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10. Application information
The image will appear to freeze again at 3,000 FPM. At this
rate, the fan appears to be very bright. You can now use
the FINE ADJUSTMENT knob to vary the rate above and
below 3,000 to make the fan appear to move both clok-
kwise and counterclockwise.
Helpful Hints:
- Harmonic images appear at both whole number multi-
ples as well as fractional intervals of the object's actual
rate.
For example, a fan rotating at 1,000 RPM will appear to
be frozen at the whole number multiples of 2,000 (2x),
3,000 (3x), 4,000 (4x) etc., as well as at the
fractional rates of 500 (1/2x), 750 (3/4x) and 1,500
(1 1/2x), etc.
- Some of the harmonic images are "singular" in appea-
rance while others are "multiple". This becomes impor-
tant if you want to determine the objects actual rate as
discussed in chapter 10.4 Determing an object's true
RPM.
10.4 Determing an object's true RPM
The Pocket-Strobe can be used as a digital tachometer to
determine the true RPM and / or the reciprocation rate of an
object. This is done by visually "freezing" the object's
movement and then reading the LCD display. As with all
stroboscopes, it is important to verify that this frozen image
is not a harmonic of the object's actual rate.
Helpful Hints:
- Knowing the approximate rate of the object in advance
gives you a useful starting point.
- If the object has a uniform shape, like a multi-blade fan
or motor shaft, you must give it an identifying mark
(using paint or reflective tape or equivalent) in order to
differentiate its orientation.
- A single image always appears if the rotational speed
set on the instrument matches the rotational speed of
the object or if an integer divisor (1/2, 1/3, ...) of the
object speed has been set on the instrument.
15
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