Triggering
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TDS5000 Series User Manual
Trigger holdoff can help stabilize triggering. When the oscilloscope recognizes a
trigger event, it disables the trigger system until acquisition is complete. In
addition, the trigger system remains disabled during the holdoff period that
follows each acquisition. Adjust holdoff to obtain stable triggering when the
oscilloscope is triggering on undesired trigger events, as shown in Figure 3--21.
A digital pulse train is a good example of a complex waveform. Each pulse looks
like any other, so many possible trigger points exist. Not all of these will result
in the same display. The holdoff period allows the oscilloscope to trigger on the
correct edge, resulting in a stable display.
Indicates trigger points
Trigger level
At the longer holdoff time for the top waveform, unstable triggering occurs. With a shorter holdoff set for
the bottom waveform, triggers all occur on the first pulse in the burst to remedy the unstable trigger.
Holdoff Holdoff Holdoff
Trigger level
Holdoff Holdoff Holdoff Holdoff
Figure 3- 21: Holdoff adjustment can prevent unwanted triggers
The Holdoff setting range is 250 ns (minimum holdoff available) to 12 seconds
(maximum holdoff available). To see how to set holdoff, refer to Set Holdoff on
page 3--59. You can also set a default holdoff. The default holdoff is the general
purpose holdoff for most applications and varies with the horizontal scale. It is
equal to five times the current horizontal scale setting.
Trigger coupling determines what part of the signal is passed to the trigger
circuit. Edge triggering can use all available coupling types: AC, DC, Low
Frequency Rejection, High Frequency Rejection, and Noise Rejection. All of the
advanced trigger types use DC coupling only. See Set the Trigger Coupling on
page 3--56 for a description of each coupling type.
Trigger Holdoff
Trigger Coupling
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