equal to the difference between the actual speed of the object and the
flashing rate of the stroboscope.
If the flashing rate is set slightly higher than the speed of the object
being observed, the same slow motion will result, but in the opposite
This stroboscopic technique of slowing down motion can be ex -
tremely useful in investigating the operation of a device under normal
operating conditions. Excessive vibration, misalignment of parts, mode
of vibration of equipment on a shake table, operation of vibrating reeds,
actual relation between traveler and thread during a complete revolution
of the traveler on a textile spinning frame -these are only a few examples
of slow-motion studies that are possible with the Type 1531.
2-9. EXTERNAL SYNCHRONIZATION
2.9.1 SYNCHRONIZING TO POWER-LINE FREQUENCY.
When using a 50- or 60-cycle power line, synchronization of the
flashing rate is obtained automatically by setting the range switch to the
LINE /EXT INPUT position. For 400-cycle operation, set the range switch
to the EXT INPUT, LOW INTENSITY position and inject a 400-cycle
signal at the INPUT jack (refer to paragraph 2.9.5).
2.9.2 USE WITH FLASH DELAY AND PICKOFF.
Two very useful accessories for the stroboscope are the Type
1531 -P2 Flash Delay and the Type 1536 Photoelectric Pickoff. The com-
bination of these three instruments makes it possible to synchronize the
flash of the Type 1531 with the moving object at any desired point in the
cycle of operation of the object. These synchronizing devices can operate
at very high speeds and do not load the machine under observation. See
The Type 1531-P2 Flash Delay is a small, portable, time-delay
unit that is used to insert a controlled delay period between an externally
generated trigger pulse and the resulting light flash from the stroboscope.
The flash delay also provides a convenient method of obtaining single-
flash photographs at any desired point in the cycle of the moving object.
The Type 1536 Photoelectric Pickoff is used to convert the motion
of a moving object to electrical impulses that can be applied to the strob -
oscope. It consists of a light source, a simple cylindrical optical system,
and a photocell. Variations in ref Iectivity, produced by the motion of the
object being observed, produce electrical signals which are amplified,
delayed, and shaped by the Flash Delay, and then fed to the stroboscope.
Power for both the photocell and the lamp are supplied by the Type
1531 -P2 Flash Delay.
The reader should refer to the Operating Instructions for the Type
1531 -P2 Flash Delay and the Type 1536 Photoelectric Pickoff for further
information concerning these instruments and their use with the Type