Postby osborni » Mon Dec 13, 2010 5:24 pm
If I'm arguing just to argue, then you guys are being WAY too picky or not flexible enough with the available tools at your disposal.
Since the only time people do less then 5mph on track is when they messed up, I'm not sure why low speed accuracy matters. If it matters THAT much to you, then use GPS speed, not wheel speed. At least then you don't have to worry about tire diameter calibrations. If it's a street car, then sure a wheel speed sensor is sometimes needed for road certification, but then absolute accuracy isn't THAT important. +/- 2 mph is good enough.
ABS will show up as a transient in the wheel speed reading. Regardless if it's zero or not, it will show up - which is all that matters. A simple way to do an ABS flag in Analysis is to divide wheel speed by GPS speed. Anything other then 1 is wheel slip.
Not all ABS applications are with a fully stopped wheel, some just have 20% slip, not ~5% at threshold or 100% slip at fully locked. To detect THAT, you really need to use a VRS sensor and pickup wheel at 40 or more pulses per rev, not a hall effect sensor.
At least on the wheel speed sensors that I'm using (Cherry), the rise/fall times of the sensor will get saturated about about 130 mph, with more then about 6-8 bolt heads (according to their spec sheet). Obviously, this depends on the size of the bolt head and the radius of the sensor from the axle center line.
So regardless of the intention of the sensor, it's probably close to saturation, which makes details like the original complaint pretty academic (in addition to the other basic issues and available alternatives of the OP's premise).
Additionally, using a pressure sensor (recorded at high enough frequency) can also pick up ABS applications. A decent dual purpose application of a sensor.
Could probably also look at picking up the voltage to the ABS pump or solenoids. Bot that solution doesn't serve a dual purpose.
So there are alternatives.
Last edited by
osborni on Mon Dec 13, 2010 5:46 pm, edited 1 time in total.
BMW 2000 M Coupe