5. Advanced User Guidebook
Term interpretation
1. Source: Trigger can occur from several sources: Input channels (CH1, CH2), Ext,
Ext/5.
z Input: It is the most commonly used trigger source. The channel will work when
selected as a trigger source whatever displayed or not.
z Ext Trig: The instrument can be triggered from a third source while acquiring data
from CH1 and CH2. For example, to trigger from an external clock or with a signal
from another part of the test circuit. The EXT, EXT/5 trigger sources use the
external trigger signal connected to the EXT TRIG connector. Ext uses the signal
directly; it has a trigger level range of -0.6V to +0.6V. The EXT/5 trigger source
attenuates the signal by 5X, which extends the trigger level range to -3V to +3V.
This allows the oscilloscope to trigger on a larger signal.
2. Trigger Mode:
The trigger mode determines how the oscilloscope behaves in the absence of a trigger
event. The oscilloscope provides three trigger modes: Auto, Normal, and Single.
z Auto: This sweep mode allows the oscilloscope to acquire waveforms even when
it does not detect a trigger condition. If no trigger condition occurs while the
oscilloscope is waiting for a specific period (as determined by the time-base
setting), it will force itself to trigger.
z Normal: The Normal mode allows the oscilloscope to acquire a waveform only
when it is triggered. If no trigger occurs, the oscilloscope keeps waiting, and the
previous waveform, if any, will remain on the display. Single: In Single mode,
after pressing the Run/Stop key, the oscilloscope waits for trigger. While the
trigger occurs, the oscilloscope acquires one waveform then stop.
z Single: In Single mode, after pressing the Run/Stop key, the oscilloscope waits for
trigger. While the trigger occurs, the oscilloscope acquires one waveform then
stop.
3. Coupling:
Trigger coupling determines what part of the signal passes to the trigger circuit.
Coupling types include AC, DC, LF Reject and HF Reject.
z AC: AC coupling blocks DC components.
z DC: DC coupling passes both AC and DC components.
z LF Reject: LF Reject coupling blocks DC component, and attenuates all signal
with a frequency lower than 8 kHz.
z HF Reject: HF Reject coupling attenuates all signals with a frequency higher
than 150 kHz.
4. Holdoff: Trigger holdoff can be used to stabilize a waveform. The holdoff time is
the oscilloscope's waiting period before starting a new trigger. The oscilloscope will
not trigger until the holdoff time has expired. It provides a chance for user to check
the signal in a short period and helps to check some complex signals, such as AM
waveform etc.
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