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10. Application information
Using the orientation mark, it is now clear that the images
appearing at 3,300, 1,650 and 825 RPM are multiple-
image harmonics. In each of these cases, three identifica-
tion marks appear. On the other hand, a singular image
appears at 1,100 and again at 550.
The first single image with only one reflection mark appears
if 1.100 rpm has been set on the instrument, another one
at 550. Please remember, a single image always appears if
the rotational speed set on the instrument matches the
rotational speed of the object or if an integer divisor (1/2,
1/3, ...) of the object speed has been set on the instru-
ment. The true rotational speed therefore is 1.100 rpm. If
the instrument is set to 550 rpm, only every second rotor
revolution will be flashed.
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:
Image No.:
1
2
3
4
Flash Rate:
6,000
4,000
3,000
1,500
The harmonic images at 6,000 and 4,000 RPM are not sin-
gular, but double and quadruple. A singular image does
appear at 3,000 and again at 1,500 RPM. 3.000 rpm is the
actual rotational speed.
17
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