New subject: Line Frequency Time Standard was Re: Multiplexing

1 Nov 2011

On Tue, 1 Nov 2011 09:06:45 -0400, David Riley <fraveydank at gmail.com> wrote:

...
  For example, most cheap clock radios have one 4-pin
DIP running the whole show (and it's pretty much been the same chip since the
'80s).  It uses the 60/50 Hz zero crossing on the AC line to keep time, which gives it
very precise time (Laurent Hammond, inventor of the AC synchronized motor which ran both
home clocks and the Hammond organ, took advantage of this and now the power companies must
make sure that the power cycles average 60/50 Hz over the day to a few ppm, if anecdotes
inform correctly) and also gives it a handy time base for multiplexing half the LED
segments.  Normally, as mentioned earlier, a 60 Hz refresh frequency might cause a
headache, but I imagine there are holdup caps on the LEDs so they're not quite so
obnoxious.

 - Dave 
The ability to depend on time error correction on the US power grid might be going away.
There was supposed to be a test starting this last summer whereby the grid was not going
to be corrected. However, at the moment, it's back in committee.

See:
<http://radiomagonline.com/infrastructure/power/60hz-stability-going-away-0627/> for
a story written prior to the scheduled test and
<http://www.nerc.com/page.php?cid=6|386> the North American Electric Reliability
Corporation (the folks who set the standards) blurb on the proposed test.

Perhaps it time to start looking for some of the early GPS network time servers that
started showing up in the '80s (i.e. classic) to attach to those PDP's to ensure
that one is not late for lunch...

	-> CRC