Trigger Options - PeakTech 2035 Bedienungsanleitung

(b) TV-V Coupling (c) TV-H Coupling
(d) Sync Polarity
Fig. 2-3 Using the TV SYNC Separator
2.2.5

Trigger Options

Triggering is often the most difficult operation to perform on an oscilloscope because of the many options
available and the exacting requirements of certain signals.
Trigger Mode Selection:
When the NORM trigger mode is selected, the CRT beam is not swept horizontally across the face o the
CRT until a sample of the signal being observed, or another signal harmonically related to it, triggers the
timebase. However, this trigger mode is inconvenient because no baseline appears on the CRT screen in
the absense of a signal, or if the trigger controls improperly set. The AUTO trigger mode solves this
problem by causing the timebase to automatically free run when not triggered. This yields a single
horizontal line with no signal, and a vertically-deflected but non-synchronized display when vertical signal
is present but the trigger controls are improperly set. This immediately indicates what is wrong. The only
hitch with AUTO operation is that signals below 25 Hz cannot, and complex signals of any frequency may
not realiably trigger the timebase. Therefore, the usual practice is to leave the trigger MODE switch (14)
set to AUTO, but reset it to NORM if any signal (particulary one below 25 Hz) fails to produce a stable
display.
The TV-V and TV-H positions of the Trigger MODE switch insert a TV sync separator into the trigger
chain, so a clean trigger signal at either the vertical-or horizontal-repetition rates can be removed from a
composite video signal (Fig. 2-3 a). To trigger the scope at the vertical rate (Fig. 2-3 b), set the Trigger
MODE switch to TV-V. To trigger the scope at the horizontal (line) rate (Fig. 2-3 c) set the trigger Mode
switch to TV-H. For best results, the TV sync polarity should be negative (Fig. 2-3 d) when the sync
separator is used.
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