Digitizing Scopes

[Jeffers]

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.

 

[Tim Shoppa]

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?

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.

 

[[email protected]]

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?

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.

 

[Jeffers]

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?

 

[Frank Bemelman]

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?

Pre-trigger events, single events etc.

 

[Frank Bemelman]

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?

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.

 

[Fred Bloggs]

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?

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?

 

[BFoelsch]

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?

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).

 

[Roger Hamlett]

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?

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

 

[[email protected]]

Pre-trigger events, single events etc.

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.

 

[Rich Webb]

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?

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.

 

[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).

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

 

[Chris Jones]

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.

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

 

[Fred Bloggs]

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

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?

 

[martin griffith]

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?

Jim Williams?


martin

 

[Tim Shoppa]

If they only come into their own with VLF signals [...]

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.

 

[Hal Murray]

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.

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

 

[Hal Murray]

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?

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.

 

[Don Lancaster]

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.

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
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Don Lancaster]

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?

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
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com