Thickness measuring device and thickness measuring method

Abstract

To reduce the influence of the temperature of a measurement environment in a measurement of the thickness of a target object.SOLUTION: A thickness measuring device 10 includes: an excitation unit 71 for applying an excitation current to an excitation coil 11 and inducing an eddy current in a target object 9; a detection unit 72 for detecting an eddy current in the target object 9 by a detection coil 12; a thickness deriving unit 84 for determining the thickness d of the target object 9 on the basis of the duration time τ of the eddy current detected by the detection unit 72; a substrate 68 equipped with the excitation unit 71 and the detection unit 72; and a correction unit 85 for correcting a thickness d. The correction unit 85 corrects the thickness d on the basis of the temperature characteristics of the duration time τ related to the temperature of the substrate 68 and the temperature of the excitation coil 11.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed herein relates to a thickness measurement device and a thickness measurement method. [Background technology]

[0002] Measuring devices using eddy currents have been known for some time. For example, Patent Document 1 discloses a measuring device that uses eddy currents to detect flaws in an object. The measuring device in Patent Document 1 corrects detection signals and the like based on the temperature of the object, taking into account the temperature dependency of magnetic permeability and the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-open No. 58-102150 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, among measuring devices using eddy currents, there is a thickness measuring device that measures the thickness of an object. Even in such a thickness measuring device, the measurement accuracy can be affected by the temperature of the measurement environment. The temperature of the measurement environment that can affect the measurement accuracy is not limited to the temperature of the object. In other words, there is still room for improvement in measurement accuracy related to the temperature of the measurement environment.

[0005] The technique disclosed herein has been made in view of the above points, and its purpose is to reduce the influence of the temperature of the measurement environment on the thickness measurement of an object. [Means for solving the problem]

[0006] The thickness measuring device disclosed herein comprises an excitation unit that applies an excitation current to an excitation coil to induce eddy currents in an object, a detection unit that detects the eddy currents in the object via a detection sensor, a thickness derivation unit that determines the thickness of the object based on the duration of the eddy current detected by the detection unit, a substrate on which the excitation unit and the detection unit are mounted, and a correction unit that corrects the thickness, and the correction unit corrects the thickness based on the temperature characteristics of the duration related to the temperature of the substrate and the temperature of the excitation coil.

[0007] The thickness measurement method disclosed herein includes applying an excitation current to an excitation coil to induce eddy currents in an object, detecting the eddy currents in the object via a detection sensor, determining the thickness of the object based on the duration of the detected eddy currents, and performing a correction process to correct the thickness, wherein the correction process corrects the thickness based on the temperature of a substrate on which an excitation unit that applies an excitation current to the excitation coil and a detection unit that detects the eddy currents via the detection sensor are mounted, and the temperature characteristics of the duration related to the temperature of the excitation coil. [Effects of the Invention]

[0008] According to the thickness measuring device, the influence of the temperature of the measurement environment on the thickness measurement of the object can be reduced.

[0009] According to the thickness measurement method, the influence of the temperature of the measurement environment on the thickness measurement of the object can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of a thickness measurement device. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control system of the control unit of the processing device. [Figure 3] FIG. 3 is a block diagram showing the configuration of a control system of the control unit of the arithmetic device. [Figure 4] FIG. 4 is a graph showing the change over time of a voltage signal V(t) corresponding to an eddy current. [Figure 5] FIG. 5 is a flowchart of the thickness measurement. DETAILED DESCRIPTION OF THE INVENTION

[0011] Exemplary embodiments will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a thickness measurement system 100. The thickness measurement system 100 includes a probe 1 and a thickness measurement device 10. The thickness measurement device 10 measures the thickness of an object 9 by pulsed eddy current (PEC). The thickness measurement device 10 includes a processing device 6 that controls the probe 1 and a computing device 8 that calculates the thickness of the object 9. For example, the object 9 is a metal pipe through which crude oil, refined petroleum products, etc. are distributed. The pipe is formed in a cylindrical shape.

[0012] The probe 1 is used to generate an eddy current in the object 9 and to detect the generated eddy current. The probe 1 is a non-contact type probe and is placed in close proximity to the object 9. Note that the term "non-contact type" means that it can be used without contact, and does not exclude use in a contact state. The probe 1 is placed so as to face the surface of the object 9. For example, the probe 1 is placed on the object 9 via a spacer (not shown) having thermal insulation properties.

[0013] The probe 1 generates eddy currents in the object 9 by forming a fluctuating magnetic field. The probe 1 also detects changes in the eddy currents generated in the object 9 as induced voltages. Specifically, the probe 1 includes an excitation coil 11 that induces eddy currents in the object 9 with magnetic flux generated by an excitation current, and a detection coil 12 that detects the eddy currents in the object 9. The probe 1 induces eddy currents in the object 9 using the excitation coil 11, and detects the induced eddy currents using the detection coil 12. The detection coil 12 is an example of a detection sensor.

[0014] Furthermore, the probe 1 further includes a second temperature sensor 15 that detects the temperature of the object 9. The second temperature sensor 15 is, for example, a thermocouple. Furthermore, the probe 1 may further include a casing that houses the excitation coil 11, the detection coil 12, and the second temperature sensor 15.

[0015] In the example of Fig. 1, the excitation coil 11 and the detection coil 12 are arranged so that the axis of the excitation coil 11 and the axis of the detection coil 12 are aligned in a straight line. In this case, the detection coil 12 is arranged closer to the object 9. The probe 1 may have multiple pairs of excitation coils 11 and detection coils 12. In Fig. 1, the probe 1 has two pairs of excitation coils 11 and detection coils 12.

[0016] Furthermore, the probe 1 may include a core 13 inserted into the excitation coil 11 and the detection coil 12. The core 13 is formed into a generally U-shape overall. More specifically, the core 13 is formed by stacking a plurality of generally U-shaped thin plates made of permalloy. A linear portion at one end of the core 13 is inserted into one set of the excitation coil 11 and the detection coil 12. A linear portion at the other end of the core 13 is inserted into the other set of the excitation coil 11 and the detection coil 12. The core 13 magnetically connects the two sets of the excitation coil 11 and the detection coil 12.

[0017] When a current is applied to the excitation coil 11, the excitation coil 11 generates a magnetic field in the direction of its axis. Current is applied to one excitation coil 11 and the other excitation coil 11 so that they generate magnetic fields in opposite directions in the direction of the axis. As a result, a magnetic field is generated in the core 13 along the longitudinal direction of the core 13. That is, when one end of the core 13 becomes a north pole, the other end of the core 13 becomes a south pole. Conversely, when one end of the core 13 becomes a south pole, the other end of the core 13 becomes a north pole. For example, magnetic flux is generated from one excitation coil 11 toward the object 9, and magnetic flux is generated from the object 9 toward the other excitation coil 11. More specifically, most of the magnetic flux generated from one excitation coil 11 exits toward the axis of the one excitation coil 11, enters the object 9, passes through the object 9 in a substantially arc shape, returns toward the axis of the other excitation coil 11, and enters the other excitation coil 11. By varying the current applied to the excitation coil 11, the magnetic field generated in the object 9 varies, and an eddy current is generated in the object 9.

[0018] Meanwhile, eddy currents generated in a portion of the object 9 near the detection coil 12 form magnetic fluxes that penetrate the detection coil 12. When the magnetic flux that penetrates the detection coil 12 changes, an induced electromotive force is generated in the detection coil 12. The detection coil 12 detects this induced electromotive force, thereby detecting the eddy currents in the object 9. In other words, detecting the induced electromotive force by the detection coil 12 is also referred to as detecting eddy currents.

[0019] The processing device 6 uses the probe 1 to generate an eddy current in the object 9 and detects the generated eddy current. The calculation device 8 calculates the thickness of the object 9 based on the duration of the eddy current detected by the processing device 6 (the time until the eddy current rapidly decays, which will be described in detail later). In addition, the calculation device 8 corrects the calculated thickness of the object 9.

[0020] The processing device 6 is disposed, for example, close to the object 9. For example, the processing device 6 is installed on the object 9 via a spacer. The processing device 6 has a transmitting unit 61, a first receiving unit 62, a second receiving unit 63, a temperature measuring unit 64, a communication unit 65, a control unit 66, a memory unit 67, a substrate 68, and a first temperature sensor 69.

[0021] The transmitter 61 applies a pulsed excitation current to the excitation coil 11. The transmitter 61 has a pulse generator 61a and a transmission amplifier 61b. The pulse generator 61a generates a pulse signal based on a command from the control unit 66. The transmission amplifier 61b amplifies the pulse signal from the pulse generator 61a and outputs it to the excitation coil 11 as an excitation current.

[0022] The first receiving unit 62 receives an induced electromotive force generated in the detection coil 12 in response to an eddy current in the object 9. The first receiving unit 62 has at least a receiving amplifier 62a that receives the voltage generated in the detection coil 12 and amplifies the voltage. The first receiving unit 62 may further have a filter that filters the voltage signal.

[0023] The second receiving unit 63 receives the voltage across the exciting coil 11. The second receiving unit 63 has at least a receiving amplifier 63a that receives the voltage generated in the exciting coil 11 and amplifies the voltage. The second receiving unit 63 may further have a filter that filters the voltage signal.

[0024] The temperature measuring unit 64 receives the output of the first temperature sensor 69. The temperature measuring unit 64 may have a receiving amplifier that receives the detection signal of the first temperature sensor 69 and amplifies the detection signal. Furthermore, the temperature measuring unit 64 receives the output of the second temperature sensor 15. The temperature measuring unit 64 may have a receiving amplifier that receives the detection signal of the second temperature sensor 15 and amplifies the detection signal. The temperature measuring unit 64 does not have to be shared by the first temperature sensor 69 and the second temperature sensor 15, and may be provided separately.

[0025] The communication unit 65 performs wireless communication with external devices. For example, the communication unit 65 transmits the voltage signal (i.e., the detection signal) detected by the first receiving unit 62, the voltage signal (i.e., the detection signal) detected by the second receiving unit 63, and the detection signal detected by the temperature measuring unit 64 to the calculation device 8.

[0026] The control unit 66 controls the entire processing device 6. The control unit 66 performs various types of arithmetic processing. For example, the control unit 66 is formed of a processor such as a CPU (Central Processing Unit). The control unit 66 may also be formed of an MCU (Micro Controller Unit), an MPU (Micro Processor Unit), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), a system LSI, or the like.

[0027] For example, the control unit 66 causes the transmitting unit 61 to output an excitation current for only a predetermined period of time. The control unit 66 acquires a detection signal via the second receiving unit 63 while the excitation current is being output. The control unit 66 acquires a detection signal via the first receiving unit 62 after the output of the excitation current has stopped. The control unit 66 also acquires a detection signal from the temperature measuring unit 64 at the same time that it acquires the detection signal from the first receiving unit 62. The control unit 66 stores the detection signals from the first receiving unit 62, the second receiving unit 63, and the temperature measuring unit 64 in the memory unit 67, and transmits the detection signals stored in the memory unit 67 to the calculation device 8 via the communication unit 65 as appropriate.

[0028] The storage unit 67 stores various data and programs executed by the control unit 66. For example, a control program is stored in the storage unit 67. The storage unit 67 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), or the like.

[0029] On the board 68, a transmitting unit 61, a first receiving unit 62, a second receiving unit 63, a temperature measuring unit 64, a communication unit 65, a control unit 66, and a storage unit 67 are mounted.

[0030] The first temperature sensor 69 detects the temperature of the substrate 68. The first temperature sensor 69 is disposed on the substrate 68. The first temperature sensor 69 is, for example, a temperature sensor IC.

[0031] 2 is a block diagram showing the configuration of a control system of the control unit 66 of the processing device 6. The control unit 66 realizes various functions by reading a control program from the storage unit 67 into memory and expanding the program. Specifically, the control unit 66 functions as an excitation unit 71 that applies an excitation current to the excitation coil 11 to induce an eddy current in the object 9, a detection unit 72 that detects the eddy current in the object 9 via the detection coil 12, a voltage acquisition unit 73 that acquires the voltage of the excitation coil 11 when the excitation current is applied to the excitation coil 11, a first temperature acquisition unit 74 that acquires the temperature of the substrate 68, and a second temperature acquisition unit 75 that acquires the temperature of the object 9.

[0032] The excitation unit 71 causes the transmission unit 61 to apply an excitation current to the excitation coil 11. Specifically, the excitation unit 71 outputs a command to the pulse generator 61a, causing the pulse generator 61a to generate a pulse signal. As a result, an excitation current is applied to the excitation coil 11 from the transmission amplifier 61b.

[0033] The detection unit 72 detects a voltage signal corresponding to the eddy current as the eddy current in the object 9. Specifically, the detection unit 72 detects a voltage signal corresponding to the induced electromotive force in the detection coil 12. More specifically, the detection unit 72 continues to detect the voltage signal for a predetermined period after the application of the excitation current to the excitation coil 11 is stopped. In other words, the detection unit 72 detects a time-varying change (i.e., a transient change) in the eddy current in the object 9 after the application of the excitation current to the excitation coil 11 is stopped. The detection unit 72 stores the detected eddy current, i.e., the voltage signal, in the storage unit 67. Hereinafter, for convenience of explanation, the voltage signal detected by the detection unit 72 may be simply referred to as the "eddy current." For example, the voltage signal corresponding to the eddy current stored in the storage unit 67 will also be simply referred to as the "eddy current."

[0034] The voltage acquisition unit 73 acquires a voltage signal corresponding to the voltage across the excitation coil 11. The voltage acquisition unit 73 acquires a voltage signal when an excitation current is applied to the excitation coil 11. The voltage acquisition unit 73 stores the detected voltage across the excitation coil 11, i.e., the voltage signal, in the storage unit 67. Hereinafter, for convenience of explanation, the voltage signal acquired by the voltage acquisition unit 73 may be simply referred to as the "voltage of the excitation coil 11." For example, the voltage signal corresponding to the voltage across the excitation coil 11, stored in the storage unit 67, will also be simply referred to as the "voltage of the excitation coil 11."

[0035] The first temperature acquisition unit 74 acquires the temperature of the substrate 68 after the excitation unit 71 stops applying the excitation current to the excitation coil 11. For example, the first temperature acquisition unit 74 acquires the temperature of the substrate 68 when the detection unit 72 detects the eddy current. The first temperature acquisition unit 74 acquires the temperature of the substrate 68 measured by the first temperature sensor 69 arranged on the substrate 68, i.e., the actual measured temperature. The first temperature acquisition unit 74 stores the acquired temperature of the substrate 68 in the memory unit 67.

[0036] The second temperature acquisition unit 75 acquires the temperature of the object 9 measured by the second temperature sensor 15, i.e., the actual measured temperature. The second temperature acquisition unit 75 stores the acquired temperature of the object 9 in the storage unit 67.

[0037] In the storage unit 67, the eddy current detected by the detection unit 72, the voltage of the excitation coil 11 acquired by the voltage acquisition unit 73, the temperature of the substrate 68 acquired by the first temperature acquisition unit 74, and the temperature of the object 9 acquired by the second temperature acquisition unit 75 are stored in association with one another. In other words, the storage unit 67 stores the eddy current of the object 9, the voltage of the excitation coil 11, the temperature of the object 9, and the temperature of the substrate 68 as one set.

[0038] The control unit 66 transmits the eddy current of the object 9, the voltage of the exciting coil 11, the temperature of the object 9, and the temperature of the substrate 68 stored in the storage unit 67 to the calculation device 8 via the communication unit 65.

[0039] The arithmetic device 8 is formed by a computer or a computer network (so-called cloud). The arithmetic device 8 has a communication unit 81, a control unit 82, and a storage unit 83.

[0040] The communication unit 81 performs wireless communication with external devices. For example, the communication unit 81 receives signals from the processing device 6.

[0041] The control unit 82 controls the entire arithmetic device 8. The control unit 82 performs various types of arithmetic processing. For example, the control unit 82 is formed of a processor such as a CPU (Central Processing Unit). The control unit 82 may also be formed of an MCU (Micro Controller Unit), an MPU (Micro Processor Unit), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), a system LSI, or the like.

[0042] The memory unit 83 stores programs and various data executed by the control unit 82. For example, the memory unit 83 stores a control program. The memory unit 83 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), or the like. The memory unit 83 also stores signals transmitted from the processing device 6. Specifically, the memory unit 83 stores the eddy current of the object 9, the voltage of the excitation coil 11, the temperature of the object 9, and the temperature of the substrate 68, which are acquired by the processing device 6.

[0043] 3 is a block diagram showing the configuration of a control system of the control unit 82 of the calculation device 8. The control unit 82 realizes various functions by reading out a control program from the storage unit 83 into memory and expanding it. Specifically, the control unit 82 functions as a thickness derivation unit 84 and a correction unit 85.

[0044] The thickness derivation unit 84 determines the thickness of the object 9 based on the duration of the eddy current in the object 9. As will be described in more detail, the eddy current induced in the object 9 by the excitation coil 11 penetrates from the front surface of the object 9 (the surface facing the probe 1) to the back surface, and rapidly attenuates when it reaches the back surface. The duration of the eddy current in the object 9 is the time from when the eddy current is induced in the object 9 to when it rapidly attenuates. The duration of the eddy current in the object 9 is correlated with the thickness of the object 9.

[0045] The thickness derivation unit 84 determines the duration of the eddy current (specifically, the voltage signal) detected by the processing device 6. The thickness derivation unit 84 determines the thickness of the object 9 from the duration based on the correlation between the duration and the thickness.

[0046] The correction unit 85 corrects the thickness calculated by the thickness calculation unit 84. Specifically, the correction unit 85 corrects the thickness based on the temperature characteristics of the duration related to the temperature of the substrate 68 and the temperature of the exciting coil 11. Furthermore, the correction unit 85 corrects the thickness based on the temperature characteristics of the duration related to the temperature of the object 9 in addition to the temperature characteristics of the duration related to the temperature of the substrate 68 and the temperature of the exciting coil 11. Note that "temperature characteristics of the duration related to the temperature of ..." refers to the relationship between the change in the duration and the change in the temperature of ....

[0047] Here, the relationship between eddy currents and the thickness of the object 9 will be described in detail. FIG. 4 is a graph showing the time variation of a voltage signal V(t) corresponding to an eddy current. The graph in FIG. 4 is a double logarithmic graph. In FIG. 4, voltage signal V0(t) is the voltage signal of an object 9 having a thickness d0, and voltage signal V1(t) is the voltage signal of an object 9 having a thickness d1 that is thinner than d0.

[0048] The eddy current decays as it penetrates into the object 9. The eddy current decays gradually from the front surface of the object 9 (the surface facing the probe 1) until it reaches the back surface, and then decays rapidly once it reaches the back surface. The voltage signal V(t) also shows the same change as the eddy current. In other words, the transient change in the voltage signal V(t) corresponds to the transient change in the eddy current. The change in the voltage signal V(t) until the eddy current reaches the back surface of the object 9 is represented linearly on a double logarithmic graph. Thereafter, the voltage signal V(t) decays rapidly. This changing voltage signal V(t) is expressed as in the following equation (1).

[0049]

number

[0050] As can be seen from equation (1), the voltage signal V(t) gradually decays but continues until time τ, at which point it rapidly decays. For convenience of explanation, τ will be referred to as the "duration." The duration τ is expressed by the following equation (2):

[0051] τ=σμd 2 ···(2) where σ is the electrical conductivity of the object 9 , μ is the magnetic permeability of the object 9 , and d is the thickness of the object 9 .

[0052] That is, the duration τ changes depending on the thickness d of the object 9. Assuming that the electrical conductivity σ and magnetic permeability μ of the object 9 are constant, the duration τ changes depending on the thickness d of the object 9. Also, even if the duration τ and the thickness d change, the time τ / d 2 is constant. Therefore, if the duration τ0 for a known thickness d0 and the duration τ for an unknown thickness d are known, the unknown thickness d can be calculated based on the following equation (3). Equation (3), the known thickness d0, and the duration τ0 are stored in the memory unit 83.

[0053]

number

[0054] For example, comparing voltage signals V0(t) and V1(t) in Figure 4, the voltage signal V0(t) of object 9 with thickness d0 continues until duration τ0. As the thickness d of object 9 decreases from d0 to d1, duration τ decreases from τ0 to τ1. Note that the change in the linear portion of voltage signal V(t) on a log-log graph does not depend on thickness d, as can be seen from equation (1), and therefore is substantially the same for voltage signals V0(t) and V1(t). The thickness d1 can be calculated by substituting thickness d0 and durations τ0 and τ1 into equation (3).

[0055] However, the duration τ thus determined, and thus the thickness d, are affected by the temperature of the measurement environment, such as the temperature of the object 9, the temperature of the excitation coil 11, and the temperature of the substrate 68.

[0056] Specifically, the electrical conductivity σ and magnetic permeability μ of the actual object 9 have temperature dependence. For example, in the case of carbon steel, the electrical conductivity σ generally has a negative temperature characteristic, and the magnetic permeability μ generally has a positive temperature characteristic. When the electrical conductivity σ and the magnetic permeability μ have temperature dependence, the duration τ also has temperature dependence.

[0057] Furthermore, because the excitation coil 11 is placed on or near the object 9, the temperature of the excitation coil 11 may change depending on the temperature of the object 9. The resistance of the excitation coil 11 is temperature dependent. When the resistance of the excitation coil 11 changes due to a change in the temperature of the excitation coil 11, the magnetic field formed by the excitation coil 11 also changes. As a result, the duration τ also changes.

[0058] Furthermore, since the processing device 6 is placed on or near the object 9, the temperature of the substrate 68 may change depending on the temperature of the object 9. When the temperature of the substrate 68 changes, the temperatures of the circuits related to transmission, such as the transmitter 61, and the circuits related to reception, such as the first receiver 62, change. These circuits also have temperature dependency. When the temperature of the circuits related to transmission changes, the excitation current may change. When the temperature of the circuits related to reception changes, the voltage signal corresponding to the induced electromotive force output from the first receiver 62 may change. As a result, the duration τ also changes.

[0059] When the duration τ changes in this way, the thickness d calculated from the duration τ also changes. Therefore, the correction unit 85 corrects the thickness d so as to reduce the fluctuation in the duration τ caused by the temperatures of the object 9, the substrate 68, and the exciting coil 11, i.e., the fluctuation in the thickness d.

[0060] More specifically, with regard to the temperature of the substrate 68 and the temperature of the excitation coil 11, the correction unit 85 corrects the thickness d using a parameter related to the temperature of the substrate 68 and a parameter related to the temperature of the excitation coil 11. In this example, the parameter related to the temperature of the substrate 68 and the parameter related to the temperature of the excitation coil 11 are the voltage of the excitation coil 11 when an excitation current is applied to the excitation coil 11. Changes in the voltage of the excitation coil 11 reflect changes in the excitation current applied to the excitation coil 11 and changes in the resistance of the excitation coil 11. If the temperature of the substrate 68, particularly the temperature of the transmission-related circuits, changes, the excitation current of the excitation coil 11 may change. If the temperature of the excitation coil 11 changes, the resistance of the excitation coil 11 may change. In other words, the voltage of the excitation coil 11 changes depending on the temperature of the substrate 68 and the temperature of the excitation coil 11.

[0061] The correction unit 85 corrects the thickness d using the characteristics of the duration τ related to the voltage of the excitation coil 11 (i.e., the relationship between the change in the duration τ and the change in the voltage of the excitation coil 11; hereinafter referred to as the "transmission voltage characteristics") as the temperature characteristics of the duration τ related to the temperature of the substrate 68 and the temperature of the excitation coil 11 (hereinafter referred to as the "substrate-coil temperature characteristics"). The transmission voltage characteristics of the duration τ reflect the substrate-coil temperature characteristics of the duration τ. The transmission voltage characteristics of the duration τ mainly reflect the temperature characteristics of the duration τ related to the temperature of the transmission circuit, among the temperature characteristics of the duration τ related to the temperature of the substrate 68.

[0062] That is, the correction unit 85 corrects the thickness d according to the transmission voltage characteristics of the duration τ using the voltage of the excitation coil 11. The correction unit 85 corrects the thickness d using the voltage of the excitation coil 11 so as to reduce the change in the duration τ (i.e., the change in the thickness d) caused by the change in the voltage of the excitation coil 11.

[0063] In addition, the correction unit 85 also corrects the thickness d based on the temperature itself of the substrate 68. In other words, the correction unit 85 uses the transmission voltage characteristics of the duration τ and the temperature characteristics of the duration τ related to the measured temperature of the substrate 68 (hereinafter referred to as the "measured temperature characteristics") as the substrate-coil temperature characteristics of the duration τ. The measured temperature characteristics of the duration τ reflect, among the temperature characteristics of the duration τ related to the temperature of the substrate 68, the temperature characteristics of the duration τ related to the temperature of the circuit related to reception in addition to the temperature characteristics of the duration τ related to the temperature of the circuit related to transmission.

[0064] That is, the correction unit 85 corrects the thickness d using the measured temperature of the substrate 68 in accordance with the measured temperature characteristics of the duration τ. The correction unit 85 corrects the thickness d using the measured temperature of the substrate 68 so as to reduce the change in the duration τ (i.e., the change in the thickness d) caused by the temperature change of the substrate 68.

[0065] Furthermore, with regard to the temperature of the object 9, the correction unit 85 corrects the thickness d according to the temperature of the object 9. The correction unit 85 corrects the thickness d based on the temperature characteristics of the duration τ related to the temperature of the object 9 (hereinafter referred to as "object temperature characteristics") in addition to the substrate-coil temperature characteristics of the duration τ.

[0066] That is, the correction unit 85 corrects the thickness d depending on the temperature of the object 9 in accordance with the object temperature characteristics of the duration τ.

[0067] Specifically, the correction unit 85 corrects the thickness d based on the following approximate formula (4).

[0068]

number

[0069] Approximation formula (4) reflects the object temperature characteristics for duration τ, the measured temperature characteristics for duration τ, and the transmission voltage characteristics for duration τ. The measured temperature characteristics for duration τ and the transmission voltage characteristics for duration τ correspond to the substrate-coil temperature characteristics for duration τ. Specifically, the term related to the object temperature deviation ΔTm corresponds to the object temperature characteristics for duration τ. The term related to the substrate temperature deviation ΔTb corresponds to the measured temperature characteristics for duration τ. The term related to the coil voltage deviation ΔVc corresponds to the transmission voltage characteristics for duration τ.

[0070] The terms related to the object temperature deviation ΔTm, the substrate temperature deviation ΔTb, and the coil voltage deviation ΔVc are obtained by acquiring data on thickness d at various object temperatures Tm, substrate temperatures Tb, and coil voltages Vc in advance and approximating the data with a quadratic function. Thickness d is obtained from duration τ. Therefore, the relationship of thickness d to object temperature Tm corresponds to the relationship of duration τ to object temperature Tm. The relationship of thickness d to substrate temperature Tb corresponds to the relationship of duration τ to substrate temperature Tb. The relationship of thickness d to coil voltage Vc corresponds to the relationship of duration τ to coil voltage Vc.

[0071] Specifically, after the excitation unit 71 applies an excitation current to the excitation coil 11 to excite it, the excitation current output is stopped, and the detection unit 72 detects the eddy current generated in the object 9. The detection unit 72 continues detecting the voltage signal for a predetermined period of time. In this way, the transient change (change over time) of the induced electromotive force in the detection coil 12, i.e., the transient change of the eddy current generated in the object 9, is detected. At this time, the object temperature Tm, substrate temperature Tb, and coil voltage Vc are also acquired. The duration τ is calculated from the detected transient change of the eddy current, and the thickness d is calculated from the duration τ. The acquisition of the transient change of the eddy current and the derivation of the thickness d are repeated for different object temperatures Tm, substrate temperatures Tb, and coil voltages Vc, and multiple sets of data on the object temperature Tm, substrate temperature Tb, coil voltage Vc, and thickness d are acquired.

[0072] From the acquired data, the average values ​​of the object temperature Tm, substrate temperature Tb, coil voltage Vc, and thickness d are determined. The average value of the object temperature Tm is set to the reference object temperature Tmr. The average value of the substrate temperature Tb is set to the reference substrate temperature Tbr. The average value of the coil voltage Vc is set to the reference coil voltage Vcr. The average value of the thickness d is set to the reference thickness dr. The reference object temperature Tmr is subtracted from each object temperature Tm to determine the object temperature deviation ΔTm (= Tm - Tmr). The reference substrate temperature Tbr is subtracted from each substrate temperature Tb to determine the substrate temperature deviation ΔTb (= Tb - Tbr). The reference coil voltage Vcr is subtracted from each coil voltage Vc to determine the coil voltage deviation ΔVc (= Vc - Vcr). The thickness ratio d / dr is determined by dividing each thickness d by the reference thickness dr. From multiple sets of object temperature deviation ΔTm, substrate temperature deviation ΔTb, coil voltage deviation ΔVc, and thickness ratio d / dr, for example, using the least squares method, an approximation formula of a quadratic function showing the relationship between the object temperature deviation ΔTm, substrate temperature deviation ΔTb, and coil voltage deviation ΔVc and the thickness ratio d / dr, i.e., a quadratic function with the object temperature deviation ΔTm, substrate temperature deviation ΔTb, and coil voltage deviation ΔVc as variables, is obtained. The coefficients in the obtained quadratic function are coefficients A1, A2, B1, B2, C1, and C2 in approximate formula (4).

[0073] Approximation formula (4) is calculated in advance and stored in the storage unit 83. The reference object temperature Tmr, the reference substrate temperature Tbr, and the reference coil voltage Vcr are also calculated in advance and stored in the storage unit 83.

[0074] The correction unit 85 corrects the thickness d using the approximate formula (4), thereby obtaining the corrected thickness d', that is, the final thickness d.

[0075] Such thickness measurement will be explained in more detail using a flowchart, as shown in Figure 5.

[0076] The thickness derivation unit 84 determines whether a predetermined measurement period has arrived in step S101 of the thickness measurement flowchart. The measurement period is a period for obtaining thickness measurements of the object 9. If the measurement period has not arrived, the thickness derivation unit 84 repeats the determination in step S101 and waits for the arrival of the measurement period.

[0077] When the measurement period arrives, the thickness derivation unit 84 outputs a command to the processing device 6 to cause the processing device 6 to acquire measurement data. The measurement data is data for measuring the thickness of the object 9, specifically, the eddy current of the object 9, the temperature of the object 9, the temperature of the substrate 68, and the voltage of the excitation coil 11. Specifically, when the processing device 6 receives a command from the arithmetic device 8, the excitation unit 71 applies an excitation current to the excitation coil 11 to excite it in step S102. The excitation coil 11 generates a magnetic field in the axial direction by applying the excitation current. One excitation coil 11 and the other excitation coil 11 generate magnetic fields in opposite directions in the axial direction. For example, a magnetic flux is generated from one excitation coil 11 toward the object 9, and a magnetic flux is generated from the object 9 toward the other excitation coil 11. Step S102 corresponds to applying an excitation current to the excitation coil to induce an eddy current in the object.

[0078] At this time, in step S103, the voltage acquisition unit 73 acquires the voltage Vc of the excitation coil 11 when the excitation current is applied.

[0079] Subsequently, in step S104, the excitation unit 71 stops outputting the excitation current, and the detection unit 72 detects the eddy current generated in the object 9. The detection unit 72 continues detecting the voltage signal for a predetermined period. In this way, the detection unit 72 detects the transient change (change over time) of the induced electromotive force in the detection coil 12, i.e., the transient change of the eddy current generated in the object 9. Step S104 corresponds to detecting the eddy current of the object via the detection sensor.

[0080] Furthermore, in step S105, the first temperature acquisition unit 74 acquires the measured temperature Tb of the substrate 68, and the second temperature acquisition unit 75 acquires the temperature Tm of the object 9. That is, the measured temperature Tb of the substrate 68 acquired by the first temperature acquisition unit 74 is the temperature of the substrate 68 at the time of detecting the eddy current after the output of the excitation current has been stopped.

[0081] The processing device 6 transmits one set of measurement data, including the eddy current, the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc, to the calculation device 8. The calculation device 8 stores the received one set of measurement data, including the eddy current, the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc, in the memory unit 83.

[0082] Next, in step S106, the thickness derivation unit 84 determines the duration τ of the eddy current from the measurement data stored in the memory unit 83. Furthermore, in step S107, the thickness derivation unit 84 substitutes the duration τ into equation (3) to determine the thickness d of the object 9. Step S107 corresponds to determining the thickness of the object based on the duration of the detected eddy current.

[0083] Then, in step S108, the correction unit 85 executes the correction process. The correction unit 85 corrects the thickness d using the approximate formula (4) and the object temperature Tm, substrate temperature Tb, and coil voltage Vc of the measurement data. Specifically, the correction unit 85 calculates the object temperature deviation ΔTm (=Tm-Tmr) from the object temperature Tm, calculates the substrate temperature deviation ΔTb (=Tb-Tb) from the substrate temperature Tb, and calculates the coil voltage deviation ΔVc (=Vc-Vcr) from the coil voltage Vc. The correction unit 85 substitutes the thickness d, the object temperature deviation ΔTm, the substrate temperature deviation ΔTb, and the coil voltage deviation ΔVc into the approximate formula (4) to calculate the corrected thickness d'. Step S108 corresponds to executing the correction process to correct the thickness.

[0084] Thereafter, in step S109, the thickness derivation unit 84 determines whether or not to end the thickness measurement. For example, the thickness derivation unit 84 determines whether or not a command to end the thickness measurement has been input. For example, the user operates the arithmetic device 8 to input an end of the thickness measurement. If an end command has not been input, the thickness derivation unit 84 returns to step S101 and determines whether or not the next measurement cycle has arrived. When the next measurement cycle arrives, measurement data is acquired again, and the thickness d of the object 9 is found based on the measurement data. In other words, the arithmetic device 8 repeats the acquisition of measurement data and the derivation and correction of the thickness of the object 9 for each measurement cycle.

[0085] In step S109, if an end command has been input, the thickness measurement is ended.

[0086] In this way, the thickness measurement device 10 generates an eddy current in the object 9, detects the generated eddy current, and calculates the thickness d of the object 9 based on the duration τ of the eddy current. Because the duration τ of the eddy current is temperature-dependent, the thickness measurement device 10 corrects the thickness d using an approximation formula that indicates the temperature characteristics of the duration τ. Specifically, the thickness measurement device 10 corrects the thickness d based on the substrate-coil temperature characteristics of the duration τ, i.e., the temperature characteristics of the duration τ relative to the temperature of the substrate 68 and the temperature of the excitation coil 11. When the temperature of the substrate 68 changes, the magnitude of the excitation current applied to the excitation coil 11 and the magnitude of the voltage signal corresponding to the induced electromotive force in the detection coil 12 change. When the temperature of the excitation coil 11 changes, the resistance of the excitation coil 11 changes, and the magnetic field generated by the excitation coil 11 also changes. As a result, the duration τ also changes. Therefore, the thickness measurement device 10 corrects the thickness d calculated from the duration τ according to the temperature of the substrate 68 and the temperature of the excitation coil 11. This improves the accuracy of temperature correction of the thickness d of the object 9, and the thickness d can be determined with high accuracy.

[0087] Furthermore, the thickness measurement device 10 corrects the thickness d using the voltage of the excitation coil 11 as a parameter related to the temperature of the substrate 68 and a parameter related to the temperature of the excitation coil 11. Specifically, the thickness measurement device 10 corrects the thickness d using the coil voltage characteristic of the duration τ, i.e., the characteristic of the duration τ related to the voltage of the excitation coil 11, as the substrate-coil temperature characteristic of the duration τ. The coil voltage reflects both temperature changes of the substrate 68 and temperature changes of the excitation coil 11. Therefore, by correcting the thickness d according to the coil voltage, the thickness d can be corrected according to both the temperature of the substrate 68 and the temperature of the excitation coil 11.

[0088] Furthermore, the thickness measurement device 10 corrects the thickness d based on the measured temperature characteristics of the duration τ, i.e., the temperature characteristics of the duration τ relative to the measured temperature of the substrate 68. The coil voltage described above reflects temperature changes in the substrate 68, mainly temperature changes in the transmission circuits. By correcting the thickness d according to the measured temperature of the substrate 68, i.e., the temperature of the substrate 68 itself, the thickness d can also be corrected according to temperature changes in the reception circuits.

[0089] Furthermore, by using two characteristics, the coil voltage characteristic of duration τ and the measured temperature characteristic of duration τ, as the temperature characteristic of duration τ related to the temperature of substrate 68, it is possible to effectively reduce the influence of temperature changes in the transmission circuit and the reception circuit, respectively, and as a result, the thickness d can be calculated with higher accuracy.

[0090] Furthermore, the thickness measuring device 10 corrects the thickness d based on the temperature of the object 9 in addition to the temperature of the substrate 68 and the temperature of the exciting coil 11. This allows the thickness measuring device 10 to determine the thickness d with even higher accuracy.

[0091] As described above, the thickness measuring device 10 includes an excitation unit 71 that applies an excitation current to the excitation coil 11 to induce eddy currents in the object 9, a detection unit 72 that detects the eddy currents in the object 9 via the detection coil 12 (detection sensor), a thickness derivation unit 84 that determines the thickness d of the object 9 based on the duration τ of the eddy current detected by the detection unit 72, a substrate 68 on which the excitation unit 71 and the detection unit 72 are mounted, and a correction unit 85 that corrects the thickness d, and the correction unit 85 corrects the thickness d based on the temperature characteristics of the duration τ related to the temperature of the substrate 68 and the temperature of the excitation coil 11.

[0092] In other words, the thickness measurement method includes applying an excitation current to the excitation coil 11 to induce eddy currents in the object 9, detecting the eddy currents in the object 9 via the detection coil 12 (detection sensor), determining the thickness d of the object 9 based on the duration τ of the detected eddy currents, and performing a correction process to correct the thickness d, in which the correction process corrects the thickness d based on the temperature of the substrate 68 on which the excitation unit 71 that applies the excitation current to the excitation coil 11 and the detection unit 72 that detects the eddy currents via the detection coil 12 are mounted, and the temperature characteristics of the duration τ related to the temperature of the excitation coil 11.

[0093] According to these configurations, basically, an eddy current is induced in the object 9, the induced eddy current is detected, and the thickness d of the object 9 is determined based on the duration τ of the detected eddy current. The duration τ is affected by temperature changes of the substrate 68 and the exciting coil 11. Therefore, the thickness d determined from the duration τ is also affected by temperature changes of the substrate 68 and the exciting coil 11. Therefore, the thickness d is corrected based on the temperature characteristics of the duration τ related to the temperatures of the substrate 68 and the exciting coil 11. This allows the thickness d to be more appropriately corrected according to the temperature of the measurement environment, thereby improving the measurement accuracy of the thickness d.

[0094] In addition, the thickness measuring device 10 further includes a voltage acquiring unit 73 that acquires the voltage of the excitation coil 11 when an excitation current is applied to the excitation coil 11, and the correction unit 85 uses the characteristics of the duration τ related to the voltage of the excitation coil 11 as the temperature characteristics of the temperature of the substrate 68 and the duration τ related to the temperature of the excitation coil 11, and corrects the thickness d using the voltage of the excitation coil 11 acquired by the voltage acquiring unit 73.

[0095] According to this configuration, the correction unit 85 corrects the thickness d in accordance with the voltage of the exciting coil 11, thereby being able to correct the thickness d in consideration of the temperature characteristics of the duration τ related to both the temperature of the substrate 68 and the temperature of the exciting coil 11. In other words, it is possible to easily achieve correction of the thickness d based on the temperature characteristics of the duration τ related to the temperature of the substrate 68 and the temperature of the exciting coil 11.

[0096] Furthermore, the thickness measuring device 10 further includes a first temperature acquisition unit 74 that acquires the temperature of the substrate 68 measured by a first temperature sensor 69 arranged on the substrate 68, and the correction unit 85 uses the characteristic of the duration τ with respect to the voltage of the excitation coil 11 and the temperature characteristic of the duration τ with respect to the actual measured temperature of the substrate 68 as the temperature characteristic of the duration τ with respect to the temperature of the substrate 68 and the temperature of the excitation coil 11, and corrects the thickness d based on the voltage of the excitation coil 11 detected by the voltage acquisition unit 73 and the temperature of the substrate 68 acquired by the first temperature acquisition unit 74.

[0097] According to this configuration, two characteristics are taken into consideration as the temperature characteristic of the duration τ related to the temperature of the substrate 68: the characteristic of the duration τ related to the voltage of the excitation coil 11 and the temperature characteristic of the duration τ related to the measured temperature of the substrate 68. The characteristic of the duration τ related to the voltage of the excitation coil 11 mainly reflects the temperature change of the transmission-related circuits of the substrate 68. The temperature characteristic of the duration τ related to the measured temperature of the substrate 68 reflects the temperature change of not only the transmission-related circuits of the substrate 68 but also the reception-related circuits. In other words, by correcting the thickness d based on these two characteristics, it is possible to make a correction that appropriately corresponds to the temperature change of the transmission-related circuits and the temperature change of the reception-related circuits, respectively.

[0098] Furthermore, the first temperature acquisition unit 74 acquires the temperature of the substrate 68 after the excitation unit 71 stops applying the excitation current to the excitation coil 11.

[0099] According to this configuration, the first temperature acquisition unit 74 acquires the temperature of the substrate 68 in which the influence of the temperature rise of the substrate 68 when the excitation current is output is reduced. When the excitation current is output, the temperature of the substrate 68 may rise. The temperature of the substrate 68 after the output of the excitation current has stopped has a greater influence on the detection of eddy currents by the detection unit 72 than the temperature of the substrate 68 when the excitation current is output. By correcting the thickness d using the temperature of the substrate 68 acquired by the first temperature acquisition unit 74, it is possible to achieve a correction that takes into greater consideration the influence of temperature changes in the substrate 68 on the detection of eddy currents by the detection unit 72.

[0100] In addition, the thickness measuring device 10 further includes a second temperature acquisition unit 75 that acquires the temperature of the object 9, and the correction unit 85 further corrects the thickness d using the temperature of the object 9 acquired by the second temperature acquisition unit 75 based on the temperature characteristics of the duration τ related to the temperature of the object 9.

[0101] According to this configuration, the correction unit 85 corrects the thickness d based on the temperature characteristics of the duration τ related to the temperature of the object 9, in addition to the temperature characteristics of the duration τ related to the temperature of the substrate 68 and the temperature of the exciting coil 11. The duration τ can change in accordance with changes in the temperature of the object 9. By correcting the thickness d in consideration of the temperature characteristics of the duration τ related to the temperature of the object 9, the thickness d can be more appropriately corrected in accordance with the temperature of the measurement environment, and as a result, the measurement accuracy of the thickness d can be further improved.

[0102] Other Embodiments As described above, the above embodiment has been described as an example of the technology disclosed in this application. However, the technology of the present disclosure is not limited to this and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the above embodiment can be combined to create new embodiments. Furthermore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately determining that these non-essential components are essential.

[0103] The above embodiment may be configured as follows.

[0104] For example, the configuration of the thickness measuring device 10 is merely an example. The processing device 6 and the arithmetic device 8 may be configured integrally. That is, one device may have the functions of the processing device 6 and the arithmetic device 8. The processing device 6 and the arithmetic device 8 may be connected by a wire. A plurality of processing devices 6 may be connected to one arithmetic device 8. The arithmetic device 8 may also transmit data related to the calculated thickness to another device connected wirelessly or by a wire.

[0105] The probe 1 is not limited to the configuration described above. For example, the probe 1 includes two sets of excitation coils 11 and detection coils 12, but the number of excitation coils 11 and detection coils 12 may be one set or three or more sets. The excitation coils 11 and detection coils 12 do not have to be arranged so that their respective axes are aligned. When the excitation coils 11 and detection coils 12 are arranged so that their respective axes are aligned, the excitation coil 11 may be arranged closer to the object 9 than the detection coil 12. Furthermore, the detection unit of the probe 1 is not limited to the detection coil 12. The detection unit may be any unit that can directly or indirectly detect eddy currents in the object 9, and may be, for example, a Hall element. The probe 1 does not have to include the core 13.

[0106] The first temperature sensor 69 is not limited to a temperature sensor IC. The second temperature sensor 15 is not limited to a thermocouple. The first temperature sensor 69 and the second temperature sensor 15 may be, for example, a thermistor as long as they can detect the temperature of the object. The number of first temperature sensors 69 is not limited to one, and may be multiple. The number of second temperature sensors 15 is not limited to one, and may be multiple.

[0107] The object is not limited to a circular pipe. The object may be a square pipe instead of a circular pipe. The object may be a plate instead of an object with a closed cross section like a pipe.

[0108] Furthermore, the thickness measurement using the thickness measurement device 10 is merely an example. There are various thickness measurement methods using PEC, so any desired measurement technique can be adopted.

[0109] The method of correcting the thickness d is also merely an example. In approximation formula (4), the object temperature characteristic of the duration τ, the measured temperature characteristic of the duration τ, and the transmission voltage characteristic of the duration τ are each expressed as a quadratic function. However, one or more of these characteristics may be expressed as a linear function or a cubic or higher order function.

[0110] Furthermore, approximate formula (4) includes a term related to the object temperature deviation ΔTm corresponding to the object temperature characteristics for the duration τ, a term related to the substrate temperature deviation ΔTb corresponding to the measured temperature characteristics for the duration τ, and a term related to the coil voltage deviation ΔVc corresponding to the transmission voltage characteristics for the duration τ. For example, at least one of the term related to the object temperature characteristics for the duration τ and the term related to the measured temperature characteristics for the duration τ may be omitted.

[0111] Furthermore, the correction unit 85 uses the transmission voltage characteristics of the duration τ as the substrate-coil temperature characteristics of the duration τ, but is not limited to this. The correction unit 85 may correct the thickness d according to the measured temperature of the substrate 68 based on the temperature characteristics of the duration τ related to the measured temperature of the substrate 68, and may also correct the thickness d according to the measured temperature of the excitation coil 11 based on the temperature characteristics of the duration τ related to the measured temperature of the excitation coil 11. In this case, the probe 1 may have a temperature sensor disposed near the excitation coil 11 and that actually measures the temperature of the excitation coil 11.

[0112] In the above description, the thickness measurement device 10 calculates the thickness d from the duration τ of the eddy current and corrects the calculated thickness d. However, the thickness measurement device 10 may correct the duration τ and calculate the thickness d from the corrected duration τ. Even with this method, the thickness d is essentially corrected. For example, the thickness derivation unit 84 calculates the duration τ of the eddy current from the measurement data. The correction unit 85 corrects the duration τ based on the following approximate formula (5). Then, the thickness derivation unit 84 calculates the thickness d from the corrected duration τ' using formula (3).

[0113]

number

[0114] The flowchart is merely an example. Steps in the flowchart may be changed, replaced, added, omitted, etc. as appropriate. The order of steps in the flowchart may also be changed, and serial processing may be performed in parallel. For example, in the thickness measurement flowchart (FIG. 5), the excitation in step S102 and the coil voltage acquisition in step S103 may be performed in parallel. Furthermore, the temperature acquisition in step S105 is not limited to being performed after the eddy current detection, but may be performed before the excitation in step S102, or may be performed in parallel with the eddy current detection in step S104.

[0115] The functions performed by the components described herein may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered a circuit or processing circuit. A processor may also be a programmable processor that executes a program stored in a memory.

[0116] In this specification, a circuit, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions.

[0117] If the hardware is a processor considered to be a type of circuitry, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or processor. [Explanation of symbols]

[0118] 10 Thickness measuring device 11 Excitation coil 12 Detection coil (detection sensor) 6 Processing equipment 68 PCB 69 First temperature sensor 71 Excitation section 72 Detector 73 Voltage acquisition unit 74 1st temperature acquisition section 75 Second temperature acquisition section 8 Arithmetic unit 84 Thickness extraction section 85 Correction unit 9 Objects

Claims

1. an excitation unit that applies an excitation current to an excitation coil to induce an eddy current in the object; a voltage acquisition unit that acquires a voltage of the excitation coil when the excitation current is applied to the excitation coil; a detection unit that detects the eddy current of the object via a detection sensor; a thickness deriving unit that determines the thickness of the object based on the duration of the eddy current detected by the detecting unit; a substrate on which the excitation unit and the detection unit are mounted; a correction unit that corrects the thickness based on temperature characteristics of the duration related to the temperature of the substrate and the temperature of the excitation coil, The correction unit uses the duration characteristics related to the voltage of the excitation coil as temperature characteristics of the duration related to the temperature of the substrate and the temperature of the excitation coil, and corrects the thickness using the voltage of the excitation coil acquired by the voltage acquisition unit.

2. 2. The thickness measuring device according to claim 1, a first temperature acquisition unit that acquires a temperature of the substrate measured by a temperature sensor disposed on the substrate; The correction unit uses the duration characteristic of the voltage of the excitation coil and the temperature characteristic of the duration of the voltage of the excitation coil and the actual temperature characteristic of the duration of the voltage of the excitation coil as the temperature characteristic of the substrate and the duration of the temperature of the excitation coil, and corrects the thickness based on the voltage of the excitation coil detected by the voltage acquisition unit and the temperature of the substrate acquired by the first temperature acquisition unit.

3. 3. The thickness measuring device according to claim 2, The first temperature acquisition unit acquires the temperature of the substrate after the excitation unit stops applying an excitation current to the excitation coil.

4. An excitation unit that applies an excitation current to an excitation coil to induce eddy currents in an object; a detection unit that detects the eddy current of the object via a detection sensor; a thickness deriving unit that determines the thickness of the object based on the duration of the eddy current detected by the detecting unit; a substrate on which the excitation unit and the detection unit are mounted; a second temperature acquisition unit that acquires the temperature of the object; a correction unit that corrects the thickness, The correction unit corrects the thickness based on the temperature characteristics of the duration related to the temperature of the substrate and the temperature of the excitation coil, and further corrects the thickness using the temperature of the object acquired by the second temperature acquisition unit based on the temperature characteristics of the duration related to the temperature of the object.

5. applying an excitation current to an excitation coil to induce an eddy current in the object; acquiring a voltage of the excitation coil when the excitation current is applied to the excitation coil; detecting the eddy current of the object via a detection sensor; determining a thickness of the object based on a duration of the detected eddy currents; performing a correction process to correct the thickness based on the temperature of a substrate on which an excitation unit that applies an excitation current to the excitation coil and a detection unit that detects the eddy current via the detection sensor are mounted, and on the temperature characteristic of the duration related to the temperature of the excitation coil; In the correction process, the characteristic of the duration related to the voltage of the excitation coil is used as the temperature characteristic of the duration related to the temperature of the substrate and the temperature of the excitation coil, and the thickness is corrected using the voltage of the excitation coil acquired when the excitation current is applied.

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