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dataPAC User’s Guide
Chapter 5 - Balancing Measurements
Below the display are six buttons which control the operation of the stroboscope.
There are three major operating modes for the strobe: Internal, External and Charging. In the
Internal mode, the knob adjusts the flash rate from 30 to 14,000 Flashes Per Minute (FPM).
In the External mode, an external signal from a remote sensor is used to trigger the flash and
the knob has no effect. The strobe is in External mode when the dataPAC is connected to it.
The Charging mode occurs when the strobe has the battery charger plugged into it.
The strobe is in the external mode whenever there is a plug in the input jack. The input jack
is indicated with an up (in) triangle.
In the External mode the dataPAC makes all the flash rate adjustments. The Alt Function
mode and triangle is automatically set in this mode, since the primary function of the
buttons have no use in this mode.
Refer to the dataPAC Strobe dB+ Operating Guide for more information about using the
Strobe dB+.
Measuring Speed with a Strobe
The primary use for a stroboscope is to stop motion for diagnostic inspection purposes.
However, the stroboscope can also be used to measure speed. In order to do this several
factors need to be considered. First, the object being measured should be visible for all 360°
of rotation, such as 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 you need to mark the object with a piece of tape or paint in a
single location only, to be used as a reference point.
If the speed of rotation is within the range of the stroboscope, start at the highest flash rate
and adjust the flash rate down. At some point you will stop the motion with only a single
image of the object in view. Note that at a flash rate twice the actual speed of the image you
will see two images. 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 1/2 X softkey on the dataPAC. 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 keyway 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 shafts 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
ACTUAL
RPM
1/3 times
1000
1/2 times
1500
1 times
3000
2 times
6000
3 times
9000
4 times
12000
Stopped Image
Flash Rate (FPM)
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