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In order to reduce the complexity of software and hardware design in multi-channel eddy current testing, a multi-channel real-time eddy current testing system based on lock-in amplifier technology and self- balancing technology is designed. The system uses graphical programming language platform (LabVIEW), Myrio1900 data acquisition control card and lock-in amplifier as key components. The lock-in amplifier adopts the lock-in technology to detect the amplitude and phase of the weak eddy current signal. The Myrio1900 card outputs multiple analog switch control signals and collects the amplitude component of the weak eddy current signal. The LabVIEW platform uses self-balancing technology to eliminate the imbalance of the bridge itself. The detection system realizes the real-time and reliable display of the amplitude and XY components of the 6-channel eddy current signal. Experimental results show that the designed system has a detection width of 56.00 mm at one time, and can detect artificial grooves with a covering layer of 2.90 mm. The artificial grooves have a width of 1.00 mm, a depth of 1.00 mm and a length of 50.00 mm. The system design process described in the article can be used as a reference for equipment developers and can also be used for educational purposes.

This paper is focused on the real-time characterization of weld in high speed high-end drawn metallic wires using encircling coil eddy current sensor. Emphasis was laid on the evaluation of weld-length and its span of stability with a special reference to signal pattern recognition through the improvised non-linear regression tool. A 3-D CIVA simulation electromagnetic testing module was implemented to evaluate the theoretical expected response of the system. The qualitative and quantitative analysis of welds was studied using signal processing of EC data. The percentage deviations in weld-span between simulated and experimental results were found to be around 1.6% and 12.5% at welding location of 1st and 8th pass respectively. This demonstrates the non- uniformity of the weld on relatively smaller diameter wire (8th pass) as compared to the larger diameter wire (1st pass). A good agreement was observed between the theoretical and experimental results. From the applications perspective, these findings indicate the importance on achieving higher efficiency combined with reliable quality control. On-line implementation of the proposed method satisfies both the requirements; detection accuracy and detection speed.

Eddy-current sensors are the most commonly used position sensors in a magnetic bearing application. Most commercial eddy current sensor outputs analog voltage of 0–2 V or 0–5 V in their measurement range. Such eddy current sensors are quite expensive and are in the price range of $2500 (USD). This paper presents a design of a $20 (USD) low-cost eddy current sensor capable of resolving displacements of 7 micron which is suitable for high-speed position control in active magnetic bearings. A novel method of directly converting the time period of the square wave signal from the eddy current sensor output for digital servo position feedback is employed in this design. This paper presents a scheme to implement digital position servo control algorithm on Texas Instruments C2000 real-time microcontroller to control the position of magnetically levitated object by controlling the magnetic actuator’s coil current. The magnetic actuators are electromagnetic coils that generate the magnetic force in the bearing.

Generally, the thickness of thick metallic plates is measured by exploitation of some physical phenomenon outside of eddy currents which are naturally limited for thin plates with respect to the skin effect. Indeed, it is the capacitive or ultrasound sensors which are the commonly used for thick plates. This paper proposes an alternative for thickness evaluation of thick metallic plates using eddy currents. The measurement system consists mainly of two eddy current sensors, an impedance analyzer LCR-meter and a personnel computer equipped with the Labview software. The plate we want to measure its thick thickness is placed between the two sensors. The proposed measurement procedure is based on lift-offs evaluation of a bi-eddy current sensor. The system has been verified and validated with success using several thick aluminum plates. The realized experimental setup can be used for online thickness measurement in some industrial applications.

The necessity of studying the Bernstein effect "repetition without repetition" is dictated by the absence of quantitative description of this effect and models that could describe such unique phenomena as repeated limb movements in a person in various mental states. In 30 nominally healthy volunteers (15 men, 15 women aged 24-25 years), tappingrams and tremorograms were recorded using an eddy current sensor with an oscillatory circuit (1 MHz) and an amplifier with recording frequency 0-1000 Hz and minimum amplitude of 0.01 mm. The results were recorded as files, processed as matrices of paired comparisons of samples, the number of matching sample pairs was determined (significance level p>0.05), and phase trajectories of finger movement were plotted. The effect was observed for both tapping and tremor and it is advisable to calculate the parameters of quasi-attractors that changed upon shifts in homeostasis.

Manufacturing a high-pressure sensitive diaphragm type sensor is a complex task. Due to it’s complex shape, several parts are designed individually. It involves welding of several parts. As welding involves several parameters it’s difficult to control the welding geometry where it is being fused. So it is likely that the physical boundary condition of the welded region will be different from the theoretical boundary conditions. So the change in boundary condition will make the deflection of the diaphragm different. For a precision device, any effect of a change in boundary condition can affect the deflection of the diaphragm largely. Thus, any effect of imperfect welding in a high precision measuring device can hamper the sensitivity of the particular device. A welded diaphragm of steel for a pressure sensor using eddy current sensor to detect it’s deflection due to pressure can lose it’s effectivity, due to the unpredictable boundary conditions created after the welding. In this paper, we will be trying to find the cause of deviation between the theoretical and experimental results due to the effect of a change in boundary conditions at the welded region.

Eddy current (EC) sensors placed in the vicinity of a rail track and sensitive to passing train components are safety-critical components commonly used in the railway sector. From the engineering point of view they form a system with numerous variables including their geometry, the lift-off, magnetic properties of the applied materials, the operating frequency and electrical characteristics of the built-in circuits. Although some simple configurations of the EC devices have been studied experimentally, numerically and analytically, there have so far been no universal algorithm allowing for predicting, understanding and optimizing output signals for arbitrarily device/track/wheel characteristics. A significant step towards such an universal algorithm is presented in this work, combining a linear 3D finite element modelling and a set of analytical formulas derived directly from the constants of the resonance circuit. Functions correlating the magnetic induction space/time characteristics with the circuit outputs are proposed and validated against experiment in three stages: (a) by determination of the signal from a flat thin FeSi plate (i.e. in fully controlled laboratory conditions), (b) by laboratory measurements of a highly degraded rail with uncertain material properties, (c) by tests of a commercial EC wheel detector, with reference to averaged service data. The proposed methodology can be extended to any NDT field where EC devices are applied.

Bearing defective inspection plays a vital role in bearing quality control. Unlike signals in the process of condition monitoring and fault diagnosis, the signal characteristic of defective bearings is much weaker and difficult to be quantified through the acceleration based techniques. In this paper, a novel system is developed to inspect automatically the small defects of roller bearings for on-line quality control. Rather than using acceleration based techniques the system employs a high sensitive eddy current sensor to measure the displacement profiles of the outer race for high signal to noise ratio. Furthermore, a morphological filter is used to enhance the feature signal which is subsequently measured by Kolmogorov complexity measure. Both simulated signals and measured data show that this system is able to diagnose defects including abnormal surface roundness, waviness, misaligned races which are typical quality problems in bearing manufacturing lines.

A non-contact vibration sensor based on the fiber Bragg grating (FBG) sensor has been presented, and it is used to monitor the vibration of rotating shaft. In the paper, we describe the principle of the sensor and make some experimental analyses. The analysis results show that the sensitivity and linearity of the sensor are −1.5 pm/μm and 4.11% within a measuring range of 2 mm–2.6 mm, respectively. When it is used to monitor the vibration of the rotating shaft, the analysis signals of vibration of the rotating shaft and the critical speed of rotation obtained are the same as that obtained from the eddy current sensor. It verifies that the sensor can be used for the non-contact measurement of vibration of the rotating shaft system and for fault monitoring and diagnosis of rotating machinery.

A method for the laminar determination of the hydrogen concentration in titanium, using eddy currents of different frequency, is proposed. The procedure for using a standard sample and a measuring system for specific technical situations are described.

The present paper investigates monitoring of fatigue cracks of a metal structure using an eddy current micro sensor. Fatigue cracks tend to occur at bolt-jointed structures on an aircraft. In order to detect the damage quantitatively, a kind of change-prone micro eddy current sensor is designed and fabricated with flexible printed circuit board (FPCB) technology. A forward semi-analytical model is built by extracting a material’s conductivity as the damage feature parameter, and characteristics analysis is conducted based on the model. The research focuses on setting up and utilizing the eddy current fields to analyze interaction of adjoining coils when the damage occurs, and investigating optimization on the working parameters of the sensor. In the experimental section, several common connection structures are applied to explore the sensor’s monitoring ability both in air and in a corrosive environment. The result shows that the optimal working frequency is about 1 MHz. The eddy current micro sensor is capable of monitoring the crack growth with an accuracy of 1 mm, the average error being 4.6 % compared to fracture analysis. The sensor keeps high resolution of damage in aqueous corrosion. Due to the fretting fatigue, wear appears on the polyimide foil, leading to the decreases of the monitoring signal.

The problems of obtaining high reliability in the automated contactless monitoring of the geometric parameters of freight car wheels during the motion of a train under practical operating conditions using laser equipment are discussed. The factors which influence the reduction in the monitoring reliability are analyzed, and methods of reducing this influence (by a factor of 2–10) are demonstrated. An eddy-current sensor and a subsystem based on it for detecting defects in the rolling surface of wheel pairs are described.

In this paper a new modeling method for an eddy current sensor is presented using geometric and electromagnetic data of a sensor and a measuring target It can predict not only sensor output but also medium behavior related to sensor output The geometric data of a sensor coil and the eddy current generated on a measuring target are simplified to an array of circular loops. And to perform computations of the network circuit between sensor coil loops and eddy current loops using the geometric and electromagnetic data in order to consider all possible interactions, the equivalent network circuit of eddy current sensor’s behavior has been drawn. Because the sensor’s initial value, medium behavior, and final value can be shown quantitatively by the proposed modeling method as the geometric and electromagnetic data varies, it can precisely predict the sensor output depending on the measuring goal and application field. Thus the model can be utilized to improve accuracy, eliminate the need for calibration before use, and produce the best design for any given purpose.

A complete, computer based design methodology is described, aiming to develop an eddy current sensor with increased sensitivity to flaws, and reduced sensitivity to probe lift-off. The first part of the paper contains an analysis performed in order to establish detailed criteria for an effective design. Numerical investigations have been carried out and their results are discussed, regarding various problems of detectability and lift-off noise level. Based on these results, in the second part two probe arrangements are proposed, and it is shown how their performance parameters could be further improved.

This article presents a feed speed optimization method for the circular saw lateral stability in wood cutting. The saw blade lateral deflection was monitored and the workpiece feed speed controled. An eddy current sensor was used to measure the saw deflection. Results showed that it was possible to keep the saw blade lateral deflection within a desired limit. This method may represent a promising technique in high speed cutting during the optimization process.

Multi multi frequency eddy current testing method has been a novel technique for defect characterisation and classification. In this technique any particular type of defect in a component can be detected in the presence of different type of other defects. In the present investigation attempts have been made to detect cracks in the interfaces between a weld pool and the bulk material in a thick austenitic stainless steel plate using this technique. The eddy current signals from the weld pool (having different magnetic permeability and electrical resistivity from the bulk) and the “lift off” of the eddy current sensor have been successfully suppressed by judicious choice of the experimental parameters and utilizing a software ‘mix algorithm’. This technique can be very effectively used as an NDT tool for a ‘Go/No Go’ test for any particular type of defect in components of mass production.

A combination multifrequency eddy current and laser ultrasonic sensors have been used to measure the pore expansion kinetics and elastic moduli evolution during the annealing of low density core (LDC) Ti-6Al-4V sandwich structures. The LDC samples were heated to 920°C and held there for up to 12 hr. The eddy current sensor measured the sample thickness (i.e. relative density) and revealed that the samples began to expand early during heating and was nearly complete after 4 hr at 920°C. The laser ultrasonic sensor measurements indicated a concomitant decrease in the elastic moduli with the reduction in relative density. The combination of an eddy current and laser ultrasonic sensor is therefore able to measure both the density and the elastic moduli independently during the annealing stage of LDC Ti-6Al-4V sandwich structure processing providing a simple method for directly controlling the parameters most critical to aerospace applications of these new materials.