <E+1である。

number

[0093] n(j) is a positive divisor of E (excluding 1 and E). The representation of E is not unique. If E has two or more representations (i.e., two or more ways of factorization), the implementer of the interface sensor 200 can arbitrarily select one representation, taking into consideration the ease of implementation of the interface sensor 200, the manufacturing cost of the interface sensor 200, the environment in which the interface sensor 200 will be used, and the like. In other words, two or more representations of E mean greater freedom in the design of the interface sensor 200. From the perspective of reducing the total number L of conducting wires 700, it is preferable that n(j) is a prime factor of E, that is, the right-hand side of equation (7) is a prime factorization (see equation (8)).

[0094] The second electrical conductor 500b is, for example, a metal. The shape of the second electrical conductor 500b is not limited to the following example and may be a rectangular plate or a circular plate. In the sensor block 300, E electrode pairs are formed between the first electrical conductor 500a and E second electrical conductors 500b. The E electrode pairs have the same capacitance C when, for example, a first substance is filled between each of the E electrode pairs. From another perspective, to satisfy the condition that "E electrode pairs have the same capacitance C when, for example, a first substance is filled between each of the E electrode pairs," the area of ​​the m-th second electrical conductor 500b among the E second electrical conductors 50b included in the sensor block 300 and the distance between the m-th second electrical conductor 500b and the first electrical conductor 500a are appropriately set. m is a parameter representing an integer satisfying 1≦m≦E, that is, m∈{x∈N:1≦x≦E}. For example, if the E second electrical conductors 500b included in the sensor block 300 have the same area, the above condition is met if the distances between the first electrical conductor 500a and the E second electrical conductors 500b are equal to each other. In the first example shown in FIG. 16 and the second example shown in FIG. 17, the shape of the first electrical conductor 500a is a rectangular flat plate having an area larger than that of the substrate 900. In the first example shown in FIG. 16 and the second example shown in FIG. 17, the sensor block 300 is located on one side of the substrate 900, and the first electrical conductor 500a is located parallel to and faces the one side of the substrate 900. In FIGS. 16 and 17, for ease of viewing, the first electrical conductor 500a is regarded as a transparent object, and only the outline of the first electrical conductor 500a is shown. When the interface sensor 200 is viewed head-on (i.e., when viewed from the front of the paper in FIG. 16 or 17), the first electrical conductor 500a overlaps with all of the second electrical conductors 500b included in the sensor block 300, and the distance between the edge of the first electrical conductor 500a and each of the second electrical conductors 500b is sufficiently large. In the first example shown in FIG. 16 and the second example shown in FIG. 17, the above condition is easily achieved when the E second electrical conductors 500b included in the sensor block 300 have the same area.

[0095] The E second electrical conductors 500b are located on E planes that are not coincident with each other and are parallel to each other, in an order according to the magnitude relationship of the elements of the set {x∈N:1≦x≦E}. The E planes P(1),...,P(E) are arranged in space in an order according to the magnitude relationship of the elements of the set {x∈N:1≦x≦E} (i.e., the magnitude relationship of natural numbers). Specifically, the first plane P(1) and p a th (p a ∈{x∈N:3≦x≦E}) a ) between p b th (p b ∈{x∈N:2≦x≦p a -1}) plane P(p b ) exists. More simply, when the normal direction of E planes P(1), ..., P(E) that are parallel to each other is called the first direction, the E planes P(1), ..., P(E) are arranged in this order in the first direction. For any g∈{x∈N: 1≦x≦E-2}, h∈{x∈N: g+1≦x≦E-1}, the distance between the gth plane P(g) and the g+1th plane P(g+1) may or may not be equal to the distance between the hth plane P(h) and the h+1th plane P(h+1). For example, it is preferable to narrow the interval between adjacent planes in a measurement range where the position of the interface is desired to be more accurately identified. The pth second electrical conductor 500b among the E second electrical conductors 500b is located on the pth plane P(p) among the E planes. p is a parameter representing an integer satisfying 1≦p≦E, that is, p∈{x∈N:1≦x≦E}. The E second electrical conductors 500b are usually arranged in a straight line, but this is not a limitation and they may be arranged, for example, in the form of footprints. Note that when the first direction is the vertical direction, the "plane" may be rephrased as, for example, a "level."

[0096] For each p∈{x∈N:1≦x≦E-1}, the pth second electrical conductor 500b among the E second electrical conductors 500b is connected to the s(p)th conductive wire 700 among the L conductive wires 700. The pth (p∈{x∈N:1≦x≦E-1}) second electrical conductor 500b and the s(p)th conductive wire 700 are connected to each other via a branch wire 700x in this example. s(p) is expressed by equation (9). In equation (9), the symbol "mod" represents a modulo operation, and a mod b is the remainder of Euclidean division of the dividend a by the divisor b. In equation (9), the symbol " / " appearing in the dividend of the modulo operation represents division. In this description, n(0)=1.

number

[0097] In equation (9), r is identified by p∈W(r), that is, the set W(r) to which p belongs. For each k∈{x∈N:1≦x≦K}, the kth set W(k) is expressed by equation (10). The K+1th set W(K+1) is the empty set φ. In equation (10), the symbol "|" represents a multiple, so a|b means "b is a multiple of a."

number

[0098] If we define W={W(j):j∈N ∧ 1≦j≦K}, as is clear from equation (10), 1)∀W(j)∈W,W(j)≠φ 2)W(i)∈W,W(j)∈W,W(i)≠W(j) ⇒ W(i)∩W(j)=φ 3)∪ j=1 K W(j) = {x∈N:1≦x≦E} Therefore, ∀p∈{x∈N:1≦x≦E-1},∃!W(r)∈W st p∈W(r). In other words, the set W(r) to which p belongs is uniquely determined.

[0099] The Eth second electrical conductor 500b of the E second electrical conductors 500b is connected to the Lth electrical wire 700 of the L electrical wires 700.

[0100] The conductor selector 800 can select any one of the L conductors 700 .

[0101] Alternatively, for each k∈{x∈N:1≦x≦K}, the lead selector 800 may select 1) If k≠K and n(k)≠2, For each y∈{x∈N:1≦x≦n(k)−2}, two conductors 700 determined by elements belonging to the set Y(y) are selected simultaneously from among the L conductors 700, and for y=n(k)−1, two conductors 700 determined by elements belonging to the set Y(y) are selected simultaneously. a (y) is determined by the element (2+Σ j=k+1 K (n(j)-1)) conducting wires 700 are selected simultaneously; 2) If k≠K and n(k)=2, For y=n(k)−1, the set Y a (y) is determined by the element (2+Σ j=k+1 K (n(j)-1)) conducting wires 700 are selected simultaneously; 3) When k=K, For each y∈{x∈N: 1≦x≦n(k)−1}, two conductors 700 determined by elements belonging to the set Y(y) are simultaneously selected from the L conductors 700. However, the set Y(y) is expressed by equation (11), and the set Y a (y) is expressed by equation (12). These sets are expressed as unions of singletons.

number

[0102] Thus, when the interface sensor 200 includes a conductor selector 800 that can simultaneously select two or more conductors 700, the conductor selector 800 preferably connects the two or more simultaneously selected conductors 700 to two conductors (conductor a and conductor b) as follows: A) Regarding equation (11), connect the conductor 700 determined by the elements belonging to the set expressed by equation (13) to conductor a, and connect the conductor 700 determined by the elements belonging to the set expressed by equation (14) to conductor b. B) Regarding equation (12), connect the conductor 700 determined by the elements belonging to the set expressed by equation (13) to conductor a, and connect the conductor 700 determined by the elements belonging to the set expressed by equation (15) to conductor b.

number

[0103] Since the interface sensor 200 is equivalent to the interface sensor 2, the method for identifying the position of the interface using the interface sensor 200 is the same as the method for identifying the position of the interface using the interface sensor 2. When the interface sensor 200 includes a conductor selector 800 that can simultaneously select two or more conductors 700, a detection circuit (not shown) in the interface sensor 200 compares a difference D between the sum of the physical quantities (e.g., the sum of the capacitances) generated in each of the electrode pairs connected to conductor a through the conductors 700 selected by the conductor selector 800 and the sum of the physical quantities (e.g., the sum of the capacitances) generated in each of the electrode pairs connected to conductor b through the conductors 700 selected by the conductor selector 800 with a predetermined threshold δ. The detection circuit may be a component of the interface sensor 200, or may be a physical entity independent of the interface sensor 200. In the latter case, the detection circuit may be a component of a liquid level meter that includes the interface sensor 200. The detection circuit may be, without limitation, a detection circuit of the prior art, a detection circuit including an AC signal generator that generates AC signals to be applied to the L number of conductive wires 700 and a comparator, the detection circuit shown in Figures 2 and 6 (including a carrier wave generation circuit 50 and a discrimination means 90), the detection circuit shown in Figure 9 (including a charging circuit 130, a plurality of switches controlled by the control means 110, and a discrimination means 90'), the detection circuit shown in Figure 12 (including charging circuits 130, 140, a plurality of switches controlled by the control means 110, and a discrimination means 90'), or a detection circuit including a programmable logic device (PLD). An example of a PLD includes a field-programmable gate array (FPGA).

[0104] As an example, the position of the interface can be identified by the algorithm shown in Table 2. In this algorithm, C(13) represents the combination of physical quantities (e.g., combined capacitance) occurring in each of the electrode pairs connected to the conductor 700, which is determined by the elements belonging to the set expressed by equation (13), C(14) represents the combination of physical quantities (e.g., combined capacitance) occurring in each of the electrode pairs connected to the conductor 700, which is determined by the elements belonging to the set expressed by equation (14), and C(15) represents the combination of physical quantities (e.g., combined capacitance) occurring in each of the electrode pairs connected to the conductor 700, which is determined by the elements belonging to the set expressed by equation (15). If the output is P(0) or P(1), this indicates that the interface has not reached the plane P(1). Note that this algorithm does not perform overflow determination processing or error avoidance processing. [Table 2]

[0105] When the total number Z of the aforementioned "observation points" is a prime number equal to or greater than 5, Z-1 is a composite number. Therefore, by setting the value of E to Z-1, an interface sensor having Z observation points (where Z is a prime number equal to or greater than 5) can be configured. Specifically, the interface sensor 200 includes E (where E=Z-1) second electrical conductors 500b, L conductors 700, and a conductor selector 800, and is configured to add one second electrical conductor and one conductor. In this configuration, the added second electrical conductor is located on the P(E+1)th plane, and is connected to the added conductor. The detection circuit determines whether the capacitance value between the added second electrical conductor and the first electrical conductor 500a exceeds a predetermined reference value, thereby determining whether the interface has crossed the P(E+1)th plane.

[0106] FIGS. 16 and 17 show first and second examples of specific configurations of the interface sensor 200, respectively. These configuration examples are for the case where E=30 and K=3. In each of the examples shown in FIGS. 16 and 17, E=2×5×3 is used as the factorization based on the three factors of E. That is, n(1)=3, n(2)=5, and n(3)=2. In this case, L=8. See equations (7) and (8) for these facts.

[0107] As shown in FIGS. 16 and 17, the pth (pε{xεN: 1≦x≦30}) electrode pair 500 is located on the pth plane P(p).

[0108] From equation (10), W(3), W(2), and W(1) are determined as follows: W(3)={15,30} W(2)={3,6,9,12,18,21,24,27} W(1)={1,2,4,5,7,8,10,11,13,14,16,17,19,20,22,23,25,26,28,29}

[0109] For example, when p=12, p∈W(2), that is, r=2. Therefore, from equation (9), s(p)=6, and the 12th (=p) second electrical conductor 500b is connected to the 6th (=s(p)) conducting wire 700. All calculation results are as follows: p∈{1, 4, 7, 10, 13, 16, 19, 22, 25, 28}→s(p)=1, p∈{2, 5, 8, 11, 14, 17, 20, 23, 26, 29}→s(p)=2, p∈{3, 18}→s(p)=3, p∈{6, 21}→s(p)=4, p∈{9, 24}→s(p)=5, p∈{12, 27}→s(p)=6, p∈{15}→s(p)=7, The 30th (=E) second electrical conductor 500b is connected to the 8th (=L) conducting wire 700.

[0110] The interface sensor 200 shown in FIG. 16 includes a conductor selector 800 that can select any one of the L conductors 700. Such a conductor selector 800 includes, without being limited to the following example, L single-pole, single-throw switches. One end of each of the L single-pole, single-throw switches is connected to a corresponding one of the L conductors 700. The other end of each of the L single-pole, single-throw switches is connected to a C / V converter. If the value of L is not large, the conductor selector 800 may be a single-pole, single-throw switch. If the conductor selector 800 is a single-pole, single-throw switch, the number of C / V converters connected to the conductor selector 800 may be one.

[0111] The interface sensor 200 shown in FIG. 17 includes a conductor selector 800 that can simultaneously select two or more conductors 700. Such a conductor selector 800 includes, without limitation to the following example, L single-pole, triple-throw switches. Input terminals of the single-pole, triple-throw switches are connected to corresponding conductors 700 of the L conductors 700. A first output terminal of the single-pole, triple-throw switch is connected to conductor b, a second output terminal is terminated, and a third output terminal is connected to conductor a. Without limitation to the following example, conductors a and b are connected to a comparator. In this configuration example, the conductor selector 800 connects the two or more simultaneously selected conductors 700 to conductor a and conductor b as follows:

[0112] The conductor selector 800 performs the following selection operation in the configuration shown in FIG. For k=1: From n(k)=3 and equations (11) and (12), Y(1)={1}∪{2}, Y a ={2}∪{3,4,5,6,7,8} Therefore, When y=1, the conductor selector 800 Select the third output terminal of the single-pole, triple-throw switch connected to the first conductor 700; Select the first output terminal of the single-pole, triple-throw switch connected to the second conductor 700; By selecting the second output terminal of each single-pole, triple-throw switch connected to the third to eighth conductors 700, the first conductor 700 and the second conductor 700 are selected simultaneously. When y=2, the conductor selector 800 is Select the second output terminal of the single-pole, triple-throw switch connected to the first conductor 700; Select the third output terminal of the single-pole, triple-throw switch connected to the second conductor 700; By selecting the first output terminal of each single-pole triple-throw switch connected to the third to eighth conductors 700, the second to eighth conductors 700 are simultaneously selected. For k=2: From n(k)=5 and equations (11) and (12), Y(1)={3}∪{4}, Y(2)={4}∪{5}, Y(3)={5}∪{6}, Y a ={6}∪{7,8} Therefore, When y=1, the conductor selector 800 Select the third output terminal of the single-pole, triple-throw switch connected to the third conductor 700; Select the first output terminal of the single-pole, triple-throw switch connected to the fourth conductor 700; By selecting the second output terminal of each single-pole triple-throw switch connected to the first, second, and fifth-eighth conductors 700, the third conductor 700 and the fourth conductor 700 are simultaneously selected. When y=2, the conductor selector 800 is Select the third output terminal of the single-pole, triple-throw switch connected to the fourth conductor 700; Select the first output terminal of the single-pole, triple-throw switch connected to the fifth conductor 700; By selecting the second output terminal of each single-pole triple-throw switch connected to the first-third and sixth-eighth conductors 700, the fourth conductor 700 and the fifth conductor 700 are simultaneously selected. When y=3, the conductor selector 800 is Select the third output terminal of the single-pole, triple-throw switch connected to the fifth conductor 700; Select the first output terminal of the single-pole, triple-throw switch connected to the sixth conductor 700; By selecting the second output terminal of each single-pole triple-throw switch connected to the first, fourth, seventh, and eighth conductors 700, the fifth conductor 700 and the sixth conductor 700 are simultaneously selected. When y=4, the conductor selector 800 is Select the second output terminal of the single-pole, triple-throw switch connected to the 1st-5th conductor 700, Select the third output terminal of the single-pole, triple-throw switch connected to the sixth conductor 700; By selecting the first output terminal of each single-pole triple-throw switch connected to the seventh and eighth conducting wires 700, the sixth to eighth conducting wires 700 are simultaneously selected. For k=3: From n(k)=2 and equation (11), Y(1)={7}∪{8} Therefore, When y=1, the conductor selector 800 Select the second output terminal of the single-pole, triple-throw switch connected to the 1st to 6th conductors 700, Select the third output terminal of the single-pole, triple-throw switch connected to the seventh conductor 700; By selecting the first output terminal of each single-pole, triple-throw switch connected to the eighth conductor 700, the seventh conductor 700 and the eighth conductor 700 are simultaneously selected.

[0113] The controller for controlling the operation of the conductor selector 800 is well known and therefore has not been shown or described.

[0114] The liquid level meter of the present disclosure includes the above-described interface sensor 200, and the first substance is a liquid and the second substance is a gas. In the liquid level meter, the first direction is preferably, but not limited to, the vertical direction.

[0115] <Additional Notes> The embodiments shown in FIGS. 2 to 14 are level meters in which E is expressed as a power of 2, and one of the E second electrical conductors is an electrode pair having a predetermined capacitance to improve accuracy.

[0116] <Addendum> While the present invention has been described with reference to exemplary embodiments, those skilled in the art will recognize that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. Furthermore, many modifications can be made to adapt a particular system, device, or component thereof to the teachings of the present invention without departing from the essential scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

[0117] Furthermore, the use of terms such as "first" and "second" does not denote order or importance, and terms such as "first" and "second" are used to distinguish elements. The terms used herein are for the purpose of describing embodiments and are not intended to limit the present invention in any way. The term "comprises" and its conjugations, when used in this specification and / or the appended claims, reveal the presence of the mentioned features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The term "and / or" includes any and all combinations of one or more of the associated listed elements, if any. In the claims and the specification, unless otherwise specified, the use of words such as "connected," "coupled," "joined," "connected," or their equivalents, and all forms thereof, does not necessarily negate the presence of one or more intermediate elements between two elements that are, for example, "connected" or "coupled" to each other or "coupled" to each other. In the claims and the specification, the term "optional," if any, should be understood as a term that represents the same meaning as the universal symbol ∀, unless otherwise specified. For example, the phrase "for any X" has the same meaning as "for all X" or "for each X."

[0118] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Furthermore, terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art and this disclosure, and should not be interpreted ideally or excessively formally unless explicitly defined.

[0119] It will be understood that in describing the present invention, many techniques and steps are disclosed. Each of these has distinct advantages, and each can be used in combination with one or more, or in some cases all, of the other disclosed techniques. Therefore, to avoid cluttering, this specification will refrain from describing every possible combination of individual techniques or steps. Nevertheless, the specification and claims should be read with the understanding that such combinations are fully within the scope of the present invention and claims.

[0120] The corresponding structure, material, acts, and equivalents of all functional elements combined with means or steps in the following claims are intended to include the structure, material, or acts, if any, that perform the function in combination with other elements.

[0121] Although the present invention has been described above with reference to exemplary embodiments, it is not limited to these embodiments. Various modifications and variations are possible without departing from the spirit of the present invention. The selected and described embodiments are intended to illustrate the principles of the present invention and its practical application. The present invention may be used in various embodiments with various modifications and variations, which are determined according to the expected use. All such modifications and variations are intended to be included within the scope of the present invention, as defined by the appended claims, and are intended to be accorded the same protection when interpreted in accordance with the breadth that is fairly, legally, and equitably to be given. [Explanation of symbols]

[0122] 1 aquarium 2 Interface sensor 3 Sensor Block 5 electrode pairs 5a electrode 5b electrode 6 electrode pairs 7 Conductor 7x branch line 7y branch line 9 Substrate 10 Reference Line 11~17 Judgment means 20 Water level output means 30 Sensor unit 31 electrode 40 Grounding Conductor 50 Carrier wave generation circuit 61,62 Resistor 70 Adjustment section 80 Switching Method 81 Switch 90,90' Discrimination means 100 Water level determination means 110 Control means 120 Switching Method 121 Switch 130,140 Charging circuit 150 A / D conversion section 160 Adjustment value memory section 200 Interface Sensor 300 Sensor Block 500a First Electrical Conductor 500b Second electrical conductor 700 conductor 700x branch line 800 Conductor Selector 900 boards

Claims

1. a ground conductor extending in the liquid level detection direction; a sensor unit including a plurality of electrodes arranged in a liquid level detection direction and forming capacitance between the electrodes and the ground conductor; An adjustment unit; A switching means; A discrimination means; a liquid level determining means; The plurality of electrodes are divided into n groups, and the i-th group (i=1, 2, . . . , n) is the second group from the bottom in the liquid level detection direction. i-1 (2k-1)th (k is 1 to 2 n-i The electrode is located at a position (a natural number up to 1000). the plurality of electrodes belonging to the same group are connected in parallel to each other and connected to the switching means; the determining means determines the magnitude relationship between the capacitance of the i-th group and the capacitance of the combined group of the (i+1)-th group to the n-th group for i=1, 2, ..., n-1, and further determines the magnitude relationship between the capacitance of the n-th group and the capacitance of the adjusting unit; the switching means sequentially switches the connection between the group and the discrimination means so as to enable discrimination by the discrimination means; A liquid level meter characterized in that the liquid level determining means determines the liquid level based on the determination by the determining means.

2. 2. The liquid level meter according to claim 1, The liquid level meter is characterized in that the adjusting section functions so that the two capacitances whose magnitude relationship is determined by the determining means always have different values.

3. 3. The liquid level meter according to claim 2, A liquid level meter comprising a plurality of the adjusting units, and switching the adjusting unit to function depending on the group connected to the determining means.

4. The liquid level meter according to any one of claims 1 to 3, A liquid level meter characterized in that the ground conductor is in the shape of a pipe surrounding the periphery of the sensor portion.

5. The liquid level meter according to any one of claims 1 to 3, A liquid level meter characterized in that an A / D converter is provided between the switching means and the determining means.

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