To stabilize a waveform displayed on your oscilloscope, a trigger is needed. A specific, pre-defined event occurs – for example, an edge that rises beyond a certain voltage level – that lets the oscilloscope start a trace. Once it’s completed, the scope waits for it to occur again. This process is also called a sweep.
An untriggered display would be virtually useless because the waveform is not shown as stable on the display: It is the trigger that pinpoints a specific section of the signal in question and synchronizes individual repetitions of the wave to create a coherent image.
The trigger controls let you set the event to start recording the waveform you’re interested in. Here are some of the most common triggering types:
As in the example mentioned above, edge triggering is one of the most straightforward triggering modes. The trigger event defines a threshold value, which is activated when the voltage level surpasses it. It is possible to trigger on either a rising edge or a falling one.
The glitch trigger targets glitches and other infrequent and unexpected events. The trigger here is any event shorter or longer than a specified time span, in other words its width. Glitch triggering catching many errors that could otherwise be missed.
This type of triggering is not dissimilar to glitch triggering in that it also zeros in on specific widths of pulses. However, the widths are more general and not linked to a specified time span. Polarity is available for definition as well. You can also set the horizontal position of the trigger. This pushes what happened just before and after the trigger event onto the display, a feature especially useful when looking for causality relationships in the signal. Setting horizontal delay to zero, will center your trigger event in the middle of the screen along the horizontal axis.
There are many more triggering types available, getting more complex as the respective device under test does. There is also no requirement to trigger on the signal itself – you may just as well trigger on a related signal.
For more information, have a look at our Keysight YouTube channel (LINK) for our series on triggering and common measurement errors.
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