My setup is pretty simple indeed. This is 9.830400MHZ OCXO which
clocking MCU. Then it is Zero-Cross detector which connected to capture
timer.
The MCU counting the intervals between of each zero-cross event and
number of events occurred.

 if (htim->Instance == TIM5 && htim->Channel == 

HAL_TIM_ACTIVE_CHANNEL_1) {
uwIC2Value2 = (HAL_TIM_ReadCapturedValue(htim, TIM_CHANNEL_1));
if (uwIC2Value2 >= prevtimer) {
uwDiffCapture = (uwIC2Value2 - prevtimer);
} else {
uwDiffCapture =((0xFFFFFFFF - prevtimer) + uwIC2Value2);
}

     prevtimer = uwIC2Value2;

     // MAIN Time calculation
     if(++uwCapT > 59) {                  // Every 60 cycles (60hz)
         if(++maintime.Seconds > 59) {
             maintime.Seconds = 0;
             if(++maintime.Minutes > 59) {
                 maintime.Minutes = 0;
                 if(++maintime.Hours > 23)
                     maintime.Hours = 0;
             }
         }
         uwCapT = 0;
    }

Once an hour the program prints its internal clock (MCU time), RTC time
and MAIN time

Uptime:      476 hours

RTC time:    13:00:00

MCU time:    13:00:00

MAIN time:    13:00:01

The graph shows the "delta" between of RTC and MAIN.

On 2017-12-15 12:14, Jeremy Nichols wrote:

--
WBW,

V.P.

Hi

It depends a lot on just where you are and how the “gird” is managed. Many years
ago, we figured out that the local power company corrected things between 4 and 5 PM.
It became a habit to fire up WWV and watch them slip seconds one way or the other. A
ten second delta was not at all unusual. ( as in 10 seconds over the hour …). Our
guess (later confirmed) was that they ran local generation part of the day (independent
of the grid) and then went over to interconnect.

Bob

Jeremy wrote:

When was the earliest time (year) you started looking seriously at the
offset/frequency of your grid?  (California is part of the [North
American] Western Interconnection.)

I have only closely observed the line frequency and offset when I have
been living within the Eastern Interconnection.  For years and years
between the 1960s and the 1980s, it was not unusual to observe offsets
of +/- 30 seconds, and +/- 60 seconds was not unheard of.  I believe the
policy has always been to provide 5.184e6 cycles per 24-hour day, so the

• and - offsets had to cancel over a specific 24 hour period.

I then didn't pay any attention to the mains frequency until the late
aughties, and I found that things have changed.  Now, I rarely see
offsets greater than +/- 4 to 6 seconds (very rarely, +/- 15 seconds) --
but it does not follow a gaussian distribution, to my (totally
anecdotal) observation.  It appears to me (again, completely
anecdotally) that it is more often within the lowest 25% or the highest
25% [combined] than it is the middle 50%, indicating a process that is
being controlled with a marginally stable loop.  (Of course, it is
being controlled -- with a massively distributed feedback system.  So no
surprise there.)

Best regards,

Charles

Yo All!

Jeremy wrote:

I live in Central Oregon.  Next to the Pacific Intertie and the Paccific
DC Intertie.  Near the Round Butte Dam, Pelton Dam, and other power
generating dams.

The Interties connect the massive hydropower generation of the Columbia
River system with southern California.

The hypropower system includes the best technology of the 1930's, 1940's
and 1950's.

I've had converstations with some of the dam operators about how
they keep frequency.  Pretty simple really.  Huge tonnages of spinning
steel and copper being pushed by falling water.  The water is regulated
by flapper valves.  Pretty stable short term.

Now imagine when a 300MVA intertie blows over, or is burned by a fire,
and instantly disconnects.  Or a steel mill shuts down for the day, or...

The electrical backpressure to the generators drops, so the generators
speed up, increasing the line frequency and voltage.

When this happens, the dam operators literally pick up the phone, and
talk to the other dams to decide what to do.  Usually that involves
one or more dams closing down a few flapper vavles.

That is how the short term frequency of your local power line is
controlled.

The control room also has a AC synchronous clock, off the power line,
and an accurate digital clock.  Once a day they manually get the
AC clock to agree with the digital clocl.

None of this is rocket science, don't use it for anything you need
any accuracy for.

RGDS
GARY

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
gem@rellim.com  Tel:+1 541 382 8588

    Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin