Re: Probes for Nicolet 3091 scope?

From: TekMan (and7_at_bigfoot.com)
Date: 09/28/04 

Date: 28 Sep 2004 00:10:35 -0700

larwe@larwe.com (Lewin A.R.W. Edwards) wrote in message news:<608b6569.0409250434.67d2e645@posting.google.com>...
> I recently acquired a Nicolet 3091 digital storage scope, vintage
> circa 1982. The manual is amusing; for instance, it says that the
> device has 16x12 of RAM, and a single screenful is 4096 12-bit words -
> it is possible to dump out an entire screenful on the RS232 interface,
> but "due to memory limitations of personal computers, you will
> probably not want to acquire the entire image".
>
> It's an audio-bandwidth scope (speced 300kHz BW, up to 1MS/s). I have
> a much better digital scope, but this freebie has RS232 built in, and
> it also has a couple of useful features like a "virtual pen-recorder"
> mode. I want to use it for unattended analysis of battery chargers.
>
> Anyway, I'm having trouble finding a probe that will match this scope
> properly. Here's what the calibrator output looks like:
> <http://www.larwe.com/dsc00461.jpg>. That's the best I can adjust it
> to using the trimcap on the probes available to me (mostly x1/x10
> switchable units of post-1998 vintage at oldest). If I just hook a
> piece of wire to the cal output, the trace looks nice and square. So
> it's a probe capacitance issue.
>
> What characteristics should I look for in a probe for such an ancient
> scope?

The probe you use does not satisfy the scope'S input capacitance with
it's (the probes trimmer) compensation range.

That is NOT unusual: The 3091 has a quite high (compared to nowadays)
scopes capcitance (AFAIK 1Mohm par. 47 or 60pF). Only a few probes you
can buy nowadays can satisfy that input.
check the probes data, or go for an older probe (e.g. Tektronix has
some probes for the "legacy" scopes from the 70's to satify the
range). I don'T know the product number by heart, but you can look it
up in the Tektronix catalogue together with the probe data.

hth,
Andreas

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