Re: [LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
In message 20140110050534.e4388406...@ip-64-139-1-69.sjc.megapath.net, Hal Mu rray writes: Do you have data or references for that? If I heard it from anybody less credible, I'd guess it was an urban legend? Was it accurate 50 years ago? Several people deeply involved in the Danish electricity grid have told me the same thing: The utilities prided themselves by their frequency precision and used a lots of synchronous motor clocks internalll. At the local powerplant, they would call up the speaking clock every day at noon, compare it to the clock in the control-room and log the difference. (I have seen this myself as a kid.) The winter/summer variation doesn't make sense to me. If the PLL can cover daily changes, anything lower frequency would be covered for free. The winter/summer variation has also puzzled me, but the consenus seems to be that it was caused by electrical heating running through the night, preventing them for regaining the lost cycles due to business load during the day. (The danish grid was surprisinly marginally provisioned until everybody started conserving electricity after the OPEC-stunt in the winter 1973-74.) It's easy to collect data. Take an AC wall wart type transformer and connect it to a modem control pin that the kernel is setup to use for NTP's PPS signals. (Contact me off list if you want the software.) I've done that many years ago, right when the deregulation too effect in Denmark, and the average frequency dropped by 0.05Hz because they could save fuel that way. Since then the frequency has just wandered aimlessly around 50Hz, leaving the phase to do a random walk. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@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. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
[LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
The IBM 360 systems starting in 1964 used the power line frequency. (A location in low memory got bumped at 300 counts per second. 5 per cycle on 60 Hz and 6 per cycle on 50 Hz.) I wonder how much the power timekeeping wandered back then relative to today. Does anybody know what the guys in the power company control rooms do about leap seconds? Leap seconds started in 1972. I was at Xerox in the late 1970s. At boot time, Altos got the time from a local time server. Altos used the system crystal (5.88 MHz) for timekeeping. Personal Altos were rebooted frequently so it didn't matter if their clock drifted a bit. The time server was packaged with the routers. (We called them gateways.) On the few systems that were up a long time (file servers, routers), we hand tweaked a fudge factor to adjust the clock rate. It wasn't hard to get to a second per week. I think the units for the fudge factor (from a config file) were seconds per day, but it would read at least one digit past the decimal point. I don't remember any mention of leap seconds. When were there enough (Unix?) boxes on the net running NTP and keeping good enough time to notice things like leap seconds? I should go browse the old RFCs and see when the API for telling the kernel about pending leap seconds was published. But somebody may have good stories or folklore. -- These are my opinions. I hate spam. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
Hal Murray wrote: When were there enough (Unix?) boxes on the net running NTP and keeping good enough time to notice things like leap seconds? De facto, late 1990s, I think. What one would notice would depend rather on one's habits; early adopters vs late adopters of NTP. I should go browse the old RFCs and see when the API for telling the kernel about pending leap seconds was published. RFC 1589, D. Mills, A Kernel Model for Precision Timekeeping, 1994-03. -zefram ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
Does anyone know if the NERC experiment (see below) happened or is still underway? -- Richard Langley From Wikipedia: Regulation of power system frequency for timekeeping accuracy was not commonplace until after 1926 and the invention of the electric clock driven by a synchronous motor. Today network operators regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at the nominal value within a few hundred parts per million.[17] In the synchronous grid of Continental Europe, the deviation between network phase time and UTC (based on International Atomic Time) is calculated at 08:00 each day in a control center inSwitzerland. The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60 sec × 60 min × 24 hours = 4,320,000 cycles per day.[18] In North America, whenever the error exceeds 10 seconds for the east, 3 seconds for Texas, or 2 seconds for the west, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half hour.[19][20] Real-time frequency meters for power generation in the United Kingdom are available online - an official National Grid one, and an unofficial one maintained by Dynamic Demand.[21][22] Real-time frequency data of the synchronous grid of Continental Europe is available at mainsfrequency.com. The Frequency Monitoring Network (FNET) at the University of Tennessee measures the frequency of the interconnections within the North American power grid, as well as in several other parts of the world. These measurements are displayed on the FNET website. Smaller power systems may not maintain frequency with the same degree of accuracy. In 2011, The North American Electric Reliability Corporation (NERC) discussed a proposed experiment that would relax frequency regulation requirements for electrical grids[23] which would reduce the long-term accuracy of clocks and other devices that use the 60 Hz grid frequency as a time base. And spoofing the power grid: http://gpsworld.com/wirelessinfrastructuregoing-against-time-13278/ On Thursday, January 9, 2014,9, at 12:00 PM, Poul-Henning Kamp wrote: In message 20140109110353.35874406...@ip-64-139-1-69.sjc.megapath.net, Hal Mu rray writes: The IBM 360 systems starting in 1964 used the power line frequency. (A location in low memory got bumped at 300 counts per second. 5 per cycle on 60 Hz and 6 per cycle on 50 Hz.) I wonder how much the power timekeeping wandered back then relative to today. It used to be pretty good, because people used synchronous motors to drive clocks so the power companies tried to keep the long-term frequency correct. In Denmark they usually lost a couple of seconds during the day and gained them back during the night, similarly they lost half a minute over winter and gained it back over summer. After deregulation nobody gets paid to keep the long term frequency, so mains is no good, actually down-right bad, for timekeeping anymore. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@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. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs - | Richard B. LangleyE-mail: l...@unb.ca | | Geodetic Research Laboratory Web: http://gge.unb.ca/ | | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3| |Fredericton? Where's that? See: http://www.fredericton.ca/ | - ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
On Jan 9, 2014, at 4:03 AM, Hal Murray wrote: The IBM 360 systems starting in 1964 used the power line frequency. (A location in low memory got bumped at 300 counts per second. 5 per cycle on 60 Hz and 6 per cycle on 50 Hz.) I wonder how much the power timekeeping wandered back then relative to today. Does anybody know what the guys in the power company control rooms do about leap seconds? Leap seconds started in 1972. I was at Xerox in the late 1970s. At boot time, Altos got the time from a local time server. Altos used the system crystal (5.88 MHz) for timekeeping. Personal Altos were rebooted frequently so it didn't matter if their clock drifted a bit. The time server was packaged with the routers. (We called them gateways.) On the few systems that were up a long time (file servers, routers), we hand tweaked a fudge factor to adjust the clock rate. It wasn't hard to get to a second per week. I think the units for the fudge factor (from a config file) were seconds per day, but it would read at least one digit past the decimal point. I don't remember any mention of leap seconds. When were there enough (Unix?) boxes on the net running NTP and keeping good enough time to notice things like leap seconds? I should go browse the old RFCs and see when the API for telling the kernel about pending leap seconds was published. But somebody may have good stories or folklore. I know there were documented problems in the leap seconds that happened in the late 1990s. I was involved in GPS steered OCO in the early 2000's, and they were definitely a problem by then. That's when i developed most of my opinions about their impact on general time keeping and imperfect fit with POSIX and the leap second standard. A fit that's only grown more chafing to this day. Warner ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
Re: [LEAPSECS] When did computer timekeeping get good enough for leap seconds to matter?
p...@phk.freebsd.dk said: It used to be pretty good, because people used synchronous motors to drive clocks so the power companies tried to keep the long-term frequency correct. Microwave ovens still use the line for timekeeping. 1/2 :) I wonder how many old mechanical (synchronous) clocks are still ticking? I have two. One on a clock radio and one on my oven. In Denmark they usually lost a couple of seconds during the day and gained them back during the night, similarly they lost half a minute over winter and gained it back over summer. Do you have data or references for that? If I heard it from anybody less credible, I'd guess it was an urban legend? Was it accurate 50 years ago? The winter/summer variation doesn't make sense to me. If the PLL can cover daily changes, anything lower frequency would be covered for free. It's easy to collect data. Take an AC wall wart type transformer and connect it to a modem control pin that the kernel is setup to use for NTP's PPS signals. (Contact me off list if you want the software.) I have data from Silicon Valley and Zurich. I can't see any strong daily cycles. Some days are flat, some days it drifts one way, and some days it drifts the other. Mostly it wanders around. Typical peak-peak (SV) is 4 seconds per day. Here is a graph for the last 24 days: http://www.megapathdsl.net/~hmurray/time-nuts/60Hz/Dec-2013.png Midnight UTC is 4 PM local. Peak-to-peak over 24 days is 12 seconds. After deregulation nobody gets paid to keep the long term frequency, so mains is no good, actually down-right bad, for timekeeping anymore. At least in the US, the power companies are still required to keep good time. I don't know any details. There was a proposal a year or so ago to drop that. I gather it's a pain-in-the-ass type constraint on their overall operations. The proposal was dropped and I haven't heard anything since. Maybe somebody told them that microwave ovens have replaced synchronous motors. Maybe somebody figured out that it was cheaper to pay a few engineers to get things right rather than pay dozens of lawyers to get their proposal through Washington. This is getting off topic for leap-seconds, but maybe there are some details from the power industry that will shed some light on the leap-second issues. -- These are my opinions. I hate spam. ___ LEAPSECS mailing list LEAPSECS@leapsecond.com http://six.pairlist.net/mailman/listinfo/leapsecs
