2.9.4 USE WITH A CONTACTOR.
For low -speed application (below 1000 rpm), where significant
speed variations are encountered, it may be desirable to use a mech -
anical contactor, such as the General Radio Type 1535, for synchroni -
zation and phasing. The phase adjustment of this contact or is independent
of the speed of rotation. The Type 1531 stroboscope will flash on the
opening of the mechanical contact (refer to paragraph 3.2.7),
Before connecting the contactor to the strobo-
scope, make sure the range switch is not in any
one of the EXT INPUT positions. This precaution
will prevent holdover of the thyratron when the
the range switch can be set to any desired posi-
tion. If the stroboscope fails to flash because
o f holdover. turn the instrument off, and then
on again after 10 seconds (refer to paragraph
After making sure the range switch is not in an EXT INPU T position,
connect the contactor to the INPUT jack, using the standard phone plug
supplied. Then the synchronization procedure is as follows:
a. Set the range switch to one of the EXT INPUT positions, depend-
ing on the speed of the object being observed. The maximum speeds
indicated can be exceeded up to the point where the lamp flashes errati -
tally. Generally, the highest intensity position that allows satisfactory
flashing of the instrument should be used.
b. Set the RPM control fully clockwise. If this control is not fully
clockwise, the flash will occur at a delayed time after the contacts close
and the unit will not operate properly at high speeds.
c. At speeds above 1000 rpm, some difficulty may result from
multlple flashes when the Type 1535 Contactor is used to synchronize
2.9.5 USE OF ELECTRICAL -SIGNAL TRIGGERS.
The instrument can be triggered by any electrical signal of at
least 6 volts peak-to-peak amplitude (maximum of 500 volts). For sine -
wave inputs, the unit will operate with a 2 -volt rms signal down to 5 c/s.
For pulse inputs (i.e., step -wavefront signals), the repet it ion rate
has no minimum value. The instrument can be synchronized with external
signals of frequencies up to at least 24,000 rpm, 400 c/s. (Refer to para -
graph 3.2.7.) Since a positive-going signal is required at the input to flash
the stroboscope, positive pulses are required to synchronize on the lead-
ing edge. Negative pulses will result in a delay, depending on the trailing-
edge characteristics of the input pulse.
To operate the unit from an external electrical signal, turn the
range switch to one of the EXT INPUT positions, depending on the fre -
quency of the driving signal. Connect the external -signal source to the
INPUT jack. Observe the precaution given in NOTE, paragaph 2.9.4.