Table of Contents
Advertisement
TYPE 1391-B PULSE, SWEEP, AND TIME-DELAY GENERATOR
e. Adjust R104 s o that the direct synchronizing pulse is
-
. .
formed with minimum voltage input. With correct adjustment, the
input voltage will be l e s s than 0.3 volt rms.
3.3.2 ADJUSTMENT OF C102.
a. Set the TRIGGER SELECTOR switch to POS GOING AC.
b. Set the SWEEP TRIGGER switch to DIRECT.
c. Connect the oscilloscope probe to the center (output) ter-
minal of S203, the SWEEP TRIGGER switch.
d. Adjust C102 for a trigger amplitude of 5 to 6 volts peak-
to-peak.
3.4 DELAY
CIRCUITS.
3.4.1 ADJUSTMENT OF THE TIME DELAY MICROSECONDS
DIAL MINIMUM AND MAXIMUM. This adjustment should be ne-
cessary only when eitherV203, V204, or V205 has been replaced.
The time delay between the direct and delayed synchronizing
pulses must be measured accurately, and should be within 0.3
percent.
There are three different ways to measure the time delay
between the direct and delayed synchronizing pulse. The first
two ways require the use of only the high-speed oscillograph
and the precision time-marker generator. The third method, most
convenient for the three longer delay ranges, requires the use of
the time-interval measuring device (refer t o paragraph 3.2).
3.4.1.1
First Method. In this method, the time-marker generator
is used to s e t the prf of the Type 1391-B a t a rate considerably
slower than the period corresponding to the delay range to be
checked. A second output from the time-marker generator is pre-
sented to calibrate the oscilloscope sweep. An electronic switch
that will simultaneously present the delayed synchronizing sig-
nal and the timing markers to the oscilloscope is recommended.
Timing markers can also be presented if they are placed on the
oscilloscope gate input terminals either to brighten or to blank
the oscilloscope sweep to display the marker interval. The posi-
tion of the direct synchronizing pulse relative to the timing
markers is carefully determined and the oscilloscope probe is
moved to the DELAYED SYNC terminal. The delay dial calibra-
tion can then be checked at the cardinal points represented by
the timing markers. This procedure is the only effective means
for calibration of the lower two delay ranges, 1-10 and 10-100
p s e c .
3.4.1.2 Second Method. In the second method, the timing-mark-
er generator is used to s e t the prf of the Type 1391-B a s in the
first method, but the higher-frequency timing markers corres-
ponding to the cardinal points on the delay dial are fed t o the
appropriate COINCIDENCE DRIVE terminals and the coincidence
system i s adjusted s o that coincidence is established only when
the coincidence gate is produced a t the same time a s one of the
marker pulses. Since there is a finite rise time of about 0.2 p s e c
a t the early edge of the coincidence gate, the correct alignment
of the early edge of this gate with a given marker pulse to light
the DELAY MONITOR lamp will permit sufficiently accurate cali-
bration only above 100 p s e c , and therefore this method becomes
effective only on the third range and above. If, for example, i t is
desired to calibrate the 100-psec-to-1-psec range a t 100-psec
cardinal points, the timing-marker generator should s e t the prf a t
100 cps, and 100-psec calibration markers should be fed to the
COINCIDENCE DRIVE terminal corresponding to marker polarity.
The COINCIDENCE GATE DURATION control should be s e t at a
value considerably l e s s than 100 p s e c , say 20. Now suppose
the TIME DELAY MICROSECONDS dial is rotated s o that the
actual delay is 190 psec. The second 100-psec marker pulse
from the timing generator will lie in the center of the coincidence
gate, and the DELAY MONITOR lamp will glow. As the delay
dial setting i s increased to exactly 200 p s e c , the leading edge
of the coincidence gate will move out from under the 100-psec
marker and the lamp will go out. It is apparent, therefore, that
the accurate calibration point is attained when the delay dial is
moved from higher to lower delay reading a t the point where the
DELAY MONITOR lamp just lights. For the calibration of longer
delay ranges, correspondingly longer time-duration coincidence-
gate settings can be used. The accuracy, determined by rise
time of the coincidence gate and the ignition voltage of the DE-
LAY MONITOR lamp, increases.
3.4.1.3
Third Method. A time-interval measuring system, capa-
ble of being operated by the direct and delayed synchronizing
signals, provides a convenient method of calibration. Suppose
the time-interval meter is capable of resolving and counting
1-psec pulses. The delay circuit can be calibrated to an accuracy
of 0.1 percent a t 1 msec by the plus or minus one-count limita-
tion. Four decade registers are necessary for this precision a t
the low end of a range. The procedure is to connect the start
terminals of the time-interval meter to the DIRECT SYNC OUT
terminals of the Type 1391-B, and the stop terminal to the DE-
LAYED SYNC OUT terminal of the Type 1391-B. A simple trig-
ger, derived on the longer ranges simply by the tapping of a fin-
ger against the P R F DRIVE terminal or by the use of a switch
and a battery, initiates a "single stroke" delay-circuit action
and opens and closes the timing gate of the time-interval meter
a t the delay period. The delay then reads directly in the decade
registers of the interval counter.
By any one of the above three methods, the accuracy a t
both ends of the TIME DELAY MICROSECONDS dial should first
be established for two or three ranges. If the minimum or maxi-
mum is consistently off on all these ranges, then either the de-
lay minimum control (R238) and/or the delay maximum control
(R236) should be readjusted. This readjustment should be ac-
complished on the 10-100-msec range. It i s necessary to s e t both
the minimum and the maximum controls for correct value a t dial
readings of 200 for the minimum and 1000 for the maximum. Hav-
ing calibrated the 10-100-msec range in this manner, check o v e r
a l l dial linearity by checking the delay a t cardinal dial points,
and t e s t the other ranges to establish their accuracy. If only one
range deviates from the correct readings, adjust the appropriate
potentiometer (R228 to R233). Note that the 100 msec-to-1-sec
range has two adjustments: R233 adjusts the time constant
COP
rectly to produce the accurate maximum delay a t 1 s e c and R232
adjusts the amplitude of the initial voltage step for the correct
dial reading a t 100 msec. If V203 has been replaced, it may be
necessary to readjust C222 of the I-10-psec range to restore
dial calibration due to small changes in stray capacitance.
3.4.2 COINCIDENCE GATE ADJUSTMENTS. If, upon replace-
ment of V206, i t
is
found that either the minimum or maximum co-
incidence gate duration departs intolerably far from 3 or 1000
p s e c , adjust R255, the 1000-psec adjustment, or R249, the
3-psec adjustment. Usually only a cathode-ray oscillograph con-
nected a t TP204 is necessary to establish the desired measure-
ment accuracy. Of course, a more precise adjustment of either
the minimum, maximum, or any point between can be made if
higher accuracy is desired. It is necessary to repeat the
3-
and
Advertisement
Table of Contents
