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How variable reluctance sensors are used to measure the position and speed of moving metal components
Gallery spotlightSensors & NDT
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.
METHODS and RESULTS
MAXIMUM and MINIMUM FLUX LINKAGE
The path of the flux generated by the permanent magnet varies as the toothed ring rotates in the field of the VR sensor. These images show the positions of maximum and minimum flux linkage.
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FLUX LINKAGE VARIATION
The flux linkage varies periodically as the teeth pass the sensor. The flux linkage variation converts to a voltage signal that can be modeled in MagNet. Here, the rotational speed of the ring of 600 RPM with 36 teeth around the ring translates to a period of 2.8 ms for the sensor's output signal.
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Video 1 - MAGNETIC FLUX DENSITY in the RING
This animation shows the magnetic flux density in the ring as the sensor operates. The distortion in the field due to eddy currents in the conductive ring is noticable.
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