Mxsmanic wrote:
writes:

Andy Baxter wrote:

Not an answer to your question, but if this is a problem
for you and you have a broadband or frequent dial-up
connection, you can synchronise your clock with a time
server on the internet using a protocol called ntp.

That improves the accuracy of the reported time but not of the clocks
themselves.

It improves both. A good NTP server can hold your system clock to
within milliseconds of the correct time; with an accurate local
reference, it can do perhaps 100 times better. The hardware RTC in
your PC won't be any more accurate, but the actual time of date
returned by the system will. It works extremely well.

Unfortunately I need a solution for non-networked computers, and it
looks like I'll have to resort to hardware.

writes:

Unfortunately I need a solution for non-networked computers, and it
looks like I'll have to resort to hardware.

Without a network you need hardware. However, you can purchase an
inexpensive, radio-controlled clock that connects to the serial port
on your machine and then use NTP to sychronize to that, with excellent
results.

--
Transpose mxsmanic and gmail to reach me by e-mail.

wrote in message
oups.com...

Andy Baxter wrote:

Not an answer to your question, but if this is a problem for you and you
have a broadband or frequent dial-up connection, you can synchronise your
clock with a time server on the internet using a protocol called ntp.

That improves the accuracy of the reported time but not of the clocks
themselves.


Sure, but a least you know what time it is.

wrote:
Why do the battery powered clocks in personal computers tend to keep
worse time than quartz watches, even the $1 ones?

The computer batteries measure fine, at least 3.15V.

I thought that the problem was temperature swings in the computers
(25-38C), but a couple of cheapo watches taped inside the computers
kept better time.


Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.

On 6 Nov 2005 17:55:04 -0800, wrote:

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.


OK, so we eliminated the obvious. The typical PC crystal costs $.25 and is
accurate to 20ppm, or 1.7 sec/day, at room temp. It gets worse at other
temps. You can buy a pci clock card with a tempurature compensated crystal
that is accurate to plus or minus 2ppm for $60, and make it your time
server for you network, or if stand alone systems, in each one if it is
that important. Here is one: http://www.beaglesoft.com/clcaspecs.htm

BH

Brad Houser wrote:

OK, so we eliminated the obvious. The typical PC crystal costs
$.25 and is accurate to 20ppm, or 1.7 sec/day, at room temp. It
gets worse at other temps.

Is there a simple relationship like slower-cooler and faster-hotter
(or the reverse) involved here, or is the relationship not that
simple?


--
Blinky
Killing all Google Groups posts.
http://blinkynet.net/comp/uip5.html

The crystal time function also gets worse when voltage to
that oscillator varies. And that voltage variation is part of
the CMOS date time clock design. Oscillator accuracy, which
addressed the OP's original question, was answered at the very
beginning of this thread. Variation of oscillator crystal is
why watches have a trimmer capacitor. But this too was
answered up top, at the beginning, maybe about 100 replies
ago. Worse still, something like 3 out of 4 responses still
post about external time sources - WWV, internet time,
Operating System response to a interrupts from a completely
different clock, etc. All those were obviously and totally
irrelevant to the question originally asked by do_not_spam_me.

His question was answered early on in the very first
responses. Following posts should deal with these - two
factors of oscillator variation - no trimmer capacitor and
voltage variations to that oscillator. So many reponses that
never once even considered these factors that cause CMOS RTC
timing variations.

BTW, John Popelish also provides good information on how
crystal cuts and other factors contribute to these
variations. Another post that answers the OP's original
question and a comment about many posts that don't.

Brad Houser wrote:
OK, so we eliminated the obvious. The typical PC crystal costs $.25
and is accurate to 20ppm, or 1.7 sec/day, at room temp. It gets worse
at other temps. You can buy a pci clock card with a tempurature
compensated crystal that is accurate to plus or minus 2ppm for $60,
and make it your time server for you network, or if stand alone
systems, in each one if it is that important. Here is one:
http://www.beaglesoft.com/clcaspecs.htm

BarryNL wrote:

Maybe 'cos if you really care about accuracy on a PC you can just set it
to update from an NTP server.

Do you honestly believe I'd be interested in accurate oscillators if I
could simply get the time from a network? Much of the equipment is
placed so even WWV isn't available.