Digital does not mean Accurate

[ceagle]

One of the weirdest quandaries of our technological day and age is that we have little clocks on just about everything... our computers, cel phones, vcrs, etc.... but, they STILL don't each keep the same time! ;P
They used to say if it was "quartz", then it would be, but most aren't. My pager runs fast, and my car clock runs slow, etc etc etc.... why can't we come up with a cheap, ubiquitous, non-quartz circuit that will keep accurate digital time? 8|

Comments

[androgynism.livejournal.com]

I read somewhere that quartz clocks lose time if they're exposed to large temperature changes. They usually lose about 10 seconds per year.

[c-eagle.livejournal.com]

oooo... I s'pose that is plausible :9
Had not herded that though!

[androgynism.livejournal.com]

Just the heat from your body is enough to make quartz wrist watches lose twice as much time, because you take it off and put it on.

[c-eagle.livejournal.com]

I'da woulda thotted theyda compensated fo dat though... *pips, and scritches hayd*..

[orv.livejournal.com]

Yeah, they're affected by temperature, in both directions. For really precision applications quartz crystals are put in little temperature-controlled "ovens."

The accuracy also depends on how accurately the quartz crystal was cut to begin with. If the original "grind" was off the crystal may be stable, but stable on the wrong frequency. The more carefully the crystal is ground, the more expensive it is, so the crystals in cheap mass-produced items are likely to vary a lot.

Devices that plug into the wall are usually referenced to the power line instead. This can actually be better on a long-term basis than a quartz crystal, but will be less accurate over the short term (hours to days).

Increasingly, devices that have radios or network connectivity, like cell phones, are using clocks referenced to some central source, which in turn is probably referenced to an atomic clock somewhere -- either via NTP or GPS. This can give exceptional accuracy if it's done right.