David Woolley wrote: > Greg Dowd wrote: > >> If I understand correctly, the question regards slew rate limits. > > That's not my understanding. My understanding is that he want to > constrain the first derivative of the frequency correction.
Correct. I want to know if it's possible to constrain the acceleration. > That is > the second derivative of the offset. Slew rate is used to describe > the frequency correction, particular when it is being used to reduce > an offset error. > > What's probably implicit is that, in the specification he is trying > to implement, this is the derivative including the first derivative of > the crystal frequency, so the 25mHz/27MHz/s (about 0.001 ppm/s) NB: it's 75 mHz/s / 27 MHz i.e. 10 ppm/h > might > be totally taken up by variations in the crystal frequency. Actually, > given that he wants this condition met after one minute, but the machine > probably won't reach thermal equilibrium for more like 15 minutes, I think > it will almost certainly be violated by the crystal frequency on its own. Assume the systems have been running for 24 hours. As far as I understand, clock drift rate (what I call acceleration) is a function of temperature, voltage, and what else? Assume temperature is kept almost constant. I can't say anything about voltage. Since we are using ordinary power supplies, it could probably be slightly improved. > In that case, the only way of achieving conformance is to NOT constrain > the first derivative of frequency correction, so that there is some > chance of the frequency being compensated fast enough to compensate for > the crystal drift. Would the oscillator drift rate be that bad in the situation described above? Regards. _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
