Finding out fan RPM even with one wire or even w/o any? Yep, also possible
|. . . For the first you need a properly
tuned at least one (1) guitar chord/string, for the second a
piano or an accordion ! There would be
a need also of a small thin plastic tube too
! Some basic natural musical talent is
involved & required also .
The procedure: first you have to count how many rotor blades the fan has & remember it. Than you start the fan to spin at desired speed & thru that mentioned thin plastic tube blow the air thru fans rotor blades spinning. Now you should hear a "windy" tone of certain height & remember it to compare it with some musical instrument tones like a guitar ones. When you find out to which musical note that fan tone corresponds, check the frequency of it on the lower partial chart !
[Another similar way is to take one meter of flexible 0,5cm diameter plastic tube & one end stick it in your ear & another end put it as close as possible to a rotating fans rotor blades.
|You should hear a weak
tone; if two, remember a higher one for same procedure of
finding out a frequency of tone! (if the tone is strong,
could be that your head is resonating ... )]
If you are not certain if the note is correct, repeat the procedure (some people have difficulties to recognize proper tone hight because of tone harmonics - octave or third & fifth of it) !
The frequency you got you have to divide it with a number of fan rotor blades to get a proper number of fan rotor revolutions per second, which you than multiply with 60 to get a RPM number. Computer fans usually have 5,7,9 or 11 rotor blades ...
Example: 7-rotor blades TTvolcano-II fan at 12V gives close to tone Cis 2 (Des, C#), which is an octave higher (double frequency) than Cis 1 (277,2 Hz). So: [554,4 / 7] x 60 = 4.752 Rpm. Simple as that . . . . .
....Clicking the speaker icon, DownLoads & plays a tone (with a bit of delay, on Dial-Up few seconds )
|. . . Tone & frequency, higher to lower||. . . piano key color, guitar tone & string remarks|
|.E 2||.659,3 Hz||.w¶¶. - (guitar 1st string = thinest, on 12th field pressed, octave up)|
|.A 1.....(standard !)||.440,0 Hz||.w¶¶ -. ... .... ....... ..(guitar 1st string = on fifth field pressed)|
|.Gis /As (G#)||.415,4||.b¶¶¶|
|.Fis /Ges (F#)||.370,0||.b¶¶¶|
|.E||.329,7||.w¶¶ - ....................(guitar 1st string = thinest empty)|
|.Dis /Es (D#)||.311,2||.b¶¶¶|
|.Cis /Des (C#)||.277,2||.b¶¶¶|
|.H||.246,9||.w¶¶ - ....................(guitar 2nd string = second thinest empty)|
|.A 0||.220,0 Hz||.w¶¶|
|.Gis /As (G#)||.207,7||.b¶¶¶|
|.G||.196,0||.w¶¶ - ....................(guitar 3th string = third thinest empty)|
|.Fis /Ges (F#)||.185,0||.b¶¶¶|
|.Dis /Es (D#)||.155,6||.b¶¶¶|
|.D||.146,9||.w¶¶ - ....................(guitar 4th string = third thickest empty)|
|.Cis /Des (C#)||.138,6||.b¶¶¶|
|.B /Ais (A#)||.116,6||.b¶¶¶|
|.A -1||.110,0 Hz||.w¶¶ - ................. .(guitar 5th string = second thickest empty)|
|.E -1||...82,4 Hz||.w¶¶ - .................... (guitar 6th string = thickest "empty" one)|
As you can see, this upper chart only partially covers the audio/music spectrum, but with knowing that a tone difference of an octave up/down (once higher/lower tone) covers double/half of determined frequency, is no problem to calculate the rest of them ! This was discovered practically more than 2.000 years ago by famous old-Greek mathematician Pitagora, who found out, that at the same string tension if the string is shortened to half, it resonates at double vibration speed (frequency) = same tone but octave (once) higher! No, it was not the same man that found out that famous Pi number ( P = 3,14xx...) useful in geometry & more /that one was Archimed/ ... ... Similar is with lowering tones!
If you make some calculations, you can find out by yourself, that the two neighbor half-tones are approx. for factor 1,05922x...in frequency away from each other. And if you look at the chart with a head turned left closer to the left shoulder, you can realize, that piano key colors are in fact its keyboard (except first & last tone non correspondent) for better recognition of chart tones ...
This chart is also very useful to find out a frequency of a tone produced by some electronic audio oscillator if fiddling with that & not having some kind of frequency-meter ; hey & if having it, can be used also to tune a guitar !
© Zdenko Jerman-Spajky