Carlos E. R. wrote:
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The Saturday 2006-09-09 at 10:24 +0200, Per Jessen wrote:
Basil Chupin wrote:
Ok, if you want me to call it a "speed controller" rather than a rheostat then to make you happy I'll call it a "speed controller" :-) Personally, I'd prefer potentiometer. I had to go lookup what a "rheostat" is :-)
| From The Collaborative International Dictionary of English v.0.48 [gcide]: | | Rheostat \Rhe"o*stat\ (r[=e]"[-o]*st[a^]t), n. [Gr. "rei^n + | stato`s standing still.] (Elec.) | A contrivance for adjusting or regulating the strength of | electrical currents, operating usually by the intercalation | of resistance which can be varied at will. --Wheatstone. | --{Rhe`o*stat"ic}, a. | [1913 Webster]
Here, in Spain, the word is old fashioned; by rheostat I understand a coiled wire device designed for power, ie, for directly controlling the current of a (relatively) high power device, as a motor or fan. A potentiometer is always very low power.
Thinking about what Basil reported, the only explanation I can think of is that the computer was turning on and off the current fast on the fan circuit; being a coil, the rheostat can vibrate. That is, if his circuit is really a rheostat and not an active electronic circuit.
The heatsink has a "smart IC controller" which provides "linear fan speed and noise control" and this is also controlled by a "VR control function". The "VR control function" I read to be "variable resistor control function" which in my limited electrical knowledge equates to a rheostat or potentiometer :-) .
I have found that effect when using a tyristor circuit (dimmer) to control an open air coiled wire stove: at some settings it vibrated, but softly. In fact, if you put a dimmer at middrange controlling a bulb, and poise a magnet to the bulb, you can see the filament oscillating wildly (and finally breaking).
Now I find this explanation most interesting. This may explain why I get a high-pitched vibrating sound from the "control knob" for the PSU/case fans at a certain (low) speed. Cheers. -- This computer is environment-friendly and is running on OpenSuSE 10.1