[time-nuts] Know thy components

Hal Murray hmurray at megapathdsl.net
Thu Aug 6 17:02:09 EDT 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.

These are my opinions.  I hate spam.

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