Digitizing Scopes

Hi guys,

I'm aware of situations when you just can't beat an analogue scope, but some people claim that in certain (more limited) circumstances, you just can't beat a digitizing scope. What might those more limited circumstances be?

Jeff.

Reply to
Jeffers
Loading thread data ...

Situations where you can use deep digital buffers to trigger off of transient events where you don't know the delay between trigger and the point of interest. And then you can store multiple incidents for compare/contrast.

I also end up using them as essentially chart or strip recorders. Yeah, you can set up an analog storage scope to do this but you don't get the time resolution or scrolling that really shine on a digital scope.

Tim.

Reply to
Tim Shoppa

Looking at relatively slow signals - anything reapeating at less than

20Hz, where the presistence of vision breaks down. The other response describes this as using the scope and an alternaitve to a chart recorder.

And if your digital scope can transfer screen images into your computer, using a digital scope can vastly simplify remote collaboration. I can remember a time - some ten years ago now - when a colleague in Spain was struggling with a problem, and it was only when he faxed me a pencil sketch of his waveform that I was able to realise that he had too much capacitive load on his clock line. As a specialist in digital hardware, he hadn't made the connection. A little bit of extra buffering, and the whole problem went away.

-------------- Bill Sloman, Nijmegen

Reply to
bill.sloman

Okay, so it's pointless paying extra for the highest bandwidth digital scopes, then? If they only really come into their own with VLF signals, I might as well just get a cheapie low-bandwidth one?

Reply to
Jeffers

For me it's definitely single events and waveform storage. Cheap, high resolution digital scopes tend to be cheaper than high resolution logic analysers. So I use a scope to debug software, monitor serial transmission etc. Put a fast enough scope at the end of your modem and you can even extract TCP/IP packets. I do a lot of real-time systems and I use digital scopes to analyse and verify response times.

So the next obvious question is in what circumstances does a digital scope beat logic analysers? Well, scopes measure voltage, not just ones and zeros. So you can spot hardware problems like capacitance that makes your softare fail.

Reply to
slebetman

I have all three - 547, 7104, several TDS2012s - in the lab, plus a TDS3052 and a bunch of 11801-series samplers. The workhorse is the TDS2012, and lately we just plop a rackmount 2012 in every test rack we make.

The slower analog scopes are great for low-level stuff... a 1A7A or

7A22 plugin has switchable bandwidth and 10 uV/cm resolution, hard to beat for analyzing hum and DAC noise.

One nice thing about the digital scopes is infinite persistance, great for snooping digital data streams and noting worst-case timings in realtime firmware. You can pull up/down test points at the start/end of routines, like IRQs maybe, and run the sucker for a couple of hours and see the extremes. I recently had a rare flakey temperature reading from an LM71 and found the cause (occasional insufficient chip-select setup time... it's a long story) with the TDS.

If I had to pick a single scope on a budget, it would be the TDS2012, although the new Chinese "Agilent" might be good, too. Anybody use one of those yet?

John

Reply to
John Larkin

I'd agree, with only the comment that the lowest-end digital scopes are sometimes lacking in screen resolution and memory. The low end Tek stuff has only 320 x 240 screen resolution. I use one of these as my everyday scope, but to see very subtle detail I occasionally drag out an old Tek 547 which has a .009 inch spot size. However, if you talk about REAL digital scopes, and not the lowest end units, they blow analog completely away.

I have access to scopes of all vintages and capabilities, and I will say without a moment's hesitation that my lowest-end digital scope (Tek TDS2012) gets far more use than the highest-end analog unit (Tek 7104).

Reply to
BFoelsch

I may have unintentionally implied that with my comment about using them as chart recorders, but unlike a mechanical chart recorder (which might be variable between one inch an hour and 10 or 20 inches a second) a fast digital scope with deep buffers can record a million inches at

10 or 100 million or a billion inches a second with somehwat elaborate triggering capabilities. So while the concept may be the same as the old-fashioned pen-and-ink recorders, the speeds are blindingly fast in comparison.

Tim.

Reply to
Tim Shoppa

Only if the memory is deep enough.

We have a nice/fancy Agilent scope. The common gripes are: memory-too-small (and what there is not used right) the time it takes to boot noise

--
The suespammers.org mail server is located in California.  So are all my
other mailboxes.  Please do not send unsolicited bulk e-mail or unsolicited
 Click to see the full signature
Reply to
Hal Murray

The top of my list:

ability to see the signal before the trigger point. (I usually run with the trigger in the middle of the screen)

ability to easily see single events, or very slow sweep speed (for example power up sequences that take human interaction)

ability to capture screen shots for documentation or email

Other people have mentioned other reasons. For me they are minor.

--
The suespammers.org mail server is located in California.  So are all my
other mailboxes.  Please do not send unsolicited bulk e-mail or unsolicited
 Click to see the full signature
Reply to
Hal Murray

"Jeffers" schreef in bericht news: snipped-for-privacy@o13g2000cwo.googlegroups.com...

Pre-trigger events, single events etc.

--
Thanks, Frank.
(remove \'q\' and \'.invalid\' when replying by email)
Reply to
Frank Bemelman

"Jeffers" schreef in bericht news: snipped-for-privacy@g43g2000cwa.googlegroups.com...

No, of course not. It depends on what you want to do with it. There are more advantages than just VLF signal measurement, read the replies again.

If you don't have any need for the mentioned advantages, you don't need a digital scope at all; not even a cheapie one.

--
Thanks, Frank.
(remove \'q\' and \'.invalid\' when replying by email)
Reply to
Frank Bemelman

There is no situation today where an analog scope even comes close to a digital scope, and the same goes for spectrum and network analyzers. Are there any high end analog scope products?-or just kick around cheapies for field work?

Reply to
Fred Bloggs

Any time you want to look at a slow waveform or a rare transient event.

Analyzing the code on a Radio Shack thermometer, ferinstance.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

A rare waveform distortion on a repeating waveform is tricky to spot with a digital scope but obvious on an analog one.

Many high end digital scopes can even deal with this situation.

--
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
 Click to see the full signature
Reply to
Don Lancaster

I have to disagree. Both have their place, but the 'crossover' has increasingly shifted in favour of digital units. Have a look at the TS-80000 from Iwatsu, for a typical modern 'high end' analog scope. I have both a 500MHz analog unit, and a 1.5Gs/sec digital unit, and for some low noise measurements, the analog unit still wins 'hands down'.

Best Wishes

Reply to
Roger Hamlett

Single-shot events, for one. There are (were? haven't tested the market for this in ages) high speed analog scopes with a "latching phosphor" effect, but catching one particular event in a fast, non-repeating wave train is a heck of a lot cheaper in the digital realm.

Complex triggers. Trigger on pulse width less than or greater than a set value. Again, do-able in an analog scope but it's done more affordably with a digital setup.

Assorted measurements and maths, such as rise/fall time and windowed FFTs. Also can be done in analog scopes but at some cost whereas that functionality is almost "by default" available in digital scopes.

Screen captures and data dumps. Handy to be able to grab a screen image in digital format for the archives or to e-mail or to get tagged data for post- analysis.

Fit-to-envelope. Is the signal at the test point in spec or not?

Multi-colored traces. Perhaps just eye candy for dual-trace models but pretty handy to be able to easily sort out which trace is what signal for the four-channel models.

Size and weight. No bulky CRT, no high voltage stage. Easy to move, takes up little space on the bench, can be battery powered.

--
Rich Webb   Norfolk, VA
Reply to
Rich Webb

Yeah, I've got a MSO6054 at work. I now prefer it over the Tek TDS3054, due mainly to the much deeper memory, and of course 16 digital channels.

I only wish Agilent would have made a 100MHz MSO model, so someday I could afford to replace my TDS3014 at home.

Good day!

--
_____________________
Christopher R. Carlen
 Click to see the full signature
Reply to
CC

In general, if you have at least $2000 or equivalent to spend and you are only going to have one scope then a digital one is probably best.

If you have less than $500, then you can usually buy a second hand analogue one which would be better than anything digital in that price range.

The worst situation for digital scopes is something like looking for a 50Hz amplitude modulation envelope on a 100MHz carrier. Only the more expensive digital scopes would be good at this, whereas relatively cheap analogue ones would do it easily.

There are some truly crap digital scopes in the world, for example there is an Agilent infinium thing at my place of work which defaults to 1024 words of acquisition memory, and even if you manually override this with the maximum value, it can only do 32k words/channel, which is less memory than my pocket calculator has. For the above situation of looking for slow modulation on a RF carrier, that Agilent scope is useless, whereas for the same price I could buy a dozen Tek 475s which would do the job with no fuss. With one analogue and one digital scope you can get most things done.

Chris

Reply to
Chris Jones

I have an old Iwatsu dual full function analog/digital with membrane switch panel, 200MHz analog and something like 20MSPS, all the triggering anyone would need. If that scope is representative of their products then you can't go wrong with an Iwatsu. Who measures noise with a scope anyway?

Reply to
Fred Bloggs

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.