[time-nuts] CSAC Project(was CSAC purchase)

[Ronald Held]

Bob:
   Interesting that drift rate has a stocastic component.
   You mentioned adding code.   Was that to the software that comes
with the chip?
          Ronald


Hi

The CSAC (like any vapor cell standard) has a drift (aging) process. That’s
just the way it works. It is at a *much* lower rate than a crystal
oscillator, but
it is the same sort of idea. It is one of their basic differences from a Cesium
beam tube.

Can you “estimate” aging in advance? Everything I’ve seen suggests that you
are simply guessing when you do. You will be right in some cases and wrong in
other cases. You can do better estimating warmup drift and short term effects.
Working out what will happen over months (or years) is not very easy.

A *very* basic example:

I observe a couple of units and they all go positive by 0.8 ppb / mo. I put in
some code to work with that. The unit I happen to have goes 0.8 ppb negative
a month. My code has actually made the unit 2X worse than it would have
been if I just stayed away from it.

Yes there are papers on aging estimation. They mainly focus on coming up
with a “worst case” number. If they guess that 0.8 ppb will go on forever and
it drops off a bit from there, they did ok. For correction purposes …
not so much.

On a practical basis, you *will* have to dock this beast up with a charger on
a regular basis. A solar powered WWVB watch is not unusual. A solar powered
Apple watch or CSAC watch … not so much. When it goes to the charger,
sync it up with GPS.

Bob