Triggering Coupling; Triggering Source - Tektronix 7B10 Instruction Manual

Operating Instructions—
7B10
Operators
Normal
The
NORM MODE
provides
a triggered display
with the
correct settings
of
the
LEVEL
control
whenever
an
adequate
trigger signal
is
applied.
The TRIG'D
light
indicates
when
the display
is
triggered.
The
normal
trigger
mode
must
be used
to
produce
triggered
displays
with
trigger repetition
rates
below
about
30
hertz.
When
the
TRIG'D
light
is off,
no
trace
is
displayed.
Single
Sweep
When
the signal
to
be displayed
is
not
repetitive
or varies
in
amplitude, waveshape,
or repetition
rate,
a
conventional
repetitive
type display
may
produce an
unstable
presentation.
Under
these circumstances,
a
stable display can
often be obtained by
using the
single-
sweep
feature
of this
unit.
The
single-sweep
mode
is
also
useful to photograph
non-repetitive
or
unstable
displays.
To
obtain
a
single-sweep
display
of a repetitive signal,
first
obtain the best possible display
in
the
NORM
MODE.
Then, without changing
the other
TRIGGERING
controls,
press the
SINGLE
SWP
RESET
button.
A
single trace
is
presented each time
this
button
is
pressed.
Further
sweeps
cannot be presented
until
the
SINGLE
SWP
RESET
button
is
pressed
again.
If
the displayed
signal
is
a
complex waveform
composed
of
varying amplitude
pulses, successive single-sweep
displays
may
not
start at
the
same
point on the waveform. To
avoid confusion due
to
the
crt
persistence,
allow the
display
to
disappear
before pressing the
SINGLE
SWP
RESET
button
again.
At
fast
sweep
rates,
it
may
be
difficult to
view
the
single-
sweep
display.
The
apparent
trace
intensity
can be
increased by reducing the
ambient
light level
or
by using
a
viewing hood
as
recommended
in
the mainframe
instruction manual.
When
using the single-sweep mode
to photograph
waveforms,
the
graticule
may
have
to
be photographed
separately
in
the normal manner
to
prevent
over
exposing the
film.
Be
sure the camera system
is
well
protected against
stray
light, or
operate the
system
in
a
darkened room.
For
repetitive waveforms,
press the
SINGLE
SWP
RESET
button only once
for
each waveform
unless the
signal
is
completely symmetrical. Otherwise,
multiple
waveforms may
appear on
the
film.
For
random
signals, the lens can be
left
open
until
the
signal triggers
the
unit.
Further information
on
photographic techniques
is
given
in
the appropriate camera
instruction manual.
TRIGGERING COUPLING
The
TRIGGERING COUPLING
push
buttons
select the
method
in
which
the
trigger signal
is
connected
to
the
trigger
circuits.
Each
position permits
selection
or
rejection of
some
frequency components
of
the
signal
which
triggers the sweep.
AC
AC
COUPLING
blocks the dc component
of the
trigger
signal. 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 other
COUPLING
switch
positions
will
provide
a better display.
AC
LF
REJ
AC
LF REJ
COUPLING
rejects dc,
and
attenuates low-
frequency
trigger
signals
below
about 50
kilohertz.
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-mode
vertical displays
at fast
sweep
rates
when
comparing two
or
more
unrelated
signals.
AC
HF REJ
AC
HF REJ COUPLING
passes
all
low-frequency
signals
between
about 30
hertz and 30
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
DC COUPLING
can
be used
to provide
stable triggering
from low-frequency
signals which would
be attenuated
in
the other
COUPLING
switch
positions.
DC COUPLING
can be used
to trigger the
sweep
when
the
trigger signal
reaches
a
dc
level set by the
LEVEL
control.
When
using
internal triggering, the
setting of the
vertical unit
position
control affects the
triggering
point.
TRIGGERING
SOURCE
The TRIGGERING
SOURCE
push
buttons
select
the
source
of the
trigger signal
which
is
connected
to the
trigger
circuits.
Internal
The
INT
position connects
the
trigger signal from
the
vertical plug-in
unit. Further
selection
of the
internal
trigger signal
may
be provided
by the
vertical plug-in
unit
or
by the mainframe; see the
instruction manuals
for
these
instruments
for
more
information.
For
most
applications, the
internal source can be
used. However,
some
applications
require
special
triggering
which
cannot be
obtained
in
the INT
position.
In
such
cases, the
LINE
or
EXT
positions
of
the
SOURCE
switches must
be
used.
Line
The
LINE
position connects
a
sample
of
the power-line
voltage from
the mainframe
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.