[volt-nuts] Voltage standard
richiem5683 at gmail.com
Sat Sep 12 23:59:26 EDT 2015
The Datron 1071 is capable of holding to a few ppm (better than 10?) stability for quite some time (weeks to months), if my experience with two 1082s is an example. So a DCV standard capable of holding to within a few ppm is needed. A Fluke 731A or B would be a good choice after a cal — the 10V output of the one I have seems to hold within 2ppm over the time I’ve had it, which is now a few months, as measured with my HP 3458A.
If I were going to fix a 731 with a bad ref, I would use an LM399 or an LTZ1000A as the ref source, and keep the very stable Fluke dividers in place. Circuit mods will be needed but are not extreme.
Another option is to build a DCV standard box using an LTZ1000A, in the circuit straight from the datasheet. Some precision wire-wound resistors or Vishay metal foil resistors are needed, but the overall cost can be well under $200.
I built my DCV standard around an HP reference board from a 3458A, which sometimes show up on ebay for around $100. I buffered the zener output (mine is 7.134577V) with an LTC2057 zero-drift opamp, and used a second LTC2057 as a gain amp to get a 10V output. Gain setting resistors need to have low temp drift and preferably be matched for Tc, so some more precision WW or metal foils resistors are needed. I got mine from Edwin Pettis at Ultrohm.
There is a *very* long thread on EEVBlog.com concerning the LTZ1000/1000A — start at page 13 and read the comments for the next 3 or 4 pages, especially those from Dr. Frank.
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