Hello,
I have recently started dabbling in ordering salvaged electronic components (e.g. obsolete packages of precision components, etc) from taobao, including LM399's, and I had an idea of a service which might be of interest to forum members, particularly the volt-nuts on a budget who would like to track the volt at home.
Background:
If you try to track the drift of an LM399 by measuring it directly, you need to at least use a 6.5-digit meter, but even then, on the 10V range you are really just comparing your LM399 to the LM399 inside of the meter. So what exactly are you measuring?
If you instead measure the difference between two LM399's, you can use the 1V range, which gives you better resolution, and also attenuates the perceived drift of your meter 10x relative to the drift of the LM399.
Even better, if you get lucky and have two LM399's which are less than 100mV apart, you get to use the 100mV range, with 100nV resolution and 100x attenuation. Fantastic!
But that's just for 6.5-digit meter owners. What about ballers on a budget, with 5.5-digit meters?
Well, some 5.5-digit meters (e.g. Keithley 195A, HP 3478A, etc) support a 20mV or 30mV scale with 100nV resolution. This can allow you to track the drift of a few LM399's with results comparable to 6.5-digit meters, but for less money (the Keithley 195A can be found on ebay for under $100 if you are patient, and the 3478A as well if you are more patient).
The problem is, LM399's output voltage can vary quite a bit from unit to unit.
So, for a budget-minded volt-nut to track the volt, he needs access to cheap LM399's, and they need to be binned pretty tightly.
The LM399's are indeed cheaply available (about $3) on taobao, so to make this happen, we just need one person who can order a big enough batch to ensure tight enough binning.
The service I'm thinking about offering:
So, I had an idea to order batches of these LM399's, give them a quick measurement and bin them according to Vz, then sell bundles of them to forum members, binned according to the requirements of the lowest DCV range of their meter.
Would anyone be interested in this kind of service?
Edit: I was thinking bundles of 3 or 4, as you could keep 3 at home and track their drift while mailing a 4th to another forum member (to exchange calibration), and you'd have a reasonable guess at whether the 4th drifted when it was returned to you. Users with just 3 refs could track them at home and wait for a cal-club ref to be mailed to them.