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

Bob kb8tq kb8tq at n1k.org
Fri Jan 26 14:17:16 EST 2018


One way or the other you will need some “smarts” to do aging compensation.
That implies adding a CPU of some sort to the “system” you are building. There
is no built in subsystem on the CSAC that will do any of this for you. You also 
need some sort of display for your “wrist watch”. Having the CPU handle that 
at the same time makes a lot of sense. 


> On Jan 26, 2018, at 2:12 PM, Ronald Held <ronaldheld at gmail.com> wrote:
> 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
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