On Wed, 20 Oct 2004, Michael Rigby-Jones wrote:

>> simple coil based VR sensor would be much cheaper to manufacture and 
>> more robust, but I don't know of any sources for low quantities at good 
>> prices.
>>
>> imho you don't want one of those for his application. Traction control
>> must work at ~0 wheel speed.
>>
>> Peter
>
> Why would this not work at zero wheel speed?  Hall effect devices work fine
> with static magnetic fields.  Also I am a little unsure as to why this would
> be a problem anyway, zero output = zero wheel speed. Also surely zero wheel
> speed is not a common condition for traction control, ABS perhaps...

A VR sensor of the kind described is passive, it consists of a coil and a 
magnet. The output voltage is nearly zero at low speed. The active type of 
VR sensor (using lm*** and mitsumi chips) does give signal at very low 
speed but may be more expensive than differential gmr. The only reason I'd 
think of to use active VR instead of gmr is low temperature behavior. But 
they have that fixed now.

Peter
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