Conductivity sensor and conductivity measurement method

Abstract

A conductivity sensor (101) is for measuring the conductivity of a liquid (LQ) and comprises: an insulating layer (10); a first detection electrode (21) disposed on the insulating layer (10); a second detection electrode (22) disposed on the insulating layer (10) so as to be spaced apart from the first detection electrode (21); and a protective layer (50) that is constituted by an insulator and that covers the first detection electrode (21) and the second detection electrode (22). The first detection electrode (21) and the second detection electrode (22) are positioned in an alternating manner, thereby forming a first line-and-space pattern (PTa) having a first space width (WSa) and a second line-and-space pattern (PTb) having a second space width (WSb) which is different from the first space width (WSa).

Description

[Technical Field]

[0001] The present invention relates to a conductivity sensor and a conductivity measurement method, and more particularly to a conductivity sensor for measuring the conductivity of a liquid and a conductivity measurement method using the same. [Background technology]

[0002] International Publication No. 2021 / 241628 (Patent Document 1) discloses a capacitance-type sensor. The sensor includes an insulating layer, a first detection electrode, a second detection electrode, and a protective layer. The first detection electrode is provided on the insulating layer. The second detection electrode is provided on the insulating layer at a distance from the first detection electrode and forms the capacitance together with the first detection electrode. The protective layer covers the first and second detection electrodes, has a thickness d that satisfies 1 μm≦d≦10 μm, and is made of zirconia or alumina.

[0003] Japanese Patent Application Laid-Open Publication No. 2019-109224 (Patent Document 2) discloses a compact conductivity sensor intended to be capable of measuring a wide range of liquid conductivity even when the measurement area is small. The conductivity sensor includes first and second electrodes, each having a surface area that determines the cell constant of the sensor. At least one of the electrodes is provided with switching means arranged to change the surface area of ​​each electrode, thereby changing the cell constant of the sensor. For example, the first and second electrodes include multiple finger electrodes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2021 / 241628 [Patent Document 2] Japanese Patent Application Publication No. 2019-109224 Summary of the Invention [Problem to be solved by the invention]

[0005] A method for measuring the conductivity of a liquid over a wide conductivity range with sufficient sensitivity and linearity using a capacitance sensor configured as described in Patent Document 1 has not been thoroughly investigated. For example, the technology described in Patent Document 2 does not appear to contemplate the formation of a protective layer as disclosed in Patent Document 1. This is because the formation of a protective layer leads to the formation of capacitance between the electrode and the liquid. According to Patent Document 2, the increase in electrode impedance due to the capacitance at the interface between the electrode and the liquid is considered problematic in ensuring a wide measurement range for the conductivity of the liquid. Furthermore, Patent Document 2 only discloses the use of an inert conductive material as the electrode material to prevent chemical interactions between the electrode and the liquid, but does not mention the use of a protective layer as such a measure. This is likely because the technology described in Patent Document 2 does not contemplate the addition of a protective layer, which would increase impedance.

[0006] The present invention has been made to solve the above-mentioned problems, and its object is to provide a conductivity sensor that can widen the conductivity range in which the conductivity of a liquid can be measured with sufficient sensitivity and linearity, and a conductivity measurement method using the same. [Means for solving the problem]

[0007] A first aspect is a conductivity sensor for measuring the conductivity of a liquid, comprising an insulating layer, a first detection electrode provided on the insulating layer, a second detection electrode provided on the insulating layer at a distance from the first detection electrode, and a protective layer made of an insulator that covers the first detection electrode and the second detection electrode. The first detection electrode and the second detection electrode are alternately positioned to form a first line-and-space pattern having a first space width and a second line-and-space pattern having a second space width different from the first space width.

[0008] A second aspect is the conductivity sensor of the first aspect, wherein the first space width is 100 μm or less, and the second space width is greater than 100 μm.

[0009] A third aspect is the conductivity sensor of the first or second aspect, wherein the second space width is 10 to 70 times the first space width.

[0010] A fourth aspect is a conductivity sensor according to any one of the first to third aspects, wherein each of the multiple lines constituting the first line and space pattern has a line length of 1 mm or more, and each of the multiple lines constituting the second line and space pattern has a line length of 1 mm or more.

[0011] A fifth aspect is the conductivity sensor according to any one of the first to fourth aspects, wherein the first line-and-space pattern and the second line-and-space pattern each include a plurality of spaces.

[0012] A sixth aspect is a conductivity sensor according to any one of the first to fifth aspects, wherein the first line and space pattern and the second line and space pattern are adjacent to each other by sharing one line.

[0013] A seventh aspect is a conductivity measurement method for measuring the conductivity of a liquid using the conductivity sensor according to any one of the first to sixth aspects, comprising: a) measuring a complex impedance between the first detection electrode and the second detection electrode in a state where the liquid is in contact with the protective layer so as to face each of the first detection electrode and the second detection electrode through the protective layer; b) extracting an extracted value from the complex impedance according to a predetermined extraction rule; c) determining the conductivity of the liquid based on the extracted value; Equipped with. [Effects of the Invention]

[0014] According to one embodiment, the first detection electrodes and the second detection electrodes are alternately positioned to form a first line-and-space pattern having a first space width and a second line-and-space pattern having a second space width different from the first space width, thereby widening the conductivity range over which the conductivity of a liquid can be measured with sufficient sensitivity and linearity.

[0015] The protective layer may be made of zirconia or alumina and have a thickness of 1 μm to 10 μm. In this case, the capacitance formed by the protective layer between the liquid and each of the first and second detection electrodes has a large effect on the measurement of the impedance between the first and second detection electrodes. However, according to the above embodiment, even under this effect, the conductivity of the liquid can be measured with sufficient sensitivity over a wide conductivity range.

[0016] The protective layer may be made of a sintered body. This avoids a decrease in manufacturing efficiency during the manufacture of the conductivity sensor, which would be caused by forming a protective layer made of a non-sintered body. Furthermore, since the protective layer and the insulating layer are a sintered body as an integrated structure, defects originating from the interface between them are less likely to occur. This improves properties such as chemical resistance and thermal shock resistance.

[0017] The objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a front view schematically showing the configuration of a measurement system having a conductivity sensor according to an embodiment. [Figure 2] FIG. 2 is a schematic rear view of FIG. 1. [Figure 3]FIG. 3 is a schematic partial cross-sectional view taken along line III-III in FIGS. 1 and 2. [Figure 4] FIG. 4 is a schematic partial cross-sectional view taken along line IV-IV in FIGS. 1 and 2. [Figure 5] 5 is a schematic partial cross-sectional view showing the state during the implementation of the conductivity measurement method in the field of view of FIG. 4. FIG. [Figure 6] FIG. 6 is a circuit diagram showing an approximate equivalent circuit corresponding to FIG. 5. [Figure 7] 2 is a schematic front view showing the configuration of the conductivity sensor in the measurement system of FIG. 1, with the protective layer omitted. FIG. [Figure 8] FIG. 10 is a graph showing simulation results for different line and space pattern configurations for the relationship between the conductivity of a liquid and the absolute value of admittance extracted from the complex impedance measured by a conductivity sensor. [Figure 9] FIG. 1 is a schematic flow diagram of a conductivity measurement method. [Figure 10] 1 is a partial cross-sectional view schematically illustrating a step in a method for manufacturing a conductivity sensor. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0020] (composition) FIGS. 1 and 2 are a front view and a rear view, respectively, schematically illustrating the configuration of a measurement system 500 having a conductivity sensor 101 according to the present embodiment. FIG. 3 is a schematic partial cross-sectional view taken along line III-III in FIGS. 1 and 2. FIG. 4 is a schematic partial cross-sectional view taken along line IV-IV in FIGS. 1 and 2. FIG. 5 is a schematic partial cross-sectional view showing the state of a conductivity measurement method being performed in the field of view of FIG. 4. FIG. 6 is a circuit diagram showing an approximate equivalent circuit corresponding to FIG. 5. FIG. 7 is a schematic front view showing the configuration of the conductivity sensor 101, with the protective layer 50 omitted. Note that in FIGS. 1 and 2, the liquid LQ whose conductivity is to be measured by the conductivity sensor 101 is shown by a virtual line. Also, FIG. 5 illustrates the liquid LQ. To facilitate understanding of the directional relationships between the drawings, an XYZ Cartesian coordinate system is shown in each drawing. In this embodiment, the direction Z corresponds to the vertically upward direction.

[0021] The measurement system 500 includes a conductivity sensor 101 and a measuring instrument 200. The conductivity sensor 101 is a sensor for measuring the conductivity of the liquid LQ. The conductivity sensor 101 includes an insulating layer 10, a first detection electrode 21, a second detection electrode 22, and a protective layer 50. The conductivity sensor 101 may further include a first pad electrode 31, a second pad electrode 32, a first via electrode 41, and a second via electrode 42. The conductivity sensor 101 generally includes an insulating base in which electrodes including the first detection electrode 21 and the second detection electrode 22 are embedded. The insulating base is made up of the insulating layer 10 and the protective layer 50. A first pad electrode 31 and a second pad electrode 32 are provided on the conductivity sensor 101 for electrical connection to the embedded electrodes from outside the conductivity sensor 101.

[0022] The insulating layer 10 is preferably made of a ceramic insulator, and more preferably made of the same material as the protective layer 50. The thickness of the insulating layer 10 is, for example, about 1 mm.

[0023] 3 to 5, the first detection electrode 21 is provided on one surface of the insulating layer 10. The second detection electrode 22 is provided on the same surface of the insulating layer 10 at a distance from the first detection electrode 21.

[0024] In the conductivity sensor 101, the first detection electrodes 21 and the second detection electrodes 22 are alternately positioned, thereby forming a first line-and-space (L / S) pattern PTa having a first space width WSa and a second line-and-space pattern PTb having a second space width WSb different from the first space width WSa, as shown in FIG. 7 . Here, the second space width WSb is different from the first space width WSa. The first space width WSa may be 100 μm or less, and the second space width WSb may be greater than 100 μm. Furthermore, the second space width WSb may be 10 to 70 times the first space width WSa. FIG. 8 (described later) shows an example in which the second space width WSb is 20 times the first space width WSa. If the difference between the first and second space widths needs to be relatively small, the second space width WSb may be 10 to 20 times the first space width WSa. Each of the first line-and-space pattern PTa and the second line-and-space pattern PTb may include a plurality of spaces. The first space width WSa (in terms of the lower limit) may be, for example, 15 μm or more, or 30 μm or more. The second space width WSb (in terms of the upper limit) may be, for example, 2000 μm or less, or 1000 μm or less.

[0025] 7, each of the line and space patterns PTa and PTb has a length direction along the X direction and a width direction along the Z direction. The first line and space pattern PTa is formed by alternating between at least one line (line L1a and line L1ab in FIG. 7) included in the first detection electrode 21 and at least one line (multiple lines L2a in FIG. 7) included in the second detection electrode 22. The second line and space pattern PTb is formed by alternating between at least one line (multiple lines L1b and line L1ab in FIG. 7) included in the first detection electrode 21 and at least one line (multiple lines L2b in FIG. 7) included in the second detection electrode 22.

[0026] The first line-and-space pattern PTa and the second line-and-space pattern PTb are adjacent to each other by sharing one line L1ab. In the example of FIG. 7, the line shared by the first line-and-space pattern PTa and the second line-and-space pattern PTb is line L1ab included in the first detection electrode 21, but as a modified example, it may be a line included in the second detection electrode 22. Also, a modified example in which there is no shared line may be used, in which case the first line-and-space pattern PTa and the second line-and-space pattern PTb may be separated from each other.

[0027] Each of the multiple lines constituting the first line-and-space pattern PTa, i.e., line L1a and line L2a, may have a line length LLa of 1 mm or more and 20 mm or less. Each of the multiple lines constituting the second line-and-space pattern PTb, i.e., line L1b and line L2b, may have a line length LLb of 1 mm or more and 20 mm or less. The line lengths LLa and LLb may be the same as each other, as shown in FIG. 7, or may be different from each other. The line L1ab shared by the first line-and-space pattern PTa and the second line-and-space pattern PTb may have the line length LLa or the line length LLb.

[0028] The lines L1a and L2a of the first line-and-space pattern PTa may have a common line width WLa, which is preferably 30 μm or more and 2000 μm or less, and more preferably 30 μm or more and 1000 μm or less. The lines L1b and L2b of the second line-and-space pattern PTb may have a common line width WLb, which is preferably 30 μm or more and 2000 μm or less, and more preferably 30 μm or more and 1000 μm or less. The line width WLb may be larger than the line width WLa. The line L1ab may have the line width WLa or the line width WLb.

[0029] The first detection electrode 21 and the second detection electrode 22 are preferably made of a high-melting-point metal that is resistant to oxidation, such as platinum, tungsten, or cobalt. The thickness of the first detection electrode 21 and the second detection electrode 22 is, for example, about 5 μm.

[0030] The protective layer 50 covers the first detection electrode 21 and the second detection electrode 22. Specifically, the protective layer 50 has a surface SF and a surface opposite the surface SF that faces the first detection electrode 21 and the second detection electrode 22. The protective layer 50 has a thickness d, which preferably satisfies 1 μm≦d≦10 μm, and more preferably 1 μm≦d≦5 μm. The protective layer 50 is made of an insulator. In particular, when the protective layer 50 is made of zirconia or alumina, the corrosion resistance and chemical resistance of the conductivity sensor 101 are enhanced. The protective layer 50 has a relative dielectric constant ε, preferably ε≧10. For example, an ε of approximately 30 can be obtained by using zirconia, and an ε of approximately 10 can be obtained by using alumina. Preferably, ε / d≧1 is satisfied. The protective layer 50 is preferably made of a sintered body, for example, from the viewpoint of manufacturing efficiency.

[0031] The protective layer 50 shown in FIGS. 1 and 3 to 5 is a single layer that continuously covers both the first detection electrode 21 and the second detection electrode 22 and does not have a particular pattern. In this case, the shape of the protective layer 50 can be simple. On the other hand, if a more complex shape of the protective layer is allowed, the protective layer may have some kind of pattern as a modified example. This pattern may have first and second portions that are separated from each other, with the first portion covering the first detection electrode 21 and the second portion covering the second detection electrode 22. In this case, the first and second portions of the protective layer 50 are separated by an area where the protective layer 50 is not provided.

[0032] The first pad electrode 31 is provided on the surface of the insulating layer 10 opposite to the one surface. The second pad electrode 32 is provided on the surface of the insulating layer 10 opposite to the one surface, spaced apart from the first pad electrode 31. The first via electrode 41 penetrates the insulating layer 10, and has one end connected to the first detection electrode 21 and the other end connected to the first pad electrode 31. The second via electrode 42 penetrates the insulating layer 10, and has one end connected to the second detection electrode 22 and the other end connected to the second pad electrode 32.

[0033] The measuring instrument 200 has the function of measuring a complex impedance and the function of extracting an extracted value from the complex impedance according to a predetermined extraction rule. The measuring instrument 200 may be a typical impedance analyzer, but may also be a measuring instrument with a simpler configuration as long as it can implement the measurement method described below. The extraction rule may be to extract, for example, a reactance component, a resistance component, or an impedance absolute value from the complex impedance as an extracted value. Note that some arithmetic processing, such as reciprocal processing, may be performed during the extraction.

[0034] Measuring instrument 200 is electrically connected to first pad electrode 31 and second pad electrode 32. Referring to the equivalent circuit of FIG. 6, complex impedance IMP is the complex impedance between first detection electrode 21 and second detection electrode 22 in the state shown in FIG. 5. In the state shown in FIG. 5, liquid LQ is in contact with protective layer 50 so as to face each of first detection electrode 21 and second detection electrode 22 through protective layer 50. The effects of the complex impedances of first pad electrode 31, first detection electrode 21, and the first via electrode 41 therebetween, and the complex impedances of second pad electrode 32, second detection electrode 22, and the second via electrode 42 therebetween on complex impedance IMP are almost negligible. Therefore, the complex impedance measured by measuring instrument 200 is essentially the complex impedance IMP between first detection electrode 21 and second detection electrode 22 (FIG. 6).

[0035] Complex impedance generally has a resistance component and a reactance component. In the configuration of this embodiment, the reactance component is mainly due to the capacitance value formed by the protective layer 50 and the liquid LQ being disposed in the electrical path between the first detection electrode 21 and the second detection electrode 22. Therefore, hereinafter, the reactance component may be referred to as the capacitance value.

[0036] FIG. 8 is a graph showing the simulation results for different line-and-space pattern configurations regarding the relationship between the conductivity of the liquid LQ and the admittance absolute value extracted from the complex impedance measured by the conductivity sensor. Note that this simulation was performed at 1000 kHz. In the figure, "50 / 50 μm + 1000 / 1000 μm" corresponds to the conductivity sensor 101 of this embodiment ( FIG. 7 ), in which the L / S of the first line-and-space pattern PTa is 50 / 50 μm and the L / S of the second line-and-space pattern PTb is 1000 / 1000 μm. Furthermore, "50 / 50 μm" corresponds to a comparative example having only a line-and-space pattern with an L / S of 50 / 50 μm. Furthermore, "1000 / 1000 μm" corresponds to a comparative example having only a line-and-space pattern with an L / S of 1000 / 1000 μm.

[0037] In the conductivity range shown in this graph, the sensitivity of the admittance absolute value to the conductivity of the liquid LQ is sufficiently high in the conductivity range of 6 to 600 μS / cm for the "50 / 50 μm" conductivity sensor 101, difficult to detect in the entire range for the "1000 / 1000 μm" conductivity sensor 101, and sufficient in the conductivity range of 10 to 500 μS / cm for the "50 / 50 μm + 1000 / 1000 μm" conductivity sensor 101. On the other hand, it is preferable that the conductivity sensor not only has a wide detectable range but also has high linearity. In this regard, the coefficient of determination R of the regression line in the conductivity range of 1 to 500 μS / cm is 2 are shown in Table 1 below.

[0038] [Table 1]

[0039] Compared to the "50 / 50" conductivity sensor 101, the "50 / 50 μm + 1000 / 1000" conductivity sensor 101 has a coefficient of determination R closer to 1. 2It can be seen that the conductivity sensor 101 of "1000 / 1000" has high linearity, but does not ensure detectable conductivity.

[0040] In this specification, the term "detectable conductivity" refers to a range of conductivity in which the slope of the extracted value with respect to the conductivity (unit: μS / cm) (in other words, the derivative of the extracted value with respect to the conductivity) is equal to or greater than the reference value. When the extracted value is the absolute admittance value (unit: S) or the reciprocal of the resistance component (unit: S), the reference value is 10 kHz at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1000 kHz. -10 , 10 -9 , 10 -8 , 10 -7 [Unit: S / (μS / cm)]. Also, if the extracted value is a capacitance value [unit: F], the reference value is 10 -14 The frequency dependence of the "detectable conductivity" is [unit: F / (μS / cm)] when the extracted value is the absolute admittance value [unit: S] or the reciprocal of the resistance component [unit: S]. This is because the frequency dependence of measurement variability is large in such cases, and this is taken into account so that the reference value can be reasonably determined. In Table 2 below, the symbol "-" indicates that the detectable conductivity range is not found within the simulation range. For example, the larger the line width or measurement frequency, the smaller the change in the extracted value relative to a change in conductivity tends to be. If this tendency progresses excessively, it becomes difficult to detect the conductivity, in other words, to calculate the conductivity with sufficient accuracy.

[0041] The results in Table 1 above show that at a measurement frequency of 1000 kHz, the linearity is improved for "1000 / 1000" compared to "50 / 50," but the detectable conductivity range is not achieved. On the other hand, the linearity is improved for "50 / 50 + 1000 / 1000" compared to "50 / 50," while the detectable conductivity range is roughly maintained. This shows that by combining the line-and-space patterns PTa and PTb, it is possible to achieve a detectable conductivity range that is difficult to achieve by simply adjusting the dimensions of a single line-and-space pattern, while still maintaining high linearity.

[0042] Each of the line width WL and the space width WS may be, but is not limited to, 50 μm or more and 1000 μm or less as exemplified in Table 1. Also, although the line width WL and the space width WS are the same in Table 1, they may be different from each other.

[0043] Table 2 below shows the simulation results for detectable conductivities at more different frequencies.

[0044] [Table 2]

[0045] From the above, it can be seen that "50 / 50 + 1000 / 1000" has the effect of increasing the maximum detectable conductivity at measurement frequencies of 100 kHz or less compared to "50 / 50", and this effect is particularly large at 10 kHz or less. Furthermore, at 10 kHz or less, the minimum detectable conductivity is well secured in the case of "50 / 50 + 1000 / 1000" as well as in the case of "50 / 50".

[0046] FIG. 9 is a schematic flow diagram of a conductivity measurement method for measuring the conductivity of the liquid LQ using the conductivity sensor 101.

[0047] In step S110, in the state of FIG. 5, a first complex impedance between the first detection electrode 21 and the second detection electrode 22 is measured. In the state shown in FIG. 5, as described above, the liquid LQ is in contact with the protective layer 50 so as to face each of the first detection electrode 21 and the second detection electrode 22 via the protective layer 50. This measurement may be performed by a complex impedance measurement unit (not shown) included in the measuring instrument 200. The complex impedance measurement unit has a function of measuring complex impedance. In other words, the function of measuring complex impedance is a function of applying an AC signal to the object to be measured and measuring the ratio and phase difference between the voltage and current of the AC signal.

[0048] In step S120, an extracted value is extracted from the complex impedance in accordance with a predetermined extraction rule. This extraction may be performed by an extraction unit (not shown) included in measuring instrument 200. The extracted extracted value may be stored in a storage unit (not shown) included in measuring instrument 200.

[0049] In step S130, the conductivity of the liquid LQ is determined based on the extracted value. This determination may be made based on a correspondence relationship between the extracted value and the conductivity that has been investigated in advance. This correspondence relationship may be determined experimentally, for example. This determination may be made by a determination unit (not shown) included in the measuring instrument 200.

[0050] In this way, the conductivity of the liquid LQ is determined.

[0051] The storage unit, judgment unit, and decision unit may be realized by a control device (not shown). The control device may be configured by a general computer having an electric circuit. The general computer has a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a storage device, an input unit, a display unit, a communication unit, and a bus line connecting these units to each other.

[0052] (Manufacturing method) FIG. 10 is a partial cross-sectional view schematically showing one step in the method for manufacturing the conductivity sensor 101 according to the present embodiment.

[0053] 3 and 10, a laminate is prepared including a green sheet 10G that will become the insulating layer 10, a paste layer 21G that will become the first detection electrode 21, a paste layer 22G that will become the second detection electrode 22, a paste layer 31G that will become the first pad electrode 31, a paste layer 32G that will become the second pad electrode 32, a paste layer 41G that will become the first via electrode 41, and a paste layer 42G that will become the second via electrode 42. Each paste layer can be formed by printing a paste containing metal powder and ceramic powder onto the green sheet 10G. The green sheet 10G may be a single layer, or may be formed by laminating multiple green sheets.

[0054] A green sheet 50G that will become the protective layer 50 is pressure-bonded onto the above-mentioned laminate as shown by the arrow (FIG. 10). This pressure-bonding is preferably performed while heating.

[0055] Next, the laminate with the green sheet 50G pressed thereon is fired, thereby obtaining the conductivity sensor 101. In this case, the protective layer 50 is therefore made of a sintered body.

[0056] (effect) According to this embodiment, a first line-and-space pattern PTa having a first space width WSa and a second line-and-space pattern PTb having a second space width WSb different from the first space width WSa are configured, thereby widening the conductivity range in which the conductivity of a liquid can be measured with sufficient sensitivity and linearity.

[0057] Each of the line lengths LLa and LLb (FIG. 7) is preferably 1 mm or more and 20 mm or less. By making this dimension 1 mm or more, the sensitivity of the conductivity sensor 101 can be increased. By making this dimension 20 mm or less, the probability of defects due to the adhesion of foreign matter on the line and space pattern can be reduced. Furthermore, by making this dimension 20 mm or less, the size of the conductivity sensor 101 can be prevented from becoming excessively large.

[0058] Each of the space widths WSa and WSb is preferably 30 μm or more and 2000 μm or less, and more preferably 30 μm or more and 1000 μm or less. By setting this dimension to 30 μm or more, the dimension can be easily controlled using common multilayer ceramic technology. By setting this dimension to 2000 μm or less (more preferably 1000 μm or less), it is possible to prevent the electrical coupling between the first detection electrode 21 and the second detection electrode 22 via the liquid LQ from becoming too weak, which makes it easier to prevent the sensitivity of the conductivity sensor 101 from becoming too weak.

[0059] When the protective layer 50 is made of zirconia or alumina and has a thickness d of 1 μm or more and 10 μm or less, the capacitance formed by the protective layer 50 between the first detection electrode 21 and the second detection electrode 22 and the liquid LQ significantly contributes to the impedance IMP (FIG. 6). However, according to this embodiment, even under this influence, the conductivity of the liquid LQ can be measured with sufficient sensitivity over a wide conductivity range. Note that while reducing the ε / d of the protective layer 50 can suppress this influence, the sensor sensitivity is likely to decrease due to the weakened electrical coupling between the first detection electrode 21 and the second detection electrode 22 and the liquid LQ. When high sensitivity is prioritized, the material for the protective layer 50 preferably has a high relative dielectric constant ε. From this perspective, zirconia or alumina is preferred, and zirconia is more preferred. On the other hand, in order to suppress the temperature dependence of the conductivity sensor 101, alumina is preferred over zirconia as the material for the protective layer 50. From the viewpoint of the heat resistance of the conductivity sensor 101 as well, alumina is more preferable than zirconia as the material for the protective layer 50.

[0060] The protective layer 50 may be made of a sintered body. This avoids a decrease in manufacturing efficiency during the manufacture of the conductivity sensor, which would be caused by forming a protective layer made of a non-sintered body. Furthermore, because the protective layer 50 and the insulating layer 10 are sintered bodies as an integrated structure, defects originating from the interface between them are less likely to occur. This improves properties such as chemical resistance and thermal shock resistance.

[0061] Both the insulating layer 10 and the protective layer 50 are preferably made of a ceramic insulator, and more preferably made of the same material. This reduces the difference in shrinkage rate during the firing process for manufacturing the conductivity sensor 101. Therefore, even if the thickness d of the protective layer 50 is relatively small, a pinhole-free protective layer 50 can be obtained. Therefore, the thickness d can be reduced while still fully achieving the effect of improving the corrosion resistance and chemical resistance of the protective layer 50.

[0062] The portion that becomes the protective layer 50 is preferably formed by pressing a green sheet 50G (FIG. 10). This makes it possible to obtain a pinhole-free protective layer 50 even if the thickness d of the protective layer 50 is relatively small, compared to when the portion is formed by applying a ceramic paste.

[0063] The first detection electrode 21 and the second detection electrode 22 are preferably made of a high-melting point metal, such as platinum, tungsten, or cobalt, which can prevent the electrodes from volatilizing or melting during the firing process for manufacturing the conductivity sensor 101.

[0064] The simulation results shown in this embodiment at frequencies of 1 kHz, 10 kHz, 100 kHz, and 1000 kHz are expected to roughly reflect the characteristics of frequencies on the order of 1 kHz, 10 kHz, 100 kHz, and 1000 kHz. In particular, the inventors' studies have shown that the characteristics at frequencies of 1 kHz ±10%, 10 kHz ±10%, 100 kHz ±10%, and 1000 kHz ±10% are roughly the same as the characteristics disclosed above for frequencies of 1 kHz, 10 kHz, 100 kHz, and 1000 kHz. Note that "100 kHz order" refers to frequencies between frequencies on the order of 10 kHz, one digit lower, and frequencies on the order of 1000 kHz, one digit higher, and naturally includes frequencies of approximately 100 kHz (e.g., frequencies of 100 Hz ±10%). The same applies to other frequency orders.

[0065] Furthermore, in the simulation results shown in this embodiment, the characteristics at the line width and space width are considered to be approximately the same as the characteristics at the line width ±10% and space width ±10%.

[0066] Although the present invention has been described in detail, the above description is in all respects illustrative and is not intended to limit the present invention, and it is understood that numerous variations not illustrated can be envisaged without departing from the scope of the present invention. [Explanation of symbols]

[0067] 10: Insulating layer 21: First detection electrode 22: Second detection electrode 31: First pad electrode 32: Second pad electrode 41: First via electrode 42: Second via electrode 50 :Protective layer 101: Conductivity sensor 200: Measuring instruments 500: Measurement system PTa: First line and space pattern PTb: Second line and space pattern

Claims

1. 1. A conductivity sensor for measuring the conductivity of a liquid, comprising: an insulating layer; a first detection electrode provided on the insulating layer; a second detection electrode provided on the insulating layer and spaced apart from the first detection electrode; a protective layer made of an insulator and covering the first detection electrode and the second detection electrode; Equipped with A conductivity sensor in which the first detection electrodes and the second detection electrodes are alternately positioned to form a first line-and-space pattern having a first space width and a second line-and-space pattern having a second space width different from the first space width.

2. The conductivity sensor according to claim 1 , wherein the first space width is equal to or less than 100 μm, and the second space width is greater than 100 μm.

3. The conductivity sensor according to claim 1 , wherein the second space width is 10 to 70 times the first space width.

4. 3. The conductivity sensor according to claim 1, wherein each of the plurality of lines constituting the first line-and-space pattern has a line length of 1 mm or more, and each of the plurality of lines constituting the second line-and-space pattern has a line length of 1 mm or more.

5. The conductivity sensor according to claim 1 , wherein each of the first line-and-space pattern and the second line-and-space pattern includes a plurality of spaces.

6. The conductivity sensor according to claim 1 , wherein the first line-and-space pattern and the second line-and-space pattern are adjacent to each other by sharing one line.

7. 3. The conductivity sensor according to claim 1, wherein the protective layer is made of zirconia or alumina and has a thickness of 1 μm or more and 10 μm or less.

8. 3. The conductivity sensor according to claim 1, wherein the protective layer is made of a sintered body.

9. 3. A conductivity measurement method for measuring the conductivity of a liquid using the conductivity sensor according to claim 1 or 2, comprising: a) measuring a complex impedance between the first detection electrode and the second detection electrode in a state where the liquid is in contact with the protective layer so as to face each of the first detection electrode and the second detection electrode through the protective layer; b) extracting an extraction value from the complex impedance according to a predetermined extraction rule; c) determining the conductivity of the liquid based on the extracted value; A conductivity measurement method comprising:

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