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Post- and pre-trigger time selections can be extremely useful for certain
applications. For example, by selecting an appropriate post-trigger time,
you can :set the HP
7090
to begin recording data at a specified time after the
occurrence of a trigger. Pre·trigger times can be used
to
capture data in the
buffers for events that
occurred
immediately
before
a selected triggering
event. The following section describes the post- and prc-trigger setup condi
tion used
to
select post- or pre-trigger times .
The P08t Trigger / Pre Trigger Setup Condition
Default Value:
0.0
seconds .
Range of Selectable Values:
0.01
second
to 24
hours (post-trigger).
-0.01
second to-24 hours (prc-trigger).
Pre-trigger selections disp
l
a
y
ed on
the
LeO
are
preceded by
a
minus (
-
)
sign. The selectable time increments for prc- and post-time settings are
dependent upon the
TOTAL TIME
setting - smaller
total
time settings allow
smaller selectable time increments.
For the default setting of
0.0
seconds (no prc- or post-trigger time) recording
begins the moment a valid trigger is received. However, all trigger modes
(except internal with the inside-window option) are subject
to
post-trigger
time selections.
Post-trigger time
is the amount of time delay that must
elapse after triggering before recording occurs.
Pre-trigger time,
on the other hand, applies only to internally or externally
triggered, buffered recordings.
A
prc-tigger time value specifies what por
tion of
TOTAL TIME
is to be used for storing digitized input signal data
occurring immediately before the trigger. Refer
to
the following illustration.
With a pre-trigger time specified, the buffers begin filling as soon as you
press
FILL BUFFER.
They continue filling until the specified pre-trigger time
has elapsed, at which time the buffer contents are continuously updated
until the valid trigger arrives. Upon arrival of the trigger, the data cur
rently captured in the buffers (representing the prc-trigger time) is frozen,
and the remaining buffer space is filled. If the trigger occurs
before
the
specified prc-trigger time has elapsed, the pre-trigger time is cut short and
the buffers are allowed
to fill.
MEASUREMENT INITIATED
TRIGGER
RECORDING ENDS!
(FILL BUffER PRESSED]
OCCURS
MEASUREMENT COMPLETE
PRE·TRIGGER
DATA
PRE·TRIGGER TIME ......
POST-TRIGGER
DATA
TOTAL TIME
(BUFFER FILL TIMEI
CHANNEL
BUFFER
Post- and Pre
Trigger Time
Capturing Pre-Trigger Data
ina Buffer