[volt-nuts] Keithley 2001 vs HP 3457A multimeters / Any problems to watch out for on Keithley 2001? (Todd Micallef)

[David]

Ah, the Keithley 1801 Nanovolt Preamp in combination with the 2001
brings back memories.  Although I never got to use either, I remember
the advertisements for them.

I went looking for the Keithley 1801 Nanovolt Preamp on their web page
a couple of years before Tektronix bought them and could not find it.
Your web page says they discontinued it which answers my first
question.  Did they replace it with some other integrated product like
the currently produced 2182A Nanovoltmeter?

My last experiment with low noise involved a pair of LT1028s
configured as a standard x1000 differential amplifier with a pair of
LTC1150s correcting their low frequency noise by driving their offset
adjust pins.  The next step up would have been a low noise discrete
JFET input stage for lower input bias current but I was working with
low impedance sources so the LT1028s were fine.  Three things scared
me about this circuit:

1. I measured the low frequency noise using a Fluke 8505A by taking DC
voltage measurements and calculating the standard deviation to get the
RMS noise.  The numbers I got back were exactly as theory predicted.
The Fluke did not have the AC measurement option and given the low
frequencies involved, it would not have worked for what I was doing
anyway.

2. Measuring the RMS noise allowed me to adjust the frequency
breakpoint between the LT1028s and the LTC1150s for minimum total
noise.  The empirically determined breakpoint was also exactly as
theory predicted.

3. This x1000 preamplifier could be used to accurately measure the
resistance of low values resistors just from their Johnson noise.  At
this point I started to wonder if I was dreaming, living in a
simulation, or unknowingly part of the cast of a horror or science
fiction movie.

On Sat, 25 Jun 2016 00:38:49 +0800, you wrote:

>...
>
>Also 2001 support scan-card addons so you can easily expand DMM with 
>scanner function, or even nanovolt-preamp if you dedicated enough. I'm 
>working on nanovolt support with 2001, but that's long story. Some 
>details with DIY card I covered here: https://xdevs.com/review/ema10/
>
>...