In the electromagnetic world, there are phenomena invisible to the human eye, such as the electromagnetic field, in which forces operate. These forces follow trajectories called field lines, and they can be presented with demonstration models. We described and created a demonstration model of a longitudinal traveling magnetic field to support and improve the educational process. This visual tool would help students understand the flow of magnetic field lines and the functioning of the traveling magnetic field.
We studied the theory of the magnetic field, ferromagnetic properties, and linear magnetic field. A magnetic field, which can be naturally present or produced by a magnet or an electromagnetic device, loops around the source, illustrated by field lines. It originates at the North pole and concludes at the South pole. Weiss domains in ferromagnetic materials align in the direction of the magnetic field, thus amplifying it, making such material the right choice for demonstrating the magnetic field. After understanding the theory, we proceeded to design the demonstration model (DM). We had the winding or primary part (primary) of the linear asynchronous motor LAF 121 (LAM) by Indramat, a Danfoss series 302 frequency converter (FC), and fine ferromagnetic powder at our disposal. LAM can be imagined as an unfolded asynchronous motor (AM) that produces a traveling linear magnetic field. We control it with the FC, designed to control rotating electric motors, so we first learned how it works with AM. Then, we calculated all the necessary LAM values into rotating equivalents and entered them into the FC. We set all the necessary limits to avoid damaging the motor winding or the FC.
We designed operation in both manual and automatic modes. In manual mode, the DM is operated using a control panel with hidden electrical connections to indicators and switches. We can change the direction and speed of the magnetic field's travel. For the automatic mode, we used Smart Logic in the MCT 10 program, where we visually programmed sequences where the speed and direction of travel change automatically in different orders. When the DM is turned on, iron filings move along with the produced magnetic field, seen as a sort of wave. Over extended operation, clumpy structures form in the powder, as some particles remain in place above the primary, despite the magnetic field. When the DM is turned off, a remanent field appears in the ferromagnetic powder, maintaining a spiky curtain shape, weak enough to be nullified by shaking the plexiglass housing containing the ferromagnetic powder.
We successfully connected all the electrical components, thus creating a demonstration model that operates under optimal conditions and serves the visual representation of the linear magnetic field.
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