Frequency isn't regulated on a per-plant basis. The system operator will
monitor the grid frequency and lead or lag from an ideal 60 Hz cycle count.
They will schedule generation to be added or subtracted based on these
figures. Unless your plant is intended to run islanded on occasion, such
frequency regulation is unneeded.
Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
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.
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.
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.
I used to do such calibrations.
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.
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.
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
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.
Many digital clocks listen to WWV NIST radio stations to set the time. I
bought such a clock years ago and just a few years ago I bought an
inexpensive Sony clock radio that had the same feature. I'm not sure if
it got its time signal from WWV or there is something now being
broadcast by radio stations or if it picks it up from a cellphone tower.
There seem to be a lot of things sending out time signals. Heck, if I'm
remembering right, POTS line caller ID does it too.
Power outage causes it to display 88:88:88, and it's line locked, no
crystal. He said it started to be off by a few seconds a month,
starting a couple of years ago, and he suspects the power company.
On Sun, 26 Jun 2011 15:13:34 -0700 (PDT), "larry moe 'n curly"
I knew several *engineers* who had the government buy these things for them
under the GI bill. They were "studying to become TV repairmen". Right.
Displaying 88:88:88 makes more sense than 12:00:00. Some will then start
incrementing - *bad* design.
The power company is likely more accurate than a crystal. The cumulative
error over a long period (month) should be zero. The error could also be the
zero-crossing detector getting noisy. Often it'll get much worse.
I think a lot of them did it only to get free equipment or maybe a
monthly stipend. Actually I don't know if the GI Bill paid stipends
for courses by mail. One of my father's buddies mentioned ending up
with a bunch of Heathkits, including a big TV (big for the time), but
another friend went with a differnet company that furnished a line of
kits that weren't nearly as good. (something about the TV failing
every month, just after becoming very bright and smelling like tar).
My father didn't major in electronics or engineering but did manage to
design and build a digital clock from TTL chips. He hated its LED
display so much that he bought a second Heathkit clock.
On Thu, 30 Jun 2011 23:41:02 -0700 (PDT), "larry moe 'n curly"
Yep. That's why I said "Right.". They were IBM design engineers, not likely
to take up TV repair for a career but the "free" TV was worth their time. They
would sit around the office and "dry lab" the tests needed to get the next
part. There were a dozen of so of them, including my manager.
I think they did originally, then dropped that. Or it may have been means
I never liked digital clocks so never bothered making one.
On Sat, 25 Jun 2011 09:04:48 -0400, "Ed Pawlowski"
A digital clock is a counter. A plug-in clock counts the cycles of the
AC coming in. A battery clock uses a crystal oscillator.
A plug in clock with battery backup probably does NOT have a crystal,
but a cheap RC circuit. That's not very precise. Most seem to be fast
during power failures. If power fails from 6:00 to 7:00, the clock may
BTW, I once worked on a fancy clock that runs a chart recorder. It
used a PLL to convert the 60Hz to something higher (6.4KHZ IIRC),
which would then be divided down to 64Hz to drive a stepper motor.
This extra complexity had to do with being able to get the exact same
speeds while using 50Hz.
Four devices with digital clocks in my house regularly gain 10-20
seconds/week, even when there are no power outages: (1)2 year old DVR
(non-TIVO) connected to an antenna for input (no cable/satellite/FIOS)
that has only a 30 second memory in case of power failure (probably a
small capacitor), 3 year old microwave oven, (3) 10 year old
clock-radio, and (4) 15 year old VCR with a 1 hr. memory in case of
power failure. All 4 are on different circuit breakers. I've had our
power company check our line for noise, voltage, and/or frequency
abnormalities and they found none. 3 other digital clock radios,
varying in age from 1-15 years old, some on the same and some on
different house circuits keep essentially perfect time. I use timer
recording on the VCR and DVR regularly and if I don't reset their clocks
weekly, I can lose the end of programs I record unless I always add time
at the end. No one has ever proposed an explanation or a serious fix
for this situation.
Thanks for the suggestion Lloyd. However, with 4 digital clocks
behaving this way, I find it hard to believe that the clocks are at
fault. I suspect the power line is despite the power company's failure
to find problems here. Given that my power is provided by the infamous
PEPCO, I don't exactly have faith in their reassurances. This is the
same power company that caused me to waste $150 when I called them to
report an open neutral in their supply and they told me to hire an
electrician because they insisted that problem must be in my house.
(The electrician confirmed my diagnosis and when PEPCO repaired the
supply line, there wasn't a word of apology - or a refund/rebate of my
So what. Cumulative phase error on rhe grid was allowed to grow pretty
large. I think I remember a minute error or more. The total cycle count,
however was always corrected, often late at night.
Applications that required accurate frequency provided their own
standards. It was a big business for HP and others. Television used a
field rate of 60/sex. My entire remembrance of commercial TV has been
standards that provided their own synchroinzation that did not require
accurate timing from the grid.
Conservatives are against Darwinism but for natural selection.
To change the frequency they have to brake or accelerate the generator. What
I can't understand is which station is in charge of monitoring the frequency
and issuing commands to other power stations to speed up or slow down?
Frequency variation is not a big deal. When you have a power outage, the
voltage and hence frequency go to zero in a haphazard way. So if line
frequency variation would cause chaos, power outage should cause many times
But we have been living with the ocassional power outage, I think the minute
line frequency variation is not going to do any worse than power outage. In
fact it probably won't affect anyone at all.
This is one of those cases where statistics mask the issue.
When the power goes out, it's obvious. I go around the house fixing all
that are no longer accurate. Life returns to normal.
Not knowing whether the clock on the wall is correct is a much bigger
problem. How often do I have to get out the ladder to climb up and
reset the clock?
I'll bet there'll be lots of consequences.
The clock on my 40-year-old stove will be affected. And I ain't
I'll bet there are lots of legacy timepieces used in employee time clocks,
old buildings, etc.
The question is not, whether I'm able to find the correct time.
The question is, can I get accurate time from every time
indicator in view.
Knowing that most newer devices will not be affected is comforting
only to those who don't have legacy devices.
The 60 Hz has never been the "rock" you think it is. While its long
term accuracy is pretty good its short term accuracy isnt that great
and very rarely exactly 60hz. As a matter of fact my freq counter says
it is 60.07xxx Hz, the xxx means that these digits are constantly
chnging. Georgia Power used to give a tour of their Plant Hatch
facility and one of the topics mentioned was frequency accuracy. I
would like a couple of examples of any products that use the power
line frequency as a CRITICAL reference as I know of none.
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