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Sensors & NDT
How variable reluctance sensors are used to measure the position and speed of moving metal components
Variable reluctance sensors are used to measure position and speed of moving metal components. This sensor consists of a permanent magnet, a ferromagnetic pole piece, a pickup coil, and a rotating toothed wheel. As the wheel rotates, the reluctance of the flux path through the coil changes, and the flux linkage through the coil changes, which results in a change in voltage that is measured by an external circuit.
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Using the Mesh Layers feature on Nondestructive Testing Problems
For NDT problems, there is a need to model the magnetic fields and eddy currents accurately in the regions under inspection. The fields decay rather quickly to zero in the surrounding regions. Further, the fields tend to change very quickly (exponential decay) with increasing depth into the test specimen (skin depth effects), and not nearly as rapidly in the two perpendicular directions. The Mesh Layers feature allows the construction of a mesh that is optimized for these types of problems.
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Design Optimization of an NDT Sensor Probe
Design of the probe and its suitability for detecting particular types of defects: starting from a model based on the WFNDEC Eddy Current Benchmark Problem 2, OptiNet was used to determine the optimal coil geometry and frequency at which the inspection should be performed.
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WFNDEC Benchmark Problem 2 - Eddy Current Inspection of Inconel Pipe
WFNDEC's1 Eddy Current Benchmark Problem 2 involves the inspection of an Inconel pipe using an internal pancake coil situated with its axis perpendicular to the axis of the pipe. Small defects of various depths in the external wall of the pipe are scanned in the axial and circumferential directions. Defects are detected as a change in the impedance of the coil.
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TEAM Workshop Problem 8 - Coil Above A Crack
The objective is to detect a crack by measuring the difference of magnetic fluxes through two solenoids. Using MagNet's Time Harmonic solver, the induced eddy currents are accurately computed. The comparison between the experimental results and the simulation results obtained from MagNet demonstrates how MagNet can be used to deal accurately with NDT problems.
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TEAM Workshop Problem 27 - Eddy Current NDT and Deep Flaws
A coil is stationary over a sheet of aluminum that contains a screw hole. Inside of the screw hole, a flaw is to be detected by two Hall effect sensors. Solved in MagNet by using the Transient 3D solver. A step waveform is created to power the coil; once the current is shut off, the horizontal flux densities at either end of the screw hole are differenced. The transient solver correctly models induced eddy currents inside the aluminum plate after the current in the coil is turned off. This allows for the calculation of values such as the differential flux density.
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TEAM Workshop Problem 15 - Rectangular Slot in a Thick Plate
A circular coil moves along an aluminum plate that contains a slot. The goal is to detect the slot by calculating the resistance and inductance of the driving coil at various positions. Sensor problems require accurate calculation of induced eddy currents in order to detect flaws in samples. MagNet's Time Harmonic solver automatically calculates eddy currents. Comparing published experimental results with MagNet shows the accuracy of the software.
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