Thickness measuring device and thickness measuring method

Abstract

To improve the accuracy of measurement of thickness by using the temperature of an object.SOLUTION: A thickness measurement device 100 comprises: an excitation unit 77 that induces an eddy current with respect to an object 9 via an excitation coil 11; a detection unit 78 that detects the eddy current of the object 9 via a detection coil 12 (a detection sensor); a temperature acquisition unit 79 that acquires the temperature of the object 9; a correction unit 86 that corrects the duration time of the eddy current detected by the detection unit 78 by using an approximate expression indicative of the relation of the duration time to temperature and the temperature acquired by the temperature acquisition unit 79; a thickness derivation unit 84 that obtains the thickness of the object 9 on the basis of the duration time corrected by the correction unit 86; and an approximation unit 85 that obtains an approximate expression on the basis of reference data including a plurality of eddy currents at different temperatures of the object 9 and can change a condition in obtaining the approximate expression.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

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

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

[0004] Incidentally, among measuring devices using eddy currents, there is a thickness measuring device that measures the thickness of an object. Even in such thickness measuring devices, the measurement accuracy can be improved by taking the temperature of the object into consideration, as in the measuring device of Patent Document 1. However, there is still room for improvement in improving measurement accuracy, such as how to use the temperature of the object.

[0005] The technology disclosed herein has been made in consideration of the above points, and its purpose is to improve the measurement accuracy in measuring the thickness of an object by using the temperature of the object. [Means for solving the problem]

[0006] The thickness measuring device disclosed herein comprises an excitation unit that induces eddy currents in an object via an excitation coil, a detection unit that detects the eddy currents in the object via a detection sensor, a temperature acquisition unit that acquires the temperature of the object, a correction unit that corrects the duration of the eddy currents detected by the detection unit using an approximation formula that indicates the relationship of the duration to the temperature and the temperature acquired by the temperature acquisition unit, a thickness derivation unit that calculates the thickness of the object based on the duration corrected by the correction unit, and an approximation unit that calculates the approximation formula based on reference data including multiple eddy currents at different temperatures of the object and is configured to be able to switch conditions when calculating the approximation formula.

[0007] The thickness measurement method disclosed herein includes inducing eddy currents in an object via an excitation coil, detecting the eddy currents in the object via a detection sensor, acquiring the temperature of the object, correcting the duration of the detected eddy currents using an approximation formula that indicates the relationship between the duration and the temperature and the acquired temperature, and determining the thickness of the object based on the corrected duration, wherein the approximation formula is determined based on reference data that includes multiple eddy currents at different temperatures of the object, and the conditions for determining the approximation formula are switchable. [Effects of the Invention]

[0008] According to the thickness measuring device, it is possible to improve the accuracy of thickness measurement by using the temperature of the object.

[0009] According to the thickness measurement method, the accuracy of thickness measurement can be improved by using the temperature of the object. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram of a thickness measurement device. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control system of the control unit of the processing device. [Figure 3]FIG. 3 is a block diagram showing the configuration of a control system of the control unit of the arithmetic device. [Figure 4] FIG. 4 is a graph showing the change over time of a voltage signal V(t) corresponding to an eddy current. [Figure 5] FIG. 5 is a flowchart of the thickness measurement. [Figure 6] FIG. 6 is a flowchart of a data collection subroutine for collecting reference data. [Figure 7] FIG. 7 is a flowchart of the subroutine for creating an approximate expression. [Figure 8] FIG. 8 is a graph showing the duration deviation Δτ and the temperature deviation ΔT. [Figure 9] FIG. 9 is a graph showing another example of the duration deviation Δτ and the temperature deviation ΔT. DETAILED DESCRIPTION OF THE INVENTION

[0011] Exemplary embodiments will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of a thickness measurement device 100. The thickness measurement device 100 measures the thickness of an object 9 by pulsed eddy current (PEC). The thickness measurement device 100 includes a processing device 7 that controls a probe 1 and a computing device 8 that calculates the thickness of the object 9. For example, the object 9 is a metal pipe through which steam or drain flows. The pipe is formed in a cylindrical shape.

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

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

[0014] In addition, the probe 1 further includes a temperature sensor 15 that detects the temperature of the object 9. The temperature of the object 9 is detected by the temperature sensor 15. The probe 1 may further include a casing that houses the excitation coil 11, the detection coil 12, and the temperature sensor 15. The detection coil 12 is an example of a detection sensor.

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

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

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

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

[0019] The temperature sensor 15 is, for example, a thermocouple.

[0020] The processing device 7 uses the probe 1 to generate an eddy current in the object 9, detects the generated eddy current, and acquires the temperature of the object 9 at that time. The calculation device 8 calculates the thickness of the object 9 based on the duration of the eddy current detected by the processing device 7 (the time until the eddy current rapidly decays, which will be described in detail later). In addition, the calculation device 8 corrects the duration used to calculate the thickness of the object 9 based on the temperature of the object 9.

[0021] The processing device 7 has a transmitting unit 71, a receiving unit 72, a temperature measuring unit 73, a communication unit 74, a control unit 75, and a storage unit 76.

[0022] The transmitter 71 applies a pulsed excitation current to the excitation coil 11. The transmitter 71 has a pulse generator 71a and a transmission amplifier 71b. The pulse generator 71a generates a pulse signal based on a command from the control unit 75. The transmission amplifier 71b amplifies the pulse signal from the pulse generator 71a and outputs it to the excitation coil 11 as an excitation current.

[0023] The receiver 72 receives the induced electromotive force generated in the detection coil 12 in response to the eddy current in the object 9. The receiver 72 has at least a receiver amplifier 72a that receives the voltage generated in the detection coil 12 and amplifies the voltage. The receiver 72 may further have a filter that filters the voltage signal.

[0024] The output of the temperature sensor 15 is input to the temperature measuring unit 73. The temperature measuring unit 73 may have a receiving amplifier that receives the detection signal of the temperature sensor 15 and amplifies the detection signal.

[0025] The communication unit 74 performs wireless communication with external devices. For example, the communication unit 74 transmits the voltage signal (i.e., the detection signal) detected by the receiving unit 72 and the detection signal detected by the temperature measuring unit 73 to the arithmetic device 8.

[0026] The control unit 75 controls the entire processing device 7. The control unit 75 performs various types of arithmetic processing. For example, the control unit 75 is formed of a processor such as a CPU (Central Processing Unit). The control unit 75 may also be formed of an MCU (Micro Controller Unit), an MPU (Micro Processor Unit), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), a system LSI, or the like.

[0027] For example, the control unit 75 causes the transmission unit 71 to output an excitation current for a predetermined period, and after the output of the excitation current is stopped, acquires a detection signal via the reception unit 72. The control unit 75 also acquires a detection signal from the temperature measurement unit 73 at the same time that it acquires the detection signal from the reception unit 72. The control unit 75 stores the detection signals from the reception unit 72 and the temperature measurement unit 73 in the memory unit 76, and transmits the detection signal stored in the memory unit 76 to the calculation device 8 via the communication unit 74 as appropriate.

[0028] The storage unit 76 stores various data and programs executed by the control unit 75. For example, a control program is stored in the storage unit 76. The storage unit 76 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), or the like.

[0029] 2 is a block diagram showing the configuration of a control system of the control unit 75 of the processing device 7. The control unit 75 realizes various functions by reading out a control program from the storage unit 76 into memory and expanding the program. Specifically, the control unit 75 functions as an excitation unit 77 that induces eddy currents in the object 9 via the excitation coil 11, a detection unit 78 that detects the eddy currents in the object 9 via the detection coil 12, a temperature acquisition unit 79 that acquires the temperature of the object 9, and a data collection unit 710 that collects reference data for correcting the duration.

[0030] The excitation unit 77 causes the transmission unit 71 to apply an excitation current to the excitation coil 11. Specifically, the excitation unit 77 outputs a command to the pulse generator 71a, causing the pulse generator 71a to generate a pulse signal. As a result, an excitation current is applied to the excitation coil 11 from the transmission amplifier 71b.

[0031] The detection unit 78 detects a voltage signal corresponding to the eddy current as the eddy current in the object 9. Specifically, the detection unit 78 detects a voltage signal corresponding to the induced electromotive force in the detection coil 12. More specifically, the detection unit 78 continues to detect the voltage signal for a predetermined period after the application of the excitation current to the excitation coil 11 is stopped. In other words, the detection unit 78 detects a time-varying change (i.e., a transient change) in the eddy current in the object 9 after the application of the excitation current to the excitation coil 11 is stopped. The detection unit 78 stores the detected eddy current, i.e., the voltage signal, in the storage unit 76. Hereinafter, for convenience of explanation, the voltage signal detected by the detection unit 78 may be simply referred to as the "eddy current." For example, the voltage signal corresponding to the eddy current stored in the storage unit 76 will also be simply referred to as the "eddy current."

[0032] The temperature acquisition unit 79 acquires the temperature of the object 9 at the time when the detection unit 78 acquires the voltage signal via the temperature sensor 15. The temperature acquisition unit 79 stores the temperature of the object 9 in the storage unit .

[0033] The storage unit 76 stores the eddy current detected by the detection unit 78 and the temperature of the object 9 acquired by the temperature acquisition unit 79 when the eddy current was detected, in association with each other. In other words, the storage unit 76 stores the eddy current and the temperature as one combination.

[0034] The data collection unit 710 acquires measurement data for thickness measurement and reference data for correction. In either case of measurement data or reference data, the data collection unit 710 acquires combined data of eddy current and temperature by performing excitation by the excitation unit 77, detection of eddy current by the detection unit 78, and acquisition of temperature by the temperature acquisition unit 79. The data collection unit 710 stores the acquired eddy current and temperature in the memory unit 76. When acquiring measurement data, the data collection unit 710 acquires combined data of eddy current and temperature at each predetermined measurement cycle.

[0035] When acquiring reference data, the data collection unit 710 collects multiple sets of eddy currents and temperatures during a predetermined collection period before correcting the duration of the eddy currents. Specifically, the data collection unit 710 collects multiple sets of eddy currents and temperatures as reference data by performing excitation by the excitation unit 77, detection of eddy currents by the detection unit 78, and acquisition of temperatures by the temperature acquisition unit 79 multiple times. The collection period is a period during which changes in the thickness of the object 9 can be ignored and varies depending on the physical properties and usage conditions of the object 9. As a result, the data collection unit 710 collects multiple eddy currents at different temperatures of the object 9. The multiple eddy currents are hardly affected by changes in the thickness of the object 9. The differences between the collected multiple eddy currents mainly depend on the temperature of the object 9.

[0036] The control unit 75 transmits the eddy current and temperature of the object 9 stored in the storage unit 76 to the calculation device 8 via the communication unit 74.

[0037] The arithmetic device 8 is formed by a computer or a computer network (so-called cloud). The arithmetic device 8 has a communication unit 81, a control unit 82, and a storage unit 83.

[0038] The communication unit 81 performs wireless communication with external devices. For example, the communication unit 81 receives signals from the processing device 7.

[0039] The control unit 82 controls the entire arithmetic device 8. The control unit 82 performs various types of arithmetic processing. For example, the control unit 82 is formed of a processor such as a CPU (Central Processing Unit). The control unit 82 may also be formed of an MCU (Micro Controller Unit), an MPU (Micro Processor Unit), an FPGA (Field Programmable Gate Array), a PLC (Programmable Logic Controller), a system LSI, or the like.

[0040] The memory unit 83 stores programs and various data executed by the control unit 82. For example, the memory unit 83 stores a control program. The memory unit 83 is formed of a non-volatile memory, a hard disk drive (HDD), a solid state drive (SSD), or the like. The memory unit 83 also stores signals transmitted from the processing device 7. Specifically, the memory unit 83 stores the eddy current and temperature of the target object 9 acquired by the processing device 7.

[0041] 3 is a block diagram showing the configuration of a control system of the control unit 82 of the calculation device 8. The control unit 82 realizes various functions by reading out a control program from the storage unit 83 into memory and expanding it. Specifically, the control unit 82 functions as a thickness derivation unit 84, an approximation unit 85, and a correction unit 86.

[0042] The thickness derivation unit 84 determines the thickness of the object 9 based on the duration of the eddy current in the object 9. As will be described in more detail, the eddy current induced in the object 9 by the excitation coil 11 penetrates from the front surface of the object 9 (the surface facing the probe 1) to the back surface, and rapidly attenuates when it reaches the back surface. The duration of the eddy current in the object 9 is the time from when the eddy current is induced in the object 9 to when it rapidly attenuates. The duration of the eddy current in the object 9 is correlated with the thickness of the object 9.

[0043] The thickness derivation unit 84 determines the duration of the eddy current (specifically, the voltage signal) detected by the processing device 7. The thickness derivation unit 84 determines the thickness of the object 9 from the duration based on the correlation between the duration and the thickness.

[0044] The approximation unit 85 obtains an approximation formula that indicates the relationship between the duration and the temperature of the object 9, based on the reference data. The approximation unit 85 obtains the duration of each eddy current from the reference data stored in the storage unit 83. The approximation unit 85 obtains the approximation formula based on multiple sets of duration and temperature.

[0045] The correction unit 86 corrects the duration used to derive the thickness by the thickness derivation unit 84 described above, using the approximation formula and the temperature of the object 9. That is, the eddy current of the object 9 and the temperature of the object 9 when the eddy current is detected are stored in the memory unit 83. The thickness derivation unit 84 obtains the duration from the eddy current stored in the memory unit 83. The correction unit 86 corrects the obtained duration based on the approximation formula and the temperature of the object 9. The thickness derivation unit 84 obtains the thickness of the object 9 based on the corrected duration.

[0046] Next, the relationship between eddy currents and the thickness of the object 9 will be described in detail. FIG. 4 is a graph showing the time variation of a voltage signal V(t) corresponding to an eddy current. The graph in FIG. 4 is a double logarithmic graph. In FIG. 4, voltage signal V0(t) is the voltage signal of an object 9 having a thickness d0, and voltage signal V1(t) is the voltage signal of an object 9 having a thickness d1 that is thinner than d0.

[0047] The eddy current decays as it penetrates into the object 9. The eddy current decays gradually from the front surface of the object 9 (the surface facing the probe 1) until it reaches the back surface, and then decays rapidly once it reaches the back surface. The voltage signal V(t) also shows the same change as the eddy current. In other words, the transient change in the voltage signal V(t) corresponds to the transient change in the eddy current. The change in the voltage signal V(t) until the eddy current reaches the back surface of the object 9 is represented linearly on a double logarithmic graph. Thereafter, the voltage signal V(t) decays rapidly. This changing voltage signal V(t) is expressed as in the following equation (1).

[0048]

number

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

[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. Also, even if the duration τ and the thickness d change, the time τ / d 2 is constant. Therefore, if the duration τ0 for a known thickness d0 and the duration τx for an unknown thickness dx are known, the unknown thickness dx can be calculated based on the following equation (3).

[0052]

number

[0053] For example, comparing voltage signals V0(t) and V1(t) in Figure 4, the voltage signal V0(t) of object 9 with thickness d0 continues until duration τ0. As the thickness d of object 9 decreases from d0 to d1, duration τ decreases from τ0 to τ1. Note that the change in the linear portion of voltage signal V(t) on a log-log graph does not depend on thickness d, as can be seen from equation (1), and therefore is substantially the same for voltage signals V0(t) and V1(t). The thickness d1 can be calculated by substituting thickness d0 and durations τ0 and τ1 into equation (3).

[0054] However, the electrical conductivity σ and magnetic permeability μ of the actual object 9 are temperature dependent. Therefore, the duration τ is also temperature dependent. 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. For example, considering the temperature dependence of the electrical conductivity σ and magnetic permeability μ, the duration τ can be expressed as in the following equation (4).

[0055]

number

[0056] By correcting the duration τ so that it corresponds to the first-order term of T and the second-order term of T in equation (4), a corrected duration τ′ according to the temperature of the object 9 can be obtained.

[0057] In the thickness measurement device 100, the approximation unit 85 obtains an approximation equation that indicates the relationship between the temperature of the object 9 and the duration, and the correction unit 86 corrects the duration τ using the approximation equation. Then, the thickness derivation unit 84 obtains the thickness of the object 9 based on the corrected duration τ'. Such thickness measurement will be described in more detail using a flowchart. Figure 5 is a flowchart of thickness measurement.

[0058] First, in step S101, as a preparation stage for thickness measurement, the processing device 7 collects reference data. For example, the processing device 7 receives an external command and executes collection of reference data. Specifically, after the probe 1 has been installed on the object 9 and before starting to measure the thickness of the object 9, the user operates the arithmetic device 8 to input a command to execute collection of reference data. The processing device 7 receives the collection command via the arithmetic device 8 and starts collecting reference data. Note that the user may also operate the processing device 7 to directly input a command to execute collection to the processing device 7.

[0059] Collection of reference data is performed according to the flowchart of FIG. 6. FIG. 6 is a flowchart of a data collection subroutine for collecting reference data. In step S201, the processing device 7 determines whether a collection period has arrived. The collection period is a period during which eddy current detection and the like are repeatedly performed. The collection period is longer than the measurement period during which measurement data is acquired. If the collection period has not arrived, the processing device 7 repeats the determination of step S201 and waits for the arrival of the collection period.

[0060] When the collection period arrives, the processing device 7 determines in step S202 whether or not the current time is within a predetermined collection period. Specifically, the processing device 7 determines whether or not the collection period has elapsed since the start of collection of the reference data. The collection period is a period longer than the collection period.

[0061] If it is within the collection period, the processing device 7 acquires a set of reference data. Specifically, in step S203, the excitation unit 77 applies an excitation current to the excitation coil 11 to excite it. The excitation coil 11 generates a magnetic field in the axial direction by applying the excitation current. One excitation coil 11 and the other excitation coil 11 generate magnetic fields in opposite directions in the axial direction. For example, a magnetic flux is generated from one excitation coil 11 toward the object 9, and a magnetic flux is generated from the object 9 toward the other excitation coil 11.

[0062] Subsequently, in step S204, the excitation unit 77 stops outputting the excitation current, and the detection unit 78 detects the eddy current generated in the object 9. The detection unit 78 continues detecting the voltage signal for a predetermined period. In this way, the detection unit 78 detects the transient change (change over time) of the induced electromotive force in the detection coil 12, i.e., the transient change of the eddy current generated in the object 9.

[0063] Furthermore, in step S205, the temperature acquisition unit 79 acquires the temperature of the object 9. The processing device 7 stores the set of eddy currents and temperatures in the storage unit 76. This completes the acquisition of the set of reference data.

[0064] Then, the processing device 7 returns to step S201 to determine whether the next collection period has arrived. When the next collection period arrives, if it is within the collection period, another set of reference data is acquired. That is, the processing device 7 acquires one set of reference data for each collection period until the collection period ends.

[0065] If the collection period has ended in step S202, the processing device 7 transmits the reference data stored in the memory unit 76, i.e., the plurality of sets of eddy currents and temperatures, to the calculation device 8. This completes the collection of reference data by the processing device 7. The calculation device 8 stores the received reference data in the memory unit 83.

[0066] Next, in step S102 of the thickness measurement flowchart, the arithmetic device 8 creates an approximate equation. The creation of the approximate equation is executed according to the flowchart of Fig. 7. Fig. 7 is a flowchart of the subroutine for creating the approximate equation.

[0067] First, in step S301, the approximation unit 85 obtains the duration of each eddy current from the reference data stored in the storage unit 83. That is, the approximation unit 85 creates multiple sets of data of duration and temperature from multiple sets of reference data of eddy current and temperature.

[0068] Next, in step S302, the approximation unit 85 creates an approximation formula from a plurality of pairs of duration and temperature. The approximation formula created in step S302 is a provisional approximation formula.

[0069] For example, the approximation unit 85 determines a reference duration τr and a reference temperature Tr from multiple sets of durations and temperatures. The approximation unit 85 sets the average value of the multiple durations as the reference duration τr, and sets the average value of the multiple temperatures as the reference temperature Tr. Alternatively, the approximation unit 85 may set the duration closest to the average value of the multiple durations and the temperature at that time as the reference duration τr and the reference temperature Tr, respectively. Alternatively, the approximation unit 85 may set the temperature closest to the average value of the multiple temperatures and the duration at that time as the reference temperature Tr and the reference duration τr, respectively. Alternatively, the approximation unit 85 may set the earliest detected duration and temperature from among the multiple sets of durations and temperatures as the reference duration τr and the reference temperature Tr, respectively.

[0070] The approximation unit 85 calculates the duration deviation Δτ (=τ-τr) and temperature deviation ΔT (=T-Tr), which are deviations from the reference duration τr and reference temperature Tr, from multiple sets of durations and temperatures. For example, FIG. 8 is a graph showing the obtained duration deviation Δτ and temperature deviation ΔT. Each point in the graph represents one set of duration deviation Δτ and temperature deviation ΔT.

[0071] The approximation unit 85 obtains an approximation formula from multiple sets of duration deviation Δτ and temperature deviation ΔT by the least squares method. That is, the approximation unit 85 obtains an approximation formula showing the relationship of the duration deviation Δτ to the temperature deviation ΔT as an approximation formula showing the relationship of the duration to the temperature of the object 9. At this time, conditions for obtaining the approximation formula are set. First, the approximation unit 85 sets the conditions for obtaining the approximation formula to a quadratic function as shown in equation (5) and obtains the approximation formula. In the example of FIG. 8, an approximation formula of a quadratic function as shown by the solid line is obtained.

[0072]

number

[0073] Next, in step S303, the approximation unit 85 determines whether the coefficient γ1 of the quadratic term in the obtained approximation formula is positive. In the example of Fig. 8, the coefficient γ1 of the quadratic term is positive. If the coefficient γ1 of the quadratic term is positive, the approximation unit 85 determines the obtained approximation formula as a definite approximation formula and ends the creation of the approximation formula.

[0074] FIG. 9 is a graph showing another example of the duration deviation Δτ and the temperature deviation ΔT. The solid line in the figure is a curve corresponding to the approximate expression of the quadratic function. In the example of FIG. 9, the coefficient γ1 of the quadratic term is negative. If the coefficient γ1 of the quadratic term is negative, the approximation unit 85 changes the condition for determining the approximate expression to a linear function as shown in equation (6) in step S304 and determines the approximate expression again. In the example of FIG. 9, the approximation unit 85 determines the approximate expression of the linear function as shown by the two-dot chain line. The approximation unit 85 regards the determined approximate expression as a definitive approximate expression and ends the creation of the approximate expression.

[0075]

number

[0076] When the creation of the approximation formula is completed, thickness measurement is started. For example, the thickness derivation unit 84 determines whether a predetermined measurement period has arrived in step S103 of the thickness measurement flowchart. The measurement period is a period for obtaining thickness measurements of the object 9. If the measurement period has not arrived, the thickness derivation unit 84 repeats the determination in step S103 and waits for the arrival of the measurement period.

[0077] When the measurement period arrives, the thickness derivation unit 84 outputs a command to the processing device 7 to cause the processing device 7 to acquire measurement data. The measurement data is eddy currents and temperatures for measuring the thickness of the object 9. Specifically, when the processing device 7 receives a command from the calculation device 8, the excitation unit 77 applies an excitation current to the excitation coil 11 to excite it in step S104. Subsequently, in step S105, the detection unit 78 detects eddy currents generated in the object 9. Furthermore, in step S106, the temperature acquisition unit 79 acquires the temperature of the object 9. The processing device 7 transmits a set of eddy currents and temperatures as measurement data to the calculation device 8. The calculation device 8 stores the received set of eddy currents and temperatures in the memory unit 83.

[0078] Subsequently, in step S107, the thickness deriving unit 84 obtains the duration τx of the eddy current from the measurement data stored in the storage unit 83.

[0079] Thereafter, in step S108, the correction unit 86 corrects the duration τx using the approximation formula and the temperature of the measurement data. Specifically, the correction unit 86 calculates a temperature deviation ΔT (=Tx-Tr), which is the deviation between the reference temperature Tr and the temperature Tx of the measurement data. The correction unit 86 substitutes the calculated temperature deviation ΔT into the approximation formula to calculate the duration deviation Δτ. The correction unit 86 corrects the duration τx with the calculated duration deviation Δτ to calculate the corrected duration τx' (=τx+Δτ).

[0080] Then, in step S109, the thickness derivation unit 84 obtains the thickness dx of the object 9 by substituting the corrected duration τx′ for τx in equation (3).

[0081] Thereafter, in step S110, the thickness derivation unit 84 determines whether or not to end the thickness measurement. For example, the thickness derivation unit 84 determines whether or not a command to end the thickness measurement has been input. For example, the user operates the arithmetic device 8 to input an end of the thickness measurement. If an end command has not been input, the thickness derivation unit 84 returns to step S103 and determines whether or not the next measurement cycle has arrived. When the next measurement cycle arrives, measurement data is acquired again, and the thickness of the object 9 is found based on the measurement data. In other words, the arithmetic device 8 repeats the acquisition of measurement data and the derivation of the thickness of the object 9 for each measurement cycle.

[0082] In step S110, if an end command has been input, the thickness measurement is ended.

[0083] In this manner, the thickness measurement device 100 generates an eddy current in the object 9, detects the generated eddy current, and measures the thickness of the object 9 based on the duration τ of the eddy current. Here, since the duration τ of the eddy current is temperature-dependent, the thickness measurement device 100 corrects the duration τ with the temperature of the object 9 using an approximation formula that indicates the relationship between the duration and the temperature of the object 9. The thickness measurement device 100 obtains the approximation formula from multiple sets of reference data of duration and temperature. In this case, the thickness measurement device 100 can improve the accuracy of the approximation formula to the reference data by switching the conditions for obtaining the approximation formula. By correcting the duration τ using the approximation formula thus obtained, the thickness measurement device 100 can improve the accuracy of the temperature correction of the duration τ, and ultimately determine the thickness of the object 9 with high accuracy.

[0084] The relationship of duration to temperature varies depending on the object 9. For example, whether the duration increases or decreases with temperature, and whether the change is quadratic or linear, are determined depending on the object 9. In this example, the thickness measurement device 100 first determines the approximate equation by setting the conditions for determining the approximate equation to a quadratic function. If the coefficient of the quadratic term in the determined approximate equation is positive, that approximate equation is adopted. If the coefficient of the quadratic term is negative, the approximate equation is changed to a linear function as a condition for determining the approximate equation. As a result, an approximate equation of a linear function is determined. In this example, the change in duration depending on the temperature of the object 9 is best suited to a quadratic function with a positive coefficient for the quadratic term. Next, a linear function is more suitable than a quadratic function with a negative coefficient for the quadratic term to determine the change in duration depending on the temperature of the object 9. By determining the approximate equation under the conditions described above, an approximate equation that suits this tendency can be determined.

[0085] As described above, the thickness measuring device 100 includes an excitation unit 77 that induces eddy currents in the object 9 via the excitation coil 11, a detection unit 78 that detects the eddy currents in the object 9 via the detection coil 12 (detection sensor), a temperature acquisition unit 79 that acquires the temperature of the object 9, a correction unit 86 that corrects the duration of the eddy current detected by the detection unit 78 using an approximation equation that shows the relationship between the duration and the temperature and the temperature acquired by the temperature acquisition unit 79, a thickness derivation unit 84 that calculates the thickness of the object 9 based on the duration corrected by the correction unit 86, and an approximation unit 85 that calculates the approximation equation based on reference data including multiple eddy currents in the object 9 at different temperatures and is configured to be able to switch the conditions for calculating the approximation equation.

[0086] In other words, the thickness measurement method includes inducing eddy currents in the object 9 via an excitation coil 11, detecting the eddy currents in the object 9 via a detection coil 12 (detection sensor), acquiring the temperature of the object 9, correcting the duration of the detected eddy currents using an approximation formula showing the relationship between the duration and the temperature and the acquired temperature, and determining the thickness of the object 9 based on the corrected duration, wherein the approximation formula is determined based on reference data including multiple eddy currents at different temperatures of the object 9, and the conditions for determining the approximation formula are switchable.

[0087] According to this configuration, basically, eddy currents are induced in the object 9, the induced eddy currents are detected, and the thickness of the object 9 is determined based on the duration of the detected eddy currents. At this time, the duration is corrected using an approximation formula indicating the relationship between the duration and the temperature of the object 9 and the temperature of the object 9. The approximation formula is determined based on reference data including multiple eddy currents at different temperatures of the object 9. Here, the conditions for determining the approximation formula are configured to be switchable, so that an approximation formula that is more suited to the reference data can be determined. This allows the duration of the eddy currents to be more appropriately corrected according to the temperature of the object 9, thereby improving the accuracy of measuring the thickness of the object 9.

[0088] Specifically, the approximation unit 85 is configured to be able to switch between obtaining an approximation formula using a linear function or a quadratic function.

[0089] According to this configuration, the approximation formula can be switched between a linear function and a quadratic function so as to improve compatibility with the reference data. The manner in which the duration changes according to the temperature of the object 9 differs depending on the physical properties and usage conditions of the object 9. By switching the approximation formula between a linear function and a quadratic function, the accuracy of the approximation of the approximation formula can be improved.

[0090] Alternatively, the approximation unit 85 is configured to be able to switch the coefficient of the quadratic term of the quadratic function between positive and negative when the approximation formula is obtained using a quadratic function.

[0091] According to this configuration, the coefficient of the quadratic term in the approximate equation of the quadratic function can be switched between positive and negative depending on the physical properties and usage conditions of the object 9, thereby improving the accuracy of the approximation of the approximate equation.

[0092] In addition, the thickness measuring device 100 further includes a data collecting unit 710 that collects reference data. The data collecting unit 710 collects multiple combinations of eddy currents and temperatures as reference data by performing excitation by the excitation unit 77, detection of eddy currents by the detection unit 78, and acquisition of temperatures by the temperature acquisition unit 79 multiple times during a predetermined collection period before correcting the duration.

[0093] According to this configuration, the thickness measurement device 100 includes a data collection unit 710 that collects reference data for determining an approximate equation. The data collection unit 710 performs excitation by the excitation unit 77, detection of eddy currents by the detection unit 78, and acquisition of temperature by the temperature acquisition unit 79, just as when acquiring data for thickness measurement. In other words, the data collection unit 710 can collect reference data from the same object 9 and under the same conditions as when performing thickness measurement. As a result, reference data that is in line with the actual circumstances of thickness measurement can be acquired.

[0094] Furthermore, the data collecting unit 710 collects reference data before the thickness deriving unit 84 starts deriving the thickness.

[0095] According to this configuration, the thickness measurement accuracy can be improved by correcting the duration from the start of thickness derivation by the thickness derivation unit 84 using the temperature of the object 9. Furthermore, since the reference data is collected before thickness derivation starts, it is collected at a time when there is little variation in the thickness of the object 9. In other words, it is possible to collect reference data that is little affected by thickness variations.

[0096] Other Embodiments As described above, the above embodiment has been described as an example of the technology disclosed in this application. However, the technology of the present disclosure is not limited to this and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, the components described in the above embodiment can be combined to create new embodiments. Furthermore, the components described in the accompanying drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem in order to exemplify the technology. Therefore, the fact that these non-essential components are described in the accompanying drawings or detailed description should not be interpreted as immediately determining that these non-essential components are essential.

[0097] The above embodiment may be configured as follows.

[0098] For example, the configuration of the thickness measurement device 100 is merely an example. The processing device 7 and the arithmetic device 8 may be configured integrally. That is, one device may have the functions of the processing device 7 and the arithmetic device 8. The processing device 7 and the arithmetic device 8 may be connected by a wire. Furthermore, a plurality of processing devices 7 may be connected to one arithmetic device 8. Furthermore, the arithmetic device 8 may transmit data related to the calculated thickness to another device connected wirelessly or by a wire.

[0099] The probe 1 is not limited to the configuration described above. For example, the probe 1 includes two sets of excitation coils 11 and detection coils 12, but the number of excitation coils 11 and detection coils 12 may be one set or three or more sets. The excitation coils 11 and detection coils 12 do not have to be arranged so that their respective axes are aligned. When the excitation coils 11 and detection coils 12 are arranged so that their respective axes are aligned, the excitation coil 11 may be arranged closer to the object 9 than the detection coil 12. Furthermore, the detection unit of the probe 1 is not limited to the detection coil 12. The detection unit may be any unit that can directly or indirectly detect eddy currents in the object 9, and may be, for example, a Hall element. The probe 1 does not have to include the core 13.

[0100] The temperature sensor 15 is not limited to a thermocouple. Any temperature sensor may be used as long as it can detect the temperature of the object, and may be, for example, a thermistor. The number of temperature sensors 15 is not limited to one, and may be multiple.

[0101] Furthermore, thickness measurement using the thickness measurement device 100 is merely an example. There are various thickness measurement methods using PEC, so any measurement method can be adopted. Furthermore, the method of calculating the thickness of the object 9 taking the temperature of the object 9 into consideration is not limited to the above-mentioned method.

[0102] Furthermore, the method of correcting the duration τ of the eddy current is merely one example. For example, the reference data does not have to be data acquired using the probe 1 and object 9 that actually perform the thickness measurement. In other words, the reference data may be acquired using a probe 1 and object 9 that are the same type as but different from the probe 1 and object 9 that perform the thickness measurement. The calculation device 8 may externally receive reference data acquired separately from the probe 1 and object 9 that perform the thickness measurement, and use the reference data to create an approximation equation.

[0103] The method for finding an approximate equation from reference data may be a method other than the least squares method. The conditions for finding an approximate equation are not limited to the above-mentioned conditions. The conditions for finding an approximate equation and the conditions for switching between those conditions (hereinafter referred to as "switching conditions") may be changed depending on the object 9. For example, the conditions for finding an approximate equation that are initially set may not be a quadratic function, but may also be a linear function. Alternatively, the conditions for finding an approximate equation may not simply be a linear function, but may also be limited to whether the slope is positive or negative.

[0104] As described above, the switching condition is not limited to the quadratic term of the quadratic function being negative. For example, if the initial condition for determining an approximate equation is a linear function, the switching condition may be that the slope of the determined linear function (i.e., the coefficient of the linear term) is positive. Alternatively, the switching condition may be that the sum of squares of the residuals of the approximate equation is equal to or greater than a predetermined threshold.

[0105] Alternatively, the thickness measurement device 100 may be configured to allow a user to set conditions for determining an approximate equation. For example, the thickness measurement device 100 may be configured to allow a user to select and set conditions for determining an approximate equation, such as a linear function, a quadratic function with a positive coefficient for the quadratic term, and a quadratic function with a negative coefficient for the quadratic term. In this case, the thickness measurement device 100 may be configured to first create a provisional approximate equation based on provisional conditions, and then present the provisional approximate equation to the user and accept changes to the conditions from the user. Alternatively, the thickness measurement device 100 may create an approximate equation based on conditions set by the user from the beginning.

[0106] Furthermore, the approximate equation may not necessarily be created before the start of thickness measurement. For example, the approximate equation may be created before the start of thickness measurement, and the reference data may be re-collected after the start of thickness measurement to update the approximate equation.

[0107] The flowchart is merely an example. Steps in the flowchart may be changed, replaced, added, omitted, etc. as appropriate. The order of steps in the flowchart may also be changed, and serial processing may be performed in parallel. For example, in the thickness measurement flowchart (FIG. 5), temperature acquisition in step S106 may be performed before or in parallel with excitation in step S104 or eddy current detection in step S105.

[0108] The functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor. [Explanation of symbols]

[0109] 100 Thickness measuring device 11 Excitation coil 12 Detection coil (detection sensor) 15 Temperature Sensor 7 Processing equipment 77 Excitation section 78 Detector 79 Temperature acquisition section 710 Data Collection Department 8 Arithmetic unit 84 Thickness extraction section 85 Approximation part 9 Objects

Claims

1. an excitation unit that induces an eddy current in the object via an excitation coil; a detection unit that detects the eddy current of the object via a detection sensor; a temperature acquisition unit that acquires the temperature of the object; a correction unit that corrects the duration of the eddy current detected by the detection unit using an approximation expression that indicates a relationship between the duration and the temperature and the temperature acquired by the temperature acquisition unit; a thickness deriving unit that determines the thickness of the object based on the duration corrected by the correcting unit; A thickness measurement device comprising: an approximation unit that calculates the approximation formula based on reference data including a plurality of the eddy currents at different temperatures of the object, and that is configured to be able to switch conditions when calculating the approximation formula.

2. 2. The thickness measuring device according to claim 1, The thickness measuring device is configured so that the approximation unit can switch between obtaining the approximation formula using a linear function or a quadratic function.

3. 2. The thickness measuring device according to claim 1, The thickness measuring device is configured such that when the approximation formula is obtained using a quadratic function, the approximation unit can switch the coefficient of the quadratic term of the quadratic function between positive and negative.

4. 4. The thickness measuring device according to claim 1, further comprising a data collection unit that collects the reference data; The data collection unit performs excitation by the excitation unit, detection of the eddy current by the detection unit, and acquisition of the temperature by the temperature acquisition unit multiple times during a predetermined collection period, thereby collecting multiple combinations of the eddy current and the temperature as the reference data.

5. 5. The thickness measuring device according to claim 4, The data collection unit collects the reference data before the thickness derivation unit starts deriving the thickness.

6. Inducing eddy currents in the object via an excitation coil; detecting the eddy current of the object via a detection sensor; acquiring a temperature of the object; correcting the detected duration of the eddy current using an approximation formula indicating a relationship between the duration and the temperature and the acquired temperature; determining a thickness of the object based on the corrected duration; the approximation formula is obtained based on reference data including a plurality of the eddy currents at different temperatures of the object; The condition for determining the approximation formula is a thickness measurement method that can be switched.

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