Re: ABS - exactly how does it work?
- From: "Jens" <jens@xxxxxxxxx>
- Date: 21 Aug 2006 10:46:48 -0700
Well, not quite.
A Hall effect sensor is used to measure magnetic field strength, and
there is nothing magnetic involved.
What's used is a socalled proximity switch. It consists of a coil,
which is part of an oscillator circuit. When a metal object gets close
to the coil, the frequency of the oscillator will change slightly
depending on the distance and the metal. By monitoring the frequency,
the internal circuit will determine whether metal is present or not,
thereby swtching the output on or off.
There is a "toothwheel" attached to the wheel hub, and the proximity
switch is facing this with a small distance. When the wheel turns, the
teeth of the toothwheel will pass the switch with different distance
between top and bottom of the teeth, causing the output to pulse
according to the speed of the wheel.
/Jens
drd wrote:
Guenter Scholz wrote:
Many thanks, good explanation there. What they don't make to clear
is how they ascertain that the wheel has slowed down too fast. quite
easy to do though, likely some kind of induced voltage which
increases with rate of deceleration of the cog wheel/sensor ....
you're exactly right - it's called a Hall effect sensor ...
http://en.wikipedia.org/wiki/Hall_effect#Wheel_rotation_sensing
atb
Steve
.
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