Overview
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Magnetic sensors have been used as automotive sensors.
It is important that the accuracy, sensitivity and the responsiveness of
the sensors must be ensured while the car is operating.
The sensor performance improves if magnetic core is placed close to the
wheel. However, it is also important to have adequate distance between
them to avoid some dirt or foreign objects from being stuck.
This note presents the use of magnetic field analysis to evaluate the voltage
signal that varies with distance. |
Flux Density Distribution
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Figure 1 shows the flux density distribution at a rotation of 5.0 degrees
when the gap width is 0.5 mm.
As shown in the figures, the flux from the magnet flows through the yoke
and reaches the rotating ring. When the wheel rotates, the permeance in
the magnetic circuit changes due to shape of the teeth. This changes the
amount of flux that passes through the yoke, thus generating the electromotive
force in the coil. |
Voltage Signal
Figure 2 shows the voltage signal waveform at each gap width. Figure 3
shows that the voltage signal varies with the distance.
When the gap width is large, the electromotive force is small. It is because
the variation of the permeance is smaller than those with small gap width,
and the variation of the flux amount that flows through the yoke is also
small. |
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