Checkline QB-LED - Manual (Page 16)

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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 affixed
with an identification marking (using color or a reflective 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)
The example shows the importance of using identification markings. Say you
want to determine the actual rotational speed of this ventilator.
The only thing you know is that its rotational speed is less than 3,500 rpm. The
following “frozen” images will appear if you reduce the flashing rate based on
3,500 FPM (flashes 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.