[time-nuts] Clock accuracy

[Graham / KE9H]

All:

I think the leap-second correction is real important, or you have to change
references.
The whole (original) point of time is all about Sun time.
What time to get up?  When is noon?  What is my longitude?
But, the Earth is slowing down.
According to Wikipedia, the Earth's rotation is slowing at the rate of 2.3
ms per day, per century.
Or, Donald's super accurate free running clock is going to be off by about
42 seconds, relative to Sun time, after a century. (Assuming linear change
for simplified calculations.)
That means the accuracy of the Earth's rotation is only about 1.3 in 10E-8.
(and slowing down.)
Lots of leap-seconds on the way.

Bezos' 10000 year clock continuously sets/resets itself to Sun time.

--- Graham

==



On Sat, Jul 20, 2019 at 2:00 AM donald collie <donaldbcollie at gmail.com>
wrote:

> ...and speaking of electrolytic capacitors and reliability : I own a Rohde
> & Schwarz POLYSCOP made in 1965 which has a 1000uF capacitor in the LV psu
> that is still functioning well after 54 years. Mind you it`s a physically
> large item compared to todays capacitors.
>
> Cheers!.......................................................................................................................................................................................Donald
> C.
>
> On Sat, Jul 20, 2019 at 10:20 AM donald collie <donaldbcollie at gmail.com>
> wrote:
>
> > Thanks to all who replied! It looks like the antioxidants will win and
> the
> > clock will fail before the 100 years are up. Assuming the "accuracy" of
> the
> > GPSDO is 1 part in 10^12 then the inaccuracy after 100 years will be up
> to
> > : 60x60x24x365.25x100x1x10^-12= 3ms [approximately] - which is probably
> > good enough for an old fella. I have to admit that I have an ulterior
> > motive for asking this question : I wanted to know what sort of long term
> > accuracy I could expect from the GPS constellation - looks as if 1 part
> in
> > 10 to the 12th is about right.
> >
> Cheers!...............................................................................Donald
> > C.
> >
> > On Sat, Jul 20, 2019 at 7:01 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> >
> >> Hi
> >>
> >> The simple answer is that your clock is locked directly to a set of time
> >> sources built
> >> into the GPS satellites. Those sources are corrected by ground stations
> >> via comparison
> >> to NRL and NIST (and indirectly other sources as well). The various
> >> ground reference
> >> time systems get measured and evaluated to form what we call the right
> >> time. This
> >> is done by BIH in Paris. That process also keeps NRL and NIST “in sync”
> >> with the correct time.
> >>
> >> Since everything is locked together, there really isn’t any long term
> >> drift. As long as
> >> everything is functioning (and the PPS is from GPS not some random
> >> divider) you
> >> should be “on time” to within 100 ns pretty much forever. The time
> >> involved could
> >> be GPS time or UTC depending on how you associate time stamps with your
> >> PPS edges.
> >>
> >> If indeed something goes wrong with GPS ( as unfortunately happened to
> >> Galileo
> >> very recently), your time could be just about anything if the error is
> >> undetected. If
> >> it is detected, your will go into holdover. The drift then depends very
> >> much on just
> >> what “Trimble” you have inside your setup. 10 us a day for the first day
> >> is not an
> >> uncommon number to see. Since it’s really frequency drift rather than
> >> time drift,
> >> the second day will be worse and it just goes downhill from there.
> >>
> >> If your PPS *is* from some random divider off of (say) 10 MHz, then
> every
> >> time power
> >> goes out, it will come back up at a random point in the second. If you
> >> punch
> >> a button to “sync” it, you will only be able to move it in 100 ns steps
> (
> >> the period
> >> of 10 MHz). If the 10 MHz edge is “right on” with GPS that’s fine. If
> >> it’s off by some
> >> random amount ….. not so fine.
> >>
> >> This gets into a vary basic gotcha: A typical GPSDO *does* get the
> output
> >> PPS from
> >> the 10 MHz. The PPS output direct from a GPS module probably is closer
> to
> >> “on time”
> >> that the GPS PPS. It will bounce around a lot more, but it likely is
> >> closer to being correct.
> >>
> >> Lots of twists and turns …...
> >>
> >> Bob
> >>
> >> > On Jul 19, 2019, at 1:17 AM, donald collie <donaldbcollie at gmail.com>
> >> wrote:
> >> >
> >> > Without wanting to show my ignorance by confusing accuracy, and
> >> precision,
> >> > etc, would some kind person please answer the following : Let me
> >> explain -
> >> > I have my prototype GPS diciplined [ Trimble inside] standard
> frequency
> >> > source connected to both a divide by 5,2,5 and 2 producing all the
> >> > reference frequencies necessary for the various bits of equipment in
> my
> >> > workshop, AND the 1pps
> >> > output connected to a 7474 "T" flipflop and thence via a 100uF
> >> capacitor to
> >> > a modified $10 analogue wall clock. Can anybody tell me this : If I
> live
> >> > another 100 years [Let`s say I take antioxidants ;-)  ] what sort of
> >> error
> >> > should I expect in this clock? [I know that it`s better than 1 second
> >> per
> >> > day]
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> >>
> >>
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