Frequently Asked Questions about Magneto-Electric Rotation Detector

Change in duty cycle (dependent on rotational speed)

When a magnetic material moves through a magnetic field, eddy currents are generated on its surface, and these eddy currents generate a magnetic field (green arrow). This magnetic field interferes with the magnetic field generated by the magnetoresistive sensor, causing a change in the midpoint voltage.

The direction of eddy currents changes depending on the direction in which the magnetic material moves.
Furthermore, since eddy currents increase in proportion to speed, the change in midpoint voltage also increases as the rotational speed increases.

Change in duty cycle (temperature dependent)

Magnetoresistive elements exhibit temperature dependence. Since the MP-981 uses two magnetoresistive elements, slight differences in the temperature characteristics between the elements cause the midpoint voltage to change. The diagram below shows an example.

Change in the midpoint voltage of the output

The signal amplitude obtained from the magnetoresistive sensor is small, only a few tens of mV, so it is amplified and then shaped to produce the final signal. Since changes in the midpoint voltage are also amplified, if the midpoint voltage changes due to temperature changes or increases in rotational speed, changes in the duty cycle of the final output signal or the disappearance of pulse output may occur.