How does the fan RPM sensor work?

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mrchaos

Limp Gawd
Joined
Feb 13, 2001
Messages
415
As far as I can tell, it sends out a signal across the single sensor wire everytime fan blade comes around. The signal sent out is a 1, returning to 0 when contact is lost.

correct so far?

and the actual RPM count is done by the mobo, counting the number of 1's sent in a minute?
 
Originally posted by mrchaos
As far as I can tell, it sends out a signal across the single sensor wire everytime fan blade comes around. The signal sent out is a 1, returning to 0 when contact is lost.

correct so far?

and the actual RPM count is done by the mobo, counting the number of 1's sent in a minute?
Click to expand...

Sort of... Execpt it's a 12V pulse that is produced every time the hub rotates once- not every time a blade goes by. There is a hall effect sensor on the circuit board in the fan and a small magnet on the hub that triggers it.
 
perfecto.......just trying to design a circuit and needed to know how it sensed the RPMs


i assume its a common ground as well?!
 
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