Trigger Modes; Auto Untriggered Roll Trigger Mode; Normal Trigger Mode; Holdoff Trigger Mode - Tektronix TBS2000B Series User Manual

• 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
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noise when measuring higher-frequency signals.
Noise Reject reduces the trigger circuit input sensitivity. This reduces false triggering when measuring signals with
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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.

Normal trigger mode

Normal mode sets the oscilloscope to acquire a waveform only when a trigger condition occurs. If no trigger occurs, the last
waveform record acquired remains on the display. If no last waveform exists, no waveform is displayed.

Holdoff trigger mode

The Holdoff trigger mode lets you set a time period during which the oscilloscope ignores trigger events. For example, to
trigger on the first pulse of a pulse burst, you would set the trigger conditions to trigger on a positive edge, and set the
holdoff value so that the trigger is disabled for a period of time after the trigger event but before the next bust occurs. Using
Holdoff in this case prevents the oscilloscope from triggering on any positive signal edge.
Use Set Holdoff to minimum to set the holdoff value to the minimum value.
Note: The trigger mode does not set the trigger conditions; those are set with the trigger Type controls. See
Available trigger types

Trigger delay acquisition mode

In normal acquisition modes, the trigger point is located at the center of the waveform record, and is positioned at the
center-screen expansion point so that horizontal scale changes are centered around the trigger point. The Delay function in
TBS2000B Series Oscilloscopes User Manual
on page 44.
Oscilloscope concepts
45