[time-nuts] temperature sensor
kb8tq at n1k.org
Mon Jul 21 18:19:29 EDT 2014
If you look at the people running very precise thermometers (sub 0.001C) they are doing better with thermistors than with PRT’s. Both the PRT’s and the thermistors come with notes on them requiring on location re-certification below he 0.01C level. A triple point of water cell is typically what’s used for both.
On Jul 21, 2014, at 10:12 AM, Attila Kinali <attila at kinali.ch> wrote:
> On Mon, 21 Jul 2014 04:39:51 -0700
> Alexander Pummer <alexpcs at ieee.org> wrote:
>> NTC are not that very stable, they are amorphous material winch could
>> recrystallize slowly and therefore change it's electrical behavior ,
>> PT100 style is more reliable since it is pure metal
> How long is the time constant for NTCs?
> I guess, it wouldn't matter for most of the measurements we do,
> as NTCs need to be "calibrated" before precision measurements
> anyways. Unless one measures over several months, or years.
> But on this timescales, i wouldn't really trust an off the shelf
> PT100 either. Not unless i measure its stability
> For use in GPSDOs and OCXOs, i guess it doesn't really matter,
> as long as the NTC stays within spec. There an external loop
> corrects for the variation/drift of the measurement.
> While we are at it: what is a good way to calibrate/characterize
> temperature sensors that is available to hobbyists?
> Attila Kinali
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