Liquid level gauge and sensor for identifying position of interface

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

Sensors and level gauges for identifying the position of the interface

[0001] The present disclosure relates to a sensor for identifying the position of an interface between two types of substances (hereinafter referred to as an interface sensor), and a liquid level meter including the interface sensor.

[0002] Figure 1 is a copy of Figure 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 (e.g., 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) are set in advance. In the example shown in FIG. 1, Z=7, and there are seven observation points Q １ ~Q ７ is shown.

[0003] Electrode pair P １ ~P ７ is observation point Q １ ~Q ７ The determination means 11 to 17 are arranged one-to-one at the level of the electrode pairs P １ ~P ７ Each of the determination means 11 to 17 is connected to the electrode pair P １ ~P ７ For example, the capacitance value of the corresponding electrode pair at the observation point Q ３ Electrode pairs P arranged at the level of ３ If the determination means 13 determines that the capacitance value of the observation point Q exceeds a predetermined reference value, ３ There is liquid at the observation point Q ３ Electrode pairs P arranged at the level of ３ If the determination means 13 determines that the capacitance value of the observation point Q does not exceed the predetermined reference value, ３ There is no liquid at the level.

[0004] When i determination means (iε{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 i-th observation point. In the example shown in FIG. 1, the electrode pair P below the liquid level L (i.e., immersed in the liquid) １ ~P ４ The determination means 11 to 14 corresponding to the electrode pairs P above the liquid surface L (i.e., not immersed in the liquid) output a determination result indicating that the reference value has been exceeded. ５ ~P ７ The determination means 15 to 17 corresponding to the fourth observation point Q outputs a determination result indicating that the reference value is not exceeded. ４ Outputs information indicating the level of

[0005] Japanese Patent Application Publication No. 11-311562

[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 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, when 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 one 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-mentioned background technology, we disclose an interface sensor having a configuration that allows the total number of conductors L drawn from the interface sensor to be less than Z+1 (where Z is the total number of observation points), and a liquid level meter including the interface sensor.

[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] The sensor disclosed herein is a sensor for identifying 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). The sensor includes a first electrical conductor, E second electrical conductors, L conductors, and a conductor selector. The following equations hold for E and L: In these equations, K is a predetermined integer satisfying 2≦K, and for each j∈{x∈N: 1≦x≦K}, n(j) is a predetermined integer satisfying 2≦n(j), and N is the set of all positive integers. The E second electrical conductors are located in E mutually disjoint and parallel planes in an order according to the magnitude relationship of the elements in the set {x∈N:1≦x≦E}. For each p∈{x∈N:1≦x≦E-1}, the pth second electrical conductor among the E second electrical conductors is connected to the s(p)th conductor among the L conductors. The following equation holds for s(p): In this equation, n(0)=1. In the above equation, r is specified by p∈W(r). For each k∈{x∈N: 1≦x≦K}, the kth set W(k) is expressed by the following equation. In this equation, the K+1th set W(K+1) is an empty set. The Eth second electrical conductor among the E second electrical conductors is connected to the Lth conductor among the L conductors. The conductor selector can select any one conductor among the L conductors. Alternatively, for each k∈{x∈N: 1≦x≦K}, the conductor selector: 1) if k≠K and n(k)≠2, for each y∈{x∈N: 1≦x≦n(k)-2}, select two conductors among the L conductors determined by elements belonging to set Y(y), where For y=n(k)-1, the element (2+Σ j=k+1 K Select (n(j)-1)) conducting wires, where: 2) When k≠K and n(k)=2, among the L conducting wires, the element belonging to the set Y is determined as (2+Σ j=k+1 K Select (n(j)-1)) conducting wires, where: 3) for k=K, for each y∈{x∈N: 1≦x≦n(k)−1}, select two conductors from the L conductors that are determined by elements belonging to the set Y(y), where is.

[0011] According to this invention, the total number L of conductors drawn out from the interface sensor can be made smaller than Z+1 (where Z is the total number of observation points).

[0012] 1 is a diagram showing an example of the configuration of a water level sensor of the prior art. FIG. 1 is a diagram for explaining the configuration of Example 1 of a water level meter according to the present invention. (a) A diagram for explaining the operation of the water level meter shown in FIG. 2, and (b) A diagram for explaining the operation of the water level meter shown in FIG. 2. A flowchart showing the flow of water level measurement using the water level meter shown in FIG. 2. A table showing the operation of switches in water level measurement using the water level meter shown in FIG. 2. FIG. 1 is a diagram for explaining the configuration of Example 2 of a water level meter according to the present invention. A flowchart showing the flow of water level measurement using the water level meter shown in FIG. 6. A table showing the operation of switches in water level measurement using the water level meter shown in FIG. 6. FIG. 1 is a diagram for explaining the configuration of Example 3 of a water level meter according to the present invention. (a) A diagram for explaining the operation of the water level meter shown in FIG. 9, and (b) A diagram for explaining the operation of the water level meter shown in FIG. 9. A table showing the operation of switches in water level measurement using the water level meter shown in FIG. 9. FIG. 1 is a diagram for explaining the configuration of Example 4 of a water level meter according to the present invention. A table showing the operation of switches in water level measurement using the water level meter shown in FIG. 12. FIG. 1 is a diagram for explaining the configuration of Example 5 of a water level meter according to the present invention. SUMMARY OF THE INVENTION An example of the configuration of an interface sensor related to the interface sensor of the present disclosure, but not protected by the scope of the claims of the present application. An example of the configuration of an interface sensor of the present disclosure.

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

[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 FIG. 2, the 15 electrodes 31 are numbered C1 to C15, starting from the bottommost electrode 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 the second to nth electrodes 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] First group: C1, C3, C5, C7, C9, C11, C13, C15 Second group: C2, C6, C10, C14 Third group: C4, C12 Fourth group: C8 All electrodes 31 belonging to the same group are connected in parallel and connected 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 adjusting section 70 is a capacitor having a capacitance as will be described later, one end of which is connected to a wiring extending from the switching means 80 to the input b of the determining means 90, and the other end of which is grounded.

[0021] The determining 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 When this is done, 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 ａ >C ｂ Therefore, the delay of the waveform at point b is smaller. In this example, the discrimination means 90 is provided with a circuit for binarizing each waveform using voltage s as a threshold value, and a logic circuit that sets Hi at the rising edge of the binarized waveform at point a and Lo at the rising edge of the binarized 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 ｂIn this case, the waveform of the discrimination process becomes Hi for a time exceeding half a period, and therefore the Hi time is longer than the Lo time.

[0023] C ａ <C ｂ In this case, the waveform at point a has a smaller delay, and the waveform of the discrimination process is as shown in FIG. 3(b) due to the circuit configuration described above, and since it becomes Lo for a time exceeding half a cycle, the Lo time is longer than the Hi time. Therefore, by comparing the Hi time and Lo time of the discrimination process waveform, C ａ and C ｂ The discrimination means 90 can discriminate between the magnitude of C ａ >C ｂ When C ａ <C ｂ When , 0 is output.

[0024] The water level determining means 100 determines the water level based on the determination by the determining means 90 operating in this manner, and outputs the result 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 determining means 100.

[0025] Next, the flow of the water level output by the water level meter having such a configuration will be described with reference to the flowchart shown in Figure 4. In Figure 4, the number of groups is n, and G ｉ indicates the i-th group, and G i+1 , G i+2 , G ｎ indicate the (i+1)th group, the (i+2)th group, and the nth group, respectively.

[0026] First, set i=1 (step M1), and turn off all the switches 81 of the switching means 80 (step M2). ｉ The switch 81 connecting the inputs b and G of the determining means 90 is turned on. i+1 , G i+2 , ..., G ｎThe switch 81 that connects the two inputs a and b is turned on (steps M3 and M4). The determining means 90 determines the magnitude relationship between the inputs a and b (step M5). If a>b, it outputs 1 to the water level determining means 100, and if a<b, it outputs 0 to the water level determining means 100. The water level determining means 100 converts this into 2 i-1 The value is stored as a bit value (steps M6 and M7).

[0027] Next, i is set to i+1 (step M8), and it is determined whether i=n (step M9). If i=n is not true, the process returns to step M2 and steps M2 to M9 are repeated until i=n.

[0028] When i=n, ​​all the switches 81 of the switching means 80 are turned OFF (step M10), and then the inputs a and G of the determining means 90 are ｎ The switch 81 that connects the inputs a and b is turned on (step M11). The discrimination means 90 determines the magnitude relationship between the inputs a and b (step M12), 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 converts this into 2 n-1 The water level determining means 100 stores the two-bit value thus obtained (steps M13 and M14). ０ Bit 2 n-1 The bit value, i.e., the binary number, is converted into a water level by referring to the memory and output (step M15).

[0029] 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, and further measures the water level by discriminating the magnitude relationship between the detection value obtained by the n-th group and the detection value obtained by the adjustment unit 70, and the switching means 80 sequentially switches the connection between the group of sensor units 30 and the discrimination means 90 to enable such discrimination by the discrimination means 90.

[0030] Table 1 shown in Fig. 5 shows the ON / OFF of seven switches 81, i.e., S1 to S7, of the switching means 80 for i = 1 to 4 in the water level meter shown in Fig. 2, i.e., in the water level meter where the number n of groups of sensor units 30 is 4 and i ranges from 1 to 4 in the flowchart shown in Fig. 4. In the water level meter shown in Fig. 2, the first to fourth groups are designated as G １ ~G ４ When expressed as follows, the connections of the groups to the two inputs a and b of the discriminator 90 are as follows for i=1 to 4:

[0031] Input a Input b i=1:2 ０ Bit determination G １ G ２ +G ３ +G ４ i=2:2 １ Bit determination G ２ G ３ +G ４ i=3:2 ２ Bit determination G ３ G ４ i=4:2 ３ Bit determination G ４ N / 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 shown 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 located 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: G １　 =C1+C3+C5+C7+C9+C11+C13+C15 =5C water+3C air =403C air Input b: G ２ +G ３ +G ４ =C2+C4+C6+C8+C10+C12+C14+C99 =4.5C water +3C air =363C air <i=2:2 １ Bit Determination> Input a: G ２ =C2+C6+C10+C14 =2C water +2C air =162C air Input b: G ３ +G ４ =C4+C8+C12+C99 =2.5C water +C air =201C air <i=3:2 ２ Bit Determination> Input a: G ３ =C4+C12 =C water +C air =81C air Input b: G ４ =C8+C99 =1.5C water = 120C air <i=4:2 ３ Bit Determination> Input a: G ４ =C8 =C water =80C air Input b: N / A = C99 = 0.5C water = 40C air From the above, when i = 1, a > b, so 2 ０ The bit becomes 1, and when i=2, a<b, so 2 １ The bit becomes 0. Also, when i=3, a<b, so 2 ２ The bit becomes 0, and at i=4, a>b, so 2 ３ The bit is 1. Therefore, adding these together gives the binary number 1001, 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 a low water level where none of the electrodes 31 are submerged, the binary number is 0000, and at a high water level where all of the electrodes 31 are submerged, the binary number is 1111 (15 in decimal).

[0034] In this example, the adjustment unit 70 water The capacitor is always connected to the input b of the discrimination means 90, and i=4, 2 ３ When determining the bit, ４ The adjustment unit 70 functions to compare the two detected values ​​(capacitances) whose magnitude relationship is determined by the determination means 90, and to always make them different from each other, in other words, 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.

[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 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 connected to +0.5 C. 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: G １ =C1+C3+C5+C7+C9+C11+C13+C15 =5C water +3 Ｃair =403C air Input b: G ２ +G ３ +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: G ２ =C2+C6+C10+C14 =2C water +2C air =162C air Input b: G ３ +G ４ =C4'+C8+C12+C99 =2.5C water +C air +C99=201C air +C99 <i=3:2 ２ Bit Determination> Input a: G ３ =C4'+C12 =1.5C water +C air =121C air Input b: G ４ =C8+C99 =C water +C99=80C air +C99 <i=4:2 ３ Bit Determination> Input a: G ４ =C8 =C water =80C air Input b: N / A = C99 The true value of the binary number is 1001, so a>b must be true for i=1, a<b for i=2, a<b for i=3, and a>b for i=4. Therefore, for i=1, it is 403C. air >363C air +C99 to C99<40C air must be, and for i=3 it is 121C air <80C air +C99 to 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 a switching means 120 for switching the connection of these adjustment units 70 to the 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 the 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 flow 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' is added between steps M4 and M5 to "turn on the switch that connects the adjustment unit corresponding to i to b", and step M11' is added between steps M11 and M12 to "turn on the switch that connects the adjustment unit corresponding to n to b".

[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 prior testing.

[0042] 9 shows the configuration of a third embodiment of the water level meter according to the present invention. In this example, a charging circuit 130 is provided as an input circuit instead of a carrier wave generating circuit 50, and capacitance detection is performed using a switched capacitor. １ ~G ４ and the charging circuit 130, switches S11 to S14 are provided, respectively, １ ~G ４ A switching means 80 having seven switches 81, namely, S1 to S7, is located between the adjusting unit 70 and the determining means 90'. Furthermore, a switch S21 is provided between the adjusting unit 70 and the charging circuit 130, and a switch S22 is provided between the adjusting unit 70 and the determining 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, the 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 the inputs a and b. 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.

[0045] When the switches S13, S14, and S21 are ON and the switches S4, S7, and S22 are OFF, the third group of the sensor unit 30: G ３ , 4th group: G ４ The adjusting unit 70 adjusts the voltage E generated by the charging circuit 130. ０ The determination means 90' is ａ and C ｂ Each of these has an integrating circuit and a sample-and-hold circuit (S / H circuit). When the switches S13, S14, and S21 are OFF and the switches S4, S7, and S22 are ON, ａ and C ｂ The charges of C move to the integrating circuit. ａ and Cｂ The amplitude voltage V of each integrator circuit ａ , V ｂ is the integral capacitance C ｓ This gives us the following:

[0046]

[0047] V a , V ｂ can be obtained as a DC voltage by a sample-and-hold circuit located after the integrator circuit, and C ａ >C ｂ When C is ａ <C ｂ Therefore, by comparing the voltage values, C ａ and C ｂ The discrimination means 90' is capable of discriminating between the magnitude of C ａ >C ｂ When C ａ <C ｂ When the water level is 0, the water level determining means 100 converts the output of the determining means 90' into a water level and outputs it, similar to the water level determining means 100 in FIG.

[0048] 12 shows a water level meter according to a fourth embodiment. This water level meter is a modified example of the water level meter according to the third embodiment, and is provided with two charging circuits. The two charging circuits 130 and 140 charge the respective groups G of the sensor unit 30. １ ~G ４ The voltage to be charged can be changed. ２ ~G ４ and the charging circuit 140. In this example, for each of i=1 to 4, the switches S1 to S7, S11 to S17, and S21 to S22 are controlled as shown in Table 4 in FIG.

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

[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 portion to the discrimination means only needs to be the number of groups, and only one discrimination means is required.

[0053] Furthermore, for example, if it is desired to detect the water level in 1000 steps (a resolution of 1 / 1000 of the measurement range), in the case of a configuration such as the conventional example shown in Figure 1, the number of discrimination means and electrode pairs will be 1000, and the number of wires on the detection side leading to the discrimination means will be 1000.

[0054] In contrast, in the water level meter according to the present invention, the group configuration as described above is used to measure the number of groups by n. n -1 electrode measurement is possible, that is, 1 / (2 n -1), so if a resolution of 1 / 1000 is to be obtained, the number of groups needs to be 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, etc. When measuring the water level of a river, if the ground 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] The interface sensor 200 of the present disclosure and a liquid level meter including the interface sensor 200 will be described below from another perspective with reference to non-limiting examples shown in FIGS. 16 and 17. 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 this 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 one or zero 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) below). 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 generated at each of the E electrode pairs according to the properties of the first or second material present between the E electrode pairs. An "interface" is a 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, a substance system is a "homogeneous phase" when the physical and chemical properties of any part V of the substance system entity are the same as those of any part W that is different from part V of the substance system entity. 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 previous embodiment. Furthermore, if the 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, only the capacitance of the electrode pair will be described below, 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] Without being limited to the following example, the K sensor blocks 3 are formed on F substrates 9 each having a flat plate shape. F is a predetermined integer that satisfies 1≦F≦K. If F<K, there is a substrate 9 having two or more sensor blocks 3. In the example shown in FIG. 15 , F=1. If F≧2, the F substrates 9 are not limited to the following example, and may be arranged on a single plane, or may be arranged like angle irons or channel irons, or may be arranged like triangular pipes or square pipes.

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

[0062] When the first electrical conductor 5a is a single electrical conductor, the shape of the first electrical conductor 5a is not limited to the following examples and may be a flat plate or a cylinder. When the first electrical 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 electrical conductor 5a has a cylindrical shape, the K sensor blocks 3 are usually arranged inside the first electrical conductor 5a, but this is not limited to this.

[0063] When the first electrical conductor 5a includes two or more electrical conductors, the shape of each of the electrical conductors included in the first electrical conductor 5a 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 (i.e., 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, a 1 / 4 cylinder shape)). When the first electrical conductor 5a includes two or more electrical conductors, the two or more electrical conductors may be independent of each other. In other words, the two or more electrical conductors included in the first electrical conductor 5a do not need to be in contact with each other or 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 drawing, 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 out of 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 be apparent from equations (4) and (5) below, in order to make the total number L of conducting wires 7 drawn out 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.

[0066] In designing the interface sensor 2, the value of M(1), which is related to the resolution of the interface sensor 2, will typically be determined first. From this perspective, n(k) is a positive divisor of M(1), excluding 1 and M(1). Therefore, n(k) < M(1) for each k∈{x∈N: 1≦x≦K}. Furthermore, note that the representation of M(1) is not unique. For example, if M(1) = 60, M(1) is: M(1) = 2 x 30 (i.e., K = 2, n(1) = 30, n(2) = 2), M(1) = 3 x 20 (i.e., K = 2, n(1) = 20, n(2) = 3), M(1) = 12 x 5 (i.e., K = 2, n(1) = 5, n(2) = 12), M(1) = 4 x 3 x 5 (i.e., K = 3, n(1) = 5, n(2) = 3, n(3) = 4), M(1) = 5 x 6 x 2 (i.e., K = 3, n(1) = 2, n(2) = 6, n(3) = 5), M(1) = 2 x 3 x 2 x 5 (i.e., K = 4, n(1) = 5, n(2) = 2, n(3) = 3, n(4) = 2), For example, M(1) has two or more representations (i.e., two or more factorizations). When M(1) has two or more representations, the implementer of the interface sensor 2 can arbitrarily select one representation, taking into consideration the ease of implementation of the interface sensor 2, the manufacturing cost of the interface sensor 2, the environment in which the interface sensor 2 will be used, etc. In other words, two or more representations of M(1) mean the degree of freedom in the design 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 example, and may be a rectangular flat plate or a circular flat plate. In the kth (kε{xεN: 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 when the spaces between the M(k) electrode pairs are filled with, for example, a first substance. k From another perspective, "M(k) electrode pairs have the same capacitance C when the spaces between the M(k) electrode pairs are filled with, for example, the first substance. k In order to satisfy the condition that "has m (k) second electrical conductors 5b" among the M(k) second electrical conductors 5b included in the k-th (kε{xεN: 1≦x≦K}) sensor block 3, kthe 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, and the distances between the first electrical conductor 5a and the M(k) second electrical conductors 5b are equal to each other, the above condition is met. 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 considered to be 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 j-th (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 (kε{xεN: 1≦x≦K}) sensor block 3 k The second electrical conductor 5b is located on the r(k, m) plane of the M(1) planes. k )th plane P(r(k,m kIt is located at 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 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, the qth (q∈{x∈N: 2≦x≦p-1}) plane P(q) exists between the first plane P(1) and the pth (p∈{x∈N: 3≦x≦M(1)}) plane P(p). More simply stated, when the normal direction of the M(1) planes P(1), ..., P(M(1)) that are parallel to each other 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 in a linear fashion, but this is not limited thereto; for example, they may be arranged in the shape of a walking footprint.

[0069] From the viewpoint of ease of design and ease of manufacture of the interface sensor 2, the K sensor blocks 3 are usually arranged in a second direction perpendicular 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, the "plane" may be rephrased as, for example, a "level."

[0070] m of the M(k) second electrical conductors 5b included in the k-th (kε{xεN: 1≦x≦K}) sensor block 3 k th (m k ∈{x∈N: 1≦x≦M(k)}) is the second electrical conductor 5b of the n(k) conducting wires 7. k ) conductor 7. k th (m k ∈{x∈N: 1≦x≦M(k)}) and the second electrical conductor 5b and s(m k )-th conductors 7 are connected to each other via branch wires 7x in this example. k ) is 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 For ∈{x∈N: 1≦x≦M(k)}, the formula (3) holds. In the formula (3), the symbol mod represents a modulo operation, and m k mod n(k) is the dividend m k is the remainder when Euclidean division is performed by the divisor n(k).

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

[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 (kε{xεN: 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 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 value 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 candidates for the position 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, y=0 is defined. 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 k ) with a threshold value δ, or the detection circuit shown in FIGS. 2 and 6 (including a carrier wave generating circuit 50 and a discrimination means 90), or the detection circuit shown in FIG. 9 (including a charging circuit 130, a plurality of switches controlled by the control means 110, and a discrimination means 90′), or the detection circuit shown in FIG. 12 (including charging circuits 130, 140, a plurality of switches controlled by the control means 110, and a discrimination means 90′), or the detection circuit including a programmable logic device (PLD). Examples of PLDs include FPGAs (field-programmable gate arrays).

[0073] As an example, the position of the interface can be identified by the algorithm shown in Table 1. In other words, except for the cases where the interface has not reached the plane P(1) or the case where the interface exceeds the plane P(M(1)), the section common to each sensor block 3 is identified as the section where the interface exists. In the algorithm shown in Table 1, D(T K )>δ K It is assumed that there exists a set of x∈N: 1≦x≦n(K)−1. For example, let K′ be an integer that satisfies 1<K′<K, and then D(T K’+1 )>δ K’+1 ∈{x∈N: 1≦x≦n(K′+1)−1} does not exist, and D(T K’ )>δ K’ If ∈{x∈N: 1≦x≦n(K')-1} exists, then K can be rewritten as K' in the algorithm shown in Table 1. When K'=1, an interface exists in the section corresponding to y=0 among the b(1)+1 sections determined by the pair of two planes expressed by equation (6).

[0074] 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 example of the configuration of the interface sensor 2 is shown in FIG. 15. The example configuration 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 15th 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 m2-th (m2∈{x∈N: 1≦x≦10}) second electrical conductor 5b of the ten second electrical conductors 5b included in the second sensor block 3 is connected to the s(m2)-th conductor 7 of the five conductors 7. From equation (3), the first and sixth second electrical conductors 5b are connected to the first conducting wire 7 (1 mod 5 = 6 mod 5 = 1), the second and seventh second electrical conductors 5b are connected to the second conducting wire 7 (2 mod 5 = 7 mod 5 = 2), the third and eighth second electrical conductors 5b are connected to the third conducting wire 7 (3 mod 5 = 8 mod 5 = 3), the fourth and ninth second electrical conductors 5b are connected to the fourth conducting wire 7 (4 mod 5 = 9 mod 5 = 4), and the fifth and tenth second electrical conductors 5b are connected to the fifth conducting wire 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 (m3∈{x∈N: 1≦x≦2}) second electrical conductor 5b is connected to the s(m3)-th conductor 7 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 second electrical conductors 5b included in the exemplary configuration of the interface sensor 2 shown in FIG. 15 is 42 from equation (4), and the number L of conducting wires 7 is 10 from equation (5). Since the total number of observation points M(1) is 30, L < M(1) + 1 holds. Note that, according to the prior art water level meter shown in FIG. 1, the number of conducting wires is 31 (= M(1) + 1). Furthermore, for example, although not shown, in the case where M(1) = 1440, K = 5, n(1) = 5, n(2) = 3, n(3) = 2, n(4) = 8, and n(5) = 6, the number L of conducting wires 7 in the interface sensor 2 is 24, and according to the prior art water level meter shown in FIG. 1, the number of conducting wires is 1441 (= M(1) + 1).

[0083] 15, the number F of substrates 9 is 1, but it may be 2 or 3. When 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 that 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, for accurate determination of 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) below). 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 the 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 the 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 (i.e., 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, a 1 / 4 cylinder 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 drawn from the sensor block 300 and connected to a conductor selector 800, which will be described later. In FIGS. 16 and 17, for ease of viewing, 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. In other words, E is equal to the total number of "observation points" (this total number was represented by the symbol Z in the description of the prior art). Under the above-mentioned condition, L<E+1.

[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 prime factorized (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 flat plate or a circular flat 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 mth second electrical conductor 500b among the E second electrical conductors 500b included in the sensor block 300 and the distance between the mth 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 conductors 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 the area 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 500 a overlaps with all of the second electrical conductors 500 b included in the sensor block 300, and the distance between the edge of the first electrical conductor 500 a and each of the second electrical conductors 500 b 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 500 b 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 parallel planes P(1), ..., P(E) 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 spacing 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, pε{xεN:1≦x≦E}. The E second electrical conductors 500b are usually arranged in a straight line, but this is not limited thereto 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 conductor 700 among the L conductors 700. The pth (p∈{x∈N:1≦x≦E-1}) second electrical conductor 500b and the s(p)th conductor 700 are connected to each other via a branch line 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 the 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.

[0097] In formula (9), r is specified 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 formula (10). The K+1th set W(K+1) is the empty set φ. In formula (10), the symbol "|" represents a multiple, that is, a|b means "b is a multiple of a."

[0098] If we define W = {W(j): j∈N ∧ 1≦j≦K}, then 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 conductive wire 700 of the L conductive 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 conductor selector 800: 1) When k≠K and n(k)≠2, for each y∈{x∈N: 1≦x≦n(k)−2}, simultaneously select two conductors 700 determined by elements belonging to the set Y(y) from among the L conductors 700, and for y=n(k)−1, simultaneously select two conductors 700 determined by elements belonging to the set Y(y) from among the L conductors 700. a (y) is determined by the element (2 + Σ j=k+1 K 2) When k≠K and n(k)=2, for y=n(k)-1, select a set Y of L conductors 700. a (y) is determined by the element (2 + Σ j=k+1 K (n(j)-1)) conducting wires 700 are selected simultaneously, and 3) when k=K, for each y∈{x∈N: 1≦x≦n(k)-1}, two conducting wires 700 determined by elements belonging to a set Y(y) are selected simultaneously from among the L conducting wires 700. Here, 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.

[0102] In this way, 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) With respect to formula (11), the conductor 700 determined by the elements belonging to the set expressed by formula (13) is connected to conductor a, and the conductor 700 determined by the elements belonging to the set expressed by formula (14) is connected to conductor b. B) With respect to formula (12), the conductor 700 determined by the elements belonging to the set expressed by formula (13) is connected to conductor a, and the conductor 700 determined by the elements belonging to the set expressed by formula (15) is connected to conductor b.

[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 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 the electrode pairs connected to conductor b through the conductors 700 selected by the conductor selector 800 with a predetermined threshold value 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 conductors 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 is an FPGA (field-programmable gate array).

[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 sum of the physical quantities (e.g., the sum of the capacitances) occurring in each of the electrode pairs connected to the conductor 700, which are determined by the elements belonging to the set represented by equation (13). C(14) represents the sum of the physical quantities (e.g., the sum of the capacitances) occurring in each of the electrode pairs connected to the conductor 700, which are determined by the elements belonging to the set represented by equation (14). C(15) represents the sum of the physical quantities (e.g., the sum of the capacitances) occurring in each of the electrode pairs connected to the conductor 700, which are determined by the elements belonging to the set represented 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.

[0105] When the total number Z of the aforementioned "observation points" is a prime number greater than or equal to 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 greater than or equal to 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, to which one second electrical conductor and one conductor are added. 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 x 5 x 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, pεW(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) conductor 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, L-throw switch. If the conductor selector 800 is a single-pole, L-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. The first output terminal of the single-pole, triple-throw switch is connected to conductor b, the second output terminal is terminated, and the 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. 17. When k = 1: From n(k) = 3 and equations (11) and (12), Y(1) = {1} ∪ {2}, Y a = {2} ∪ {3, 4, 5, 6, 7, 8} is obtained. Therefore, when y = 1, the conductor selector 800 simultaneously selects the first conductor 700 and the second conductor 700 by selecting the third output terminal of the single-pole triple-throw switch connected to the first conductor 700, selecting the first output terminal of the single-pole triple-throw switch connected to the second conductor 700, and selecting the second output terminal of each single-pole triple-throw switch connected to the third to eighth conductors 700. When y = 2, the conductor selector 800 simultaneously selects the second output terminal of the single-pole triple-throw switch connected to the first conductor 700, selecting the third output terminal of the single-pole triple-throw switch connected to the second conductor 700, and selecting the first output terminal of each single-pole triple-throw switch connected to the third to eighth conductors 700. When 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} is obtained. Therefore, when y = 1, the conductor selector 800 simultaneously selects the third output terminal of the single-pole triple-throw switch connected to the third conductor 700, selects the first output terminal of the single-pole triple-throw switch connected to the fourth conductor 700, and selects the second output terminal of each of the single-pole triple-throw switches connected to the first, second, and fifth-eighth conductors 700. When y = 2, the conductor selector 800 simultaneously selects the fourth conductor 700 and the fifth conductor 700 by selecting the third output terminal of the single-pole triple-throw switch connected to the fourth conductor 700, selects the first output terminal of the single-pole triple-throw switch connected to the fifth conductor 700, and selects the second output terminal of each of the single-pole triple-throw switches connected to the first-third and sixth-eighth conductors 700. When y=3, the conductor selector 800 simultaneously selects the fifth conductor 700 and the sixth conductor 700 by selecting the third output terminal of the single-pole triple-throw switch connected to the fifth conductor 700, selecting the first output terminal of the single-pole triple-throw switch connected to the sixth conductor 700, and selecting the second output terminal of each single-pole triple-throw switch connected to the first to fourth, seventh, and eighth conductors 700. When y=4, the conductor selector 800 simultaneously selects the sixth to eighth conductors 700 by selecting the second output terminal of the single-pole triple-throw switch connected to the first to fifth conductors 700, selecting the third output terminal of the single-pole triple-throw switch connected to the sixth conductor 700, and selecting the first output terminal of each single-pole triple-throw switch connected to the seventh and eighth conductors 700. When k=3: From n(k)=2 and equation (11), we obtain Y(1)={7}∪{8}. Therefore, when y=1, the conductor selector 800 selects the second output terminal of the single-pole triple-throw switch connected to the first to sixth conductors 700, selects the third output terminal of the single-pole triple-throw switch connected to the seventh conductor 700, and selects the first output terminal of each single-pole triple-throw switch connected to the eighth conductor 700, thereby simultaneously selecting the seventh conductor 700 and the eighth conductor 700.

[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] <Note> 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] <Appendix> Although 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 any order or importance, and terms such as "first" and "second" are used to distinguish between 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 synonyms thereof, 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 a person skilled 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.

[0122] 1 Water tank 2 Interface sensor 3 Sensor block 5 Electrode pair 5a Electrode 5b Electrode 6 Electrode pair 7 Conductor 7x Branch line 7y Branch line 9 Substrate 10 Reference line 11-17 Determination means 20 Water level output means 30 Sensor unit 31 Electrode 40 Ground conductor 50 Carrier wave generating circuit 61, 62 Resistor 70 Adjustment unit 80 Switching means 81 Switch 90, 90' Discrimination means 100 Water level determination means 110 Control means 120 Switching means 121 Switch 130, 140 Charging circuit 150 A / D conversion unit 160 Adjustment value storage unit 200 Interface sensor 300 Sensor block 500a First electrical conductor 500b Second electrical conductor 700 Conductor 700x Branch line 800 Conductor selector 900 Board

Claims

1. A ground conductor extending in a liquid level detection direction; a sensor unit including a plurality of electrodes arranged in a liquid level detection direction to form a capacitance between the sensor unit 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 the switching means, the discrimination means discriminates the magnitude relationship between the capacitance of the i-th group and the capacitance of the combined group from the (i+1)-th group to the n-th group for i=1, 2, ..., n-1, and further discriminates the magnitude relationship between the capacitance of the n-th group and the capacitance of the adjustment unit, the switching means sequentially switches the connections between the groups 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 gauge according to claim 1, wherein the adjustment unit functions so that the two capacitances whose magnitude relationship is determined by the determination means always have values ​​different from each other.

3. 3. The liquid level meter according to claim 2, A liquid level meter comprising a plurality of the adjustment units, and switching between the adjustment units to be operated depending on the group connected to the determination means.

4. The liquid level meter according to any one of claims 1 to 3, A liquid level gauge, wherein the ground conductor is in the form 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 comprising an A / D converter provided between the switching means and the determining means.

6. 1. A sensor for identifying a position of an interface between a first material and a second material, comprising: a first electrical conductor, E second electrical conductors, L conductors, and a conductor selector, wherein: [0019] where K is a predetermined integer such that 2≦K, and for each j ∈ {x ∈ N : 1≦x≦K}, n(j) is a predetermined integer such that 2≦n(j), and N is the set of all positive integers; The E second electrical conductors are located in E planes that are mutually disjoint and parallel to each other, in an order according to the magnitude relationship of the elements of the set {x∈N:1≦x≦E}; For each p∈{x∈N:1≦x≦E−1}, a p-th second electrical conductor among the E second electrical conductors is connected to an s(p)-th conductor among the L conductors, where [0020] where n(0)=1, and for each k∈{x∈N:1≦x≦K}, the k-th set W(k) is ##EQU00021## The K+1-th set W(K+1) is an empty set, p∈W(r), an E-th second electrical conductor among the E second electrical conductors is connected to an L-th conductor among the L conductors; The conductor selector is capable of selecting any one of the L conductors. Sensor.

7. 1. A sensor for identifying a position of an interface between a first material and a second material, comprising: a first electrical conductor, E second electrical conductors, L conductors, and a conductor selector, wherein: [0022] where K is a predetermined integer such that 2≦K, and for each j ∈ {x ∈ N : 1≦x≦K}, n(j) is a predetermined integer such that 2≦n(j), and N is the set of all positive integers; The E second electrical conductors are located in E planes that are mutually disjoint and parallel to each other, in an order according to the magnitude relationship of the elements of the set {x∈N:1≦x≦E}; For each p∈{x∈N:1≦x≦E−1}, a p-th second electrical conductor among the E second electrical conductors is connected to an s(p)-th conductor among the L conductors, where [0023] where n(0)=1, and for each k∈{x∈N:1≦x≦K}, the k-th set W(k) is ##EQU00024## The K+1-th set W(K+1) is an empty set, p∈W(r), an E-th second electrical conductor among the E second electrical conductors is connected to an L-th conductor among the L conductors; For each k ∈ {x ∈ N: 1≦x≦K}, the conductor selector 1) If k ≠ K and n(k) ≠ 2, For each y∈{x∈N: 1≦x≦n(k)−2}, select two conductors among the L conductors that are determined by elements belonging to the set Y(y), where [0025] and For y=n(k)-1, the element belonging to the set Y among the L conductors is determined as (2+Σ j=k+1 K Select (n(j)-1) conductors, where [0026] and 2) If k ≠ K and n(k) = 2, Among the L conductors, the elements belonging to the set Y are determined (2 + Σ j=k+1 K Select (n(j)-1) conductors, where [0027] and 3) When k=K, For each y∈{x∈N: 1≦x≦n(k)−1}, select two conductors from the L conductors that are determined by elements belonging to the set Y(y), where: [0028] is Sensor.

8. The sensor according to claim 6 or 7, For each j ∈ {x ∈ N: 1≦x≦K}, n(j) is a prime factor of E. A sensor characterized by:

9. The sensor according to claim 6 or claim 7, a distance between one of any two of the E second electrical conductors and the first electrical conductor is equal to a distance between the other of the E second electrical conductors and the first electrical conductor; A sensor characterized by:

10. The sensor of claim 8, a distance between one of any two of the E second electrical conductors and the first electrical conductor is equal to a distance between the other of the E second electrical conductors and the first electrical conductor; A sensor characterized by:

11. A liquid level gauge comprising: A sensor according to claim 6 or claim 7, the first substance is a liquid; The second substance is a gas; Liquid level gauge.

12. A liquid level meter, comprising: A sensor according to claim 8, the first substance is a liquid; The second substance is a gas; Liquid level gauge.

13. A liquid level meter, comprising: A sensor according to claim 9, the first substance is a liquid; The second substance is a gas; Liquid level gauge.

14. A liquid level meter, comprising: A sensor comprising: the first substance is a liquid; The second substance is a gas; Liquid level gauge.

15. 12. The liquid level meter according to claim 11, The normal direction of the E planes is the vertical direction. Liquid level gauge.

16. A liquid level meter as claimed in claim 12, The normal direction of the E planes is the vertical direction. Liquid level gauge.

17. A liquid level meter as claimed in claim 13, The normal direction of the E planes is the vertical direction. Liquid level gauge.

18. A liquid level meter as claimed in claim 14, The normal direction of the E planes is vertical. Liquid level gauge.

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