Operating instructions

Operating Instructions-71380
The normal trigger mode must be used
to
produce triggered
displays with
trigger repetition rates belowabout
30
hertz .
When the TRIG'D
light is
off,
no
trace
is
displayed .
SINGLE SWEEP . When the signal to be displayed is not re-
petitive 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 present-
ed each time this button is pressed . Further sweeps cannot
be presented until the SINGLE SWP RESET button is pres-
sed 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 wave-
form . 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 diffi-
cult 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 wave-
forms, 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 sig-
nal
is
completely
symmetrical . Otherwise, multiple wave-
forms
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 .
Trigger Coupling
The TRIGGERING COUPLING
push buttons select the
method in
which the
trigger signal is connected to the trig-
ger circuits . Each
position permits selection or rejection of
some frequency components of the
signal
which
triggers
the sweep .
AC . AC COUPLING blocks the
do
component
of the trig-
ger signal . Signals
with low-frequency components below
about 30 hertz are attenuated . In
general, ACCOUPLING
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 do level, one of
the other COUPLING switch positions will provide a better
display .
AC LF REJ . AC LF REJ COUPLING rejects dc, and atten-
uates low-frequency trigger signals below about 30 kilo-
hertz . 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 trig-
ger signal contains line-frequency components . Also, the
AC LF REJ position provides the best alternate-mode verti-
cal displays at fast sweep rates when comparing two or
more unrelated signals .
ACHF REJ . AC HF REJ COUPLING passes all low-
frequency signals between about 30 hertz and 50 kilohertz .
Dc is rejected and signals outside the above range are atten-
uated . When triggering from complex waveforms, this posi-
tion is useful to provide a stable display of the low-
frequency components .
DC . DC COUPLING can be used to provide stable trigger-
ing 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 do level set by the LEVEL control . When using
internal triggering, the setting of the vertical unit position
control affects the triggering
point .
Trigger Source
The TRIGGERING
SOURCE push buttons select the
source of the trigger signal which is connected
to
the trigger
circuits .
INTERNAL . TheINT position connects the trigger signal
from the
vertical plug-in unit . Further selection of the in-
ternal 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 applica-
tions, the internal source can be used . However, some
applications require special triggering which cannot be ob-
tained in the INT positicn . 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 .