Just finished building 2 units with the Dr. Frank PCB
I'm only on page 20 on this subject, but I got the impression that these should be powered on for about a month continously to burn in? As I'm limited to just a Keithley 2015 before we get some 3458A's to the lab I work in, is the correct way to do this by measuring the difference between 2 units on mV range and when they don't drift against each other that much, then I'll start trimming to desired output? After that time we should have the HPAK meters, put the boxes in a weather cabinet, run from lets say from 15 to 35 degrees °C and trim the 400k resistor? And lastly finish the project by having them calibrated against 732B(?) at the company cal lab.
Does that sound like a solid plan? I'm currently using 13k/1k and non-A LTZ1000. These references are going to end up in homelab with high'ish oven set point as the tempereture can reach around 30°C on the hottest summerdays inside.
Obligatory picture
Don't mind the missing power jack for now. I'll grab it later with the Hammond boxes when I'll order some more components to other projects.
Glad to see another new born pair of references.. welcome in the club.
These non -A references are quite fine, but you've set their oven temperature to probably 60..65°C, instead of using 12k/1k for 50..55°C.
Therefore you can expect a typical drift rate of about -2ppm/year, after the initial higher rate drift phase of 3..6 months.
Note: A 'burn-In' would mean that you'd run the LTZ1000 or LTZ1000A at elevated room temperatures, say over 120°C to let interior epoxy / silicon crystal anneal or create sped-up drift of exterior components.
(This process might be necessary on the A version.)
That's not necessary at all, because the LTZ1000 simply will show an initial drift of about -1..-3ppm/ 3 months, and then the drift will change to the typical rates mentioned above.
So you can directly build the completed tuner box , thermal isolation and Jacks and start trimming the overall T.C., as the references voltages will change during that process.
Your 6 1/2 digit meter is quite fine for tracking the initial drift, if you don't let it run continuously.. any reference which is not powered, will probably drift at nearly zero rate, especially when it's already aged.
So you will compare in the end 3 different references with 3 different drift rates.. in the beginning you LTZs will also differ, but might show the same rate later.
Later on, your new LTZ references will take over as fix points, hopefully you can transfer absolute readings into your lab by comparison.
The T.C. trimming process by bootstrapping is a bit more difficult using a LM399 based instrument, so you need to take care for constant environmental temperature.. Have you got basements in houses in Finland?
Frank