[volt-nuts] Fluke 731B

Orin Eman orin.eman at gmail.com
Mon Mar 23 01:36:20 EDT 2015


Some really good information has already been posted.  Here is what I have

I posted a comparison of the 731B against the Geller Labs SVR-T here:


There were within 1ppm of each other over 48 hours and 3.8 deg K.

I'm currently running a comparison against the reference from an HP 3458A,
using an Agilent 34461A in _ratio_ mode.  A screen capture follows if the
list lets it through.  There is only 5 hours here as I just updated the
34461A firmware (it adds another digit to the scaling limits on the trend
chart and is definitely worthwhile).

One thing about the 731B is that it if the NiCd pack is dead or fully
charged(!), there will be much more noise on the output.  I designed a
'high-side' switch to switch between AC and battery power and it improves
noise when the NiCd is fully charged.  (The original design is a diode
switch and if you have a NiCd pack which has a high voltage when fully
charged, the half-wave rectified AC that is used to charge the NiCd pack
leaks through to the voltage reference power supply.)

A big WARNING.  If a 731B still has its NiCd pack installed, replace it.  I
had Batteries Plus make me a replacement pack.  About $30 as I recall.  If
the NiCd pack isn't installed, you need to remove the diode that goes from
the battery pack to the voltage reference supply, or you'll get unfiltered
half-wave rectified AC on your voltage reference power supply and it does
get into the output!

My 731B seems to be doing quite well IMO, being within 1ppm of the new at
the time Geller SVR-T.  It has also been reading 9.99996 to 9.99997 on the
34461A for the last year (as long as I don't turn on the 8568A that is next
to the 34461A... the 8568A blows warm air into the 34461A and then all bets
are off).


[image: Inline image 1]

On Sat, Mar 21, 2015 at 1:02 PM, Richard Moore <richiem5683 at gmail.com>

> Hi all — realisitcally, what sort of stability can be expected from a
> fully functional 731B regarding variation in ambient temp a few degrees C
> around 23, and for long-term drift?
> Fluke’s specs are very conservative, and I think the 731 is far better
> than the specs would lead you to believe, but I have no practical
> experience with these units.
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