JP2013205023A - Electromagnetic induction inspection device and inspection method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which a Patent Document 1 discloses that, for extracting a weak eddy current signal from an inside of an inspected body contained in a detection signal of a detection coil, a giant eddy current from a surface layer part is cancelled by a sinusoidal signal with an adjusted amplitude and phase; however, according to a method illustrated in an embodiment, a masking signal is cancelled by adding a signal with a manually adjusted amplitude and phase of a signal exciting an excitation coil to the detection signal, and a manual operation exists, resulting in obstruction of an automatic measurement.SOLUTION: An electromagnetic induction inspection device is configured to prepare: a first DA converter that supplies a driving alternate current signal to a driving coil; and an AD converter that converts a sum signal of an output signal of a detection coil and an output of a second DA converter. The electromagnetic induction inspection device causes the first DA converter to output the driving alternate current signal periodically and causes a signal reversing polarity of an alternate current collected by the second DA converter in a state of the second DA converter being stopped to be output from the second AD converter in synchronization with a period upon collection. Thereby, a signal cancellation of a front layer part described in the Patent Document 1 is automatically achieved.

Description

  The present invention relates to an apparatus and method using electromagnetic induction for flaw detection of a subject by applying an alternating magnetic field to a conductive subject and detecting a magnetic field due to an eddy current generated in the subject.

  Patent Document 1 proposes a nondestructive inspection method in which an alternating magnetic field is applied to a subject to detect eddy currents. In eddy current flaw detection, the output of the magnetic field due to the eddy current flowing on the surface of the subject is strong, and the output of the magnetic field due to the eddy current inside the subject is extremely weak, so the signal (alternating current signal) detected by the detection coil is There is a reality that the minute output inside the specimen is masked.

  In contrast to the above reality, a circuit for generating a sine wave signal having substantially the same amplitude and opposite phase to the detection signal of the detection coil is provided, and the sum of the output of the anti-phase sine wave generation circuit and the detection signal of the detection coil is output. Or a circuit that generates a sine wave signal having substantially the same phase and amplitude as the detection signal of the detection coil, and outputs a difference between the output of the same phase sine wave generation circuit and the detection signal of the detection coil A circuit means for detecting the residual signal of the sum signal output or the difference signal output, canceling the detection output of the subject surface layer due to the skin effect, and detecting the output of the subject surface layer It is an invention to detect the output of the inside or back surface of the subject that has been masked.

Japanese Patent No. 4756409 Japanese Patent No. 3896489 Japanese Patent No. 3266128 JP 2010-48552 A Japanese Patent No. 3753499

  In Patent Document 1, in order to extract a weak eddy current signal from the inside of the subject from a huge eddy current in the subject surface layer included in the detection signal of the detection coil, a sine in which the amplitude and phase of the detection signal are adjusted. The wave signal is canceled by reversing the polarity and taking the sum. However, the method shown in the embodiment generates a signal obtained by manually adjusting the amplitude and phase of the signal for exciting the exciting coil from the exciting signal, and manual operation is involved, and measurement automation is performed. It is a hindrance.

  A first DA converter for supplying a drive AC signal to the drive coil and an AD converter for converting the sum signal of the output signal of the detection coil and the output of the second DA converter are prepared.

  In a state where the driving AC signal is periodically output to the first DA converter and the second DA converter is stopped, data of an interval that is an integral multiple of the period of the AC signal is collected by the AD converter. After removing noise from the collected data, the masking signal of Patent Document 1 is automatically generated and executed by outputting the signal obtained by reversing the polarity of this signal from the second DA converter in synchronization with the measurement. To achieve.

  In the present invention, the cancel function restricted by the sine wave in Patent Document 1 can be extended to its harmonic components. Further, the data collected by the AD converter is Fourier transformed, and only the fundamental wave component or the harmonic component is taken out, and the signal obtained by removing the noise signal mixed at the time of AD conversion by performing the inverse Fourier transform on the signal is a canceling signal. Can be automatically generated.

  Also, analysis using multiple frequencies simultaneously can be performed by changing the circuit configuration of the present invention.

Examples of the present invention

  An electromagnetic induction flaw detection method using two frequencies is shown below. First, excitation signal data for the first DA converter is prepared by calculation. For example, when 2 KHz and 7 KHz are used simultaneously, data having sine waves of 2 periods (2 KHz) and 7 periods (7 KHz) is created in a 1-msec section, and repeatedly output by the first DA converter. In preparation for measurement, the second DA converter is set to the output zero state, and the AD converter accurately captures data for 1 msec. Computation processing such as noise removal is performed on the captured data, and finally a signal with inverted polarity is generated as a cancellation signal. The signal is output by the second DA converter in synchronization with the 1 ms interval at the time of sampling. Is released.

FIG.
101: sensor body 102: sensor drive coil 103: detection coil 104: subject 105: first DA converter (for drive coil excitation)
106: Second DA converter (for cancel signal output)
107: Signal addition circuit 108: Sum signal conversion AD converter 109: AD converter, DA converter control circuit, etc. 110: PC interface circuit 111 such as USB, etc .: Connection cable to PC, etc.

Claims (3)

  A first DA converter and an output amplifier for driving an electromagnetic sensor having a drive coil and a detection output are provided, and a signal obtained by arithmetically summing the detection output of the electromagnetic sensor and the output of the second DA converter is digitally converted. Electromagnetic induction inspection apparatus having an AD converter and having an interface for connecting input / output and control signals of the DA and AD converter to an external control device such as a PC   2. The apparatus according to claim 1, wherein no object to be sensed is placed in the detection area of the electromagnetic sensor, or a known object is set to a known condition, and the first DA converter has a known sine wave or different. A set of sine waves having a known frequency is supplied, the second DA converter is set to a no-signal state, and an AD converter is used to collect interval data that is an integral multiple of the supplied sine wave or set period. The signal that masks the target signal is automatically canceled by supplying the inverted signal of the signal itself or the inverted signal of the calculated signal to the second DA converter.   In the inspection apparatus according to claim 1, two types of known lift-off (distance between the sensor and the subject) and known thickness samples of the subject are prepared, and the frequency ratios of the four types of combinations are relatively prime. Measure with a composite signal of at least two types of sine wave, and decompose the measurement result into amplitude and phase for each fundamental wave of sine wave used by FFT calculation etc. Using these data and frequency-dependent air permeability and frequency-dependent subject properties and local linearity, the thickness is estimated from the measurement data of a subject sample of unknown thickness. Thing.