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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: How to build your own Oscilloscope?
References: <0vcj9.172680$Jo.55878@rwcrnsc53> <firstname.lastname@example.org>
Date: Sun, 22 Sep 2002 20:35:26 GMT
NNTP-Posting-Date: Sun, 22 Sep 2002 13:35:26 PDT
The little lost angel wrote:
> On 22 Sep 2002 11:20:19 -0700, email@example.com (Glenn Gundlach)
> >Just looked at eBay. Tek 475 dc-250 mHz less than $100. If you have a
> >computer, I bet you can afford $100. Tek 3012 DPO starts at $3000.
> sorry to butt in but how does a newbie know if the oscope is working
> or not? I want to get a scope but know next to nothing about chosing
> one :D
The choice depends on a lot of issues.
Is real time display of slow events a requirement? If yes, digital
scopes are useless and you must find make an archeological find to
obtain a useful instrument.
Windows based instruments tend to be nearly useless. Our Tek Windows
based logic analyzer is about 10X harder to use than models before the
Windows based model. It is far costlier to upgrade than older models and
is generally a kind of paper weight that gets dusted off in desperation
at rare intervals (don't look at me - it's the logic designer who hates
it - I won't touch it unless something I need is under it). A peculiar
property of Windows based instruments is that they crash. This is a nice
excuse as it happens. "I actually caught the malfunction but the
analyzer crashed." It beats saying, "The dog ate my homework."
Digital scopes are sort of useful after you resign yourself to the fact
that what you see on the screen is something that may have happened
several days ago. Fast sample rates are available at reasonably
astronomical prices and output formats for further processing in your
computer are generally proprietary and unfathomable. One popular scope
has Excel spread sheet output which is as useless as teats on a boar hog
if you use Matlab.
In selecting a digital scope, you must select a sample rate and memory
depth that will work for your application. Great memory depth causes a
scope to be sluggish. The scope I use is so busy screwing around with
its internal memory that it tends to ignore the front panel controls. On
the rare occasions that I can get its attention, it presents a
bewildering array of completely nonintuitive menus invariably lacking
the function needed.
In my group, we were forced by the hopeless inadequacy of digital scopes
for some measurements to go out and invest a few hundred bucks in 20
year old analog scopes to supplement our more than $10,000 digital
In the last 30 years, some areas of measurement technology have
regressed significantly. This seems to be because of a mentality that
does not appreciate real time significance. For example, I personally
own both analog and digital multimeters. The digital meters are OK for
most measurements but the analog meters are still absolutely essential
even though hard to find.
And so ends my hobby horse ride over the realm of test and measurement.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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