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Section IV
Paragraphs
4-36
to
4-43
Model 1821A
MAIN
SWEEP
I82IA-B-I2A
Figure
4-3.
Delayed
Sweep
Circuit
Block
Diagram
is
also
coupled through
CR309
to the
base
of
Q306.
The
negative pulse
from
the collector
of
Q306
fires
CR401
starting the
delayed
gate.
In
AUTO,
therefore,
the
delayed
gate
and
the
delayed
sweep
start
immedi-
ately after the delay.
4-36. Setting the
delayed Trigger Source switch
to
either
EXT,
EXT-4-10 or INT, reverse
biases
CR309.
The
auto trigger
from Q410
is
blocked and
the gate
circuit
is
not fired
until
the
selected trigger signal
produces a
negative trigger
pulse.
In
EXT,
EXT-4-10
or
INT
the
delayed
gate
and
sweep
start
on
the
first
trigger signal after the delay.
4-37.
The
delayed
trigger generator,
gate generator,
and
integrator
operate similarly
to
the
main sweep
circuits
which are
explained
in
Paragraph
4- 13
to
4-
20.
4-38.
When
the
main sweep
ends
(Figure
8-8),
Q411
turns
off,
switching
CR423
to
a low-voltage
state.
The
negative output
from
the collector
of
Q410
turns
off
Q403, switching
the
Schmitt
trigger
to
its
pretrigger
state.
The
current
to
CR401
is
removed,
the gate
ends,
and
the
delayed
sweep
is
terminated. This
action
insures
that
the
delayed
sweep
ends
with the
main
sweep, preventing
the
main sweep from
being
trig-
gered
again while
the
delayed
sweep
is
being generated.
4-39.
SWEEP
DISPLAYS.
4-40.
The main
and delayed
gates
and
the
main
and
delayed
sweeps
are
applied
to
the
Sweep
Display
switch.
As
the
switch
is
rotated
between
the
MAIN, MIXED,
and
DELAYED
positions,
various combinations
of
the
4-4
applied signals
are coupled
to
the
Model
180-series
Oscilloscope.
A
schematic
diagram
of the
Sweep
Display
switch, S502,
is
given
in
Figure
8-10.
4-41.
Figure 4-4
shows
the
displays obtained
in
the
three
positions
of
the
Sweep
Display
switch.
For
illustration
purposes,
the vertical input signal
is
shown
to
be
a
repetitive
series
of
six
pulses.
The
first
pulsehas
some minimum
amplitude and each suc-
cessive pulse
is
larger.
The main
gate
and
sweep
start
on
the
first
pulse.
The
delayed
gate
and
sweep
are
2.
5
times
faster than the
main, and
start
(at
end
of
delay)
just
before
the
second
pulse.
4-42.
MAIN.
Setting the
Sweep
Display switch
to
MAIN,
couples
the
main sweep
to
the
Oscilloscope
for
deflection.
The main
and delayed
gates
are
combined
and coupled
to
the
Oscilloscope
for intensity.
The
portion
of
the
display
that
occurs during
the
delayed
gate
time
is
intensified.
Diode
CR502
limits the
maximum
amplitude
of
the
delayed
gate
to
a voltage
selected by R525.
4-43.
MIXED.
Selecting
MIXED,
combines
the
main
and delayed sweeps and
applies
them
to
the Oscillo-
scope.
CR501
prevents
the
main sweep from
feeding
back
into
the
delayed
circuit.
The
delayed
sweep
however,
couples through
when
it
exceeds
the
amplitude
of
the
main
sweep.
The main
gate
is
coupled
to
the
Oscilloscope
for
intensity.
The
first
part
of
the dis-
play
is
on
main sweep
time and
the last
part on delayed
sweep
time.
The
display
is
an even
intensity
except
for the difference
caused by
the different
speeds
of
the
main
and delayed sweeps.
When
the
delayed
sweep
02591-3
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