[time-nuts] Trimble Tbolt temperature

[Didier Juges]

Maybe the Khalman  filter does not want to know the crystal temperature and
is more interested in the ambient temperature which is better acquired away
from the internals, i.e. in the corner of the board. The oven regulates the
crystal temperature so if it does its job, there should not be too much
variation to measure and the drift of the DAC and reference which I assume
are outside the oven would not be compensated.

On Wed, Dec 4, 2019, 9:23 PM Charles Steinmetz <csteinmetz at yandex.com>
wrote:

> Tom wrote:
>
> > Section 5.1.2 (Kalman Filtering) on page 5-4 (PDF page 48) says:
> >
> > Oscillator performance is subject to two basic effects. First, changes
> > in environmental temperature can cause the oscillator to speed up to
> > slow down. Second, the oscillator has a natural tendency to drift over
> > time. This is called aging.
> >
> > Both temperature and aging can be mathematically predicted. However, the
> > characteristics vary from crystal to crystal. The Kalman filtering
> > monitors the unique oscillator performance over time and temperature and
> > records this behavior.
>
> The DS1620, perched way over in the corner of the board, cannot provide
> useful crystal temperature data, even by inference.  That would need to
> come from within the oven at the very least, more likely from inside the
> crystal envelope itself using, e.g., an IR thermometer.
>
> Instead, Kalman filters in GPSDOs track the oscillator frequency
> continuously and do their best to separate the drift effects from the
> temperature effects using software algorithms (note "mathematically
> predicted" in the paragraph above).  You can see a hint of this by
> monitoring the statistics from one of the older HP units like a Z3801.
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to
> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.
>