Trigger coupling
Trigger coupling sets what part of the input signal is used by the trigger circuit.
Trigger coupling choices are DC, LF Reject, HF Reject, and Noise Reject.
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DC Coupling passes the trigger signal to the trigger circuit with no filtering.
The scope may trigger on false events if the signal is noisy.
■
HF Reject attenuates signals above 85 kHz from the trigger circuit. This
reduces false triggering on high-frequency noise when measuring lower-
frequency signals.
■
LF Reject attenuates signals below 65 kHz from the trigger circuit. This
reduces false triggering from low frequency noise when measuring higher-
frequency signals.
■
Noise Reject reduces the trigger circuit input sensitivity. This reduces false
triggering when measuring signals with higher levels of noise.
Trigger modes
The Trigger Mode sets how the oscilloscope behaves in the absence or presence
of a trigger. Trigger mode also enables the trigger holdoff function.
Auto Untriggered Roll trigger mode
The Auto (Untriggered Roll) mode sets the oscilloscope to acquire a waveform
even if a trigger does not occur. Auto mode uses a timer that starts when the
acquisition is started, and the pretrigger information is obtained. If a trigger event
is not detected before the timer times out, the oscilloscope forces a trigger. The
length of time it waits for a trigger event depends on the time base setting
(Horizontal Scale).
Auto mode, when forcing triggers in the absence of valid triggering events, does
not synchronize the waveform on the display. The waveform will appear to roll
across the screen. If valid triggers occur, the display will become stable.
Sampling oscilloscope concepts
TBS1000C Series Oscilloscopes User Manual 43
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