Nice project! Word of advice from a newb: simpler=better.
A fully automated kvd would be pretty cool but would require not only expensive resistors but also expensive relays (low resistance, low leakage, low thermal EMF) and would be a major pain to verify without a proper high resolution dmm.
Have a look at the calibrator from Ian Johnston: http://www.ianjohnston.com/index.php/videos/20-video-blog-022-handheld-precision-digital-voltage-source#compare
He uses a (highly linear) 18 bit dac, good enough for 4,1/2 digits possible 5,1/2 dmm's.
Not saying you should go and buy one but just have a look at the design.
You are definitely right that keeping it simple reduces the possibility of unintended errors being introduced to the system. I think I kind of have a fascination with the KVD more than anything.
Ah, I remember reading about/watching videos about Ian's calibrator. Cool device! I thought about using a DAC, but I guess in my head, I was thinking, "No DAC could possibly match the performance of a voltage reference plus KVD"...but that probably isn't so. Doing device matching on the silicon level probably isn't that hard compared to the macro/discrete equivalent.
That said, with an 18-bit DAC (maybe 16-bits usable?), you can't calibrate ultra-precise meters, but the guaranteed performance of the DAC might be more important than the hypothetical higher resolution of a 6 or 7 decade KVD. i.e. I might be more confident in a fully tested/spec'd DAC (of lower resolution) than my attempt at an automated KVD. That
also said, if I could characterize the KVD, and it turned out pretty good, then maybe it'd be worth something...
Before I scratch this idea completely, would there be any application where an automated KVD (like the one I sketched up) would be beneficial/out perform a DAC based device? Probably not.
Thanks for the insight!