Azelio,
Grab a copy of the TBolt user manual; google ThunderBoltBook2003.pdf
Section 5.1.2 (Kalman Filtering) on page 5-4 (PDF page 48) says:
----
Kalman filtering is a technique that improves the performance of a GPS
disciplined clock when GPS drops out. This state is called holdover.
During holdover the clock relies solely on the oscillator.
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.
Then when the clock goes into holdover this filtering corrects for these
effects producing a more accurate clock. The longer a clock has to
’train’ the better the Kalman filtering performance will be. 24 hours is
considered the minimum necessary for good performance.
----
/tvb
On 12/4/2019 7:57 AM, Azelio Boriani wrote:
'The temperature chip is there to “learn” the TC of the unit while it
is in lock.'
I think this is news for the group: as of my knowledge, we don't know
if the 1620 has an active role in the TBolt other than measuring
temperature for the TSIP output.
On Wed, Dec 4, 2019 at 4:04 PM Bob kb8tq <[email protected]> wrote:
Hi
The temperature chip is there to “learn” the TC of the unit while it is in
lock. If and when the unit goes into holdover that information is used
to compensate the unit. If the environment does not change much when
you are in holdover this may be a benefit. If the HVAC goes when the
holdover happens …. maybe not so much.
The DAC and voltage reference on the E-911 TBolts has a pretty
substantial temperature coefficient. On top of the wide tune range of the
OCXO this gives thepart a pretty substantial temperature wander. If holdover
is part of the “plan” the temperature chip probably is worth having.
The Nortel GPSDO’s have a very different OCXO in them (normally a double
oven) with a narrower tuning range The DAC and voltage reference are
done very differently as well. On top of that, the Nortel spec for holdover
was much tighter than the E-911 requirement . Net is that the temperature
chip in the Nortel versions may not be as important, even in holdover.
Yes, way more than you wanted to know …...
Bob
On Dec 4, 2019, at 2:52 AM, Christophe Huygens <[email protected]>
wrote:
Thanks all - if of no consequence, case closed.
On 04/12/19 03:03, Tom Van Baak wrote:
Most TBolt measure board temperature to about 1/100th C resolution.
This is the correct behavior. Some TBolt report temperatures that seem
to step in 1 C increments, or they report a constant -55 C, or they
glitch once in a while. These are bugs.
You can replace the DS1620 chip if you want. It's perhaps best to
locate the 20-year old version of the chip. There are lots of threads
about this in the archive.
The DS1620, working or not, has no effect on the performance of a
running TBolt. So I've never bothered replacing any of mine. It may
have a slight effect on extended holdover performance. It's a long
story and I'm not sure if anyone has actually verified or quantified
this.
Here's additional info about the TBolt & DS1620; it's more complex
than you think:
"Strange temperature peak"
https://lists.febo.com/pipermail/time-nuts_lists.febo.com/2011-May/039188.html
"Trimble Thunderbolt GPSDO Temperature Sensor Details"
http://leapsecond.com/pages/tbolt-1620/
"Dallas state machine glitch"
https://www.digitemp.com/docs/ds1820-report.pdf
/tvb
On 12/3/2019 1:47 AM, Christophe Huygens wrote:
Hi all,
I am back on time-nuts after many moons.
Lady heather shows constant -55deg C for my Tbolt.
all else seems to function fine (is in a constant T environment, sort
of)
Any thoughts....
br and thanks
Xtof
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prof. dr. ir. Christophe Huygens iMEC-KULeuven-DistriNet
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