JP2012198122A - Sensor device and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor device and a measuring method that are capable of measuring over a long period of time changes in pH of an object to be measured, in a wide range of pH.SOLUTION: A sensor device 1 of the present invention has: a measuring electrode 3 composed of a metallic material forming a passivation film; a referential electrode 4 provided apart from the measuring electrode 3; a sensitive film 8 that is provided so as to cover the measuring electrode 3, is composed of the same material as the passivation film, and has sensitivity to ions; and a nonsensitive film 9 that is provided so as to cover the referential electrode 4 and does not substantially have the sensitivity to ions. An electric potential difference between the measuring electrode 3 and the referential electrode 4 changes in association with changes in pH.

Description

  The present invention relates to a sensor device and a measurement method.

As a sensor device, for example, a device that measures the corrosion state of a reinforcing bar in concrete is known (see, for example, Patent Document 1).
The concrete in the concrete structure immediately after construction usually exhibits strong alkalinity. Therefore, the reinforcing bars in the concrete structure immediately after construction are stable because a passive film is formed on the surface. However, in concrete structures that have been affected by acid rain or exhaust gas after construction, the concrete is gradually acidified, and the steel bars are corroded.

Therefore, for example, in the sensor device according to Patent Document 1, a thin wire made of the same kind of material as a reinforcing bar in a concrete structure is embedded in the concrete structure, and the presence or absence of the disconnection of the fine wire due to corrosion is detected. Predict the corrosion status of reinforcing bars.
However, the sensor device according to Patent Document 1 knows the state of reinforcing bars and concrete (more specifically, for example, pH and chloride ion concentration) in a concrete structure from when the fine wire starts to corrode until it is disconnected. I can't. In addition, the corrosion of the reinforcing bars in the concrete structure proceeds from the time when the fine wire starts to corrode until the wire breaks. Therefore, there was a problem that corrosion of the reinforcing bars in the concrete structure could not be avoided completely.

Japanese Patent Laid-Open No. 11-153568

In the sensor device according to Patent Document 1, it is possible to know the time when the corrosion of the reinforcing bars in the concrete structure has started, based on the timing at which the thin wire is cut. However, in the sensor device according to Patent Document 1, there is a problem that it is not possible to grasp the state of the reinforcing bars and concrete that change with the passage of time until the corrosion starts after the reinforcing bars are constructed.
The object of the present invention is to measure the state change of a measurement object during the period from when a reinforcing bar is constructed to when corrosion starts, and to use the obtained information for the planned maintenance of concrete structures. It is to provide an apparatus and a measurement method.

Such an object is achieved by the present invention described below.
The sensor device of the present invention includes a measurement electrode made of a metal material that forms a passive film,
A reference electrode provided apart from the measurement electrode;
A sensitive film that is provided so as to cover the measurement electrode, is made of the same material as the passive film, and has sensitivity to ions;
A non-sensitive membrane provided so as to cover the reference electrode and having substantially no sensitivity to ions;
A potential difference between the measurement electrode and the reference electrode changes with a change in pH.

According to such a sensor device of the present invention, pH can be measured based on the potential difference between the measurement electrode and the reference electrode.
In the present invention, since the sensitive film is made of the same material as the passive film, it is chemically stable in a relatively wide pH range. Therefore, the pH can be stably measured in a relatively wide pH range.

In the sensor device of the present invention, it is preferable that the reference electrode has a base portion made of a metal material that is the same as or close to that of the measurement electrode, and a passive film provided so as to cover the base portion.
Accordingly, the pH can be measured with higher accuracy based on the potential difference between the measurement electrode and the reference electrode.

In the sensor device of the present invention, the metal material is preferably an iron-based material.
Iron-based materials are cheap and easy to obtain.
In the sensor device of the present invention, it is preferable that the iron-based material contains Al.
The Fe-based alloy containing Al stably forms a passive film in a relatively wide pH range. Therefore, the measurement electrode can withstand the pH change in the concrete.

In the sensor device of the present invention, it is preferable that the sensitive film is made of FeAl ₂ O ₄ .
As a result, the sensitive membrane can be stably present in a relatively wide pH range (pH 4 to 14).
In the sensor device of the present invention, it is preferable that the non-sensitive film is made of a resin material.
Thereby, a non-sensitive film can be formed easily and reliably.

In the sensor device of the present invention, it is preferable to have a comparison electrode provided separately from the measurement electrode and the reference electrode.
Thereby, pH can be measured with higher accuracy.
In the sensor device of the present invention, it is preferable that the comparative electrode is made of a noble metal.
Thereby, the comparative electrode can be formed easily and reliably. Precious metals are chemically stable, have a very low sensitivity to ions, and have excellent conductivity. Therefore, the noble metal is suitable as a constituent material for the comparative electrode.
The sensor device of the present invention preferably includes a functional element having a function of measuring a potential difference between the measurement electrode and the reference electrode.
Accordingly, the pH can be measured with higher accuracy based on the potential difference between the measurement electrode and the reference electrode.

In the measurement method of the present invention, the measurement electrode and the reference electrode of the sensor device of the present invention are respectively embedded in a measurement object,
The state of the measurement object is measured based on a potential difference between the measurement electrode and the reference electrode.
Thereby, the state change accompanying the pH change of a measurement object can be measured in a wide pH range.
In the measurement method of the present invention, the measurement object is preferably concrete.
Thereby, the state change accompanying the pH change of concrete can be detected.

It is a figure which shows an example of the use condition of the sensor apparatus which concerns on embodiment of this invention. It is a block diagram which shows schematic structure of the sensor apparatus shown in FIG. FIG. 3 is a plan view for explaining a measurement electrode, a reference electrode, a comparison electrode, and a functional element shown in FIG. 2. It is sectional drawing for demonstrating the electrode for a measurement shown in FIG. 2, the electrode for a reference, and the electrode for a comparison (AA sectional view taken on the line in FIG. 3). It is sectional drawing for demonstrating the functional element shown in FIG. 2 (BB sectional drawing in FIG. 3). FIG. 3 is a circuit diagram showing a differential amplifier circuit provided in the functional element shown in FIG. 2. FIG. 3 is a circuit diagram showing a differential amplifier circuit provided in the functional element shown in FIG. 2. It is a figure which shows the pH-potential of FeAl.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a sensor device and a measurement method of the invention will be described with reference to the accompanying drawings.
First, a first embodiment of the present invention will be described.
FIG. 1 is a diagram showing an example of a usage state of a sensor device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of the sensor device shown in FIG. 1, and FIG. 3 is for measurement shown in FIG. FIG. 4 is a sectional view for explaining the measurement electrode, the reference electrode, and the comparison electrode shown in FIG. 2 (in FIG. 3). 5 is a cross-sectional view for explaining the functional element shown in FIG. 2 (cross-sectional view along the line BB in FIG. 3), and FIG. 6 is a cross-sectional view of the functional element shown in FIG. FIG. 7 is a circuit diagram showing the differential amplifier circuit provided in the functional element shown in FIG. 2, and FIG. 8 is a diagram showing the pH-potential of FeAl.
Hereinafter, a case where the sensor device and the measurement method of the present invention are used for quality measurement of a concrete structure will be described as an example.

A sensor device 1 shown in FIG. 1 measures the quality of a concrete structure 100.
The concrete structure 100 has a plurality of reinforcing bars 102 embedded in a concrete 101. The sensor device 1 is embedded in the vicinity of the reinforcing bar 102 in the concrete 101 of the concrete structure 100 (between the reinforcing bar 102 and the outer surface of the concrete 101). When the concrete structure 100 is placed, the sensor device 1 may be fixed and embedded in the reinforcing bars before the concrete 101 is introduced, or may be embedded in the concrete 101 hardened after the placement.

The sensor device 1 covers a main body 2, a measurement electrode 3 provided on the main body 2, a reference electrode 4 and a comparison electrode 7, a sensitive film 8 that covers the measurement electrode 3, and a reference electrode 4. And a non-sensitive film 9. In the present embodiment, the measurement electrode 3, the reference electrode 4, and the comparison electrode 7 are installed such that the distances from the outer surface of the concrete structure 100 are equal to each other. In addition, the measurement electrode 3, the reference electrode 4, and the comparison electrode 7 are each installed such that the electrode surfaces are parallel or substantially parallel to the outer surface of the concrete structure 100. And the sensor apparatus 1 is comprised so that pH can be measured based on the electric potential of the electrode 3 for a measurement, the electrode 4 for a reference, and the electrode 7 for a comparison.
In addition, as shown in FIG. 2, the sensor device 1 includes a functional element 51 electrically connected to the measurement electrode 3, the reference electrode 4, and the comparison electrode 7, a power source 52, a temperature sensor 53, and a communication device. A circuit 54, an antenna 55, and an oscillator 56, which are housed in the main body 2.

Hereinafter, each part which comprises the sensor apparatus 1 is demonstrated sequentially.
(Body)
The main body 2 has a function of supporting the measurement electrode 3, the reference electrode 4, the comparison electrode 7, the functional element 51, and the like.
As shown in FIGS. 4 and 5, the main body 2 has a substrate 21 that supports the measurement electrode 3, the reference electrode 4, the comparison electrode 7, and the functional element 51. The substrate 21 also supports the power supply 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56. However, in FIGS. 3 to 5, for convenience of explanation, the power supply 52, the temperature sensor 53, and the communication circuit 54 are used. The antenna 55 and the oscillator 56 are not shown.

The substrate 21 has an insulating property. The substrate 21 is not particularly limited, and for example, a mounting substrate such as an alumina substrate or a resin substrate can be used.
On this substrate 21, an insulating layer 23 made of an insulating resin composition such as a solder resist is provided. The measurement electrode 3, the reference electrode 4, the comparison electrode 7, and the functional element 51 are mounted on the substrate 21 with the insulating film 23 interposed therebetween.

The main body 2 has a function of housing the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56.
In particular, the main body 2 is configured to store the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56 in a liquid-tight manner.
Specifically, as shown in FIGS. 4 and 5, the main body 2 has a sealing portion 24. The sealing unit 24 has a function of sealing the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56. Thereby, when the sensor apparatus 1 is installed in the presence of moisture or concrete, it is possible to prevent the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56 from being deteriorated.

Here, the sealing part 24 has the opening part 241 (refer FIG. 3 and FIG. 4). Thereby, the sensor device 1 can perform measurement while protecting the portion where the sealing portion 24 should prevent deterioration.
Examples of the constituent material of the sealing portion 24 include thermoplastic resins such as acrylic resins, urethane resins, and olefin resins, epoxy resins, melamine resins, thermosetting resins such as phenol resins, and the like. Various resin materials etc. are mentioned, Among these, it can use combining 1 type (s) or 2 or more types.

(Measurement electrode, reference electrode)
As shown in FIG. 4, the measurement electrode 3 and the reference electrode 4 are respectively provided on the outer surface of the main body 2 (more specifically, on the substrate 21). In particular, the measurement electrode 3 and the reference electrode 4 are provided on the same plane. Therefore, it is possible to prevent a difference in installation environment between the measurement electrode 3 and the reference electrode 4 from occurring.
Further, the measurement electrode 3 and the reference electrode 4 are separated to such an extent that they are not influenced by the potential (for example, several mm).

In the present embodiment, each of the measurement electrode 3 and the reference electrode 4 has a thin film shape.
The constituent material of the measuring electrode 3 is not particularly limited, but Fe or an alloy containing Fe (particularly, an Fe-based alloy containing 0.1 to 3.5 wt% of Al), that is, an iron-based material. Is preferred. Iron-based materials are cheap and easy to obtain. Further, the Fe-based alloy containing 0.1 to 3.5 wt% of Al stably forms a passive film (FeAl ₂ O ₄ ) in a relatively wide pH range (pH _{4 to} 14) (see FIG. 7). . Therefore, the sensitive film 8 on the measurement electrode 3 can withstand a change in pH in the concrete for a long time.

On the other hand, as shown in FIG. 4, the reference electrode 4 includes a base 41 and a passive film 42 that covers the base 41.
The base 41 is made of a metal material that is the same as or close to that of the measurement electrode 3. The passive film 42 is made of a material (metal oxide) obtained by passivating the metal material that forms the base 41. A non-sensitive film 9 (pH non-sensitive film) is formed on the surface of the reference electrode 4. Thereby, the behavior of the natural potential of the reference electrode 4 does not depend on pH. Therefore, for example, when the passive film 42 is made of FeAl ₂ O ₄ , a good sensitivity of 58 mV / pH can be obtained in a wide range of concrete pH from 4 to 14.
Such a reference electrode 4 has the same configuration as that of the measurement electrode 3 and the sensitive film 8 described above. Therefore, the pH can be measured with higher accuracy based on the potential difference between the measurement electrode 3 and the reference electrode 4 covered with the non-sensitive film 9.

  Such a measurement electrode 3 and a reference electrode 4 are formed by chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, laser CVD, vacuum vapor deposition, sputtering (low temperature sputtering), ion plating, etc., respectively. It can be formed by wet plating methods such as dry plating, electrolytic plating, immersion plating, electroless plating, thermal spraying, sol-gel method, MOD method, metal foil bonding, and the like.

(Comparative electrode)
As shown in FIG. 4, the comparative electrode 7 is provided on the outer surface of the main body 2 (more specifically, on the substrate 21). The comparison electrode 7 is provided on the same plane as the measurement electrode 3 and the reference electrode 4 described above.
The comparison electrode 7 is provided at a distance from the measurement electrode 3 and the reference electrode 4. Further, the comparison electrode 7 has a shape such that the distance to the measurement electrode 3 and the distance to the reference electrode 4 are equal to each other.
The potentials of the measurement electrode 3 and the reference electrode 4 can be detected using the potential of the comparison electrode 7 as a reference. The potential difference between the measurement electrode 3 and the reference electrode 4 can be detected from the potential difference between the two potentials. Thereby, pH can be measured with higher accuracy.

In the present embodiment, the comparative electrode 7 has a thin film shape.
Such a comparison electrode 7 is made of a chemically stable and conductive material. Although it does not specifically limit as this material, For example, metal materials (noble metals), such as Pt, Au, Ag, can be used. Thereby, a stable reference potential can be acquired. In addition, the comparison electrode 7 can be formed easily and reliably. Precious metals are chemically stable, have a very low sensitivity to ions, and have excellent conductivity. Therefore, the noble metal is suitable as a constituent material of the comparative electrode 7.
Such a comparative electrode 7 includes, for example, chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, and laser CVD, vacuum deposition, sputtering (low temperature sputtering), dry plating methods such as ion plating, electrolytic plating, It can be formed by wet plating methods such as immersion plating and electroless plating, thermal spraying methods, sol-gel methods, MOD methods, metal foil bonding, and the like.

(Sensitive membrane)
The sensitive film 8 is provided so as to cover the measurement electrode 3. The sensitive film 8 has sensitivity to changes in ions (changes in pH). Thereby, the electric potential of the electrode 3 for a measurement can be changed with pH change.
The sensitive film 8 is made of the same material (passivated material) as the passive film formed by the metal material constituting the measurement electrode 3 described above.

The sensitive film 8 is made of the same material as or similar to the material constituting the passive film 42 of the reference electrode 4 described above.
The sensitive film 8 made of such a material is chemically stable in a relatively wide pH range. Therefore, the pH can be stably measured in a relatively wide pH range.

The thickness of the sensitive film 8 is not particularly limited, but is about 10 nm or more and 200 nm or less.
Such a sensitive film 8 can be formed by subjecting the surface of the measuring electrode 3 to thermal oxidation treatment, chemical oxidation treatment, or the like. In this case, a more uniform sensitive film 8 with a thickness of 100 to 200 nm can be formed.
The sensitive film 8 is formed by, for example, chemical vapor deposition (CVD) such as plasma CVD, thermal CVD, or laser CVD, vacuum plating, sputtering (low temperature sputtering), dry plating methods such as ion plating, electrolytic plating, or immersion plating. It can also be formed by wet plating methods such as electroless plating, thermal spraying methods, sol-gel methods, MOD methods, thin film bonding, and the like.

(Non-sensitive membrane)
The non-sensitive film 9 is provided so as to cover the reference electrode 4. The non-sensitive film 9 has substantially no sensitivity to changes in ions (changes in pH). Thereby, it can prevent or suppress that the electric potential of the reference electrode 4 fluctuates with the change of ions. That is, the non-sensitive film 9 does not affect the potential of the reference electrode 4 even if the amount of ions changes. Therefore, the potential difference between the measurement electrode 3 and the reference electrode 4 corresponds to the amount of change in the potential of the measurement electrode 3 due to the pH change. Here, “substantially has no sensitivity” means that there is no sensitivity at all, or even if there is sensitivity, the sensitivity of the sensitive film 8 described above is extremely small (specifically Less than 5%).

The constituent material of such a non-sensitive film 9 is not particularly limited, but for example, a resin material can be used. The resin material is stable against pH change. Therefore, the pH can be stably measured in a relatively wide pH range. Further, the non-sensitive film 9 can be formed easily and reliably.
Examples of the resin material include polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer (EVA), cyclic polyolefin, modified polyolefin, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide. , Polyimide, polyamideimide, polycarbonate, poly- (4-methylpentene-1), ionomer, acrylic resin, polymethyl methacrylate, acrylonitrile-butadiene-styrene copolymer (ABS resin), acrylonitrile-styrene copolymer (AS Resin), butadiene-styrene copolymer, polyoxymethylene, polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), polyethylene terephthalate (PET) Polybutylene terephthalate (PBT), Polycyclohexane terephthalate (PCT) and other polyesters, polyethers, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherimide, polyacetal (POM), polyphenylene oxide, modified polyphenylene oxide , Polysulfone, polyethersulfone, polyphenylene sulfide, polyarylate, aromatic polyester (liquid crystal polymer), polytetrafluoroethylene, polyvinylidene fluoride, other fluorine resins, styrene, polyolefin, polyvinyl chloride, polyurethane, Various thermoplastic elastomers such as polyester, polyamide, polybutadiene, trans polyisoprene, fluoro rubber, and chlorinated polyethylene Mer, epoxy resin, phenol resin, urea resin, melamine resin, unsaturated polyester, silicone resin, polyurethane, etc., or copolymers, blends, polymer alloys, etc. mainly comprising these, one of these Alternatively, two or more kinds can be used in combination (for example, as a laminate of two or more layers).
Such a non-sensitive film 9 is not particularly limited, but can be formed by, for example, a method of applying and drying a solution, a method of polymerizing after applying a monomer solution, a thin film bonding, or the like.

(Functional element)
The functional element 51 is embedded in the main body 2 described above.
The functional element 51 has a function of measuring a potential difference between the measurement electrode 3 and the reference electrode 4. Thereby, a change in the potential of the measurement electrode 3 with respect to the potential of the reference electrode 4 can be detected. Therefore, the pH can be measured with higher accuracy based on the potential difference between the measurement electrode 3 and the reference electrode 4.
The functional element 51 also has a function of calculating the pH of the measurement target portion of the concrete structure 100 that is a measurement target based on the potentials of the measurement electrode 3, the reference electrode 4, and the comparison electrode 7. Thereby, the state change accompanying the pH change of the concrete structure 100 is detectable.

Such a functional element 51 is, for example, an integrated circuit. More specifically, the functional element 51 is, for example, an MCU (micro control unit), and includes a CPU 511, an A / D conversion circuit 512, and a differential amplifier circuit 514 as shown in FIG.
More specifically, as shown in FIG. 5, the functional element 51 includes a substrate 513, a plurality of transistors 514a, 514b, and 514c provided on the substrate 513, and an interlayer insulation covering the transistors 514a, 514b and 514c. Films 515a and 515b, conductor portions 516a, 516b, 516c, 516d, 516e, and 516f that constitute wiring and conductor posts, a protective film 25, and conductor portions 61, 62, and 63 that constitute electrode pads are included.

The substrate 513 is, for example, an SOI substrate, on which a CPU 511 and an A / D conversion circuit 512 are formed. By using an SOI substrate as the substrate 513, the transistors 514a to 514c can be SOI MOSFETs.
Each of the plurality of transistors 514a, 514b, and 514c is, for example, a field effect transistor (FET), and constitutes a part of the differential amplifier circuit 514.

As shown in FIG. 6, the differential amplifier circuit 514 includes three transistors 514a to 514c and a current mirror circuit 514d.
Further, the differential amplifier circuit 514 includes operational amplifiers 201 and 202 and an operational amplifier 203 as shown in FIG.
The operational amplifier 201 detects the potential of the measurement electrode 3 with reference to the comparison electrode 7. The operational amplifier 202 detects the potential of the reference electrode 4 with the comparison electrode 7 as a reference. The operational amplifier 203 detects a difference between the output potential of the operational amplifier 201 and the output potential of the operational amplifier 202.

  One end of the conductor portion 516a is connected to the gate electrode of the transistor 514a, and the other end is connected to the above-described conductor portion 516d. The conductor portion 516d is electrically connected to the measurement electrode 3 via the conductor portion 61. Thereby, the gate electrode of the transistor 514a and the measurement electrode 3 are electrically connected. Therefore, the drain current of the transistor 514a changes according to the change in the potential of the measurement electrode 3.

Similarly, the conductor portion 516b has one end connected to the gate electrode of the transistor 514b and the other end connected to the above-described conductor portion 516e. The conductor portion 516 e is electrically connected to the reference electrode 4 through the conductor portion 62. Thereby, the gate electrode of the transistor 514b and the measurement electrode 4 are electrically connected. Therefore, the drain current of the transistor 514b changes according to the change in the potential of the reference electrode 4.
The conductor portion 516c has one end connected to the gate electrode of the transistor 514c and the other end connected to the above-described conductor portion 516f.

The functional element 51 is electrically connected to the comparison electrode 7 via the conductor portion 63.
The functional element 51 is activated by energization from the power source 52. The power source 52 is not particularly limited as long as it can supply power capable of operating the functional element 51. For example, the power source 52 may be a battery such as a button-type battery or has a power generation function such as a piezoelectric element. It may be a power source using an element.

The functional element 51 is configured to be able to acquire temperature information detected by the temperature sensor 53. Thereby, the information regarding the temperature of a measurement site | part can also be obtained. By using such temperature-related information, the state of the measurement site can be measured more accurately, or a change in the measurement site can be predicted with high accuracy.
The temperature sensor 53 has a function of detecting the temperature of the measurement site of the concrete structure 100 that is a measurement object. Such temperature sensor 53 is not particularly limited, and various types of known temperature sensors such as a thermistor and a thermocouple can be used, for example.

  The functional element 51 also has a function of driving and controlling the communication circuit 54. For example, the functional element 51 includes information on the potential difference between the measurement electrode 3 and the reference electrode 4 (hereinafter also simply referred to as “potential difference information”) and information on the pH of the measurement site (hereinafter simply referred to as “pH information”). ) Are respectively input to the communication circuit 54. The functional element 51 also inputs information related to the temperature detected by the temperature sensor 53 (hereinafter also simply referred to as “temperature information”) to the communication circuit 54.

The communication circuit 54 has a function of supplying power to the antenna 55 (transmission function). Thereby, the communication circuit 54 can wirelessly transmit the input information via the antenna 55. The transmitted information is received by a receiver (reader) provided outside the concrete structure 100.
The communication circuit 54 includes, for example, a transmission circuit for transmitting electromagnetic waves, a modulation circuit having a function of modulating a signal, and the like. Note that the communication circuit 54 receives a down-converter circuit having a function of converting a signal frequency to a low level, an up-converter circuit having a function of converting a signal frequency to a large level, an amplifier circuit having a function of amplifying a signal, and electromagnetic waves. And a demodulator circuit having a function of demodulating a signal.

The antenna 55 is not particularly limited, but is made of, for example, a metal material, carbon or the like, and has a form such as a winding or a thin film.
Further, the functional element 51 is configured to be able to acquire a clock signal from the oscillator 56. Thereby, each circuit can be synchronized and time information can be added to various information.
The oscillator 56 is not particularly limited. For example, the oscillator 56 includes an oscillation circuit using a crystal resonator.

The measurement method using the sensor device 1 configured as described above (an example of the measurement method of the present invention) includes the sensor device 1 embedded in a concrete structure 100 that is a measurement object, the measurement electrode 3, Based on the potentials of the reference electrode 4 and the comparative electrode 7, the state of the concrete structure 100 is measured.
Thereby, the sensitive film 8 changes the potential of the measurement electrode 3 in accordance with the amount of ions (hydrogen ion concentration). On the other hand, the non-sensitive film 9 does not affect the potential of the reference electrode 4 even if the amount of ions (hydrogen ion concentration) changes. Therefore, the potential difference between the measurement electrode 3 and the reference electrode 4 corresponds to the amount of change in the potential of the measurement electrode 3 due to the pH change. Therefore, the pH can be measured based on the potential difference between the measurement electrode 3 and the reference electrode 4.
In the present invention, since the sensitive film is made of the same material as the passive film, it is chemically stable in a relatively wide pH range. Therefore, the pH can be stably measured in a relatively wide pH range. For example, when the sensitive film 8 is made of FeAl ₂ O ₄ , the pH can be stably measured over a wide range from pH 4 to pH 14.

As mentioned above, although the sensor apparatus and the measuring method of this invention were demonstrated based on embodiment of illustration, this invention is not limited to this.
For example, in the sensor device of the present invention, the configuration of each part can be replaced with any configuration that exhibits the same function, and any configuration can be added. In addition, for example, in the measurement method of the present invention, one or two or more optional steps may be added.

In the above-described embodiment, the case where the measurement electrode and the reference electrode are provided on the substrate has been described as an example. However, the embodiment is not limited thereto. For example, the measurement electrode and the reference electrode include, for example, a sensor. You may provide on the outer surface of the part comprised with sealing resin of the main body of an apparatus.
Further, in the above-described embodiment, the case where the measurement electrode and the reference electrode are each in the form of a thin film has been described as an example. However, the present invention is not limited to this, and the shape of the measurement electrode and the reference electrode is, for example, a block. It may be in the form of a line, a line, or the like. In the above-described embodiment, the measurement electrode and the reference electrode are provided along the outer surface of the main body of the sensor device. However, the measurement electrode and the reference electrode are protruded from the outer surface of the main body of the sensor device, respectively. May be.

In the above-described embodiment, the case where the functional element includes a CPU, an A / D conversion circuit, and a differential amplifier circuit has been described as an example. However, the functional element is not limited thereto. Other circuits such as a drive circuit may be incorporated.
In the above-described embodiment, the case where the information regarding the potential difference between the measurement electrode and the reference electrode is transmitted to the outside of the sensor device by wireless transmission using active tag communication is described as an example. However, the present invention is not limited to this. Information may be transmitted to the outside of the sensor device using tag communication, or information may be transmitted to the outside of the sensor device by wire.

  In the above-described embodiment, the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56 are accommodated in the main body 2, and these are measured together with the measurement electrode 3 and the reference electrode 4. Although the case of embedding in the concrete structure 100, which is an object, has been described as an example, the functional element 51, the power source 52, the temperature sensor 53, the communication circuit 54, the antenna 55, and the oscillator 56 may be provided outside the measurement object. Good.

DESCRIPTION OF SYMBOLS 1 ... Sensor device 2 ... Body 3 ... Measuring electrode 4 ... Reference electrode 7 ... Comparison electrode 8 ... Sensitive film 9 ... Non-sensitive film 21 ... Substrate 22b ... Conductor part 22c ... Conductor 23 ... Insulating layer 24 ... Sealed part 41 ... Base 42 ... Passive film 43 ... Electrode 51 ... Functional element 52 ... Power supply 53 ... Temperature sensor 54 ... Communication circuit 55 ... Antenna 56 ... Oscillator 61 ... Conductor part 62 ... Conductor part 63 ... Conductor part 100 ... Concrete structure 101 ... Concrete 102 ... Reinforcing bars 201, 202, 203 ... Operational amplifier 241 ... Opening part 511 ... CPU 512 Conversion circuit 513 Substrate 514 Differential amplification circuit 514a Transistor 514b Transistor 514c Transistor 514d ‥ current mirror circuit 515a, 515b ‥‥ interlayer insulating film 516a ‥‥ conductor portion 516b ‥‥ conductor portion 516c ‥‥ conductor portion 516d ‥‥ conductor portion 516e ‥‥ conductor portion 516f ‥‥ conductor portion

Claims (11)

A measurement electrode composed of a metal material forming a passive film;
A reference electrode provided apart from the measurement electrode;
A sensitive film that is provided so as to cover the measurement electrode, is made of the same material as the passive film, and has sensitivity to ions;
A non-sensitive membrane provided so as to cover the reference electrode and having substantially no sensitivity to ions;
A sensor device, wherein a potential difference between the measurement electrode and the reference electrode changes with a change in pH.   The sensor device according to claim 1, wherein the reference electrode includes a base portion made of a metal material that is the same as or close to that of the measurement electrode, and a passive film provided so as to cover the base portion.   The sensor device according to claim 1, wherein the metal material is an iron-based material.   The sensor device according to claim 3, wherein the iron-based material includes Al. The sensor device according to claim ₄ , wherein the sensitive film is made of FeAl ₂ O ₄ .   The sensor device according to claim 1, wherein the non-sensitive film is made of a resin material.   The sensor device according to claim 1, further comprising a comparison electrode provided separately from the measurement electrode and the reference electrode.   The sensor device according to claim 7, wherein the comparison electrode is made of a noble metal.   The sensor device according to claim 1, further comprising a functional element having a function of measuring a potential difference between the measurement electrode and the reference electrode. The measurement electrode and the reference electrode of the sensor device according to any one of claims 1 to 9, are embedded in a measurement object, respectively.
A measurement method comprising measuring a state of the measurement object based on a potential difference between the measurement electrode and the reference electrode.   The measurement method according to claim 10, wherein the measurement object is concrete.

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