The ageing can also be determined, if you would have a set of equivalent resistors, which you might compare against each other over one year, or so.
Can you really do it this way or isn't it likely that the two equivalent resistors also have equivalent drifts?
Long ago I also tried it this way with voltage references but was cheated. Now I believe that you at least need to have some traceable calibration points with some time difference in between and specified uncertainty for all points. Of course if you have say VHP202 resistors and want to characterize some less good resistors you probably can do some assumptions from data from others (a kind of uncertainty spec?). From my (few) VHP long-term tests I have never seen more than 10ppm drift the first year.
Lars
Well, I call this the man-with-two/three clocks-problem.
In principle, you can determine any extensive drift of one member of a group of standards.
That's your only choice, if you've got "nothing better".
How else could the metrologists identify the kilogram prototype in Sèvre to be the 'stinker', which drift apart out of the whole group of its international copies?
How else could the Cesium-clocks be characterized, (w/o Masers and these new optical clocks), to have about 1E-15 stability, if not by comparing several units against each other?
Your objection is legitimate, that all these members might drift in the very same direction, due to the very same systematic drift mechanism.
Well, the probability is quite low, if all these members don't drift that much apart, over several years, i.e. if the spread of drift is very narrow also.
My five VHP202Z resistors have the same value, within about < 0.5ppm, over > 5 years. So I can assume, that the absolute drift is about on this order of magnitude.
I have never seen drifts of 10ppm/year, like you, obviously, and Vishay declares them to be stable to about <2ppm/6years, which I now believe, that this is true.
Another example is from Joe Geller, he monitored several dozens of LM199 over a year, or so. The spread was quite high, but he could clearly draw a baseline, where the zero-drift members would be situated.
You have to pay attention with zener references, the SZA 263 inside the 732B would probably drift +1ppm/year, and the LTFLU, líke the LTZ1000 mostly drift about -1ppm/year. (all at 45°C)
Again, you will always find units, which have drift in the opposite direction, which detects probable drift-correlations.
Well, I also tried to get reasonable fix-points from time to time (for free, of course) by comparison to calibrated material, but always found the deviation to be within the expected drift values.
Frank