Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future.

This paper provides a technical review of position and speed sensorless methods for controlling Brushless Direct Current (BLDC) motor drives, including the background analysis using sensors, limitations and advances. The performance and reliability of BLDC motor drivers have been improved because the conventional control and sensing techniques have been improved through sensorless technology. Then, in this paper sensorless advances are reviewed and recent developments in this area are introduced with their inherent advantages and drawbacks, including the analysis of practical implementation issues and applications. The study includes a deep overview of state-of-the-art back-EMF sensing methods, which includes Terminal Voltage Sensing, Third Harmonic Voltage Integration, Terminal Current Sensing, Back-EMF Integration and PWM strategies. Also, the most relevant techniques based on estimation and models are briefly analysed, such as Sliding-mode Observer, Extended Kalman Filter, Model Reference Adaptive System, Adaptive observers (Full-order and Pseudoreduced-order) and Artificial Neural Networks.

Abstrac/-Currently, for many applications, it is necessary to know the speecl and position oF motors. This can be achievecl nsing mechanical sensors coupled to the motor shaFt or using sensorless technic¡ues. The sensorless technic¡ues in brushed de motors can be classifiecl into two types: 1) technic¡ues basecl 011 the clynamic brushed de motor moclel ancl 2) technic¡ues basecl 011 the ripple componen! oF the curren!. This paper presents a new methocl, based on the ripple component, for speed ancl position estimation in brushed de motors, using support vector machines. The ¡>roposecl methocl only measures the curren! and detects the pulses in this signal. The motor speed is estimated by using the inverse clistance between the cletected pulses, and the position is estimat. ed by counting ali detected pulses. The ability to cletect ghost pulses and to discard false pulses is the main aclvantage oF this methocl over other sensorless methods. The perFormed tests on two fractional horsepower brushed de motors inclicate that lile methocl works correctly in a wicle range oF speeds ami situations, in which the speed is constan! or varíes clynamically. lndex Terms-Brushed de motor, curren! ripple, de motor, pattern recognition, position, sensorless, speed, support vector machines (SVMs). l. INTRODUCTIONS ENSORLESS techniques estímate the speed and position of motors without mechanical sensors coupled to the motor shaft, measuring only the current and/or the voltage of the mo tors. Sensorless techniques are not a recent idea. as is evidenced by the work of Allured and Strzelewigz [ 1 ]. Nevertheless, due to the complexity of these methods, they have not yet re placed conventional sensors such as encoders, potentiometers, lachometers, Hall effect sensors, or other mechanical sensors coupled to the motor shaft. The main advantages of these, compared to conventional sensors, are as follows: 1) decreased maintenance, number of connections. and cost of the final

Many motor applications require accurate speed measurement. For brushed dc motors, speed can be measured with conventional observers or sensorless observers. Sensorless observers have the advantage of not requiring any external devices to be attached to the motor. Instead, voltage and/or current are measured and used to estimate the speed. The sensorless observers are usually divided into two groups: those based on the dynamic model, and those based on the ripple component. This paper proposes a method that measures the current of brushed dc motors and analyses the position of its spectral components. From these spectral components, the method estimates the motor speed. Three tests, performed each with the speeds ranging from 2000 to 3000 rpm either at constant-speed, at slowly changing speeds, or at rapidly changing speeds, showed that the average error was below 1 rpm and that the deviation error was below 1.5 rpm. The proposed method: (i) is a novel method that is not based on either the dynamic model or on the ripple component; (ii) requires only the measurement of the current for the speed estimation; (iii) can be used for brushed dc (direct current) motors with a large number of coils; and (iv) achieves a low error in the speed estimation.

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