Thickness measurement using liftoff point of intersection in pulsed eddy current responses for elimination of liftoff effect

Eddy current testing can be used to interrogate steels but it is hampered by the lift-off distance of the sensor. Previously, the lift-off point of intersection (LOI) feature has been found for the pulsed eddy current (PEC) testing. In this paper, a lift-off invariant inductance (LII) feature is proposed for the multi-frequency eddy current (MEC) testing, which merely targets the ferromagnetic steels. That is, at a certain working frequency, the measured inductance signal is found nearly immune to the lift-off distance of the sensor. Such working frequency and inductance are termed as the lift-off invariant frequency (LIF) and LII. Through simulations and experimental measurements of different steels under the multi-frequency manner, the LII has been verified to be merely related to the sensor parameters and independent of different steels. By referring to the LIF of the test piece and using an iterative inverse solver, one of the steel properties (either the electrical conductivity or magnetic permeability) can be reconstructed with a high accuracy.

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Thickness measurement for non-ferromagnetic metal under the large liftoff based on the last peak point of differential pulsed eddy current signals

International Journal of Applied Electromagnetics and Mechanics ◽

10.3233/jae-209428 ◽

2020 ◽

Vol 64 (1-4) ◽

pp. 1119-1126

Author(s):

Yun Song ◽

Xinjun Wu

Keyword(s):

Measurement Error ◽

Wall Thickness ◽

Eddy Current ◽

Thickness Measurement ◽

Eddy Current Testing ◽

Metallic Component ◽

Current Testing ◽

Pulsed Eddy Current ◽

Peak Point ◽

Acceptable Range

Pulsed Eddy Current Testing (PECT) has been used to measure the wall thickness of ferromagnetic metallic component with thick insulation. However, for the non-ferromagnetic metallic component, there is still the problem to be solved. The main purpose of this study is to find an effective feature, to measure wall thinning of the non-ferromagnetic metallic component under the large liftoff, and further expand application of the PECT technology. Hence, the time to the last peak point (TLPP) is proposed based on the analytical predicted signals. Furthermore, the influence of the variable liftoff is studied, and the error caused by the liftoff is within the acceptable range. Two sets of experiments are conducted to test the performance of the TLPP under various liftoffs. The results show that when the wall thickness is reduced by more than 40%, the measurement error based on the TLPP is within 11%.

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Probe lift-off compensation method for pulsed eddy current thickness measurement

Proceedings of 2014 3rd Asia-Pacific Conference on Antennas and Propagation ◽

10.1109/apcap.2014.6992656 ◽

2014 ◽

Cited By ~ 4

Author(s):

Chen Huang ◽

Xinjun Wu

Keyword(s):

Eddy Current ◽

Thickness Measurement ◽

Compensation Method ◽

Pulsed Eddy Current ◽

Lift Off

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Measurement of Wall Thinning through Insulation with Ferromagnetic Cladding Using Pulsed Eddy Current Testing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.301-303.426 ◽

2011 ◽

Vol 301-303 ◽

pp. 426-429

Author(s):

Zhi Yuan Xu ◽

Xin Jun Wu ◽

Chen Huang ◽

Yi Hua Kang

Keyword(s):

Eddy Current ◽

Steel Plate ◽

Thickness Measurement ◽

Measurement Range ◽

Galvanized Steel ◽

Shielding Effect ◽

Pulsed Eddy Current ◽

Wall Thinning ◽

The Common ◽

Lift Off

Pulsed eddy current (PEC) technique has been successfully used for measuring wall thinning of carbon steel equipments without removal of the insulation. In field applications, the probe performance decreases in presence of ferromagnetic claddings. This paper presents a method based on saturation magnetization to solve this problem. The main principle of this method is to weaken the magnetic shielding effect of the cladding by magnetizing it to saturation. A U-shaped magnetizer is designed to realize this method. Contrast experiments are performed on a Q235 steel plate covered by a galvanized steel cladding. The experiment results show that the thickness measurement range and lift-off range are increased by applying this method to the common PEC probe.

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Time-to-peak of time derivative signals of pulsed eddy current testing for evaluating the thickness of ferromagnetic samples

Insight - Non-Destructive Testing and Condition Monitoring ◽

10.1784/insi.2021.63.2.88 ◽

2021 ◽

Vol 63 (2) ◽

pp. 88-94

Author(s):

Dongdong Wen ◽

Shuchen Wang ◽

Lei Zhang ◽

Jianhua Zhang

Keyword(s):

Eddy Current ◽

Measurement Accuracy ◽

Time Derivative ◽

Thickness Measurement ◽

Processing Method ◽

Current Testing ◽

Time To Peak ◽

Pulsed Eddy Current ◽

Precision Evaluation ◽

Lift Off

The time-to-peak serves as a popular signal feature of pulsed eddy current (PEC) signals and is widely used in thickness measurement and defect detection. In order to further improve the ability of time-to-peak independent of the lift-off effect, a time derivative processing method is proposed in this paper to obtain a better time-to-peak feature of time derivative signals of PEC for reducing the lift-off effect. The method is used to improve the thickness measurement accuracy of ferromagnetic samples. The results of simulation and experimentation demonstrate that a time-to-peak feature of time derivative signals of PEC can be obtained using the time derivative processing method and the timeto-peak obtained from time derivative signals of PEC can be used to measure the thickness and improve the thickness measurement accuracy of ferromagnetic samples. This means that the use of the time-to-peak of time derivative signals of PEC is feasible for high-precision evaluation of the thickness of ferromagnetic samples.

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