Quote:
Originally Posted by Kevin Sevcik
Exactly which sensor are you using? There's about 10, heh.
At any rate, rough calculations indicate that you probably want a wider strip of retro tape. At 12,500 RPM, your 3/4" strip is in view for something like 500-600 microseconds.
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For students wanting to know how to do this calculation:
tapeWidthInches = 3/4
0.75
radius = 1
1
theta = asin(tapeWidthInches/2/radius)
0.384
tapeWidthRevs = (2*theta)/(2*pi)
0.122
rpm = 12500
1.25e+004
minutes = tapeWidthRevs/rpm
9.79e-006
seconds = minutes*60
0.000587
microseconds=seconds*1e6
587
Quote:
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Which is right at the response time of your sensor.
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I don't see where they define what they mean by "response time". Is there a generally understood meaning of that phrase in this context? It seems it could have different meanings:
a) the pulse width must be at least that long in order to reliably be detected, or
b) the sensor takes that amount of time to respond to a pulse (and the minimum required pulse width is not specified)
Also, the "repeatability" is listed at 95 us. If that means random +/- peak noise, at 12500 rpm your sensed speed could range from 12,300 to 12,800.
Quote:
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...until you disable your PID.
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He's not using a PID. But I suppose the same thing could happen.