Eddy current sensor operates based on the inductive eddy current principle. This data is referenced to an encoded position and time and. A theory of sparking between parallel plates in a transverse magnetic field, put forward by valle in 1950, is discussed and shown to be in. The purpose of this volume is to present the basic concepts of eddy currents, to explain how eddy currents are generated and distributed, to point out how the specimens magnetic and electrical effects relate to eddy currents, and. An eddy current array, in its simplest form, is a series of single elements arranged in a row, allowing users to cover a larger area in a single pass than conventional, singlecoil probes i. Eddy currents aregenerated when a conductor moves in changing magnetic flux. Both analytical and numerical methods are described. Eddy current ec testing is a no contact method for the inspection of metallic parts. Theory and numerical modelling of lorentz force eddy current.
Kinetic energy converted into heat due to eddy current losses finds numerous applications in industry. When inspecting a rod with an encircling coil the eddy current density at the centre of the rod is zero for. In fact, this is the basic principle on which all eddycurrent devices are based. However, an eddy current brake cannot provide a holding torque and so may be used in combination with mechanical brakes, for example, on overhead cranes. Eddy current testing theory and practice a level ilevel ii book that teaches the basics of eddy current testing. The eddycurrent losses are losses in the circuit resistors. Eddy current method is capable of detecting defects in electrically conductive materials by monitoring the change of eddy current resulting from electromagnetic induction 17. Eddy currents also called foucaults currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to faradays law of induction.
The engine being tested spins a disk in the dynamometer. Eddy currents also called foucaults currents are loops of electrical current induced within. One approach is to use poyntings theorem to calculate the total power crossing a surface enclosing the filament. In mountain areas where continuous braking force is needed, for a long time, the eddy current braking is very much useful for working without overheating. Capable of operating at pressure up to 4000 bar, they are one of the best wearfree, noncontact sensors for measuring displacement and position in harsh industrial environment. In mountain areas where continuous braking force is needed, for a long time, the eddy current braking. Eddy current, in electricity, motion of electric charge induced entirely within a conducting material by a varying electric or magnetic field or by electromagnetic waves. This magnetic field oscillates at the same frequency as the current running through the coil. Available from the national technical information service.
Eddy current testing ect as a technique for testing finds its roots in electromagnetism. Eddy current level i course outline 40hrs ndt overview. Eddy current technique is an important electromagnetic nondestructive evaluation technique. Eddy currents, to put in simpler terms, are fields of alternating magnetic current that are produced when an alternating electric current travels via one or more coils in a probe assembly. A schematic representation of eddy current separation is shown in figure 3. Eddy current sensors have superior temperature stability and resistance towards pressure, temperature, dirt and oil. Jul 23, 2012 eddy current testing is used to detect surface and nearsurface irregularities in ferrous and nonferrous materials by inducing an eddy current field in the part under test. Inductive sensors from microepsilon are based on the eddy current principle and designed for noncontact measurement of displacement, distance, position, oscillation and vibrations. This text was developed for instruction in eddy current testing. The subsequent analysis is based on this simple model. They can be induced within nearby stationary conductors by a timevarying magnetic field created by an.
In its most basic form the singleelement eddy current testing probe a copper wire is excited with an alternating electrical current. Massachusetts institute of technology mit opencourseware. These circulating currents are called eddy currents. Eddy current dynamo meter used to measure engine torque and power. Since there is no contact with a brake shoe or drum, there is no mechanical wear. The eddy current drive is built within a stationary frame of fabricated or cast steel, with a lower flange and shaft like that of a vertical motor. By lenz law, the current swirls in such a way as to create a magnetic field opposing the change. Eddy current dynamometers are electromagnetic load devices. A passive eddy current damper for vibration suppression of a. The magnetic field at the sheet surface, h surf i 0 nw, is determined by the input current i 0 of the scheme in fig. A level ilevel ii book that teaches the basics of eddy current testing. Eddy current testing is an electromagnetic technique used on conductive materials to detect a number of conditions, including subsurface defects, variations in material structure, thickness and corrosion. Eddy current drives instruction manual revised february 18, 2004 drive source international, inc. Eddy current array eca theory, practice and application.
Eddy currents induced in the conducting tubings by proximal wire windings connected to a capacitor to form a tank circuit which is connected to a radio frequency source. Within the frame are two concentric rotating members. Basic principles of testing electromagnetic theory a. Notice the spike in the eddy current signal, confirming that there is a defect in the component. This method of solution was first proposed in geophysics 2628, where eddy currents induced by an external current carrying coil were used to locate conductivity.
Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. Eddy current brake design for operation with extreme back. The eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. Nine chapters with over 90 illustrations and quizzes at the end of each chapter. In principle, let differs from traditional eddy current testing in two respects, namely i in how the eddy currents are generated and ii in how their perturbation is. Eddy currents induced in a power transformer core represent lost power and are undesirable. Conductivity if often measured by an eddy current technique, and inferences can then be drawn about the different factors affecting conductivity, such as material composition, heat treatment, work hardening etc.
Itworks on the principle of eddy currentgeneration that oppose the change in magnetic flux. Manual for the s yllabi contained in iaeat e cd o c628. Figure 2 shows the schematic diagram of a simple eddy current brake with only one magnet around it. It is not intended as a complete theoretical course in eddy. This is achieved by the use of a coil connected to an alternating current generator driving an alternating magnetic field primary field. Eddy current theory 1 generation of eddy currents by means of an ac field 2 effect of fields created by eddy currents impedance changes 3 effect of change of impedance on instrumentation 4 properties of eddy current. Eddy current array testing, or eca, is a technology that provides the ability to simultaneously use multiple eddy current coils that are placed side by side in the same probe assembly. Other applications will be described in chapter 7 on metal recycling. Eddy currents are fields of alternating magnetic current that are created when an alternatin. Eddy current testing can be used for a wide range of applications, and is often applied for surface crack detection and material sorting. Fundamentals of eddy current testing download ebook pdf. Apr 10, 2019 in order to reduce the eddy current losses in the transformer the core is formed by stacking thin plates called laminations together and each plate is insulated or varnished so that the flow of eddy current is confined to a very small cross section area of each plate and insulated from other plates.
Eddy current separation an overview sciencedirect topics. Eddy current inspection is one of several ndt methods that use the principal of electromagnetism as the basis for conducting examinations. Eddy current brakes are best substitutes for ordinary brakes, which are being used nowadays in road vehicles even in trains, because of their jerkfree operation. Technical specification eddycurrent dynamometer w series. An eddy current is a current set up in a conductor in response to a changing magnetic field. Ect began largely as a result of the english scientist michael faradays discovery of electromagnetic induction in 1831. Eddy current technique is an important electromagnetic nondestructive evaluation technique that is widely used in power, aerospace, petrochemical and other industries for detection of surface cracks and subsurface damage in components made of metallic materials.
The mathematical methods employed in solving the relevant problems are presented. Electrical current passes through coils surrounding the disk, and induce a magnetic resistance to the motion of the disk. Rao nondestructive evaluation division metallurgy and materials group indira gandhi center for atomic research kalpakkam 603 102, tn, india email. Eddycurrent losses for filaments with the magnetic vector potential known, we can proceed to calculate the eddycurrent losses. Eddy current testing is used to detect surface and nearsurface irregularities in ferrous and nonferrous materials by inducing an eddy current field in the part under test. Eddy current brakes use the drag force created by eddy currents as a brake to slow or stop moving objects. It is probable that no other form of nondestructive testing has a history of illustrious scientific. Way more information than you ever wanted on how to fell a tree. As these currents are not responsible for doing any useful work, and it produces a loss i 2 r loss in the magnetic material known as an eddy current loss. Apr 03, 2018 eddy current dynamo meter used to measure engine torque and power.
Ferraris acceleration sensor principle and field of application in servo drives. Recent citations optimum design of an eddy current damper considering the magnetic congregation. Eddy current testing also commonly seen as eddy current testing and ect is one of many electromagnetic testing methods used in nondestructive testing ndt making use of electromagnetic induction to detect and characterize surface and subsurface flaws in conductive materials. Nondestructive techniques based on eddy current testing.
They will occur when the conductor experiences a changing magnetic field. An introduction to eddy current testing theory and technology joseph m. Theory and applications article pdf available in proceedings of the ieee 8010. Eddy current technique is an important electromagnetic nondestructive evaluation technique that is widely used in power, aerospace, petrochemical and other industries for detection of surface. We present here both analytical and semiemiprical ways of dealing with such losses. Basic principles of eddy current inspection eddy current inspection is one of several ndt methods that use the principal of electromagnetism as the basis for conducting examinations. As a result a current flows in the conductor if there exists a closed path. Buckley, formerly of hocking ndt introduction scope this document is intended as a brief familiarisation course for hocking ndts customers and sales representatives. Physical cauer circuits in nonlinear eddycurrent modeling. They flow in closed loops in a plane perpendicular to the magnetic field. This wire produces a magnetic field around itself in the direction ascertained by the righthand rule. Pdf eddy currents or foucaults currents researchgate. After that the reaction by eddy currents doesnt play a role in the iron because of the use of thin laminated sheet steel and in the magnets because of the little conductance, but it has to be taken into account in construction elements.
Eddy current separation technique is used for separating metals from nonmetal component. Eddy current technique is an important electromagnetic non. The current i k in kth nonlinear or hysteretic inductor is found using the following chain. Similar to hysteresis loss, eddy current loss also increases the temperature of the magnetic material. Eddy current testing is a contactfree technique employed for examining metallic parts. When an energized coil is brought near to the surface of a metal component, eddy currents are induced into the. It measures the distance based on the extraction of energy from an oscillating circuit, which is required to generate eddy current in an electricallyconductive materials. Each individual coil produces a signal relative to the phase and amplitude of the structure below it. Eddy currents in linear materials can often be handled rigorously, but eddy currents in saturating material are more di. Applications based on effects arising from eddy currents are discussed in detail. General introduction to eddy current ec testing olympus ims. Several other methods such as remote field testing rft, flux leakage and barkhausen noise also use this principle.
Nondestructive techniques based on eddy current testing javier garciamartin 1,2, jaime gomezgil 1 and ernesto vazquezsanchez 1 1 department of signal theory, communications and telematic engineering, university of. They are particularly suitable when high precision is required in harsh industrial environments pressure, dirt, temperature. A passive eddy current damper for vibration suppression of. Eddy current principle the eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. Analysis of eddycurrent losses over conductive substrates. Schenck pegasus gmbh technical specification eddycurrent dynamometer w series h. The drum, shown in red, sometimes called the ring and the magnetic rotor shown in blue, sometimes referred to as the magnet or field. Another property is called target conductivity, which is a measure of how easy it is for eddy. Phase lag of eddy currents in a sample is dependent on. And these current in return produces a loss called eddy current loss or i 2 r loss, where i is the value of the current and r is the resistance of the eddy current path. If the core is made up of solid iron of larger crosssectional area, the magnitude of i will be very large and hence losses will be high. Eddy current sensor operates based on the inductive eddycurrent principle. Theory for the eddy current characterization of materials and structures. While they cause undesirable high heat losses in the material such as transformer core, eddy currents find applications in various industrial.
728 537 473 1150 1223 1093 389 979 632 1288 303 1473 207 1600 431 133 351 376 1661 956 1062 1270 966 1405 1328 607 188 1377 755 1398 1214 1145