EEVblog #159 - Oscilloscope Trigger Holdoff Tutorial

[Russel]

Excellent subject for the blog Dave!

I didn't have a clue that my Rogol DS1052E had a trigger holdoff setting, much less how it can be used! Your choice of blog subjects has me checking EEVblog.com daily for new videos! Looking forward to more oscilloscope tutorials, if that is a direction you wish to persue.

Russ

[Ferroto]

Hey Dave your video on trigger hold off was used as a reference on this Wikipedia page.

http://en.wikipedia.org/wiki/Trigger_holdoff

[david77]

Cheers Dave!

Another knob on my oscilloscope explained.

A proper tutorial on what the controlls on an analog scope do would be nice.

David

[Neilm]

Ìt is amazing how few people know how to setup an oscilloscope. When I was at university studing electronics it was not taught - not even during the "practicals". The closest it ever got to being mentioned was a passing comment on how well triggered by scope was.

One question though - has anyone EVER pressed the autoset button and got the picture they wanted on the screen?

Neil

[ShiftPlusOne]

In the first year of uni, the labs we used had analogue scopes with no autoset, so we did spend some time learning how to set them up. However, after first year, everyone goes straight for autoset. There are a few who set them up manually, but they tend to be arrogant pricks for some reason.

[hans]

Ìt is amazing how few people know how to setup an oscilloscope. When I was at university studing electronics it was not taught - not even during the "practicals". The closest it ever got to being mentioned was a passing comment on how well triggered by scope was.

One question though - has anyone EVER pressed the autoset button and got the picture they wanted on the screen?

Neil

No NEVER

We either had mixed up dual channel setup, inappropriate scaling between signals (we either want overlap, we either want signals on top and the bottom - the scope doesn't understand), we wanted to see at a smaller/larger time factor, etc.

Really, manually fiddling with the controls is just as fast on a digital scope as using the auto set button. For the auto set you need to wait, figure out what's wrong with your view and correct it once again.

I personally never heard of this feature. It works great for repetitive signals that would otherwise trigger multiple times.

[Bored@Work]

One question though - has anyone EVER pressed the autoset button and got the picture they wanted on the screen?

Yes, in artificial situations with a sin wave, or another of the typical showcase waveforms, from a function generator as input.

[tnt]

Or when adjusting the compensation on the probes :p

[Russel]

[...]One question though - has anyone EVER pressed the autoset button and got the picture they wanted on the screen?

For me...No. But, I consider the AUTO button to be the "get the signal on the screen button" so that I can adjust the display as needed to examine the waveform. It sometimes saves me a little time when I'm impatient, sometimes it is useless.

[w2aew]

I used the "bust the chops" of the scope sales guy that would come in to demo a new scope to me, and would immediately hit the AutoSet button.  I told him that it was a WIMP button!  And, if he didn't know how to drive the scope, he should get out of the seat!

For what it's worth, returning the the thread topic, Trigger Holdoff is one of the controls I talk about and demonstrate on the oscilloscope triggering controls video I posted on my YouTube channel:

[vk6zgo]

At my old work at the TV Station back in the 1990s,the Tek & HP blokes would come in with the latest & greatest DSOs.
We would ask them to set it to show one field of PAL video,& chuckle when it looked like my unmowed back yard,& nothing like a video signal.
They were primed up to show us "technical dinosaurs" that we were talking nonsense,but that simple test stopped them in their tracks!
Not a rewarding job being a salesman for an Oscilloscope maker,with all these grumpy old sods around!

VK6ZGO

[CarlG]

Correct me if I'm wrong, but:

It might be worth noting a fundamental difference of this feature on DSOs compared to analog scopes:

When the Holdoff is set to e.g. 100 ns, it actually means that the next data acquisition will be armed at some integer multiple of 100ns after the previous acquisition time, when also the minimum re-arm time is exceeded!

This is of course due to the low capture rate of DSOs. Even with a (DSO) state-of-the-art capture rate of 1 000 000 wfrm/s, the scope can't acquire a new data set as soon as just 100 ns after the previous acquisition, it's at least 1 us in between.

So on a DSO the term "Capture holdoff" might be a better description of the feature than "Trigger holdoff".

It's a bit of shame that this useful feature has been moved down into some meny selection on DSOs, but it's also understandable, partly due to all other features that would be nice to have separate knobs for, partly due to the facts above. It would be misleading to place it in the trigger section of the scope's front panel, but (maybe) confusing to place it in the horizontal section.

I think it's interesting to speculate on how DSO's trigger section might be designed. It seems reasonable to me that the max trigger rate (not to be confused with capture rate which is what we can detect at "Trig out") actually is the Holdoff value (inverted). Otherwise I don't see how the scope could "sync" to the above mentioned capture holdoff?

Or is it just that we think that it work as good as on analog scopes? I admit I haven't tested, anyone else who has?

//C