Re: Variations on XTAL clock AND time synchronization

Sunwaesh
Date: 02/19/05 

Date: Sat, 19 Feb 2005 22:21:45 +1100

Jerry G.,

Thank you for your valuable answer.
In a project I need to have time synchronization between a set of computers
where some of them are networked together on a LAN (no internet) and some
others are running stand alone. I am planning to use the
one-pulse-per-second (1PPS) signal from the GPS receivers. The networked
computers will have one GPS receiver and all the other stand alone computers
will have their own GPS receivers. GPS receivers will generate 1PPS signals
to interrupt the computers to set their internal time clocks. Applications
will use the computer timer (get the time of the day). I want to model (some
how, but I do not know how) the probable variation that a computer clock may
have between 1PPS signals.

Would anyone comment/argue/recommend/suggest/propose how one can model the
variation on a PC clock frequency ?

Regards,

> What you are asking would be dependent on the grade crystal materials that
> they select for manufacturing them. The crystals have a thermo, and
> internal
> pressure coefficient factor to deal with. They are also a bit voltage
> sensitive, as in part of the feedback circuit employed in the design of
> the
> oscillator that they are part of.
>
> For home computers, they do not need to use an expensive high stability
> type
> crystal, as such that is used for precision instrumentation. I would not
> be
> surprised if the clocking frequency in a home PC machine is drifting about
> 1% to 2%. As long as everything keeps properly synchronized there will be
> no
> problem, no matter what the master clocking frequency is.
>
> The time keeping crystal in a PC is different from the one used for the
> main
> system. The actual real time clock is a separate operation. It is read by
> the main system, only at the times where it needs to get the time of day,
> and the date data. The time of day accuracy of most computers is about the
> same as any low cost quartz watch. I found the time of day on most
> computers
> to drift as much as several minutes a month, if not corrected. A typical
> Timex or Casio watch can do better than 15 seconds per month.
>
> There are softwares available to re-set the clock automatically from some
> of
> the various time standard services around the world. I believe that XP
> comes
> with such a software. This can be done over the internet.
>
> If you have the budget you can install a GPS time standard system, and
> install the hardware and software in your computer to work with it. The
> GPS
> antenna would have to be installed at a location where it can clearly see
> the sky to receive the GPS satellite data. This type of installation would
> result in the most possible accurate time of day standard for a PC
> computer.
>
> --
>
> Jerry G.
> =====
>
> <Sunwaesh> wrote in message
> news:4217077d$0$1023$afc38c87@news.optusnet.com.au...
> Is there any published research/report about how much "uncertainity"
> and/or
> variations must be expected on a PC clock frequency ?
>
>
>

Relevant Pages

  • Re: Variations on XTAL clock AND time synchronization
    ... > computers will have one GPS receiver and all the other stand alone computers ... GPS receivers will generate 1PPS signals ... > variation on a PC clock frequency? ... >>install the hardware and software in your computer to work with it. ...
    (comp.arch.embedded)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers will have one GPS receiver and all the other stand alone computers ... GPS receivers will generate 1PPS signals ... > variation on a PC clock frequency? ... >>install the hardware and software in your computer to work with it. ...
    (sci.electronics.misc)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers will have one GPS receiver and all the other stand alone computers ... GPS receivers will generate 1PPS signals ... > variation on a PC clock frequency? ... >>install the hardware and software in your computer to work with it. ...
    (sci.electronics.components)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers where some of them are networked together on a LAN ... > computers will have their own GPS receivers. ... > computer clock may have between 1PPS signals. ... You should always be measuring the drift so that you ...
    (comp.arch.embedded)
  • Re: Variations on XTAL clock AND time synchronization
    ... > computers where some of them are networked together on a LAN (no internet) ... > computers will have their own GPS receivers. ... > computer clock may have between 1PPS signals. ...
    (sci.electronics.misc)
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