User guide
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5.0 DETERMINING THE ROTATIONAL SPEED OF OBJECTS
The stroboscope can be used as a digital revolution indicator to determine an object’s
actual rotational speed and/or the frequency of cyclical movements. The stroboscope
does this by visually “freezing” the object’s movement and then taking a reading of the
rotational speed or frequency from the LCD display. As is the case with all stroboscopes,
it is vital to ensure that this “frozen” image is not a harmonic of the object’s actual
rotational speed.
Useful information:
• It’s helpful to have a rough idea of the object’s rotational speed beforehand.
• Regular shaped objects, e.g. a fan with several vanes or a motor shaft, must be afxed
with an identication marking (using color or a reective strip etc.) in order to be able
to differentiate its orientation of movement.
• A still image always appears exactly at integer division of the speed of the object’s
actual rotational speed!
Example 1 (marking required)
e example shows the importance of using identication markings. Say you
want to determine the actual rotational speed of this ventilator.
e only thing you know is that its rotational speed is less than 3,500 rpm. e
following “frozen” images will appear if you reduce the ashing rate based on
3,500 FPM (ashes per minute):
What is the actual rotational speed of the fan? Images 1, 3, 5, 6 and 8 correspond to the
original one, which means the rotational speed could be 3300, 1650, 1100, 825 or 550 rpm.