Triggering and Autoset

Triggering is post-capture

On a conventional oscilloscope, a comparator watches the input continuously and starts the acquisition at the instant the trigger condition is met. The hardware decides when to capture.

On WaveLink there is no such comparator dedicated to triggering, and no timebase generator. The board captures a burst of samples, sends them, and the trigger logic then searches that captured buffer for the edge you asked for and aligns the display to it.

What this means in practice

A stable trace requires the event to be in the buffer. If your trigger condition happens once every few seconds and each burst covers a few milliseconds, most bursts will not contain it. Post-capture triggering cannot wait for an event; it can only find one that was already recorded.

Periodic signals work well. If the signal repeats within the captured window, a burst will reliably contain edges to trigger on, and the display will be stable.

One-shot events are unreliable. There is no arming, no pre-trigger buffer maintained by hardware, and no guarantee that the burst started before the event. Do not use this instrument to catch a single glitch.

Timing is derived, not measured by a timebase. Sample intervals come from the known conversion timing of the selected acquisition path, not from a hardware sweep generator.

Trigger controls

Auto displays the buffer regardless of whether the trigger condition was found — you always see something, which is what you want while hunting for a signal. Normal only updates the display when the condition is found in the captured buffer, which gives a stable trace on a periodic signal and a frozen display when the condition stops occurring.

The trigger level is applied in the same units as the displayed trace.

Autoset

Autoset is a single control that finds a workable gain setting for the signal currently on the input.

It searches from minimum gain upward. This ordering is the whole point. A search that began at maximum gain and worked downward would slam the comparator stage into its limit on the very first step whenever a large signal was present. Starting at minimum gain means every step of the search is at a gain the signal has already been shown to survive, and the search stops as soon as the signal occupies a useful fraction of the converter’s full scale.

Use Autoset when:

• You do not know the amplitude of the signal you are about to measure.
• The trace is clipped and you want a safe starting point rather than guessing.
• You have changed to a different signal source.

Autoset does not change the operating mode, and it does not choose the acquisition path for you beyond falling back to the internal ADC in modes where the SAR is unavailable.

Getting a good trace

1. Choose the mode first. Oscilloscope mode if you only need to measure; CH2 Generator + Scope if you are driving the circuit as well and can accept 10-bit resolution.
2. Autoset, or set the gain manually if you know the amplitude.
3. Pick the acquisition path. SAR for resolution when it is available; internal ADC for rate.
4. Set the sample count. Larger bursts cover more time but take longer over the link and can time out — see Acquisition Paths.
5. Set the trigger to Normal with the appropriate slope once you have a signal you can see.

If the trace is stable in Auto but jumps around in Normal, the trigger condition is not being found consistently in the captured buffer. Adjust the trigger level, or capture more samples per burst so each buffer covers more cycles.