On Wed, May 09, 2001 at 05:38:31PM +0800, Alex Salmon ([EMAIL PROTECTED]) wrote:
> hi
> i have one of those 3 wire fans on my cpu. My question is how do i measure
> the rpm of my fan from it. not through software like lm_sensors but in real
> life ie so it dosent even have to be in a pc.
>
> Is there some kind of eq i can use so i can measure the voltage across the
> 3rd wire and get a rpm value.
This is not tested.
Every motor becomes when rotated a generator, too (simply spoken).
This effect can be used to measure its rotational speed (ie revs).
I just looked at one and I assume that the yellow wire together
with the black wire is used (12V) to drive the motor.
So the red wire is probably used to detect its revs.
What you could do is attach 12V to the yellow cable and a multimeter
to the red wire (reference point 0V is the black wire).
Then measure the voltage and slightly slow down the motor,
you should see a lower voltage on the multimeter.
This is probably the way MB test the revs. If you go into
the bios you can see that the detected speed is rather "corse",
meaning it has big steps:
5000 .. 4500 .. 4000 ... etc
I assume they have some kind circuitry (caps and resistors) to
detect a a range of voltages and then display it...
jobst
--
Share your knowledge. It's a way to achieve immortality.
| __, Jobst Schmalenbach, [EMAIL PROTECTED], Technical Director|
| _ _.--'-n_/ Barrett Consulting Group P/L & The Meditation Room P/L |
|-(_)------(_)= +61 3 9532 7677, POBox 277, Caulfield South, 3162, Australia|
--
SLUG - Sydney Linux User Group Mailing List - http://slug.org.au/
More Info: http://lists.slug.org.au/listinfo/slug
