Tektronix 545A Instruction Manual page 17

Operating
Instructions
—
Type
545A
frequency range from dc
to
approximately
5 me.
The
DC
mode
also permits the selection of the point on
the trigger-
ing
waveform where
the
sweep
is
triggered through
the
use
of the
TRIGGERING
LEVEL
control.
To
use
the
DC
triggering
mode
you
must
set
the
STA-
BILITY
and
TRIGGERING
LEVEL
controls after
first
selecting
the triggering signal
source
and
slope.
The
method
used
to
set
the
STABILITY and
TRIGGERING
LEVEL
controls
is
the
same
for the
DC
mode,
AC
mode, and
AC
Low
Frequency
Reject
mode. The STABILITY
control
must be
set properly
before
the
TRIGGERING
LEVEL
control
can be
adjusted.
The STABILITY
control
has a PRESET
position at the
fully
counterclockwise
setting
of the
control. This position per-
mits
proper
triggering
in
most
applications without
necessi-
tating additional adjustment
of the
STABILITY
control.
If
it
becomes
impossible or
difficult for
you
to
obtain proper
triggering with the STABILITY
control at
PRESET, you must
then adjust the
control. This
is
done
with the
TRIGGERING
LEVEL
control
fully
counterclockwise.
The STABILITY
control
is
rotated clockwise from
the
PRESET
position
until
a trace
appears on
the screen.
The
proper
setting for the control
is
then obtained by
rotating the
knob
slowly counterclock-
wise
until
the trace
just
disappears.
The
TRIGGERING
LEVEL
control
determines
the point
on
the triggering
waveform where
triggering of the
sweep
occurs.
This control
is
set to
provide the display you
want
while at the
same
time causing stable
triggering. Rotating
the control clockwise causes the
sweep
to
trigger at
more
positive points
on
the
waveform
while
rotating the control
counterclockwise causes
the
sweep
to trigger at
more
nega-
tive points.
If
the
displayed
waveform
is
vertically centered
under the
graticule, setting the
TRIGGERING
LEVEL control
at
0
will
cause
the
sweep
to
start
at
approximately
the
mid-
voltage
point of the
waveform.
In
the
DC
mode,
rotating
the vertical position control
will
change
the point on the
triggering
waveform where
the
sweep
is
started.
The
+
and
—
markings
for
the
TRIGGERING
LEVEL
control
should
not
be confused with
similar
markings
for
the
TRIGGER SLOPE
control.
The markings on
the
TRIGGER
SLOPE
control indicate only whether
triggering occurs
on
the
rising or
falling
portion of the
triggering
waveform.
The markings
for the
TRIGGERING
LEVEL
control indicate
whether
triggering occurs
on
the
upper
portion or lower
portion of the
waveform.
AC
Triggering
Mode
Selection of the
AC
triggering
mode
is
made
by placing
the
TRIGGERING
MODE
switch
in
the
AC
position. This
mode
provides
useful
triggering
in
the
frequency range
of
approximately
15 cycles to 5 me. These frequency
limits
vary
slightly
depending upon
the
shape
and
amplitude
of
®I
2-7