Massachusetts institute of technology department of electrical engineering and computer science 6. History of eddy current testing eddy current testing fig. Chapter 5 basic electrical concepts related to eddy current testing. 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. Theory and applications article pdf available in proceedings of the ieee 8010. The eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. A level ilevel ii book that teaches the basics of eddy current testing. Eddy currents, surface impedances and loss mechanisms c 2005 james l.
General introduction to eddy current ec testing olympus ims. 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. Nov 01, 2016 eddy current testing can be used for a wide range of applications, and is often applied for surface crack detection and material sorting. Block i theory of eddy current testing the student must be able to. Computer based eddy current test instrument manufactured by highline automation. Buckley pdf, 429 kb eddy current testing at level 2, international atomic energy agency, vienna, 2011 pdf 5. In the paper, theorems for the electric vector potential t and magnetic scalar potential uare discussed, which occur in the boundaryvalue problems for eddy. Basic eddy current testing system the flow of eddy current within the material is disrupted by the presence of discontinuities, such. This is achieved by the use of a coil connected to an alternating current generator driving an alternating magnetic field primary field. What is eddy current eddy currents are currents induced in conductors to oppose the change in flux that generated them. Eddy current testing free download as powerpoint presentation.
Variable frequency drives vfds popular speed control devices used in industrial, commercial and residential applications. The eddy currents interact with the magnetic field to produces forces of levitation. Apr 30, 2010 what is eddy current eddy currents are currents induced in conductors to oppose the change in flux that generated them. Block ii eddy current testing equipment the student must be able to. 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. Blog 5 applications of eddy current brakes head rush tech. 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. The standard depth of penetration in mm is given by the. The eddy current probe is placed on or near the test part and the ac magnetic field penetrates the part, a conductor eddie currents are produced in the part an eddy current magnetic field secondary field is generated as eddy currents flow in the test part.
Basic principles of testing electromagnetic theory a. When starting eddy current clutch operates at 100% slip allow the driver motor to accelerate. 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. Analysis of eddycurrent losses over conductive substrates. Download the use of eddy current sensor based blade tip timing for. Eddy current testing uses the principle of electromagnetic induction to detect flaws in conductive materials. 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. Apr 11, 2019 download the use of eddy current sensor based blade tip timing for. Rao nondestructive evaluation division metallurgy and materials group indira gandhi center for atomic research kalpakkam 603 102, tn, india email. Astm e3052 standard practice for examination of carbon steel welds using eddy current array. Vessels have their tubes labeled by row and column or by x and y.
It is caused when a conductor is exposed to a changing magnetic field due to. It is traditional for eddy current calibration groups collections of related data to have 3 calibration scans in a row. Manual for the s yllabi contained in iaeat e cd o c628. Department of energys does advanced manufacturing office amo with support from the copper development association cda. The instrument is a dual channel dual frequency instrument. Eddy current testing theory and practice a level ilevel ii book that teaches the basics of eddy current testing. Tube testing is the most common type of eddy current testing. Since there are never 000 tubes in a vessel, it is always safe to reserve tube row999 and column999 for files that do not contain tube data. Read online the use of eddy current sensor based blade tip timing for. All books are in clear copy here, and all files are secure so dont worry about it. 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.
Illustrate, on paper, test coil arrangement for surface. Nine chapters with over 90 illustrations and quizzes at the end of each chapter. Eddy current is the swirling current produced in a conductor, which is subjected to a change in magnetic field. Eddy current ec testing is a no contact method for the inspection of metallic parts. Eddy current theory 1 generation of eddy currents by means of an ac field. Interruptions crack or discontinuity to eddy currents create a measurable change in impedance induced eddy current magnetic field lines conductive specimen ac source meter 3. Figure 1 shows these eddy currents in relation to the metal plate which moves perpendicular to the magnetic field.
Theory and numerical modelling of lorentz force eddy current. Eddy current technique is an important electromagnetic nondestructive evaluation technique. It is mathematically convenient to define the standard depth of penetration where the eddy current is 1e 37% of its surface value. In this study the amount of the pearlite content is analyzed using the eddy current testing response. Eddy current clutches or eddy current slip coupling are available in a broad range of sizes and speed up to thousands of kilowatts in both vertical and horizontal configurations. Finding the effective length over which the eddy currents form scott b. Eddy current testing is a contactfree technique employed for examining metallic parts.
As a result, a magnetic breaking force is induced on the eddy currents which opposes the motion of the sheet. Available from the national technical information service. One approach is to use poyntings theorem to calculate the total power crossing a surface enclosing the filament. Explain the basic principle of eddy current testing. Meyer, fellow, ieee abstract in this paper, a closedform integral representation. The eddy current density, and thus the strength of the response from a flaw, is greatest on the surface of the metal being tested and declines with depth. Eddy currents appear in extended conducting media if these media are. Eddy current testing has its origins with michael faradays discovery of electromagnetic induction in 1831. We present here both analytical and semiemiprical ways of dealing with such losses. Nondestructive testing eddy current basic principles. The third edition of the ndt handbook on et covers the latest developments in electromagnetic testing, with emphasis on digital technologies. Eddy currents generated in conducting materials by electromagnetic. Like we said when the metal sheet passes between the poles of the magnet, circulating currents eddy currents are generated.
Eddy currents in linear materials can often be handled rigorously, but eddy currents in saturating material are more di. Hughes physics department, the college of wooster, wooster, ohio 44691 may 5, 2000 this experiment uses a square copper plate attached to a cart which moves along a track underneath a magnet. Eddy but much of the content referencing him can be found under his nickname jack which he preferred to use. Eddy current testing technology 1st edition be exceptional 9 7 8 0 9 9 1 7 0 9 5 2 6. Vessels have their tubes labeled by row and column or by x. 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.
A sourcebook for industry i acknowledgments improving motor and drive system performance. Massachusetts institute of technology mit opencourseware. Faraday was a chemist in england during the early 1800s and is credited with the discovery of electromagnetic induction, electromagnetic rotations, the magnetooptical effect, diamagnetism, and other phenomena. Induces current eddy current into specimen which has corresponding magnetic field that works against coils field mutual inductance ac source magnetic field lines induced eddy current conductive specimen 3. Eddy current clutch working, application, advantages and disadvantages mecholic no comments eddy current clutches or eddy current slip coupling are available in a broad range of sizes and speed up to thousands of kilowatts in both vertical and horizontal configurations. Ptte1421 page 2 of 6 eddy current testing of aerospace materials figure 1.
Eddy current array eca theory, practice and application. To accommodate advancements in ndt technology, later versions of this publication were issued in 1991, 2002 and 2008, the current. Eddycurrent losses for filaments with the magnetic vector potential known, we can proceed to calculate the eddycurrent losses. Several other methods such as remote field testing rft, flux leakage and barkhausen noise also use this principle. Buckley, formerly of hocking ndt introduction scope this document is intended as a brief familiarisation course for hocking ndts customers and sales representatives. Eddy current level i ii course outline 40hrs ndt overview and certification requirements introduction to electromagnetic testing eddy currentflux leakage a. Eddy current brakes use the drag force created by eddy currents as a brake to slow or stop moving objects. The highline automation ec14 has a frequency range of 40hz to2 mhz the instrument will meet or exceed the requirements of appendix a.
As a result, current flows in the conductor if there exists a closed current path. Rao 9 et al investigated the basics of eddy current testing. Another property is called target conductivity, which is a measure of how easy it is for eddy. Also, a calibration file is usually labeled with a 999. Now, excellent tutorial information is available for scientists and engineers without advanced degrees. Eddy currents also called foucaults currents are loops of electrical current induced within. 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.
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. In addition, eddy current theory did not become available until the late 1970s. The coil generates a changing magnetic field using an alternating current, which interacts with the component generating eddy currents. The ability to detect defects in multilayer structures up to about 14 layers, without interference from the planar interfaces. Eddy current testing technology eclipse scientific. Eddy current drives instruction manual revised february 18, 2004 drive source international, inc. Notice the spike in the eddy current signal, confirming that there is a defect in the component. According to faraday s law a voltage is induced in a conductor loop, if it is subjected to a timevarying magnetic flux. John allen jack eddy march 25, 1931 june 10, 2009 was an american astronomer who published professionally under the name john a.
The fact that the material affects the flow of eddy currents provides the basis for a nondestructive testing system. An introduction to eddy current testing from the ndendt resource center. Some theorems of the eddycurrent theory springerlink. 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.
Huge energy savings potential operating centrifugal fans, pumps and compressors vary frequency of electrical supply to an induction motor to vary the motor speed. It is not clear if such models are suitable for applications including highfrequency switching harmonics. The eddy current testing programmed instruction series is two volumes which provide the background material you will need before you perform actual eddy current testing. Since there is no contact with a brake shoe or drum, there is no mechanical wear. Eddy currents in metals can also be used beneficially e. Tai services will supply all materials, labor and test equipment needed for the inspection. Eddy current inspection is one of several ndt methods that use the principal of electromagnetism as the basis for conducting examinations. Eddy currents are fields of alternating magnetic current that are created when an alternatin. Principles of theory, application and instrumentation are presented. One component is the same shape as the transmit signal. Title eddy current, magnetic particle and hardness testing. An excitation coil carrying current is placed in proximity to the component to be inspected. Theory for the eddy current characterization of materials and structures. Eddy current testing inductor electrical impedance.
Analysis of force harmonics and eddy current damping for 2. Great presentation by a pakistani jabran younas on eddy current testing of heat exchagers especially stripper and carbamate condenser,this presentation explains the concept of eddy current testing,basic theory,equipment how to. 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. They are an adjustable speed drive and provide soft starting capability. Eddy published a landmark paper in science titled the maunder minimum where, using the nineteenth century. Show by diagram, eddy current patterns induced by a surface coil, by an inside coil. Eddy current clutch working, application, advantages and.
Eddy current principle the eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. Simulink model for pwmsupplied laminated magnetic cores. What are the advantages and disadvantages of eddy current. 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. This unique braking system takes the simple function of magnetic and nonmagnetic forces and turns it into a high tech masterpiece.