[volt-nuts] Fluke 731B

John Phillips john.phillips0 at gmail.com
Fri Mar 27 02:40:51 EDT 2015

I would never adjust any pots on a working fluke voltage standard. When the
pot moves you introduce more drift.
Just keep track of differences.
By the same token I do not turn off my 3458As as long as the line power is
There was a time I had a rack of 15 3458As running waiting to be sold.
We have a power outage about 1 time per year long enough to trip our julian
date and time clock. We use it to track power up time.

I do not see anyone posting 3458A in stat mode data: mean, SDEV, High, and
Low, Range, and Number of samples over extended time.
then reverse polarity and do it again.
Also DC cal values before and after Auto cal and Keysight cal would be nice
to know.
Also using Before and after cal data from Keysight to correct values.
Do not adjust the Flukes  but keep a spreadsheet of best guess of its value.
Something like  mean of present guess + before cal data correction + after
cal data correction.
Say you present guess (guess1) is 9.9999468 cal the meter using 9.9999468
and then read the cal var 1 (I think that is the one for the reference
Your as found data should indicate how far off your reference is.  correct
and call that guess2
After you get the meter back read cal var 1 and then use successive
approximation to when caling to get the same value in var 1. That should be
So new guess is mean (guess1, guess2, guess3).
If you have better confidence in one guess or less confidence in an other
the values could be weighted.
You never really know what the actual value is  a given time but do know it
is changing.  You can guess at it's value like 9.9999468 is just a guess
even if the real value is 9.99994681 or even 9.9999468 with what we have
you just cannot know for sure. There can alway be another digit.

Anyone want to poke some holes in what I wrote?
Does anyone have a better way to come up with a Cal value for a fluke 10
volt reference without sending it out for calibration?
Where could send it to get a better calibration and what would it cost?

On Thu, Mar 26, 2015 at 8:03 PM, J. L. Trantham <jltran at att.net> wrote:

> A couple of years ago, I sat my 735C, a (at that time) recently Agilent
> calibrated 3458A, and two 731B's on a bench and have left the references
> on, with battery back-up for any power failure.  I have turned the 3458A
> off and on a number of times in the interim.
> When I set all this up, I adjusted the 735C to 10.000000 VDC as best I
> could using the then recently calibrated 3458A and adjusted the 731B's to
> match the 735C using the 3458A as a 'null' meter.
> Tonight, after the 3458A had been on for several weeks, I did the 'AutoCal
> All' on the 3458A and read each of the references.
> The 735C measures about 10.000016 VDC, and the 731B's measure about
> 10.000005 VDC each, within about 2 uV of each other.
> In the next couple of months, I plan to send the 3458A back to
> Agilent/Keysight for recalibration and see what the meter measures 'as
> received' and 'as left'.
> We'll see how close it is to being 'in tolerance' 'as received'.
> Hope this helps.
> Joe
> -----Original Message-----
> From: volt-nuts [mailto:volt-nuts-bounces at febo.com] On Behalf Of Orin Eman
> Sent: Monday, March 23, 2015 12:36 AM
> To: Discussion of precise voltage measurement
> Cc: richiem5683 at gmail.com
> Subject: Re: [volt-nuts] Fluke 731B
> Richard,
> Some really good information has already been posted.  Here is what I have
> found.
> I posted a comparison of the 731B against the Geller Labs SVR-T here:
> http://www.eevblog.com/forum/testgear/geller-labs-svr-and-svr-t/msg282582/#msg282582
> 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).
> Orin.
> [image: Inline image 1]
> On Sat, Mar 21, 2015 at 1:02 PM, Richard Moore <richiem5683 at gmail.com>
> wrote:
> > 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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*John Phillips*

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