Im using an allegro A1308 linear ratiometric hall sensor to measure the rpm and angular position in a shaft rotating at 20K rpm. My magnet is a 2mm dia 1120 mT magnet placed at around 15mm from the shaft. The TEAG(total effective air gap) of the sensor and the magnet is 1.5 mm. I notice that the output voltage of the sensor falls dramatically as the RPM increases, and by 10000rpm falls to such a level its indistinguishable from the sensors no-flux output. Im trying to figure out why exactly this is -
is this because the magnet flux experienced by the sensor at such high speed is actually less,
or is this because the sensors output cant rise fast enough?
any thoughts will be welcome thanks harsha
Edit After Sunnysky and Andy s answers below :
3.If I used 2 latching hall effect sensors -the ones that go high when it sees a N pole and stay high till it sees a S pole, with two magnets 180 degrees apart and with opposite poles facing the sensors - would that work? The frequency then should be just double the rps and well within the sensors bandwidth. Thanks