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 [email protected] > Circuit Concepts, Inc. 281-331-2744 > > ------------------------------------------------------------------------ > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
