Operating
Instructions—
7B53A/7B53AN Operators
AC.
In the AC
position of the COUPLING switch,
the
DC component
of the trigger signal is blocked. Signals with
low-frequency components
below about
30 hertz
are
attenuated.
In
general, AC
COUPLING can be used for
most
applications.
However, if the signal contains unwanted
frequency components
or if the
sweep is to be triggered at a
low
repetition rate or
DC level, one
of the remaining
COUPLING
switch positions will provide
a better display.
The triggering
point in
the AC position
of the
COUPLING
switch depends upon the average voltage level
of the trigger
signal. If the trigger
signal occurs randomly,
the average
voltage level will vary,
causing the triggering
point
to vary
also. This shift of the triggering point
may
make
it impossible to maintain
a stable display. In such
cases, use DC COUPLING.
AC LF
REJ.
In the
AC LF
REJ position of the
COUPLING switch,
DC is
rejected and
low-frequency
trigger
signals
below about 30 kilohertz
are attenuated.
Therefore,
the
sweep is triggered only
by the higher-
frequency
components
of
the trigger signal. This position
is
particularly
useful for providing stable triggering if the
trigger
signal contains line-frequency components. Also, the
AC
LF
REJ
position provides
the best alternate vertical
displays at fast sweep rates
when comparing two or more
unrelated
signals.
AC
HF REJ.
The
AC
HF
REJ position of the
COUPLING
switch
passes all
low-frequency signals between
about 30
hertz and 50 kilohertz. DC
is rejected and signals
outside
the above range are attenuated. When triggering
from
complex
waveforms, this position is useful to provide
a
stable
display of the low-frequency components.
DC.
The
DC
position of the COUPLING switch can be
used
to
provide stable triggering with low-frequency signals
which would
be
attenuated in the other modes, or with
low-repetition rate signals. It
can also be used to trigger the
sweep
when
the trigger signal reaches a DC
level selected by
the
setting
of the LEVEL control.
When using internal
triggering,
the
setting of the vertical unit position control
affects
the DC
triggering point.
Main
Triggering
Source
The
MAIN
TRIGGERING
pushbutton located below the
SOU
RCE title select the source of the trigger signal
which
is
connected
to the main
triggering circuits.
INT.
In
the INT position of the SOURCE switch, the
trigger
signal is
derived from the associated vertical unit.
Further
selection
of the internal trigger signal may
be
provided by
the associated vertical unit or indicator
oscilloscope;
see the instruction manuals for these instru
ments
for information. For most applications,
the INT
position of the SOURCE switch
can be used.
However,
some applications
require special triggering which cannot be
obtained
in
the
INT position of the SOURCE switch. In
such
cases
the LINE or EXT positions
of the SOURCE
switch must
be used.
LINE.
The LINE
position
of the SOURCE switch
connects
a
sample
of the power-line voltage from the
indicator
oscilloscope to
the trigger circuit. Line triggering
is useful
when
the input signal is time-related (multiple or
submultiple)
to
the
line
frequency. It is also useful for
providing a
stable display of a line-frequency component in
a complex waveform.
EXT.
An
external signal
connected to the MAIN TRIG
IN connector
can be used to trigger
the sweep in the
EXT
position of the SOURCE
switch. The external signal must
be
time-related to
the displayed waveform for a stable
display.
An external trigger signal can provide a
triggered
display
when the
internal
signal is too low in amplitude for
correct
triggering, or contains signal components on which
it is
not
desired to trigger. It is
also useful when
signal
tracing in amplifiers,
phase shift networks, waveshaping
circuits, etc. The signal from a single
point in the
circuit
under
test can be connected to the EXT TRIG IN
connector
with a probe or cable. The sweep is then
triggered
by
the
same signal at all times and allows
amplitude,
time relationship, or
waveshape changes of
signals
at
various points
in the circuit to be examined
without
resetting
the MAIN
TRIGGERING
controls.
EXT
4-
10.
Operation
in the EXT
4- 10
position of the
SOURCE
switch is the same as described for EXT
except
that
the external
signal
is attenuated 10 times. Attenuation
of high-amplitude
external trigger signals is desirable to
broaden the range of the LEVEL control.
Trigger Slope
The
MAIN TRIGGERING SLOPE switch
(concentric
with
the MAIN TRIGGERING
LEVEL control) determines
whether
the trigger circuit responds on the positive-going or
negative-going
portion of
the trigger signal. When
the
SLOPE switch is in
the + position, the display starts on the
positive-going
portion of the waveform; in the - position,
the
display starts with the
negative-going portion of the
waveform (see
Fig.
1-6). When several cycles of a signal
appear
in a
display, the setting of the SLOPE switch is
often
unimportant.
However, if only a certain portion of a
cycle is
to
be displayed, correct setting
of the SLOPE
switch
is important to provide a display which starts on the
desired
slope of the input signal.
1-9
