[time-nuts] Re: Power line timing -- setting a clock

[Clive Blackledge]

Hi Bob,

There are some 3 letter agencies that use power frequency variations to
help determine when video or audio is recorded. Tom Scott did a Youtube
video about it here https://youtu.be/e0elNU0iOMY ..

There are a few frequency disturbance recorders out there; one is called
GridEye. IEEE has a paper or two on FNET. The Federal Power Act in 2009
required automatic time error correction (ATEC) so people with older alarm
clocks without an oscillator can wake up on-time.

It's fun stuff. I'm glad someone brought it up so I can geek out for a
minute :)

-Clive

On Fri, Mar 22, 2024 at 2:47 PM Bob Camp via time-nuts <
time-nuts at lists.febo.com> wrote:

> Hi
>
> Back in the 1960’s what you describe is pretty much “how it was done”. We
> figured out that the local power company “lined things up” between 4 and
> 5PM each day. Tune into WWV and you could watch them bring your wall clock
> (hooked to AC power) into line with WWV. Indeed seconds / ten’s of seconds
> sort of corrections occurred. We suspected there must be a reason. One of
> the gang went on a tour of the power plant and asked them why? The answer
> turned out to be that they connected back up to the grid at 5 PM. Mid day,
> they generated the power locally. Just like us, they had a radio that
> listened to WWV.
>
> These days, if you are hooked to one of the grids, drifting seconds is
> pretty unusual. Everybody needs to stay “in phase” and that (since the
> late 1980’s) usually goes back to GPS (at least in the US and Canada). If
> you are “off grid” then I suspect you are right back to the 1960’s
> approach, at least in some cases.
>
> Do the corrections get logged? I suspect they do indeed get documented in
> some way. It could easily be a paper form sitting in an office somewhere.
> Find out the phone number for that office and you probably could get the
> after the fact info. There also does need to be a “how many microseconds of
> phase shift” sort of number. It would be specific to this or that source
> feeding the grid. Without that, you would have a very hard time controlling
> things. No idea how to get at that number or if it actually would be of any
> use.
>
> Bob
>
> > On Mar 21, 2024, at 6:13 AM, Hal Murray via time-nuts <
> time-nuts at lists.febo.com> wrote:
> >
> >
> > All sorts of gear uses the power line to drive their clock.
> >
> > I picture that a corner of the control room has 2 clocks, one tracking
> UTC and
> > the other tracking the power grid.  The difference between that pair
> feeds
> > into their complicated control system that includes some sort of PLL
> that
> > keeps the power line clock
> > tracking UTC.
> >
> > Is there any way to get a copy of their power line clock?  So I can set
> my
> > power line clocks to a similar offset so they will have a better chance
> of
> > being right tomorrow after they correct for today's offset?  I'm not
> looking
> > for microseconds, just microwave-setting accuracy.
> >
> > Do they have a graph showing the offset for the last week or month?  I
> can
> > line that up with my graphs.
> >
> >
> >
> > Here is a graph from Feb/Mar 2024 where it drifted a minute over 2 weeks.
> >  https://www.glypnod.com/TimeNuts/60Hz/60Hz-2024-FebMar.png
> > That's 4 seconds per day.
> >
> >
> > --
> > These are my opinions.  I hate spam.
> >
> >
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