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Bolt links and riveted joints, although widely used in aerospace and other mechanical systems, are susceptible to stress concentrations and fatigue cracks, which are undesirable. The flexible rosette eddy current sensor is typically used for the structural monitoring of bolt connections and riveted joints. This study proposes a method to improve the sensitivity of a flexible rosette eddy current sensor by reducing the cloud zenith angle of the pickup coil. First, the effect of the cloud zenith angle upon the sensitivity of the flexible rosette eddy current sensor is analyzed theoretically; the results show that a larger cloud zenith angle corresponds to a larger background signal. This diminishes the relative rate of change of the crack signal when the sensitivity of the sensor is evaluated based upon the maximum rate of change of the output. Therefore, the sensitivity is optimized by reducing the cloud zenith angle. Subsequently, through simulation and experimental methods, the relationship between sensor sensitivity and cloud zenith angle was studied. The results indicate that the cloud zenith angle significantly affects the sensitivity and that reducing the cloud zenith angle effectively reduces the background and improves the sensitivity. [ABSTRACT FROM AUTHOR]

To measure the micro-displacement reliably with high precision, a single-ended eddy current sensor based on temperature compensation was studied in detail. At first, the principle of the eddy current sensor was introduced, and the manufacturing method of the probe was given. The overall design plan for the processing circuit was induced by analyzing the characteristics of the probe output signal. The variation in the probe output signal was converted to pulses with different widths, and then it was introduced to the digital phase discriminator along with a reference signal. The output from the digital phase discriminator was processed by a low-pass filter to obtain the DC component. At last, the signal was amplified and compensated to reduce the influence of temperature. The selection criteria of the frequency of the exciting signal and the design of the signal conditioning circuit were described in detail, as well as the design of the temperature-compensating circuit based on the digital potentiometer with an embedded temperature sensor. Finally, an experimental setup was constructed to test the sensor, and the results were given. The results show that nonlinearity exists in the single-ended eddy current sensor with a large range. When the range is 500 μm, the resolution can reach 46 nm, and the repeatability error is ±0.70% FR. Within the temperature range from +2 °C to +58 °C, the voltage fluctuation in the sensor is reduced to 44 mV after temperature compensation compared to the value of 586 mV before compensation. The proposed plan is verified to be feasible, and the measuring range, precision, and target material should be considered in real-world applications. [ABSTRACT FROM AUTHOR]

In this research, the design of non-destructive eddy current evaluation systems was improved using Harris Hawks optimization (HHO). To determine the orientation of cracks from eddy current data, a numerical approach was developed based finit elements methode FEM and on an iterative inversion technique that minimizes a non-linear least squares objective function that evaluates the overall difference between forecasts and observationsin axisymmetric model. In this paper the HHO optimization and steepest descent methods were compared and studied in order to minimize the objective function. To measure the precision of the estimated crack orientation, the lower bounds of the HHO optimization on crack orientation were obtained. This work explores the concept of an HHO algorithm that searches for the optimal solution within a large solution space for a specific crack orientation problem.The algorithm starts its search at any point in the solution space and looks for better solutions by searching in the "local" area surrounding the start point. The algorithm ends when it finds what it believes to be the best solution or when predetermined stopping criteria are met. • The damage (micro-cracks) is detected by NDT-EC using 2D-Axisymmetric FEM. • The effect of micro-crack orientation was studied using an eddy current test. • The proposed HHO algorithm is tested for crack-orientation detection. • The performance of HHO is also examined on several parametric problems. [ABSTRACT FROM AUTHOR]

With the development of power plants towards high power and intelligent operation direction, the vibrations or failures of blades, especially the last stage blades in steam turbines, happen more frequently due to the unstable operating conditions brought by flexible operation. A vibration measuring method for the shrouded blades of a steam turbine based on eddy current sensors with high frequency response is proposed, meeting the requirements of non-contact heath monitoring. The eddy current sensors produce the signals which are related to the area changing of every blade's shroud resulting from the rotation of stator. Then an improved blade tip timing (BTT) technique is proposed to detect the vibrations of shrouded blades by measuring the arrival time of each area changing signal. A structure of eddy current sensors is developed in steam turbines and an amplitude modulation/demodulation circuit is designed to improve the response bandwidth up to 250 kHz. Vibration tests for the last stage blades of a steam turbine were carried out and the results validate the efficiency of the improved BTT technique and the high frequency response of the eddy current sensors presented. [ABSTRACT FROM AUTHOR]

Disc cutter is the main rock breaking tool of TBM. It is angled worn frequently because of locked-rotor; as a result, monitoring relevant operating parameters of TBM disc cutter has become an urgent technical problem. This paper studies nondestructive and non-contact online detection disc cutter rotational speed method of based on eddy current sensor: applies eddy current sensor to detecting six 2 mm-high metal bumps setting on the disc cutter, so as to detect the rotational speed of disc cutter. K60 MCU is applied as the main control core. The experimental results show that the on-line rotational speed monitor system of disc cutter features high anti-jamming ability and is reliable. [ABSTRACT FROM AUTHOR]

Eddy current testing is quite a popular non-contact and cost-effective method for nondestructive evaluation of product quality and structural integrity. Excitation frequency is one of the key performance factors for defect characterization. In the literature, there are many interesting papers dealing with wide spectral content and optimal frequency in terms of detection sensitivity. However, research activity on frequency optimization with respect to characterization performances is lacking. In this paper, an investigation into optimum excitation frequency has been conducted to enhance surface defect classification performance. The influences of excitation frequency for a group of defects were revealed in terms of detection sensitivity, contrast between defect features, and classification accuracy using kernel principal component analysis (KPCA) and a support vector machine (SVM). It is observed that probe signals are the most sensitive on the whole for a group of defects when excitation frequency is set near the frequency at which maximum probe signals are retrieved for the largest defect. After the use of KPCA, the margins between the defect features are optimum from the perspective of the SVM, which adopts optimal hyperplanes for structure risk minimization. As a result, the best classification accuracy is obtained. The main contribution is that the influences of excitation frequency on defect characterization are interpreted, and experiment-based procedures are proposed to determine the optimal excitation frequency for a group of defects rather than a single defect with respect to optimal characterization performances. [ABSTRACT FROM AUTHOR]

In order to make an effective on-line thickness measurement of thick coating in hemispherical steel shells, a strategy using combined laser and eddy current (EC) sensors based on displacement differential method was proposed. To enhance the measuring precision, an EC displacement sensor with large test range was adopted and the effect of shell curvature on its output was reduced by applying the polynomial curve fitting. Its feasibility was verified by experimental results. [ABSTRACT FROM AUTHOR]

Eddy current (EC) sensor detects measurand by the change of coil impedance, which is introduced by coupling the magnetic energy between coil and measurement target. Therefore, it is of great significance for both the forward and inverse eddy current problems to study on the approaches to coil impedance calculation. In the current paper, two approaches are presented to calculate coil impedance of EC sensor. First, the theoretical calculation model of coil impedance is simplified as an air-cored cylindrical coil, over an infinite measurement target. And the integral expression of coil impedance is derived according to the sensor operation principle and electromagnetic field theory. Then, the integral expression is expanded as series form in cylindrical coordinate system in order to compute the coil impedance easily, and computed using MathematicaTM. Next, based on the finite element modeling theory, two different finite element models of eddy current measurement system are built. The infinite boundary in mode1 is truncated, while in model 2, it is simulated completely by an infinite element. Furthermore, the appropriate location where the air domain is truncated at is determined. Finally, the coil impedance and the magnetic distribution of eddy current testing system are obtained by finite element method, respectively. By comparison, the results from the theoretical calculation approach and finite element method are in very good agreement, and the accuracy of two approaches is validated with each other. [ABSTRACT FROM AUTHOR]

• The peak frequency is linear to the lift-offs between the centre of coil and ball. • The slope of peak frequencies versus lift-offs is linked to the radius of ball. • The radius of the metallic ball can be deduced by using the measured slope. • The radius of the metallic ball is retrieved with an error of less than 2%. 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%. [ABSTRACT FROM AUTHOR]

This paper describes a measurement method for the quality control of cylinders for printing machines based on roll-to-roll presses. If the surface finishing of the cylinders is not adequate, the printing is unacceptable, and the defective cylinders must be reworked. The performed quality check of the cylinder surface roughness by means of contact methods was unable to identify the cylinder defects, and acceptance of the manufactured cylinders before integration was demanded to the visual inspection performed by trained operators. In this work a contactless measurement method based on the eddy current displacement sensor was proposed and validated as a tool for quality check as an alternative to optical roughness measurements. A test bench for the characterization of printer cylinders was designed and manufactured, allowing for the validation of the proposed method on different batches of cylinders and the identification of a threshold to guide the acceptance of tested cylinders prior to mounting on the roll-to-roll press. [ABSTRACT FROM AUTHOR]

In view of the fact that the mature eddy current sensors on the market have a small measuring range and a certain requirement for the measured conductor area, which cannot meet the requirement of TBM disc cutter Wear monitoring, Ansoft Maxwell simulation was used to optimize the coil geometry parameters and circuit structure of eddy current sensor in this study. A special sensor for measuring disc cutter wear was designed, and the feasibility of the design was verified by measuring a 17-inch disc cutter. The results indicate that the linear range of the eddy current sensor is 35 mm under the condition that the measured blade width is 19 mm, which can meet the requirement of disc cutter wear measurement and provide monitoring data for real-time disc cutter wear monitoring system. [ABSTRACT FROM AUTHOR]