• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.770-772
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• 2002

In this paper, the eddy current sensor is develped for observing the ability of detecting defect with variation of frequency and velocity. The circuit designed for processing detected voltage and changing frequency is used for eddy current sensor to detect defect with variation of frequency. The ability of eddy current sensor to detect defects is studied with variation of velocity adjusted by rotating the circular plate. This study shows that the ability of eddy current sensor for detecting defect is increased and decreased by frequency. This fact means that the sensor has its best ability at a certain frequency. And the ability of eddy current sensor by velocity is decreased by increased velocity. Therefore, the eddy current sensor has to be developed with consideration of its operation velocity and frequency.

• Proceedings of the KIEE Conference
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• 2003.07b
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• pp.1000-1002
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• 2003

The characteristics of eddy current sensor has been analyzed by using numerical analysis which is performed by modeling eddy current sensor and analytic object into three-dimension axis-symmetry in this paper. The eddy current sensor is modeled as cylindrical shape with variation of inside and outside diameter and frequency range between 1[kHz] and 1[MHa] for numerical analysis. The value of impendence on eddy current sensor depending on frequency variation was calculated through numerical analysis. The characteristics of eddy current sensor can be studied by normalized impendence which is gained from the calculated impendence. Therefore, sensitivity of eddy current sensor depending on frequency, inside and outside diameter can be known by investigating diameter of half circle impendence and its locus.

• Journal of Power System Engineering
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• v.15 no.3
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• pp.65-69
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• 2011

This paper introduces the multi-coil eddy current sensor and its characteristic in magnetic material gas turbine rotor. In the past, magnetic particle inspection method was used for qualitative defect evaluation in magnetic material gas turbine rotor. And the ultrasonic inspection method was used for quantitative defect evaluation. Nowadays, eddy current method is used in magnetic gas turbine rotor inspection due to advanced sensor design technology. We developed multi-coil eddy current sensor for the rotor dovetail inspection. At first, rotor stress is analyzed for the determination of sensor position and number. The sensor coils are designed to cover the stress concentration area of rotor dovetail. We select optimum frequency according to material standard penetration data and experiment results. The rotor mock-up and artificial defects were made for the signal detection and resolution analysis of multi-coil eddy current sensor. The results show that signal detection and resolution capabilities are enhanced in comparison to the commercialized sensor enough for the gas turbine rotor inspection. So, this developed multi-coil eddy current sensor substituted for commercialized one and it applied in real gas turbine rotor inspection.

• Journal of Power System Engineering
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• v.15 no.4
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• pp.37-41
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• 2011

This paper introduces the special eddy current sensor and its characteristic for bolt hole defect evaluation in gas turbine rotor. In the past, Fluorescent penetration inspection method was used for qualitative defect evaluation in gas turbine rotor bolt hole. This method can defect the bolt hole defect but can not evaluate the defect size. Nowadays, eddy current method is used quantitative defect evaluation due to advanced sensor design technology. And eddy current method is more time and cost saving than the old method. We developed bolt shape eddy current sensor for the rotor bolt hole defect detection and evaluation. The eddy current sensor moves to the bolt hole guided by screw nut and detects the defect on the bolt hole. The bolt hole mock-up and artificial defects were made and used for the signal detection & resolution analysis of eddy current sensor. The results show that signal detection capability is enough to detect 0.2 mm depth defect. And the resolution capability is enough to differentiate 02, 0.5, 1.0 and 2.0 mm depth defect.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1788-1792
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• 2005

Eddy current sensor is representative instrument measuring gap to base metal and sensing trouble in base metal. The existing eddy current sensor works as measuring variance of sensor coil's inductance. But, sensor coil have phenomenon that not only inductance but also real resistance varies in real action. Conductivity and Permeability are main variable in sensor coil's varying impedance(inductance, real resistance). By searching relationship between conductivity-permeability and sensor coil's impedance, eddy current sensor gain advantage of elevation of accuracy, removal of alignment to each base metal, and continuous sensing to varying base metal.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.6
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• pp.524-530
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• 2008

The spin valve tunneling magnetoresistance (SV-TMR) sensor performance is analyzed using Stoner-Wohlfarth model for the detection of eddy current signals in nondestructive testing applications. The SV-TMR response in terms of the applied AC magnetic field dominantly generates the second harmonic amplitude in hard axis direction. The second harmonic eddy current signal detection using SV-TMR sensor shows higher performance than that of the coil sensor at lower frequencies. The SV-TMR sensor with high sensitivity gives a good solution to improve the low frequency performance in comparison with the inductive coil sensors. Therefore, the low frequency eddy current techniques based on SV-TMR sensors are specially useful in the detection of hidden defects, and it can be applied to detect the deeply embedded flaws or discontinuities in the conductive materials.

• Journal of Ocean Engineering and Technology
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• v.29 no.2
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• pp.199-206
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• 2015

Regular high-strength carbon steel is currently the most commonly used pipe material for onshore and offshore pipelines. The corrosion of offshore pipelines is a major problem as they age. The collapse of these structures as a result of corrosion may have a heavy cost is lives and assets. Therefore, their monitoring and screening is a high priority for maintenance, which may ensure the integrity and safety of a structure. Monitoring risers and subsea pipelines effectively can be accomplished using eddy current inspection to detect the average remaining wall thickness of corroded low-alloy carbon steel pipelines through corrosion scaling, paint, coating, and concrete. A test specimen for simulating the offshore pipeline is prepared as a standard specimen for an analysis and experiment with differential bobbin eddy current sensors. Using encircling coils, the signals for the defect in the simulated specimen are analyzed and evaluated in experiments. Differential bobbin eddy current sensors can diagnose the defects in a specimen, and experiments have been carried out using the developed bobbin eddy current sensor. As a result, the most optimum coil parameters were selected for designing differential bobbin eddy current sensors.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.322-327
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• 2014

Internal corrosion of the distribution line can be detected in order to develop techniques of non-destructive inspection methods that operate only on the metal track eddy current diagnosis is possible by applying the technique investigated. Sensor for the production of a finite element method modeled by using an eddy current sensor, a distribution line by using an accelerated aging samples of sodium hydroxide was prepared. Sheathed cables for internal corrosion studies detected using an eddy current sensor is considered to be possible.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.3
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• pp.27-32
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• 2010

The OMM(On-Machine-Measurement) system has many advantages compare to conventional measurement in the way the time and cost. But, the sensor suitable to OMM system is restrictive use. Touch trigger probe sensor has long time for measurement and non-contact sensor has directional demerit. Because the long mechanical parts such as gear and lead screw for pump, injector and machine tools has big and heavy, unclamp and transferring for measurement in machining process is very difficult. This paper presents a development of ultra miniature eddy current displacement sensor with 3 axes for On-Machine-Measurement system. The accuracy of the sensor is experimentally proved in the grinding machine. In experimental results, the accuracy has under ${\pm}5\;{\mu}m$.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.697-699
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• 2002

In this paper, the characteristics analysis of the eddy current sensor by using boundary element method package is presented. For the boundary element analysis. Faraday, which is the commercial package of the integrated engineering software, is used. To observe the impedance characteristic of the eddy current senor with the sensor position and lift-off, the eddy current testing analysis is performed on the ferromagnetic plate with defect. Considering the skin depth of the ferromagnetic specimen, the 800(Hz) driving source is chosen. The result shows that electro motive force is reduced as the probe moves to near the defect and the lift-off of the probe increases.