How good is your scope? (problem with capturing offset signals)

> Then for a sanity check I hooked up a Tek TDS3032B and it showed the
> correct signal all the way down to 20mV/Div setting
>
> Then I took a Tek DPO4000 scope, and it had the same fault, allthough
> at a different volt/div setting
>
> Tried with a TDS220 (low end scope), it has the fault beginning at
> below 2V/div
>
> Tried a PicoScope 3000 series, had the fault at below 2V/div
>
> Tried a Agilent DSO 4000 series, had the fault at AFAIR 5V/div

I'm surprised at the Agilent... that's ridiculous.  Using something
like your test waveform (100 kHz, 10V pk-pk, DC offset = 6V), all
three DSOs within reach did reasonably well.  On my MSO6054A (the one
I will take with me to Hell to hack the HVAC controller), the base of
the waveform at ~1V was visible and accurate down to 500 mV/div, but
could not be brought back onscreen at 200 mV/div.  It actually looked
good down to 200 mV/div on a DSO3062A (rebadged Rigol), and likewise
for the old Tek 2430A.

No complaints, they performed about as I'd expected... except that I
figured the $200 Rigol would have dropped the ball as soon as the
waveform went offscreen.  I don't expect commodity DSOs to ship with
7A13 front ends, so that TDS3032B is pretty impressive.

-- john, KE5FX

Klaus Bahner wrote:

[snip]
> 
> Interesting. Just a question of understanding (I'm not a user of Tek
> scopes, hence apologies if I miss the obvious information): in the
> screen shots there are different numbers of acquisitions displayed (86
> vs. 226). Is the scope set into averaging mode? And what is the coupling
> you selected, AC or DC?

I was going to ask the AC vs DC thing as well. I don't see an obvious
indication of this setting for either trace.

But I'm always suspicious about a trace that runs off the top (or bottom) of
a scale significantly. One really has to know how one's scope handles over
range inputs.

-- 
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Eagles may soar, but weasels don't get sucked into jet engines.

On Mon, 26 Sep 2011 17:15:58 -0700, Joerg wrote:

> In a nutshell, yes. Maybe not throw out the $10k scope though but I'd
> send this info to Tektronix support. If they can't answer I'd ask the
> sales rep who sold it to you to come out there.

The photos look similar to an instrument we had demonstrated a while ago.
As soon as the guys saw "My Scope" on screen, they howled with laughter,
and most just walked out. The Tek rep beat a hasty retreat, never to be
seen again.

>
> I can't count the times where I've had to ask clients "Do you have a
> real scope?" and out came a big old Tektronix boat anchor where people
> took a step back when I pulled the power switch handle ... bzzzt ...
> TUNGGGG ... blueish green traces showed up and ... tada ... fuzz could
> be seen that the DSO simply was unable to show.
> 
> Here I have a Tektronix 7704, a Telequipment D66 and I also still have
> my old Hameg that I had as a highschool student (but that doesn't get
> used much anymore). I would not want to be without a real scope. They
> don't make them like that anymore. So if your workplace does not have
> something like a Tek 7000 series or a Tek 2465 I'd ask them to go on
> Ebay and get one :-)

Seems that a 770X or 790X with a couple of 7A13s in it would suit Klaus.

I have two 7905s, a 7905A, a 7105, in daily use, with a 7705A in reserve.
All  the extenders and calibration fixtures, too.

-- 
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

On Tue, 27 Sep 2011 11:08:21 -0700, Joerg wrote:

> Of course, the trusty old Tex 7704 and its 7A26 insert sail through all
> that without flinching. I don't know whats so difficult about that. In
> ultrasound we build amplifiers that must listen to microvolts and they
> get hit with pulses of up to 200V. Takes some time but I didn't find
> such designs particularly difficult to do. It's not rocket science.

Do they teach analog engineering any more?

Most, if not all analog engineers I know, including, I believe, those who
inhabit this NG, are well into middle age and beyond.

The modern approach seems to be to throw lots of software into mediocre
hardware.

-- 
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

On Tue, 27 Sep 2011 13:16:01 -0700, Klaus Kragelund wrote:

> Today I asked them to find a analog guy from Tektronix

Don't hold your breath :-)

-- 
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Fred Abse wrote:
> On Tue, 27 Sep 2011 11:08:21 -0700, Joerg wrote:
> 
>> Of course, the trusty old Tex 7704 and its 7A26 insert sail through all
>> that without flinching. I don't know whats so difficult about that. In
>> ultrasound we build amplifiers that must listen to microvolts and they
>> get hit with pulses of up to 200V. Takes some time but I didn't find
>> such designs particularly difficult to do. It's not rocket science.
> 
> Do they teach analog engineering any more?
> 

Sort of, but you can't learn it sitting in an auditorium. It needs to be
lived, and that's hardly happening anymore.


> Most, if not all analog engineers I know, including, I believe, those who
> inhabit this NG, are well into middle age and beyond.
> 
> The modern approach seems to be to throw lots of software into mediocre
> hardware.
> 

Yup, that's the Western way, it seems. In Asia it seems the other way
around at times. Well, obviously not with some scopes. Anyhow, I got
this Chinese arb generator from a company I never heard of, that isn't
even found on the web. First one was bad. Finally I got a new one and it
works great. Can do stuff that many gens 4x its price can't do. The
software and manual? Full of spelling bugs and stuff ... but ... it
works :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

On Wed, 28 Sep 2011 10:44:47 -0700, Joerg wrote:

> The
> software and manual? Full of spelling bugs and stuff

Reminds me of a manual written by compatriots of yours that I once read:

"Manufactured with a pure technic"

WTF does that mean?

-- 
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Fred Abse wrote:
> On Wed, 28 Sep 2011 10:44:47 -0700, Joerg wrote:
> 
>> The
>> software and manual? Full of spelling bugs and stuff
> 
> Reminds me of a manual written by compatriots of yours that I once read:
> 
> "Manufactured with a pure technic"
> 
> WTF does that mean?
> 

Don't have the foggiest. Maybe it relates to the German purity law for beer.

I emm out off zee Rrreinlannd ... :-)

-- 
Regards, Joerg

http://www.analogconsultants.com/

On 28 Sep., 17:25, "Paul Hovnanian P.E." <p...@hovnanian.com> wrote:
> Klaus Bahner wrote:
>
> [snip]
>
>
>
> > Interesting. Just a question of understanding (I'm not a user of Tek
> > scopes, hence apologies if I miss the obvious information): in the
> > screen shots there are different numbers of acquisitions displayed (86
> > vs. 226). Is the scope set into averaging mode? And what is the coupling
> > you selected, AC or DC?
>
> I was going to ask the AC vs DC thing as well. I don't see an obvious
> indication of this setting for either trace.
>
> But I'm always suspicious about a trace that runs off the top (or bottom) of
> a scale significantly. One really has to know how one's scope handles over
> range inputs.
>

Its DC coupling. Even if it was ac, the input would still be
overdriven, and if I use ac, then I cannot "see" the details at GND,
since it will be shifted away

Joerg wrote:

> Fred Abse wrote:
> 
>>On Tue, 27 Sep 2011 11:08:21 -0700, Joerg wrote:
>>
>>
>>>Of course, the trusty old Tex 7704 and its 7A26 insert sail through all
>>>that without flinching. I don't know whats so difficult about that. In
>>>ultrasound we build amplifiers that must listen to microvolts and they
>>>get hit with pulses of up to 200V. Takes some time but I didn't find
>>>such designs particularly difficult to do. It's not rocket science.
>>
>>Do they teach analog engineering any more?
>>
> 
> 
> Sort of, but you can't learn it sitting in an auditorium. It needs to be
> lived, and that's hardly happening anymore.
> 
> 
> 
>>Most, if not all analog engineers I know, including, I believe, those who
>>inhabit this NG, are well into middle age and beyond.
>>
>>The modern approach seems to be to throw lots of software into mediocre
>>hardware.
>>
> 
> 
> Yup, that's the Western way, it seems. In Asia it seems the other way
> around at times. Well, obviously not with some scopes. Anyhow, I got
> this Chinese arb generator from a company I never heard of, that isn't
> even found on the web. First one was bad. Finally I got a new one and it
> works great. Can do stuff that many gens 4x its price can't do. The
> software and manual? Full of spelling bugs and stuff ... but ... it
> works :-)
> 
I have a 20mhz Ab Rigol that just seems to work perfectly. Not bad for
chinese junk.

Jamie