This is an electric braking system which works on the principle that eddy current produced in it opposes the driving torque. Eddy current testing equipment contains a conductive metal coil which is electrified with an alternating current. Basic eddy current concepts, eddy current generation and distribution, coilspecimen coupling factors, specimens magnetic and electrical effects, and basic electrical concepts related to eddy current testing. The instrument is a dual channel dual frequency instrument. Computer based eddy current test instrument manufactured by highline automation. This paper gives a brief account of basic principle, features, applications, limitations of the eddy current technique. In mountain areas where continuous braking force is needed, for a long time, the eddy current braking. Dynomite aircooled eddycurrent absorbers offer very quick load control, moderate inertia, and high specific load capacity, especially in the lower rpm working ranges of most industrialtype engines. Our baseline testing will ensure that your products are free of manufacturing defects and will perform at their peak. What is mean by eddy current, how eddy current works, principle of. They can be induced within nearby stationary conductors by a timevarying magnetic field created by an. In this technique, a coil also called probe or sensor is excited with sinusoidal alternating current frequency, f, 50 hz5.
For oems, we can eddy test your heat exchangers at the factory prior to shipping. Noncontact displacement and position sensors eddy current displacement sensors measure distances, displacements, or positions of any electricallyconductive target. 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. Leon foucault 18191868 discovered eddy currents produce heat when a permanent magnetic is placed at the edge of a rotating metal disk.
Ppt eddy current sensor powerpoint presentation free. Eddy currents are named so because the current looks like eddies or whirlpools. Our eddy current inspection analysts are highly experienced and can evaluate 1,200 to 1,600 tubes a day, depending on their length. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. The principle enables noncontact and wear free measurements. With the external multiplexer box one board can drive 16. The measuring systems use the principle of the eddy current effect. The coil generates a changing magnetic field using an alternating current, which interacts with the component generating eddy currents. Eddy current dynamometers are electromagnetic load devices. Pdf eddy current technique is an important electromagnetic nondestructive evaluation technique that is. Analysis of eddycurrent losses over conductive substrates.
The reaction between the eddy currents in a moving conductor. Figure 2 shows the schematic diagram of a simple eddy current brake with only one magnet around it. In this video i use lenz law to explain how eddy currents form when a piece of metal passes through a magnetic field. Eddy current dynamometer working principle, sales powerlink. What is mean by eddy current, how eddy current works. The eddy current method is based on the principle of generating circular electrical currents eddy currents in a conductive material. Itworks on the principle of eddy currentgeneration that oppose the change in magnetic flux. Eddy current nde is commonly used in the inspection of. Eddy current testing uses the principle of electromagnetic induction to detect flaws in conductive materials. The coil which excites the magnetic pole is wound in circumference direction. The test equipment consists of a generator ac power supply, a test coil and recording equipment, e. Magnetic field induces currents eddy currents in test specimen.
Principle ec testing works on the principles of electromagnetic induction. An eddy current brake, also known as an induction brake, electric brake or electric retarder, is a device used to slow or stop a moving object by dissipating its kinetic energy as heat. Eddy currents generated in conducting materials by electromagnetic induction have. Pmmc instrument working principle permanent magnet moving coil instrument the permanent magnet moving coil pmmc instrument is an electromechanical meter that can be connected with additional components to function as an ammeter, a voltmeter, or an ohmmeter. Nondestructive techniques based on eddy current testing mdpi. It is very useful video to learn about eddy current and its principles. It is a highly sensitive technique and completely nondestructive. Eddy current inspection for detection of surface and near. Eddy current dynamo meter used to measure engine torque and power.
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. Ferraris acceleration sensor principle and field of application in servo. Pmmc instrument working principle permanent magnet. Eddy current testing can be used on all electrically conducting materials with a reasonably smooth surface. If the object is free of defects, the resulting lorentz force remains constant. This is achieved by the use of a coil connected to an alternating current generator driving an alternating magnetic field primary field. The principle of the eddy current technique is based on the interaction between.
Eddy currents aregenerated when a conductor moves in changing magnetic flux. Eddy current testing can be used in applications other than flaw detection. It is an abrasionfree method for braking of vehicles including trains. Hughes 18311900 is believed to have used the eddy current principle to sort metals in 1879, the first practical use. Eddy current brakes are best substitutes for ordinary brakes, which are being used nowadays in road vehicles even in trains, because of their jerk free operation. This paper is intended to provide insight into these phenomena so that improved high fre. This opposing torque is used to brake the automobiles. The subject is presented under the following headings.
Eddy current testing ect eddy current testing is an electromagnetic testing technique usually used to inspect nonferromagnetic materials. For the australian rock band, see eddy current suppression ring. Eddy current definition of eddy current by the free. The subsequent analysis is based on this simple model. Any electrically conductive object will conduct an induced current if it is placed in a changing magnetic field. The process relies upon a material characteristic known as electromagnetic induction. A current induced in a conductor when subject to a varying magnetic field.
Eddy current dynamometer working principle the powerlink eddy current dynamometer measures the torque and power of the prime mover motor or engine. 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. Electrical current passes through coils surrounding the disk, and induce a magnetic resistance to the motion of the disk. High quality eddy current testing solutions for complete inspections. The engine being tested spins a disk in the dynamometer. This is the basis of eddy current testing, by monitoring the voltage across the coil in such an arrangement we can detect changes in the material of interest.
In this technique, a coil also called probe or sensor is excited with sinusoidal alternating current frequency, f, 50 hz5 mhz, 100 ma. Get more information about eddy current brakes pdf download by visiting this link. Zetec is the industry leader for costeffective eddy current testing ect in complex applications. Eddy currents also called foucaults currents are loops of electrical current induced within. When a current runs through exciting coil, a magnetic flux loop is formed around the exciting coil through stators and a rotor. Eddy current inspection is one of several ndt methods that use the principal of electromagnetism as the basis for conducting examinations. Eddy current brake design for operation with extreme back. Several other methods such as remote field testing rft, flux leakage and barkhausen noise also use this principle.
The rotor rotates with the help of the prime mover shaft and the voltage is applied to the coil or stator housing. On the next page you will learn more about eddy current testing and be able to try an inspection yourself. Each board can multiplex up to 16 frequency channels. In other words, the first term is the solution of the free space problem for the impressed filamental currents, whereas the second term is due to the response eddy currents in the substrate.
Note that cracks must interrupt the surface eddy current flow to be detected. Therefore, a highfrequency magnetic field is generated and the sample is placed in the magnetic field. Induced electromotive force is produced in the coil when there is a change in the magnetic flux linked with that coil. 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. These high frequency effects are caused by the magnetic field resulting from current flow in transformer windings and circuit wiring.
The current generates a magnetic field around the coil. No damage to test object it is quick, safe and costeffective to use eddy current testingbasic. Theory for the eddy current characterization of materials and structures. This is often also referred to as electromagnetic braking. For applications that do not require stallspeed loading, an aircooled eddycurrent absorber is usually the most costeffective electric absorber you can buy. We have the most extensive experience, and we develop the highest quality ect inspection products. The eddy current method is widely used to inspect metallic aircraft components for surface cracks and corrosion damage. Eddy current losses in transformer windings and circuit wiring. The highline automation ec14 has a frequency range of 40hz to2 mhz the instrument will meet or exceed the requirements of appendix a. Eddy current testing is an inspection method that can be used for a variety of purposes including the detection of cracks and corrosion, material and coating thickness measurement, material identification and, in certain materials, heat treatment condition. This dissertation is brought to you for free and open access by the iowa state university.
When a conductor is placed in the changing magnetic field, the induced current in the conductor is termed as eddy currents. Eddy current sensor operates based on the inductive eddycurrent principle. The conductive material acts on the resonant circuit, such as a resistive load and thus leads to a. Download basic principles of eddy current inspection. The rotation of rotor produces density difference, then eddycurrent goes to stator. Mainly this system is purely based on faradays laws of electromagnetic induction and lenzs law. Seminar on eddy current brake report pdf download abstract. Such currents are a source of energy dissipation eddy current loss in alternating current machinery.
Theory and applications article pdf available in proceedings of the ieee 8010. An excitation coil carrying current is placed in proximity to the component to be inspected. Key trends and opportunities for 20162021 the global eddy current sensor market research report 2016 is a valuable source of insightful data for business strategists. It also covers instruments and sensors to enable better appreciation of the. However, unlike friction brakes, in which the drag force that stops the moving object is provided by friction between two surfaces pressed together, the drag force in an eddy current brake is an electromagnetic. 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. The measurement objects may have either ferromagnetic or nonferromagnetic properties.
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