SM0486
(5) The Stroboscope.
The stroboscope is an electronic tachometer that
provides a direct and accurate means of measuring rotary speeds from 60 to 15,000
rpm.
The stroboscope is especially versatile in application because it does not
require mechanical connection to the device under observation and will not absorb
power or influence operational speeds.
Remote or inaccessible mechanisms may be
observed at considerable distance provided a "line of sight" is available and
ambient light levels are lower than the stroboscope's output.
a. Stroboscope principles.
Stroboscopic effects may be produced when
an intense light of short duration, is repeated at precise intervals.
If this
light is directed upon a rotating or vibrating object, the stroboscopic effect will
be observed when the repetition frequency of the light is in proper ratio to
movement frequency. If the frequency of movement and light repetition are exactly
matched, the moving object will be viewed distinctly only once each cycle.
The
object will appear to be stationary, since it will be illuminated by the flash of
light at precisely the same phase of each cycle.
This "single image" apparent
cessation of motion will also occur when the light frequency is submultiple (half,
third, quarter, etc.) of movement frequency. Multiple images occur when the light
frequency is a multiple of movement frequency. This phenomenon occurs because the
moving object is illuminated more than once each cycle. Satisfactory stroboscopic
effects will occur only when the pulsed light is more intense than the ambient
light and the light pulses are short enough to prevent smear of blur.
b. Stroboscope operation and use.
The stroboscope
shown in Figure 7
operates from a 115-volt, 60-cycle AC powerline.
It consists
of a power supply,
oscillator, pulse amplifier, and a flasher tube. The complete
unit is mounted in
an easily portable metal case. The flashing rate is varied by
turning a knob and
reading rpm directly from the scale.
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