Operating instructions

Operating Instructions---7887
11 . To
trigger the single-sweep display,
set the amplifier
unit input coupling to dc .
Triggering occurs when the
amplifier coupling switch is
set to dc . The first six
milliseconds of the display is
pretrigger . (Noise in the
Stored Single Sweep
may be displayed at the Single
Sweep Trigger Point as
a result of the coupling switch
contact closure .)
TRIGGERING SWITCH LOGIC
The MODE, COUPLING,
and SOURCE pushbuttons
of the
TRIGGERING
switches are arranged in a
sequence which
places the most-often
used position at the top
of each
series of
pushbuttons . With this
arrangement, a stable
display
can usually be obtained
by pressing the top
pushbuttons :
P-P AUTO, AC,
INT . When an adequate
trigger
signal is applied and the
LEVEL control is correctly
set, the
unit is triggered as indicated by
the illuminated
TRIG'D light .
If the TRIG'D light is
not on, the LEVEL
control is
either at a setting
outside the range of the
trigger
signal applied to this unit
from the vertical unit,
the
trigger signal amplitude
is inadequate, or its
frequency is below the
lower frequency limit of the AC
COUPLING switch position
. If the desired display is not
obtained with these
buttons pushed in, other selections
must be made .
Refer to the following
discussions or the
instruction
manuals for the associated oscilloscope
mainframe
and vertical unit(s) for more
information .
TRIGGERING
MODES
The
MODE pushbutton switches
select the mode in
which
the sweep is triggered
.
P-P AUTO . The
P-P AUTO MODE provides a
triggered
display at
any setting of the LEVEL control
whenever an
adequate trigger signal
is applied . The range of the
LEVEL control in
the P-P AUTO MODE is between
approximately
10% and 90% of the
peak-to-peak
amplitude of the
trigger signal . The LEVEL control
can be
set so that
the displayed waveform starts
at any point
within
this range on either slope
. 'The trigger circuits
automatically
compensate for a
change in trigger signal
amplitude
. Therefore, if the
LEVEL control is set to start
the
waveform display at a
certain percentage point on the
leading
edge of a low-amplitude
signal, it also triggers at
the same
percentage point on
the leading edge of a high-
amplitude signal, if the
LEVEL control is not changed .
When
the trigger repetition
rate is outside the parameter
given in the Specification
section, or when the
trigger
signal is inadequate,
the sweep free runs at the
rate
indicated by the TIME/DIV
switch to produce a
bright
base-line, reference
trace (TRIG'D light
off) . When an
adequate
trigger signal is again applied,
the free-running
condition
ends and a triggered
display is presented .
The
P-P AUTO MODE is
particularly useful when
observing a series of
waveforms, since it is not necessary
to reset the LEVEL
control for each observation . The P-P
AUTO MODE is used
for most applications because of
the
GENERAL . OPERATING
INFORMATION
ease of obtaining a
triggered display . The AUTO, NORM,
and SINGLE-SWP MODE
settings may be used for
special applications .
AUTO .
The AUTO MODE provides a triggered
display
with the
correct setting of the LEVEL control
whenever
an adequate
trigger signal is applied (see Trigger Level
discussions) . The
TRIG'D light indicates when the display
is triggered
.
When
the trigger repetition rate is
outside the frequency
range selected by the COUPLING switch or
the trigger
signal
is inadequate, the sweep free runs
at the rate
indicated by the TIME/DIV
switch (TRIG'D indicator off) .
An adequate trigger
signal ends the free-running
condition and a
triggered display is presented . The sweep
also free runs at
the rate indicated by the TIME/DIV
switch when the
LEVEL control is at a setting outside the
amplitude range of the trigger signal
. This type of free-
running display is useful when it is
desired to measure
only
the peak-to-peak amplitude
of a signal without
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
OPERATION . The 71387 single-sweep
function can be
used with both digitizing
and non-
digitizing oscilloscopes
. A discussion of each
follows :
Non-Digitizing
Oscilloscope 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 obtainedby
using the single-sweep
feature of this unit . The
single-sweep mode is useful to
photgraph non-repetitive or
unstable displays .
To obtain a single-sweep
display of a repetitive signal,
first obtainthe 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 display
signal is a
complex
waveformcomposed 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 persistance,
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 .
observing the waveshape
measurements) .
(suchas bandwidth
NORMAL . The NORM
MODE provides a triggered
display with the
correct setting of the LEVEL control
whenever an adequate
trigger signal is applied . The