Re: When to keep quiet (was about ABS Sensors)

[Land Shark <lndshrk@xxxxxxxxxxxx>]

At 07:54 AM 1/19/99 PST, you wrote:
>Lets find out who is right.
>
>
>>A single "particle" weighing 0.01 GRAM can screw up the 
>>ABS if it sticks between two teeth, changing the wheel
>>from X teeth to X-1 as far as the edge detector inside
>>the ABS software sees.
>
>What teetth??

  What exactly do you think the ABS sensor reads.. a BOOK??

  take a look DOWN .. on the WHEELHUB.. a simple piece
  of metallic garbage CAN and HAS stuck to the that wheel
  'tween the teeth (like a bit of food) and caused it to
  see one less tooth!

>When the wheel is in motion, 
>ABS sensor produces a sinosoid. Magnetic parcticles can reduce the 
>amplitude of the curve,

 And that is ALL they need to do, the SINUSOID as you call it
 gets fed into a schmidt trigger.. if the amplitude isn't great
 enough, the signal can and will be ignored.

 But further.. block the "space" between two teeth with something
 that sticks to the hub and has magnetic permeability and you
 will see that the sinusoid skips a beat.

 Since that sinusoid gets converted to a square wave and then
 edge detected.. the CPU sees ONE LESS TOOTH per rev on one
 wheel than the other 3 and assumes it's slipping.

>>WHOOPS it's SLIPPING.. (in Picard's voice) #1 ENGAGE (abs/ast/etc)
>What are you talking about??? Let me get my R2D2 for calculations :-)) 

 How do you think ABS knows wheelspeed (MAGIC?) no it takes the number
 of "pulses" (which are edge counts on a converted sinusoid now square
 wave) and from there calculates the wheelspeed and slip numbers

>"Cleaning sensor advise" wastes people's time. Any person with good 
>knowledge of Sencond semester college physics will tell you, that metal, 
>which is not moving relatively to the magnet and the coil, can not 
>change the phase. Otherwise, show me the formula!!

 Mike.. take the 2nd semester college physics and stick it.. this has 
 nothing to do with PHASE.. it has to do with COUNT..

 Or better yet, retake it along with "Knowing when not to butt heads with
 the professor 201"

 You need to check and clean the whole sensor AREA, which is the sensor
 itself and the reluctor wheel built into the hub, which can and DOES
 get "junked up" and that DOES cause ABS problems..

 The resistance of those sensors is such that MOST people don't have
 a meter good enuf.. MOST DIY'er DONT have a Fluke 88 or other DMM

 Jim

 PS: If you HAD experience, you'd be saying that some 80% of "ABS" 
      problems are in fact wheelsize/tiresize problems.  especially
     in the performance oriented community such as this list!

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