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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 flash rate and adjust the flash 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 flash 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 first SINGLE
image you see is the true speed. To confirm 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 first 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, of
the actual speed. You will see 2 images of the key way at 2 times the actual
speed, 3 key way at 3 times, etc.
The FPM equals the shaft’s Revolutions
Per Minute (RPM) at the highest flash rate that gives only one stationary
image of the key way.
Example: Object rotating at 3000 RPM
If the speed is outside the full scale range of the stroboscope (500,000
FPM), it can be measured using the method of harmonics and multipoint
calculation. Start at the highest flash rate and adjust the flash rate down.
You will encounter multiple images so be aware of these. Note the flash rate
Stopped Image
1/4 times 1/2 times
1 time
2 times
3 times
4 times
Flash Rate (FPM)
1000
1500
3000
6000
9000
12000
Actual RPM