Well, hope nobody mind if I jump in with few practical items into this nice talk.
I was talking to one of volt-nuts (not known member here), and we decided to build and test another
KX LTZ-reference for him.
Complete assembly will be tested for tempco and aged for 168 hours and later shipped cold to the final destination via regular mail.
To keep things bit more exiting for me, I decided to try few new things this time.
A. Use VPG VHD200 divider, 1K/13K hermetic oil-filled resistor. My previous LTZ references were using separate resistors.
In theory this should provide better thermal stability, as temperature setpoint divider is now tightly coupled thermally in same oil-filled package.
Rest of resistors are custom 2 x VPG 75K 1%, VPG 120R 0.01%. These have custom PO VFR part-numbers, but I'd expect they are VHP101-based.
Whole lot was bought for 190$USD from eBay, including unrelated resistors on photo.
Chip will be LTZ1000ACH.
B. I want to try ADA4522-1ARZ opamp instead of my usual LTC2057's to see if any difference would be visible on output noise/short-term stability (I expect none, but who knows).
And initial check, using 3458A.
Usual datalog:
Not a bad start, eh? -1ppm from 120 Ω.
Ignore first hour when ACAL was ran. 8:15 to 10:30 is measurement with DELAY 5 on 100ohm range. Few samples were overflow, as 3458A's max overrange is just 120 ohms, so data from 11:15 is with 1KΩ range and DELAY 1. All samples NPLC100, AZER ON, with resistor right at therminals as on photo.
P.S. Bonus quiz, what are rest resistors are for?