[time-nuts] List of time synchronization hardware and software
neal at mcburnett.org
Mon Jan 16 20:04:08 EST 2006
On Mon, Jan 16, 2006 at 03:14:44PM -0800, Brooke Clarke wrote:
> Hi James:
> Astronomical methods, such as sundials might deserve a place on the list.
Absolutely. Over the long term, these are often the most accurate,
where the periodic motion of some astronomical body provides a
frequency source, and humans do the calculating and counting.
That is certainly true historically, where observations of the
positions of the sun rise/set on the horizon, observations of the
positions of moon and planets, eclipses of moons of jupiter, etc
provided the definition of time until recent decades.
And it is still the case that an independent check on our atomic
clocks by counting pulsar pulses is very valuable input. As I
understand it, astronomical observations contributed to the steering
of the frequency rate of TAI, possibly as recently as 1977 and 1995
on 1977-01-01 the rate of TAI was reduced by one part in 10^12
In 1995 a CCTF working group determined that the length of TAI
seconds was longer than the SI second because the clocks contributing
to TAI were not corrected for the effects of blackbody
radiation. Over the next three years the frequency of TAI was steered
to reduce the length of its seconds by about 2 parts in
10^14. Therefore the length of UTC seconds was also reduced. This
change is evident as the final kink in the plot of TT(BIPM04).
And if you want a device that is intended to work for a LONG time,
The 10,000 Year Clock
The idea to build a monument scale, multi-millennial, all mechanical
clock as an icon to long term thinking
Two prototypes now exist, and work continues.
Finally, clearly a computer can function as a clock, as originally
pointed out, but missing from James' list.
=> D.6 Devices that synchronize with the NTP or SNTP protocol.
Neal McBurnett http://bcn.boulder.co.us/~neal/
> Brooke Clarke, N6GCE
> w/Java http://www.PRC68.com
> w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
> >A clock consists of a frequency standard plus a counter. Accordingly, a
> >list of "hardware" that provides time would include:
> >A. Mechanical wrist watches and mechanical clocks. For these, the
> >frequency standard might be a pendulum, and the the counter might be an
> >arrangement of gears to count seconds, minutes, houts, etc., and display
> >them on mechanical dials for the user to observe.
> >B. Electrically powered wristwatches and clocks that include tuning
> >forks as their frequency standard.
> >C. Electrically powered wristwatches and clocks that include crystal
> >oscillators as their frequency standards. Most retail clocks and
> >wristwatches fall into this category.
> >D. Wristwatches and clocks that include crystal oscillators that are
> >"synchronized" from time to time with radio receivers. These include,
> >for example:
> >D.1. "Atomic Time" and other brands of wristwatches and clocks that
> >synchronize their dials (counters) against the 60 kHz LF signal from
> >WWVB near Ft. Collins, Colorado.
> >D.2. Similar products that synchronize their dials against other LF
> >signals from other LF (low frequency) or MF (medium frequency) time
> >signal stations such as MSF (Rughy, United Kingdom, 60 kHz); TDF
> >(Allouis, France, 162 kHz); HBG (Prangins, Switzerland, 75 kHz); etc.
> >D.3. Similar products with HF radio receivers for such time and
> >frequency stations as WWV (Colorado, USA: 2.5 MHz, 5.0 MHz, 10.0 MHz,
> >15.0 MHz, 20.0 MHz), WWVH (Hawaii, USA: 5.0 MHz, 10.0 MHz, 15.0 MHz),
> >CHU (Ontario, Canada: 3330 kHz, 7335 kHz, 14670 kHz), BPM (Shaanxi,
> >China: 2.5 MHz, 5.0 MHz, 10.0 MHz, 15.0 MHz), etc.
> >D.4. Similar products that both "synchronize" their counters and
> >"syntonize" their frequency references against standard time and
> >frequency broadcasts.
> >D.5 Similar products that either "synchronize" their counters (or both
> >"synchronize" their counters and "syntonize" their frequency standards)
> >against signals received from GPS satellites. Almost any GPS receiver
> >will display time of day. (Many will not, however, display it in a
> >"timely" manner!) GPS receivers that are to be used for precise timing
> >purposes should provide a 1 Hz (1 pulse per second) output. Some of the
> >better ones will provide 5 Hz or 10 Hz outputs, if they provide fixes 5
> >or 10 times per second.
> >As Rob Kimberly said, a list of hardware timing devices could be rather
> >lengthy! It would help if you could be more specific, and perhaps rule
> >out such devices as mechanical clocks and chronometers.
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