Hal Murray <hmurray@...> writes: > > Also the carbon composition resistor drifted with time at elevated > > temperature. > > I assume the drift is slow enough so that any any control loop will easily > track it. Actually, "ageing" is a better word than "drift". After the major change in resistance due to temperature, the change in resistance was a slow exponential, taking several weeks to level off. The change in the first day or so was pretty dramatic, causing an error of about 2E-9 per day in the oscillator. Since my application was looking at the source signal over the course of a day, the error was appreciable. Even with a GPSDO, the window has to be in the range of 10000s for the level of precision I am shooting for.
After the oven stabilized, the changes due to temperature were quicker and on the order of 2e-10 in a few minutes. This was unacceptable for my application due to the averaging times. Even the average diurnal change in ambient temperature was visible in the error plot. > > What is the drift like at non-elevated temperatures? I have not studied this, but I would think that, like other ageing processes, it would be less. > > What is the drift like for good resistors? Also not studied yet. > If I'm using 2 resistors as a divider, how well do they track? Does it > matter if they have same or different values? IF you assume they have the same change in percent of their value per degree C, it would not make any difference, regardless of their relative sizes. However, I cannot write that "IF" big enough. Even resistors out of the same batch may not change in the same way. I would not rely on them tracking. Also if other resistors are included in a configuration that is not a divider, all bets are off. > > The problem I see with resistors (or voltage reference or ???) drifting is > that it gets tangled up with the crystal drifting. ... Exactly. And exactly why I have changed the resistors to ones I have tested to be less than -1ppm/deg C. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
