[volt-nuts] Solartron 7081 testing

[J. L. Trantham]

Mickle,

Happy to help.  

The meter I have I got from a list member in California for a reasonable
price.  It seemed to work OK but I researched the original manufacturer and
sent it to AMETEK in Oak Ridge, TN, who, in turn, sent it to AMETEK in
England, the current 'owner' of Solartron/Schlumberger, who ceased 'full
support' for the 7081 in 2008.  However, they still support it 'best
efforts' and returned my unit with a full set of CAL data along with the
removed and replaced parts consisting of a back up battery, the front panel
connector and three 1K resistors, all for $800, including return shipping.
My shipping to Oak Ridge was about $50.

If you would like a copy of the calibration data, I can send it to you.

I have generally left it on for weeks at a time and I can repeat the test,
warmed up, if you like.  I have left it connected to a Fluke 731B along with
two 3458A's.  Interestingly, the 7081 seems to be the most stable.  After a
few days, the 3458A's will be 5 or 10 uV off but, after an 'ACAL ALL', they
come back very close, typically about 1 uV from the 7081.

My 3458A's have not been calibrated yet but will be just as soon as I figure
out how to read the CALRAM via HPIB.  That is proving to be quite the
challenge.  I am going to need some serious education in IEEE 488.2 before
this is all over.

Sounds like you are quite dedicated to digesting all the intricacies of the
7081.

Joe



-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of ??????
Sent: Sunday, December 04, 2011 1:52 PM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] Solartron 7081 testing


Joe,
I am very grateful to you! All of the data your acquired was completely
coincided with my results. Now I'm think I'm found a bottleneck in the
Solartron 7081 perfomance. Slow analog multiplexor that are part of the
Ratio Circuit leads to improper function of the periodic drift correction
(ADC Zero,
AutoZero) and to large DC voltage measurement errors, up to 5-7 ppm at the
all ranges. This is the simple description of the problem I found:
http://img31.imageshack.us/img31/9798/solartron7081autozerobu.jpg
This is the summary of the your measurement results:
http://img856.imageshack.us/img856/636/adczero.png
This is the multiplexor and ADC schematic diagrams with my comments:
http://img822.imageshack.us/img822/2377/solartron7081adc.jpg
http://img40.imageshack.us/img40/371/solartron7081ratiocircu.jpg

Mickle T.

Sunday, December 4, 2011, 12:54:41 AM, you wrote:
JLT> Mickle,
JLT> Just sent you the file by PM.
JLT> Would love to know what it was I just did.  Hope it helps Joe


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