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Chapter 5
Trigger Modes and Operations
Introduction to Trigger Modes
A
trigger
can generally be thought of as an event that starts the recording
of data. You can use the front-panel controls of the HP
7090
to
define a
trigger by specifying conditions that must be met before triggering occurs.
Three trigger modes - manual, external, and internal - are selectable.
The following list describes how recording is triggered for each mode:
•
Manual trigger mode.
Recording is triggered when the
RECORD DIRECT
or
FILL BUFFER
push button is pressed.
•
External trigger mode.
Recording is triggered when the
EXT TRIG
con
nector receives a low (logic
0) TI'L
level or contact closure to ground.
•
Internal trigger mode.
Recording
is
triggered when the amplitude and/or
slope of the Channel ! input signal fulfills conditions specified using the
TRIGGER LEVEL
and
TRIGGER WIDTH
setup conditions.
Post- or pre-trigger times may also be specified, allowing data to be recorded
at a predetermined time after or before triggering.
POST TRIGGER
selections
act as a delay - the selected delay time must elapse after receipt of a valid
trigger before recording begins. Post-trigger times may be specified for
either the buffered or the direct recording modes. (post-trigger time may not
be used, however, for the inside-window option of the internal trigger mode.)
PRETRrGGER
selections, on the other hand, apply only to buffered recordings,
and are used to specify a time during which data is recorded immediately
before
the occurrence of a valid trigger. Because the recording of pre-trigger
events is not possible unless recording has started before the trigger occurs,
pre-trigger times can only he used for internally or externally triggered,
buffered recordings. Pre-trigger time settings can be extremely useful for
certain applications, as they allow you
to
capture data in the buffers that
transpired immediately before the triggering event occurred.
All front-panel measurements are initiated by pressing
RECORD DIRECT
(for
direct recordings) or
FILL BUFFER
(for buffered recordings). Before recording
begins, however, two conditions must be satisfied:
(1)
the specified trigger
must have occurred, and
(2)
the specified post-trigger time (if any) must
have elapsed. The
TRIGGER SEARCH
indicator on the left front panel shows
the status of these two conditions during a measurement.
Trigger Search
Status
Trigger Modes and Operations
5-1