Variations on XTAL clock frequency

Is there any published research/report about how much "uncertainity" and/or
variations must be expected on a PC clock frequency ?

 

[Hans-Bernhard Broeker]

[X-posted without a F'up2 concentrator. Fixed.]

In comp.arch.embedded Sunwaesh wrote:

Is there any published research/report about how much "uncertainity" and/or
variations must be expected on a PC clock frequency ?

I doubt there'll be much about PC clocks in particular --- but I'm
sure there's plenty about crystal oscillator stability in general,
which will apply to PCs quite seamlessly.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.

 

[Phil Allison]

"Phil Allison"


** Correction.

So, the month to month variation should be maybe +/- 10ppm or 0.86
seconds per day at the worst.

.............. Phil

 

[Stef]

In comp.arch.embedded,
larwe@larwe.com <larwe@larwe.com> wrote:

The battery-powered RTC clock is frequently VERY inaccurate, though.
For reasons I've never had explained to me, they almost always have a
trimcap on that xtal. Their Q/C processes to set that trimcap appear to
be FUBAR.

It's just there because the appnote says to put it there. And it allows

a demanding customer to calibrate the clock himself if he wants to. ;-)

--
Stef (remove caps, dashes and .invalid from e-mail address to reply by mail)

Living your life is a task so difficult, it has never been attempted before.

 

[Nicholas O. Lindan]

There are clock correction programs that either apply a daily
correction to the time or query the NIST clock in Colorado.

--
Nicholas O. Lindan, Cleveland, Ohio
Consulting Engineer: Electronics; Informatics; Photonics.
To reply, remove spaces: n o lindan at ix . netcom . com
psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

 

[Tauno Voipio]

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

 

[Richard Freeman]

"Phil Allison" <philallison@tpg.com.au> wrote in message
news:380i5rF5k6g88U1@individual.net...

"Richard Freeman"

I would not have expected an un-trimmed Crystal to drift more than 100
Parts per Million or 86.4 mS per day,


** 100 ppm = 1 part in 10,000.

A day has 24 x 60 x 60 seconds or 86,400 seconds.

So a 100 pm error is 8.64 seconds !!!

You are only 1000 times out.

oops You are right .... dunno how I missed that one ? .. actually looks like
I forgot to multiply by 100 ..... ;-)

 

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 ?