[volt-nuts] Fluke 731B
J. L. Trantham
jltran at att.net
Thu Mar 26 23:03:22 EDT 2015
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.
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
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:
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).
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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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