Jim Yanik wrote:

"Pete C." wrote in
ster.com:


Ed Pawlowski wrote:

"Dean Hoffman" wrote in message
...
On 6/25/11 7:11 AM, wrote:
On Jun 25, 12:23 am, wrote:
I smell issues arising with this...

http://www.google.com/hostednews/ap/...HrMC9wYlOzOkUg
9wN... Kugkw?docId=371623ab59694aef9f0a02fe83faca8a

Erik

I have one issue already. The linked article comes up as
unavailable.


A short article he http://tinyurl.com/5vk4lc4

Does it really take that much effort to synchronize the grid's
frequency?


I have no idea, but according to the articles, yes.

I know that a clock motor will be affected as you change from 60
cycles, but digital? I thought they had something to do with a
crystal frequency oscillation. Or is that just watches?

"But wall clocks and those on ovens and coffeemakers - anything that
flashes "12:00" when it loses power - may be just a bit off every
second, and that error can grow with time."

Most anything that "flashes 12:00" is going to be using a crystal
timebase and not care about power line frequency. They flash 12:00
since when they loose power they need to have the time set again, not
anything to do with line frequency.

There are still a great many timing devices that rely on synchronus
motors and thus line frequency, and these mostly have just dials, such
as timers for sign and landscape lighting, water softener
regeneration, water heater timers and the like.


many of those "flashing 12:00" clocks DO need line frequency to count time.
Not all of them have xtal or ceramic resonators providing the 1 sec pulses
needed for the time count.

Nope, that was the very very early days of digital clocks with discrete
logic. Any device built in the last few decades that "flashes 12:00" is
microprocessor based and will not be using line frequency for reference.

Otherwise,a simple lithium coin cell or Supercap backup would retain the
timekeeping for a long time,and short power interruptions would not send
the clock back to flashing 12:00.

Adding such a backup adds cost to the device, which is why many do not
have such backup. Most actual clocks have a backup battery compartment
for use with regular batteries.


Actually,using line freq is usually more accurate than the xtal or ceramic
resonator timebases,over a long time frame. Unless an xtal timebase is
precisely tuned and temp compensated,they are not accurate over long times.

Sure, but the crystal is accurate enough for consumer use. Many of the
consumer devices don't even have AC power available to them to monitor
the line frequency of since they use wall wart or line lump DC power
supplies.


I used to do such calibrations.

I've soldered PTC thermister heaters onto crystals to provide
temperature stabilization. Most applications, including consumer timing
don't need that level of accuracy, particularly given that most such
devices have their time reset at least twice a year.