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I have a 4.5Khz bi-phasic square wave signal that ramps down from an amplitude of 20v peak to peak to 0v over 500ms. I would like to trigger in the middle of that amplitude ramp to 0v in order to zoom in and inspect the timing and details of the ramp. I've tried to get lucky and take a single sequence but I never catch it, not to mention I feel like a fool for trying! :) I'm imaging a technique where I can trigger when the peak to peak value is <= 10v, if anything like that is possible.

I'm using a Tektronix TDS 3032. I'm not an engineer, I'm not even really a hobbyist, just trying to help someone with a question and would like to learn an advanced triggering technique, if there is one.

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  • \$\begingroup\$ Can't you differentiate and trigger on that? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jul 6, 2016 at 4:28
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    \$\begingroup\$ Use the delay trigger. Trigger on the rising edge at 9V, with a 250 ms delay. OR set the trigger for 5V with the trigger mode set to normal. The last wave to trigger the scope will be near the middle, and it will stay on the scope in normal trigger mode. Auto mode will retrigger the scope even if there is no trigger present, but normal mode won't do that. \$\endgroup\$
    – user57037
    Commented Jul 6, 2016 at 4:31
  • \$\begingroup\$ @mkeith - I wish you had provided an answer so I could select it. Your suggest to change the trigger to normal mode was exactly what I needed. Sure enough, when the signal dropped below the trigger I was left with a nice screen with my samples I cared about. Thanks! \$\endgroup\$
    – Steve K
    Commented Jul 13, 2016 at 6:40
  • \$\begingroup\$ You can always answer your own question and select it. This is considered a good practice on this forum. And I give you permission and blessing to copy mine to whatever degree it seems useful. \$\endgroup\$
    – user57037
    Commented Jul 13, 2016 at 8:00

2 Answers 2

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Accepted comment from mkeith as answer:

Use the delay trigger. Trigger on the rising edge at 9V, with a 250 ms delay. OR set the trigger for 5V with the trigger mode set to normal. The last wave to trigger the scope will be near the middle, and it will stay on the scope in normal trigger mode. Auto mode will retrigger the scope even if there is no trigger present, but normal mode won't do that.

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  • \$\begingroup\$ Give him a bit and he will probably write up a more detailed answer. \$\endgroup\$
    – Captainj2001
    Commented Jul 13, 2016 at 15:21
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It is difficult to trigger at maximum because that's the point where voltage changes with respect to time are zero (that's the mathematical definition of extrema), i.e. voltage levels before or after that point are very similar and you won't get a stable trigger point in time (because of noise).

Therefore, as mkeith pointed out, it's much better to trigger at a point where the waveform has maximum change with respect to time (for a sine wave it'd be at zero crossing) and add delay to inspect the part of the waveform that you are interested in.

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  • \$\begingroup\$ thank you for the details and confirming mkeiths approach. \$\endgroup\$
    – Steve K
    Commented Jul 13, 2016 at 6:40

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