Measurement of Radius of a Metallic Ball Using Eddy Current Testing Based on Peak Frequency Difference Feature

This paper proposes a linear eddy-current feature to determine the radius of a metallic ball in a non-contact manner. An electromagnetic eddy-current sensor with two coils is placed co-axially to the metal ball during measurement. It is well known that the distance between the sensor and test piece (i.e. lift-off) affects eddy-current signals. In this paper, it is found that the peak frequency feature of inductance spectrum is linear to the lift-off spacing between the centre of coil and ball. Besides, the slope of peak frequencies versus lift-offs is linked to the radius of ball. The radius of metallic balls is retrieved from the experimental and embedded analytical result of the slope. Measurements have been carried out on 6 metallic balls with different radii. The radius of the metallic ball can be retrieved with an error of less than 2 %.

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Measurement of radius of a metallic ball using eddy current testing based on peak frequency difference feature

Measurement ◽

10.1016/j.measurement.2021.109876 ◽

2021 ◽

pp. 109876

Author(s):

Gang Hu ◽

Ruochen Huang ◽

Mingyang Lu ◽

Lei Zhou ◽

Wuliang Yin

Keyword(s):

Eddy Current ◽

Peak Frequency ◽

Eddy Current Testing ◽

Frequency Difference ◽

Current Testing

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Lift-off tolerant pancake eddy-current sensor for the thickness and spacing measurement of non- magnetic plates

10.36227/techrxiv.13143620.v1 ◽

2020 ◽

Author(s):

Mingyang Lu ◽

Xiaobai Meng ◽

Ruochen Huang ◽

Liming Chen ◽

anthony peyton ◽

...

Keyword(s):

Eddy Current ◽

Test Piece ◽

Triple Helix ◽

Outer Radius ◽

Small Error ◽

Current Sensor ◽

Magnetic Vector Potential ◽

Eddy Current Sensor ◽

Spacing Distance ◽

Lift Off

The lift-off spacing distance between the eddy current sensor and test piece will influence the detected signals and accuracy of the measurement. <a>Various techniques including novel sensor designs, features (lift-off point of intersection, lift-off invariance phenomenon), and algorithms have been proposed for the compensation of error caused by the lift-off effect using the eddy current sensor. However, few of these have directly measured the lift-off spacing distance, particularly for the distance up to 15 mm. </a>In this paper, a lift-off tolerant pancake sensor has been designed. By analysing the sensitive region of the magnetic vector potential change (due to the test piece), the receiver of the sensor is designed as a circular spiral pancake coil with a large mean radius and span length (the difference between inner and outer radius). Experiments on the inductance measurement of three different non-magnetic samples have been carried out using both the designed pancake sensor and the previous triple-helix sensor. From the experiment result, the detected signal of the designed sensor has been proved much larger than that of the triple-helix sensor. Besides, simplified algorithms have been proposed for the measurement of the lift-off spacing and thickness of non-magnetic samples when using the proposed pancake sensor. Results show that the lift-off spacing and thickness can be measured with a small error of 0.14 mm (absolute error under 209.66 kHz), and 1.35 % (relative error, under low working frequencies of 142, 238, and 338 Hz) for the lift-off spacing from 1 to 15 mm.

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Lift-off tolerant pancake eddy-current sensor for the thickness and spacing measurement of non- magnetic plates

10.36227/techrxiv.13143620 ◽

2020 ◽

Author(s):

Mingyang Lu ◽

Xiaobai Meng ◽

Ruochen Huang ◽

Liming Chen ◽

anthony peyton ◽

...

Keyword(s):

Eddy Current ◽

Test Piece ◽

Triple Helix ◽

Outer Radius ◽

Small Error ◽

Current Sensor ◽

Magnetic Vector Potential ◽

Eddy Current Sensor ◽

Spacing Distance ◽

Lift Off

The lift-off spacing distance between the eddy current sensor and test piece will influence the detected signals and accuracy of the measurement. <a>Various techniques including novel sensor designs, features (lift-off point of intersection, lift-off invariance phenomenon), and algorithms have been proposed for the compensation of error caused by the lift-off effect using the eddy current sensor. However, few of these have directly measured the lift-off spacing distance, particularly for the distance up to 15 mm. </a>In this paper, a lift-off tolerant pancake sensor has been designed. By analysing the sensitive region of the magnetic vector potential change (due to the test piece), the receiver of the sensor is designed as a circular spiral pancake coil with a large mean radius and span length (the difference between inner and outer radius). Experiments on the inductance measurement of three different non-magnetic samples have been carried out using both the designed pancake sensor and the previous triple-helix sensor. From the experiment result, the detected signal of the designed sensor has been proved much larger than that of the triple-helix sensor. Besides, simplified algorithms have been proposed for the measurement of the lift-off spacing and thickness of non-magnetic samples when using the proposed pancake sensor. Results show that the lift-off spacing and thickness can be measured with a small error of 0.14 mm (absolute error under 209.66 kHz), and 1.35 % (relative error, under low working frequencies of 142, 238, and 338 Hz) for the lift-off spacing from 1 to 15 mm.

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Research on Detection Mechanism of Weld Defects of Carbon Steel Plate Based on Orthogonal Axial Eddy Current Probe

Sensors ◽

10.3390/s20195515 ◽

2020 ◽

Vol 20 (19) ◽

pp. 5515

Author(s):

Linnan Huang ◽

Chunhui Liao ◽

Xiaochun Song ◽

Tao Chen ◽

Xu Zhang ◽

...

Keyword(s):

Carbon Steel ◽

Eddy Current ◽

Steel Plate ◽

Difficult Problem ◽

Eddy Current Testing ◽

Detection Sensitivity ◽

Detection Mechanism ◽

Current Testing ◽

Weld Defects ◽

Lift Off

The uneven surface of the weld seam makes eddy current testing more susceptible to the lift-off effect of the probe. Therefore, the defect of carbon steel plate welds has always been a difficult problem in eddy current testing. This study aimed to design a new type of eddy current orthogonal axial probe and establish the finite element simulation model of the probe. The effect of the probe structure, coil turns, and coil size on the detection sensitivity was simulated. Further, a designed orthogonal axial probe was used to conduct a systematic experiment on the weld of carbon steel specimens, and the 0.2 mm width and 1 mm depth of weld defects of carbon steel plates were effectively detected. The experimental results showed that the new orthogonal axial eddy current probe effectively suppressed the unevenness effect of the weld surface on the lift-off effect during the detection process.

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Evaluation of Coating Thickness Using Lift-Off Insensitivity of Eddy Current Sensor

Sensors ◽

10.3390/s21020419 ◽

2021 ◽

Vol 21 (2) ◽

pp. 419

Author(s):

Xiaobai Meng ◽

Mingyang Lu ◽

Wuliang Yin ◽

Abdeldjalil Bennecer ◽

Katherine J. Kirk

Keyword(s):

Eddy Current ◽

Coating Thickness ◽

Thickness Measurement ◽

Eddy Current Testing ◽

Thickness Variation ◽

Testing Technique ◽

Current Testing ◽

Thin Skin ◽

Embedded Algorithms ◽

Lift Off

Defect detection in ferromagnetic substrates is often hampered by nonmagnetic coating thickness variation when using conventional eddy current testing technique. The lift-off distance between the sample and the sensor is one of the main obstacles for the thickness measurement of nonmagnetic coatings on ferromagnetic substrates when using the eddy current testing technique. Based on the eddy current thin-skin effect and the lift-off insensitive inductance (LII), a simplified iterative algorithm is proposed for reducing the lift-off variation effect using a multifrequency sensor. Compared to the previous techniques on compensating the lift-off error (e.g., the lift-off point of intersection) while retrieving the thickness, the simplified inductance algorithms avoid the computation burden of integration, which are used as embedded algorithms for the online retrieval of lift-offs via each frequency channel. The LII is determined by the dimension and geometry of the sensor, thus eliminating the need for empirical calibration. The method is validated by means of experimental measurements of the inductance of coatings with different materials and thicknesses on ferrous substrates (dual-phase alloy). The error of the calculated coating thickness has been controlled to within 3% for an extended lift-off range of up to 10 mm.

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Differential coupling double-layer coil for eddy current testing with high lift-off

IEEE Sensors Journal ◽

10.1109/jsen.2021.3076880 ◽

2021 ◽

pp. 1-1

Author(s):

Kefan Chen ◽

Bin Gao ◽

G.Y. Tian ◽

Yupei Yang ◽

Changrong Yang ◽

...

Keyword(s):

Double Layer ◽

Eddy Current ◽

Eddy Current Testing ◽

High Lift ◽

Current Testing ◽

Lift Off ◽

Differential Coupling

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Inversion of lift-off distance and thickness for non-magnetic metal using eddy current testing

IEEE Transactions on Instrumentation and Measurement ◽

10.1109/tim.2020.3038289 ◽

2020 ◽

pp. 1-1

Author(s):

Xiaobai Meng ◽

Mingyang Lu ◽

Wuliang Yin ◽

Abdeldjalil Bennecer ◽

Katherine J Kirk

Keyword(s):

Eddy Current ◽

Eddy Current Testing ◽

Current Testing ◽

Magnetic Metal ◽

Lift Off

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Methods of Controlling Lift - off in Conductivity Invariance Phenomenon for Eddy Current Testing

10.36227/techrxiv.12400910.v1 ◽

2020 ◽

Author(s):

Zhongwen Jin ◽

Yuwei Meng ◽

Rongdong Yu ◽

Ruochen Huang ◽

Mingyang Lu ◽

...

Keyword(s):

Linear Relationship ◽

Eddy Current ◽

Coating Thickness ◽

Test Sample ◽

Common Point ◽

Coil Design ◽

Current Testing ◽

Lift Off ◽

Two Parameters ◽

The Relationship

Previously, a conductivity invariance phenomena (CIP) has been discovered – at a certain lift-off, the inductance change of the sensor due to a test sample is immune to conductivity variations, i.e. the inductance – lift-off curve passes through a common point at a certain lift-off, termed as conductivity invariance lift-off. However, this conductivity invariance lift-off is fixed for a particular sensor setup, which is not convenient for various sample conditions. In this paper, we propose using two parameters in the coil design – the horizontal and vertical distances between the transmitter and the receiver to control the conductivity invariance lift-off. The relationship between these two parameters and the conductivity invariance lift-off is investigated by simulation and experiments and it has been found that there is an approximate linear relationship between these two parameters and the conductivity invariance lift-off. This is useful for applications where the measurements have restrictions on lift-off, e.g. uneven coating thickness which limits the range of the lift-off of probe during the measurements. Therefore, based on this relationship, it can be easier to adjust the configuration of the probe for a better inspection of the test samples.

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