Re: Variations on XTAL clock AND time synchronization

From: Tauno Voipio (tauno.voipio_at_iki.fi.NOSPAM.invalid)
Date: 02/19/05 

Date: Sat, 19 Feb 2005 12:37:18 GMT

Sunwaesh wrote:
> 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.
>>

I'd consider installing a NTP service / daemon. It is able to slowly
adjust the clock division ratio so that the timing stays put. Even
without an external server, NTP is able to use your GPS 1pps tick
as the reference clock.

For more information, Google for NTP or Network Time Protocol.

NTP is also excellent for keeping your networked computers in sync. 

-- 
Tauno Voipio
tauno voipio (at) iki fi

Relevant Pages

  • Re: Variations on XTAL clock AND time synchronization
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  • Re: Variations on XTAL clock AND time synchronization
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    (sci.electronics.misc)
  • Re: Variations on XTAL clock AND time synchronization
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    (sci.electronics.components)
  • 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)