[volt-nuts] Ye Olde HP3458A

[John Devereux]

Frank Stellmach <frank.stellmach at freenet.de> writes:

Hi Frank,

Thanks for such a detailed and interesting reply. "high SNR list" is
correct I see. I don't want to clutter the list with individual replies
but thanks to all others too, much appreciated.

[...]

> It has got the best (differential) linearity, over Keithley 2002,
> Fluke 8508A, Datron 1281, Fluke 57xx and even the Primary Ratio
> standard 720A! Only the JJ array can test its linearity!

Linearity is probably more important to me than absolute accuracy, so
that is good to know.

[...]

> Placing its internal volt and ohm standards in a lower and more stable
> environment would have been better, but then, it could not have been a
> DMM-in-one-box.

These days one might consider a thermoelectric cooler? 

> So the internal LTZ1000A reference has to be running  on 90°C.
> If powerered constantly, this gives at least 20 times higher drift
> rates over time compared to a Fluke 7000A, which is running on 45°C.
> Other DMM are specified for metrological temp. range and have
> certainly slightly better drift rates (two times).
>
> I have set (pimped) the LTZ to about 55°C for lower drift.
>
> The HV divider cannot be corrected for power dissipation effects, so
> the 1000V range is quite mediocre.
> I have built my own 100:1 Hammond type divider (~ 752A) to get around
> 1ppm for 1000V.

Nice. (For the benefit of others who - like me - had not heard of it I
think it's "hammon" divider, based on my googling).

<http://conradhoffman.com/HamonResistor.html> (an interesting site)

[...]

> So my advice, get one used 3458A, it's simply a nice and ultra precise
> box, and build yourself some standards which you would need also if
> you got a newer DMM.

You all have me convinced, I will do this.

> Btw.: A good, absolute calibration is nearly impossible to acquire for
> us amateurs. Even Fluke and agilent obviously offer 2nd grade
> calibrations only.

Take the night shift in a national standards lab I guess :)

Thanks,

-- 

John Devereux