4.
Once a waveform is digitized, it can be stored in
long-term memory by pressing the SAVE ALL or
SAVE CH2 switches. The SAVE CH2 switch imme-
diately stores the channel 2 waveform. The SAVE
ALL switch immediately freezes the display and
stores both waveforms. Once a waveform is stored by
engaging either of these switches, it will be stored until
the switch is disengaged or the power is turned off.
NOTES
Any of the operating modes previously dis-
cussed in analog operation (e.g. DUAL,
ADD, etc.) can be used in digital mode,
except for X–Y operation.
Time base settings of 10
µ
s/div and faster
result in a display that is acquired through
“equivalent time sampling”. This process
develops the digitized image over many
cycles of the repetitive signal; therefore,
these higher sweep speeds cannot be used
for capture of one-time events. Equivalent
time sampling is discussed in detail in Ap-
pendix II, “Unique Characteristics of Digi-
tal Storage Oscilloscopes”.
Digitizing One-Time Events
One of the most powerful features of a digital storage
oscilloscope (DSO) is its ability to capture one-time events.
To capture one-time events, single-sweep operation is em-
ployed. This is done through the use of the SINGLE switch.
When pushed, this switch releases the REFRESH or ROLL
mode if previously engaged, and readies the digital storage
circuit to receive a trigger signal — presumably the event to
be captured or some other time-related occurrence. When
the event arrives, it is stored in the memory and displayed.
The procedure is as follows:
1.
Set the oscilloscope to run in analog mode (ANA-
LOG/DIGITAL s w i t ch to ANALOG). Select
NORM triggering, and adjust the TRIG LEVEL
control so that the unit triggers on the event to be
captured.
2.
Set the oscilloscope to digital (STORAGE) mode by
engaging the ANALOG/STORAGE switch.
3.
Initially, set the PRE TRIG switch to 50%. A more
detailed discussion of pre- and post-triggering is given
later in this section of the manual.
4.
Press the RESET switch. The READY indicator will
momentarily light as the scope awaits the arrival of the
trigger signal. When that trigger occurs, the READY
indicator will go off, and the event being monitored
will roll to the center of the display and stop.
NOTES
Depending on the sweep TIME/DIV set-
ting, the anticipated event may roll to the
center of the screen very rapidly, or very
slowly, after the READY indicator goes
out.
Single-sweep mode can be used in the pres-
ence of very rapidly occurring events, even
continuous waveforms if desired. In that
case, the period between pushing the RE-
SET switch and the arrival of the trigger
may be very short or almost instantaneous.
As a result, the READY indicator may
light for only a very short time, perhaps not
being visible at all.
Pushing the SINGLE switch automatically
disengages both the REFresh and ROLL
modes, which are continuous modes.
5.
Once the waveform is captured, it can be stored in
long-term memory through the use of the SAVE CH2
or SAVE ALL switches.
Pre- and Post-Trigger Capture
Another powerful feature of a DSO is is ability to display
“pre-trigger” information, that is, events occurring before
the arrival of a trigger event. On the Model 2522B, pre-trig-
ger operation is available in single-sweep mode by setting
the PRE TRIG switches. As shown in the above section on
“Digitizing One-Time Events”, when 50% pre-trigger op-
eration is selected, the event to be captured is situated in the
center of the memory (roughly the center of the display) after
storage. The waveform to the left of center represents activ-
ity which occurred before that trigger arrived. Pre-Trigger
selection of 25% and 75% are also available.
If the PRE-TRIG switches are released (0% pretrigger),
then no pre-trigger information is stored, and the trigger
event rolls to the extreme left of the display. In this case, all
the information displayed on the screen represents activity
after the trigger event. You may wish to use post-trigger
operation first to observe where the trigger is occurring on
the waveform of interest, and then switch to pre-trigger
mode.
Roll Mode
In this mode of operation, the waveform rolls across the
CRT from right to left (as opposed to standard oscilloscopes,
which have the trace moving from left to right) in the same
manner as most strip chart recorders. It is most commonly
used for viewing very slow events.
1.
Set up the oscilloscope in analog mode so that the event
to be observed is properly positioned on the display.
you may wish to use AUTO triggering so that the
scope continues to draw a trace even if the event is
especially slow.
2.
Switch to digital mode (ANALOG/STORAGE
switch to STORAGE), and depress the ROLL switch.
Select a TIME/DIV setting that produces a roll at the
desired speed. As the sweep speed is decreased, the
waveform will move across the screen more slowly
and the Roll feature will become more apparent. It can
also be slowed by a factor of 100 on some ranges; see
the discussion in the next section.
OPERATING INSTRUCTIONS
16