Looking for a wheel speed sensor...

[thomas walter x5955]

> From: Chris Howard <choward at extro.ucc.su.oz.au>

> I'm currently building a data logger for a thesis project and I need a wheel
> speed sensor. I'm thinking of using a proximity sensor with a magnetic
> trigger on the front hub. Does anyone know of a suitable sensor and where I
> could get one from ? (I'm in Sydney but anywhere will do!)

Couple of posibilities:

VDO 'speed sensor'. If there is a VDO retail source, check into looking
for a  sending unit that splices into the speedometer cable. Usual standard
is 1000/res per mile for the cable. VDO gave 8 pulses per rev. 

Front wheel sensor is what I used on my rear wheel drive rally Datsun:
Look at any of the rally magazine's, to see who sells "Trip Odomoters"
Then phone the local rep and inquire for just a sending unit. Best are
ones that sense the passing of a bolt head (common on the back of disc
brake). Had some neat German built units that used an enclosed hall 
effect sensor, with a buffered output. Self contained, easy to use. 

[I also made up some coils of wire - with a magnetic center - everything
housed in a section of stainless steel threaded tube, filled in with
expoxy. At the time it was not the best sensor, as it worked with very
little gap. As the wheel bearing grease heated up, it allowed enough
movement to shave off the end of the sensor. ;-( ].

Hall effect sensors and driveline mounted magnets also work, but in 
order to keep the magnents on the driveline, wrap them with some 
fiberglass after placing them. Take care to wrap the direction as 
same as the driveline. Magnets, held just by epoxy tend to fly off 
after time. ;-)

Cheers,

Tom Walter     '67 & '68 Datsun 2000's (Sports)
Austin, Texas  '71 & '72 Datsun 510's (P510 - 1600)
			   '95 Ford Aerostar to haul kids & tow with! ;-)