# oscilloscope to measure RPM?

Discussion in 'The Projects Forum' started by 03GTS, Jun 2, 2009.

Jan 5, 2007
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2. ### mik3 Senior Member

Feb 4, 2008
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Does it output DC or AC voltage?

3. ### Externet AAC Fanatic!

Nov 29, 2005
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With your generator running at a somewhat steady speed, connect the oscilloscope to its output and if there is any repetitive waveform or spike, you can discern its period on the oscilloscope.
Turns per second = frequency = 1 / period. If you want turns per minute instead of per second, multiply by 60.
Miguel

4. ### KL7AJ AAC Fanatic!

Nov 4, 2008
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If you have a photocell or photoresistor you could aim at the blades (assuming you have some daylight) you might get enough of a reflection to see on a scope.

5. ### studiot AAC Fanatic!

Nov 9, 2007
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Yes except that you may have to divide by the number of poles on the generator.

6. ### 03GTS Thread Starter Member

Jan 5, 2007
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looks ac just by hooking up my multimeter to it. it reads 0 volts on DC. I am able to get a reading on AC

will try this weekend

i dont. but will remember this for future reference thank you

noted. thanks

will report back with what i find this weekend

7. ### studiot AAC Fanatic!

Nov 9, 2007
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Unless your multimeter is very sophisticated it reads average on AC. This can be seriously misleading on waveforms very different from sinusoids.

8. ### mik3 Senior Member

Feb 4, 2008
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If it is AC, use the scope to measure its frequency and then calculate the angular velocity by using:

ω=2*pi*f

If you want rpm=ω*60/2pi