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7 Application information
reflective tape or equivalent) in order to differentiate its
orientation.
•
A singular image always appears at exactly one half of the
object's true RPM!
Example 1 (mark needed):
This example shows why identifying marks are important. Suppose
you want to determine the true RPM of this fan. The only thing you
know is that its speed is less than 3,500 RPM. If you slowly
decrease the flash rate starting from 3,500 FPM, the following
"frozen" images appear:
Image No.: 1
Flash Rate: 3,300
Image No.: 1
Flash Rate: 1,100
What is the actual rate of the fan? Images 1, 3, 5, 6 and 8 are all
"frozen," so the rate could be taken as 3,300, 1,650, 1,100, 825 and
550.
Which is correct?
In order to determine the fan's actual speed, a mark is added to
one of the blades and the test is run again.
40
2
3
2,200
1,650
2
3
825
733.3
4
1,320
4
550
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