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Model 1821A
Section
IV
Paragraphs
4-1
to
4-10
SECTION
IV
PRINCIPLES
OF OPERATION
4-1.
INTRODUCTION.
4-2.
The Model 1821A
Time
Base and Delay Genera-
tor
produces two
linear
sweeps
for
use
as
time bases
in
the
Model
180-series Oscilloscopes.
Either sweep,
or
a
combination
of
both,
may
be selected by front
panel
controls.
The
selected
sweep
is
applied
to
the
Oscilloscope
to
drive
tlie
horizontal
amplifier.
Figure
4-1
is
an over-all block
diagram
that
shows
the
principal
circuits
of
the
Model 1821A
and
their rela-
tionship
to
each
other.
4-3.
The
trigger
generators each produce a
fast- rise
negative pulse
at
some
point on the trigger signal.
The
gate
generators are
"fired" by these
pulses and
produce
negative gates
that
are coupled
to
the inte-
grators.
Each
integrator
generates
a positive
sweep
during
the
time
it
is
undamped
by
the gates.
4-4.
The sweep comparator
generates a
positive
pulse
at
some
time
after the start
of
the
main
sweep.
This
pulse "resets"
the
delayed
gate
generator
to
a
pre-
trigger
condition.
Since
the
delayed
gate
generator
can
not
be
fired
until
it
is
reset, the
delayed
gate
and
sweep
always
start after the
main
gate
and sweep.
4-5.
The main
and delayed
gates
from
the
gate
gen-
erators,
and
the
main
and delayed
sweeps from
the
integrators
are applied
to
the
Sweep
Display
switch.
This
front
panel
control couples
the
main
and delayed
signals,
in
various combinations,
to
the
Model
180-
series Oscilloscope.
4-6.
MAIN
SWEEP.
4-7.
The main sweep
circuit
is
explained
in
the fol-
lowing paragraphs.
The
Block
Diagram
Description
is
a
general explanation
of
circuit function
while
Circuit Details
provides
more
complete
information.
4-8.
BLOCK
DIAGRAM
DESCRIPTION.
4-9.
A
block
diagram
of
the
main sweep
circuit
is
shown
in
Figure
4-2.
4-10.
NORMAL.
Setting the
SWEEP MODE
switch
to
NORM
disables
the
auto
circuit
and allows
the
main
sweep
circuit
to
operate normally.
The
selected
trigger signal
is
applied
to
the
trigger
generator which
produces
a fast-rise negative pulse
at
some
point
on
the
trigger
signal.
The
gate
generator
is
"fired"
by
this
pulse
and produces
a
negative
signal
that
is
ap-
plied
to the
Sweep
Display switch and
to
the integrator.
When undamped
by
this signal,
the
integrator begins
to
generate
the
main
sweep.
This
linear positive-
going
sweep
is
applied
to
the
Sweep
Display switch and
Figure
4-2.
Main Sweep
Circuit
Block
Diagram
02591-3
4-1
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