[time-nuts] PRS-10 Warm-up Time, Calibrating/Adjusting, and long-term poweron

[Attila Kinali]

今日は

On Fri, 8 Mar 2019 14:09:20 +0000 (UTC)
Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:

> Why?  Because nature of GPSDO and Rb, time constant is set to 2 to 3 hours.  
> (still experimenting)  It takes few cycles of this to lock and stabilize.  In 
> short, you'll be safe if you wait 24 to 48 hours.  Rb modules are relatively 
> cheap.  I really don't see a need to baby it.

There are techniques to cut the "first lock time" down quite a bit.
Most of them involve either switching of all the long time constant
parts of the control loop or switching between different configurations
(ie different multiplicative constants or even different topologies).

The working principle of all is, that once you are reasonably close
in frequency/phase, your long-time-constant loop will not have a
large difference to work with and its internal state converges quickly
to something close of what it should be.

One very simple approach (which not always works) is to decompose your
PI controller into a P and I part, and disable on startup the I part.
Wait until the P part has gotten the error to something stable (not 
neccesarily small) then switch on the I term, with its internal state
initialized to zero. A more sophisticated variant of this, uses an I
part with a smaller time constant first to reduce the residual error,
then estimates from its internal state the state of the real I part and
switches over to that.

Analysis of these dynamic loops can be a bit cumbersome and I recomend
to read a good textbook on this topic before attempting to do something
like this, as it's very easy to shot your foot.

				Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neal Stephenson