13
remains constant*. The degree of rotation visible changes to keep the
pulse width of the fl ash constant*.
*Note: There are two limits maintained by the strobe – the pulse can
never be greater than 1300 µs nor can it exceed 10° of rotation. The
strobe automatically adjusts these values as the fl ash rate is increased
or decreased to maintain these limits at all times.
7.0 USING THE STROBOSCOPE TO MEASURE
RPM
The primary use for a stroboscope is to stop motion for diagnostic inspection
purposes. However the stroboscope can be used to measure speed (in RPM
/ RPS). In order to do this several factors need to be considered. First, the
object being measured should be visible for all 360° of rotation (e.g. The
end of a shaft). Second, the object should have some unique part on it, like a
bolt, key way or imperfection to use as a reference point. If the object being
viewed is perfectly symmetrical, then the user needs to mark the object with
a piece of tape or paint in a single location to be used as a reference point.
Look only at the reference point.
If the speed of rotation is within the range of the stroboscope, start at a
higher fl ash rate and adjust the fl ash rate down. At some point you will stop
the motion with only a single reference point of the object in view. Note that
at a fl ash rate twice the actual speed of the image you will see two images
(reference points). As you approach the correct speed you may see three,
four or more images at harmonics of the actual speed. The fi rst SINGLE
image you see is the true speed. To confi rm the true speed, note the reading
and adjust the stroboscope to exactly half this reading, or just press the ÷2
button. You should again see a single image (which may be phase shifted
with respect to the fi rst image seen).
For example, when viewing a shaft with a single key way you will see one
stationary image of the key way at the actual speed and at 1/2, 1/3, 1/4, etc.
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