[time-nuts] Know thy components
Hal Murray
hmurray at megapathdsl.net
Thu Aug 6 21:02:09 UTC 2015
james.flynn at csun.edu said:
> carbon composition 5% -550 ppm/deg C
> cheap 5 % metal film -240 ppm/deg C
> 1% metal film axial lead <-1 ppm/deg C
> 1% thick film surface mount <-1 ppm/deg C
...
> 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.
What is the drift like at non-elevated temperatures?
What is the drift like for good resistors?
If I'm using 2 resistors as a divider, how well do they track? Does it
matter if they have same or different values?
The problem I see with resistors (or voltage reference or ???) drifting is
that it gets tangled up with the crystal drifting. If you are expecting the
crystal to drift and trying to measure it by something like set the DAC
controling the EFC to some constant (say half range) and then measure the
frequency, it will be easy to overlook the drift from non-crystal sources and
get a bogus answer. It might even be too good or the wrong sign if the
resistors and such are drifting in the other direction.
--
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