trader_4 wrote:
On Sunday, February 18, 2018 at 11:19:21 AM UTC-5, James Wilkinson Sword wrote:
On Sun, 18 Feb 2018 03:53:54 -0000, Ralph Mowery wrote:
In article ,
says...
trader_4 wrote:
AC isn't
consistent polarity in the positive/negative sense. It changes. In
the case of the states, roughly 60 times a second.
I don't think it is "roughly". AC powered clocks keep very good time for
long periods. Though I have heard that sometimes the power generating
companies keep track of how many cycles have taken place over some fixed
period of time and slow down or speed up the generators to correct things.
Jeff
It is sort of roughly 60 Hz. The power company has at times slowed the
frequency some ( maybe 1/2 or 1 Hz) during peak power loads. They will
then raise it a small ammount during lower loads to keep an average over
a long period of time. This keeps all the line powered clocks very close
over a period of time.
Surely nobody uses clocks like that anymore.
The old ones were synched by virtue of the motor. But there is no reason
some new clocks that are AC powered and digital could not use the AC
freq as a reference to keep the clock always synched. IDK if any do it.
There are also clocks now that use the National Stds Bureau atomic clock
to stay synched. They put out a radio broadcast with the time info
encoded.
I'm sure the digital clocks in our home appliances, clock radios and
other stuff use the 60 Hz line to sync them to the world.That would be
easier and cheaper than adding receivers for the RF time signals.
BTW my last job before retiring about 15 years ago was building and
testing cesium atomic clocks for use in the GPS satellites. Now THEY
were ACCURATE without any external syncing. That's how GPS can determine
just where you are to within less that a hundred feet despite the
satellites being so far above you.
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.