Low cost synchronization
Hi,
I have a challenging research project to build thousands, perhaps
millions, of devices that maintain mutual synchronization. The
devices need to be low cost (under $20 retail, $8 manufacturing),
small in size (key chain fob), and low power (operate at least 18
months on a battery). Synchronization ideally needs to be within
a second or two over a year but there is some leeway to trade
cost for performance here up to perhaps 10 seconds of variation
per year. Ideally, the device works anywhere in the world but we
may have to limit it to North America.
- Crystal Modeling
First idea was to get stable 32.768KHz watch crystals, perform a
factory initial calibration, and use a temperature sensor to
correct for the crystal temp curve. This idea is the cheapest,
simplest, works everywhere, and uses the lowest power.
Initial tolerance on the crystals is +/- 20 ppm (I've not found
better in commodity parts), which equates to +/- 10 minutes a
year, clearly unacceptable. I suspect that if I did an initial
factory calibration and tracked temperature, I might improve this
to +/- 2 ppm much like Maxim did with this part:
http://pdfserv.maxim-ic.com/en/ds/DS32kHz.pdf
But even so, +/- 1 minute per year is not really good enough. I
suspect getting to a few seconds (+/- 0.1ppm) is unrealistic with
any algorithm one can come up with. The base physics is simply
not that predictable.
- WWVB Receiver
A second idea is to provide some external reference and the most
logical choice is WWVB as used in several wrist watches. A
little more cost but manageable. We've dissected several wrist
watches and found they use a small ferrite antenna. The
reception performance is spotty, however. I was unable to lock
at work (lots of equipment) but did well at home (electrically
quiet). If we go to the NE tip of Maine, that's twice as far
from WWVB as we are here, so I wonder if the watch will ever pick
up the signal. The saving grace is that the device needs to get
the signal only sporadically, once a week or even once a month
would do it since we can feed that back into correcting the local
crystal.
The negatives are that such a device is limited to the US and
nearby, and it may have poor performance in many locales due to
weak signals, local interference, and the small antenna rod we
are limited to due to size (less than 1 inch). It does cost
more, maybe $1-2 more in production quantity. Right now, this
seems like the best option available to us.
There are similar time broadcasting stations in Europe and China.
We could build a unit that works in those regions, either as
different models, or as a unit with multiple receivers. Still
not global, but perhaps covering 50% of the world's population?
- GPS Receiver
A more precise external reference, use a GPS receiver. This gets
us global coverage and is very precise. Uses a lot of power, so
we would only activate it very briefly and not very often (once a
week perhaps) to save battery.
Major issue here is cost. Best I can do for an OEM module is
around $25 in qty which busts the budget severely. It also has
similar problems of being used in a place with no sky visibility.
Size can be a problem in the cheaper modules. Some modules are
quite small:
http://www.u-blox.com/products/lea_la.html
Cute, huh?
- GPS Time Receiver
This is fantasy land. I don't need the 100ns time reference, all
I need is something good to one second or so. In this case, it
seems possible to receive only 1 satellite, decode the digital
data, and extract the time. It would be off by the variation in
pseudo range which can't be corrected for. But I don't care
about that level of accuracy.
The question is, if you don't have to track multiple satellites
and don't need to recover the pseudo range accurately, can you
build a wickedly cheaper GPS time receiver? My expectation is no.
You probably can get down to maybe half if you are very diligent,
which still puts me out of the budget plus has a ridiculous high
NRE. Unless this already exists, anyone?
- Cellular
We've done extensive work with embedded cell phone modules.
These modules are most often used for wireless remote monitoring
and transport digital data. They do get the time from the cell
system.
Again, cost is a major issue. An OEM cell module runs over $65
in qty so this idea is sunk. It would also suffer from lack of
global and local coverage.
- TV Stations
TV stations broadcast a time signal that VCRs/DVRs use for clock
setting.
Again, lack of global or even regional coverage. Some TV
stations, annoyingly, broadcast the wrong time, too. Cost is
probably high, but this idea was rejected before this was
investigated.
- Atomic Reference
Still research, but NIST has a small scale atomic reference:
http://www.nist.gov/public_affairs/releases/miniclock.htm
Unfortunately, not ready for commercial apps, probably will be
too expensive, and it uses too much power. The best I could do
on power is to power it up periodically and adjust the local
crystal to it which integrates long term error.
- Other?
So, did I leave anything out?
It seems obvious to me that no amount of effort to make a local
crystal stable will meet the requirements. Thus we need to look
for external references. The best we can do is WWVB as it is the
only thing that can possibly meet our cost objectives. If it
works in the continental US, that would be acceptable for now.
That leaves me with two basic questions:
-
How well do the WWVB wrist watches work?
-
What merchant silicon exists for receiving WWVB?
On the first, the three watches we bought do sync up here (950
miles from WWVB). I wonder how well they work in Maine and
Florida (1900 miles from WWVB).
On the second, I've only found these leads so far:
http://www.mas-oy.com/archive/da9180.pdf
http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf
These chips appear to be basic receiver circuits using an
external 60KHz crystal as a filter. At 60KHz, I was wondering
why there aren't direct digital radios? It would seem like
building in the DSP logic would be cheaper/better than the old
fashioned methods shown here and could greatly enhance the
ability to pick out weak WWVB signals. Has anyone performed such
experiments, basically digitize the antenna signal and done DSP
on it?
Thanks for all who read this far!
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Mike - I've spent a fair amount of time looking in to this as part of
my Internet testbed. At the moment, I have about 25 nodes using
EndRun's CDMA time receivers ($1k-ish each), so I've been very
interested in cheaper solutions, for obvious reasons.
I assume that the devices of which you're speaking are standalone
items? Something like a sensor deployment, possibly networked?
Knowing more about how you actually plan on using these would help a
bit. For example, if they're networked within particular regions,
that gives you an easy way to synch to within milliseconds.
WWVB: Are you going to be deploying inside buildings? Buildings
with electronics and UPSes? If so, be very careful.
Most cheap WWVB watches and clocks don't work very well on the east
coast, from my experience. I poked around at a few in my old lab in
Boston, and they were a no-go.
Your analysis of GPS seems correct. You can probably build a $50 GPS
time receiver to synch to milliseconds, but not much cheaper. On the
other hand, as the 911 location requirements for cell phones expand,
this may change. But not yet.
Atomic reference: I'd say no chance in the next 5+ years.
Local stable crystal: Actually, you could make it more than stable
enough, but it would exceed your power requirements, because you'd
probably fall back to an oven controlled oscillator. There goes your
battery. But why did you try your initial experiments with 32.768Khz
watch crystals? You're much more likely to find a good, solid 10Mhz
reference with an SC cut TCXO. For instance, that maxim IC you
mentioned has +- 2ppm, which is really quite awful by instrumentation
standards. Compare to this one:
http://www.bdelectronic.com/frequency/oscillatorTCXO.html
.3ppm tempco, +- 1ppm/year. They don't show their overall allen
deviation curves, but you get the idea - it'll be within 1ppm by the
end of the year, and since that aging will probably happen over time,
I'd guess it would probably get you something like 10 seconds within
a year. Or something like:
http://www.vectron.com/products/tcxo/tc140.pdf
(... which is probably expensive, but which you can get in 0.2 ppm
accuracy vs. temperature and <2ppm/10 years).
Another option you may have just eliminated on principle: Internet
synchronization. Very easy to keep synched to within a few hundred
ms. (Internet can also be replaced by ACTS telephone, or your
favorite other technology). Very limited in where you can deploy if
you want outdoor deployment.
WWVB and its kin may well be your best bet, if you can hear them
enough places.
-Dave
On Aug 18, 2005, at 1:29 PM, Mike Ciholas wrote:
Hi,
I have a challenging research project to build thousands, perhaps
millions, of devices that maintain mutual synchronization. The
devices need to be low cost (under $20 retail, $8 manufacturing),
small in size (key chain fob), and low power (operate at least 18
months on a battery). Synchronization ideally needs to be within
a second or two over a year but there is some leeway to trade
cost for performance here up to perhaps 10 seconds of variation
per year. Ideally, the device works anywhere in the world but we
may have to limit it to North America.
- Crystal Modeling
First idea was to get stable 32.768KHz watch crystals, perform a
factory initial calibration, and use a temperature sensor to
correct for the crystal temp curve. This idea is the cheapest,
simplest, works everywhere, and uses the lowest power.
Initial tolerance on the crystals is +/- 20 ppm (I've not found
better in commodity parts), which equates to +/- 10 minutes a
year, clearly unacceptable. I suspect that if I did an initial
factory calibration and tracked temperature, I might improve this
to +/- 2 ppm much like Maxim did with this part:
http://pdfserv.maxim-ic.com/en/ds/DS32kHz.pdf
But even so, +/- 1 minute per year is not really good enough. I
suspect getting to a few seconds (+/- 0.1ppm) is unrealistic with
any algorithm one can come up with. The base physics is simply
not that predictable.
- WWVB Receiver
A second idea is to provide some external reference and the most
logical choice is WWVB as used in several wrist watches. A
little more cost but manageable. We've dissected several wrist
watches and found they use a small ferrite antenna. The
reception performance is spotty, however. I was unable to lock
at work (lots of equipment) but did well at home (electrically
quiet). If we go to the NE tip of Maine, that's twice as far
from WWVB as we are here, so I wonder if the watch will ever pick
up the signal. The saving grace is that the device needs to get
the signal only sporadically, once a week or even once a month
would do it since we can feed that back into correcting the local
crystal.
The negatives are that such a device is limited to the US and
nearby, and it may have poor performance in many locales due to
weak signals, local interference, and the small antenna rod we
are limited to due to size (less than 1 inch). It does cost
more, maybe $1-2 more in production quantity. Right now, this
seems like the best option available to us.
There are similar time broadcasting stations in Europe and China.
We could build a unit that works in those regions, either as
different models, or as a unit with multiple receivers. Still
not global, but perhaps covering 50% of the world's population?
- GPS Receiver
A more precise external reference, use a GPS receiver. This gets
us global coverage and is very precise. Uses a lot of power, so
we would only activate it very briefly and not very often (once a
week perhaps) to save battery.
Major issue here is cost. Best I can do for an OEM module is
around $25 in qty which busts the budget severely. It also has
similar problems of being used in a place with no sky visibility.
Size can be a problem in the cheaper modules. Some modules are
quite small:
http://www.u-blox.com/products/lea_la.html
Cute, huh?
- GPS Time Receiver
This is fantasy land. I don't need the 100ns time reference, all
I need is something good to one second or so. In this case, it
seems possible to receive only 1 satellite, decode the digital
data, and extract the time. It would be off by the variation in
pseudo range which can't be corrected for. But I don't care
about that level of accuracy.
The question is, if you don't have to track multiple satellites
and don't need to recover the pseudo range accurately, can you
build a wickedly cheaper GPS time receiver? My expectation is no.
You probably can get down to maybe half if you are very diligent,
which still puts me out of the budget plus has a ridiculous high
NRE. Unless this already exists, anyone?
- Cellular
We've done extensive work with embedded cell phone modules.
These modules are most often used for wireless remote monitoring
and transport digital data. They do get the time from the cell
system.
Again, cost is a major issue. An OEM cell module runs over $65
in qty so this idea is sunk. It would also suffer from lack of
global and local coverage.
- TV Stations
TV stations broadcast a time signal that VCRs/DVRs use for clock
setting.
Again, lack of global or even regional coverage. Some TV
stations, annoyingly, broadcast the wrong time, too. Cost is
probably high, but this idea was rejected before this was
investigated.
- Atomic Reference
Still research, but NIST has a small scale atomic reference:
http://www.nist.gov/public_affairs/releases/miniclock.htm
Unfortunately, not ready for commercial apps, probably will be
too expensive, and it uses too much power. The best I could do
on power is to power it up periodically and adjust the local
crystal to it which integrates long term error.
- Other?
So, did I leave anything out?
It seems obvious to me that no amount of effort to make a local
crystal stable will meet the requirements. Thus we need to look
for external references. The best we can do is WWVB as it is the
only thing that can possibly meet our cost objectives. If it
works in the continental US, that would be acceptable for now.
That leaves me with two basic questions:
-
How well do the WWVB wrist watches work?
-
What merchant silicon exists for receiving WWVB?
On the first, the three watches we bought do sync up here (950
miles from WWVB). I wonder how well they work in Maine and
Florida (1900 miles from WWVB).
On the second, I've only found these leads so far:
http://www.mas-oy.com/archive/da9180.pdf
http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf
These chips appear to be basic receiver circuits using an
external 60KHz crystal as a filter. At 60KHz, I was wondering
why there aren't direct digital radios? It would seem like
building in the DSP logic would be cheaper/better than the old
fashioned methods shown here and could greatly enhance the
ability to pick out weak WWVB signals. Has anyone performed such
experiments, basically digitize the antenna signal and done DSP
on it?
Thanks for all who read this far!
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
David Andersen wrote:
Local stable crystal: Actually, you could make it more than stable
enough, but it would exceed your power requirements, because you'd
probably fall back to an oven controlled oscillator. There goes your
battery. But why did you try your initial experiments with 32.768Khz
watch crystals? You're much more likely to find a good, solid 10Mhz
reference with an SC cut TCXO. For instance, that maxim IC you
mentioned has +- 2ppm, which is really quite awful by instrumentation
standards. Compare to this one:
http://www.bdelectronic.com/frequency/oscillatorTCXO.html
.3ppm tempco, +- 1ppm/year. They don't show their overall allen
deviation curves, but you get the idea - it'll be within 1ppm by the
end of the year, and since that aging will probably happen over time,
I'd guess it would probably get you something like 10 seconds within a
year. Or something like:
http://www.vectron.com/products/tcxo/tc140.pdf
(... which is probably expensive, but which you can get in 0.2 ppm
accuracy vs. temperature and <2ppm/10 years).
-Dave
Dave,
The requirement that you seem to have missed is the 18 month battery
lifetime. A 10 MHz oscillator is a couple milliapmeres, so it won't do
the trick. The watch crystal needs only about 10 microamperes to
oscillate.
Mike,
The 32K crystal may be usable, but you'd have to put some effort into
the design to get the temp compensation tuned to the particular
crystal, and you'd have to grade the crystals for tempco in the mfg
stage. That might be doable in quantity, if you come up with the right
sort of computerized test fixture in an oven.
I have built a few nixie tube wristwatches using the cheap 32KHz
crystals, so I have direct experience in this matter. (Has anyone else
on this list built an electronic wristwatch?) Getting the crystal
adjusted to 1ppm is not too hard. You'd have to temperature compensate
it to get to 0.1 ppm, and that would be limited to perhaps 10C-30C
temperature range.
It's a lot easier to compensate the crystal if it's worn on the wrist
rather than sitting in a car, since a person's wrist is essentially an
oven. The real world has ridiculous temperature extremes - don't even
think about stabilizing a crystal used outdoors unless it's thermally
connected to a human.
You should be able to evaluate the feasibility of using a compensated
crystal based on the above.
A couple of points here.
Yes, a 10MHz oscillator will severely blast the budget - power wise. But
you should remember that 10MHz is also not actually a good frequency for
temperature coefficient of crystals - except for SOME SC cut types.
Generally speaking the zero tempco rollover frequency for many SC's and
most AT's is between 4.5 and 5.5MHz. You can actually get very good
tempco's by running two oscillators either 500kHz or 1MHz apart and mixing
them. Mounted in a thermal mass but without an oven they will oven give
better than TCXO and moderate oven type performance.
Real time temperature compensation is actually quite common. In several
radio applications I have designed systems using two techniques.
1.. Have the manufacturer supply AT crystals with carefully controlled cut
angles - for a given cut angle the tempco will not vary much. Then use a
simple compensation table based on angle.
2.. Learn the crystal characteristics. In a couple of chamber runs measure
the characteristics of each crystal. You probably only need to do 20
temperatures to cover -10 to +60C. Work out the slope and using some nice
interpolation algorithm work out a correction table. Then voltage control
the Xtal osc to keep the frequency on target.
#2 works well enough that a pretty standard crystal will deliver TCXO or
better performance because very few TCXO's use active compensation.
But really, can we fit all of this ins key fob? Nope! I suspect in the best
research tradition the OP needs to look at WHY his application demands
synchronization at this sort of level. In one project where my client
initially asked for timing accuracy of this order, we found that we could
collect data with timestamps and temperatures, and when we looked at the
logger and the data we could measure the offset for a particular logger and
then back correct the timestamps on the data. In that case we used a
correction system like #1 above, but we had something like 150x50x10mm to
work in, not a key fob!
John
At 02:18 PM 8/18/2005, you wrote:
David Andersen wrote:
Local stable crystal: Actually, you could make it more than stable
enough, but it would exceed your power requirements, because you'd
probably fall back to an oven controlled oscillator. There goes your
battery. But why did you try your initial experiments with 32.768Khz
watch crystals? You're much more likely to find a good, solid 10Mhz
reference with an SC cut TCXO. For instance, that maxim IC you
mentioned has +- 2ppm, which is really quite awful by instrumentation
standards. Compare to this one:
http://www.bdelectronic.com/frequency/oscillatorTCXO.html
.3ppm tempco, +- 1ppm/year. They don't show their overall allen
deviation curves, but you get the idea - it'll be within 1ppm by the
end of the year, and since that aging will probably happen over time,
I'd guess it would probably get you something like 10 seconds within a
year. Or something like:
http://www.vectron.com/products/tcxo/tc140.pdf
(... which is probably expensive, but which you can get in 0.2 ppm
accuracy vs. temperature and <2ppm/10 years).
-Dave
Dave,
The requirement that you seem to have missed is the 18 month battery
lifetime. A 10 MHz oscillator is a couple milliapmeres, so it won't do the
trick. The watch crystal needs only about 10 microamperes to oscillate.
Mike,
The 32K crystal may be usable, but you'd have to put some effort into the
design to get the temp compensation tuned to the particular crystal, and
you'd have to grade the crystals for tempco in the mfg stage. That might
be doable in quantity, if you come up with the right sort of computerized
test fixture in an oven.
I have built a few nixie tube wristwatches using the cheap 32KHz crystals,
so I have direct experience in this matter. (Has anyone else on this list
built an electronic wristwatch?) Getting the crystal adjusted to 1ppm is
not too hard. You'd have to temperature compensate it to get to 0.1 ppm,
and that would be limited to perhaps 10C-30C temperature range.
It's a lot easier to compensate the crystal if it's worn on the wrist
rather than sitting in a car, since a person's wrist is essentially an
oven. The real world has ridiculous temperature extremes - don't even
think about stabilizing a crystal used outdoors unless it's thermally
connected to a human.
You should be able to evaluate the feasibility of using a compensated
crystal based on the above.
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
On Thu, 18 Aug 2005, David Andersen wrote:
I assume that the devices of which you're speaking are
standalone items? Something like a sensor deployment, possibly
networked? Knowing more about how you actually plan on using
these would help a bit.
Yes, it would. The devices are part of a social experiment and
are meant to be carried by humans. The devices, at preprogrammed
times, signal the human with an audio signal. We want all the
devices to create this signal "simultaneously", which means
something on the order of a few seconds variation among all the
units anywhere in the world. There is no network, no display, no
user interface, zip. A key fob would be ideal and low cost is
critical.
Most cheap WWVB watches and clocks don't work very well on the
east coast, from my experience. I poked around at a few in my
old lab in Boston, and they were a no-go.
Yes, this is my worry. Switching power supplies in the
vicinity seem to be the determining factor in how well these
systems work.
Local stable crystal: Actually, you could make it more than
stable enough, but it would exceed your power requirements,
because you'd probably fall back to an oven controlled
oscillator. There goes your battery.
It is important to note that we don't need an accurate time
reference, we need s stable one. That means we're happy to
correct, in software, a crystal that is running 10ppm slow if
it holds that error throughout it's life. We can build
adjustments into the software, so no need to pull, tweak, or PLL
to some arbitrary frequency.
But why did you try your initial experiments with 32.768Khz
watch crystals?
Power. A CR1620 battery is 75mAH and a CR2032 is 225 mAH. For
18 months, this is 6uA or 17uA average current draw. The only
thing that can meet that is a low KHz crystal.
You're much more likely to find a good, solid 10Mhz reference
with an SC cut TCXO. For instance, that maxim IC you mentioned
has +- 2ppm, which is really quite awful by instrumentation
standards. Compare to this one:
http://www.bdelectronic.com/frequency/oscillatorTCXO.html
.3ppm tempco, +- 1ppm/year.
One idea is to keep the TCXO off most of the time, turn it on and
let it stabilize, then compare it to the low power crystal. Make
an adjustment based on that. But, I suspect the constant on/off
will affect the TCXO poorly, and you miss most of the low power
crystal variations (temperature, shock, etc). So this doesn't
seem possible. I'd also guess these TCXOs are >$10 in qty.
Lastly, +/- 1ppm is +/- 30 seconds per year which is still not
really good enough.
Another option you may have just eliminated on principle:
Internet synchronization.
Technically, this works really well. The concept we had for this
was a USB key fob. Plug it in to an Internet connected computer
and capture the time. The device could also have a super cap on
board for power, charge it from the USB slot, and you don't need
a battery. I was thinking this would be an ideal concept with all
sorts of flexibility. The sync operation would not need to be
done too often, perhaps once every 90 days, so limited access is
okay as long as it occurs often enough.
However, there are issues. Namely that the USB device would need
software on the computer to make the connection and that the
experiment wants to be as accessible to people as possible, even
those which have no access to a computer.
A possible compromise was suggested: build a GPS time module with
USB ports on it that serves the role of the time provider. This
would replace or augment the PC. This complicated the experiment
as well but provided a way for unconnected or distant people to
sync up. It would only work well if people using the device are
"grouped" which may not be compatible with the experiment's
goals.
WWVB and its kin may well be your best bet, if you can hear
them enough places.
Yes, so far that is the leading candidate. Maybe if we all
chipped in a $0.01 each ($3M total), they can get the power up to
1MW? That would probably get world wide coverage (and cook
nearby hot dogs... :-).
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Are the subjects all within major metro areas? I wonder if the TV stations
are sending usable time codes in their blanking intervals these days.
-- john, KE5FX
On Thu, 18 Aug 2005, David Forbes wrote:
The 32K crystal may be usable, but you'd have to put some
effort into the design to get the temp compensation tuned to
the particular crystal, and you'd have to grade the crystals
for tempco in the mfg stage. That might be doable in quantity,
if you come up with the right sort of computerized test fixture
in an oven.
All of the temp compensation can be in software and "after the
fact". I don't need the crystal "tweaked", I just need to know
what numerical corrections I need to apply to the counter. Thus
it becomes zero electronics (besides some temp sensor) and only
software.
I have built a few nixie tube wristwatches using the cheap
32KHz crystals, so I have direct experience in this matter.
(Has anyone else on this list built an electronic wristwatch?)
Getting the crystal adjusted to 1ppm is not too hard. You'd
have to temperature compensate it to get to 0.1 ppm, and that
would be limited to perhaps 10C-30C temperature range.
You give me more hope than I had previously. I understand how to
capture the initial tolerance (operate the device at the factory
and record the variation in internal memory). I know how to
correct the temperature curve (the parabolic deviation away from
25C). But I am left with aging as a concern. Most of these
crystals claim aging to be +/- 3ppm the first year. That's +/-
1.5 minutes for a year which is unacceptable. Maybe crystals
from one batch all age the same, maybe they age based on
shock/vibration (which will vary from unit to unit). I just
don't know.
Here is an example datasheet:
It's a lot easier to compensate the crystal if it's worn on the
wrist rather than sitting in a car, since a person's wrist is
essentially an oven. The real world has ridiculous temperature
extremes - don't even think about stabilizing a crystal used
outdoors unless it's thermally connected to a human.
Just like someone who leaves their watch in the car on a sunny
day, I can't be sure the device will be in a temperature stable
environment. The best I can do is try to model the temperature
effect and correct for it. Hence the temp curve in the
datasheet. Tracking it to within +/- 0.1ppm seems tough.
You should be able to evaluate the feasibility of using a
compensated crystal based on the above.
Yes, I think it is going to be possible to achieve +/- 1.0ppm. I
think +/- 0.5ppm can be done with some hard work. I don't think
+/- 0.1ppm (+/- 3 seconds/year) is realistic.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Mike Ciholas wrote:
Hi,
I have a challenging research project to build thousands, perhaps
millions, of devices that maintain mutual synchronization. The
devices need to be low cost (under $20 retail, $8 manufacturing),
small in size (key chain fob), and low power (operate at least 18
months on a battery). Synchronization ideally needs to be within
a second or two over a year but there is some leeway to trade
cost for performance here up to perhaps 10 seconds of variation
per year. Ideally, the device works anywhere in the world but we
may have to limit it to North America.
- Crystal Modeling
Phase lock the crystal to the 50/60 Hz powerline? The signal seems
to be ubiquitous.
-Chuck
On Thu, 18 Aug 2005, John Day wrote:
You can actually get very good tempco's by running two
oscillators either 500kHz or 1MHz apart and mixing them.
Mounted in a thermal mass but without an oven they will oven
give better than TCXO and moderate oven type performance.
Curious idea. I guess the assumption is that the two crystals
experience the same environment and that has the same effect on
them.
I wonder if you did the same thing with two 32.768KHz crystals?
You would learn their initial calibration at the factory, then
track the time so that the difference is maintained. I'd have to
sit down and do the math to see if this makes sense as this would
be only a few ppm typically. The assumption here is that the two
crystals, being of the same type in the same environment, would
age and change at the same rate. An experiment can be performed
to check this.
Quick example: One crystal is 1ppm faster than the other. Then
the two counters will "slip" 1 count every 30.5 seconds. You
count the "slips" to record time, the slips per unit time being
measured at the factory. My intuition says there is something
mathematically wrong here, the slip rate probably won't be stable
to <1ppm.
I guess this would generalize to more than 2 crystals. We could
put a dozen in there and average the results to reduce the error.
Seems like it would reach diminishing returns fairly quickly,
though.
Random question: Any good books on the finer details of crystals?
I'm looking for something that goes into all the gory details of
how they vary, age, drift, etc.
Real time temperature compensation is actually quite common. In
several radio applications I have designed systems using two
techniques.
1.. Have the manufacturer supply AT crystals with carefully
controlled cut angles - for a given cut angle the tempco will
not vary much. Then use a simple compensation table based on
angle.
2.. Learn the crystal characteristics. In a couple of chamber
runs measure the characteristics of each crystal. You probably
only need to do 20 temperatures to cover -10 to +60C. Work out
the slope and using some nice interpolation algorithm work out
a correction table. Then voltage control the Xtal osc to keep
the frequency on target.
I can get a start from the chart in the datasheet on the crystal:
http://www.ecsxtal.com/pdf/ecs-3x8.pdf
I don't actually need to adjust the crystal itself, all I need to
do is accumulate the error mathematically and "fix" the answer
past the counter output. So no need for additional circuits.
#2 works well enough that a pretty standard crystal will
deliver TCXO or better performance because very few TCXO's use
active compensation.
Are we well under +/- 1ppm? If we can get down to +/- 0.1 or 0.2
ppm, I think that would do it, but 1ppm isn't enough.
But really, can we fit all of this ins key fob? Nope!
I was thinking a tiny microcontroller, a small watch crystal, and
a thermistor would easily fit into a key fob. The question is
whether the embedded algorithm in the device can be good enough
to keep it on time.
Still, the WWVB approach seems like the best bet so far but the
crystal only approach would be so nice.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Thu, 18 Aug 2005, John Miles wrote:
Are the subjects all within major metro areas? I wonder if the
TV stations are sending usable time codes in their blanking
intervals these days.
No, not limited to metro areas. TV receiver probably just as
costly and power hungry as GPS.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Mike:
The 1 Hz difference leads to the problems of 'is it +1 or -1; Or at zero,
there is no output to count.
With the 1 MHz referrec to in John's email, you can run a reliable counter.
Does anyone in the group have expertise in "forced aging" of crystals. In
the 'good old days' before precision trimmed parts, we commonly 'aged'
parts with temperature cycles and voltage cycles to get past all the first
year variations. This gave long term stability as well as sorting out all
the early life failures of parts. Would take care of the 'first year
drift' variable.
Tom Buehl
At 04:13 PM 8/18/2005, you wrote:
On Thu, 18 Aug 2005, John Day wrote:
You can actually get very good tempco's by running two
oscillators either 500kHz or 1MHz apart and mixing them.
Mounted in a thermal mass but without an oven they will oven
give better than TCXO and moderate oven type performance.
Curious idea. I guess the assumption is that the two crystals
experience the same environment and that has the same effect on
them.
I wonder if you did the same thing with two 32.768KHz crystals?
You would learn their initial calibration at the factory, then
track the time so that the difference is maintained. I'd have to
sit down and do the math to see if this makes sense as this would
be only a few ppm typically. The assumption here is that the two
crystals, being of the same type in the same environment, would
age and change at the same rate. An experiment can be performed
to check this.
Quick example: One crystal is 1ppm faster than the other. Then
the two counters will "slip" 1 count every 30.5 seconds. You
count the "slips" to record time, the slips per unit time being
measured at the factory. My intuition says there is something
mathematically wrong here, the slip rate probably won't be stable
to <1ppm.
I guess this would generalize to more than 2 crystals. We could
put a dozen in there and average the results to reduce the error.
Seems like it would reach diminishing returns fairly quickly,
though.
Random question: Any good books on the finer details of crystals?
I'm looking for something that goes into all the gory details of
how they vary, age, drift, etc.
Real time temperature compensation is actually quite common. In
several radio applications I have designed systems using two
techniques.
1.. Have the manufacturer supply AT crystals with carefully
controlled cut angles - for a given cut angle the tempco will
not vary much. Then use a simple compensation table based on
angle.
2.. Learn the crystal characteristics. In a couple of chamber
runs measure the characteristics of each crystal. You probably
only need to do 20 temperatures to cover -10 to +60C. Work out
the slope and using some nice interpolation algorithm work out
a correction table. Then voltage control the Xtal osc to keep
the frequency on target.
I can get a start from the chart in the datasheet on the crystal:
http://www.ecsxtal.com/pdf/ecs-3x8.pdf
I don't actually need to adjust the crystal itself, all I need to
do is accumulate the error mathematically and "fix" the answer
past the counter output. So no need for additional circuits.
#2 works well enough that a pretty standard crystal will
deliver TCXO or better performance because very few TCXO's use
active compensation.
Are we well under +/- 1ppm? If we can get down to +/- 0.1 or 0.2
ppm, I think that would do it, but 1ppm isn't enough.
But really, can we fit all of this ins key fob? Nope!
I was thinking a tiny microcontroller, a small watch crystal, and
a thermistor would easily fit into a key fob. The question is
whether the embedded algorithm in the device can be good enough
to keep it on time.
Still, the WWVB approach seems like the best bet so far but the
crystal only approach would be so nice.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
On Thu, 18 Aug 2005, Chuck Harris wrote:
Phase lock the crystal to the 50/60 Hz powerline? The signal
seems to be ubiquitous.
I considered that. There are many problems:
The person with the device may move from one place to another and
may pick up anyone of three possible phases of power or different
utilities (they are sync'ed?). In this case, it may become hard
to constantly watch your phase and adjust. At best, you can make
short temporal measurements based on stable signals and use that
to look at you local crystal.
But, on short time scales, the 60Hz wave has poor stability. It
is controlled well on longer time scales (witness all the clocks
using it), but we can't assure a stable environment to measure
that against.
60Hz is also very low frequency. I wasn't sure I could pick it
up reliably despite all my experience getting it when I don't
want it!
Worth thinking about, though (says the man with a 250KV three
phase trunk outside his building...)
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Thu, 18 Aug 2005, buehl wrote:
The 1 Hz difference leads to the problems of 'is it +1 or -1;
I can deal with this with a digital counter. You will always
know if A is ahead of B or not.
Or at zero, there is no output to count.
Yes, this is a problem. Perhaps it is better to make sure the
crystals are different, like 32KHz and 38KHz. But still, is the
difference between them stable to 0.1ppm? I'm skeptical
(otherwise everyone would do it this way), but I'd be happy for
it to be so!
Does anyone in the group have expertise in "forced aging" of
crystals. In the 'good old days' before precision trimmed
parts, we commonly 'aged' parts with temperature cycles and
voltage cycles to get past all the first year variations.
This gave long term stability as well as sorting out all the
early life failures of parts. Would take care of the 'first
year drift' variable.
If it is a simple bake, that we can do. But if it more complex
than that, the manufacturing cost might exceed other solutions.
I was thinking we would build the PCB (which goes through a
reflow heat cycle), then bake the end result at 100C or something
for an hour. But this was just speculation on my part that it
would help with long term aging.
I guess I would find out in a year... :-(
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Phase lock the crystal to the 50/60 Hz powerline? The signal seems
to be ubiquitous.
Tom Van Baak wrote:
Phase lock the crystal to the 50/60 Hz powerline? The signal seems
to be ubiquitous.
Tom,
I'm not sure if it is true, but I understand in the UK there are
50243600=4,320,000 cycles of the mains between midnight and midnight.
So whilst a clock set right at 2pm in the afternoon might not be right
at 2pm tommorow, one set correct at midnight will always be right at
midnight.
That was my understanding, but it might be an urban myth, with no basis
at all.
Given that there are very few electric clocks around now in the UK, I
doubt keeping exactly 4,320,000 cycles between midnight and midnight is
that important to the electricity companies now.
I wish they could keep the voltage a bit more stable though - I have
measured as low as 183V here, when its supposed to be 230V. Some houses
near a friend of mine managed to get 415V instead of 240V (as it was
then), when some idiot repaired a cable but managed to hook up two
phases rather than a phase and neutral. Quite a few TV's and videos did
not like 415V too much!
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
In message Pine.LNX.4.63.0508181135520.24373@piano.ciholas.com, Mike Ciholas writes:
- WWVB Receiver
This is probably the most feasible means.
There are receiver chips for all the VLF stations: WWVB, DCF,
MSF and the one in Japan, and they use next to no power.
The company used to be called "Temic", not sure if they
are still called that.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
----- Original Message -----
From: "Mike Ciholas" mikec@ciholas.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Friday, August 19, 2005 7:34 AM
Subject: Re: [time-nuts] Low cost synchronization
Yes, it would. The devices are part of a social experiment and
are meant to be carried by humans. The devices, at preprogrammed
times, signal the human with an audio signal. We want all the
devices to create this signal "simultaneously", which means
something on the order of a few seconds variation among all the
units anywhere in the world.
Mike
While a fascinating engineering challenge, I fail to see the need for
such accurate timing, given the typically wide ranging timeframe for
human response to similar signals -eg cell phones ringing, etc.
Or is it enough for the user to merely be aware of the audible prompt?
Is it possible to elaborate?
Regards
Dave Brown, NZ
--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.10.12/77 - Release Date: 18/08/2005
Yes, it would. The devices are part of a social experiment and
are meant to be carried by humans.
Speaking of social experiments.
I thought I had a reasonable idea as to what a GPS 1PPS is used for -
until I read this:
http://home.connection.com/~louis/globalchimes/proposal.htm
Regards, Kiwi Geoff.
http://www.geocities.com/kiwi_36_nz/kiwi_osd/kiwi_osd.htm
On Fri, 19 Aug 2005, Geoff wrote:
Speaking of social experiments.
I thought I had a reasonable idea as to what a GPS 1PPS is used
for - until I read this:
Interesting. This isn't our application, but it shares many of
the same traits.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Fri, 19 Aug 2005, Dave Brown wrote:
While a fascinating engineering challenge, I fail to see the
need for such accurate timing, given the typically wide ranging
timeframe for human response to similar signals -eg cell phones
ringing, etc. Or is it enough for the user to merely be aware
of the audible prompt? Is it possible to elaborate?
I can't go into details but suffice it to say that the
requirements are driven by the parameters of the experiment and
not from a technical requirement flow down.
Imagine passing out thousands of little devices, all them beep at
predetermined times within some tolerance (a few seconds give or
take).
The precision comes not from the human response time so much, as
to what happens when the devices come back together again. It
will be real obvious to people when they all go off at different
times. The "man with two clocks" problem. We even thought of a
low power peer to peer radio to synchronize any units in the same
area to avoid this "oops", but that doesn't help for things like a
phone call.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Fri, 19 Aug 2005, Poul-Henning Kamp wrote:
- WWVB Receiver
This is probably the most feasible means.
Yes, I concur for at least the US. A 60KHz will get us US,
something in England, and Japan (decoding software needs to be
different, but not the radio parts). Maybe that's good enough.
The company used to be called "Temic", not sure if they are
still called that.
I've found two:
http://www.mas-oy.com/archive/da9180.pdf
This looks like the winning solution. Here is the TEMIC:
http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf
This seems to not be as well supported.
If anybody knows any more, please let me know.
I have disassembled several WWVB watches. Of course, they are
all COB (chip on board), but just from the chip dimensions, I
know the chips they use (and the WWVB part seems to be separate
from the watch logic otherwise) aren't either one of the above.
Strange. Must be a high volume bare die house somewhere that is
doing this.
Our concept might well benefit from COB due to our volumes
(>10,000, perhaps millions).
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
From: Mike Ciholas mikec@ciholas.com
Subject: [time-nuts] Low cost synchronization
Date: Thu, 18 Aug 2005 12:29:40 -0500 (CDT)
Message-ID: Pine.LNX.4.63.0508181135520.24373@piano.ciholas.com
Hi Mike,
- GPS Time Receiver
This is fantasy land. I don't need the 100ns time reference, all
I need is something good to one second or so. In this case, it
seems possible to receive only 1 satellite, decode the digital
data, and extract the time. It would be off by the variation in
pseudo range which can't be corrected for. But I don't care
about that level of accuracy.
The question is, if you don't have to track multiple satellites
and don't need to recover the pseudo range accurately, can you
build a wickedly cheaper GPS time receiver? My expectation is no.
You probably can get down to maybe half if you are very diligent,
which still puts me out of the budget plus has a ridiculous high
NRE. Unless this already exists, anyone?
I have some VHDL code lying around... but no, I think it will effectively be hard to beat
the integration level of modern receivers. The E911 work as well as wish for small
portable receivers has forced integration to go further. On principle of doing a single-
receiver GPS that will work. The first line of analogue receivers where 1-channel
receivers multiplexing between satelites. Checkout the GPS chips again.
- Cellular
We've done extensive work with embedded cell phone modules.
These modules are most often used for wireless remote monitoring
and transport digital data. They do get the time from the cell
system.
Again, cost is a major issue. An OEM cell module runs over $65
in qty so this idea is sunk. It would also suffer from lack of
global and local coverage.
It is a shifting buissness and in longterm you may be toast.
- TV Stations
TV stations broadcast a time signal that VCRs/DVRs use for clock
setting.
Again, lack of global or even regional coverage. Some TV
stations, annoyingly, broadcast the wrong time, too. Cost is
probably high, but this idea was rejected before this was
investigated.
Also, the analogue signal is hitting the deck as ATSC and DVB enters. Sad but true.
However, if you listen to ATSC or DVB pilot-tones ;O)
- Atomic Reference
Still research, but NIST has a small scale atomic reference:
http://www.nist.gov/public_affairs/releases/miniclock.htm
Unfortunately, not ready for commercial apps, probably will be
too expensive, and it uses too much power. The best I could do
on power is to power it up periodically and adjust the local
crystal to it which integrates long term error.
Small physics package does not say anything about the electronics package ;O)
Cheers,
Magnus
So, does it have to handle leap seconds?
On Thu, 18 Aug 2005, Bill Hawkins wrote:
So, does it have to handle leap seconds?
Hmnm, interesting question. Obviously if we track WWVB, it can.
The important part is that the units stay synchronized. So if
all of them miss the leap second, that is okay. This would be
the case if we had only an internal reference. Absolute accuracy
is not an issue.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Mike,
If you're interested in LF chip-level products, you
might want to try:
http://www.c-maxgroup.com/home/index.php
The U4223B looks like the Temic. It was a bit difficult
to get samples from them here in the US, but I've used
both the U4223B and CME8000 with reasonable results.
Some of their product line is now available from Digikey.
Joe Landers
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Mike Ciholas
Sent: Thursday, August 18, 2005 10:30 AM
To: time-nuts@febo.com
Subject: [time-nuts] Low cost synchronization
On the second, I've only found these leads so far:
http://www.mas-oy.com/archive/da9180.pdf
http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf
These chips appear to be basic receiver circuits using an
external 60KHz crystal as a filter.
In message 000201c5a490$b4826ee0$9c8aa8c0@games, "Joe Landers" writes:
Mike,
If you're interested in LF chip-level products, you
might want to try:
You can buy finished receiver modules here:
http://www.hkw-elektronik.de/
Here are a bunch of receiver modules:
http://www.hkw-elektronik.de/produkte/Baugruppen___Sub_-_assembly/baugruppen___sub_-_assembly.html
This is appearantly a multi-frequency capable gadget:
http://www.hkw-elektronik.de/pdf/UE6010-DE%20V1.4.pdf
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
On Fri, 19 Aug 2005, Joe Landers wrote:
If you're interested in LF chip-level products, you might want
to try:
Thanks! This is very helpful.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
Hi Mike,
Sorry for the late reply. You raise an interesting
question and here are some thoughts.
- Crystal Modeling
Standard 32 kHz crystals won't work. TCXO aren't
good enough either. OCXO are too power hungry.
A couple of quartz wrist watches are good to 5 or
10 seconds per year. This may be close enough
for your needs. The Pulsar PRS10 is one example.
I think they use dual mode crystals to achieve their
exceptional accuracy and relative temperature
insensitivity. With the quantities you are talking
about a dual mode crystal may fit the requirement.
Dual-mode crystals are a niche market, however,
so making arrangements with a manufacturer will
not be simple.
- WWVB Receiver
These are exceedingly cheap now and should fit
all your requirements. Contact Rod Mack who has
probably done more WWVB R&D than anyone on
the list (he did the Ultralink receivers using Temic
chips). Email me offline for his contact info.
WWVB reception quality is not an issue since
it's only used to intermittently re-synchronize the
internal XO. One decent reception every couple
of days or even weeks will take care of your
requirements.
Note also that many WWVB chipsets are now
"global", meaning they will also receive signals
from LF time services in Europe and Japan
- GPS Receiver
- GPS Time Receiver
As many cell phones now include GPS receivers
sizes and prices are dropping. But I'm guessing
you are not going to meet your fob-size nor power
specs with GPS (or other satellite nav systems).
- Cellular
What percent of your thousands to millions of
users world-wide already have a cell phone? To
me this is the obvious solution. I would guess
all cell phones know the time to a millisecond
internally and this means a billion people on the
planet are already carrying just what you need.
Battery life is not a problem because all users
already know how to recharge theirs.
Now if each brand of cell phone would just have
a standardized 1PPS output connector you'd be
all set.
- TV Stations
Two methods come to mind. The XDS timecode
(used by PBS stations) is good in principle but
perhaps not in practice. The other approach is
to discipline a 32 kHz XO against the 3.58 MHz
colorburst frequency. This seems dated, though.
- Atomic Reference
In 10 years maybe.
- Other?
-
Look into an interface with Sirius/XM satellite radio.
-
Or piggy-back on the existing paging networks.
-
Lock onto the carrier of a high-power local AM
or FM station. If these stations use Rb or GPSDO
referenced carriers you'll get a long-term stable
frequency for free.
3b) For extra credit use DSP. Since AM/FM radio
and TV frequencies have assigned slots world-wide
you can simultaneously receive many local stations
and combine their frequency stabilities to a common
mean time/frequency. This would make a wonderful
project for someone; commercial or university.
For any solutions that give you stable frequency
only (XO, RF carriers, 60 Hz) you will need a way
to set the initial time and to reset the time when
the batteries fail.
For any solutions that give you time only you will
presumably need to convert from UTC to local
time. Also, are you concerned with DST?
At least with your requirements, you don't have
to worry about leap seconds!
From: "Tom Van Baak" tvb@leapsecond.com
Subject: Re: [time-nuts] Low cost synchronization
Date: Sat, 20 Aug 2005 11:59:45 -0700
Message-ID: 00a701c5a5b9$55fe7740$470ff204@computer
Tom,
- WWVB Receiver
These are exceedingly cheap now and should fit
all your requirements. Contact Rod Mack who has
probably done more WWVB R&D than anyone on
the list (he did the Ultralink receivers using Temic
chips). Email me offline for his contact info.
WWVB reception quality is not an issue since
it's only used to intermittently re-synchronize the
internal XO. One decent reception every couple
of days or even weeks will take care of your
requirements.
Note also that many WWVB chipsets are now
"global", meaning they will also receive signals
from LF time services in Europe and Japan
This is indeed a solution that should be looked at.
- GPS Receiver
- GPS Time Receiver
As many cell phones now include GPS receivers
sizes and prices are dropping. But I'm guessing
you are not going to meet your fob-size nor power
specs with GPS (or other satellite nav systems).
Just as with WWVB receivers, he does not have to have the GPS powered up very long for and
then only once a week or so to keep the oscillator tuned up. Once a GPS solution has been
found, the local time and the GPS solution time give a time-difference and by remembering
the GPS solution time from the last time you have the /|t you need to calculate the
frequency error. So, a GPS solution could be possible.
BTW, recall that it is mostly US cell phones that has the GPS in them for the moment.
The big markets does not have them (yeat). Never the less, small GPS solutions is around
and affordable.
- Cellular
What percent of your thousands to millions of
users world-wide already have a cell phone? To
me this is the obvious solution. I would guess
all cell phones know the time to a millisecond
internally and this means a billion people on the
planet are already carrying just what you need.
Battery life is not a problem because all users
already know how to recharge theirs.
Now if each brand of cell phone would just have
a standardized 1PPS output connector you'd be
all set.
Depending on which standard you have, the phones only may have a sense of "real" time.
In GSM for instance, the phones traces network time only in a relative aspect, but there
is no real way to get an accurate UTC. The phones is being synchronised to the base
stations such that the transmitted slot from the phone fits right into the timeslot at the
base-station, which is done by having the base station continously sending advance time
corrections which could be used backwards to know the time from the base-station. However,
this is only relative timing from the base station, but the base station is not even
guaranteed to be synchronised to UTC or even a PRC. Infact, some GSM vendors is proud of
this fact since synchronisation is such a hassle in their eyes. Sigh! Also, this
correction is only available as when you are transmitting.
Then, getting the time from the cellular network may not be as easy as you think either.
The operator of the network may choose to turn on the optional time announcement and last
time I checked this was not universally done.
Yes, these networks could potentially be capable of giving good time, but I think the
real life prooves a bit more disappointing than at least I first thought. It all depends
on which cellular standard and maybe also details about how a certain operator is actually
using the technology.
I would not look at cellular technology for a global solution since there is so many
standards in operation right now and will continue to be. Also, there is a shift towards
3G which is slowly progressing.
- TV Stations
Two methods come to mind. The XDS timecode
(used by PBS stations) is good in principle but
perhaps not in practice. The other approach is
to discipline a 32 kHz XO against the 3.58 MHz
colorburst frequency. This seems dated, though.
Ah well, that will become toughter as the analogue TV stations is being shut down. DVB
and ASTC is taking over. There is a goal to have the signals traceable to TAI/UTC and work
is undergoing, such as the SMPTE EPOCH and other work.
For any solutions that give you stable frequency
only (XO, RF carriers, 60 Hz) you will need a way
to set the initial time and to reset the time when
the batteries fail.
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be
a bad idea to depend on it.
For any solutions that give you time only you will
presumably need to convert from UTC to local
time. Also, are you concerned with DST?
At least with your requirements, you don't have
to worry about leap seconds!
Leave that to us others! ;O)
Cheers,
Magnus
Just as with WWVB receivers, he does not have to have the GPS powered up
very long for and
then only once a week or so to keep the oscillator tuned up. Once a GPS
solution has been
found, the local time and the GPS solution time give a time-difference and
by remembering
the GPS solution time from the last time you have the /|t you need to
calculate the
frequency error. So, a GPS solution could be possible.
I'm curious what the power requirements are.
My Casio WWVB wrist watch works on one
battery for two years while my Casio GPS
wristwatch is lucky to run for more than a
two days, even when in intermittent mode.
Depending on which standard you have, the phones only may have a sense of
"real" time.
In GSM for instance, the phones traces network time only in a relative
aspect, but there
is no real way to get an accurate UTC. The phones is being synchronised to
the base
This sounds odd to me given that cell phones
I've seen can display the date & time and they
appear to be accurate to a second.
All we need are some counter-examples. Does
anyone on this list have a cell phone that displays
the time of day with an error greater than a few
seconds? (if yours has a HH:MM-only display
compare the instant when MM changes). If so,
then Mike can scratch cell phones from his list
of accurate time sources.
By the way, Mike, have you considered if your
battery-operated, fob-sized, world-wide, low-cost,
synchronization device will be allowed through US
airports?
/tvb
Now that cell phones are raised, it is possible to use a
two step process to synchronize a world-wide "Ommm" or to
focus hatred on a particular person. (That last is from an
old SF story about criminals being executed in an arena by
public hating. In practice, it doesn't work any better than
any other form of mental power except hypnotism.) You see,
speculation can run wild when there is no data. Perhaps
this is a means to coordinate an attack.
Assuming that everyone involved has access to a clock and a
telephone, it is possible to call a number minutes before an
event. The synchronization is from a tone on the telephone.
Telcos have numbers that many people can call to handle local
events. Negotiations could be made with telcos to set up the
synchronization number. The cost would be spread over many
individuals. Perhaps network broadcasts could be persuaded
to broadcast a beep (or pips) at the right time.
OTOH, if the problem is to establish a world-wide heart beat
at a certain frequency, then point synchronization is not
the answer.
Regards,
Bill Hawkins
Hoping this scheme is mostly harmless, as the Guide puts it.
On Sat, 20 Aug 2005, Tom Van Baak wrote:
- Crystal Modeling
Standard 32 kHz crystals won't work. TCXO aren't good enough
either. OCXO are too power hungry.
Yup.
A couple of quartz wrist watches are good to 5 or 10 seconds
per year. This may be close enough for your needs.
Yes, that would be very tempting, especially the 5 seconds
number. If we could do that, we'd probably go for it and live
with the error.
The Pulsar PRS10 is one example.
I found web reports of them being off 15-20 seconds per year, so
the claims might not be valid for this watch. I fear the same
issue with us, great research effort to develop a stable timing
reference in the lab, but it fails to deliver in the field.
There are just so many variables.
I think they use dual mode crystals to achieve their
exceptional accuracy and relative temperature insensitivity.
With the quantities you are talking about a dual mode crystal
may fit the requirement.
Dual-mode crystals are a niche market, however, so making
arrangements with a manufacturer will not be simple.
Time to expose my ignorance, what is a dual mode crystal? Can
you give me pointers to the manufacturers? If they would work,
we can invest the time to make the arrangements.
- WWVB Receiver
WWVB reception quality is not an issue since it's only used to
intermittently re-synchronize the internal XO. One decent
reception every couple of days or even weeks will take care of
your requirements.
Even once a quarter would be good enough in most cases. Once you
learn how your local XO is doing, you can apply that in the
future.
Note also that many WWVB chipsets are now "global", meaning
they will also receive signals from LF time services in Europe
and Japan
Ideally, the device would work anywhere, but WWVB (US 60 KHz),
JJY (Japan 40 and 60 KHz), DCF (Germany 77.5 KHz), MSF (UK 60
KHz) only cover so much of the world. We're still missing sub
equatorial Africa, western Asia, South America, Australia,
Hawaii, and Alaska. Still, we can probably cover 80% of the
world's population with what we can get. There are a few
"global" VLF time receiver chips, notably those from C-max and
MAS. They get three frequencies, usually chosen to be 40, 60,
and 77.5 KHz.
Due to the key fob size, we can't have a very large ferrite rod
antenna so our sensitivity will be poor. It's not even clear we
can get eastern US reliably.
One wonders if you can build some sort of long term reception
processing that would pick out the signal from the noise. Since
you know what you should be getting, you can overlay multiple
minutes of reception to cancel out the noise. I wonder how much
processing that will take. Would it be possible to recover
enough signal fro the noise to make VLF receivable worldwide?
- GPS Receiver
- GPS Time Receiver
As many cell phones now include GPS receivers sizes and prices
are dropping. But I'm guessing you are not going to meet your
fob-size nor power specs with GPS (or other satellite nav
systems).
Actually, size and power are not the limiting factor. Consider
this module:
http://www.u-blox.com/products/lea_la.html
Size wise, this will fit (we have one for another project, pretty
awesome, about a postage stamp in lateral footprint). Power
wise, using it once a week for one minute would use 43 mAH, or
about 20% of a CR2032 coin cell (our preferred power source).
We could get by with a solid time hit every two months. I don't
care about the 1 pps output, just the NMEA date message.
The real killer is cost. This module is probably $30 in qty ($70
in qty 1). Maybe, if we are very lucky, we could source
something similar for $15 in very high volume. The WWVB style
receiver is probably under $2. The concept is fairly price
sensitive so we have to be under $5 total manufacturing cost.
Now if only I could "duty cycle" the cost, then the GPS would
cost me less than $0.01. :-)
- Cellular
Now if each brand of cell phone would just have a standardized
1PPS output connector you'd be all set.
We've done a lot of work on embedded cellular. It's a mess
building something that works everywhere or with everything. Do
cell phones even know UTC or do they just know "local" time? It
is important that a device in central time go off at the same UTC
time as one in eastern time, not at the same numeric local time.
- Other?
- Look into an interface with Sirius/XM satellite radio.
Hmmm. I'll research that. One imagines the chipset cost is on
par with GPS, however, and may not have had the commodity
development attached to it yet.
- Or piggy-back on the existing paging networks.
Too spotty, too much testing. Pagers are a dying service as cell
phones take their business.
- Lock onto the carrier of a high-power local AM or FM
station. If these stations use Rb or GPSDO referenced
carriers you'll get a long-term stable frequency for free.
Only if I track it all the time. And I bet not all have stable
carriers. This is the cost of the WWVB receiver at best (and
probably worse since it has to tune instead of being fixed) and
the transmission produces no numeric encoding. I'd have to run
it much longer and more often than WWVB.
For any solutions that give you stable frequency only (XO, RF
carriers, 60 Hz) you will need a way to set the initial time
and to reset the time when the batteries fail.
Initial time can be set at factory. Batteries are never customer
removed so there should never be a need to reset it. When
battery is dead, device is dead.
For any solutions that give you time only you will presumably
need to convert from UTC to local time. Also, are you concerned
with DST?
No, all timing we do will be UTC and local time is irrelevant.
At least with your requirements, you don't have to worry about
leap seconds!
Yes. All that matters is that the devices go off at the same
time (+/- a few seconds). If they all are a minute late relative
to the desired time, that's okay. But I don't think that helps
much.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Sat, 20 Aug 2005, Tom Van Baak wrote:
This sounds odd to me given that cell phones I've seen can
display the date & time and they appear to be accurate to a
second.
In my experience, cell phones are accurate to within a second as
compared to the WWVB sources. That is more than we need.
By the way, Mike, have you considered if your battery-operated,
fob-sized, world-wide, low-cost, synchronization device will be
allowed through US airports?
What sort of problems would you expect? It should be no
different than a WWVB wrist watch since that basically the same
internals without the display. It will look like a harmless
inert key fob, much like RFID key fobs used for keyless entry.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
At 4:07 PM -0500 8/20/05, Mike Ciholas wrote:
One wonders if you can build some sort of long term reception
processing that would pick out the signal from the noise. Since
you know what you should be getting, you can overlay multiple
minutes of reception to cancel out the noise. I wonder how much
processing that will take. Would it be possible to recover
enough signal fro the noise to make VLF receivable worldwide?
Mike,
This is what I do for a living - integrating radio signals over long
time periods to get a signal from what looks like pure noise.
The basic formula is that the S/N increases by the square root of the
integration time, as long as the sample phase remains correct. This
is the limiting factor - the PPM of the fob's timebase determines
this and will be another watch crystal which is good to maybe 1PPM.
There are two ways to proceed: One is to try to actually learn the
time of day form WWVB, and the other is to just keep your local clock
synchronized to the one second pulses from WWVB.
The standard time signals such as WWVB use a one-bit-per-second
coding scheme where the signal is amplitude modulated, so you'd need
to measure the phase of this modulation to perhaps 5% of a cycle, or
0.05 seconds. Your 1PPM oscillator will be off by .05 seconds in
50,000 seconds or 14 hours. So you could integrate data for 14 hours.
That should give you sqrt(50,000) improved S/N, or 200 times better
S/N ratio (23dB).
If you just want to maintain your oscillator's 1PPS phase against
WWVB, then you just need to do a pulsar synchronization technique of
splitting a second into perhaps 20 bins and accumulating the signal
strength during each bin. You are looking for the rising edge of the
carrier which indicates the top of the second. That is, a bin with
very little signal followed by one with lots of signal is when the
pulse starts.
If you want to learn the time, then the next problem is that you're
integrating data which is changing, so you have to deal with that by
some fancy integration tricks such as using separate bins for 1 and 0
level bits.
I hope this makes some sense. If not, then read up on pulsar
detection and timing techniques.
--David Forbes, Tucson, AZ
http://www.cathodecorner.com/
Mike Ciholas mikec@ciholas.com writes:
On Sat, 20 Aug 2005, Tom Van Baak wrote:
This sounds odd to me given that cell phones I've seen can
display the date & time and they appear to be accurate to a
second.
In my experience, cell phones are accurate to within a second as
compared to the WWVB sources. That is more than we need.
CDMA phones (mostly US-ONLY) seems to have good timing
information. The FDMA system GSM (rest of the world except Japan) IIRC
does not use absolute time in the base station and has no time service
to the terminals (phones).
--
Björn
On Sat, 20 Aug 2005, Bill Hawkins wrote:
Perhaps this is a means to coordinate an attack.
Ah, the age of paranoia. Rest assured, the experiment's purpose
is as far from that as possible.
If you look at my requirements (accurate to a few seconds, lasts
more than a year, low cost, built in thousands), I don't think
that is consistent with enabling any evil purposes that you could
not have done more easily some other way that already exists.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
From: "Tom Van Baak" tvb@leapsecond.com
Subject: Re: [time-nuts] Low cost synchronization
Date: Sat, 20 Aug 2005 13:35:05 -0700
Message-ID: 001701c5a5c6$a68ea100$8633f304@computer
Tom,
Just as with WWVB receivers, he does not have to have the GPS powered up
very long for and
then only once a week or so to keep the oscillator tuned up. Once a GPS
solution has been
found, the local time and the GPS solution time give a time-difference and
by remembering
the GPS solution time from the last time you have the /|t you need to
calculate the
frequency error. So, a GPS solution could be possible.
I'm curious what the power requirements are.
My Casio WWVB wrist watch works on one
battery for two years while my Casio GPS
wristwatch is lucky to run for more than a
two days, even when in intermittent mode.
It all depends on what you aim for. If you really wish to, you can run an
ordinary 32k oscillator, have a GPS receiver turned on for say 15 min every
week or so. With the GPS constellation in memory and the local time to within
a few seconds it should be possible to keep the hot-time of the GPS receiver
down to a minimum. Doing linear or exponential backoff on failure to grab
signal should make the failure handling less power-insensitive.
Depending on which standard you have, the phones only may have a sense of
"real" time.
In GSM for instance, the phones traces network time only in a relative
aspect, but there
is no real way to get an accurate UTC. The phones is being synchronised to
the base
This sounds odd to me given that cell phones
I've seen can display the date & time and they
appear to be accurate to a second.
As I said, this all depends on the particular technology (there is a so many
that I don't recall them all) and in some cases how the operator have chosen to
operate their network. All I am saying is that it may not be as simple and
straightforward as one first may think. When time synchronisation is there,
the relative effects are more important than absolute time. This is true for
CDMA too, infact it is imperative or else the network fails miserably as I have
understood it. In GSM it fails more gracefully, so much infact that
synchronising base stations is not always done.
All we need are some counter-examples. Does
anyone on this list have a cell phone that displays
the time of day with an error greater than a few
seconds? (if yours has a HH:MM-only display
compare the instant when MM changes). If so,
then Mike can scratch cell phones from his list
of accurate time sources.
I have. My GSM phone is not updated over the GSM network, since my particular
operator have chosen not to transmitt the necessary signals. The reason I know
all this is since I wondered why I could not have the service, and I was
enlightend on this particular issue. Remember, if you are a time-nut, you do
expect things to be synchronised just to learn that people doesn't care as much
as you do. On the other hand, I can correct time of my GSM phone when I feel it
is out of time. I usually only care about hours and rought minutes.
So, I think this option should be taken out of the list since it may not be
universally applicable.
By the way, Mike, have you considered if your
battery-operated, fob-sized, world-wide, low-cost,
synchronization device will be allowed through US
airports?
What the hitch?
Cheers,
Magnus
Hi Mike:
It may not be possible to get what you are asking for as a stand alone
time keeper but I think could be done by periodically resetting.
Using a radio signal for resetting has problems with the coverage area
and/or power consumption.
Maybe the resetting signal could be an audio time code optimized for
this application. The user could call an 800 phone number and a
microphone in the device would hear the code and reset. Or at a public
meeting the audio code could be put on the P.A. system so all present
would be synchronized.
If the microphone can hear the beeper of another unit there might be a
way to use a button on a unit to cause it to send it's audio time sync
signal so other nearby units would sync to it.
The device could learn it's aging rate at each reset and so change the
divisor number to match the current aging rate.
After sync the device might emit beeps or Morse code telling the user
how far off it was allowing the user to gauge how often they need to resync.
A TCXO should work for this.
Have Fun,
Brooke Clarke, N6GCE
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com
Mike Ciholas wrote:
Hi,
I have a challenging research project to build thousands, perhaps
millions, of devices that maintain mutual synchronization. The
devices need to be low cost (under $20 retail, $8 manufacturing),
small in size (key chain fob), and low power (operate at least 18
months on a battery). Synchronization ideally needs to be within
a second or two over a year but there is some leeway to trade
cost for performance here up to perhaps 10 seconds of variation
per year. Ideally, the device works anywhere in the world but we
may have to limit it to North America.
- Crystal Modeling
First idea was to get stable 32.768KHz watch crystals, perform a
factory initial calibration, and use a temperature sensor to
correct for the crystal temp curve. This idea is the cheapest,
simplest, works everywhere, and uses the lowest power.
Initial tolerance on the crystals is +/- 20 ppm (I've not found
better in commodity parts), which equates to +/- 10 minutes a
year, clearly unacceptable. I suspect that if I did an initial
factory calibration and tracked temperature, I might improve this
to +/- 2 ppm much like Maxim did with this part:
http://pdfserv.maxim-ic.com/en/ds/DS32kHz.pdf
But even so, +/- 1 minute per year is not really good enough. I
suspect getting to a few seconds (+/- 0.1ppm) is unrealistic with
any algorithm one can come up with. The base physics is simply
not that predictable.
- WWVB Receiver
A second idea is to provide some external reference and the most
logical choice is WWVB as used in several wrist watches. A
little more cost but manageable. We've dissected several wrist
watches and found they use a small ferrite antenna. The
reception performance is spotty, however. I was unable to lock
at work (lots of equipment) but did well at home (electrically
quiet). If we go to the NE tip of Maine, that's twice as far
from WWVB as we are here, so I wonder if the watch will ever pick
up the signal. The saving grace is that the device needs to get
the signal only sporadically, once a week or even once a month
would do it since we can feed that back into correcting the local
crystal.
The negatives are that such a device is limited to the US and
nearby, and it may have poor performance in many locales due to
weak signals, local interference, and the small antenna rod we
are limited to due to size (less than 1 inch). It does cost
more, maybe $1-2 more in production quantity. Right now, this
seems like the best option available to us.
There are similar time broadcasting stations in Europe and China.
We could build a unit that works in those regions, either as
different models, or as a unit with multiple receivers. Still
not global, but perhaps covering 50% of the world's population?
- GPS Receiver
A more precise external reference, use a GPS receiver. This gets
us global coverage and is very precise. Uses a lot of power, so
we would only activate it very briefly and not very often (once a
week perhaps) to save battery.
Major issue here is cost. Best I can do for an OEM module is
around $25 in qty which busts the budget severely. It also has
similar problems of being used in a place with no sky visibility.
Size can be a problem in the cheaper modules. Some modules are
quite small:
http://www.u-blox.com/products/lea_la.html
Cute, huh?
- GPS Time Receiver
This is fantasy land. I don't need the 100ns time reference, all
I need is something good to one second or so. In this case, it
seems possible to receive only 1 satellite, decode the digital
data, and extract the time. It would be off by the variation in
pseudo range which can't be corrected for. But I don't care
about that level of accuracy.
The question is, if you don't have to track multiple satellites
and don't need to recover the pseudo range accurately, can you
build a wickedly cheaper GPS time receiver? My expectation is no.
You probably can get down to maybe half if you are very diligent,
which still puts me out of the budget plus has a ridiculous high
NRE. Unless this already exists, anyone?
- Cellular
We've done extensive work with embedded cell phone modules.
These modules are most often used for wireless remote monitoring
and transport digital data. They do get the time from the cell
system.
Again, cost is a major issue. An OEM cell module runs over $65
in qty so this idea is sunk. It would also suffer from lack of
global and local coverage.
- TV Stations
TV stations broadcast a time signal that VCRs/DVRs use for clock
setting.
Again, lack of global or even regional coverage. Some TV
stations, annoyingly, broadcast the wrong time, too. Cost is
probably high, but this idea was rejected before this was
investigated.
- Atomic Reference
Still research, but NIST has a small scale atomic reference:
http://www.nist.gov/public_affairs/releases/miniclock.htm
Unfortunately, not ready for commercial apps, probably will be
too expensive, and it uses too much power. The best I could do
on power is to power it up periodically and adjust the local
crystal to it which integrates long term error.
- Other?
So, did I leave anything out?
It seems obvious to me that no amount of effort to make a local
crystal stable will meet the requirements. Thus we need to look
for external references. The best we can do is WWVB as it is the
only thing that can possibly meet our cost objectives. If it
works in the continental US, that would be acceptable for now.
That leaves me with two basic questions:
-
How well do the WWVB wrist watches work?
-
What merchant silicon exists for receiving WWVB?
On the first, the three watches we bought do sync up here (950
miles from WWVB). I wonder how well they work in Maine and
Florida (1900 miles from WWVB).
On the second, I've only found these leads so far:
http://www.mas-oy.com/archive/da9180.pdf
http://www.ortodoxism.ro/datasheets/Temic/mXyzuryv.pdf
These chips appear to be basic receiver circuits using an
external 60KHz crystal as a filter. At 60KHz, I was wondering
why there aren't direct digital radios? It would seem like
building in the DSP logic would be cheaper/better than the old
fashioned methods shown here and could greatly enhance the
ability to pick out weak WWVB signals. Has anyone performed such
experiments, basically digitize the antenna signal and done DSP
on it?
Thanks for all who read this far!
On Sat, 20 Aug 2005, David Forbes wrote:
At 4:07 PM -0500 8/20/05, Mike Ciholas wrote:
One wonders if you can build some sort of long term reception
processing that would pick out the signal from the noise.
There are two ways to proceed: One is to try to actually learn
the time of day form WWVB, and the other is to just keep your
local clock synchronized to the one second pulses from WWVB.
I can't stay sync'ed to WWVB. I don't have the power to run the
receiver all the time, and you loose the signal during the day in
many places. So we're into trying to get the signal during some
period of time.
The standard time signals such as WWVB use a one-bit-per-second
coding scheme where the signal is amplitude modulated, so you'd
need to measure the phase of this modulation to perhaps 5% of a
cycle, or 0.05 seconds. Your 1PPM oscillator will be off by .05
seconds in 50,000 seconds or 14 hours. So you could integrate
data for 14 hours. That should give you sqrt(50,000) improved
S/N, or 200 times better S/N ratio (23dB).
A >20dB improvement is huge! You might almost be able to get
some station anywhere on the globe. Of course, we might start to
get mutual interference between WWVB, MSF, and JJY when we are
between those two stations. Maybe a single receiver on DCF 77.5
KHz is better?
If you want to learn the time, then the next problem is that
you're integrating data which is changing, so you have to deal
with that by some fancy integration tricks such as using
separate bins for 1 and 0 level bits.
Yes, this will be necessary. Not really that bad if you expect
to be within, say, 4 minutes. You don't need to bin all the
minute bits and then you can apply a moving window on the binary
pattern to find the best "match".
I hope this makes some sense. If not, then read up on pulsar
detection and timing techniques. --
This was helpful. Thanks.
--
Mike Ciholas (812) 476-2721 x101
CIHOLAS Enterprises (812) 476-2881 fax
255 S. Garvin St, Suite B mikec@ciholas.com
Evansville, IN 47713 http://www.ciholas.com
On Sat, 20 Aug 2005, Bill Hawkins wrote:
Perhaps this is a means to coordinate an attack.
And Mike Ciholas replied,
"Ah, the age of paranoia. Rest assured, the experiment's purpose
is as far from that as possible."
Well, no, not so much the age of paranoia as the age of extreme
self-interest and no empathy for others. This leads to too many
liars with public exposure, followed by erosion of trust. When a
salesman says "Trust me ..." these days, it is best to walk away.
Trust is the basis for civilization. It is sad to see it replaced
by paranoid behavior as people learn not to trust other people.
Mike, I've no reason to believe that you are lying, but you have
withheld information. OTOH, if you did tell us the reason for
these ticking key fobs, how would that differ from an email from
someone who's money is trapped in Africa unless I help out? I mean,
besides the fact that you aren't asking for money, although you
could profit. Then too, your client could have misrepresented
their purpose.
I apologize if my creative mind has caused you any distress. It
has caused me some distress as I try to work out what the fobs
are for. Given the size of your market and the high probability
of some religious or New Age significance, I'll never know until
I see them for sale, if they go public.
Regards,
Bill Hawkins
Magnus Danielson wrote:
For any solutions that give you stable frequency
only (XO, RF carriers, 60 Hz) you will need a way
to set the initial time and to reset the time when
the batteries fail.
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be
a bad idea to depend on it.
I keep hearing, on this group, that the powerline is no longer sync'd to utc, and evidence for
that fact being a lack of motorized wall clocks. Well, clocks that sync to the powerline are in
universal abundance in the US. Virtually every clock on kitchen appliances is sync'd this way.
The clocks on VCR's may be reset from time to time by a tv station, but the timing signal is
still the powerline. Basically, any appliance, or device that plugs into the powerline is likely to
use the powerline for its timing function.
-chuck
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h
basis, so it may be
a bad idea to depend on it.
I keep hearing, on this group, that the powerline is no longer sync'd to
utc, and evidence for
that fact being a lack of motorized wall clocks. Well, clocks that sync
to the powerline are in
universal abundance in the US. Virtually every clock on kitchen
appliances is sync'd this way.
The clocks on VCR's may be reset from time to time by a tv station, but
the timing signal is
still the powerline. Basically, any appliance, or device that plugs into
the powerline is likely to
use the powerline for its timing function.
-chuck
Correct, my measurements clearly show that
mains power is steered to UTC. See:
http://www.leapsecond.com/pages/mains/
If there's anyone from the power industry on the
list I'd be interested to hear first-person technical
details of how phase is synchronized, both short-
and long-term.
But I'm not sure I agree with your claim about
kitchen appliances. It seems to me almost every
kitchen, electronic, wall-clock, and entertainment
appliance being sold these days uses quartz-based
clocks, regardless if they are mains, wall-wart, or
battery powered. I'm not sure how to confirm the
accuracy of this hunch, though.
I suspect there are several factors in the trend
away from mains-clocks to quartz-clocks:
-
Digital or analog quartz movements are dirt
cheap (so it's a cost saving measure). -
If the product is intended for sale in Japan
(where both 50 Hz and 60 Hz mains co-exist). -
If the product is intended for sale world-wide
(there is a healthy mix of 50 vs. 60 Hz and 120
vs. 240 V across the planet). -
The explosion in the use of switching power
supplies in home electronics (which are immune
to local voltage / frequency conventions). -
The explosion in the use of microprocessor
based control of appliances (where the CPU(s)
are driven by an n MHz XO and date/time/display
functions are managed in firmware).
/tvb
Tom Van Baak wrote:
still the powerline. Basically, any appliance, or device that plugs into
the powerline is likely to
use the powerline for its timing function.
-chuck
Correct, my measurements clearly show that
mains power is steered to UTC. See:
http://www.leapsecond.com/pages/mains/
If there's anyone from the power industry on the
list I'd be interested to hear first-person technical
details of how phase is synchronized, both short-
and long-term.
But I'm not sure I agree with your claim about
kitchen appliances. It seems to me almost every
kitchen, electronic, wall-clock, and entertainment
appliance being sold these days uses quartz-based
clocks, regardless if they are mains, wall-wart, or
battery powered. I'm not sure how to confirm the
accuracy of this hunch, though.
I am just relating my experience with having mucked about
in the insides of these appliances. Some are quartz,
but those are generally the sort that have an alarm clock
feature (coffee makers) Any that blink up at 12:00, or,
lose time while the power is off are most certainly AC
derived.
My most recent exposure to an appliance clock is in a
high end electric "double oven" made by DCS. It uses
a powerline derived clock on its controller board. The DCS
uses the same controller board as do the GE, Dacor, Kenmore,
and numerous other ovens. The ovens are of current manufacture.
You can be almost 100% certain that all domestic ovens
will use line derived clocks. It would take one heck of a
crystal to remain accurate when exposed to the temperature
variations that exist around such a device's controller board.
-Chuck
FWIW, this is a plot of the 53rd harmonic of the 50 Hz of the mains at
my house, measured not more than half a hour ago. Nominally it should be
50 x 53 = 2650 Hz, but it ain't...
http://sundry.i2phd.com/mains.html
73 Alberto I2PHD
Let's see, your graph shows for that small time interval that the frequency
is within 0.05% of being correct. If it continued at that rate of error,
it would result in an error of about 42 seconds in 24 hours. Sounds pretty
bad, until you factor in a few other variables. One, the accuracy of the spectrum
analyzer you used to measure the plot, and the other is the fact that the powerline's
variation is cyclical by design. Your spectrum analyzer appears to be soundcard
based. The absolute accuracy of such a system is not so good Soundcards don't
even trim their crystals for frequency. I would venture that the typical accuracy of
a sound card's clock is certainly no better that +/-0.01%. If you plot the
powerline frequency over a longer period, I believe you will find that it keeps coming
back to reality. The usual pattern for summer time is to lose time during the day, and
to gain it back during the night. Winter is usually the opposite.
In a synchronization problem such as the one the OP was trying to solve, you would
use the best characteristics of a xtal oscillator, and the power line in arriving
at your solution. Since the powerline is cyclical in its error, and the crystal is usually
a very slow long term drift you should base your correction on perhaps weeks of
observation of the powerline signal.
-Chuck Harris
Alberto di Bene wrote:
FWIW, this is a plot of the 53rd harmonic of the 50 Hz of the mains at
my house, measured not more than half a hour ago. Nominally it should be
50 x 53 = 2650 Hz, but it ain't...
http://sundry.i2phd.com/mains.html
73 Alberto I2PHD
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From: "Tom Van Baak" tvb@leapsecond.com
Subject: Re: [time-nuts] Low cost synchronization, kitchen appliances
Date: Sun, 21 Aug 2005 07:03:56 -0700
Message-ID: 000401c5a659$2caf18e0$7a18f204@computer
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h
basis, so it may be
a bad idea to depend on it.
I keep hearing, on this group, that the powerline is no longer sync'd to
utc, and evidence for
that fact being a lack of motorized wall clocks. Well, clocks that sync
to the powerline are in
universal abundance in the US. Virtually every clock on kitchen
appliances is sync'd this way.
The clocks on VCR's may be reset from time to time by a tv station, but
the timing signal is
still the powerline. Basically, any appliance, or device that plugs into
the powerline is likely to
use the powerline for its timing function.
-chuck
Correct, my measurements clearly show that
mains power is steered to UTC. See:
http://www.leapsecond.com/pages/mains/
I think you are makeing the wrong conclusion, just because some powergrids is
steered to match UTC does not mean that all powergrids is steered to match UTC.
Similar is the discussion relating to cellular phones, just because some have
it others may not have it.
If there's anyone from the power industry on the
list I'd be interested to hear first-person technical
details of how phase is synchronized, both short-
and long-term.
I know who to talk to, at least for a deep understanding of the US power-grid.
I had him explain how the power-grid shutdown in east US could possibly occur,
very enlightening I might add. Frequency correction methods where explained in
the theory part of the explanation. The short story is that frequency
regulation is performed by balacing energy production and energy consumption in
the powergrid as a total. Overproduction results in higher frequency, under-
production results in lower frequency. Over and under production is produced
and shared among the producers in order to maintain overall frequency.
This comes at a price (coordination) and the larger powergrid the less eager
to coordinate one might be. I'll see if I can't dig up his post. However, that
would only give some theory and some detail relating to the US situation, but
people live elsewhere and situation is thus different (besides different
frequency and voltage).
But I'm not sure I agree with your claim about
kitchen appliances. It seems to me almost every
kitchen, electronic, wall-clock, and entertainment
appliance being sold these days uses quartz-based
clocks, regardless if they are mains, wall-wart, or
battery powered. I'm not sure how to confirm the
accuracy of this hunch, though.
Simple. Use a frequency synthesizer, poweramp and a variable transformer in
backwards and then adjust frequency and see if the the clock speed changes
accordingly. I think for most things, a 32 kHz oscillator is being used, since
it can be used for simple processors too.
I suspect there are several factors in the trend
away from mains-clocks to quartz-clocks:
-
Digital or analog quartz movements are dirt
cheap (so it's a cost saving measure). -
If the product is intended for sale in Japan
(where both 50 Hz and 60 Hz mains co-exist). -
If the product is intended for sale world-wide
(there is a healthy mix of 50 vs. 60 Hz and 120
vs. 240 V across the planet).
Markets are global now. Also, there is some odd frequency (such as 24 Hz) grids
still in operation in the US if I recall things correctly.
-
The explosion in the use of switching power
supplies in home electronics (which are immune
to local voltage / frequency conventions). -
The explosion in the use of microprocessor
based control of appliances (where the CPU(s)
are driven by an n MHz XO and date/time/display
functions are managed in firmware).
I agree with all these points. There are really few things that effectively
depends on it, so these days control of the frequency is not as important as
it used to be back in the old days when the industries punch-out and wall
clocks all had their frequency from the mains.
With that background, releasing the "tight" control becomes less of a problem
than it used to be, for good and bad.
I think I recall Poul-Henning mentioned that Nord Pool removed their frequency
control some time back. Maybe I should measure the frequency locally. I can
make some investigation of the local situation.
Cheers,
Magnus
Chuck Harris wrote:
Let's see, your graph shows for that small time interval that the
frequency
is within 0.05% of being correct. If it continued at that rate of error,
it would result in an error of about 42 seconds in 24 hours. Sounds
pretty
bad, until you factor in a few other variables. One, the accuracy of
the spectrum
analyzer you used to measure the plot, and the other is the fact that
the powerline's
variation is cyclical by design. Your spectrum analyzer appears to be
soundcard
based. The absolute accuracy of such a system is not so good
Soundcards don't
even trim their crystals for frequency. I would venture that the
typical accuracy of
a sound card's clock is certainly no better that +/-0.01%.
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
If you plot the
powerline frequency over a longer period, I believe you will find
that it keeps coming
back to reality. The usual pattern for summer time is to lose time
during the day, and
to gain it back during the night. Winter is usually the opposite.
Of course. I have added another plot to that page, taken half an hour
later, and things now look better. And I have beside my bed an alarm
clock driven by the 50 Hz of the mains (I know this for sure, it was
written on the instructions), and I have to reset it very, very seldom.
The seconds are not displayed, just the minutes, and I reset it when the
error is greater than 1 minute, compared to my DCF-77 clock.
So the short term accuracy of the mains seems to be quite bad, but by
averaging on a long period things get definitely better...
73 Alberto I2PHD
Alberto di Bene wrote:
based. The absolute accuracy of such a system is not so good
Soundcards don't
even trim their crystals for frequency. I would venture that the
typical accuracy of
a sound card's clock is certainly no better that +/-0.01%.
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
No doubt, but even the best most gifted world class musician with
perfect pitch cannot resolve pitch to better than 1 cent. More usual
is around 4 cents.
Now to screw up a little math and figure out what that means:
A cent is 1/100th of the spacing between two semitones, and because
there are 12 semitones in an octave, there are 1200 cents in an octave.
The cent is, as such, logrithmic in nature. The ratio of any two frequencies,
given in cents is:
n = 1200 log2(a/b)
If our sound card is accurate to 0.01%, the ratio of a/b would be:
1.0001 so,
n = 1200 log2(1.0001) = 1200 log2(10) log10(1.0001) = 0.03 cents!
0.03 cents is merely 33 times more precise than the very best of the
best can hear! So, I think I would be safe in concluding that your sound
card may be super duper as a music processing device, and still be pretty
awful as a test instrument.
-Chuck
In message 430879AD.6060508@erols.com, Chuck Harris writes:
Magnus Danielson wrote:
For any solutions that give you stable frequency
only (XO, RF carriers, 60 Hz) you will need a way
to set the initial time and to reset the time when
the batteries fail.
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be
a bad idea to depend on it.
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
From: "Poul-Henning Kamp" phk@phk.freebsd.dk
Subject: Re: [time-nuts] Low cost synchronization
Date: Sun, 21 Aug 2005 19:21:28 +0200
Message-ID: 58496.1124644888@phk.freebsd.dk
In message 430879AD.6060508@erols.com, Chuck Harris writes:
Magnus Danielson wrote:
For any solutions that give you stable frequency
only (XO, RF carriers, 60 Hz) you will need a way
to set the initial time and to reset the time when
the batteries fail.
For some countries will 60 Hz or 50 Hz no longer be maintained on 24 h basis, so it may be
a bad idea to depend on it.
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
Which is what I recalled that you where saying. This is again my point, that
just because it is in one place, that is not universally true for all places.
The reasoning why people don't care as much should be fairly evident from the
discussion so far.
Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
been done?
Poul-Henning and I both live in the NordPool controlled powergrid.
BTW, measuring the 53rd overtone frequency may not give a clear picture of the
frequency deviations at the base frequency. Overtone spectras experience quite
a different phase shift from the way it is produced by a number of devices
which vector-add to become the seen frequency and phase. Turn on or off a
strong producer of that frequency may shift that phase quite a bit while the
fundamental is barly shifted.
Cheers,
Magnus
Alberto di Bene wrote:
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.
Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5. The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz. I'm measuring ~24998.5Hz against the
nominal 25000Hz. The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable. I've attached a
screenshot of the Baudline display.
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
John
In message 20050821.193225.53123034.cfmd@bredband.net, Magnus Danielson writes:
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
Which is what I recalled that you where saying. This is again my point, that
just because it is in one place, that is not universally true for all places.
The reasoning why people don't care as much should be fairly evident from the
discussion so far.
Just got off the phone with a guy who writes for the same paper as me,
has been teaching this stuff for ages.
As a regulation domain gets larger, (and "larger" is measured in
[MW * km * s] in this context), the inherent regulation mechanisms
may develop instabilities for which the only currently known cure
is a external frequency reference.
The reason they don't do that in NordPool is because they don't
think they are big enough to need it and because they have a
couple of HVDC lines to other larger regulation domains where they
can dump surplus or pull deficit on very short notice.
However, external frequency references are not the perfect cure because
they tend to trip more generators on faults in the network than the
traditional mostly MVAR (reactive power allocation) based regulations.
He said that the places he knew off that used it, had a two state
mode, in one state, the frequency locked state, the delta-frequency
(not delta-phase!) is limited relative to the external reference, and
an effort to keep the delta-phase low was purely manual. The other state
gives up on all external references and just tries to avoid a collapse
of the grid.
As usual with big systems, the big problem is that they never get to test
and they're never ready when they get a chance to collect experience :-)
Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
been done?
Well, since they don't encode UTC in the first place, they can just encode
leapseconds just like any other second :-)
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
BTW, measuring the 53rd overtone frequency may not give a clear picture of the
frequency deviations at the base frequency.
Even worse, it may not be a "real" overtone in the first place, it could be
a PWM tone from some regulated async motor.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 4308B7FF.6050308@erols.com, Chuck Harris writes:
No doubt, but even the best most gifted world class musician with
perfect pitch cannot resolve pitch to better than 1 cent. More usual
is around 4 cents.
That's actually not always true. Some musicians develop or have a
tinitus tone which allows the to cold tune their instrument with
much better than 1% precision.
It is theorized that people with "absolute hearing" actually reference
the tone to one or more tinitus tones which may be at the edge of
their hearing threshold but the disonances might not.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
From: "Poul-Henning Kamp" phk@phk.freebsd.dk
Subject: Re: [time-nuts] Low cost synchronization
Date: Sun, 21 Aug 2005 20:24:47 +0200
Message-ID: 58785.1124648687@phk.freebsd.dk
In message 20050821.193225.53123034.cfmd@bredband.net, Magnus Danielson writes:
For the NordPool area (Norway, Sweden, Denmark, Finland) nobody tried to keep
the average at 50Hz.
Which is what I recalled that you where saying. This is again my point, that
just because it is in one place, that is not universally true for all places.
The reasoning why people don't care as much should be fairly evident from the
discussion so far.
Just got off the phone with a guy who writes for the same paper as me,
has been teaching this stuff for ages.
As a regulation domain gets larger, (and "larger" is measured in
[MW * km * s] in this context), the inherent regulation mechanisms
may develop instabilities for which the only currently known cure
is a external frequency reference.
The reason they don't do that in NordPool is because they don't
think they are big enough to need it and because they have a
couple of HVDC lines to other larger regulation domains where they
can dump surplus or pull deficit on very short notice.
However, external frequency references are not the perfect cure because
they tend to trip more generators on faults in the network than the
traditional mostly MVAR (reactive power allocation) based regulations.
He said that the places he knew off that used it, had a two state
mode, in one state, the frequency locked state, the delta-frequency
(not delta-phase!) is limited relative to the external reference, and
an effort to keep the delta-phase low was purely manual. The other state
gives up on all external references and just tries to avoid a collapse
of the grid.
As usual with big systems, the big problem is that they never get to test
and they're never ready when they get a chance to collect experience :-)
Interesting. Thanks for the report!
Also, how do you encode a leapsecond over 50 Hz, 60 Hz or whatever and has it
been done?
Well, since they don't encode UTC in the first place, they can just encode
leapseconds just like any other second :-)
There is a simple method, just run a thad below 50 Hz (or 60 Hz) so that you
have the same number of cycles on 86401 seconds as you normally would for
86400 seconds. That would turn out to be about 49,999421303 Hz on average.
Thats -578,697 mHz or -1,157394E-5 relative.
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
BTW, measuring the 53rd overtone frequency may not give a clear picture of the
frequency deviations at the base frequency.
Even worse, it may not be a "real" overtone in the first place, it could be
a PWM tone from some regulated async motor.
That will be part of the energy, but the PWM would create sidebands around
the overtone. Diode-bridges, triacs etc. etc. all help to create overtones.
The current reactive load on the line will also affect the fundamental, and the
insertion and removal of capacitance on the power-grid will shift the phase.
If you thought the MW balance a headache, the MVAR balance is a real long
hangover all the time.
Cheers,
Magnus
In message 20050821.204040.123709461.cfmd@bredband.net, Magnus Danielson writes:
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
In Denmark they charge you $1000 extra to get a three-tariff meter :-(
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
I run a LynxOne sound card. It has clock in and out (75 ohms- TTL).
The clock can be 25 Khz to 27 Mhz. In its control software, it can use
a 13.5 Mhz video dot clock, a 27 Mhz video dot clock, a word clock or a
X256 word clock.
I had considered using a synthesizer to locked up the sound card to the
rubidium during the ARRL frequency test back a few years ago. I worked
out everything in advance. I had a heart attack about 2 hours before
the contest - so I never got to work the contest...
I did not buy the card for the clock capability. It was bought because
it could handle 24 bit resolution and had digital and analog ins/outs.
You can also use multiple cards and the way they slave them, is via the
clock.
Brian N4FMN
John Ackermann N8UR wrote:
Alberto di Bene wrote:
Hmmm, the sound card used is the M-Audio Delta 44, a professional sound
card, used also by musicians and composers for studio works. I don't
know the accuracy of its time base, but certainly it is quite good.
I previously did some rough accuracy tests of my Delta 44 cards and
found they were "pretty good" but I didn't record the results.
Just for the fun of it, I am now measuring one and see about a 1.5Hz
error at 25kHz -- that's 6x10e5. The setup is an HP3325A synthesizer,
locked to an Rb standard, feeding 0.5v p-p into the Delta 44 on an
Athlon 2200 running the Linux-based Baudline spectrum analyzer program.
I'm sampling at 96kHz and decimating by 4096; Baudline has a very cool
measurement function that will give the absolute frequency reading with
a resolution of better than a mHz. I'm measuring ~24998.5Hz against the
nominal 25000Hz. The Delta 44 has been running in the computer for
several weeks, so it should be thermally stable. I've attached a
screenshot of the Baudline display.
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
John
time-nuts mailing list
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https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
----- Original Message -----
From: "Magnus Danielson" cfmd@bredband.net
snip
BTW, measuring the 53rd overtone frequency may not give a clear
picture of the
frequency deviations at the base frequency. Overtone spectras
experience quite
a different phase shift from the way it is produced by a number of
devices
which vector-add to become the seen frequency and phase. Turn on or
off a
strong producer of that frequency may shift that phase quite a bit
while the
fundamental is barly shifted.
Quite true, the majority of loads that produce high order harmonics
back into the grid are almost always varying considerably in the short
term-thus they produce short term variations in the resultant harmonic
spectra that renders the lines somewhat broader than you might think.
Ski lift motor drives are a good example of this. Such loads, without
adequate filterimg at the point of supply for the load, produce high
harmonic levels in the associated supply network, to the detriment of
any telecom cable network that happens to run parallel for significant
distances-as they always do in rural areas!
The old manual method that used to be used for power grid frequency
checking involved a comparison of two clocks, one driven from a
reference and the other from the grid itself-more usually the output
of a local generator in the days prior to strong grid linkages. The
comparison was typically done once or twice a day and appropriate
adjustments to the generation plant made to correct the grid driven
clock and keep its reading 'syncronised' to the reference clock.
I have here the remains of an attempt in the early seventies to bring
this type of system up to date - it comprised an HP 105 series quartz
reference, a K20- HP 5280A up down counter and an HP 5321B clock.
The up down counter was driven from 100 Hz signals derived from both
the 105B and the power grid. An HP 6933A D/A converter on the BCD
output from the counter had its plus/minus 10 volt output interfaced
to the generation plant. The 5321B clock reading was initialised from
the local time service(radio time pips) and then used to fine tune the
control system (D/A conveter to generator coupling) so the up down
counter stayed at or near zero reading and grid time ran in sync with
national standard time.
I dont know how successful this system was but I think it was in
service for several years.
I have the up down counter and the D/A converter almost fully
operational again- but only have parts ratted circuit boards from the
5321B clock and I never got the 105B.
DaveB, NZ
--
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.338 / Virus Database: 267.10.13/78 - Release Date: 19/08/2005
Poul-Henning Kamp wrote:
In message 20050821.204040.123709461.cfmd@bredband.net, Magnus Danielson writes:
The interesting thing is that they have been seriously thinking
about transmitting UTC and tarriff information on the grid, but it
looks it is cheaper to just use GPRS mobile phones.
Indeed. In Sweden that has become a big thing, with the deregulated market we
have. We haven't chosen that path here at home yeat, but I guess it is a
question of time like everything else.
In Denmark they charge you $1000 extra to get a three-tariff meter :-(
Here in the UK we have "Economy 7" (it should be renamed "Rip-off 7")
where electricity is sold cheaper overnight. As far as I know, there is
no installation fee for that, but if you have "Economy 7" you pay more
for electricity during the day. So unless you make heavy usage overnight
(as one does with electrical storage heaters), it is not a good idea.
My meter, uses a clock that used to keep accurate, but which is now
usually wrong.
Whether the meter uses the 50Hz for timing I do not know, but there is
battery in there too. It may be wrong since the battery has failed and
so the clock stops when there is a power failure, or it might be low in
voltage which means the clock runs slow.
But here at least, there is nothing very clever about how the time on
those clocks is kept. Which suits me, as sometimes I get electricity
cheap during the day now!
--
David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
Hi Poul,
As a musician myself, with marginal perfect pitch, I can cold tune to
about 7 cents absolute pitch on a 440 A, and much closer with relative
5ths. So basically, just using my ear, I can tune a fiddle so I won't break
anything, but I wouldn't be any fun to play with ;-) Oddly enough, I played
guitar for years, and didn't know I could do this until I learned to play a
fiddle.
However, I have never, ever heard of anyone that could prove to
do better than 1 cent. Do you have any reference to your claim? Perfect
pitch has always been something that has fascinated me, if only because
of the total unlikeliness of the whole thing.
Also, a cent is not the same as a percent. A cent is 1/100th the distance
between two adjacent semitones (eg. C and C#). There are exactly
1200 cents in each octave. So, as you can see, the spacing between
cents is logarithmic.
I have tinitus, but for me it is a rushing noise with some tonal component.
It sounds sort of like gas running through iron pipe when the furnace kicks
in.... or perhaps a flute that is being blown into, but is just starting to show
hints of producing a pure tone.
Once I had a fever, that I was treating with aspirin, and I had an annoyingly
large tinitus tone, So I thought I would try and get a beat note with it,
purely in the interests of science, of course. On went the headphones,
and I adjusted a signal generator from well below to well above, and I could
never get a beat of any sort. And further, I could never even do a good
job of matching the frequency. I concluded that tinitus tones must be outside
of audio in some way.... but then, I was feverish at the time.
-Chuck
Poul-Henning Kamp wrote:
In message 4308B7FF.6050308@erols.com, Chuck Harris writes:
No doubt, but even the best most gifted world class musician with
perfect pitch cannot resolve pitch to better than 1 cent. More usual
is around 4 cents.
That's actually not always true. Some musicians develop or have a
tinitus tone which allows the to cold tune their instrument with
much better than 1% precision.
It is theorized that people with "absolute hearing" actually reference
the tone to one or more tinitus tones which may be at the edge of
their hearing threshold but the disonances might not.
In message 4308F567.3020205@erols.com, Chuck Harris writes:
However, I have never, ever heard of anyone that could prove to
do better than 1 cent. Do you have any reference to your claim? Perfect
pitch has always been something that has fascinated me, if only because
of the total unlikeliness of the whole thing.
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
John Ackermann N8UR wrote:
One thing I want to explore is how difficult it would be to provide an
external clock for the Delta 44. Higher-end boards in the M-Audio
series have a "wordclock" input, and I suspect that the Delta 44 PC
board may be hackable to enable that.
If you succeed in that, please report your results here (or, if deemed
of no general interest, send me a private message). I could then derive
the clock for the Delta 44 from my Z3801A. thanks.
73 Alberto I2PHD
Poul-Henning Kamp wrote:
In message 4308F567.3020205@erols.com, Chuck Harris writes:
However, I have never, ever heard of anyone that could prove to
do better than 1 cent. Do you have any reference to your claim? Perfect
pitch has always been something that has fascinated me, if only because
of the total unlikeliness of the whole thing.
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
Did you make this measurement, or were you just told of it? What was the
repeatablity?
1 cent sharp at 440Hz is approximately 440.25Hz
1 cent flat at 440Hz is approximately 439.75Hz
(1 cent at any freq = 1: 2**(1/1200) = 1.0005777895)
The pitch one gets out of an open A string on a fiddle varies more than 1 cent depending
on how you support the neck of the instrument, how hard you bow the string,
where you bow the string, and what day of the week it is...
Even playing very softly, my violin is drastically louder than my tinitus.
-Chuck
Here's the story on frequency regulation of power lines:
You can control a few synchronized generators to an external
time standard. You will not be able to get phase control
unless the electric loads are steady. Think of the load
variations as you would temperature variations, except the
load can pull the generator out of phase with the external
frequency. And you can't insulate a generator from its load.
Power companies bill on time-integrated power - watt-hour
meters in the US. Watt-hour meters are still mostly driven
by electric clocks, in a way. The frequency does matter.
Power networks, large or small, cannot be automatically
controlled for frequency - especially not by independent
controllers in each powerhouse. Instead, the network is phase
controlled by the use of synchronous generators. Any single
generator will exchange energy with the network to hold
itself in phase with the network.
If the loads on the network do not match the steam power from
the power plants, then the whole network will rise or fall in
frequency until it reaches a balance of power. This is why
under-frequency relays are used to disconnect plants and loads
from the network in order to save part of the network.
The balance of power is so important that network dispatch
centers monitor generated and consumed power, doing what they
can to maintain balance. They usually lose frequency during the
day when loads are large. As the loads fall off during the
night, excess generated power is used to raise the frequency.
The frequency changes do not exceed 0.1% in large networks.
The basis for controlling the frequency is a cycle-counting
clock that is compared to a time standard. The goal is to have
the clocks match once every 24 hours. This assures fair allocation
of the cost of power - it isn't something that the dispatchers
just do for fun on the night shift.
Based on this:
-
It is unlikely that any power network just lets itself go,
with no standard time/frequency to hold. The under-frequency
relays would make that hazardous. -
Point measurements of line frequency are pointless. The
cycle count must be integrated over 24 hours. I don't know
what time the dispatchers aim for to match clocks. Back in the
fifties I was taught that the time of minimum activity is 4:30
AM, according to an Air Force study of the best time to bomb.
Traffic counters confirm this number. -
Leap seconds are easily integrated into the cycle count
during the following 24 hours.
Regards,
Bill Hawkins
In message 43090342.8000301@erols.com, Chuck Harris writes:
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
Did you make this measurement, or were you just told of it? What was the
repeatablity?
I did.
The pitch one gets out of an open A string on a fiddle varies more than 1 cent depending
on how you support the neck of the instrument, how hard you bow the string,
where you bow the string, and what day of the week it is...
We measured the tone he produced and asked him to make it as steady as possible.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
In message 001301c5a6a2$74803840$0500a8c0@darius.domain.actdsltmp, "Bill Hawkins" writes
:
Power companies bill on time-integrated power - watt-hour
meters in the US. Watt-hour meters are still mostly driven
by electric clocks, in a way. The frequency does matter.
Uhm, sorry, that is just plain wrong. The Ferrantis (sp?) power
meter which is the most widely used meter in the world is not
frequency sensitive within a band of +/- 10% or more.
- It is unlikely that any power network just lets itself go,
with no standard time/frequency to hold. The under-frequency
relays would make that hazardous.
Does not follow.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Poul-Henning Kamp wrote:
In message 001301c5a6a2$74803840$0500a8c0@darius.domain.actdsltmp, "Bill Hawkins" writes
:
Power companies bill on time-integrated power - watt-hour
meters in the US. Watt-hour meters are still mostly driven
by electric clocks, in a way. The frequency does matter.
Uhm, sorry, that is just plain wrong. The Ferrantis (sp?) power
meter which is the most widely used meter in the world is not
frequency sensitive within a band of +/- 10% or more.
I have never seen a power meter made by Ferranti in the US. Landis-gyr,
definitely, but not Ferranti. To quote Landis-gyr's website:
" Landis+Gyr Inc. is the world's leading supplier of electricity revenue meters.
Our products include solid-state and electromechanical residential meters,
a full line of solid-state commercial and industrial meters, high-end precision
meters and extensive automated meter reading (AMR) solutions. "
You cannot make a credible claim of "the most widely used meter in the world"
without including the US. We certainly have as many power meters
as all of Europe.
Here most of our meters are of the induction type, which work on the principles of a
split-phase induction motor. They are very easy to recognize by their
horizontal 4 inch corrugated aluminum disk that rotates (hopefully) slowly.
With the induction type power meter, power line frequency is very
important in determining the "hours" part of kilowatt-hours.
A 10% variation in line frequency would cause a 10% variation in power
consumption registered. Induction type power meters will remain accurate
with a 10% variation in power line voltage, however.
Someday, our utilities will convert all of our meters to solidstate units which might
not be so frequency sensitive, but that will be a few hundred billion dollars from now.
-Chuck Harris
Poul-Henning Kamp wrote:
In message 43090342.8000301@erols.com, Chuck Harris writes:
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
Did you make this measurement, or were you just told of it? What was the
repeatablity?
I did.
Good, then you should remember some important details:
Could he see the counter, or was the test done blind?
What variety of counter (cycle counting, or reciprocal) ?
What was the pitch variance from 440.0Hz?
How did you deal with all of the sympathetic resonances
that naturally occur within a violin?
-Chuck
In message 4309DA8E.9040801@erols.com, Chuck Harris writes:
Uhm, sorry, that is just plain wrong. The Ferrantis (sp?) power
meter which is the most widely used meter in the world is not
frequency sensitive within a band of +/- 10% or more.
I have never seen a power meter made by Ferranti in the US. Landis-gyr,
definitely, but not Ferranti. To quote Landis-gyr's website:
Sorry, not "Ferranti", but "Ferraris" and not "made by", but "principle".
You can read about it here:
http://content.honeywell.com/sensing/prodinfo/solidstate/application/006464_1.pdf
Here most of our meters are of the induction type, which work on the principles of a
split-phase induction motor. They are very easy to recognize by their
horizontal 4 inch corrugated aluminum disk that rotates (hopefully) slowly.
That is exactly the kind I'm talking about, only they're not exactly split-phase
because the offset fields are current vs voltage.
Their frequency sensitivity is very low compared to other error
factors. Most of the installed meters are class 2 (ie: up to 2%
wrong) or worse and frequency is seldom allowed to fluctuate +/- 1%
in any civilized grid.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Chuck Harris wrote:
A 10% variation in line frequency would cause a 10% variation in power
consumption registered. Induction type power meters will remain accurate
with a 10% variation in power line voltage, however.
Someday, our utilities will convert all of our meters to solidstate
units which might
not be so frequency sensitive, but that will be a few hundred billion
dollars from now.
In Italy, almost all of the meters have been replaced by solid state
units, which are read remotely through signalling on the power lines. I
feared that would have meant an increase in radio noise (I am a
radioamateur), but so far I haven't noticed any. This system has the
advantage that now the electrical company can apply different rates
between day and night, without needing that the meter itself is able to
keep the count of the time. At the start of each period a remote command
changes the rate.
73 Alberto I2PHD
In message 4309DDC2.3020806@erols.com, Chuck Harris writes:
Poul-Henning Kamp wrote:
In message 43090342.8000301@erols.com, Chuck Harris writes:
I met a violinist some years back who suffered from a 440Hz tinitus on his
left ear. When he tuned his fiddle after that, it was 440.0Hz measured
with a frequency counter.
Did you make this measurement, or were you just told of it? What was the
repeatablity?
I did.
Good, then you should remember some important details:
Could he see the counter, or was the test done blind?
I'm not that daft buddy! :-)
Yes, we didn't mess around, and yes, he could do it.
We measured with 500msec period counting.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.