Elenco 30MHz Dual Trace - Manual (Page 45)

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OPERATING INSTRUCTIONS
TRIGGERING
The oscilloscope provides versatility in sync triggering for ability to obtain a stable,
jitter-free display in single-trace, or dual-trace operation. The proper settings depend
upon the type of waveforms being observed and the type of measurement desired. An
explanation is given to help you select the proper setting over a wide range of
conditions.
AUTO or NORM Triggering
1. In the AUTO triggering mode. (PULL NORM TRIG switch pushed in), automatic
sweep operation is selected. In automatic sweep operation, the sweep generator
free-runs to generate a sweep without a trigger signal. However, it automatically
switches to triggered sweep operation if an acceptable trigger source signal is
present. The AUTO position is handy when first setting up the scope to observe a
waveform; it provides sweep for waveform observation until other controls can be
properly set. Once the controls are set, operation is often switch back to the
normal triggering mode, since it is more sensitive. Automatic sweep must be use
for dc measurements and signals of such low amplitude that they will not trigger
the sweep.
2. In the NORM triggering mode (PULL NORM TRIG switch pulled out), normal
triggered sweep operation is selected. The sweep remains at rest until the
selected trigger source signal crosses the threshold level set by the TRIG LEVEL
control. The trigger causes one sweep to be generated, after which the sweep
again remains at rest until triggered. In the normal triggering mode, there will be no
trace unless an adequate trigger signal is present. In the ALT VERTICAL MODE
of dual-trace operation with the SOURCE switch also set to ALT, there will be no
trace unless both channel 1 and channel 2 signals are adequate for triggering.
Typically, signals that produce even one division of vertical deflection are
adequate for normal triggered sweep operation.
Trigger COUPLING Switch
1. The AC position is used for most waveforms except video. The trigger signal is
capacitvely coupled. Thus, it blocks the dc component and references the
“changing” position of the waveform.
2. The TV H and TV V positions are primarily for viewing composite video
waveforms. Horizontal sync pulses are selected as trigger when the trigger
COUPLING switch is set to the TV-H position, and vertical sync pulses are
selected as trigger when the trigger COUPLING switch is set to the TV V position.
The TV H and TV V position may also be used as low frequency reject and high
frequency reject coupling, respectively. Additional procedures for observing video
waveforms are given later in this section of the manual.