24 Nov
2007
24 Nov
'07
11:14 p.m.
On 24 Nov 2007 at 22:27, dwight elvey wrote:
I got my math wrong. The fellow is also wrong.
45/60 = .75.
100/.75 = 133.333....
If rounded to 133, you get 45.11278195----
Still, using Tony's multiple method, 400 dots
would work fine. It would be a large disk but
it would work.
45 rpm is 0.75 r/sec. The strobe lamp flashes 100 times per second
(50Hz * 2). So, the disc completes 3 complete revolutions in 4
seconds. During those same 4 seconds, the lamp flashes 400 times.
So there needs to be 400/3 bars on the disc if there is to be a bar
exactly underneath the lamp for every flash, or 133.3333 bars, which
causes the problem. If we increase the number of bars to 133
exactly, the disk will be turning at 100/133 = 0.75188 r/sc or about
45.1128 rpm.
If we put 400 bars on the disk, the lamp will flash once for every
third bar passing under it. Not the crisp display we were hoping
for, however--and I don't know what the visual error would be without
trying it.
At least that's how I compute it. So maybe the guy is right.
Cheers,
Chuck