1200y3 wrote:Show me some evidence that a power company has poorer line frequency than we can do ourself.
Have you got a dual trace oscilloscope? Hook one trace to a quartz oscillator, and the other to the AC mains & watch the 2 sinewaves.
Mains frequency is deliberately skewed too. Under high load conditions, it drops. Under light load conditions, they up the frequency at the power station to make up for lost cycles - so the total number of cycles over a 24h period is always constant.
How do you know that strobe dots are accurate then?
Just count them! What may vary is the spacing, but minor misregistration when printing or machining the dots doesn't result in any error in frequency checking when using the strobe - it may make exact evaluation of flutter imprecise, but not rotational frequency.
A portable battery operated strobe is great for the convenience, but how would you know if it slips off frequency?
Quartz crystals don't. It just doesn't happen.
then a plug in LED nightlight works excellent. For $2 you're in business. But if you use a neon lamp with a rectifier, you won't get fooled, because all bands are visible, but in motion, when one band is locked.
If your motor is synchronous, you're stuck. The strobe is affected by the same errorr that makes the platter speed erroneous. So the result is zro visible error regardless of how large the error is - it could be +/- 100% and amains driven strobe would show it as perfectly aurate.