[volt-nuts] 731A output impedance

Fred Schneider pa4tim at gmail.com
Tue Nov 27 00:12:19 UTC 2012

You can add an voltage follower. Made one using a LT1052 and LT1010 ( if i have the number right, a power opamp) the design is from Williams, he uses it in is his sub 1ppm reference. 
I use it to buffer the 731A, that is less stable as my home made LM399, that is getting more stable every week. 
I monitor rH% and temp and as temp goes down and rH% goes up I get the biggest jumps  ( around 40-50 uV) if is to soon to be sure but it looks like rH% has a bigger influence as temperature. The monitoring Solartron 7061 is modified to be kept at 39 degrees by cooling it from the outside and measuring temp inside. ( http://www.pa4tim.nl/?p=2456 ) see picture doen the page ( temp is not yet at 39 degrees there) the fan allways blows, it just goes faster when hot and slower when cold so I do not get temp jumps ( bang-bang regulation like Williams called it)


Op 27 nov. 2012 om 00:27 heeft Bob Smither <smither at c-c-i.com> het volgende geschreven:

> The 731A is specified to have an output impedance of less than 1.1K in the 10V
> setting.  A meter with 10 M input Z therefore causes a .01% (100 ppm) reading error.
> I understand that when operated using a null meter the output impedance is not a
> problem.  I would like to use my 731A as a bench standard for my DMMs.
> The 10V output is taken through a 1K resistor (R18) from the output pin of the
> op-amp.  Clearly the op-amp output pin is much lower impedance.
> The op-amp is an LM301A and appears to be conservatively compensated.
> I am thinking of shorting R18.  I understand it provides some protection to the
> op-amp and may be a factor in the op-amp stability.
> Other than the above, can anyone see why this would be a bad idea?
> Thanks,
> -- 
> Bob Smither                                             smither at c-c-i.com
> Circuit Concepts, Inc.                                       281-331-2744
> <smither.vcf>
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