Trigger Slope
The
black
TRIGGER
SELECTOR
knob
selects
the
trigger
source
and determines
whether
the
sweep
will
start
as
the
waveform
is
going
positive
or
negative. The
+
positions
of this
switch cause
triggering
to occur
during
the
rising
portion
of
the
waveform.
The
- positions
cause
triggering
to occur
during
the
falling
portion of
the
waveform.
The
trigger
slope
feature is
not
used
in
the
H
F
SYNC mode.
Triggering
Mode
The
red
TRIGGER
SELECTOR
knob selects
the
kind,
or
mode,
of
triggering
used.
The
DC
position
will
permit
triggering
on all
signals
from de
to
about
five
megacycles.
It
is
especially
useful for
signals
below
60
cycles
where the
sensitivity
of
AC
triggering begins
to fall
off.
In
the
AC
position,
the
switch
inserts
a
capacitor
in
the
trigger
circuits
to
make the
trigger settings
independent
of
the
vertical
position
of
the
trace.
This
mode
is
slightly
more
sensitive than
the
DC
mode.
The
AUTO
position
arranges
the
circuits
for
an
automatic
synchronizing
action
rather
than
a
strict
triggering
action.
In
this
position
the
trigger-shaper
multivibrator
free-runs
at
a
repetition
rate
of
about
50
cycles.
The
multivibrator
will
lock
in and
run
synchronously
with
trigger
signals
from
60
cycles
to
about
2
megacycles.
If
the
trigger
signal
is
lost
the
sweep will
not
stop
but
will
continue
at
a
reduced
repetion
rate
without synchronization.
In
the
H
F
SYNC
position
the
trigger-shaper
circuits
are
bypassed
and
the
triggering wave
form
is
used
to
synchronize
the
time base
circuits
directly.
The
time-base
generator
must
be
free-running
for
this type
of
operation.
It
free-runs
at
advanced
settings
of
the
STABILITY
control.
This mode
of
operation
is
primarily
useful
for signals
in
excess
of
two
megacycles.
Stability
The STABILITY
control
adjusts
the
bias
level
on
a
multivibrator
in
the
time-base
generator
near
the
level
at
which
the
sweep
will
free-run. Three
principal
settings
of
the
STABILITY
control
are
used;
the first
setting
is
with
the
control
advanced
to the
right, past
the
point
where
thegenerator free-runs;
second,
retarded
to
the
left
just past
the
point
where
free-running
ceases;
and
third, retarded
all
the
way
left
to
make
the
generator
inoperative.
The
second
setting
is
duplicated
by
an internal
circuit
when
the
STABILITY
control
is rotated
to
the
PRESET position.
When
the
time-base
generator free-runs,
the
sawtooth waveforms
are
produced
at
a
repetition rate
determined
by
the
generator
circuit
itself.
The
STABILITY
control
varies
this
repetition
rate
slightly. In
the
second,
or triggered,
position
of
the
STABILITY
con
trol
the
time-bas
j
generator
does
not
run
until
a
trigger
pulse
is
received
at
which
time
one
sawtooth
waveform
is
produced
and
the
generator
waits
for the
next
trigger
pulse.
This
is
also the
case when the
STABILITY
control
is
set
at
PRESET.
For
synchronized
operation
of
the
time-base
generator,
as
used in
the
H
F
SYNC
position,
set the
STABILITY
control
to the
advanced
position
so
that
the
generator
just
free-runs,
and
keep
it
to
the
right
of
this
point
while
adjusting
its
point
to synchronize the
time
base.
For
all
triggered
operation
except
AUTO.
,
the
STABILITY
control
should
be
retarded
to
the
left
of
the
free
run
point
or
set to the
PRESET
position
(S/N
1001
-up).
General-Purpose Triggering
For
most
average
triggering
applications
the
AUTO,
mode
of
triggering
is
the
easiest
to
use.
Only
one
control
need
be
adjusted
and
after
it
is
once
set the sweep
will
trigger
satisfactorily
on
a
wide
variety
of
waveforms
and
over
a
wide
range
of
sweep
speeds
without
resetting.
When
the
STABILITY
control
is
set
properly there
will
always
be
a
trace
on
the
screen,
whether
a
signal
is
present
or
not,
unless
the
trace
is positioned
off
the
screen
vertically.
This
feature
is
especially
valuable,
if the
probe
is
being
moved
from
one
point
to another
in a
circuit
under
test.
To
use
the
AUTO, mode,
set
the
red
TRIGGER
SELECTOR
knob
to
AUTO.
A
horizontal
trace
should
appear
immediately. A stable
display
should
be
obtained
on most
signals
within
the
range
of
60
cycles
to
2
megacycles
when
using this
mode.
AA
Operating
Instructions
- Type
515/515A
2-7