Thickness measuring device and thickness measuring method

Abstract

To properly reduce the influence of a measurement environment temperature in measuring the thickness of an object.SOLUTION: A thickness measuring device 10 comprises: an exciter 71 for applying an exciting current to an exciting coil 11 and inducing an eddy current in an object 9; a detector 72 for detecting the eddy current of the object 9 via a detection coil 12; a deriver 86 for deriving the thickness of the object 9 on the basis of a duration τ of the eddy current detected by the detector 72; a substrate 68 on which the exciter 71 and the detector 72 are mounted; a compensator 87 for compensating the thickness by a compensation formula including a compensation term Y corresponding to the temperature characteristic of a duration τ related to at least one of the temperature of the exciting coil 12, the temperature of the substrate 68, and the temperature of the object 9; and a corrector 88 for correcting the compensation formula when a prescribed correction condition is satisfied.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] Conventionally, measuring devices using eddy currents have been known. For example, Patent Document 1 discloses a measuring device that uses eddy currents to detect flaws in an object. The measuring device of 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 Publication No. 09-089845 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, measuring devices using eddy currents include thickness measuring devices that measure the thickness of an object. Even in such thickness measuring devices, the measurement accuracy can be affected by the temperature of the measurement environment. For this reason, it is possible to correct the thickness determined from the eddy currents based on the temperature of the measurement environment. However, there may be cases where the correction does not function effectively due to changes in the measurement environment, etc.

[0005] The technology disclosed herein has been made in consideration of the above points, and its purpose is to appropriately reduce the effect 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 exciter that applies an excitation current to an excitation coil to induce an eddy current in an object, a detector that detects the eddy current in the object via a detection sensor, a deriving device that determines the thickness of the object based on the duration of the eddy current detected by the detector, a substrate on which the exciter and the detector are mounted, a compensator that corrects the thickness using a correction equation including a correction term corresponding to a temperature characteristic of the duration for at least one of the temperature of the excitation coil, the temperature of the substrate, and the temperature of the object, and a corrector that corrects the correction equation when a predetermined correction condition is satisfied.

[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 a thickness of the object based on the duration of the detected eddy currents, performing a correction process to correct the thickness using a correction equation including a correction term corresponding to a temperature characteristic of the duration for at least one of the temperature of the excitation coil, the temperature of the substrate, and the temperature of the object, and correcting the correction equation when a predetermined correction condition is satisfied. Effect 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 appropriately 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 appropriately reduced. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of a thickness measurement device. [Diagram 2] FIG. 2 is a block diagram showing the configuration of a control system of the control unit of the processing apparatus. [Diagram 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. [Diagram 5] FIG. 5 is a flow chart of the thickness measurement. [Figure 6] FIG. 6 is a graph showing the change over time in the derived thickness and the simulated values. [Figure 7] FIG. 7 is a graph showing the change over time in the derived thickness and the corrected thickness. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an exemplary embodiment will be described in detail 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 calculation device 8 that determines the thickness of the object 9. For example, the object 9 is a metal pipe through which crude oil, refined petroleum products, etc. flow. The pipe is formed in a circular tube 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 close 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 the 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 a 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 with the excitation coil 11, and detects the induced eddy currents with 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 the excitation coil 11 and the detection coil 12. In Fig. 1, the probe 1 has two pairs of the excitation coil 11 and the detection coil 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 generally U-shaped as a whole. More specifically, the core 13 is formed by stacking a plurality of generally U-shaped thin plates made of permalloy. A straight portion at one end of the core 13 is inserted into one set of the excitation coil 11 and the detection coil 12. A straight 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 forms a magnetic field in the direction of its axis. A current is applied to one excitation coil 11 and the other excitation coil 11 so that they form magnetic fields in opposite directions in the direction of the axis. As a result, a magnetic field is formed in the core 13 along the longitudinal direction of the core 13. That is, when one end of the core 13 is an N pole, the other end of the core 13 is an S pole. Conversely, when one end of the core 13 is an S pole, the other end of the core 13 is an N pole. 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. In detail, most of the magnetic flux generated from one excitation coil 11 exits in the direction of the axis of one excitation coil 11, enters the object 9, passes through the object 9 in an approximately arc shape, and enters the other excitation coil 11 toward the axis of the other excitation coil 11. By varying the current applied to the excitation coil 11, the magnetic field generated in the target 9 varies, and an eddy current is generated in the target 9.

[0018] Meanwhile, a magnetic flux penetrating the detection coil 12 is formed by eddy currents generated in a portion of the object 9 near the detection coil 12. When the magnetic flux penetrating the detection coil 12 changes, an induced electromotive force is generated in the detection coil 12. The detection coil 12 detects the eddy current in the object 9 by detecting this induced electromotive force. In other words, detecting an induced electromotive force by the detection coil 12 is also called detecting an eddy current.

[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 determines 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 suddenly decays, which will be described in detail later). In addition, the calculation device 8 corrects the determined 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 transmitter 61, a first receiver 62, a second receiver 63, a temperature detector 64, a communication device 65, a processor 66, a memory device 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 processor 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 receiver 62 receives an induced electromotive force generated in the detection coil 12 in response to an eddy current in the object 9. The first receiver 62 has at least a receiving amplifier 62a which receives the voltage generated in the detection coil 12 and amplifies the voltage. The first receiver 62 may further have a filter which applies filtering to the voltage signal.

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

[0024] The output of the first temperature sensor 69 is input to the temperature detector 64. The temperature detector 64 may have a receiving amplifier that receives the detection signal of the first temperature sensor 69 and amplifies the detection signal. Furthermore, the output of the second temperature sensor 15 is input to the temperature detector 64. The temperature detector 64 may have a receiving amplifier that receives the detection signal of the second temperature sensor 15 and amplifies the detection signal. The temperature detector 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 communicator 65 performs wireless communication with an external device. For example, the communicator 65 transmits the voltage signal (i.e., the detection signal) detected by the first receiver 62, the voltage signal (i.e., the detection signal) detected by the second receiver 63, and the detection signal detected by the temperature detector 64 to the arithmetic device 8.

[0026] The processor 66 controls the entire processing device 6. The processor 66 performs various types of arithmetic processing. For example, the processor 66 is formed of a processor such as a CPU (Central Processing Unit). The processor 66 may 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 processor 66 causes the transmitter 61 to output an excitation current for only a predetermined period of time. The processor 66 acquires a detection signal via the second receiver 63 while the excitation current is being output. The processor 66 acquires a detection signal via the first receiver 62 after the output of the excitation current is stopped. The processor 66 also acquires a detection signal from the temperature detector 64 at the same time as acquiring a detection signal from the first receiver 62. The processor 66 stores the detection signals from the first receiver 62, the second receiver 63, and the temperature detector 64 in the memory 67, and transmits the detection signals stored in the memory 67 to the calculation device 8 via the communication device 65 as appropriate.

[0028] The storage unit 67 stores various data and programs executed by the processor 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 transmitter 61, a first receiver 62, a second receiver 63, a temperature detector 64, a communication unit 65, a processor 66 and a memory 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 processor 66 of the processing device 6. The processor 66 realizes various functions by reading out a control program from the storage device 67 into a memory and developing it. Specifically, the processor 66 functions as an exciter 71 that applies an excitation current to the excitation coil 11 to induce an eddy current in the object 9, a detector 72 that detects the eddy current in the object 9 via the detection coil 12, and an acquirer 73 that acquires a physical quantity related to at least one of the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9.

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

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

[0034] The acquirer 73 acquires a plurality of physical quantities (hereinafter referred to as "related physical quantities") related to the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9 when detecting the eddy current. Here, the "physical quantity related to temperature" may include not only any physical quantity related to temperature, but also the temperature itself. The related physical quantity is at least one of the voltage of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9. In this example, the acquirer 73 acquires all of the voltage of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9 as the related physical quantities. For example, the physical quantity related to the temperature of the excitation coil 11 is the voltage of the excitation coil 11 and the temperature of the substrate 68. The physical quantity related to the temperature of the substrate 68 is the temperature of the substrate 68. The physical quantity related to the temperature of the object 9 is the temperature of the object 9. The acquirer 73 includes a voltage acquirer 74 that acquires the voltage of the excitation coil 11 when an excitation current is applied to the excitation coil 11, a first temperature acquirer 75 that acquires the temperature of the substrate 68, and a second temperature acquirer 76 that acquires the temperature of the object 9.

[0035] The voltage acquirer 74 acquires a voltage signal corresponding to the voltage across the excitation coil 11. The voltage acquirer 74 acquires a voltage signal when an excitation current is applied to the excitation coil 11. The voltage acquirer 74 stores the detected voltage across the two ends, i.e., the voltage signal, in the memory 67. Hereinafter, for convenience of explanation, the voltage signal acquired by the voltage acquirer 74 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 memory 67 will also be simply referred to as the "voltage of the excitation coil 11".

[0036] The first temperature acquirer 75 acquires the temperature of the substrate 68 after the application of the excitation current to the excitation coil 11 by the exciter 71 has stopped. For example, the first temperature acquirer 75 acquires the temperature of the substrate 68 at the time when the detector 72 detects the eddy current. The first temperature acquirer 75 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 acquirer 75 stores the acquired temperature of the substrate 68 in the memory 67.

[0037] The second temperature acquirer 76 acquires the temperature of the object 9 measured by the second temperature sensor 15, that is, the actual measured temperature. The second temperature acquirer 76 stores the acquired temperature of the object 9 in the memory 67.

[0038] In the memory 67, the eddy current detected by the detector 72, the voltage of the exciting coil 11 acquired by the voltage acquirer 74, the temperature of the substrate 68 acquired by the first temperature acquirer 75, and the temperature of the object 9 acquired by the second temperature acquirer 76 are stored in association with each other. In other words, the memory 67 stores 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 as one set.

[0039] The processor 66 transmits 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 stored in the memory 67 to the computing device 8 via the communicator 65 .

[0040] The arithmetic device 8 is formed of a computer or a computer network (so-called cloud). The arithmetic device 8 includes a communication unit 81, a processor 82, and a storage unit 83, as shown in FIG.

[0041] The communication device 81 performs wireless communication with an external device. For example, the communication device 81 receives a signal from the processing device 6.

[0042] The processor 82 controls the entire arithmetic device 8. The processor 82 performs various types of arithmetic processing. For example, the processor 82 is formed of a processor such as a CPU (Central Processing Unit). The processor 82 may 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.

[0043] The memory 83 stores the programs and various data executed by the processor 82. For example, the memory 83 stores a control program. The memory 83 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), or the like. The memory 83 also stores signals and the like transmitted from the processor 6. Specifically, the memory 83 stores 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, which are acquired by the processor 6.

[0044] FIG. 3 is a block diagram showing the configuration of a control system of the processor 82 of the arithmetic device 8. The processor 82 realizes various functions by reading out a control program from the storage device 83 to a memory and developing it. Specifically, the processor 82 functions as a deriving device 86 that derives the thickness of the object 9, a correcting device 87 that corrects the derived thickness based on a correction formula, and a correcting device 88 that corrects the correction formula. In this example, the processor 82 also functions as a creating device 85 that creates a correction formula and an estimating device 89 that estimates the thinning rate of the object 9. That is, the processor 82 derives the thickness of the object 9 and corrects the derived thickness. Furthermore, the processor 82 appropriately corrects the correction formula. As a result, a corrected thickness with higher accuracy is obtained. Then, the processor 82 estimates the thinning rate of the object 9 from the thickness as an example of utilizing the obtained thickness.

[0045] The deriver 86 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 (the surface facing the probe 1) of the object 9 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. The deriver 86 determines the duration of the eddy current (specifically, a voltage signal) detected by the processing device 6. The deriver 86 determines the thickness of the object 9 from the duration based on the correlation between the duration and the thickness. The thickness determined by the deriver 86 is called the "derived thickness."

[0046] 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 change over time of a voltage signal V(t) corresponding to an eddy current. The graph in Fig. 4 is a double logarithmic graph. In Fig. 4, the voltage signal V0(t) shown by the dashed line is the voltage signal of the object 9 having a thickness d0, and the voltage signal V1(t) shown by the solid line is the voltage signal of the object 9 having a thickness d1 that is thinner than the thickness d0.

[0047] The eddy current attenuates as it penetrates into the object 9. The eddy current gradually attenuates from the front surface of the object 9 (the surface facing the probe 1) until it reaches the back surface, and then rapidly attenuates when it reaches the back surface. The voltage signal V(t) also shows a change similar to that of the eddy current. In other words, the transient change of the voltage signal V(t) corresponds to the transient change of 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) rapidly attenuates. The voltage signal V(t) that changes in this way is expressed by the following equation (1).

[0048]

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[0049] As can be seen from equation (1), the voltage signal V(t) gradually attenuates but continues until time τ, at which point it rapidly attenuates. For ease of explanation, τ is referred to as the "duration". The duration τ is expressed by the following equation (2).

[0050] 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 .

[0051] 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. In addition, even if the duration τ and the thickness d change, the duration τ / d 2 is constant. Therefore, if the duration τ0 for the known thickness d0 and the duration τ for the unknown thickness d are known, the unknown thickness d can be calculated based on the following formula (3). Formula (3), the known thickness d0, and the duration τ0 are stored in the memory 83.

[0052]

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[0053] <Temperature characteristics> However, the duration τ is affected by the temperature of the measurement environment. As a result, the derived thickness d obtained from the duration τ is also affected by the temperature of the measurement environment. Examples of the temperature of the measurement environment that may have an effect include the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9.

[0054] Specifically, since the excitation coil 11 is disposed 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 has temperature dependency. 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.

[0055] Furthermore, since the processing device 6 is placed on or near the object 9, the temperature of the substrate 68 may change according to 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. Such 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.

[0056] Furthermore, 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] <Thickness correction> When the duration τ changes in this way, the derived thickness d obtained from the duration τ also changes. Therefore, the corrector 87 corrects the derived thickness d so as to reduce the variation of the derived thickness d caused by the temperature characteristic of the duration τ. In detail, the corrector 87 corrects the derived thickness d based on a correction formula. The correction formula includes a correction term corresponding to the temperature characteristic of the duration related to at least one of the temperatures of the exciting coil 11, the substrate 68, and the object 9. Note that the "temperature characteristic of the duration related to the temperature" means the relationship of the change in the duration to the temperature change. In this example, the correction formula includes a correction term corresponding to the temperature characteristic of the duration related to each temperature of the exciting coil 11, the substrate 68, and the object 9. The corrector 87 corrects the derived thickness d so as to reduce the variation of the duration τ caused by the temperature of the exciting coil 11, the substrate 68, and the object 9, i.e., the variation of the derived thickness d.

[0058] More specifically, with regard to the temperature of the substrate 68 and the temperature of the excitation coil 11, the corrector 87 corrects the thickness d by a physical quantity related to the temperature of the substrate 68 and a physical quantity related to the temperature of the excitation coil 11. In this example, the physical quantity related to the temperature of the substrate 68 and the physical quantity 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. A change in the voltage of the excitation coil 11 reflects a change in the excitation current applied to the excitation coil 11 and a change in the resistance of the excitation coil 11. When the temperature of the substrate 68, particularly the temperature of the circuit related to transmission, changes, the excitation current of the excitation coil 11 may change. When the temperature of the excitation coil 11 changes, the resistance of the excitation coil 11 may change. That is, the voltage of the excitation coil 11 changes according to the temperature of the substrate 68 and the temperature of the excitation coil 11.

[0059] The corrector 87 corrects the thickness d by using the characteristic of the duration τ with respect to the voltage of the excitation coil 11 (i.e., the relationship of the change in the duration τ with respect to the change in the voltage of the excitation coil 11, hereinafter referred to as the "transmission voltage characteristic") 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 (hereinafter referred to as the "substrate-coil temperature characteristic"). The transmission voltage characteristic of the duration τ reflects the substrate-coil temperature characteristic of the duration τ. The transmission voltage characteristic of the duration τ reflects, among the temperature characteristics of the duration τ with respect to the temperature of the substrate 68, the temperature characteristic of the duration τ with respect to the temperature of the circuit related to transmission.

[0060] That is, the corrector 87 corrects the thickness d according to the transmission voltage characteristic of the duration τ by the voltage of the excitation coil 11. The corrector 87 corrects the thickness d by 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.

[0061] In addition, corrector 87 also corrects thickness d based on the temperature itself of substrate 68. In other words, corrector 87 uses the transmission voltage characteristic of duration τ and the temperature characteristic of duration τ related to the measured temperature of substrate 68 (hereinafter referred to as "measured temperature characteristic") as the substrate-coil temperature characteristic of duration τ. The measured temperature characteristic of duration τ reflects, among the temperature characteristics of duration τ related to the temperature of substrate 68, the temperature characteristic of duration τ related to the temperature of the circuit related to reception in addition to the temperature characteristic of duration τ related to the temperature of the circuit related to transmission.

[0062] That is, the corrector 87 corrects the thickness d by the actual temperature of the substrate 68 in accordance with the actual temperature characteristics of the duration τ. The corrector 87 corrects the thickness d by the actual 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.

[0063] Furthermore, with regard to the temperature of the object 9, the corrector 87 corrects the thickness d according to the temperature of the object 9. The corrector 87 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 the "object temperature characteristics") in addition to the substrate-coil temperature characteristics of the duration τ.

[0064] That is, the corrector 87 corrects the thickness d according to the temperature of the object 9 in accordance with the object temperature characteristic of the duration τ.

[0065] Specifically, the corrector 87 corrects the thickness d based on the following correction formula (4).

[0066]

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[0067] Correction formula (4) is a function of related physical quantities, namely, object temperature Tm, substrate temperature Tb, and coil voltage Vc. That is, in correction formula (4), the term ΔTm is substantially the term of object temperature Tm, the term ΔVc is substantially the term of coil voltage Vc, and the term ΔTb is substantially the term of substrate temperature Tb. In other words, correction term Y is substantially expressed as a polynomial with object temperature Tm, substrate temperature Tb, and coil voltage Vc as variables. The term of object temperature Tm corresponds to the temperature characteristic of duration τ for the temperature of object 9. The term of substrate temperature Tb corresponds to the temperature characteristic of duration τ for the temperature of substrate 68. The term of coil voltage Vc corresponds to the temperature characteristic of duration τ for the temperature of excitation coil 11 and the temperature of substrate 68.

[0068] When an eddy current is generated in the object 9 and detected, the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc are also acquired. Specifically, after the exciter 71 applies an excitation current to the excitation coil 11 to excite it, the output of the excitation current is stopped, and the detector 72 detects the eddy current generated in the object 9. The detector 72 continues to detect the voltage signal for a predetermined period. In this way, a transient change (change over time) of the induced electromotive force of the detection coil 12, that is, a transient change of the eddy current generated in the object 9, is detected. At this time, the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc are also acquired. In this way, a set of data including the eddy current, the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc is acquired. Hereinafter, a set of the eddy current and related physical quantity (specifically, at least one of the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc) is referred to as "measurement data". The measurement data also includes the elapsed time t when the measurement data was acquired. The elapsed time t is the time elapsed from the start of the thickness measurement.

[0069] The deriver 86 obtains the derived thickness d based on the eddy current included in the measurement data. The deriver 86 obtains the duration τ from the detected eddy current, and obtains the derived thickness d using the duration τ and formula (3). The corrector corrects the derived thickness d using the object temperature Tm, substrate temperature Tb, and coil voltage Vc at the time of detection of the eddy current that is the basis for deriving the derived thickness d. The corrector 87 obtains the object temperature deviation ΔTm, substrate temperature deviation ΔTb, and coil voltage deviation ΔVc from the object temperature Tm, substrate temperature Tb, and coil voltage Vc, and obtains the corrected thickness dm by substituting the object temperature deviation ΔTm and the derived thickness d, etc., into formula (4). The deriver 86 and the corrector 87 perform such derivation and correction of the derived thickness d intermittently, specifically, periodically.

[0070] <Creating the correction formula> In this example, the creator 85 creates the correction equation after the probe 1 is installed on the target 9. After the probe 1 is installed, multiple sets of measurement data, i.e., eddy currents and related physical quantities, are collected. The creator 85 creates the correction equation using multiple sets of measurement data collected during a predetermined initial collection period. The initial collection period is a period required to collect the number of sets of measurement data required to create the initial correction equation.

[0071] The creator 85 creates the correction formula using the thinning model. The thinning model simulates the change in thickness of the object 9 over time. The thickness calculated by the thinning model is a thickness derived based on the duration τ of the eddy current, that is, a thickness affected by the temperature characteristics of the duration τ. The thinning model simulates the thickness affected by the temperature characteristics of the duration τ, not based on the duration τ, but by using a related physical quantity as an input. More specifically, the thinning model simulates the thickness affected by the temperature characteristics of the duration τ using a correction term Y of the correction formula. By using the correction term Y, the thinning model can simulate the thickness according to the temperature characteristics of the duration τ for at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. The thinning model is an example of a model.

[0072] For example, the metal loss model is expressed by the following equation (5).

[0073]

number

[0074] The creator 85 creates a correction equation using the wall-reduction model and multiple sets of measurement data collected during the initial collection period. Specifically, the creator 85 calculates coefficients A, B, C, F and constant D of the wall-reduction model so that the deviation between the derived thickness d and the simulation value dx for the multiple sets of measurement data collected during the initial collection period is minimized. In this example, the creator 85 calculates coefficients A, B, C, F and constant D in the wall-reduction model so that the evaluation value Z shown in the following formula (6) is minimized, using multiple sets of measurement data collected during the initial collection period.

[0075]

number

[0076] From the eddy current of each measurement data, the thickness of each measurement data is derived d i For details, the derived thickness d i is the duration τ obtained from the eddy current i can be obtained by substituting into equation (3).

[0077] From the physical quantities related to each measurement data, the simulation value dx of each measurement data i Specifically, the reference thickness da in the attenuation model is calculated by dividing the thicknesses d i For example, the reference thickness da is calculated based on a plurality of derived thicknesses d i The median or average value of the object temperature Tm i , substrate temperature Tb i , coil voltage Vc i from the object temperature deviation ΔTm i , substrate temperature deviation ΔTb i and coil voltage deviation ΔVc i is calculated, and the elapsed time t i , object temperature deviation ΔTm i , substrate temperature deviation ΔTb i and coil voltage deviation ΔVc iis substituted into equation (5) of the thinning model. For example, the reference object temperature Tmr is obtained based on a plurality of object temperatures Tm during the initial collection period. The reference object temperature Tmr is, for example, the median or average value of the plurality of object temperatures Tm. Similarly, the reference substrate temperature Tbr is obtained based on a plurality of substrate temperatures Tb during the initial collection period. The reference substrate temperature Tbr is, for example, the median or average value of the plurality of substrate temperatures Tb. The reference coil voltage Vcr is obtained based on a plurality of coil voltages Vc during the initial collection period. The reference coil voltage Vcr is, for example, the median or average value of the plurality of coil voltages Vc. The reference object temperature Tmr is subtracted from each object temperature Tm to obtain an object temperature deviation ΔTm (=Tm-Tmr). The reference substrate temperature Tbr is subtracted from each substrate temperature Tb to obtain a substrate temperature deviation ΔTb (=Tb-Tbr). The reference coil voltage Vcr is subtracted from each coil voltage Vc to obtain the coil voltage deviation ΔVc (=Vc-Vcr). In this way, the creator 85 obtains the object temperature deviation ΔTm, the substrate temperature deviation ΔTb, and the coil voltage deviation ΔVc from the associated physical quantities of each measurement data, and substitutes them into the formula (5). At this time, the creator 85 calculates the elapsed time t i Also substitute into equation (5). At this point, the coefficients A, B, C, F and the constant D are undetermined and are treated as variables. In other words, the simulation value dx of each measurement data i can be calculated as a polynomial with A, B, C, D, and F as variables.

[0078] The creator 85 finds the coefficients A, B, C, F and constant D that minimize the evaluation value Z. The creator 85 creates a correction term Y using the found coefficients A, B, C and constant D. The created correction term Y and metal loss model are stored in the memory 83. The reference thickness da, reference object temperature Tmr, reference substrate temperature Tbr and reference coil voltage Vcr are also stored in the memory 83. The correction term Y created in this way is used to correct the derived thickness d.

[0079] <Correction of correction formula> The corrector 88 improves the accuracy of the correction by appropriately correcting the correction formula. More specifically, the temperature characteristic of the duration τ may be affected by the measurement environment. For example, if the thickness of the object 9 changes, the temperature characteristic of the duration τ may also change. The accuracy of the correction by the correction formula may decrease due to a change in the measurement environment, etc. Furthermore, by using more measurement data, the accuracy of the correction formula is expected to improve. Therefore, the corrector 88 corrects the correction formula by recreating the correction formula. The method of creating the correction formula by the corrector 88 is basically the same as the creation method by the creator 85. That is, the corrector 88 creates the correction formula using a thinning model and multiple sets of measurement data. However, the corrector 88 corrects the correction formula using at least eddy currents and physical quantities collected after the initial collection period. Furthermore, the corrector 88 creates the correction formula using a larger number of sets of measurement data than when the initial correction formula was created. In this example, the corrector 88 corrects the correction formula using both the eddy currents and physical quantities collected in the initial collection period and the eddy currents and physical quantities collected after the initial collection period.

[0080] In detail, the corrector 88 corrects the correction formula when a predetermined correction condition is satisfied. That is, the corrector 88 monitors whether the correction condition is satisfied while the derivation and correction of the thickness are continued. For example, the correction condition is that the deviation of the simulation value dx from the derived thickness d exceeds a predetermined range. Since the metal-reduction model includes the correction term Y of the correction formula, when the accuracy of the correction by the correction formula is high, the accuracy of the simulation by the metal-reduction model is also high. That is, when the correction term Y is appropriate, the metal-reduction model properly simulates the thickness, and the simulation value dx is close to the derived thickness d. When the correction term Y is inappropriate, the simulation accuracy of the metal-reduction model deteriorates, and the simulation value dx deviates significantly from the derived thickness d.

[0081] Specifically, the corrector 88 obtains the judgment value Err based on the following equation (7), and determines whether the judgment value Err is greater than a predetermined threshold value Th.

[0082]

number

[0083] From the eddy current of each measurement data, the thickness of each measurement data is derived d i For details, the derived thickness d i is the duration τ obtained from the eddy current i can be obtained by substituting into equation (3).

[0084] From the physical quantities related to each measurement data, the simulation value dx of each measurement data i The object temperature Tm i , substrate temperature Tb i , coil voltage Vc i from the object temperature deviation ΔTm i , substrate temperature deviation ΔTb i and coil voltage deviation ΔVc i is calculated, and the elapsed time t i , object temperature deviation ΔTm i , substrate temperature deviation ΔTb i and coil voltage deviation ΔVc iis substituted into the thinning model equation (5). When determining the correction conditions, coefficients A, B, C, F and constant D are set, unlike when creating the correction equation. In other words, the simulation value dx of each measurement data i is the value obtained.

[0085] The reference thickness da, the reference object temperature Tmr, the reference substrate temperature Tbr, and the reference coil voltage Vcr are values ​​calculated based on the measurement data collected during the initial collection period. In other words, the reference thickness da, the reference object temperature Tmr, the reference substrate temperature Tbr, and the reference coil voltage Vcr are the same as those when the correction formula was created.

[0086] The corrector 88 corrects the Err i The corrector 88 calculates the average value of the determined thickness dx, i.e., the judgment value Err. The corrector 88 compares the determined thickness Err with a threshold value Th. The determined thickness dx being greater than the threshold value Th indicates that the deviation of the simulation value dx from the derived thickness d exceeds a predetermined range. When the determined thickness Err is greater than the threshold value Th, the corrector 88 determines that the correction condition is satisfied. When the determined thickness Err is equal to or less than the threshold value Th, the corrector 88 determines that the correction condition is not satisfied.

[0087] The deviation of the simulation value dx from the derived thickness d may be large due to measurement errors of the object temperature Tm, etc. However, even if the deviation of the simulation value dx from the derived thickness d increases once or several times, the judgment value Err does not increase. On the other hand, if the correction term Y does not match the actual object temperature characteristics, etc., the deviation of the simulation value dx from the derived thickness d increases continuously. In that case, the judgment value Err may exceed the threshold value Th. In short, by evaluating the deviation of the simulation value dx from multiple sets of derived thicknesses d, it is possible to eliminate accidental increases in deviation and accurately determine the increase in deviation due to the incompatibility of the correction term Y.

[0088] If the correction condition is satisfied, the corrector 88 corrects the correction formula. The corrector 88 corrects the correction formula by recreating the correction formula, that is, by updating the correction formula. In detail, the corrector 88 obtains the coefficients A, B, C, F and the constant D that minimize the evaluation value Z of the formula (6) for the multiple sets of accumulated measurement data. Since the monitoring of the correction condition is performed after the creation of the initial correction formula, more sets of measurement data have been collected than when the correction formula was created. The corrector 88 creates the correction formula using more sets of measurement data than when the initial correction formula was created. The corrector 88 creates the correction formula using at least the measurement data collected after the initial collection period. In this example, the corrector 88 creates the correction formula using all the accumulated sets of measurement data, including the sets collected in the initial collection period. That is, the corrector 88 creates the correction formula using the initial first set of measurement data to the latest k-th set of measurement data. Since the revised correction formula is created based on a larger number of sets of measurement data than when the initial correction formula was created, the correction formula is more suited to the temperature characteristics of the duration τ, and the accuracy of correction is improved. Furthermore, the revised correction formula is created based on a newer set of measurement data than when the initial correction formula was created. Even if the temperature characteristics of the duration τ change due to environmental changes, etc., a correction formula that corresponds to the latest situation is created.

[0089] After the correction formula is corrected, the corrector 87 corrects the derived thickness d using the corrected correction formula. This applies a correction adapted to the latest situation to the derived thickness d. As a result, a thickness in which the temperature characteristic of the duration τ is more accurately corrected is obtained.

[0090] When the correction equation is corrected, the metal-reduction model is also corrected at the same time. That is, the correction term Y in the metal-reduction model is also updated. Therefore, the corrector 88 monitors whether the correction condition is satisfied using the corrected metal-reduction model, that is, the metal-reduction model corresponding to the corrected correction equation. Therefore, the corrector 88 can accurately determine whether the correction equation after correction needs to be further corrected.

[0091] The estimator 89 estimates the thickness reduction rate of the object 9 from the multiple corrected thicknesses. Furthermore, the estimator 89 estimates the maintenance time of the object 9 based on the thickness reduction rate. The thickness reduction rate is the reduction rate of the corrected thickness dm with respect to the elapsed time t. The estimator 89 approximates the time change of the accumulated corrected thickness dm with a linear function and obtains the slope. The slope is the thickness reduction rate. Furthermore, the estimator 89 estimates the maintenance time of the object 9 based on the thickness reduction rate. For example, the estimator 89 estimates the time when the thickness of the object 9 decreases to a predetermined lower limit value as the maintenance time. The estimator 89 estimates the time when the corrected thickness dm, which is approximated by a linear function, decreases to a lower limit value. The user can prepare in advance for maintenance of the object 9 based on the estimated maintenance time.

[0092] <Thickness measurement process> Next, a more detailed explanation will be given with reference to a flowchart of the thickness measurement process by the thickness measurement system 100. Fig. 5 is a flowchart of the thickness measurement.

[0093] The deriver 86 determines whether or not a predetermined measurement period has arrived in step S101 of the thickness measurement flowchart. The measurement period is a period for measuring the thickness of the object 9. If the measurement period has not arrived, the deriver 86 repeats the determination in step S101 and waits for the measurement period to arrive.

[0094] When the measurement period arrives, the deriver 86 outputs a command to the processing device 6 to cause the processing device 6 to acquire measurement data. Specifically, the deriver 86 causes the processing device 6 to acquire 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. When the processing device 6 receives a command from the arithmetic device 8, the exciter 71 applies an excitation current to the excitation coil 11 to excite it in step S102. The excitation coil 11 forms a magnetic field in the axial direction by applying the excitation current. One excitation coil 11 and the other excitation coil 11 form 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.

[0095] At this time, in step S103, the voltage acquirer 74 acquires the voltage Vc of the exciting coil 11 when the exciting current is applied.

[0096] Next, in step S104, the exciter 71 stops outputting the excitation current, and the detector 72 detects the eddy current generated in the object 9. The detector 72 continues detecting the voltage signal for a predetermined period of time. In this way, the detector 72 detects a transient change (change over time) in the induced electromotive force of the detection coil 12, i.e., a transient change in the eddy current generated in the object 9. Step S104 corresponds to detecting the eddy current of the object via the detection sensor.

[0097] Furthermore, in step S105, the first temperature acquirer 75 acquires the substrate temperature Tb, and the second temperature acquirer 76 acquires the object temperature Tm. That is, the substrate temperature Tb acquired by the first temperature acquirer 75 is the temperature of the substrate 68 at the time of detection of the eddy current after the output of the excitation current is stopped.

[0098] The processing device 6 transmits one set of the eddy current, the object temperature Tm, the substrate temperature Tb and the coil voltage Vc, that is, the measurement data, to the calculation device 8. The calculation device 8 stores the received set of measurement data in the memory 83.

[0099] Next, in step S106, the deriver 86 obtains the duration τ from the eddy current of the measurement data stored in the memory 83. Furthermore, in step S107, the deriver 86 obtains the derived thickness d by substituting the duration τ into equation (3). The obtained derived thickness d is linked to the corresponding measurement data and stored in the memory 83. Step S107 corresponds to obtaining the thickness of the object based on the duration of the detected eddy current.

[0100] Next, in step S108, the corrector 88 determines whether or not the correction equation has already been created. At the start of thickness measurement, that is, when the probe 1 is placed on the object 9, the correction equation has not yet been created.

[0101] If the correction formula has not yet been created (for example, the correction formula has not been saved in the memory 83), in step S109, the creator 85 determines whether or not the initial collection of measurement data has been completed. The initial collection is to collect a number of sets of measurement data required to create an initial correction formula. For example, the creator 85 determines whether or not the initial collection period has elapsed. If the initial collection period has elapsed, collection of the required number of sets of measurement data has been completed. If the initial collection period has not elapsed, the creator 85 determines that the initial collection has not been completed. If the initial collection has not been completed, the creator 85 ends the process in this measurement period. The derivation unit 86 returns to step S101 and waits until the next measurement period. Note that the creator 85 may determine the completion of the initial collection based on the number of sets of accumulated measurement data, rather than the elapse of the initial collection period. For example, the creator 85 may determine whether or not the number of sets of measurement data accumulated in the memory 83 has reached a predetermined required number of sets, and may determine that the initial collection has been completed when the number of sets of measurement data has reached the required number of sets.

[0102] The processes from step S101 to step S109 are repeated until the initial collection is completed. As a result, the number of sets of measurement data required to create the initial correction formula is accumulated. When the initial collection is completed, the creator 85 creates the correction formula in step S110. The creator 85 creates the correction formula using the metal-reduction model and the multiple sets of accumulated measurement data. In detail, the creator 85 sets the median or average value of the multiple object temperatures Tm collected in the initial collection to the reference object temperature Tmr, sets the median or average value of the multiple substrate temperatures Tb collected in the initial collection to the reference substrate temperature Tbr, sets the median or average value of the multiple coil voltages Vc collected in the initial collection to the reference coil voltage Vcr, and sets the median or average value of the multiple derived thicknesses d obtained from the multiple eddy currents collected in the initial collection to the reference thickness da. The creator 85 uses these values ​​to find the coefficients A, B, C, F and constant D of the metal-reduction model that minimize the evaluation value Z of equation (6). As a result, the metal-reduction model is completed and the correction formula is also created.

[0103] If the correction equation has already been created in step S108 (for example, the correction equation is stored in the memory 83), the corrector 88 obtains a simulation value dx of the thickness in step S111. Note that even after the correction equation is created in step S110, the corrector 88 obtains the simulation value dx of the thickness in step S111. The corrector 88 obtains the simulation value dx by using the metal loss model and the latest measurement data.

[0104] Next, in step S112, the corrector 88 determines whether or not the correction condition is satisfied. In this example, the correction condition is that the aforementioned judgment value Err is greater than the threshold value Th. However, after the correction formula is created or modified, it is determined that the correction condition is not satisfied until the number of sets (e.g., the number of sets n in formula (7)) used to calculate the judgment value Err is newly acquired. In other words, after the correction formula is created or modified, the judgment value Err is reset, and the correction condition is not satisfied until new measurement data is accumulated.

[0105] If the correction condition is not satisfied, in step S113, the corrector 87 corrects the derived thickness d. The corrector 87 obtains the corrected thickness dm using the correction formula (4) and the latest measurement data. This allows the thickness of the object 9 to be obtained with the influence of the temperature characteristics of the duration τ reduced. The corrector 87 stores the obtained corrected thickness dm in the memory 83. Step S113 corresponds to executing a correction process for correcting the thickness using the correction formula.

[0106] After the correction process, the estimator 89 calculates the wall-thinning rate based on the multiple corrected thicknesses dm in step S115. More specifically, the estimator 89 calculates the reduction rate, i.e., the reduction speed, of the corrected thickness dm from the multiple accumulated corrected thicknesses dm. At this time, the estimator 89 calculates the wall-thinning rate from all the accumulated corrected thicknesses dm.

[0107] Furthermore, in step S116, the estimator 89 estimates the maintenance timing of the object 9 based on the wall-thinning rate. The user can prepare in advance for maintenance of the object 9 based on the outputted maintenance timing.

[0108] Thereafter, the process for the current measurement period ends, and the deriving unit 86 returns to step S101 to determine whether the next measurement period has arrived. When the next measurement period arrives, data is acquired again, and the thickness of the object 9 is calculated. In other words, the computing device 8 repeats the acquisition of measurement data, the derivation of thickness, and the correction of thickness for each measurement period.

[0109] On the other hand, if the correction condition is satisfied in step S112, the corrector 88 corrects the correction formula in step S114. In detail, the corrector 88 reconstructs the correction formula using the accumulated measurement data. This corrects the correction formula. After the correction formula is corrected, the corrector 87 corrects the derived thickness d in step S113. Step S114 corresponds to correcting the correction formula when a predetermined correction condition is satisfied.

[0110] FIG. 6 is a graph showing the time-dependent changes in the derived thickness d and the simulation value dx. FIG. 7 is a graph showing the time-dependent changes in the derived thickness d and the corrected thickness dm. The dashed lines in the graphs are lines showing ideal reductions in thickness, and are shown as straight lines in this example. In FIG. 7, the first corrected thickness is the thickness corrected by the first correction formula described below, the second corrected thickness is the thickness corrected by the second correction formula described below, and the third corrected thickness is the thickness corrected by the third correction formula described below. According to the thickness measurement process described above, first, a set number of measurement data required for creating the correction formula is collected (see section A in FIG. 6). During this period, the derived thickness d is obtained, but the derived thickness d is not corrected. When the initial collection period has elapsed (i.e., the required set number of measurement data is collected), the first correction formula is created. At the same time, a wall-thinning model is also created. Hereinafter, for convenience of explanation, the first correction formula is referred to as the first correction formula, and the first wall-thinning model is referred to as the first wall-thinning model. The ordinals of the correction formula and the wall-loss model increase every time they are updated.

[0111] When the first correction formula is created, the derived thickness d is corrected based on the first correction formula. Then, the corrected thickness dm is used to estimate the thinning rate and the maintenance timing. As shown in section B of FIG. 6, the derived thickness d is corrected so as to approach the thickness due to ideal thinning (hereinafter referred to as the "ideal thickness").

[0112] While such derivation of thickness and correction of thickness are periodically repeated, the correction condition is monitored. For example, if the accuracy of the first correction formula is not high, the deviation of the simulation value dx from the derived thickness d becomes large, as shown in section C of FIG. 7. In that case, the accuracy of the correction is also not high, so the corrected thickness dm deviates slightly from the ideal thickness, as shown in section C of FIG. 6. If the state in which the deviation between the derived thickness d and the simulation value dx is large continues for a while, the correction condition may be satisfied. When the correction condition is satisfied, the correction formula is corrected, and the first correction formula is updated to the second correction formula. When the correction formula is corrected, the metal-thinning model is also corrected. In other words, the first metal-thinning model is updated to the second metal-thinning model.

[0113] After updating to the second correction formula, the corrected thickness dm becomes closer to the ideal thickness, as shown in section D of Fig. 6. After updating to the second metal-thinning model, the deviation of the simulated value dx from the derived thickness d becomes smaller, as shown in section D of Fig. 7.

[0114] However, if the adaptation of the correction term Y to the temperature characteristic of the actual duration τ is still insufficient, the corrected thickness dm may also deviate slightly from the ideal thickness, as shown in the section E of FIG. 6. In that case, the deviation of the simulated value dx from the derived thickness d may become large in time, as shown in the section E of FIG. 7. When the correction conditions are met, the correction formula and the metal-thinning model are corrected again. That is, the second correction formula is updated to the third correction formula, and the second metal-thinning model is updated to the third metal-thinning model.

[0115] After updating to the third correction formula, the corrected thickness dm becomes closer to the ideal thickness, as shown in section F of Fig. 6. After updating to the third metal-thinning model, the deviation of the simulated value dx from the derived thickness d becomes smaller, as shown in section F of Fig. 7.

[0116] In this way, by repeatedly modifying the correction formula, the correction term Y becomes more suited to the temperature characteristics of the actual duration τ, and the accuracy of the correction is improved.

[0117] In addition, the correction formula is appropriately corrected, but the already obtained corrected thickness dm is not changed. In other words, the already obtained corrected thickness dm remains corrected based on the old correction formula, and is not recalculated from the derived thickness d based on the new correction formula. Although the past correction formula does not fully fit the recent measurement data, it may fit the past measurement data better than the new correction formula. Therefore, the corrected correction formula is used to correct the future derived thickness d, but is not used to correct the past derived thickness d. In this example, the accumulated corrected thickness dm is used to estimate the wall-thinning rate. Even if the correction formula is corrected, the past derived thickness d remains corrected with the past correction formula, and the future derived thickness d is corrected based on the new correction formula, so that the estimation accuracy of the wall-thinning rate can be improved. In addition, when the correction formula is corrected, the already obtained corrected thickness dm may be recalculated with the corrected correction formula.

[0118] In this way, the thickness measuring device 10 corrects the derived thickness d using a correction formula showing the temperature characteristic of the duration τ. Specifically, the thickness measuring device 10 corrects the derived thickness d using a correction formula including a correction term Y corresponding to the temperature characteristic of the duration τ for at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. This allows the thickness of the object 9 to be determined with high accuracy. The correction formula used for thickness correction is appropriately corrected, and the accuracy of correction is improved. Even if the temperature characteristic of the duration τ changes due to a change in the measurement environment, etc., appropriate correction is realized by correcting the correction formula.

[0119] Since the thickness measuring device 10 improves the accuracy of the correction after the fact by correcting the correction formula, the correction can be started early by using a provisional correction formula. In detail, when the correction formula is created based on actual measurement data, the accuracy of the correction formula improves as the amount of measurement data increases. It takes a long time to collect a large amount of measurement data, and the start of correction is delayed accordingly. Since the thickness measuring device 10 improves the accuracy of the correction after the fact, the correction formula can be created and correction can be started at the point when enough measurement data has been collected to ensure a certain level of accuracy. The accuracy of the corrector is improved after the fact by correcting the correction formula. As a result, the thickness correction can be started early while ultimately ensuring the accuracy of the correction.

[0120] The corrector 88 judges whether or not the correction formula needs to be corrected based on whether or not the deviation between the simulation value dx obtained by a wall-thinning model that simulates the reduction over time in the thickness of the object 9 and the derived thickness d obtained from the duration τ exceeds a predetermined range. The wall-thinning model simulates the thickness using a correction term Y of the correction formula. The corrector 88 can appropriately judge whether or not the correction term Y is appropriate, i.e., whether or not the correction formula needs to be corrected, by evaluating the deviation between the simulation value dx and the derived thickness d by the wall-thinning model including the correction term Y.

[0121] More specifically, the corrector 88 judges whether the deviation between the simulation value dx and the derived thickness d exceeds a predetermined range for a predetermined number of sets of measurement data. This makes it possible to accurately judge the increase in deviation due to the incompatibility of the correction term Y while eliminating cases where the deviation between the simulation value dx and the derived thickness d accidentally increases due to measurement errors or the like.

[0122] Furthermore, the corrector 88 corrects the correction formula based on the deviation between the simulation value dx obtained by the metal-reduction model including the correction term Y and the derived thickness d obtained from the duration τ. Specifically, the corrector 88 corrects the correction term Y so that the deviation between the simulation value dx and the derived thickness d is reduced. The derived thickness d is a thickness derived from the duration τ, and is a thickness influenced by the temperature characteristics of the duration τ. The reduction in the deviation between the simulation value dx and the derived thickness d means that the metal-reduction model accurately simulates the thickness influenced by the temperature characteristics of the duration τ. As a result, the corrector 88 can obtain the correction term Y that appropriately reflects the temperature characteristics of the duration τ.

[0123] Furthermore, the thickness measuring device 10 corrects the thickness d by the voltage of the exciting coil 11 as a parameter related to the temperature of the substrate 68 and a parameter related to the temperature of the exciting coil 11. Specifically, the thickness measuring device 10 corrects the thickness d by using the coil voltage characteristic of the duration τ, i.e., the characteristic of the duration τ related to the voltage of the exciting coil 11, as the substrate-coil temperature characteristic of the duration τ. Both the temperature change of the substrate 68 and the temperature change of the exciting coil 11 are reflected in the coil voltage. 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 exciting coil 11.

[0124] Furthermore, the thickness measurement device 10 corrects the thickness d based on the measured temperature characteristic of the duration τ, i.e., the temperature characteristic of the duration τ with respect to the measured temperature of the substrate 68. The coil voltage described above mainly reflects the temperature change of the transmission-related circuits among the temperature changes of the substrate 68. 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 the temperature change of the reception-related circuits.

[0125] In addition, 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 with respect to the temperature of the substrate 68, it is possible to effectively reduce the influence of temperature changes in the circuit related to transmission and the circuit related to reception, respectively. As a result, the thickness d can be obtained with higher accuracy.

[0126] 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.

[0127] Other Embodiments As described above, the above embodiment has been described as an example of the technology disclosed in this application. However, the technology in this disclosure is not limited to this, and can be applied to embodiments in which modifications, replacements, additions, omissions, etc. are appropriately performed. In addition, it is also possible to combine the components described in the above embodiment to form a new embodiment. In addition, among the components described in the attached drawings and detailed description, 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 may be included. Therefore, the fact that these non-essential components are described in the attached drawings and detailed description should not immediately be taken to mean that these non-essential components are essential.

[0128] The above-described embodiment may be configured as follows. 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 transmit data related to the calculated thickness to another device connected wirelessly or by a wire.

[0129] The probe 1 is not limited to the above-mentioned configuration. For example, the probe 1 includes two sets of the excitation coil 11 and the detection coil 12, but the excitation coil 11 and the detection coil 12 may be one set or three or more sets. The excitation coil 11 and the detection coil 12 do not have to be arranged so that their respective axial centers are aligned. When the excitation coil 11 and the detection coil 12 are arranged so that their respective axial centers 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 anything that can directly or indirectly detect the eddy current of the object 9, and may be, for example, a Hall element. Furthermore, the probe 1 does not have to include the core 13.

[0130] 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.

[0131] 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 a pipe having a closed cross section.

[0132] Furthermore, the thickness measurement by the thickness measurement device 10 is merely an example. There are various thickness measurement methods by PEC, so any desired measurement technique can be adopted.

[0133] The method of correcting the thickness d is also merely an example. In the correction 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 by a linear function. However, one or more of these characteristics may be expressed by a quadratic function, or a cubic or higher order function.

[0134] Furthermore, the correction term Y may correspond to the temperature characteristic of the duration τ related to at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. The correction term Y may include, as a variable, a physical quantity related to at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. For example, the correction term Y may have a variable related to at least one of the object temperature Tm, the substrate temperature Tb, and the coil voltage Vc.

[0135] Furthermore, the corrector 87 adopts the temperature of the substrate 68 as the physical quantity related to the temperature of the exciting coil 11. However, the probe 1 may have a temperature sensor disposed in the vicinity of the exciting coil 11, and the corrector 87 may adopt the temperature of the exciting coil 11 substantially measured by this temperature sensor as the physical quantity related to the temperature of the exciting coil 11. In that case, the corrector 87 may correct the thickness d by the actual temperature of the exciting coil 11 based on the temperature characteristic of the duration τ related to the actual temperature of the exciting coil 11 while correcting the thickness d by the actual temperature of the exciting coil 11 based on the temperature characteristic of the duration τ related to the actual temperature of the exciting coil 11. In other words, any physical quantity may be adopted as the related physical quantity as long as it is a physical quantity related to the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. Furthermore, the correction formula may use a physical quantity other than the physical quantity related to the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9 as an input, such as the elapsed time t.

[0136] In the above description, the thickness measurement device 10 determines the thickness d from the duration τ of the eddy current, and corrects the determined thickness d. However, the thickness measurement device 10 may correct the duration τ, and determine the thickness d from the corrected duration τ. Even with this method, the thickness d is substantially corrected. For example, the deriver 86 determines the duration τ of the eddy current from the measurement data. The corrector 87 corrects the duration τ based on the following correction formula (8). The deriver 86 then determines the thickness d from the corrected duration τ' using formula (3).

[0137]

number

[0138] The method of creating and correcting the correction formula is not limited to the above-mentioned method. For example, the evaluation value Z used to create the correction formula is not limited to the value calculated based on the formula (6). The evaluation value Z can be expressed by any formula as long as it represents the magnitude of the deviation between the simulation value dx and the derived thickness d. For example, the evaluation value Z may be the average value of the square of the deviation between the simulation value dx of the thickness and the derived thickness d, the sum of the absolute values ​​of the deviation between the simulation value dx of the thickness of n sets and the derived thickness d, or the average value of the absolute values ​​of the deviation between the simulation value dx of the thickness of n sets and the derived thickness d.

[0139] In addition, when modifying the correction formula, not all of the accumulated measurement data but some of the measurement data may be used. For example, the correction formula may be modified using the same measurement data as that used to determine the modification condition. However, when modifying the correction formula, it is preferable to use more measurement data than when creating the initial correction formula.

[0140] The correction condition is not limited to whether the judgment value Err is greater than the threshold value Th. The judgment value Err can be calculated by any formula as long as it represents the magnitude of the deviation between the simulation value dx and the derived thickness d. For example, the judgment value Err may be the sum of the squares of the deviations between the simulation value dx of the thickness of the n sets and the derived thickness d, the sum of the absolute values ​​of the deviations between the simulation value dx of the thickness of the n sets and the derived thickness d, or the average value of the absolute values ​​of the deviations between the simulation value dx of the thickness of the n sets and the derived thickness d.

[0141] Alternatively, the correction condition may be that a predetermined correction period has arrived. In this case, it is not necessary to monitor the judgment value Err, etc., and it is only necessary to monitor the passage of time, so that it is easy to determine whether the correction condition has been met.

[0142] The estimation of the wall-thinning rate and the maintenance timing are merely examples of the use of the corrected thickness dm. The thickness measuring device 10 only needs to calculate the corrected thickness dm, and does not need to calculate the wall-thinning rate, etc. The corrected thickness dm may be used for purposes other than the wall-thinning rate.

[0143] 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 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 be performed after the detection of eddy currents, but may be performed before the excitation in step S102, or may be performed in parallel with the detection of eddy currents in step S104. For example, the derivation of the thinning rate in step S115 and the estimation of the maintenance timing in step S116 may be omitted.

[0144] 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 functions described. Processors include transistors and other circuits and are considered to be circuits or processing circuitry. A processor may be a programmable processor that executes a program stored in a memory.

[0145] 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 in this specification or any hardware known to be programmed to realize or perform the described functions.

[0146] If the hardware is a processor considered to be a type of circuitry, the circuit, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0147] [Aspects] The above embodiments are specific examples of the following aspects.

[0148] (Mode 1) A thickness measuring device 10 includes an exciter 71 that applies an excitation current to an excitation coil 11 to induce an eddy current in an object 9, a detector 72 that detects the eddy current in the object 9 via a detection coil 12 (detection sensor), a deriving device 86 that determines the thickness of the object 9 based on the duration τ of the eddy current detected by the detector 72, a substrate 68 on which the exciter 71 and the detector 72 are mounted, a corrector 87 that corrects the thickness using a correction equation including a correction term Y corresponding to the temperature characteristic of the duration τ for at least one of the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9, and a corrector 88 that corrects the correction equation when a predetermined correction condition is satisfied.

[0149] According to this configuration, the thickness of the object 9, i.e., the derived thickness d, is obtained by the deriver 86 based on the duration τ of the eddy current. The corrector 87 corrects the derived thickness d by a correction formula including a correction term Y. As a result, the derived thickness d is corrected so as to reduce the influence of the temperature characteristics of the duration τ on at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. The correction formula including the correction term Y is appropriately corrected by the corrector 88. As a result, the correction formula is appropriately updated in response to environmental changes, etc. As a result, the thickness measuring device 10 can accurately determine the thickness with reduced influence of the temperature characteristics of the duration τ.

[0150] (Embodiment 2) In the thickness measuring device 10 described in embodiment 1, the corrector 88 calculates a simulation value dx of the thickness using a metal-thinning model that simulates the thickness derived based on the duration τ of the eddy current using the correction term Y, and the correction condition is that the deviation between the simulation value dx and the thickness before correction derived by the deriver 86, i.e., the derived thickness d, exceeds a predetermined range.

[0151] According to this configuration, the simulation value dx calculated by the thinning model is a thickness derived based on the duration τ, and is a thickness influenced by the temperature characteristics of the duration τ. In other words, the simulation value dx is a simulated value of the derived thickness d derived from the duration τ. Furthermore, the thinning model calculates the simulation value dx in a simulated manner using the correction term Y. Therefore, the appropriateness of the correction term Y can be determined based on the deviation between the simulation value dx and the derived thickness d. In other words, a large deviation of the simulation value dx from the derived thickness d means that the accuracy of the simulation is low, and as a result, the accuracy of the correction by the correction formula is low. Therefore, by monitoring the deviation between the simulation value dx and the derived thickness d, it is possible to accurately determine whether or not the correction formula needs to be corrected.

[0152] (Embodiment 3) In the thickness measuring device 10 described in embodiment 1 or embodiment 2, the corrector 88 corrects the correction term Y included in the thinning model in correcting the correction equation so that the deviation becomes smaller, and reflects the corrected correction term Y in the correction equation.

[0153] According to this configuration, the correction term Y included in the metal-reduction model is corrected by correcting the metal-reduction model so that the deviation between the simulation value dx and the derived thickness d becomes small. By reflecting the corrected correction term Y in the correction formula, the correction term Y of the correction formula is corrected.

[0154] (Aspect 4) The thickness measuring device 10 according to any one of aspects 1 to 3 further includes an acquirer 73 that acquires a physical quantity related to at least one of the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the target object 9 when detecting the eddy current, and a creator 85 that creates the correction equation using the eddy current and the physical quantity collected during a predetermined initial collection period, and the corrector 88 corrects the correction equation using the eddy current and the physical quantity collected at least after the initial collection period.

[0155] According to this configuration, measurement data including eddy currents and physical quantities are collected. The creator 85 and corrector 88 create and correct the correction formula using a plurality of measurement data. In detail, first, the creator 85 creates the correction formula using the measurement data collected in the initial collection period. Thereafter, when the correction condition is satisfied, the corrector 88 corrects the correction formula using at least the measurement data collected after the initial collection period. The correction formula is corrected using measurement data newer than when the correction formula was created. As a result, the correction formula is corrected to adapt to the latest situation. Furthermore, since the correction formula is corrected after the fact, the accuracy of the correction is improved after the fact. Therefore, the correction formula can be created early without extending the initial collection period, and the thickness correction can be started early.

[0156] (Embodiment 5) In the thickness measurement device 10 according to any one of embodiments 1 to 4, the corrector 88 corrects the correction equation using more of the eddy currents and the physical quantities than when the correction equation was created by the creator 85.

[0157] According to this configuration, since more measurement data is used when correcting the correction formula than when the correction formula was created, the accuracy of correction using the corrected correction formula can be improved compared to the correction formula when it was created.

[0158] (Aspect 6) In the thickness measuring device 10 according to any one of aspects 1 to 5, the correction equation is a function of the physical quantity, the corrector 87 corrects the thickness using the physical quantity acquired at the time of detection of the eddy current that is the basis for deriving the thickness, the corrector 88 calculates a simulation value dx of the thickness by a thinning model that simulates the thickness derived based on the duration τ of the eddy current using the correction term Y and the physical quantity, and the correction condition is that the deviation between the simulation value dx and the thickness d before correction derived by the deriver 86 exceeds a predetermined range.

[0159] According to this configuration, the thickness derived based on the duration τ of the eddy current is corrected using a physical quantity related to at least one of the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the target object 9. Similarly, the simulation value dx is calculated using the same physical quantity and the correction term Y. In other words, a large deviation between the simulation value dx and the thickness d means that the simulation using the correction term Y and the physical quantity is inappropriate, and ultimately means that the correction using the correction term Y and the physical quantity is inappropriate. Therefore, by monitoring the deviation between the simulation value dx and the derived thickness d, it is possible to accurately determine whether or not the correction formula needs to be modified.

[0160] (Embodiment 7) In the thickness measurement device 10 according to any one of embodiments 1 to 6, the corrector 88 determines that the correction condition is satisfied when a predetermined correction period has arrived.

[0161] According to this configuration, the correction formula is periodically revised, and in this case, it is possible to determine whether the revision conditions are met simply by monitoring the revision period, i.e., by monitoring the elapsed time.

[0162] (Embodiment 8) A thickness measurement method includes applying an excitation current to an excitation coil 11 to induce an eddy current in an object 9, detecting the eddy current in the object 9 via a detection coil 12 (detection sensor), determining the thickness of the object 9 based on a duration τ of the detected eddy current, performing a correction process to correct the thickness using a correction equation including a correction term Y corresponding to a temperature characteristic of the duration τ for at least one of the temperature of the excitation coil 11, the temperature of the substrate 68, and the temperature of the object 9, and correcting the correction equation when a predetermined correction condition is satisfied.

[0163] According to this configuration, the thickness of the object 9, i.e., the derived thickness d, is obtained based on the duration τ of the eddy current. The derived thickness d is corrected by a correction formula including a correction term Y. This corrects the derived thickness d so as to reduce the influence of the temperature characteristics of the duration τ on at least one of the temperature of the exciting coil 11, the temperature of the substrate 68, and the temperature of the object 9. The correction formula including the correction term Y is appropriately modified. This allows the correction formula to be appropriately updated in response to environmental changes, etc. As a result, the thickness with reduced influence of the temperature characteristics of the duration τ can be accurately obtained. [Explanation of symbols]

[0164] 10 Thickness measuring device 11 Excitation coil 12 Detection coil (detection sensor) 68 Substrate 71 Exciter 72 Detector 73 Acquirer 85 Creator 86 Deriver 87 Corrector 88 Corrector 9. Objects τ duration

Claims

1. an exciter that applies an excitation current to an excitation coil to induce an eddy current in the target object; a detector that detects the eddy current of the object via a detection sensor; a deriver for determining a thickness of the object based on a duration of the eddy currents detected by the detector; a substrate on which the exciter and the detector are mounted; a corrector that corrects the thickness by a correction equation including a correction term corresponding to a temperature characteristic of the duration with respect to at least one of a temperature of the excitation coil, a temperature of the substrate, and a temperature of the object; and a corrector that corrects the correction formula when a predetermined correction condition is satisfied.

2. 2. The thickness measurement device according to claim 1, The corrector calculates a simulation value of the thickness using a model that uses the correction term to simulate the thickness derived based on a duration of the eddy current; The correction condition is that the deviation between the simulation value and the thickness before correction derived by the deriver exceeds a predetermined range.

3. 3. The thickness measuring device according to claim 2, The corrector corrects the correction term included in the model so that the deviation is reduced in correcting the correction equation, and reflects the corrected correction term in the correction equation.

4. 2. The thickness measurement device according to claim 1, an acquirer that acquires a physical quantity related to at least one of a temperature of the excitation coil, a temperature of the substrate, and a temperature of the object when the eddy current is detected; a generator for generating the correction equation using the eddy currents and the physical quantities collected during a predetermined initial collection period, The corrector corrects the correction equation using the eddy currents and the physical quantities collected at least after the initial collection period.

5. 5. The thickness measuring device according to claim 4, The corrector corrects the correction equation by using more of the eddy currents and the physical quantities than when the correction equation was created by the creator.

6. 5. The thickness measuring device according to claim 4, the correction equation is a function of the physical quantity, The corrector corrects the thickness by using the physical quantity obtained when detecting the eddy current that is the basis for deriving the thickness; The corrector calculates a simulation value of the thickness by a model that uses the correction term and the physical quantity to simulate the thickness derived based on a duration of the eddy current; The correction condition is that the deviation between the simulation value and the thickness before correction derived by the deriver exceeds a predetermined range.

7. 2. The thickness measurement device according to claim 1, The corrector determines that the correction condition is satisfied when a predetermined correction period has arrived.

8. applying an excitation current to an excitation coil to induce an eddy current in the target object; 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; executing a correction process for correcting the thickness using a correction equation including a correction term corresponding to a temperature characteristic of the duration with respect to at least one of a temperature of the excitation coil, a temperature of a substrate on which an exciter that applies an excitation current to the excitation coil and a detector that detects the eddy current via the detection sensor are mounted, and a temperature of the object; and modifying the correction equation if a predetermined modification condition is satisfied.

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