6. Trigger Controls
For most signals, the trigger-control settings that will yield hands off triggering are:
MODE P-P AUTO
HOLDOFF MIN
SOURCE VERT MODE
COUPLING DC
A. Which Mode to Use
P-P AUTO/TV LINE—With this mode set, the range of the LEVEL control is confined
to the values between the triggering-signal peaks. For example, selecting P-P AUTO
and rotating the LEVEL control to the center half of its range establishes a trigger point
that is about midway between the peaks of the triggering signal.
In this mode, the absence of a triggering signal causes the sweep to free-run. And
with signals below 20 Hz, the P-P AUTO circuit may not find the correct level.
Whenever P-P AUTO is active and VERT MODE source selected, the triggering
signal is supplied by the channel that is being displayed—or by Channel 1 in a two-
channel display.
The P-P AUTO mode is effective for monitoring logic signals and television lines
having at least a 20-Hz repetition rate. Selecting P-P AUTO at the instrument front
panel also sets the TV LINE triggering mode.
NORM—This mode produces a sweep only when the triggering signal meets the
criteria set by the LEVEL and SLOPE controls. With NORM mode selected, range of
the LEVEL control is sufficient to set any voltage threshold that can be displayed by
the instrument. In the absence of a triggering signal, there is no sweep.
Use the NORM mode for viewing infrequent events and erratic signals.
SQL SWP—When this mode is selected, the sweep is triggered only once. Press the
RESET button once to arm the trigger circuit and illuminate the READY indicator.
When a trigger event occurs, the sweep runs once and the READY light extinguishes.
Use the SQL SWP mode to display or photograph non-repetitive or unstable signals.
TV FIELD—This mode triggers the sweep at the beginning of a television field. To
change the TV field being displayed, you must interrupt the trigger signal by setting
the input coupling switch momentarily to GND then back to either DC or AC until the
desired field is displayed.
To display Field 1 and Field 2 at the same time, connect the same television signal to
both the CH 1 and CH 2 inputs; set VERTICAL MODE to BOTH and ALT; set the
SEC/DIV control to 0.5 ms or faster sweep speed.
If you magnify the vertical display beyond the graticule, the trigger may be degraded.
To avoid trigger overload, use either CH 1 or CH 2 for display and use the EXT
INPUT channel with an appropriate video signal as the trigger source. A composite
sync signal can be used for the trigger source as well as composite video.
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