Thickness measurement system and probe

Abstract

To measure a thickness of an object having various thicknesses.SOLUTION: A thickness measurement system 100 includes: an exciting coil 11 for inducing an eddy current in an object 9; a detection coil 12 for detecting the eddy current of the object 9; and a derivation device 86 for determining a thickness of the object 9 based on the eddy current detected via the detection coil 12. The detection coil 12 is configured to allow a change in detection sensitivity of the eddy current.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed herein relates to a thickness measurement system and a probe.

Background Art

[0002] Conventionally, measurement systems using eddy currents have been known. For example, Patent Document 1 discloses a measurement system that generates eddy currents in an object and examines the characteristics of the object by measuring the generated eddy currents.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the measurement using eddy currents as described above, the thickness of an object can be measured. In thickness measurement using eddy currents, the thickness of the object is determined based on the change over time of the eddy currents penetrating the object. However, there is a limit to the thickness range of the object for which the thickness can be appropriately measured.

[0005] The technology disclosed herein has been made in view of such a point, and its object is to realize the thickness measurement of objects of various thicknesses.

Means for Solving the Problems

[0006] The thickness measurement system disclosed herein includes an exciter that induces eddy currents in an object, a detector that detects the eddy currents of the object, and a calculator that obtains the thickness of the object based on the eddy currents detected via the detector, and the detector is capable of changing the detection sensitivity of the eddy currents.

[0007] The probe disclosed herein includes an exciter that induces eddy currents in an object, and a detector that detects the eddy currents of the object, and the detector is capable of changing the detection sensitivity of the eddy currents.

Advantages of the Invention

[0008] According to the thickness measurement system, it is possible to measure the thicknesses of objects with various thicknesses.

[0009] According to the probe, it is possible to measure the thicknesses of objects with various thicknesses.

Brief Description of the Drawings

[0010]

Figure 1

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Figure 15

[0011] Hereinafter, exemplary embodiments 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 testing (PEC). The probe 1 includes an excitation coil 11 that induces an eddy current in the object 9 and a detection coil 12 that detects the eddy current of the object 9. The thickness measurement device 10 includes a calculator 86 (see FIG. 3) that obtains the thickness of the object 9 based on the eddy current detected via the detection coil 12. The thickness measurement device 10 includes a processing device 6 that controls the probe 1 and a computing device 8 that obtains the thickness of the object 9. For example, the object 9 is a metal pipe through which crude oil, petroleum products, etc. flow. The pipe is formed in a circular tube shape.

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

[0013] Probe 1 generates eddy currents in the object 9 by forming a variable magnetic field. Also, Probe 1 detects the change in the eddy currents generated in the object 9 as an induced voltage. Specifically, Probe 1 induces eddy currents in the object 9 by the excitation coil 11 and detects the induced eddy currents with the detection coil 12. The excitation coil 11 induces eddy currents in the object 9 with the magnetic flux due to the excitation current. The detection coil 12 detects the eddy currents of the object 9. The excitation coil 11 is an example of an exciter, and the detection coil 12 is an example of a detector.

[0014] The excitation coil 11 can change the magnitude of the eddy currents induced in the object 9. That is, the excitation coil 11 can change the excitation intensity of the object 9. The "excitation intensity" can be evaluated by comparing the outputs when eddy currents are detected under the same detection conditions by the same detection coil 12. Specifically, the excitation coil 11 can change the magnitude of the eddy currents induced in the object 9 by changing the excitation current applied to the excitation coil 11.

[0015] The detection coil 12 is capable of changing the detection sensitivity of eddy currents. Specifically, the detection coil 12 includes a first detection coil 12A and a second detection coil 12B having a lower detection sensitivity of eddy currents than the first detection coil 12A. The "detection sensitivity" can be evaluated, for example, by comparing the outputs of the first detection coil 12A and the second detection coil 12B when eddy currents are induced in the object 9 under the same conditions by the excitation coil 11. That is, for the same eddy current, a larger induced electromotive force is generated in the first detection coil 12A than in the second detection coil 12B. The first detection coil 12A satisfies at least one of having a larger number of turns, a larger diameter, and a shorter distance to the object 9 than the second detection coil 12B. In this example, the first detection coil 12A has a larger number of turns, a larger diameter, and a shorter distance to the object 9 than the second detection coil 12B. Hereinafter, when the first detection coil 12A and the second detection coil 12B are not distinguished, they are simply referred to as the "detection coil 12". The first detection coil 12A is an example of a first detector, and the second detection coil 12B is an example of a second detector.

[0016] In the example of FIG. 1, the excitation coil 11, the first detection coil 12A, and the second detection coil 12B are arranged such that the axis of the excitation coil 11, the axis of the first detection coil 12A, and the axis of the second detection coil 12B are in a straight line. At this time, the first detection coil 12A is arranged closest to the object 9, and the excitation coil 11 is arranged farthest from the object 9. The probe 1 may have a plurality of sets of the excitation coil 11 and the detection coil 12 (including the first detection coil 12A and the second detection coil 12B). In FIG. 1, the probe 1 has two sets of the excitation coil 11 and the detection coil 12.

[0017] 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 formed in a U shape as a whole. More specifically, the core 13 is formed by laminating a plurality of generally U-shaped thin plates made of permalloy. The linear portion at one end of the core 13 is inserted into one set of the excitation coil 11 and the detection coil 12. The 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 two sets of the excitation coil 11 and the detection coil 12.

[0018] When a current is applied to the excitation coil 11, a magnetic field is formed in the direction of its axis. Currents are applied to one excitation coil 11 and the other excitation coil 11 so as to form magnetic fields that are opposite to each other in the direction of the axis. As a result, a magnetic field along the longitudinal direction of the core 13 is formed in the core 13. That is, when one end of the core 13 becomes the N pole, the other end of the core 13 becomes the S pole. Conversely, when one end of the core 13 becomes the S pole, the other end of the core 13 becomes the N 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. Specifically, most of the magnetic flux emitted from one excitation coil 11 exits in the direction of the axis of one excitation coil 11 and enters the object 9, passes through the object 9 in a substantially arc shape, and goes 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 eddy currents are generated in the object 9.

[0019] On the other hand, eddy currents generated in the portion of the object 9 near the detection coil 12 form magnetic flux that passes through the detection coil 12, that is, the first detection coil 12A and the second detection coil 12B. When the magnetic flux passing through the detection coil 12 changes, an induced electromotive force is generated in the detection coil 12. The detection coil 12 detects the eddy currents in the object 9 by detecting this induced electromotive force. That is, detecting the induced electromotive force by the detection coil 12 is also referred to as detecting eddy currents.

[0020] The processing device 6 uses the probe 1 to generate eddy currents in the object 9 and detect the generated eddy currents. The arithmetic device 8 obtains the thickness of the object 9 based on the duration of the eddy currents detected by the processing device 6 (specifically, the time until the eddy currents rapidly decay, which will be described in detail later).

[0021] The processing device 6 is arranged, for example, in proximity to the object 9. For example, the processing device 6 is installed on the object 9 via a spacer. The processing device 6 includes a transmitter 61, a receiver 62, a switch 63, a communicator 65, a processor 66, and a memory 67.

[0022] The transmitter 61 applies a pulsed excitation current to the excitation coil 11. The transmitter 61 includes 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 as an excitation current to the excitation coil 11. The transmission amplifier 61b is configured to be able to change the (maximum) current value of the excitation current.

[0023] The switch 63 switches the detection coil 12 connected to the receiver 62. Specifically, the switch 63 switches which of the first detection coil 12A and the second detection coil 12B is connected to the receiver 62. The switch 63 connects either the first detection coil 12A or the second detection coil 12B to the receiver 62 in response to a command from the processor 66.

[0024] The receiver 62 receives the induced electromotive force generated in the detection coil 12 in response to the eddy currents of the object 9. The receiver 62 includes at least a reception amplifier 62a that receives the voltage generated in the detection coil 12 and amplifies the voltage. The voltage of the one of the first detection coil 12A and the second detection coil 12B that is connected via the switch 63 is input to the receiver 62. The receiver 62 may further include a filter that performs a filtering process on the voltage signal.

[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 receiver 62 to the arithmetic unit 8.

[0026] The processor 66 controls the entire processing device 6. The processor 66 performs various arithmetic processes. 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 connects either the first detection coil 12A or the second detection coil 12B to the receiver 62 via the switch 63. The processor 66 changes the magnitude of the exciting current of the transmission amplifier 61b. The processor 66 causes the transmitter 61 to output an exciting current for a predetermined period. The processor 66 acquires a detection signal via the receiver 62 after the output of the exciting current stops. The processor 66 stores the detection signal from the receiver 62 in the memory 67, and appropriately transmits the detection signal stored in the memory 67 to the arithmetic unit 8 via the communicator 65.

[0028] The memory 67 stores programs and various data executed by the processor 66. For example, the memory 67 stores a control program. The memory 67 is formed of a non-volatile memory, an HDD (Hard Disc Drive), an SSD (Solid State Drive), or the like.

[0029] FIG. 2 is a block diagram showing the configuration of the control system of the processor 66 of the processing device 6. The processor 66 realizes various functions by reading and expanding a control program from the memory 67 into the memory. Specifically, the processor 66 functions as an excitation controller 71 that applies an excitation current to the excitation coil 11 to induce an eddy current in the object 9, a detection controller 72 that detects the eddy current of the object 9 via the detection coil 12, and a switching controller 73 that causes the switch 63 to switch the connection of the first detection coil 12A and the second detection coil 12B to the receiver 62.

[0030] The excitation controller 71 causes the transmitter 61 to apply an excitation current to the excitation coil 11. Specifically, the excitation controller 71 outputs a command to the pulse generator 61a and causes the pulse generator 61a to generate a pulse signal. As a result, the excitation current is applied from the transmission amplifier 61b to the excitation coil 11.

[0031] The detection controller 72 detects a voltage signal corresponding to the eddy current as the eddy current of the object 9. Specifically, the detection controller 72 detects a voltage signal corresponding to the induced electromotive force of the detection coil 12. More specifically, the detection controller 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 detection controller 72 detects the temporal change (i.e., the 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 detection controller 72 stores the detected eddy current, that is, the voltage signal, in the memory 67. Hereinafter, for the sake of convenience of explanation, the voltage signal detected by the detection controller 72 may be simply referred to as "eddy current". For example, the voltage signal corresponding to the eddy current stored in the memory 67 is also simply referred to as "eddy current".

[0032] In the memory 67, the eddy current detected by the detection controller 72 is stored.

[0033] The processor 66 transmits the eddy current of the object 9 stored in the memory 67 to the arithmetic unit 8 via the communicator 65.

[0034] The arithmetic unit 8 is formed by a computer or a computer network (so-called, cloud). As shown in FIG. 1, the arithmetic unit 8 has a communicator 81, a processor 82, and a memory 83.

[0035] The communicator 81 performs wireless communication with an external device. For example, the communicator 81 receives a signal or the like from the processing device 6.

[0036] The processor 82 controls the entire arithmetic unit 8. The processor 82 performs various arithmetic processes. 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.

[0037] The memory 83 stores programs executed by the processor 82 and various data. For example, the memory 83 stores a control program. The memory 83 is formed of a non-volatile memory, an HDD (Hard Disc Drive), an SSD (Solid State Drive), or the like. Further, the memory 83 stores a signal or the like transmitted from the processing device 6. Specifically, the memory 83 stores the eddy current of the object 9 acquired by the processing device 6.

[0038] FIG. 3 is a block diagram showing the configuration of the control system of the processor 82 of the arithmetic unit 8. The processor 82 realizes various functions by reading out and expanding the control program from the memory 83 into the memory. Specifically, the processor 82 functions as a calculator 86 that derives the thickness of the object 9. In this example, the processor 82 also functions as a setter 85 that sets the detection coil 12 connected to the receiver 62 and an estimator 87 that estimates the rate of material removal of the object 9. As an example of the utilization of the acquired thickness, the processor 82 estimates the rate of material removal of the object 9 from the thickness.

[0039] The setter 85 sets the excitation intensity and the detection sensitivity. In the memory 83, the magnitude of the excitation current is stored as the excitation intensity. In the memory 83, which of the first detection coil 12A and the second detection coil 12B is to be used is stored as the detection sensitivity. Although it will be described in detail later, for example, at the time of initial setting of the thickness measuring device 10, the user inputs to the arithmetic unit 8 the magnitude of the excitation current used for thickness measurement and the detection coil 12 according to the thickness of the object 9. The memory 83 stores the magnitude of the input excitation current and the detection coil 12. The setter 85 reads out the magnitude of the excitation current and the detection coil 12 from the memory 83 and transmits a command according thereto to the processing unit 6.

[0040] The magnitude of the excitation current set by the setter 85 can be changed continuously or discretely. In this example, the setter 85 can set a first excitation current and a second excitation current smaller than the first excitation current. That is, the user inputs either the first excitation current or the second excitation current to the arithmetic unit 8. The detection coil 12 set by the setter 85 is either the first detection coil 12A or the second detection coil 12B. The user inputs either the first detection coil 12A or the second detection coil 12B to the arithmetic unit 8.

[0041] The calculator 86 obtains the thickness of the object 9 based on the duration of the eddy current in the object 9. Although it will be described in detail later, the eddy current induced in the object 9 by the excitation coil 11 penetrates from the 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 until it rapidly attenuates. The duration of the eddy current in the object 9 is correlated with the thickness of the object 9. The calculator 86 obtains the duration of the eddy current (specifically, the voltage signal) detected by the processing unit 6. The calculator 86 obtains the thickness of the object 9 from the duration based on the correlation between the duration and the thickness.

[0042] Here, the relationship between the eddy current and the thickness of the object 9 will be described in detail. FIG. 4 is a graph showing the time change of the voltage signal V(t) corresponding to the eddy current. The graph in FIG. 4 is a double logarithmic graph. In FIG. 4, the voltage signal V0(t) indicated by the broken line is the voltage signal of the object 9 having a thickness d0, and the voltage signal V1(t) indicated by the solid line is the voltage signal of the object 9 having a thickness d1 thinner than d0.

[0043] As the eddy current penetrates the object 9, it decays. The eddy current gradually decays until it reaches the back surface from the surface of the object 9 (the surface facing the probe 1), and rapidly decays when it reaches the back surface. The voltage signal V(t) also shows the same change as the eddy current. That is, the transient change of the voltage signal V(t) corresponds to the transient change of the eddy current. The change of the voltage signal V(t) until the eddy current reaches the back surface of the object 9 is represented linearly on the double logarithmic graph. Thereafter, the voltage signal V(t) rapidly decays. The voltage signal V(t) that changes in this way is represented as follows in Equation (1).

[0044] [Number]

[0045] Here, A is a constant related to the magnitude of the voltage signal V(t), and is determined by the distance between the probe 1 and the object 9, the magnitude of the exciting current, the shape of the exciting coil 11, the shape of the detection coil 12, and the amplification factor of the receiving amplifier 62a, etc. n is a constant related to the degree of attenuation of the voltage signal V(t), and -n represents the slope of the voltage signal V(t) in the double logarithmic graph.

[0046] As can be seen from Equation (1), although the voltage signal V(t) gradually decays, it continues until the time τ, and rapidly decays at the time τ. For convenience of explanation, τ is referred to as the "continuous time". The continuous time τ is represented by the following Equation (2).

[0047] τ = σμd 2 ···(2)

[0048] Here, σ is the conductivity of the object 9, μ is the magnetic permeability of the object 9, and d is the thickness of the object 9.

[0049] That is, the duration τ changes depending on the thickness d of the object 9. Assuming that the conductivity σ and the 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, 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 obtained based on the following formula (3). The known thickness d0 and the duration τ0 are stored in the memory 83.

[0050]

Equation

[0051] For example, when comparing the voltage signals V0(t) and V1(t) in FIG. 4, the voltage signal V0(t) of the object 9 with the thickness d0 continues until the duration τ0. When the thickness d of the object 9 decreases from d0 to d1, the duration τ decreases from τ0 to τ1. Note that the change pattern of the linear portion of the voltage signal V(t) in the double logarithmic graph does not depend on the thickness d as can be seen from Equation (1), so it is substantially the same for the voltage signals V0(t) and V1(t). By substituting the thicknesses d0 and the durations τ0 and τ1 into Equation (3), the thickness d1 can be obtained.

[0052] The estimator 87 estimates the material removal rate of the object 9 from a plurality of corrected thicknesses. Further, the estimator 87 estimates the maintenance time of the object 9 based on the material removal rate. The material removal rate is the rate of decrease in thickness d with respect to the elapsed time t. The estimator 87 approximates the temporal change in the accumulated thickness d by a linear function and obtains its slope. That slope is the material removal rate. Further, the estimator 87 estimates the maintenance time of the object 9 based on the material removal rate. For example, the estimator 87 estimates the time when the thickness of the object 9 decreases to a predetermined lower limit value as the maintenance time. The estimator 87 estimates the time when the thickness d approximated by the linear function decreases to the lower limit value. The user can prepare in advance for the maintenance of the object 9 based on the estimated maintenance time.

[0053] 〈Thickness Measurement Process〉 Subsequently, the thickness measurement process by the thickness measurement system 100 will be described in more detail using a flowchart. FIG. 5 is a flowchart of thickness measurement.

[0054] In step S101, the setter 85 sets the excitation current of the excitation coil 11 and the detection coil 12. The setter 85 reads the magnitude of the excitation current and the detection coil 12 from the storage 83 and transmits a corresponding command to the processing device 6. The processor 66 of the processing device 6 changes the magnitude of the excitation current of the transmission amplifier 61b according to the command from the arithmetic unit 8. The processor 66 controls the switch 63 so that the detection coil corresponding to the command among the first detection coil 12A and the second detection coil 12B is connected to the receiver 62. In addition to the command according to the setting, the setter 85 transmits a command to execute the measurement to the processing device 6.

[0055] In step S102 of the flowchart of thickness measurement, the processor 66 determines whether a predetermined measurement period has arrived. The measurement period is the period for measuring the thickness of the object 9. If the measurement period has not arrived, the processor 66 repeats the determination in step S102 and waits for the arrival of the measurement period.

[0056] When the measurement period arrives, the excitation controller 71 applies an excitation current to the excitation coil 11 to excite it in step S103. The excitation coil 11 forms a magnetic field in the direction of the axis by applying the excitation current. One excitation coil 11 and the other excitation coil 11 form magnetic fields that are opposite to each other in the direction of the axis. 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.

[0057] Subsequently, in step S104, the excitation controller 71 stops the output of the excitation current, and the detection controller 72 detects the eddy current generated in the object 9. The detection controller 72 continues to detect the voltage signal for a predetermined period. In this way, the detection controller 72 detects the transient change (change over time) of the induced electromotive force of the detection coil 12, that is, the transient change of the eddy current generated in the object 9.

[0058] The processing device 6 transmits the eddy current, that is, the measurement data, to the arithmetic device 8. The arithmetic device 8 stores the received measurement data in the storage 83.

[0059] Subsequently, in step S105, the calculator 86 obtains the duration τ from the eddy current stored in the storage 83. Further, in step S106, the calculator 86 substitutes the duration τ into Equation (3) to obtain the thickness d. The obtained thickness d is stored in the storage 83.

[0060] The estimator 87 obtains the material removal rate based on a plurality of thicknesses d in step S107. Specifically, the estimator 87 obtains the reduction rate, that is, the reduction speed, of the accumulated plurality of thicknesses d. At this time, the estimator 87 obtains the material removal rate from all the accumulated thicknesses d.

[0061] Furthermore, in step S108, the estimator 87 estimates the maintenance time of the object 9 based on the material removal rate. The user can prepare in advance for the maintenance of the object 9 based on the output maintenance time.

[0062] After that, the processing in the current measurement cycle ends. The processor 66 performs the process of step S102 again. When the next measurement cycle arrives, data is acquired again, and the thickness of the object 9 is obtained. That is, the thickness measurement system 100 repeats the acquisition of measurement data and the derivation of thickness for each measurement cycle.

[0063] In addition, in FIG. 5, as a result of the processing device 6 and the arithmetic device 8 repeating their respective corresponding processes, as the thickness measurement system 100, the processes of the processing device 6 (steps S103, S104) and the processes of the arithmetic device 8 (steps S105, S106, S107) are periodically repeated as a series of processes. However, the periodic process of the processing device 6 (steps S103, S104) and the periodic process of the arithmetic device 8 (steps S105, S106, S107) may be performed in parallel.

[0064] Here, the influence of the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 in eddy current will be described. FIG. 6 is a graph showing the time change of the voltage signal V(t) corresponding to eddy current when the excitation intensity and the detection sensitivity are appropriate for the thickness of the object 9. The graph of FIG. 6 is a double logarithmic graph, similar to FIG. 4. While FIG. 4 is a schematic graph, FIG. 6 includes noise and the like and is closer to an actual voltage signal. The same applies to FIGS. 7-9 below.

[0065] As described above, the voltage signal V(t) decays as the eddy current penetrates the object 9. 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. When the eddy current reaches the back surface, the voltage signal V(t) decays rapidly. The thickness of the object 9 is obtained from the duration τ during which the voltage signal V(t) begins to decay rapidly.

[0066] When the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 are appropriate for the thickness of the object 9, a rapid decay of the voltage signal V(t) appears clearly, and the duration τ and thus the thickness of the object 9 are obtained appropriately.

[0067] As the object 9 becomes thicker, the time it takes for the eddy current to reach the back surface of the object 9 becomes longer, and consequently the duration τ becomes longer. FIG. 7 is a graph showing the time variation of the voltage signal V(t) corresponding to the eddy current when the thickness of the object 9 is too thick with respect to the excitation intensity and the detection sensitivity. When the object 9 is thick, the time until the voltage signal V(t) rapidly decays becomes longer. However, if the voltage signal V(t) gradually decays without a rapid decay occurring, the influence of noise becomes large. As a result, it becomes difficult to discriminate the rapid decay of the voltage signal V(t).

[0068] For a thick object 9, if at least one of the excitation intensity and the detection sensitivity is increased, even when the eddy current reaches the back surface of the object 9, the voltage signal V(t) is sufficiently larger than the noise. FIG. 8 is a graph showing the time variation of the voltage signal V(t) corresponding to the eddy current when the excitation intensity or the detection sensitivity is increased for the thick object 9. Compared with the case where the excitation intensity or the detection sensitivity is low, the change in the voltage signal V(t) becomes prominent. Before the voltage signal V(t) is affected by noise to a small extent, a rapid decay of the voltage signal V(t) appears. As a result, the duration τ and thus the thickness of the object 9 can be appropriately determined.

[0069] However, when measuring the eddy current of a thinner object 9 with the same excitation intensity and detection sensitivity as in FIG. 8, the voltage signal V(t) becomes too large. FIG. 9 is a graph showing the time variation of the voltage signal V(t) corresponding to the eddy current when the excitation intensity and the detection sensitivity are the same as in FIG. 8 for an object 9 thinner than FIG. 8. The voltage signal V(t) rapidly decays immediately, and the linear decay of the voltage signal V(t) does not appear. As a result, it becomes difficult to discriminate the duration τ.

[0070] Thus, there are appropriate excitation intensities and detection sensitivities according to the thickness of the object 9. The thickness measurement system 100 is configured to be able to change at least one of the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12. At least one of the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 can be changed according to the thickness of the object 9. Thereby, the measurable thickness range in thickness measurement can be widened. That is, even without changing the probe 1, the processing device 6, or the arithmetic device 8, the thickness measurement of objects 9 with various thicknesses can be realized.

[0071] Specifically, in the storage 83, the magnitude of the excitation current used for thickness measurement and the detection coil 12 are stored. For example, the user inputs the magnitude of the excitation current used for thickness measurement and the detection coil 12 to the arithmetic device 8 according to the thickness of the object 9 (i.e., the initial thickness) at the initial setting of the thickness measurement device 10. Specifically, the user inputs the magnitude of the excitation current and the detection coil 12 such that the excitation intensity or the detection sensitivity increases as the thickness of the object 9 increases. As a result, the setter 85 sets the magnitude of the excitation current and the detection coil 12 such that the excitation intensity or the detection sensitivity increases as the thickness of the object 9 increases.

[0072] FIG. 10 is a table showing an example of the combination of the thickness of the object 9, the excitation current, and the detection coil 12. For example, when the thickness of the object 9 is in the first range of the first thickness D1 or less, the second excitation current A2 and the second detection coil 12B are set. When the thickness of the object 9 is in the second range greater than the first thickness D1 and less than or equal to the second thickness D2 (>D1), the first excitation current A1 and the second detection coil 12B are set. When the thickness of the object 9 is in the third range greater than the second thickness D2, the first excitation current A1 and the first detection coil 12A are set. In the second range, the second excitation current A2 and the first detection coil 12A may be set. Alternatively, the second range may be further divided into a range where the first excitation current A1 and the second detection coil 12B are set and a range where the second excitation current A2 and the first detection coil 12A are set.

[0073] Still, instead of the magnitude of the excitation current and the detection coil 12, the user may input the thickness of the object 9 to the arithmetic unit 8. In the memory 83, a correspondence table of the thickness of the object 9, the excitation current, and the detection coil 12 as shown in FIG. 10 is stored. The setter 85 sets the magnitude of the excitation current and the detection coil 12 in accordance with the input thickness of the object 9 with reference to the correspondence table in the memory 83.

[0074] In this way, an appropriate magnitude of the excitation current and the detection coil 12 corresponding to the thickness of the object 9 are set. As a result, the thicknesses of objects 9 with various thicknesses are appropriately measured. As a result, the measurement range of the thickness in the thickness measurement of the object 9 is expanded.

[0075] In such a thickness measurement system 100, the probe 1 includes a first detection coil 12A and a second detection coil 12B having different detection sensitivities from each other. Therefore, by switching the detection coil 12 used for thickness measurement between the first detection coil 12A and the second detection coil 12B, the detection sensitivity of the detection coil 12 can be easily changed.

[0076] Furthermore, the first detection coil 12A and the second detection coil 12B have different detection sensitivities from each other by at least making the distances to the object 9 different. Therefore, the first detection coil 12A and the second detection coil 12B can be arranged substantially coaxially. By arranging the first detection coil 12A and the second detection coil 12B substantially coaxially, the first detection coil 12A and the second detection coil 12B can be arranged so as to go around the outer periphery of the same core 13. As a result, the first detection coil 12A and the second detection coil 12B can be compactly arranged in the probe 1.

[0077] Furthermore, in addition to the detection sensitivity of the detection coil 12, the excitation intensity can be changed. By combining the change in the detection sensitivity and the change in the excitation intensity, the measurement range of the thickness of the object 9 can be further expanded.

[0078] The change in the excitation intensity is realized by changing the excitation current. Thus, the excitation intensity can be easily changed as compared with the case of changing the physical configuration of the excitation coil 11.

[0079] Subsequently, a modification of the thickness measurement system 100 according to Modification 1 will be described.

[0080] 〈Modification 1〉 The thickness measurement system 100 according to Modification 1 changes the detection sensitivity of the detection coil 12 based on the thickness of the object 9 derived by the derivator 86. The thickness of the object 9 becomes thinner over time, and there may be a case where the thickness falls below the applicable range of the already set detection sensitivity. The thickness measurement system 100 according to Modification 1 can monitor a longer change over time of the thickness of the object 9 by lowering the detection sensitivity of the detection coil 12 in response to the decrease in the thickness of the object 9. In this example, the thickness measurement system 100 changes the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 based on the thickness of the object 9 derived by the derivator 86.

[0081] Specifically, as described above, the setter 85 sets the magnitude of the excitation current used for thickness measurement and the detection coil 12 according to the thickness of the object 9 (i.e., the initial thickness) at the time of initial setting of the thickness measuring device 10. Thickness measurement is performed by the set magnitude of the excitation current and the detection coil 12. The derivator 86 outputs the derived thickness of the object 9 to the setter 85. The setter 85 changes the magnitude of the excitation current of the excitation coil 11 and the detection coil 12 based on the derived thickness of the object 9. Specifically, when the derived thickness falls below a predetermined threshold value, the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 are changed to be lower.

[0082] The thickness measurement process by the thickness measurement system 100 according to Modification 1 will be described in more detail using a flowchart. FIG. 11 is a flowchart of the thickness measurement according to Modification 1.

[0083] For example, in the memory 83, a correspondence table of the thickness of the object 9, the excitation current, and the detection coil 12 as shown in FIG. 10 is stored. Basically, the processing from step S101 to step S106 is as described above. Here, it is assumed that in step S101, the first excitation current A1 and the first detection coil 12A in the third range are set.

[0084] After the thickness of the object 9 is derived in step S106, in step S109, it is determined whether the derived thickness is smaller than the threshold value. For example, the setter 85 determines whether the derived thickness of the object 9 is smaller than the second thickness D2 as the threshold value.

[0085] When the derived thickness is equal to or greater than the threshold value, the settings of the excitation intensity of the excitation coil 11 and the detection sensitivity of the detection coil 12 are maintained. The material removal rate is obtained in step S107, and the maintenance time is estimated in step S108. The processing of steps S107 and S108 is as described above.

[0086] On the other hand, when the derived thickness is smaller than the threshold value, in step S110, the setter 85 changes the setting of the excitation intensity of the excitation coil 11 or the detection sensitivity of the detection coil 12. For example, when the thickness of the object 9 decreases from the third range to the second range, the setter 85 changes the detection coil 12 from the first detection coil 12A to the second detection coil 12B while maintaining the excitation current at the first excitation current A1. As a result, the detection sensitivity of the detection coil 12 is reduced, and the thickness of the thin object 9 can be appropriately measured. After the setting is changed, the processing of steps S107 and S108 is performed.

[0087] In step S109 after the thickness of the object 9 has decreased to the second range, the first thickness D1 is adopted as the threshold value. That is, the setter 85 determines whether the derived thickness is smaller than the first thickness D1 as the threshold value. When the derived thickness is smaller than the first thickness D1, the setter 85 changes the exciting current from the first exciting current A1 to the second exciting current A2 in step S110. The detection coil 12 remains the second detection coil 12B. Thereby, the exciting intensity of the exciting coil 11 is reduced, and the thickness of the thinner object 9 can be appropriately measured.

[0088] In this way, while the thickness measurement is continued, it is monitored whether the thickness of the object 9 has fallen outside the measurement range of the current setting. When the thickness of the object 9 is below the measurement range of the current setting, the setting of the exciting intensity of the exciting coil 11 or the detection sensitivity of the detection coil 12 is changed to be lower. Thereby, even if the object 9 becomes thinner, the thickness measurement is appropriately executed. As a result, the measurement range of the thickness in the thickness measurement of the object 9 is expanded.

[0089] <Example of Variation 2> Subsequently, a variation of the thickness measurement system 100 according to the second variation will be described. FIG. 12 is a block diagram of the thickness measurement system 100 according to the second variation.

[0090] The processing device 206 according to the second variation does not have the switch 63 and has the first receiver 62A and the second receiver 62B as receivers. Each of the first receiver 62A and the second receiver 62B has a receiving amplifier 62a. The first detection coil 12A is connected to the first receiver 62A. The first receiver 62A receives the induced electromotive force generated in the first detection coil 12A in response to the eddy current of the object 9. The second detection coil 12B is connected to the second receiver 62B. The second receiver 62B receives the induced electromotive force generated in the second detection coil 12B in response to the eddy current of the object 9.

[0091] When detecting the eddy current generated in the object 9, the probe 1 detects the eddy current using both the first detection coil 12A and the second detection coil 12B. That is, due to the eddy current generated in the object 9, magnetic fluxes passing through both the first detection coil 12A and the second detection coil 12B are formed. As a result, induced electromotive forces are generated in both the first detection coil 12A and the second detection coil 12B. Each of the first detection coil 12A and the second detection coil 12B detects the eddy current of the object 9 by detecting the induced electromotive force. In this way, for one excitation by the excitation coil 11, the processing device 6 acquires two types of induced electromotive forces, that is, voltage signals, by the first detection coil 12A and the second detection coil 12B. Since the detection sensitivities of the first detection coil 12A and the second detection coil 12B are different from each other, even when detecting the same eddy current, the induced electromotive forces of the first detection coil 12A and the second detection coil 12B are different from each other. In this way, the probe 1 does not use the first detection coil 12A and the second detection coil 12B alternatively, but detects the eddy current using both of them to obtain two types of voltage signals.

[0092] The processing device 206 acquires two types of voltage signals of the first detection coil 12A and the second detection coil 12B via the first receiver 62A and the second receiver 62B, and transmits the two types of voltage signals to the arithmetic device 8.

[0093] The arithmetic device 8 performs thickness estimation and the like using the voltage signal of the one set by the setter 85 among the first detection coil 12A and the second detection coil 12B. That is, the arithmetic device 8 substantially switches the detection coil 12 used for thickness measurement between the first detection coil 12A and the second detection coil 12B. Thereby, the thickness measurement range in the thickness measurement of the object 9 is expanded.

[0094] <Modified Example 3> Next, a modification of the thickness measurement system 100 according to Modification 3 will be described. The thickness measurement system 100 according to Modification 3 further includes a holder 2 that changes the distance from the detection coil 12 to the object 9. FIG. 13 is a schematic diagram of the probe 301 according to Modification 3 when it is located at the first position. FIG. 14 is a schematic diagram of the probe 301 according to Modification 3 when it is located at the second position.

[0095] Specifically, the probe 301 according to Modification 3 has one type of excitation coil 11 and one type of detection coil 12. In this example, it does not have two types of detection coils 12 such as the first detection coil 12A and the second detection coil 12B like the aforementioned probe 1. Note that the probe 301 has two sets of excitation coils 11 and detection coils 12, similar to the probe 1.

[0096] The probe 301 has a casing 16 that houses the excitation coil 11 and the detection coil 12. The casing 16 also houses the core 13. The casing 16 is formed in a cylindrical shape. The axis of the casing 16 is substantially parallel to the axis of the excitation coil 11 and the axis of the detection coil 12. The probe 301 has a protrusion 317 on its outer peripheral surface.

[0097] For example, the holder 2 holds the probe 301 in such a way that the distance between the probe 301 and the object 9 can be changed. The holder 2 is an example of an adjustment mechanism. The holder 2 is attached to the outer peripheral surface of the object 9. The holder 2 is formed in a cylindrical shape. The axis of the holder 2 intersects, for example, is orthogonal to the measurement surface of the object 9, specifically the object 9. The holder 2 houses the probe 301 in the holder 2 so that it can move in the axial direction of the holder 2.

[0098] The holder 2 has a guide groove 21 that guides the protrusion 317 of the probe 301. The guide groove 21 includes a main groove 22 that extends substantially parallel to the axis of the holder 2, a first branch groove 23 that extends from the main groove 22 in the circumferential direction centered on the axis of the holder 2, and a second branch groove 24 that is arranged at a position different from the first branch groove 23 in the axial direction of the holder 2 and extends from the main groove 22 in the circumferential direction centered on the axis of the holder 2. The first branch groove 23 is arranged closer to the object 9 in the axial direction of the holder 2 than the second branch groove 24.

[0099] The probe 301 is housed in the holder 2 with the protrusion 317 disposed in the guide groove 21. The axis of the probe 301 and the axis of the holder 2 are coaxially arranged. By moving the protrusion 317 along the main groove 22, the probe 301 moves in the axial direction of the holder 2 with respect to the holder 2. That is, the probe 301 is guided by the main groove 22 so as to move in the axial direction of the holder 2 with respect to the holder 2. As shown in FIG. 13, by entering the protrusion 317 from the main groove 22 into the first branch groove 23, the position of the probe 301 in the axial direction of the holder 2 is fixed. This position is referred to as the first position. As shown in FIG. 14, by entering the protrusion 317 from the main groove 22 into the second branch groove 24, the position of the probe 301 in the axial direction of the holder 2 is fixed. This position is referred to as the second position. The probe 301 at the first position is closer to the object 9 than the probe 301 at the second position.

[0100] Thus, by changing the position of the probe 301 in the axial direction of the holder 2, the distances from each of the excitation coil 11 and the detection coil 12 to the object 9 change. The shorter the distance from the excitation coil 11 to the object 9, the higher the excitation intensity. The shorter the distance from the detection coil 12 to the object 9, the higher the detection sensitivity. By changing the position of the probe 301 in the axial direction of the holder 2, the excitation intensity and the detection sensitivity are adjusted. For example, when the thickness of the object 9 is relatively thick, the probe 301 is disposed at the first position. Thereby, the excitation intensity of the excitation coil 11 becomes relatively high, and the detection sensitivity of the detection coil 12 becomes relatively high. On the other hand, when the thickness of the object 9 is relatively thin, the probe 301 is disposed at the second position. Thereby, the excitation intensity of the excitation coil 11 becomes relatively low, and the detection sensitivity of the detection coil 12 becomes relatively low.

[0101] In short, in the thickness measurement system 100 according to the third modification, the detection sensitivity of the detection coil 12 is changed by changing the distance from the detection coil 12 to the object 9 by the holder 2. Similarly, the excitation intensity of the excitation coil 11 is changed by changing the distance from the excitation coil 11 to the object 9 by the holder 2. The distances from the excitation coil 11 and the detection coil 12 to the object 9 can be adjusted according to the thickness of the object 9. Thereby, the thicknesses of objects 9 with various thicknesses are appropriately measured. As a result, the measurement range of the thickness in the thickness measurement of the object 9 is expanded.

[0102] Note that the holder 2 may be able to change the position of the probe 301 in the axial direction of the holder 2 to three or more positions. Alternatively, the holder 2 may be able to continuously change the position of the probe 301 in the axial direction of the holder 2. For example, a female screw may be formed on the inner peripheral surface of the holder 2, and a male screw that engages with the female screw of the holder 2 may be formed on the outer peripheral surface of the probe 301. By adjusting the amount of screwing of the probe 301 into the holder 2, the position of the probe 301 in the axial direction of the holder 2 is continuously changed.

[0103] <Modification 4> Next, a modification of the thickness measurement system 100 according to Modification 4 will be described. FIG. 15 is a schematic diagram of the probe 401 according to Modification 4. The probe 401 according to Modification 4 includes a plurality of exciting coils 11.

[0104] Specifically, the exciting coil 11 includes a first exciting coil 11A and a second exciting coil 11B whose eddy current magnitude induced in the object 9, that is, the exciting intensity, is smaller than that of the first exciting coil 11A. That is, the induced electromotive force of the detection coil 12 becomes larger when the eddy current is induced by the first exciting coil 11A than when the eddy current is induced by the second exciting coil 11B. The first exciting coil 11A satisfies at least one of having a larger number of turns and a shorter distance to the object 9 than the second exciting coil 11B. In this example, the first exciting coil 11A has a larger number of turns and a shorter distance to the object 9 than the second exciting coil 11B. Hereinafter, when the first exciting coil 11A and the second exciting coil 11B are not distinguished, they are simply referred to as the "exciting coil 11".

[0105] In the example of FIG. 15, the first exciting coil 11A, the second exciting coil 11B, the first detection coil 12A, and the second detection coil 12B are arranged such that the axes of the first exciting coil 11A, the second exciting coil 11B, the first detection coil 12A, and the second detection coil 12B are in a straight line. At this time, the first detection coil 12A is arranged closest to the object 9, and the second exciting coil 11B is arranged farthest from the object 9. The probe 401 may have a plurality of sets of exciting coils 11 (including the first exciting coil 11A and the second exciting coil 11B) and detection coils 12 (including the first detection coil 12A and the second detection coil 12B). In FIG. 15, the probe 401 has two sets of exciting coils 11 and detection coils 12.

[0106] 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 formed in a U shape as a whole. The linear portion at one end of the core 13 is inserted into one set of the excitation coil 11 and the detection coil 12. The 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.

[0107] The processing device 406 according to the fourth modification includes a transmitter 61, a receiver 62, a switch 63, a switch 64, a communicator 65, a processor 66, and a memory 67.

[0108] The switch 64 switches the excitation coil 11 connected to the transmitter 61. Specifically, the switch 64 switches which of the first excitation coil 11A and the second excitation coil 11B is connected to the transmitter 61. The switch 64 connects one of the first excitation coil 11A and the second excitation coil 11B to the transmitter 61 in response to a command from the processor 66.

[0109] The transmitter 61 applies a pulsed excitation current to the one connected via the switch 64 among the first excitation coil 11A and the second excitation coil 11B.

[0110] In the thickness measurement system 100 according to Modification 4, instead of changing the excitation current of the excitation coil 11 described above, or in addition to changing the excitation current, the excitation coil 11 to be used is switched between a first excitation coil 11A and a second excitation coil 11B. For example, at the time of initial setting of the thickness measurement device 10, the user inputs the excitation coil 11 and the detection coil 12 used for thickness measurement to the arithmetic unit 8 according to the thickness of the object 9 (that is, the initial thickness). Specifically, the user inputs the excitation coil 11 and the detection coil 12 so that the excitation intensity or the detection sensitivity increases as the thickness of the object 9 increases. The input excitation coil 11 and detection coil 12 are stored in the storage 83. As a result, the setter 85 sets the magnitude of the excitation current and the detection coil 12 so that the excitation intensity or the detection sensitivity increases as the thickness of the object 9 increases.

[0111] In addition, instead of the excitation coil 11 and the detection coil 12, the user may input the thickness of the object 9 to the arithmetic unit 8. The storage 83 stores a correspondence table of the thickness of the object 9, the excitation coil 11, and the detection coil 12. The setter 85 sets the excitation coil 11 and the detection coil 12 by comparing the input thickness of the object 9 with the correspondence table in the storage 83.

[0112] In addition, the setter 85 may switch the excitation coil 11 and the detection coil 12 based on the thickness of the object 9 derived by the derivator 86.

[0113] In this way, appropriate excitation coil 11 and detection coil 12 corresponding to the thickness of the object 9 are set. As a result, the thicknesses of objects 9 with various thicknesses are appropriately measured. As a result, the measurement range of the thickness in the thickness measurement of the object 9 is expanded.

[0114] 《Other Embodiments》 As described above, the embodiments have been described as examples of the technologies disclosed in the present application. However, the technologies in the present disclosure are not limited thereto, and are also applicable to embodiments in which changes, replacements, additions, omissions, etc. are made as appropriate. Further, it is also possible to form a new embodiment by combining the respective components described in the above embodiments. Further, among the components described in the accompanying drawings and the detailed description, there may be included not only the components essential for solving the problems, but also the components not essential for solving the problems for the purpose of exemplifying the technologies. Therefore, just because those non-essential components are described in the accompanying drawings and the detailed description, it should not be immediately determined that those non-essential components are essential.

[0115] The above-described embodiment may have the following configuration. 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 integrally configured. That is, one device may have the functions of the processing device 6 and the arithmetic device 8. Further, the processing device 6 and the arithmetic device 8 may be connected by wire. Further, a plurality of processing devices 6 may be connected to one arithmetic device 8. Further, the arithmetic device 8 may transmit data regarding the calculated thickness to another device connected wirelessly or by wire.

[0116] The probe 1 is not limited to the above-described configuration. For example, although the probe 1 includes two sets of excitation coils 11 and detection coils 12, the excitation coils 11 and the detection coils 12 may be one set, or may be three sets or more. The excitation coil 11 and the detection coil 12 do not have to be arranged such that their respective axial centers are in a straight line. When the excitation coil 11 and the detection coil 12 are arranged such that their respective axial centers are in a straight line, the excitation coil 11 may be arranged closer to the object 9 than the detection coil 12. Further, the probe 1 does not have to include the core 13.

[0117] Furthermore, the detector of the probe 1 is not limited to the detection coil 12. The detector may be any device that can directly or indirectly detect the eddy current of the object 9, and for example, it may be a Hall element. When the detector is a Hall element, the detector includes a first Hall element and a second Hall element with a lower eddy current detection sensitivity than the first Hall element. Specifically, the sensitivity performance of the second Hall element itself is lower than that of the first Hall element itself. In addition to or instead of the sensitivity performance, the distance from the second Hall element to the object 9 is longer than the distance from the first Hall element to the object 9.

[0118] The object is not limited to a circular pipe. The pipe as the object may be a square pipe instead of a circular pipe. The object may be a plate instead of an object with a closed cross-section like a pipe.

[0119] Furthermore, the thickness measurement by the thickness measurement device 10 is only an example. Since there are various PEC thickness measurement methods, any measurement method can be adopted.

[0120] The estimation of the material removal rate and the maintenance time is only an example of the utilization of the thickness. The thickness measurement device 10 only calculates the thickness and does not have to calculate the material removal rate or the like. The thickness may be utilized for other purposes than the material removal rate.

[0121] The flowchart is only an example. The steps in the flowchart may be appropriately changed, replaced, added, omitted, etc. Also, the order of the steps in the flowchart may be changed, or serial processing may be performed in parallel. For example, the derivation of the material removal rate in step S107 and the estimation of the maintenance time in step S108 may be omitted.

[0122] The functions realized by the components described in this specification may be implemented in circuitry or processing circuitry including a general-purpose processor, a specific-purpose processor, an integrated circuit, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to realize the described functions. The processor includes transistors and other circuits and is regarded as circuitry or processing circuitry. The processor may be a programmed processor that executes a program stored in a memory.

[0123] In this specification, circuitry, units, and means are hardware programmed to realize the described functions or hardware that executes them. The hardware may be any hardware disclosed in this specification or any hardware known to be programmed or execute to realize the described functions.

[0124] When the hardware is a processor regarded as a type of circuitry, the circuit, means, or unit is a combination of hardware and software used to configure the hardware and / or the processor.

[0125] [Aspect] The above embodiments are specific examples of the following aspects.

[0126] (Aspect 1) The thickness measurement system 100 includes an excitation coil 11 (exciter) that induces eddy currents in the object 9, a detection coil 12 (detector) that detects the eddy currents of the object 9, and a calculator 86 that obtains the thickness of the object 9 based on the eddy currents detected via the detection coil 12, and the detection sensitivity of the detection coil 12 can be changed.

[0127] According to this configuration, the detection sensitivity of the detection coil 12 can be changed to a detection sensitivity suitable for the thickness of the object 9. That is, by increasing the detection sensitivity of the detection coil 12, thickness measurement based on eddy current can be appropriately performed on a relatively thick object 9. On the other hand, by decreasing the detection sensitivity of the detection coil 12, thickness measurement based on eddy current can be appropriately performed on a relatively thin object 9. As a result, thickness measurement of objects 9 with various thicknesses can be realized.

[0128] (Aspect 2) In the thickness measurement system 100 described in Aspect 1, the detection coil 12 includes a first detection coil 12A and a second detection coil 12B having a lower detection sensitivity for eddy current than the first detection coil 12A.

[0129] According to this configuration, the detection sensitivity of the detection coil 12 can be changed by switching the detection coil 12 used for detecting eddy current between the first detection coil 12A and the second detection coil 12B.

[0130] (Aspect 3) In the thickness measurement system 100 described in Aspect 1 or Aspect 2, the first detection coil 12A and the second detection coil 12B are each a coil, and the first detection coil 12A satisfies at least one of having a larger number of turns, a larger diameter, and a shorter distance to the object 9 than the second detection coil 12B.

[0131] According to this configuration, the first detection coil 12A having a detection sensitivity different from that of the second detection coil 12B can be easily realized.

[0132] (Aspect 4) The thickness measurement system 100 described in any one of Aspects 1 to 3 further includes a holder 2 (adjustment mechanism) for changing the distance from the detection coil 12 to the object 9, and the detection sensitivity of the detection coil 12 is changed by changing the distance from the detection coil 12 to the object 9 by the holder 2.

[0133] According to this configuration, even if a plurality of detection coils 12 are not provided, that is, even if it is the same detection coil 12, the detection sensitivity of the detection coil 12 can be changed by changing the distance between the detection coil 12 and the object 9 by the holder 2.

[0134] However, the holder 2 does not exclude a plurality of detection coils 12. The holder 2 may change the distance to the object 9 of a plurality of detection coils 12 having different detection sensitivities.

[0135] (Aspect 5) In the thickness measurement system 100 according to any one of Aspects 1 to 4, the exciting coil 11 is capable of changing the magnitude of the eddy current induced in the object 9.

[0136] According to this configuration, the exciting intensity of the exciting coil 11 can be changed to an exciting intensity suitable for the thickness of the object 9. That is, by increasing the exciting intensity of the exciting coil 11, thickness measurement based on eddy current can be appropriately performed on a relatively thick object 9. On the other hand, by decreasing the exciting intensity of the exciting coil 11, thickness measurement based on eddy current can be appropriately performed on a relatively thin object 9. In addition to the detection sensitivity of the detection coil 12, by changing the exciting intensity of the exciting coil 11, thickness measurement of objects 9 with a wider range of thicknesses can be realized.

[0137] (Aspect 6) In the thickness measurement system 100 according to any one of Aspects 1 to 5, the exciting coil 11 includes a first exciting coil 11A and a second exciting coil 11B whose magnitude of the eddy current induced in the object 9 is smaller than that of the first exciting coil 11A.

[0138] According to this configuration, the exciting intensity of the exciting coil 11 can be changed by switching the exciting coil 11 used for inducing the eddy current between the first exciting coil 11A and the second exciting coil 11B.

[0139] (Aspect 7) In the thickness measurement system 100 according to any one of Aspects 1 to 6, the first excitation coil 11A and the second excitation coil 11B are each a coil, and the first excitation coil 11A satisfies at least one of having a larger number of turns and a shorter distance to the object 9 than the second excitation coil 11B.

[0140] According to this configuration, the first excitation coil 11A having an excitation intensity different from that of the second excitation coil 11B can be easily realized.

[0141] (Aspect 8) In the thickness measurement system 100 according to any one of Aspects 1 to 7, the excitation coil 11 is a coil, and the magnitude of the eddy current induced in the object 9 can be changed by changing the excitation current applied to the excitation coil 11.

[0142] According to this configuration, the excitation intensity can be changed by electrical adjustment without changing the physical configuration of the excitation coil 11.

[0143] (Aspect 9) The probe 1, 301, 401 includes an excitation coil 11 that induces an eddy current in the object 9 and a detection coil 12 that detects the eddy current of the object 9, and the detection sensitivity of the detection coil 12 can be changed.

[0144] According to this configuration, the detection sensitivity of the detection coil 12 can be changed to a detection sensitivity suitable for the thickness of the object 9. That is, by increasing the detection sensitivity of the detection coil 12, thickness measurement based on eddy current can be appropriately performed on a relatively thick object 9. On the other hand, by decreasing the detection sensitivity of the detection coil 12, thickness measurement based on eddy current can be appropriately performed on a relatively thin object 9. As a result, thickness measurement of objects 9 with various thicknesses can be realized.

Explanation of Reference Numerals

[0145] 100 Thickness measurement system 1, 301, 401 Probe 11 Excitation coil (exciter) 12 Detection coil (detector) 12A First detection coil (first detector) 12B Second detection coil (second detector) 2 Holder (adjusting mechanism) 86 Exporter

Claims

1. An exciter for inducing eddy currents in an object, a detector for detecting the eddy currents of the object, and a calculator for obtaining the thickness of the object based on the eddy currents detected via the detector, wherein the detector is capable of changing the detection sensitivity of the eddy currents.

2. The thickness measurement system according to Claim 1, wherein the detector includes a first detector and a second detector having a lower detection sensitivity for eddy currents than the first detector.

3. The thickness measurement system according to Claim 2, wherein the first detector and the second detector are each a coil, and the coil of the first detector satisfies at least one of having a larger number of turns, a larger diameter, and a shorter distance to the object than the coil of the second detector.

4. The thickness measurement system according to Claim 1, further comprising an adjustment mechanism for changing the distance from the detector to the object, wherein the detection sensitivity of the detector is changed by changing the distance from the detector to the object by the adjustment mechanism.

5. The thickness measurement system according to Claim 1, wherein the exciter is capable of changing the magnitude of the eddy currents induced in the object.

6. The thickness measurement system according to Claim 5, wherein the exciter includes a first exciter and a second exciter having a smaller magnitude of eddy currents induced in the object than the first exciter.

7. The thickness measurement system according to Claim 6, wherein the first exciter and the second exciter are each a coil, and the coil of the first exciter satisfies at least one of having a larger number of turns and a shorter distance to the object than the coil of the second exciter.

8. The thickness measurement system according to Claim 5, wherein the exciter is a coil, and the magnitude of the eddy currents induced in the object can be changed by changing the excitation current applied to the coil.

9. An exciter for inducing eddy currents in an object, and a detector for detecting the eddy currents of the object, wherein the detector is a probe capable of changing the detection sensitivity of the eddy currents.

Images