SENSOR FOR LOCATING POSITION OF INTERFACE, AND LEVEL GAUGE

Abstract

A level gauge includes an input circuit, a sensor part, and switching means, the sensor part includes electrode pairs arranged in a liquid level detection direction, the electrode pairs are divided into n groups, the i-th (i=1, 2, . . . , n) group is constituted with an electrode pair at the 2.sup.i-1(2k1)-th (k is a natural number from 1 to 2.sup.n-i) position from the lowermost position, one ends of the electrode pairs are connected to the input circuit, and the other ends belonging to the same group are connected to each other in parallel and connected to the switching means.

Claims

1-12. (canceled)

13. A level gauge comprising an input circuit, a sensor part, an adjustment part, switching means, discrimination means, and liquid level determination means, wherein the sensor part includes a plurality of electrode pairs arranged in a liquid level detection direction, the plurality of electrode pairs are divided into n groups, the i-th (i=1, 2, . . . , n) group is constituted with an electrode pair at the 2.sup.i-1(2k1)-th (k is a natural number from 1 to 2.sup.n-i) position from a lowermost position in the liquid level detection direction, one ends of all the electrode pairs are connected to the input circuit, the other ends belonging to the same group are connected to each other in parallel and connected to the switching means, the discrimination means discriminates a larger and smaller relationship between a detection value obtained by the i-th group and a detection value obtained by a group that is a combination from the (i+1)-th group to the n-th group for each of i=1, 2, . . . , n1 and further discriminates a larger and smaller relationship between a detection value obtained by the n-th group and a detection value obtained by the adjustment part, the switching means sequentially switches connection between the groups and the discrimination means so as to enable discrimination by the discrimination means, and the liquid level determination means determines a liquid level based on the discrimination by the discrimination means.

14. The level gauge according to claim 13, wherein the adjustment part functions so that two detection values for which a larger and smaller relationship is to be discriminated by the discrimination means always become values different from each other.

15. The level gauge according to claim 14, wherein a plurality of the adjustment parts are provided, and the adjustment part to be caused to function is switched according to a group to which the discrimination means is connected.

16. The level gauge according to claim 13, wherein the electrode pairs detect a resistance value between electrodes.

17. The level gauge according to claim 13, wherein the electrode pairs detect capacitance between electrodes.

18. The level gauge according to claim 17, wherein a C/V conversion part that converts capacitance into a voltage and inputs the voltage to the switching means is provided between each group and the switching means, and addition means that enables the discrimination by the discrimination means is provided between the switching means and the discrimination means.

19. The level gauge according to claim 13, wherein an A/D conversion part that converts the detection value into a digital value is provided between the switching means and the discrimination means.

20. A sensor for locating a position of an interface between a first substance and a second substance, the sensor comprising E pairs of electrodes, L conducting lines, and a conducting line selector, where $E=\underset{j=1}{\overset{K}{.Math.}}n\left(j\right),$ $L=\underset{j=1}{\overset{K}{.Math.}}\left(n\left(j\right)-1\right)+2,$ K is a predetermined integer that satisfies 2K, n(j) is a predetermined integer that satisfies 2n(j) for any j{xN: 1xK}, and N is a set of all positive integers, wherein the E pairs of electrodes are placed in E planes in order according to an order relation of elements of a set {xN: 1xE}, the E planes not coinciding with each other and being parallel to each other, for any p{xN: 1xE1}, a p-th pair of electrodes among the E pairs of electrodes has one electrode connected to an s(p)-th conducting line among the L conducting lines and the other electrode connected to an L-th conducting line among the L conducting lines, where $s\left(p\right)=\left(p/\underset{j=1}{\overset{r}{.Math.}}n\left(j-1\right)\right)\mathrm{mod}n\left(r\right)+\underset{j=1}{\overset{r}{.Math.}}\left(n\left(j-1\right)-1\right),$ n(0)=1, pW(r), a k-th set W(k) for any k{xN: 1xK} is given by $W\left(k\right)=\left\{xN:1xE(\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)\right).Math.x\right\}-\underset{j=k}{\stackrel{K}{.Math.}}W\left(j+1\right),$ and a (K+1)-th set W(K+1) is an empty set, an E-th pair of electrodes among the E pairs of electrodes has one electrode connected to an (L1)-th conducting line among the L conducting lines and the other electrode connected to the L-th conducting line among the L conducting lines, and the conducting line selector is configured to select any one conducting line among the L conducting lines except the L-th conducting line.

21. A sensor for locating a position of an interface between a first substance and a second substance, the sensor comprising E pairs of electrodes, L conducting lines, and a conducting line selector, where $E=\underset{j=1}{\overset{K}{.Math.}}n\left(j\right),$ $L=\underset{j=1}{\overset{K}{.Math.}}\left(n\left(j\right)-1\right)+2,$ K is a predetermined integer that satisfies 2K, n(j) is a predetermined integer that satisfies 2n(j) for any j{xN: 1xK}, and N is a set of all positive integers, wherein the E pairs of electrodes are placed in E planes in order according to an order relation of elements of a set {xN: 1xE}, the E planes not coinciding with each other and being parallel to each other, for any p{xN: 1xE1}, a p-th pair of electrodes among the E pairs of electrodes has one electrode connected to an s(p)-th conducting line among the L conducting lines and the other electrode connected to an L-th conducting line among the L conducting lines, where $s\left(p\right)=\left(p/\underset{j=1}{\overset{r}{.Math.}}n\left(j-1\right)\right)\mathrm{mod}n\left(r\right)+\underset{j=1}{\overset{r}{.Math.}}\left(n\left(j-1\right)-1\right),$ n(0)=1, p=W(r), a k-th set W(k) for any k{xN: 1xK} is given by $W\left(k\right)=\left\{xN:1xE(\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)\right).Math.x\right\}-\underset{j=k}{\stackrel{K}{.Math.}}W\left(j+1\right),$ and a (K+1)-th set W(K+1) is an empty set, an E-th pair of electrodes among the E pairs of electrodes has one electrode connected to an (L1)-th conducting line among the L conducting lines and the other electrode connected to the L-th conducting line among the L conducting lines, for any k{xN: 1xK}, the conducting line selector selects: (1) in a case where k+K and n(k)2, for any y{xN: 1xn(k)2}, two conducting lines determined by elements belonging to a set Y(y), among the L conducting lines, where $Y\left(y\right)=\underset{z=y}{\stackrel{y+1}{.Math.}}\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\},$ and for y=n(k)1, (2+.sub.j=k+1.sup.K(n(j)1)) conducting lines determined by elements belonging to a set Y, among the L conducting lines, where $Y=\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)\right\}.Math.\underset{m=k+1}{\stackrel{K}{.Math.}}\underset{z=1}{\stackrel{n\left(m\right)-1}{.Math.}}\left\{\underset{j=1}{\overset{m}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\}.Math.\left\{L-1\right\},$ (2) in a case where k+K and n(k)=2, (2+.sub.j=k+1.sup.K(n(j)1)) conducting lines determined by the elements belonging to a set Y, among the L conducting lines, where $Y=\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)\right\}.Math.\underset{m=k+1}{\stackrel{K}{.Math.}}\underset{z=1}{\stackrel{y+1}{.Math.}}\left\{\underset{j=1}{\overset{m}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\}.Math.\left\{L-1\right\},$ and (3) in a case where k=K, for any y{xN: 1xn(k)1}, two conducting lines determined by the elements belonging to a set Y(y), among the L conducting lines, where $Y\left(y\right)=\underset{z=y}{\stackrel{y+1}{.Math.}}\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\},$

22. The sensor according to claim 20, wherein for any j{xN: 1xK}, the n(j) is a prime factor of the E.

23. The sensor according to claim 21, wherein for any j{xN: 1xK}, the n(j) is a prime factor of the E.

24. A level gauge comprising: the sensor according to claim 20, wherein the first substance is a liquid, and the second substance is a gas.

25. A level gauge comprising: the sensor according to claim 21, wherein the first substance is a liquid, and the second substance is a gas.

26. A level gauge comprising: the sensor according to claim 22, wherein the first substance is a liquid, and the second substance is a gas.

27. A level gauge comprising: the sensor according to claim 23, wherein the first substance is a liquid, and the second substance is a gas.

28. The level gauge according to claim 24, wherein a normal direction of the E planes corresponds to a vertical direction.

29. The level gauge according to claim 25, wherein a normal direction of the E planes corresponds to a vertical direction.

30. The level gauge according to claim 26, wherein a normal direction of the E planes corresponds to a vertical direction.

31. The level gauge according to claim 27, wherein a normal direction of the E planes corresponds to a vertical direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1 is a view illustrating a configuration example of a water level sensor in prior art;

[0027] FIG. 2 is a view illustrating a configuration of Example 1 of a water gauge according to the present invention;

[0028] FIG. 3 is a flowchart showing flow of water level measurement by the water gauge illustrated in FIG. 2;

[0029] FIG. 4 is a table showing operation of a switch in the water level measurement by the water gauge illustrated in FIG. 2;

[0030] FIG. 5 is a view illustrating a configuration of Example 2 of the water gauge according to the present invention;

[0031] FIG. 6 is a view illustrating a configuration of Example 3 of the water gauge according to the present invention;

[0032] FIG. 7 is a view illustrating a configuration of Example 4 of the water gauge according to the present invention;

[0033] FIG. 8 is a view illustrating a configuration of Example 5 of the water gauge according to the present invention;

[0034] FIG. 9 is a configuration example of an interface sensor which is related to an interface sensor of the present disclosure, but not protected by the claims of the present application;

[0035] FIG. 10 is a configuration example of the interface sensor of the present disclosure; and

[0036] FIG. 11 is a configuration example of the interface sensor of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] A level gauge of an embodiment of the present invention will be described using examples with reference to the drawings. Hereinafter, in description regarding FIGS. 2 to 8, water is employed as an example of a liquid.

Example 1

[0038] FIG. 2 illustrates a configuration of Example 1 of a water gauge according to the present invention, and the water gauge includes an input circuit 30, a sensor part 40, an adjustment part 50, switching means 60, discrimination means 70, water level determination means 80, and control means 90.

[0039] The sensor part 40 has a plurality of (in this example, 15) electrode pairs 41 arranged in a water level detection direction, and the electrode pairs 41 detect capacitance between electrodes in this example. Although a substrate is not illustrated, these electrode pairs 41 are provided on the substrate in a pattern, and waterproof coating is applied on the pattern. Note that as illustrated in FIG. 2, reference numerals C1 to C15 are assigned to the 15 electrode pairs 41 in order from the electrode pair located at the lowermost position.

[0040] The 15 electrode pairs 41 are divided into four groups. Here, in a case where the number of groups is set as n, and n groups are referred to as the first to the n-th group, the electrode pairs 41 constituting the i-th group (i=1, 2, . . . , n) are the electrode pairs 41 located at the 2.sup.i-1(2k1)-th (where k is a natural number from 1 to 2.sup.n-1) position from the lowermost position in the water level detection direction, and in this example, n=4, and thus, the electrode pairs 41, denoted by C1 to C15, constituting the respective groups are as follows.

[0041] First group: C1, C3, C5, C7, C9, C11, C13, C15

[0042] Second group: C2, C6, C10, C14

[0043] Third group: C4, C12

[0044] Fourth group: C8

[0045] One ends of all the electrode pairs 41 are connected to the input circuit 30, and the other ends of the electrode pairs 41 belonging to the same group are connected to each other in parallel and connected to the switching means 60. The input circuit 30 generates and outputs a carrier wave.

[0046] The switching means 60 includes seven switches 61 in this example as denoted by reference numerals S1 to S7 and has a configuration in which detection values (capacitance of respective groups) obtained by the respective groups of the sensor part 40 can be input (connected) to one of two inputs a and b of the discrimination means 70 by switching a path by turning ON/OFF of these switches 61.

[0047] The adjustment part 50 is a capacitor having capacitance as described later in this example and has one end connected to the input circuit 30 and the other end connected to the input b of the discrimination means 70.

[0048] The discrimination means 70 includes, for example, C/V conversion parts respectively for the two inputs a and b and discriminates a larger and smaller relationship between two detection values (capacitance) obtained by the inputs a and b by inputting outputs of the C/V conversion parts to a comparator and performing comparison.

[0049] The water level determination means 80 determines a water level based on the discrimination by the discrimination means 70 and outputs the water level to outside. Note that ON/OFF of the seven switches 61 of the switching means 60 is controlled by a control signal from the control means 90, and a signal in synchronization with this control is also input to the water level determination means 80 from the control means 90.

[0050] Next, a flow until the water gauge having such a configuration outputs a water level will be described with reference to a flowchart shown in FIG. 3. Note that in FIG. 3, the number of groups is set as n, G; indicates the i-th group, and G.sub.i+1, G.sub.i+2, and G.sub.n respectively indicate the (i+1)-th group, the (i+2)-th group, and the n-th group.

[0051] First, i=1 is set (step M1), and all the switches 61 of the switching means 60 are turned OFF (step M2). Then, the switch 61 that connects the input a of the discrimination means 70 and G.sub.i is turned ON, and further, the switches 61 that connect the input b of the discrimination means 70 and G.sub.i+1, G.sub.i+2, . . . , G.sub.n are turned ON (step M3, M4). The discrimination means 70 discriminates a larger and smaller relationship between the inputs a and b (step M5), and if a>b, outputs 1 to the water level determination means 80, and if a<b, outputs 0 to the water level determination means 80. The water level determination means 80 stores this as a value of 2.sup.i-1 bits (step M6, M7).

[0052] Then, i=i+1 is set (step M8), whether i=n or not is determined (step M9), and if i=n is false, the processing returns to step M2, and the steps M2 to M9 are repeated until i=n.

[0053] If i=n, after all the switches 61 of the switching means 60 are turned OFF (step M10), the switch 61 that connects the input a of the discrimination means 70 and G.sub.n is turned ON (step M11). The discrimination means 70 discriminates a larger and smaller relationship between the inputs a and b (step M12), if a>b, outputs 1 to the water level determination means 80, and if a<b, outputs 0 to the water level determination means 80. The water level determination means 80 stores this as a value of 2.sup.n-1 bits (step M13, M14), and the water level determination means 80 converts the value of 2.sup.0 bits to 2.sup.n-1 bits obtained in this manner, that is, binary to the water level with reference to a memory and outputs the water level (step M15).

[0054] In this manner, in this example, the discrimination means 70 discriminates a larger and smaller relationship between a detection value obtained by the i-th group and a detection value obtained by a group that is a combination from the (i+1)-th group to the n-th group for each of i=1, 2, . . . , n1 and further discriminates a larger and smaller relationship between a detection value obtained by the n-th group and a detection value obtained by the adjustment part 50, thereby measures the water level. The switching means 60 sequentially switches connection between the groups of the sensor part 40 and the discrimination means 70 so as to enable such discrimination by the discrimination means 70.

[0055] The table shown in FIG. 4 indicates ON/OFF of seven switches 61, that is, S1 to S7 of the switching means 60 if i=1 to 4 in the water gauge illustrated in FIG. 2, that is, the water gauge in which the number n of the groups of the sensor part 40 is four, and i becomes 1 to 4 in the flowchart shown in FIG. 3. In the water gauge illustrated in FIG. 2, in a case where the first group to the fourth group are indicated as G.sub.1 to G.sub.4, connections between the groups and the two inputs a and b of the discrimination means 70 becomes as follows if i=1 to 4.

TABLE-US-00001 Input Input a b i = 1: determination of 2.sup.0 bits G.sub.1 G.sub.2 + G.sub.3 + G.sub.4 i = 2: determination of 2.sup.1 bits G.sub.2 G.sub.3 + G.sub.4 i = 3: determination of 2.sup.2 bits G.sub.3 G.sub.4 i = 4: determination of 2.sup.3 bits G.sub.4 N/A (=not applicable)

[0056] Capacitance connected to the inputs a and b of the discrimination means 70 will be specifically described below using an example where a water level W is located at a position indicated by a dash-double-dot line in FIG. 2 and the electrode pairs from the lowermost electrode pair to the ninth electrode pair C9 are soaked in water.

[0057] Capacitance when the electrode pair 41 is located in the air is denoted by C.sub.air, and capacitance when the electrode pair 41 is located in the water is denoted by C.sub.water. The capacitor of the adjustment part 50 is denoted by C99 in the following description, and capacitance is set as 0.5 C.sub.water. Relative permittivity of water is 80 at 20 C., and C.sub.water=80 C.sub.air. In a case where i=1 to 4, the capacitance connected to the inputs a and b becomes as follows.

<i=1: Determination of 2.sup.0 Bits>

[00008]$\mathrm{Input}a:G_1=C1+C3+C5+C7+C9+C11+C13+C15=5C_{\mathrm{water}}+3C_{\mathrm{air}}=403C_{\mathrm{air}}$$\mathrm{Input}b:G_2+G_3+G_4=C2+C4+C6+C8+C10+C12+C14+C99=4.5C_{\mathrm{water}}+3C_{\mathrm{air}}=363C_{\mathrm{air}}$

<i=2: Determination of 2.sup.1 Bits>

[00009]$\mathrm{Input}a:G_1=C2+C6+C10+C14=2C_{\mathrm{water}}+2C_{\mathrm{air}}=162C_{\mathrm{air}}$$\mathrm{Input}b:G_3+G_4=C4+C8+C12+C99=2.5C_{\mathrm{water}}+C_{\mathrm{air}}=201C_{\mathrm{air}}$

<i=3: Determination of 2.sup.2 Bits>

[00010]$\mathrm{Input}a:G_3=C4+C12=C_{\mathrm{water}}+C_{\mathrm{air}}=81C_{\mathrm{air}}$$\mathrm{Input}b:G_4=C8+C99=1.5C_{\mathrm{water}}=120C_{\mathrm{air}}$

<i=4: Determination of 2.sup.3 Bits>

[00011]$\mathrm{Input}a:G_4=C8=C_{water}=80C_{air}\mathrm{Input}b:N/A=C99=0.5C_{water}=40_{air}$

[0058] From the above, if i=1, a>b and 2.sup.0 bits become 1, and if i=2, a<b and 2.sup.1 bits become 0. Further, if i=3, a<b and 2.sup.2 bits become 0, and if i=4, a>b and 2.sup.3 bits become 1. Thus, a result of adding these becomes 1001 in binary and becomes 9 in decimal.

[0059] In this manner, in the water gauge illustrated in FIG. 2, the water level is processed as binary, and in a case of a low water level at which all the electrode pairs 41 are not soaked in water, the result becomes 0000 in binary, and in a case of a high water level at which all the electrode pairs 41 are soaked in water, the result becomes 1111 in binary (15 in decimal).

[0060] The adjustment part 50 is a capacitor having capacitance of 0.5 C.sub.water in this example. The adjustment part 50 is constantly connected to the input b of the discrimination means 70 and functions to compare with G.sub.4 upon determination of 23 bits if i=4. The adjustment part 50 functions so that two detection values (capacitance) for which a larger and smaller relationship is to be discriminated by the discrimination means 70 always become values different from each other. In other words, the adjustment part 50 functions to avoid erroneous detection as a result of the larger and smaller relationship being inverted due to an error cause, or the like.

[0061] Examples 2 to 5 will be described below. Examples 2 to 5 are examples in which components of Example 1 are partially changed, and portions corresponding to the components of Example 1 illustrated in FIG. 2 will be denoted by the same reference numerals, and detailed description thereof will be omitted.

Example 2

[0062] As described above, the adjustment part 50 functions so that the detection value appropriately changes according to the water level and so that erroneous detection does not occur. However, for example, in a case where an error of capacitance of the electrode pairs 41 is larger or not uniform, a situation can occur in which the detection value does not appropriately change according to the water level only with capacitance of one adjustment part 50.

[0063] For example, in the water gauge illustrated in FIG. 2, suppose only the electrode pair 41 denoted by C4 has an error of +0.5 C.sub.water. In other words, in a case of the water level W, C4=1.5 C.sub.water. In this event, if i=1 to 4, the capacitance connected to the inputs a and b of the discrimination means 70 becomes as follows.

<i=1: Determination of 2.sup.0 Bits>

[00012]$\mathrm{Input}a:G_1=C1+C3+C5+C7+C9+C11+C13+C15=5C_{water}+3C_{air}=403C_{air}\mathrm{Input}b:G_2+G_3+G_4=C2+C{4}^{}+C6+C8+C10+C12+C14+C99=4.5C_{water}+3C_{air}+C99=363C_{air}+C99$

<i=2: Determination of 2.sup.1 Bits>

[00013]$\mathrm{Input}a:G_2=C2+C6+C10+C14=2C_{water}+2C_{air}=162C_{air}\mathrm{Input}b:G_3+G_4=C{4}^{}+C8+C12+C99=2.5C_{water}+C_{air}+C99=201C_{air}+C99$

<i=3: Determination of 2.sup.2 Bits>

[00014]$\mathrm{Input}a:G_3=C{4}^{}+C12=1.5C_{water}+C_{air}=121C_{air}\mathrm{Input}b:G_4=C8+C99=C_{water}+C99=80C_{air}+C99$

<i=4: Determination of 2.sup.3 Bits>

[00015]$\mathrm{Input}a:G_4=C8=C_{water}=80C_{air}\mathrm{Input}b:N/A=C99$

[0064] A true value of binary is 1001, and thus, a relationship between a and b must be such that if i=1, a>b, if i=2, a<b, and if i=3, a<b, and if i=4, a>b. Thus, a relationship must be such that if i=1, 403 C.sub.air>363 C.sub.air+C99, and thus, C99<40 C.sub.air, and if i=3, 121 C.sub.air<80 C.sub.air+C99, and thus, C99>41 C.sub.air. Accordingly, C99 that satisfies the both does not exist, and thus, one C99 that satisfies all determination of 2.sup.i bits, that is, the adjustment part 50 does not exist.

[0065] To address such a problem, in Example 2, as illustrated in FIG. 5, a plurality of (in this example, four, denoted by reference numerals C101 to C104) adjustment parts 50 are provided, and further, switching means 100 that switches connection of the adjustment parts 50 to the input b of the discrimination means 70 is provided. The switching means 100 includes four switches 101 denoted by reference numerals S11 to S14 which turn ON/OFF the connection of the respective adjustment parts 50, that is, C101 to C104 to the input b.

[0066] In this example, by providing a plurality of adjustment parts 50 in this manner and performing switching at the switching means 100, capacitance necessary for adjustment can be selected according to groups (combination of groups) connected to the discrimination means 70. Note that capacitance values of the four adjustment parts 50, that is, C101 to C104 are determined by a preliminary test and selected in accordance with respective processes of i=1 to 4 in the flowchart shown in FIG. 3. ON/OFF of the four switches 101 of the switching means 100 is controlled by a control signal from the control means 90, which is in synchronization with a control signal that controls the switching means 60.

Example 3

[0067] The switch 61 of the switching means 60 has gate capacitance, and thus, an error by the gate capacitance may affect the detection value. In Example 3, to address this problem, as illustrated in FIG. 6, C/V conversion parts 111 to 114 are provided between the respective groups (the first group to the fourth group: G.sub.1 to G.sub.4) of the sensor part 40 and the switching means 60 and convert capacitance values into voltage values in advance before being input to the switching means 60 so as to eliminate influence of the gate capacitance.

[0068] In this example, the adjustment part 50 outputs a predetermined voltage determined by a preliminary test using a DC/DC converter, or the like.

[0069] Two addition means 121 and 122 are provided between the switching means 60 and the discrimination means 70, and the switches S1, S2, S4 and S6 are connected to an input of the addition means 121, and the switches S3, S5, S7 and the adjustment part 50 are connected to an input of the addition means 122. The addition means 121 and 122 are, for example, addition circuits constituted with operation amplifiers.

[0070] An output of the addition means 121 is input to the input a of the discrimination means 70, and an output of the addition means 122 is input to the input b of the discrimination means 70. According to such a configuration, also in this example, discrimination processing is performed in accordance with switching operation indicated in the table in FIG. 4 and the flowchart shown in FIG. 3 in a similar manner to Example 1.

Example 4

[0071] Example 4 is a modification of a configuration of Example 3 in which the C/V conversion parts 111 to 114 are provided between the respective groups of the sensor part 40 and the switching means 60.

[0072] In this example, as illustrated in FIG. 7, the switching means 60 has four switches 61 denoted by S1 to S4 corresponding to the four C/V conversion parts 111 to 114, and an A/D conversion part 130 that converts a detection value into a digital value is provided between the switching means 60 and the discrimination means 70, and further, an adjustment value storage part 140 that stores an adjustment value (capacitance adjustment voltage value) obtained in advance as a digital value is provided.

[0073] An IC and a plurality of resistors are required for an analog circuit to output a voltage and, for example, as in a configuration having four adjustment parts 50 illustrated in Example 2, there is a disadvantage that as the number of the adjustment values increases, a circuit scale increases. Concerning this point, in this example, the adjustment values are stored as digital values, and thus, the circuit scale does not increase.

[0074] In this example, the four switches 61 of the switching means 60 are sequentially turned ON to obtain voltage outputs of the respective groups (the first group to the fourth group: G.sub.1 to G.sub.4) as digital values. The discrimination means 70 stores the digital values input from the A/D conversion part 130 in association with G.sub.i (i=1 to 4) in this example, and after digital values are obtained (stored) for all G.sub.i (i=1 to 4), performs determination for i=1 to 4, that is, determination of 2.sup.0 bits to 2.sup.3 bits by performing calculation using the digital values and the adjustment values (in this example, four adjustment values corresponding to i=1 to 4) stored in the adjustment value storage part 140.

Example 5

[0075] While in Examples 1 to 4 described above the electrode pair 41 detects capacitance between the electrodes, the electrode pair 41 may detect a resistance value between the electrodes. FIG. 8 illustrates such a water gauge as a modification of the water gauge in Example 1 illustrated in FIG. 2. The adjustment part 50 is a resistor in this example. In this example, reference numerals R1 to R15 are sequentially assigned to 15 electrode pairs 41 from the electrode pair located at the lowermost position.

[0076] A resistance value to be connected to the inputs a and b of the discrimination means 70 will be specifically described below using an example of a case where the water level W is located at the same position as in FIG. 2. Note that the input circuit 30 generates and outputs an input voltage in this example. The discrimination means 70 discriminates the resistance value of which of the inputs a and b is greater using a bridge circuit, or the like. In this example, the discrimination means 70 outputs 0 if a>b and outputs 1 if a<b in contrast to the case where capacitance is detected.

[0077] The resistance value when the electrode pair 41 is located in the air is denoted by R.sub.air, and the resistance value when the electrode pair 41 is located in the water is denoted by R.sub.water. A resistor of the adjustment part 50 is denoted by R99 in the following description, and a resistance value is set as 2 R.sub.water. R.sub.air can be such that R.sub.air. If i=1 to 4, the resistance values Ra and Rb to be connected to the inputs a and b become as follows.

<i=1: Determination of 2.sup.0 Bits>

[00016]$\mathrm{Input}a:G_1=R1+R3+R5+R7+R9+R11+R13+R151/\mathrm{Ra}=\left(5/R_{water}\right)+\left(3/R_{air}\right)\mathrm{Ra}=R_{water}/5\mathrm{Input}b:G_2+G_3+G_4=R2+R4+R6+R8+R10+R12+R14+R991/\mathrm{Rb}=\left(4.5/R_{water}\right)+\left(3/R_{air}\right)\mathrm{Rb}=R_{water}/4.5$

<i=2: Determination of 2.sup.1 Bits>

[00017]$\mathrm{Input}a:G_2=R2+R6+R10+R141/\mathrm{Ra}=\left(2/R_{water}\right)+\left(2/R_{air}\right)\mathrm{Ra}=R_{water}/2\mathrm{Input}b:G_3+G_4=R4+R8+R12+R991/\mathrm{Rb}=\left(2.5/R_{water}\right)+\left(1/R_{air}\right)\mathrm{Rb}=R_{water}/2.5$

<i=3: Determination of 2.sup.2 Bits>

[00018]$\mathrm{Input}a:G_3=R4+R121/\mathrm{Ra}=\left(1/R_{water}\right)+\left(1/R_{air}\right)\mathrm{Ra}=R_{water}\mathrm{Input}b:G_4=R8+R991/\mathrm{Rb}=1.5/R_{water}\mathrm{Rb}=R_{water}/1.5$

<i=4: Determination of 2.sup.3 Bits>

[00019]$\mathrm{Input}a:G_4=R81/\mathrm{Ra}=1/R_{water}=R_{water}\mathrm{Ra}=R_{water}\mathrm{Input}b:N/A=R991/\mathrm{Rb}=0.5/R_{water}\mathrm{Rb}=2R_{water}$

[0078] From the above, if i=1, a<b, and thus, 2.sup.0 bits become 1, and if i=2, a>b, and thus, 21 bits become 0. Further, if i=3, a>b, and thus, 2.sup.2 bits become 0, and if i=4, a<b, and thus, 2.sup.3 bits become 1. Thus, a result of adding these become 1001 in binary in Example 5 as well as in Example 1.

[0079] Various examples of the water gauge according to the present invention have been described above. The water gauge according to the present invention can obtain resolution corresponding to the number of electrode pairs by dividing a plurality of electrode pairs arranged in the water level detection direction into n groups, constituting the i-th group (i=1, 2, . . . , n) with electrode pairs located at the 2.sup.i-1(2k1)-th (where k is a natural number from 1 to 2.sup.n-i) position from the lowermost position in the water level detection direction and repeatedly comparing a larger and smaller relationship between the detection values while changing a combination of the groups.

[0080] Thus, the number of wires (wires on the detection side) to be connected to the discrimination means from the respective electrode pairs of the sensor part corresponds to the number of groups, and only one discrimination means is required.

[0081] Further, for example, suppose if the water level is detected at 1000 stages (resolution of 1/1000 with respect to a measurement range), in a case of a configuration as in the related art illustrated in FIG. 1, the number of discrimination means and the number of electrode pairs respectively become 1000, and the number of wires on the detection side from the electrode pairs to the discrimination means becomes 1000.

[0082] In contrast, in the water gauge according to the present invention, the group configuration as described above enables measurements of 2.sup.n1 electrode pairs by n groups, that is, enables to achieve resolution of 1/(2.sup.n1) by n groups, and thus, in order to achieve resolution of 1/1000, only 10 groups are required, and, only 10 wires are required on the detection side.

[0083] The water gauge described above can be, for example, used to measure a water level of a river, and the like, and, for example, can be applied to a liquid level gauge, or the like, that detects a liquid level of a liquid within a tank.

[0084] The interface sensor 200 herein disclosed and the level gauge including the interface sensor 200 will be described below in other points of view with reference to FIGS. 10 and 11 illustrating a non-limited example. Prior to the description thereof, in order to facilitate understanding of the interface sensor 200 herein disclosed, an interface sensor 2 related to the interface sensor 200 herein disclosed will be described with reference to FIG. 9. Note that while the interface sensor 2 is not protected by the claims of the present application, description of the interface sensor 2 is useful for understanding of the interface sensor 200, and thus, the description of the interface sensor 2 will be incorporated into the description of the interface sensor 200 as necessary. Note that the incorporation of the description will not be always explicitly performed.

[0085] The interface sensor 2 is a sensor for locating a position of an interface between two types of substances (that is, a first substance and a second substance different from each other). However, the number of interfaces has to be 1 or 0 in a range from a plane P(1) to a plane P(M(1)) as described later to accurately locate the position. As will be shown in Formula (4) later, the interface sensor 2 includes E pairs 5 of electrodes. The position of the interface between the first substance and the second substance is located by using physical quantities produced in each of the E pairs 5 of electrodes, corresponding to a property of the first substance or second substance present between electrodes of each of the E pairs 5 of electrodes. The interface is a contact boundary between the first substance as a homogeneous phase and the second substance as a homogeneous phase. The homogeneous phase is an entity of a material system which is uniform in chemical composition and physical state. In other words, when physical properties and chemical properties of any portion V of an entity of one material system are respectively the same as physical properties and chemical properties of any portion W different from the portion V of the entity of the material system, the entity of the material system is a homogeneous phase. A typical example of the interface sensor 2 is a sensor for locating a position of an interface between a liquid (for example, water) as the first substance and a gas (for example, air) as the second substance.

[0086] A configuration of the interface sensor 2 will be described. Symbols appearing in the following description are unrelated to symbols used in the description of the embodiments described above. Further, RC-Ep holds, where C is capacitance between two conductors with equal positive and negative charges, R is electrical resistance between the two conductors, is dielectric constant of a medium between the two conductors, and is electrical resistivity of the medium between the two conductors. Therefore, only the case of the capacitance of the pair 5 of electrodes will be described, and the description of the case of the electrical resistance of the pair 5 of electrodes will be omitted.

[0087] The interface sensor 2 includes K sensor blocks 3. Here, K is a predetermined integer satisfying 2K.

[0088] The K sensor blocks 3 are formed on F substrates 9 each having a flat plate shape, although not limited thereto. F is a predetermined integer satisfying 1FK. In a case where F<K, there is a substrate 9 having two or more sensor blocks 3. In the example shown in FIG. 9, F=1. In a case where F2, the F substrates 9 may be disposed on one plane, or may be arranged like an angle steel or a channel steel, or may be arranged like a triangular pipe or a quadrangular pipe, although not limited thereto.

[0089] The k-th sensor block 3 among the K sensor blocks 3 includes M(k) pairs 5 of electrodes and n(k)+1 conducting lines 7. The M(k) pairs 5 of electrodes included in the k-th sensor block 3 have the same capacitance Ck to each other in a state where interelectrode gap of each of the M(k) pairs 5 of electrodes is filled with, for example, the first substance. The capacitance Ck of each of the M(k) pairs 5 of electrodes included in the k-th sensor block 3 may be the same as or different from capacitance C.sub.j of each of M(j) pairs 5 of electrodes included in the j-th (jk) sensor block 3. The n(k)+1 conducting lines 7 are drawn from the sensor block 3 and are connected to the M(k) pairs 5 of electrodes as described later. The n(k)+1 conducting lines 7 are connected to a detection circuit as described later. In FIG. 9, only some pairs of electrodes and some conducting lines are provided with reference signs for ease of viewing the drawing. k is a parameter for representing an integer that satisfies 1kK, that is, k{xN: 1xK}. N is a set of all positive integers. For any k{xN: 1xK}, n(k) is a predetermined integer which satisfies 2n(k). For any k{xN: 1xK}, M(k) is expressed as Formula (1). x represents multiplication. M(1), that is, the number of the pairs 5 of electrodes included in the first sensor block 3 determines resolution of the interface sensor 2. In other words, M(1) matches a total number of observation points described above (this total number is represented by a symbol Z in the description of the prior art). Although details will become clear from Formula (4) and Formula (5) as described later, M(1)8 needs to be satisfied so that the total number L of the conducting lines 7 to be drawn from the interface sensor 2 can be smaller than a sum of 1 and the total number M(1) of the observation points. Further, in a case where M(1)=8, K=2 needs to be satisfied so that the total number L of the conducting lines 7 to be drawn from the interface sensor 2 can be smaller than a sum of 1 and the total number M(1) of the observation points.

[00020]$\begin{array}{cc}\left[\mathrm{Formula}8\right]& \\ M\left(k\right)=\underset{j=k}{\overset{K}{.Math.}}n\left(j\right)=n\left(K\right).Math.n\left(k\right)& \left(1\right)\end{array}$

[0090] In designing of the interface sensor 2, a value of M(1), which is related to the resolution of the interface sensor 2, is customarily determined first. In terms of this, n(k) is a positive divisor (except 1 and M(1)) of M(1). Thus, for any k{xN: 1xK}, n(k)<M(1). Further, note that notation of M(1) is not unique. For example, in a case where M(1)=60, M(1) has two or more types of notation (that is, two or more ways of factorization) such as

[00021]$$\begin{gathered} M\left(1\right)=230\left(\mathrm{that}\mathrm{is},K=2,n\left(1\right)=30,n\left(2\right)=2\right), \\ M\left(1\right)=320\left(\mathrm{that}\mathrm{is},K=2,n\left(1\right)=20,n\left(2\right)=3\right), \\ M\left(1\right)=125\left(\mathrm{that}\mathrm{is},K=2,n\left(1\right)=5,n\left(2\right)=12\right), \\ M\left(1\right)=435\left(\mathrm{that}\mathrm{is},K=3,n\left(1\right)=5,n\left(2\right)=3,n\left(3\right)=4\right), \\ M\left(1\right)=562\left(\mathrm{that}\mathrm{is},K=3,n\left(1\right)=2,n\left(2\right)=6,n\left(3\right)=5\right),\mathrm{and}M\left(1\right)=2325\left(\mathrm{that}\mathrm{is},K=4,n\left(1\right)=5,n\left(2\right)=2,n\left(3\right)=3,n\left(4\right)=2\right). \end{gathered}$$

In a case of M(1) having two or more types of notation, a person who implements the interface sensor 2 can freely select one type of notation in view of easiness of implementation of the interface sensor 2, manufacturing cost of the interface sensor 2, an environment in which the interface sensor 2 is used, and the like. In other words, two or more types of notation of M(1) mean a degree of freedom in designing of the interface sensor 2.

[0091] The m.sub.k-th pair 5 of electrodes among M(k) pairs 5 of electrodes included in the k-th (k{xN: 1xK}) sensor block 3 is placed in r(k, m.sub.k)-th plane P(r(k, m.sub.k)) among M(1) planes. m.sub.k is a parameter for representing an integer that satisfies 1m.sub.kM(k), that is, m.sub.k{xN: 1xM(k)}. For any k{xN: 1xK} and for any m.sub.k{xN: 1xM(k)}, r(k, m.sub.k) is expressed by Formula (2). M(1) planes P(1), . . . , P(M(1)) do not coincide with each other and are parallel to each other. The M(1) planes P(1), . . . , P(M(1)) are arranged in space in order according to an order relation of elements (that is, the order relation of natural numbers) of the set {xN: 1xM(1)}. Specifically, the q-th (q{xN: 2xp1}) plane P(q) exists between the first plane P(1) and the p-th (p{xN: 3xM(1)}) plane P(p). Further, in a simple term, in a case where a normal direction of M(1) planes P(1), . . . , P(M(1)) parallel to each other is referred to as a first direction, M(1) planes P(1), . . . , P(M(1)) are arranged in this order in the first direction. For any g{xN: 1xM(1)-2}, and h{xN: g+1xM(1)1}, a distance between the g-th plane P(g) and the (g+1)-th plane P(g+1) may be equal to or not equal to a distance between the h-th plane P(h) and the (h+1)-th plane P(h+1). For example, it is preferable to make narrower an interval between adjacent planes in a measurement range in which a position of the interface is desired to be more accurately located. In the k-th (k{xN: 1xK}) sensor block 3, M(k) pairs 5 of electrodes are customarily arranged linearly, but for example, the M(k) pairs 5 of electrodes may be arranged in a walking footprint shape, although not limited thereto.

[00022]$\begin{array}{cc}\left[\mathrm{Formula}9\right]& \\ r\left(k,m_k\right)=m_k\underset{j=1}{\overset{k}{.Math.}}n\left(j-1\right)& \left(2\right)\end{array}$

[0092] In terms of easiness of the designing and easiness of manufacturing of the interface sensor 2, K sensor blocks 3 are customarily arranged in a second direction orthogonal to the first direction. A total number of possible arrangement patterns of the K sensor blocks 3 in the second direction is K!, that is, .sub.k-1.sup.Kk. Note that in a case where the first direction is a vertical direction, plane may be rephrased as, for example, level.

[0093] The m.sub.k-th (m.sub.k{xN: 1xM(k)}) pair 5 of electrodes among M(k) pairs 5 of electrodes included in the k-th (k{xN: 1xK}) sensor block 3 has one electrode 5a, which is connected to the s(m.sub.k)-th conducting line 7 among n(k)+1 conducting lines 7, and the other electrode 5b, which is connected to the {n(k)+1}-th conducting line 7 among the n(k)+1 conducting lines 7. One electrode 5a of the m.sub.k-th (m.sub.k{xN: 1xM(k)}) pair 5 of electrodes and the s(m.sub.k)-th conducting line 7 are connected to each other by way of a support line 7x in this example. The other electrode 5b of the m.sub.k-th (m.sub.k{xN: 1xM(k)}) pair 5 of electrodes and the {n(k)+1}-th conducting line 7 are connected to each other by way of a support line 7y in this example. s(m.sub.k) is an integer that satisfies 1s(m.sub.k)n(k), that is, s(m.sub.k){xN: 1xn(k)}. For any k{xN: 1xK} and any m.sub.k{xN: 1xM(k)}, Formula (3) holds. In Formula (3), a symbol mod represents remainder calculation, m.sub.k mod n(k) is a remainder obtained by Euclidean division of a dividend m.sub.k by a divisor n(k).

[00023]$\begin{array}{cc}\left[\mathrm{Formula}10\right]& \\ s\left(m_k\right)=\{\begin{array}{cc}{m}_k\mathrm{mod}n\left(k\right)& \left(m_k\mathrm{mod}n\left(k\right)0\right)\\ n\left(k\right)& \left(m_k\mathrm{mod}n\left(k\right)=0\right)\end{array}& \left(3\right)\end{array}$

[0094] As is clear from the description above, the number E pairs 5 of electrodes included in the interface sensor 2 is given by Formula (4), and the number L of the conducting lines 7 to be drawn from the interface sensor 2 is given by Formula (5). Under the above-described conditions, L<M(1)+1 can be achieved.

[00024]$\begin{array}{cc}\left[\mathrm{Formula}11\right]& \\ E=\stackrel{}{\underset{k=1}{\overset{K}{.Math.}}}M\left(k\right)=\underset{}{\underset{k=1}{\overset{K}{.Math.}}\underset{j=k}{\overset{K}{.Math.}}}n\left(j\right)& \left(4\right)\end{array}$$\begin{array}{cc}L=\stackrel{}{\underset{k=1}{\overset{K}{.Math.}}}\left(n\left(k\right)+1\right)& \left(5\right)\end{array}$

[0095] One example of a method for locating the position of the interface using the interface sensor 2 will be described next. In the k-th (k{xN: 1xK}) sensor block 3, a detection circuit (not illustrated) compares a difference D(t.sub.k) with a predetermined threshold value 8. The difference D(t.sub.k) is a difference between combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the t.sub.k-th conducting line 7 and combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the (t.sub.k+1)-th conducting line 7. t.sub.k is a parameter for representing an integer that satisfies 1t.sub.kn(k)1, that is, t.sub.k{xN: 1xn(k)1}. As a result of the comparison, for example, in a case where D(T.sub.k)> for certain T.sub.k{xN: 1xn(k)1}, candidates for the position of the interface are provided as b(k)+1 sections each determined by a pair of two planes expressed by Formula (6). Here, when k=K, y=0 is defined. One section is a region between two planes expressed by Formula (6). In a case where D(t.sub.k) for all t.sub.k, the interface does not reach the plane P(1) or the interface exceeds the plane P(M(1)). Note that the detection circuit may be a component of the interface sensor 2 or a physical entity independent of the interface sensor 2. In the latter case, the detection circuit may be a component of the level gauge including the interface sensor 2. The detection circuit, without limitation, may be the detection circuit in the prior art, or may be a detection circuit including an AC signal generator that generates an AC signal to be applied to the {n(k)+1}-th conducting line 7 for any k{xN: 1xK}, and a comparator that compares a difference D(t.sub.k) with the threshold for any t.sub.k{xN: 1xn(k)1}, or may be the detection circuit illustrated in FIGS. 2 and 5 (including the input circuit 30 and the discrimination means 70), or may be the detection circuit illustrated in FIG. 6 (including the input circuit 30, the discrimination means 70, and the addition means 12 and 122), or may be the detection circuit illustrated in FIG. 7 (including the input circuit 80, the discrimination means 70 and the A/D conversion part 130), or may be a detection circuit including a programmable logic device (PLD). Examples of the PLD include a field-programmable gate array (FPGA).

[00025]$\begin{array}{cc}\left[\mathrm{Formula}12\right]& \\ P\left(\left(T_k+yn\left(k\right)\right)\underset{j=1}{\overset{k}{.Math.}}n\left(j-1\right)\right),P\left(\left(T_k+1+yn\left(k\right)\right)\underset{j=1}{\overset{k}{.Math.}}n\left(j-1\right)\right)y\left\{xN:0xb\left(k\right)\right\},b\left(k\right)=\left(\underset{j=k+1}{\overset{K}{.Math.}}n\left(j\right)\right)-1& \left(6\right)\end{array}$

[0096] As one example, the position of the interface can be located using an algorithm shown in Table 1. In other words, except a case where the interface does not reach the plane P(1) and a case where the interface exceeds the plane P(M(1)), a common section among the respective sensor blocks 3 is identified as a section in which the interface exists. In the algorithm shown in Table 1, it is assumed that T.sub.K{xN: 1xn(K)1} which satisfies D(T.sub.K)> exists in the K-th sensor block 3. For example, in the algorithm shown in Table 1 we can rewrite K to K of an integer which satisfies 1<K<K in a case where for the K, T.sub.K+1{xN: 1xn(K+1)1} that satisfies D(T.sub.K+1)> does not exist in the (K+1)-th sensor block 3 while T.sub.K{xN: 1xn(K)1} that satisfies D(T.sub.K)> exists in the K-th sensor block 3. In a case where K=1, the interface exists in a section corresponding to y=0 among b(1)+1 sections each determined by a pair of two planes expressed by Formula (6).

TABLE-US-00002 TABLE 1 [00026]$\mathrm{upper}=\left(T_K+1\right)\stackrel{K}{\underset{j=1}{.Math.}}n\left(j-1\right)$ [00027]$\mathrm{lower}=T_K\stackrel{K}{\underset{j=1}{.Math.}}n\left(j-1\right)$ for k = K 1 to 1 (step: 1) [00028]$b\left(k\right)=\left(\stackrel{K}{\underset{j=k+1}{.Math.}}n\left(j\right)\right)-1,r\left(k\right)=\stackrel{K}{\underset{j=1}{.Math.}}n\left(j-1\right)$ for y = 0 to b(k) (step: +1) if ((T.sub.k + y n(k)) r(k) > lower and (T.sub.k + 1 + y n(k)) r(k) < upper) then upper = (T.sub.k + 1 + y (k)) r(k) lower = (T.sub.k + y n(k)) r(k) goto G: end if next y G: next output: P(lower), P(upper)

[0097] The interface sensor 2 may include a pair of electrodes for determining that the interface does not reach the plane P(1) and/or a pair of electrodes for determining that the interface exceeds the plane P(M(1)). It can be known that the interface does not reach the plane P(1) in a case where D(t.sub.k) for all t.sub.k in the first sensor block 3, and thus, the former pair of electrodes is not essential.

[0098] A specific configuration example of the interface sensor 2 is illustrated in FIG. 9. The configuration example illustrated in FIG. 9 is an example in a case where M(1)=30, and K=3. In the example illustrated in FIG. 9, M(1)=253 is employed as factorization based on three factors of M(1). In other words, n(1)=3, n(2)=5, and n(3)=2. Thus, from Formula (1), M(1)=30, M(2)=10, and M(3)=2.

[0099] The m.sub.1-th (m.sub.1{xN: 1x30}) pair 5 of electrodes among 30 pairs 5 of electrodes included in the first sensor block 3 is placed in the r(1, m.sub.1)-th plane P(r(1, m.sub.1) among 30 planes. Here, from Formula (2), r(1, m.sub.1)=m.sub.1. In short, the p-th (p{xN: 1x30}) pair 5 of electrodes included in the first sensor block 3 is placed in the p-th plane P(p).

[0100] The m.sub.2-th (m.sub.2{xN: 1x10}) pair 5 of electrodes among 10 pairs 5 of electrodes included in the second sensor block 3 is placed in the r(2, m.sub.2)-th plane P(r(2, m.sub.2)) among 30 planes. Here, from Formula (2), r(2, m.sub.2)=3m.sub.2. In short, the p-th (p{xN: 1x10}) pair 5 of electrodes included in the second sensor block 3 is placed in the (3p)-th plane P(3p). For example, the seventh (p=7{xN: 1x10}) pair 5 of electrodes included in the second sensor block 3 is placed in the 21st plane P(21).

[0101] The m.sub.3-th (m.sub.3{xN: 1x2}) pair 5 of electrodes among two pairs 5 of electrodes included in the third sensor block 3 is placed in the r(3, m.sub.3)-th plane P(r(3, m.sub.3)) among 30 planes. Here, from Formula (2), r(3, m.sub.3)=15m.sub.3. In short, the p-th (p{xN: 1x2}) pair 5 of electrodes included in the third sensor block 3 is placed in the (15p)-th plane P(15p). For example, the first (p=1{xN: 1x2}) pair 5 of electrodes included in the third sensor block 3 is placed in the 15th plane P(15).

[0102] One electrode 5a of the m.sub.1-th (m.sub.1{xN: 1x30}) pair 5 of electrodes among 30 pairs 5 of electrodes included in the first sensor block 3 is connected to the s(m.sub.1)-th conducting line 7 among four conducting lines 7 and the other electrode 5b is connected to the fourth conducting line 7 among the four conducting lines 7. From Formula (3), for example, one electrode 5a of the seventh pair 5 of electrodes is connected to the first conducting line 7 (7 mod 3=1), one electrode 5a of the 17th pair 5 of electrodes is connected to the second conducting line 7 (17 mod 3=2), and one electrode 5a of the 24th pair 5 of electrodes is connected to the third conducting line 7 (24 mod 3=0).

[0103] One electrode 5a of the m.sub.2-th (m.sub.2{xN: 1x10}) pair 5 of electrodes among 10 pairs 5 of electrodes included in the second sensor block 3 is connected to the s(m.sub.2)-th conducting line 7 among 6 conducting lines 7 and the other electrode 5b is connected to the sixth conducting line 7 among the 6 conducting lines 7. From Formula (3), one electrodes 5a of the first and the sixth pairs 5 of electrodes are connected to the first conducting line 7 (1 mod 5=6 mod 5=1), one electrodes 5a of the second and the seventh pairs 5 of electrodes are connected to the second conducting line 7 (2 mod 5=7 mod 5=2), and one electrodes 5a of the third and the eighth pairs 5 of electrodes are connected to the third conducting line 7 (3 mod 5=8 mod 5=3), one electrodes 5a of the fourth and the ninth pairs 5 of electrodes are connected to the fourth conducting line 7 (4 mod 5=9 mod 5=4), and one electrodes 5a of the fifth and the tenth pairs 5 of electrodes are connected to the fifth conducting line 7 (5 mod 5=10 mod 5=0).

[0104] One electrode 5a of the m.sub.3-th (m.sub.3{xN: 1x2}) pair 5 of electrodes among 2 pairs 5 of electrodes included in the third sensor block 3 is connected to the s(m.sub.3)-th conducting line 7 among 3 conducting lines 7 and the other electrode 5b is connected to the third conducting line 7 among the 3 conducting lines 7. From Formula (3), one electrode 5a of the first pair 5 of electrodes is connected to the first conducting line 7 (1 mod 2=1), and one electrode 5a of the second pair 5 of electrodes is connected to the second conducting line 7 (2 mod 2=0).

[0105] The number E of the pairs 5 of electrodes included in the configuration example of the interface sensor 2 illustrated in FIG. 9 is 42 from Formula (4), and the number L of the conducting lines 7 is 13 from Formula (5). The total number M(1) of the observation points is 30, and thus, L<M(1)+1 holds. Note that according to the water gauge in the prior art illustrated in FIG. 1, the number of conducting lines is 31 (=M(1)+1). Further, for example, while not illustrated, in a 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 the conducting lines 7 in the interface sensor 2 is 29, whereas according to the water gauge in the prior art illustrated in FIG. 1, the number of conducting lines is 1441 (=M(1)+1).

[0106] In the example illustrated in FIG. 9, the number F of the substrates 9 is 1. However, F may be 2 or 3. In a case where 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.

[0107] The interface sensor 200 herein disclosed will be described next. Whereas the interface sensor 2 includes K sensor blocks 3, the interface sensor 200 includes one sensor block 300 and has a configuration equivalent to the configuration of the interface sensor 2.

[0108] The interface sensor 200 is a sensor for locating the position of the interface between two types of substances (that is, the first substance and the second substance different from each other). However, to accurately locate the position, the number of interfaces has to be 1 or 0 in a range from the plane P(1) to the plane P(E) as described later. As will be shown in Formula (7) later, the interface sensor 200 includes E pairs 500 of electrodes. The position of the interface between the first substance and the second substance is located by using physical quantities produced in each of the E pairs 500 of electrodes, corresponding to a property of the first substance or second substance present between electrodes of each of the E pairs 500 of electrodes. The interface and the homogeneous phase are as described above. A typical example of the interface sensor 200 is a sensor for locating the position of the interface between a liquid (for example, water) as the first substance and a gas (for example, air) as the second substance.

[0109] A configuration of the interface sensor 200 will be described. Symbols appearing in the following description are unrelated to symbols used in the description in the embodiments described above or the description of the interface sensor 2. Further, RC= holds, where C is capacitance between two conductors with equal positive and negative charges, R is electrical resistance between the two conductors, is dielectric constant of a medium between the two conductors, and is electrical resistivity of the medium between the two conductors. Thus, only capacitance of the pair of electrodes 500 will be described below, and description of electric resistivity of the pair of electrodes 500 will be omitted.

[0110] The interface sensor 200 includes E pairs 500 of electrodes, L conducting lines 700 to be drawn from the sensor block 300, and a conducting line selector 800. Customarily, the E pairs 500 of electrodes and the L conducting lines 700 are formed on a substrate 900 having a plate shape. Waterproof coating is applied to the substrate 900 except the E pairs 500 of electrodes. The conducting line selector 800 may be formed on the substrate 900 or may be formed on other substrates, although not limited thereto. In a case where the first substance is a liquid, the conducting line selector 800 is preferably located at a position not soaking in the liquid, and in a case where the conducting line selector 800 is located at a position soaked in the liquid, waterproof coating is applied.

[0111] The E pairs 500 of electrodes have the same capacitance C1 as each other in a state where interelectrode gap of each of the E pairs 500 of electrodes is filled with, for example, the first substance. The E pairs 500 of electrodes are connected to the L conducting lines 700 as described later. The L1 conducting lines 700 except the L-th conducting line 700 are connected to the conducting line selector 800 described later. In FIGS. 10 and 11, in view of clarity of the figures, reference signs are assigned to only one pair of electrodes and some conducting lines. E is expressed by Formula (7). L is expressed by Formula (8). K is a predetermined integer which satisfies 2K. j is a parameter for representing an integer that satisfies 1jK, that is, j{xN: 1xK}. For any j{xN: 1xK}, n(j) is a predetermined integer which satisfies 2n(j). N is a set of all positive integers. E, that is, the number of the pairs 500 of electrodes included in the sensor block 300 determines resolution of the interface sensor 200. In other words, E matches the total number of the observation points described above (this total number is represented by a symbol Z in description of the prior art). Under the above-described conditions, L<E+1 can be achieved.

[00029]$\left[\mathrm{Formula}13\right]$$\begin{array}{cc}E=\underset{j=1}{\overset{K}{.Math.}}n\left(j\right)& \left(7\right)\end{array}$$\begin{array}{cc}L=\underset{j=1}{\overset{K}{.Math.}}\left(n\left(j\right)-1\right)+2& \left(8\right)\end{array}$

[0112] n(j) is a positive divisor of E (except 1 and E). Notation of E is not unique. In a case where E has two or more types of notation (that is, two or more ways of factorization), a person who implements the interface sensor 200 can freely select one type of notation in view of easiness of implementation of the interface sensor 200, manufacturing cost of the interface sensor 200, an environment in which the interface sensor 200 is used, and the like. In other words, two or more types of notation of E mean a degree of freedom in the designing of the interface sensor 200. In terms of reduction in the total number L of the conducting lines 700, n(j) is preferably a prime factor of E, that is, a right side of Formula (7) is preferably factorization into prime factors (see Formula (8)).

[0113] The E pairs 500 of electrodes are placed in E planes, which do not coincide with each other and which are parallel to each other, in order according to an order relation of elements of a set {xN: 1xE}. The E planes P(1), . . . , P(E) are arranged in space in order according to an order relation of elements (that is, an order relation of natural numbers) of the set {xN: 1xE}. Specifically, the p.sub.b-th (p.sub.b{xN: 2xp.sub.a1}) plane P(p.sub.b) exists between the first plane P(1) and the p.sub.a-th (p.sub.a{xN: 3xE}) plane P(p.sub.a). Further, in a simple term, in a case where a normal direction of the E planes P(1), . . . , P(E) parallel to each other is referred to as a first direction, the E planes P(1), . . . , P(E) are arranged in this order in the first direction. For any g{xN: 1xE2} and h{xN: g+1xE1}, a distance between the g-th plane P(g) and the (g+1)-th plane P(g+1) may be equal to or not equal to a distance between the h-th plane P(h) and the (h+1)-th plane P(h+1). For example, it is preferable to make narrower an interval between adjacent planes in a measurement range in which the position of the interface is desired to be more accurately located. The p-th pair 500 of electrodes among the E pairs 500 of electrodes is placed in the p-th plane P(p) among the E planes. p is a parameter for representing an integer which satisfies 1pE, that is, p{xN: 1xE}. While the E pairs 500 of electrodes are customarily arranged linearly, the arrangement is not limited to this, and the E pairs 500 of electrodes may be, for example, arranged in a walking footprint shape. Note that in a case where the first direction is a vertical direction, plane may be rephrased as, for example, level.

[0114] For any p{xN: 1xE1}, one electrode 500a of the p-th pair 500 of electrodes among the E pairs 500 of electrodes is connected to the s(p)-th conducting line 700 among the L conducting lines 700 and the other electrode 500b is connected to the L-th conducting line 700 among the L conducting lines 700. One electrode 500a of the p-th (p{xN: 1xE1}) pair 500 of electrodes and the s(p)-th conducting line 700 are connected to each other by way of a support line 700x in this example. The other electrode 500b of the p-th (p{xN: 1xE1}) pair 500 of electrodes and the L-th conducting line 7 are connected to each other by way of a support line 700y in this example. s(p) is expressed by Formula (9). In Formula (9), a symbol mod represents remainder calculation, and a mod b is a remainder obtained by Euclidean division of a dividend a by a divisor b. In Formula (9), a symbol / appearing in the dividend in the remainder calculation represents division. In the description, n(0)=1.

[00030]$\left[\mathrm{Formula}14\right]$$\begin{array}{cc}s\left(p\right)=\left(p/\underset{j=1}{\overset{r}{.Math.}}n\left(j-1\right)\right)\mathrm{mod}n\left(r\right)+\underset{j=1}{\overset{r}{.Math.}}\left(n\left(j-1\right)-1\right)& \left(9\right)\end{array}$

[0115] In Formula (9), r is specified by pW(r), in other words, r is specified by a set W(r) to which p belongs. For any k{xN: 1xK}, the k-th set W(k) is expressed by Formula (10). The (K+1)-th set W(K+1) is an empty set . In Formula (10), a symbol | represents a multiple, that is, a|b represents that b is a multiple of a.

[00031]$\left[\mathrm{Formula}15\right]$$\begin{array}{cc}W\left(k\right)=\{xN:1xE(\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)\right).Math.x\}-\underset{j=k}{\stackrel{K}{.Math.}}W\left(j+1\right)& \left(10\right)\end{array}$

[0116] When W={W(j): jN1jK} is defined, as is clear from Formula (10), the following holds.

W(j)W,W(j)(1)

W(i)W,W(j)W,W(i)W(j).Math.W(i)W(j)=(2)

.sub.j=1.sup.KW(j)={xN: 1xE}(3)

Thus, p{xN: 1xE1}, !W(r)W s.t. pW(r). In other words, the set W(r) to which p belongs is uniquely determined.

[0117] One electrode 500a of the E-th pair 500 of electrodes among the E pairs 500 of electrodes is connected to the (L1)-th conducting line 700 among the L conducting lines 700 and the other electrode 500b is connected to the L-th conducting line 700 among the L conducting lines 700.

[0118] The conducting line selector 800 can select any one conducting line 700 among the L conducting lines 700 except the L-th conducting line 700.

[0119] Alternatively, for any k{xN: 1xK}, the conducting line selector 800 selects: [0120] (1) in a case where k+K and n(k)+2, [0121] for any y{xN: 1xn(k)2}, two conducting lines 700 determined by elements belonging to a set Y(y), among the L conducting lines 700, at the same time, and [0122] for y=n(k)1, (2+.sub.j=k+1.sup.K(n(j)1)) conducting lines 700 determined by elements belonging to a set Y.sub.a(y), among the L conducting lines 700, at the same time, [0123] (2) in a case where kK and n(k)=2, [0124] for y=n(k)1, (2+.sub.j=k+1.sup.K(n(j)1)) conducting lines 700 determined by elements belonging to the set Y.sub.a(y), among the L conducting lines 700, at the same time, and [0125] (3) in a case where k=K, [0126] for any y{xN: 1xn(k)1}, two conducting lines 700 determined by elements belonging to a set Y(y), among the L conducting lines 700, at the same time.

[0127] The set Y(y) is expressed by Formula (11), and the set Y.sub.a(y) is expressed by Formula (12). These sets are expressed as sum sets of singletons.

[00032]$\left[\mathrm{Formula}16\right]$$\begin{array}{cc}Y\left(y\right)=\underset{z=y}{\stackrel{y+1}{.Math.}}\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\}& \left(11\right)\end{array}$$\begin{array}{cc}& \left(12\right)\end{array}$$Y_a=\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+y\right\}.Math.\underset{m=k+1}{\stackrel{K}{.Math.}}\underset{z=1}{\stackrel{n\left(m\right)-1}{.Math.}}\left\{\underset{j=1}{\overset{m}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\}.Math.\left\{L-1\right\}$

[0128] In a case where the interface sensor 200 includes the conducting line selector 800 configured to select two or more conducting lines 700 at the same time in this manner, the conducting line selector 800 preferably connects the two or more conducting lines 700 selected at the same time to two conducting lines (a conducting line a and a conducting line b) as follows. [0129] (A) Regarding Formula (11), the conducting line 700 determined by the elements belonging to the set expressed by Formula (13) is connected to the conducting line a, and the conducting line 700 determined by the elements belonging to the set expressed by Formula (14) is connected to the conducting line b. [0130] (B) Regarding Formula (12), the conducting line 700 determined by the elements belonging to the set expressed by Formula (13) is connected to the conducting line a, and the conducting line 700 determined by the elements belonging to the set expressed by Formula (15) is connected to the conducting line b.

[00033]$\left[\mathrm{Formula}17\right]$$\begin{array}{cc}\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+y\right\}& \left(13\right)\end{array}$$\begin{array}{cc}\left\{\underset{j=1}{\overset{k}{.Math.}}\left(n\left(j-1\right)-1\right)+y+1\right\}& \left(14\right)\end{array}$$\begin{array}{cc}\underset{m=k+1}{\stackrel{K}{.Math.}}\underset{z=1}{\stackrel{n\left(m\right)-1}{.Math.}}\left\{\underset{j=1}{\overset{m}{.Math.}}\left(n\left(j-1\right)-1\right)+z\right\}.Math.\left\{L-1\right\}& \left(15\right)\end{array}$

[0131] The interface sensor 200 is equivalent to the interface sensor 2, and thus, a method for locating the position of the interface using the interface sensor 200 is the same as a method for locating the position of the interface using the interface sensor 2. In a case where the interface sensor 200 includes the conducting line selector 800 configured to select two or more conducting lines 700 at the same time, in the interface sensor 200, a detection circuit (not illustrated) compares a difference D with a predetermined threshold value 8. The difference D is a difference between combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the conducting line a through the conducting line 700 selected by the conducting line selector 800 and combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the conducting line b through the conducting line 700 selected by the conducting line selector 800. Note that 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 level gauge including the interface sensor 200. The detection circuit, without limitation, may be the detection circuit in the prior art, or may be a detection circuit including an AC signal generator that generates an AC signal to be applied to the L-th conducting line 700 and a comparator, or may be the detection circuit illustrated in FIGS. 2 and 5 (including the input circuit 30 and the discrimination means 70), or may be the detection circuit illustrated in FIG. 6 (including the input circuit 30, the discrimination means 70 and the addition means 12 and 122), or may be the detection circuit illustrated in FIG. 7 (including the input circuit 80, the discrimination means 70 and the A/D conversion part 130) or may be a detection circuit including a programmable logic device (PLD). Examples of the PLD include a field-programmable gate array (FPGA).

[0132] As one example, the position of the interface can be located using an algorithm shown in Table 2. In this algorithm, C(13) represents combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the conducting line 700 determined by the elements belonging to the set expressed by Formula (13), C(14) represents combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the conducting line 700 determined by the elements belonging to the set expressed by Formula (14), and C(15) represents combination of physical quantities (for example, total capacitance) produced in respective pairs of electrodes connected to the conducting line 700 determined by the elements belonging to the set expressed by Formula (15). Outputs P(0) and P(1) indicate that the interface does not reach the plane P(1). Note that in this algorithm, overflow determination processing and error avoidance processing are not performed.

TABLE-US-00003 TABLE 2 U= E, L= 0 for k = K to 1 (step: 1) [00034]$r\left(k\right)=\stackrel{K}{\underset{j=1}{.Math.}}n\left(j-1\right)$ if k = K then b(k) = 0 else b(k) =[00035]$b\left(k\right)=\left(\stackrel{K}{\underset{j=k+1}{.Math.}}n\left(j\right)\right)-1$ for y = 1 to n(k)1 (step: +1) if (k = K) or (k K and y < n(k)1) then s = |c(14)c(13)| if K and y = n(k) 1 then s = |c(15)c(13)| if s then for t = 0 to b(k) (step: +1) if (y+tn(k)r(k) L and (y+1+tn(k)r(k)U then if (y+tn(k))r(k) > L then L = (y+tn(k))r(k) if (y+1+tn(k))r(k)<U then U = (y+1+tn(k)r(k) goto G end if next f end if next y [00036]$U=L+\stackrel{K}{\underset{j=1}{.Math.}}n\left(j-1\right)$ G: next k output: P(L), P(U)

[0133] In a case where the total number Z of the observation points described above is a prime equal to or greater than 5, Z1 is the number of syntheses. Thus, by setting the value of E as Z1, the interface sensor can be configured to have Z (where Z is a prime equal to or greater than 5) observation points. Specifically, the interface sensor has a configuration in which one pair of electrodes and one conducting line are added to the interface sensor 200 including E (where E=Z1) pairs 500 of electrodes, L conducting lines 700 and the conducting line selector 800. In this configuration, the added one pair of electrodes is placed in the P(E+1)-th plane, one electrode of the added one pair of electrodes is connected to the added one conducting line, and the other electrode is connected to the L-th conducting line 700. When the detection circuit determines whether an capacitance value of the added one pair of electrodes exceeds a predetermined reference value, whether the interface exceeds the P(E+1)-th plane can be determined.

[0134] A first example and a second example that are specific configuration examples of the interface sensor 200 are illustrated in FIGS. 10 and 11 respectively. These configuration examples are examples where E=30, and K=3. In each of the examples illustrated in FIGS. 10 and 11, E=253 is employed as factorization based on three factors of E. In other words, n(1)=3, n(2)=5, and n(3)=2. In this case, L=9. See Formula (7) and Formula (8) for these facts.

[0135] As illustrated in FIG. 10 and FIG. 11, the p-th (p{xN: 1x30}) pair 500 of electrodes is placed in the p-th plane P(p).

[0136] From Formula (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}

[0137] For example, in a case where p=12, we obtain pW(2), that is, r=2. Thus, from Formula (9), s(p)=6, and one electrode 500a of the 12th (=p) pair 500 of electrodes is connected to the sixth (=s(p)) conducting line 700, and the other electrode 500b of the 12th (=p) pair 500 of electrodes is connected to the ninth (=L) conducting line 700. All calculation results are as follows:

p{1,4,7,10,13,16,19,22,25,28}.fwdarw.s(p)=1,

p{2,5,8,11,14,17,20,23,26,29}.fwdarw.s(p)=2,

p{3,18}.fwdarw.s(p)=3,

p{6,21}.fwdarw.s(p)=4,

p{9,24}.fwdarw.s(p)=5,

p{12,27}.fwdarw.s(p)=6, and

p{15}.fwdarw.s(p)=7.

[0138] One electrode 500a of the 30th (=E) pair 500 of electrodes is connected to the eighth (=L1) conducting line 700, and the other electrode 500b of the 30th (=E) pair 500 of electrodes is connected to the ninth (=L) conducting line 700.

[0139] The interface sensor 200 illustrated in FIG. 10 includes the conducting line selector 800 configured to select any one conducting line 700 among the L conducting lines 700 except the L-th conducting line 700. Such a conducting line selector 800 includes L1 single-pole-single-throw switches, although not limited thereto. One end of each of the L1 single-pole-single-throw switches is connected to the corresponding conducting line 700 among the L1 conducting lines 700 except the L-th conducting line 700. The other end of each of the L1 single-pole-single-throw switches is connected to a C/V converter, although not limited thereto. A configuration of such a conducting line selector 800 can be implemented along with the configuration of the detection circuit illustrated in FIG. 7 (including at least the A/D conversion part 130, the control means 90 and the discrimination means 70). In a case where a value of L is not great, the conducting line selector 800 may be a single-pole-(L1)-throw switch. In a case where the conducting line selector 800 is a single-pole-(L1)-throw switch, the number of the C/V converter to be connected to the conducting line selector 800 may be one.

[0140] The interface sensor 200 illustrated in FIG. 11 includes the conducting line selector 800 configured to select two or more conducting lines 700 at the same time. Such a conducting line selector 800 includes L1 single-pole-triple-throw switches, although not limited thereto. An input terminal of each of the single-pole-triple-throw switches is connected to the corresponding conducting line 700 among the L1 conducting lines 700 except the L-th conducting line 700. A first output terminal of the single-pole-triple-throw switch is connected to the conducting line b, a second output terminal is terminated, and third output terminal is connected to the conducting line a. The conducting line a and the conducting line b are connected to the comparator, although not limited thereto. In this configuration example, the conducting line selector 800 connects two or more conducting lines 700 selected at the same time to the conducting line a and the conducting line b as follows.

[0141] The conducting line selector 800 performs the following selection operation in the configuration illustrated in FIG. 11.

[0142] In a case where k=1,

from n(k)=3, and Formula (11) and Formula (12),

Y(1)={1}{2}, and

Y.sub.a={2}{3,4,5,6,7,8} are obtained.

Thus, in a case where y=1, the conducting line selector 800 selects the third output terminal of the single-pole-triple-throw switch connected to the first conducting line 700, selects the first output terminal of the single-pole-triple-throw switch connected to the second conducting line 700, and selects the second output terminal of each of the single-pole-triple-throw switches connected to the third to the eighth conducting lines 700, thereby selects the first conducting line 700 and the second conducting line 700 at the same time. In a case where y=2, the conducting line selector 800 selects the second output terminal of the single-pole-triple-throw switch connected to the first conducting line 700, selects the third output terminal of the single-pole-triple-throw switch connected to the second conducting line 700, and selects the first output terminal of each of the single-pole-triple-throw switches connected to the third to the eighth conducting lines 700, thereby selects the second to the eighth conducting lines 700 at the same time.

[0143] In a case where k=2,

from n(k)=5, and Formula (11) and Formula (12),

Y(1)={3}{4},

Y(2)={4}{5},

Y(3)={5}{6}, and

Y.sub.a={6}{7,8} are obtained.

Thus, in a case where y=1, the conducting line selector 800 selects the third output terminal of the single-pole-triple-throw switch connected to the third conducting line 700, selects the first output terminal of the single-pole-triple-throw switch connected to the fourth conducting line 700, and selects the second output terminal of each of the single-pole-triple-throw switches connected to the first, the second and the fifth to the eighth conducting lines 700, thereby selects the third conducting line 700 and the fourth conducting line 700 at the same time.

[0144] In a case where y=2, the conducting line selector 800 selects the third output terminal of the single-pole-triple-throw switch connected to the fourth conducting line 700, selects the first output terminal of the single-pole-triple-throw switch connected to the fifth conducting line 700, and selects the second output terminal of each of the single-pole-triple-throw switches connected to the first to the third, and the sixth to the eighth conducting lines 700, thereby selects the fourth conducting line 700 and the fifth conducting line 700 at the same time.

[0145] In a case where y=3, the conducting line selector 800 selects the third output terminal of the single-pole-triple-throw switch connected to the fifth conducting line 700, selects the first output terminal of the single-pole-triple-throw switch connected to the sixth conducting line 700, and selects the second output terminal of each of the single-pole-triple-throw switches connected to the first to the fourth, the seventh and the eighth conducting lines 700, thereby selects the fifth conducting line 700 and the sixth conducting line 700 at the same time.

[0146] In a case where y=4, the conducting line selector 800 selects the second output terminal of the single-pole-triple-throw switch connected to the first to the fifth conducting lines 700, selects the third output terminal of the single-pole-triple-throw switch connected to the sixth conducting line 700, and selects the first output terminal of each of the single-pole-triple-throw switches connected to the seventh and the eighth conducting lines 700, thereby selects the sixth to the eighth conducting lines 700 at the same time.

[0147] In a case where k=3,

from n(k)=2 and Formula (11),

Y(1)={7}{8} is obtained.

Thus, in a case where y=1, the conducting line selector 800 selects the second output terminal of the single-pole-triple-throw switch connected to the first to the sixth conducting lines 700, selects the third output terminal of the single-pole-triple-throw switch connected to the seventh conducting line 700, and selects the first output terminal of each of the single-pole-triple-throw switches connected to the eighth conducting line 700, thereby selects the seventh conducting line 700 and the eighth conducting line 700 at the same time.

[0148] A controller that controls operation of the conducting line selector 800 is well known, and thus, illustration and description of the controller are omitted.

[0149] The level gauge of the present disclosure includes the interface sensor 200 described above, the first substance is a liquid, and the second substance is a gas. In the level gauge, the first direction is preferably a vertical direction, but is not limited to this.

<Supplement>

[0150] The examples illustrated in FIGS. 2 to 8 indicate a level gauge in which E is expressed by a power-of-two, and one pair of electrodes among E pairs of electrodes has predetermined capacitance for improving accuracy.

<Addendum>

[0151] The present invention has been described with reference to the example embodiments. It will be understood that a person skilled in the art can make various changes and replace the elements with equivalents without deviating from the scope of the present invention. Further, to adapt a specific system, device or components thereof to teaching of the present invention, many modifications can be made without deviating from the essential scope of the present invention. Thus, the present invention is not limited to the specific embodiments disclosed for implementing the present invention and includes all embodiments included in the accompanying claims.

[0152] Further, terms such as first and second are used not to indicate order or importance but to distinguish the elements. The terms used in the present specification are used to explain the embodiments and are not intended to limit the present invention in any way. The term include and its declensions as used in the present specification and/or the accompanying claims, clarify existence of the mentioned features, steps, operations, elements and/or components, but do not exclude existence or addition of one or more other features, steps, operations, elements, components and/or a group thereof. The term and/or, when used, includes any one or more combinations of related listed elements. Unless otherwise specified, in the claims and the specification, connect, couple, join, link or synonyms thereof and all declensions do not necessarily deny existence of one or more intermediate elements between two which are, for example, connected, coupled or linked to each other. In the claims and the specification, unless otherwise specified, the term any, when used, should be understood as a term representing the same meaning as a universal quantifier V. For example, expression of concerning any X has the same meaning as concerning all X or concerning each X.

[0153] Unless otherwise noted, all the terms (including technical terms and scientific terms) used in the present specification have the same meaning as generally understood by a person skilled in the art in the field to which the present invention belongs. Further, the terms such as terms defined in dictionaries that are commonly used should be interpreted as having the same meaning as in the context of the related art and the present disclosure, and unless otherwise explicitly defined, should not be interpreted ideally or excessively formally.

[0154] It will be understood that many techniques and steps are disclosed in the description of the present invention. These respectively have individual advantages and can be used in combination with one or more or, in some cases, all of other disclosed techniques. Thus, to avoid complication, in the present specification, any possible combinations of the individual techniques and steps are not described. Nevertheless, the specification and the claims should be read and understood that such combinations are completely within the scope of the present invention and the claims.

[0155] Structures, materials, actions and equivalents corresponding to all functional elements coupled with means or steps in the following claims are intended to include, if any, structures, materials or actions for performing functions in combination with other elements.

[0156] Although embodiments of the present invention have been described above, the present invention is not limited to these embodiments. Various changes and modifications are allowed in a range not deviating from the gist of the present invention. The selected and described embodiments are provided to explain principles and actual applications of the present invention. The present invention is used as various embodiments along with various changes or modifications, and various changes or modifications are determined depending on the expected applications. All of such changes and modifications are intended to be included in the scope of the present invention defined by the accompanying claims and are intended to be protected in the same manner to the extent that they are fairly, legally and rightly interpreted.

DESCRIPTION OF REFERENCE NUMERALS

[0157] 1: Tank [0158] 2: Interface sensor [0159] 3: Sensor block [0160] 5: Pair of electrodes [0161] 5a: Electrode [0162] 5b: Electrode [0163] 6: Electrode pair [0164] 7: Conducting line [0165] 7x: Support line [0166] 7y: Support line [0167] 9: Substrate [0168] 10: Reference line [0169] 11 to 17: Determination means [0170] 20: Water level output means [0171] 30: Input circuit [0172] 40: Sensor part [0173] 41: Electrode pair [0174] 50, 50, 50: Adjustment part [0175] 60, 60: Switching means [0176] 61: Switch [0177] 70: Discrimination means [0178] 80: Water level determination means [0179] 90: Control means [0180] 100: Switching means [0181] 101: Switch [0182] 111 to 114: C/V conversion part [0183] 121, 122: Addition means [0184] 130: A/D conversion part [0185] 140: Adjustment value storage part [0186] 200: Interface sensor [0187] 300: Sensor block [0188] 500: Pair of electrodes [0189] 500a: Electrode [0190] 500b: Electrode [0191] 700: Conducting line [0192] 700x: Support line [0193] 700y: Support line [0194] 800: Conducting line selector [0195] 900: Substrate