I'm connecting wheel speed sensors to the digital inputs of an M400. I'm using the OE toothed ring for the ABS system; 44 teeth with a diameter of 83 mm so the teeth are fairly small (3 mm high with a spacing of 4 mm). I'm not using the OE sensors because my particular car did not have ABS optioned and the mountings for the sensors are not present.
I thought I would use an industrial hall effect sensor because it is relatively cheap and easy to mount, so I have tried a Cherry GS100502. I'm getting a reliable and consistent speed reading, but there is a lot of noise on the logged speed reading. See the attached image; this was logged at 20 Hz and the units are minutes and seconds on the x-axis and km/h on the y-axis. The filter level in the M400 input setup was set to 2 (i.e. the minimum filtering other than off).
Is it normal to have this much noise in the signal? I would think not. What can I do to reduce it? Obviously I could increase the filter level, but I tried level 5 and this did not reduce the noise much but did significantly reduce the response to a deliberate brake lockup.