For
any application
within
the
frequency
range
from
60
cycles
to
about
5
megacycles
where
the display
is
unstable on
AUTO.,
the
AC mode
can
be
used.
To use
this mode
of
triggering,
proceed
as
follows:
1.
Set
the
red
TRIGGER
SELECTOR
knob
to
AC.
2.
Set
the
STABILITY
control
to the
PRESET
position
(counterclockwise
S/N
101-1000).
3.
Adjust
the
TRIGGERING
LEVEL
control
for
stable triggering.
The
procedure
outlined
above
will
provide
stable triggering
for most
applications.
How
ever,
with
some triggering
waveforms
,
it may
be
necessary
to
manually
set
the
STABILITY
control.
This
is done
as
follows:
1.
Set
the
red
TRIGGER SELECTOR knob
to
AC.
2.
Turn
the
TRIGGERING
LEVEL control
counterclockwise
to
the
stop.
3.
Advance
the
STABILITY
control clockwise
until
the
time-base
generator
free-runs
then
back
it
off
just past
the
point
where the
sweep
s
tops.
4. Turn
the
TRIGGERING
LEVEL
control
clockwise
until
stable
triggering
occurs.
With
this
same
control
you
can
now
select
the
point
or
level
at
which
triggering occurs. Triggering
should
occur
near
the
0
mark.
Low-Frequency Triggering
For
waveforms having
a
slow
rise and a
repetition rate
of less than
60 cps,
the
DC
triggering
mode
is
best.
To
use this
mode
of
triggering,
proceed
as
follows:
1.
Set
the
red
TRIGGER
SELECTOR
knob
to
DC.
2. Set
the
STABILITY
control
to
the
PRESET
position
(counterclockwise
S/N
101-1000).
3.
Adjust
the
TRIGGERING
LEVEL
control
for
stable
triggering.
The
procedure
outlined
above
will
provide
stable
triggering
for most
applications.
How
ever,
with
some triggering
waveforms
,
it
may
be
necessary
to
manually
set
the
STABILITY
control.
This
is
done
as
follows:
1.
Set
the
TRIGGER
SELECTOR
red
knob
to
DC.
2. Turn
the
TRIGGERING
LEVEL
control
counterclockwise
to the
stop.
3.
Advance
the
STABILITY
control
clockwise
until
the
time-base
generator
free-runs
then
back
it
off
just
past
the
point
where
the
sweep
stops.
4.
Turn
the
TRIGGERING
LEVEL
control
clockwise
until
stable triggering
occurs.
With
this
same
control
you
can now
select
the
point
or
level
at
which
triggering
occurs.
Triggering
should occur
near
the
0 mark
if
the trace
is
centered.
Since
the
AC
mode
is
more
sensitive
than
the
DC
mode above 60
cps
and
is
not
affected
by
the
positioning
controls,
it
is
superior
to
the
DC
mode,
above
60
cps.
However,
the
DC mode
can
be
used
up
to about
5
me.
High-Frequency
Synchronization
For
stable triggering
it
is
necessary
for
the
trigger
circuits to have
a
frequency
response
considerably
in
excess
of
the
frequency
of
the
waveform
being
displayed.
At
about
five
mega
cycles
the
efficiency of the
trigger
circuits
is
reduced
and
the
H
F
SYNC
mode becomes
the
best
method
of
synchronizing
the
trace.
To
use
the
H F
SYNC
mode
simply advance
the
STABILITY
control
until
the
time
'
base
free-runs
and
then
continue
to
advance
it
until
the
time
base
locks
in
with
the
signal.
The
polarity
markings
on
the
TRIGGER
SELECTOR
switch
have no
significance
in
this
mode,
and the
TRIGGERING
LEVEL
con
trol
is
not
used.
Triggering
on
Complex Waveforms
When
the waveform
under
observation
is
complex
there
may
be
several
points
on
the
waveform
where
ordinary
triggering
circuits
may
tend
to trigger.
As
a
result,
the trace
may
be
unstable.
This
instability
may
be
encountered
occasionally
with the
AUTO, mode
of
triggering.
The
AC
and
DC
triggering
modes
allow
the
level
on
a
waveform,
at
which
trigger
ing
occurs,
to
be
selected
by
the
TRIGGERING
2-8
Operating
Instructions
- Type
515/515A
AA