Triggering
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TDS5000 Series User Manual
Triggering Concepts
Triggers create meaningful waveforms from signal displays. (See Figure 3--20.)
This oscilloscope has simple edge triggers as well as a variety of advanced
triggers.
Triggered waveform
Normal trigger mode Automatic trigger mode
Untriggered waveforms
Figure 3- 20: Triggered versus untriggered displays
The trigger event establishes the time-zero point in the waveform record. All
waveform record data are located in time with respect to that point. The
oscilloscope continuously acquires and retains enough sample points to fill the
pretrigger portion of the waveform record (that part of the waveform that is
displayed before, or to the left of, the triggering event on screen). When a trigger
event occurs, the oscilloscope starts acquiring samples to build the posttrigger
portion of the waveform record (displayed after, or to the right of, the trigger
event). Once a trigger is recognized, the oscilloscope will not accept another
trigger until the acquisition is complete and the holdoff time has expired.
The trigger source provides the signal that triggers acquisition. Use a trigger
source that is synchronized with the signal that you are acquiring and displaying.
You can derive your trigger from the following sources:
H Input channels are the most commonly used trigger sources. You can select
any one of the two or four input channels, depending on your model. The
channel you select as a trigger source will function whether it is displayed or
not.
H AC Line Voltage is often used to look at signals related to the power line
frequency (for example, signals from devices such as lighting equipment and
power supplies). Because the oscilloscope generates the trigger from the
power line, you do not have to use a channel input.
H Auxiliary Trigger (AUX IN) provides a fifth source that you can use as a
trigger input when you need to use the four input channels for other signals.
For example, you might want to trigger on a clock while displaying four
other logic signals. To use the auxiliary trigger, connect the signal to the
auxiliary input connector on the front panel. The input connector is not
The Trigger Event
Trigger Sources
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