Long term update and test.
Going to put this here as it seems to show the stability of the 7 > 10v buffer more than the LTZ1000A KX reference. The system has been powered on and at a continuous 35 deg C for about a year and a half. In that time I have only seen about 0.3ppm drift between the DMM7510 and the 10v reference, no way to know which is drifting or if they both are, but being the DMM7510 uses the LTFLU-1 and they tend to drift in the opposite direction of the LTZ1000, its safe to say neither appear to be drifting much.
So I decided to do a test and see how sensitive the KX board and 10v buffer as a system are to small temperature changes. My oven circuit can be adjusted from 31 to 39 deg C via a 25t pot for about 0.35 deg C per turn.
Link to the oven circuit;
https://www.eevblog.com/forum/metrology/kx-reference/?action=dlattach;attach=412838All measurements were taken with the DMM7510 and I held the room temp +or- 0.3 C as displayed in the 7510's internal CAL temp. The meter was set to relative offset so I could easily track the change in uV. Starting at the minimum temp of 30.8 C, I took a measurement increasing the temp by one turn then letting the reference stabilize for at least 30 min before the next measurement, or about + 0.5 C per hour max. I could not complete the entire test in one sitting, it was compiled over two day. I only hand recorded the results, no fancy plots or charts, sorry.
The results only show the limiting factor is the DMM7510 and my lab temp stability. The KX board and 10v buffer simply seem unaffected between 31 -39 C with a max measured difference of about 1 uV or 0.1 ppm. I can see initial + voltage swing as the oven heats, but then settles down right where it started, same when the oven cools I see a - swing but then comes back up as the temp stabilizes. The oven holds the temp to a stable 35 C + or - < 0.3 with an ambient temp range of 15 - 30 C, so I'm more than pleased.