EDDYCURRENT TESTING FOR A THICK SUS PLATE

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EDDY-CURRENT TESTING FOR A THICK SUS PLATE

• H.Toyama, S.Yamada, M.Iwahara, D. Roy, and
  K.Miya
•  
• Institute of Nature and Environmental
  Technology, Kanazawa University
• Department of Electrical and Electronics
  System, Faculty of Engineering,
• Kanazawa University
• International Institute of University

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Outline of Presentation

• Background
• Eddy-Current Testing technique (ECT)
• Testing thick SUS plates
• Testing thick SUS plates by ECT
• SV-Giant Magnetic Resistance (GMR)
• System structure
• Flow of induced eddy-currents
• Testing results
• Detection of deep notches on thick SUS plate
• Detection of slight scratches on SUS plate
• Conclusions

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Eddy-Current Testing(ECT)

• Nondestructive testing
• Used for testing thin non magneticmetal objects
• High sensitivity
• Simple and small testing
• system
• Quick testing

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Testing thick SUS plates
Ultrasonic Testing(UT)
Eddy-Current Testing(ECT)
Testing of thin objects with high sensitivity
and compact testing systems
Testing of both thick and thin objects
Difficulties
Difficulties

• Low sensitivity to thin objects
• Difficult to specify the location
• Big testing systems

• Difficult to test a thick objects

We want to apply ECT in the testing of thick
objects by using a SV-Giant Magnetic
Resistance(GMR) as a sensor of ECT probe
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Testing thick SUS plates by ECT

• To test thick objects
• It is necessary to induce eddy-currents that
  have enough skin depth

• To obtain enough skin depth
• It is necessary to apply low frequency
  excitation to the objects

• Because of low induced voltage
• A conventional pick up coil cannot be used
  effectively
• in the low frequency

GMR as resistive type sensor is better.
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Features of ECT with the GMR sensor

• GMR measures external magnetic
• fields as the variance of its
• resistance
• The sensitivity is independent
• on the frequency of the magnetic
• fields
• Sensitive to only one direction

We expect a better testing for thick objects
based on ECT with the GMR sensor
AC characteristic of the GMR
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Structure of the proposed probe
Structure of the proposed probe
The testing system
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Principle of detecting notch
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Detection of deep notches on the thick plate
Testing condition Exciting current 0.1 A, 1.7
kHz Lift-off height 260µm
Relation between amplitude of the signal and
depth of notch
Output voltage across the GMR sensor
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Magnitude of signal vs. frequency characteristics
Relation between amplitude of signal and
frequency of the exciting current.
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Detection from the opposite surface
Testing condition Exciting current 0.1 A, 5
kHz Lift-off height 260 mm
Tested plate and output voltage across the GMR
sensor
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Slight scratches on SUS plate
Testing condition Exciting current 0.1 A, 180
kHz Lift-off height 4.29 mm
Tested plate and output voltage across the GMR
sensor
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Conclusions

• We examined the application of a GMR sensor for
• inspecting thick SUS plates at low
  frequencies.
• 2. We examined the performance of the ECT probe
  in the testing of both deep notches and slight
  scratches from high lift-off height.
• 3. It is possible to achieve a high sensitivity
  of ECT testing for thick SUS plates by using GMR
  as the sensor of the probe.