Delayed Sweep and Holdoff - Useful ? - diyAudio
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Old 26th January 2011, 01:58 AM   #1
Grid2 is offline Grid2  United States
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Default Delayed Sweep and Holdoff - Useful ?

My scope died /20Mhz, Leader, Analog :-( putting me once again in the mode of looking across the field for a replacement. I know this forum, by and large, favors Tek. Don't worry - this isn't another oscilloscope vendor or recommendation question [that's answered aplenty in archives].

What I'd like to hear about is whether anyone has come up with examples where the Holdoff and Delayed Sweep functions came into play to analyze the analog signal chain (not digital signals and not TV receivers) in a way that could not have been achieved otherwise.

My hunch, for analog audio, is that these functions are just not applicable for non-digital sources, pre-amp or amp analog circuits. And by extension, that if looking at vintage analog scopes for analog audio service work, these features just drop to the bottom of the list and one can do quite well without. Or am I missing something? Would appreciate hearing otherwise or get affirmation on that position. Thx!
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Old 26th January 2011, 04:59 AM   #2
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Perhaps to view certain details during a transient-response test? You're feeding fixed period sig into it, and, say you wanted to view the trailing edge of the square wave to examine ringing, overshoot, etc., and you wanted it highly magnified. You might trigger on the leading edge and use delayed sweep to frame just that trailing edge and all the fur around it. I don't know, I suppose this is not *that* common a requirement, but it would surely make a cool screenshot :--)
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Old 26th January 2011, 06:28 AM   #3
gootee is offline gootee  United States
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Delayed sweep just enables you to display a highly-magnified portion of the main display, expanded in time by a factor of 100 for example, usually while highlightling the magnified portion on the main "regular size" display by intensifying that portion of the waveform's display. The delay control enables you to move the highlighting around on the normal-size waveform, so you can more-easily keep track of where you are looking, while the magnified version of the highlighted area is also displayed. I would think it might be useful for examining very high-frequency ringing near the edges of audio-rate square waves, for example. It could also be useful for examining high-frequency ringing in power supplies, and feedback systems (e.g. analog audio amplifiers). And, of course, it's good for just seeing the details of any fast periodic events and edges better.

Variable holdoff is, I think, mainly good for trying to trigger on aperiodic signals, such as complex digital waveforms. I can't think of any important use for it in analog audio. But I could easily be missing something.

I think that most full-featured scopes have both of those features, or something better. So maybe you won't have to weigh them in your decision.

Last edited by gootee; 26th January 2011 at 06:30 AM.
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Old 26th January 2011, 11:32 PM   #4
Grid2 is offline Grid2  United States
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Thanks for the input. I'm getting the picture that these features have some potential for analog signal analysis but few application in day-to-day support work. Thus, when looking for a replacement scope, these are non-critical features in comparison to things like primary scope functionality (e.g. calibrated sweep and vertical deflection built around a solid time-base). I should think that factoring in overall build quality (durability) and abilty to maintain ranks higher. As far as features go, I'd probably rate graticule illumination as having more daily value.

Agreed that a lot of the good used analog scopes out there have Holdoff and Delayed Sweep built in; but lacking these features shouldn't really have much influence in a selection/purchase decision.

If anyone else has some examples of how they used these features - please chime in!

Thanks!
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Old 27th January 2011, 04:55 AM   #5
gootee is offline gootee  United States
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One thing that could spoil you for lesser scopes is the automatic measurement cursors on scopes like the Tek 2465, 2465A, and 2465B, which are probably the best portable analog oscilloscopes ever made (with the Tek 7904A probably being the best analog scope ever made, period).
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Old 28th January 2011, 01:27 AM   #6
tomchr is offline tomchr  United States
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I use the delayed trigger for "zoom" on parts of a waveform as described above. I wouldn't be without it. It's very handy to see what's going on during glitches and other transients.

~Tom
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