7 Application information
41
Image
No.:
1 2 3 4
Flash
Rate:
3,300 2,200 1,650 1,320
Image
No.:
5 6 7 8
Flash
Rate:
1,100 825 733.3 550
Using the orientation mark, it is now clear that the images
appearing at 3,300, 1,650 and 825 RPM are multipleimage
harmonics. In each of these cases, three identification marks
appear. On the other hand, a singular image appears at 1,100 and
again at 550.
Here, only one mark appears. Recall that “a singular image always
appears at exactly one half of the object’s true RPM”. 550 is one
half of 1,100. Therefore, the rate of the fan must be 1,100 RPM.
Example 2 (no mark needed):
This example illustrates how the actual speed of an object can be
determined without the use of an orientation mark - provided that
the object has a suitable shape.
Assume that the speed of this cam is known only to be less than
7,000 RPM. Because it has a unique shape, it does not need an
identifying mark. As the flash rate is lowered from 7,000, the
following harmonic images appear:
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