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@c-c-i.com Circuit Concepts, Inc. 281-331-2744

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) Fred PA4TIM Op 27 nov. 2012 om 00:27 heeft Bob Smither <smither@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@c-c-i.com > Circuit Concepts, Inc. 281-331-2744 > <smither.vcf> > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Hi Bob, If all you intend to use the 10 volt output, perhaps it would be better to move the sense string positive terminal to the output banana jack leaving the 1K resistor in the circuit. That is, take the top connection R8A and move it to the other side of R18, preferably right at the banana jack. You would still have to be mindful of the load current (i.e., keep it under 5 ma), but that would correct for the load error at the terminals of the instrument. The only other thing to consider would be to possibly move the other end of the sense string (bottom connection of R11) directly to the minus banana jack to make sure the sense string is not part of the main current path. Bill....WB6BNQ Bob Smither wrote: > 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@c-c-i.com > Circuit Concepts, Inc. 281-331-2744 > > ------------------------------------------------------------------------ > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.