How accurate will Sun clock be over 4 hours? - SUN

This is a discussion on How accurate will Sun clock be over 4 hours? - SUN ; I have a requirement where I need two Suns (both Netra T1s) to have their clocks close to each other during an experiment that lasts 4 hours. During this time, neither Sun will have internet access and they will not ...

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Thread: How accurate will Sun clock be over 4 hours?

  1. How accurate will Sun clock be over 4 hours?

    I have a requirement where I need two Suns (both Netra T1s) to have
    their clocks close to each other during an experiment that lasts 4
    hours. During this time, neither Sun will have internet access and they
    will not be networked to each other.

    I suspect if I sync them by NTP before the experiment starts, then they
    will not drift by more than 500 ms over a 4 hour period. Does that seem
    reasonable? Has anyone actually ever made medium term (few hours)
    stability measurements of the clocks in Suns?

  2. Re: How accurate will Sun clock be over 4 hours?

    Dave wrote:
    > I have a requirement where I need two Suns (both Netra T1s) to have
    > their clocks close to each other during an experiment that lasts 4
    > hours. During this time, neither Sun will have internet access and they
    > will not be networked to each other.
    >
    > I suspect if I sync them by NTP before the experiment starts, then they
    > will not drift by more than 500 ms over a 4 hour period. Does that seem
    > reasonable? Has anyone actually ever made medium term (few hours)
    > stability measurements of the clocks in Suns?


    It would be quite easy to set up cron job to call ntpdate every 4 hours
    and check the messages logged in /var/adm/messages.

    One of my x86 boxes drifts by about 250mS/hour while another drifts by
    about 10mS/hour.

    --
    Ian Collins.

  3. Re: How accurate will Sun clock be over 4 hours?

    In comp.unix.solaris Dave wrote:
    > I have a requirement where I need two Suns (both Netra T1s) to have
    > their clocks close to each other during an experiment that lasts 4
    > hours.


    What is your definition of "close?"

    > During this time, neither Sun will have internet access and they
    > will not be networked to each other.


    Why then do they need their clocks to remain "close?"

    Will they be in a place where they can receive a GPS signal?

    > I suspect if I sync them by NTP before the experiment starts, then
    > they will not drift by more than 500 ms over a 4 hour period. Does
    > that seem reasonable? Has anyone actually ever made medium term (few
    > hours) stability measurements of the clocks in Suns?


    If you get no response in these groups and don't want to simply wait
    four hours and see what happens, you could try asking in
    comp.protocols.time.ntp (if you haven't already).

    rick jones
    wishes his systems were in a place where they could recieve a GPS signal...
    --
    oxymoron n, commuter in a gas-guzzling luxury SUV with an American flag
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

  4. Re: How accurate will Sun clock be over 4 hours?

    Dave wrote:
    > I have a requirement where I need two Suns (both Netra T1s) to have
    > their clocks close to each other during an experiment that lasts 4
    > hours. During this time, neither Sun will have internet access and they
    > will not be networked to each other.
    >
    > I suspect if I sync them by NTP before the experiment starts, then they
    > will not drift by more than 500 ms over a 4 hour period. Does that seem
    > reasonable? Has anyone actually ever made medium term (few hours)
    > stability measurements of the clocks in Suns?


    Ntpd stores the frequency error of the clock in the drift file if you
    configure a drift file. Most systems have a drift of less than 100 PPM
    in absolute value. Some systems do a lot better than that; 25 or 30
    PPM. Configure your drift file if you haven't already and see what the
    frequency error is.

    The systems will do better if you keep tight control of the temperature.

    If you leave ntpd running on both systems, it will continue to
    discipline the clocks based on the last information it had. If the
    temperature remains stable the clocks should remain very close to each other


  5. Re: How accurate will Sun clock be over 4 hours?

    Dave wrote:
    > I have a requirement where I need two Suns (both Netra T1s) to have
    > their clocks close to each other during an experiment that lasts 4
    > hours. During this time, neither Sun will have internet access and they
    > will not be networked to each other.


    Ick.

    >
    > I suspect if I sync them by NTP before the experiment starts, then they
    > will not drift by more than 500 ms over a 4 hour period. Does that seem
    > reasonable? Has anyone actually ever made medium term (few hours)
    > stability measurements of the clocks in Suns?


    It's possible... but too many variables.

    If there was some way to sync to a local "accurate" clock for each
    that would help. I know that's not much help.


  6. Re: How accurate will Sun clock be over 4 hours?

    Rick Jones wrote:
    > In comp.unix.solaris Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours.

    >
    > What is your definition of "close?"


    I can accept 500 ms, but not any more.

    >
    >> During this time, neither Sun will have internet access and they
    >> will not be networked to each other.

    >
    > Why then do they need their clocks to remain "close?"


    One will be controlling a signal generator's frequency via a GPIB
    controller fitted in the Sun. The other Sun will control the frequency
    of a receiver via another GPIB controller.

    I don't want the situation where the transmitter is at one frequency and
    the receiver a couple of GHz away! (The crystals of the transmitter and
    receiver will be locked to two rubidium sources, so stability of the
    test equipment is not an issue, but somehow I need to ensure the
    controllers direct them to the right frequencies at the right time.
    Since they are going to be changed every few seconds, I can't put long
    delays in the system.

    > Will they be in a place where they can receive a GPS signal?


    One possibly, the other definitely not Just to make matters worst,
    there could be a wide (perhaps 25 deg C) difference in temperature
    between the two.

    However, you have given me an idea. It should be possible to generate
    our own one pulse per second signal from a couple of rubidium
    oscillators. However, I'm not sure if the Netra T1's have enough serial
    ports, as one will be used to control the Suns. There are two serial
    ports are marked "LOM A" and "Serial B". I assume I can can control the
    machines from one of these and sync to `1 pps signal on the other, but
    I'm not 100% sure of that.

    >> I suspect if I sync them by NTP before the experiment starts, then
    >> they will not drift by more than 500 ms over a 4 hour period. Does
    >> that seem reasonable? Has anyone actually ever made medium term (few
    >> hours) stability measurements of the clocks in Suns?

    >
    > If you get no response in these groups and don't want to simply wait
    > four hours and see what happens,


    Unfortunately I don't have both machines here.

    > you could try asking in
    > comp.protocols.time.ntp (if you haven't already).


    I will try that. Also the time-nuts mailing list is another possibility.

    > rick jones
    > wishes his systems were in a place where they could recieve a GPS signal...


    Generally I don't have a big issue with time. I sometimes look at the
    time of the Sun when I have a train to catch, but generally exact time
    is not an issue to me. But this experiment is a bit unusual.

  7. Re: How accurate will Sun clock be over 4 hours?

    Richard B. Gilbert wrote:
    > Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours. During this time, neither Sun will have internet access and
    >> they will not be networked to each other.
    >>
    >> I suspect if I sync them by NTP before the experiment starts, then
    >> they will not drift by more than 500 ms over a 4 hour period. Does
    >> that seem reasonable? Has anyone actually ever made medium term (few
    >> hours) stability measurements of the clocks in Suns?

    >
    > Ntpd stores the frequency error of the clock in the drift file if you
    > configure a drift file. Most systems have a drift of less than 100 PPM
    > in absolute value. Some systems do a lot better than that; 25 or 30
    > PPM. Configure your drift file if you haven't already and see what the
    > frequency error is.
    >
    > The systems will do better if you keep tight control of the temperature.


    That is definately not possible. One is going to be outside.

    >
    > If you leave ntpd running on both systems, it will continue to
    > discipline the clocks based on the last information it had. If the
    > temperature remains stable the clocks should remain very close to each
    > other
    >


    In which case NTP might make matters worst than no NTP during the
    experiment.

  8. Re: How accurate will Sun clock be over 4 hours?

    Chris Cox wrote:
    > Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours. During this time, neither Sun will have internet access and
    >> they will not be networked to each other.

    >
    > Ick.
    >
    >>
    >> I suspect if I sync them by NTP before the experiment starts, then
    >> they will not drift by more than 500 ms over a 4 hour period. Does
    >> that seem reasonable? Has anyone actually ever made medium term (few
    >> hours) stability measurements of the clocks in Suns?

    >
    > It's possible... but too many variables.
    >
    > If there was some way to sync to a local "accurate" clock for each
    > that would help. I know that's not much help.
    >



    That is a possibility. I have one of these


    http://www.thinksrs.com/products/PRS10.htm

    which is a rubidium oscillator. I could get another and sync them both
    to GPS. A bit more complexity than I wanted, but it might be necessary.

  9. Re: How accurate will Sun clock be over 4 hours?

    Ian Collins wrote:
    > Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours. During this time, neither Sun will have internet access and they
    >> will not be networked to each other.
    >>
    >> I suspect if I sync them by NTP before the experiment starts, then they
    >> will not drift by more than 500 ms over a 4 hour period. Does that seem
    >> reasonable? Has anyone actually ever made medium term (few hours)
    >> stability measurements of the clocks in Suns?

    >
    > It would be quite easy to set up cron job to call ntpdate every 4 hours
    > and check the messages logged in /var/adm/messages.
    >
    > One of my x86 boxes drifts by about 250mS/hour while another drifts by
    > about 10mS/hour.
    >



    From those sorts of figures, I suspect I will be stuffed as one will be
    outside with the temperature possibly below 0 deg C and the other in a
    place which might be quite warm.

  10. Re: How accurate will Sun clock be over 4 hours?

    In comp.unix.solaris Dave wrote:
    > Rick Jones wrote:
    > > Will they be in a place where they can receive a GPS signal?


    > One possibly, the other definitely not Just to make matters worst,
    > there could be a wide (perhaps 25 deg C) difference in temperature
    > between the two.


    Yeah, that probably doesn't help at all...

    > However, you have given me an idea. It should be possible to
    > generate our own one pulse per second signal from a couple of
    > rubidium oscillators. However, I'm not sure if the Netra T1's have
    > enough serial ports, as one will be used to control the Suns. There
    > are two serial ports are marked "LOM A" and "Serial B". I assume I
    > can can control the machines from one of these and sync to `1 pps
    > signal on the other, but I'm not 100% sure of that.


    If not, perhaps you could ship the PPS to a second system at each site
    and use those as NTP servers.

    Or, you find a way to carry IP over this signal being transmitted

    > > rick jones
    > > wishes his systems were in a place where they could recieve a GPS
    > > signal...


    > Generally I don't have a big issue with time. I sometimes look at
    > the time of the Sun when I have a train to catch, but generally
    > exact time is not an issue to me. But this experiment is a bit
    > unusual.


    In my case, one day I'd like to enable netperf to make direct
    measurements of one-way latency.

    rick jones
    --
    The glass is neither half-empty nor half-full. The glass has a leak.
    The real question is "Can it be patched?"
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

  11. Re: How accurate will Sun clock be over 4 hours?

    [A complimentary Cc of this posting was sent to
    Dave
    ], who wrote in article <47e0d3cc@212.67.96.135>:
    > From those sorts of figures, I suspect I will be stuffed as one will be
    > outside with the temperature possibly below 0 deg C and the other in a
    > place which might be quite warm.


    Hmm... I wonder whether somebody already wrote software to keep the
    temperature INSIDE the case at a given level. (Like running fans on
    the "indoor" machine like crazy, and do not run them at all on the
    "outdoor" one...)

    Ilya

  12. Re: How accurate will Sun clock be over 4 hours?

    Rick Jones wrote:


    >
    >>However, you have given me an idea. It should be possible to
    >>generate our own one pulse per second signal from a couple of
    >>rubidium oscillators. However, I'm not sure if the Netra T1's have
    >>enough serial ports, as one will be used to control the Suns. There
    >>are two serial ports are marked "LOM A" and "Serial B". I assume I
    >>can can control the machines from one of these and sync to `1 pps
    >>signal on the other, but I'm not 100% sure of that.


    FWIW, a few more approaches:

    1. If you lack sufficient serial ports, use a terminal server on
    ethernet (e.g. Remote Annex, very cheap to acquire on eBay
    and elsewhere)

    2. If GPS isn't possible at one or more sites, use a WWV/WWVB receiver.

    3. A more costly option to operate would be a cellular gateway device, again
    cheap on eBay, connected to ethernet.

    I use a terminal server with a serial-interfaced remote-controlled HF
    receiver to hear WWV for a similar purpose here; the audio drives
    sound-card line-in and software decodes the timecode. The many additional
    serial ports on the terminal server handle other experimental devices.

    Michael

  13. Re: How accurate will Sun clock be over 4 hours?

    > >> I have a requirement where I need two Suns (both Netra T1s) to

    > one will be outside with the temperature possibly below 0 deg C and
    > the other in a place which might be quite warm.


    Have you checked the operating temp range for those systems and
    compared that with the expected temps? From a very cursory check if
    you get much below 0 deg C you might be pushing the envelope.

    rick jones
    --
    No need to believe in either side, or any side. There is no cause.
    There's only yourself. The belief is in your own precision. - Jobert
    these opinions are mine, all mine; HP might not want them anyway...
    feel free to post, OR email to rick.jones2 in hp.com but NOT BOTH...

  14. Re: How accurate will Sun clock be over 4 hours?

    In comp.unix.solaris Dave wrote:
    > I have a requirement where I need two Suns (both Netra T1s) to have
    > their clocks close to each other during an experiment that lasts 4
    > hours. During this time, neither Sun will have internet access and they
    > will not be networked to each other.
    >
    > I suspect if I sync them by NTP before the experiment starts, then they
    > will not drift by more than 500 ms over a 4 hour period. Does that seem
    > reasonable? Has anyone actually ever made medium term (few hours)
    > stability measurements of the clocks in Suns?


    Can you simulate the conditions beforehand (with net access)? Run NTP,
    get them all synced up. Enable logs and make sure you have driftfiles
    in place.

    On the client "disable ntp" in the config file so that polls are done,
    but the clock is not modified. Let it run that way in simulated
    conditions and see what your drift rate is.

    Temperature will likely be the biggest factor in frequency changes.

    If temperature is somewhat stable, 500ms should be achievable for a few
    days.

    --
    Darren Dunham ddunham@taos.com
    Senior Technical Consultant TAOS http://www.taos.com/
    Got some Dr Pepper? San Francisco, CA bay area
    < This line left intentionally blank to confuse you. >

  15. Re: How accurate will Sun clock be over 4 hours?

    In comp.unix.solaris Dave wrote:
    >> The systems will do better if you keep tight control of the temperature.

    >
    > That is definately not possible. One is going to be outside.


    A large box with vent holes can provide an excellent temperature
    stabilized environment, especially if someone can monitor it and
    open/close vents. It's a bit more fiddly, but very cheap.

    --
    Darren Dunham ddunham@taos.com
    Senior Technical Consultant TAOS http://www.taos.com/
    Got some Dr Pepper? San Francisco, CA bay area
    < This line left intentionally blank to confuse you. >

  16. Re: How accurate will Sun clock be over 4 hours?

    Darren Dunham wrote:
    > In comp.unix.solaris Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours. During this time, neither Sun will have internet access and they
    >> will not be networked to each other.
    >>
    >> I suspect if I sync them by NTP before the experiment starts, then they
    >> will not drift by more than 500 ms over a 4 hour period. Does that seem
    >> reasonable? Has anyone actually ever made medium term (few hours)
    >> stability measurements of the clocks in Suns?

    >
    > Can you simulate the conditions beforehand (with net access)? Run NTP,
    > get them all synced up. Enable logs and make sure you have driftfiles
    > in place.
    >
    > On the client "disable ntp" in the config file so that polls are done,
    > but the clock is not modified. Let it run that way in simulated
    > conditions and see what your drift rate is.
    >
    > Temperature will likely be the biggest factor in frequency changes.
    >
    > If temperature is somewhat stable, 500ms should be achievable for a few
    > days.


    Put the indoor machine in the refrigerator.

    RM

  17. Re: How accurate will Sun clock be over 4 hours?

    Darren Dunham wrote:
    > In comp.unix.solaris Dave wrote:
    >> I have a requirement where I need two Suns (both Netra T1s) to have
    >> their clocks close to each other during an experiment that lasts 4
    >> hours. During this time, neither Sun will have internet access and they
    >> will not be networked to each other.
    >>
    >> I suspect if I sync them by NTP before the experiment starts, then they
    >> will not drift by more than 500 ms over a 4 hour period. Does that seem
    >> reasonable? Has anyone actually ever made medium term (few hours)
    >> stability measurements of the clocks in Suns?

    >
    > Can you simulate the conditions beforehand (with net access)? Run NTP,
    > get them all synced up. Enable logs and make sure you have driftfiles
    > in place.


    One problem is I don't currently have both machines. However, I will be
    able to do some testing in this way.

    > On the client "disable ntp" in the config file so that polls are done,
    > but the clock is not modified. Let it run that way in simulated
    > conditions and see what your drift rate is.
    >
    > Temperature will likely be the biggest factor in frequency changes.


    Yes, and I suspect that it could be quite significant.
    >
    > If temperature is somewhat stable, 500ms should be achievable for a few
    > days.
    >


    I only need it for 4 hours. 500 ms in 4 hours equates to 34.7 ppm, which
    is probably expecting a bit much when crystals are not at similar
    temperatures.

    I thought at first that GPS was not going to be possible, but I'm now
    told it might be.

    Anyway, lots of people have given me lots of ideas.

  18. Re: How accurate will Sun clock be over 4 hours?

    Rex Mottram wrote:

    > Put the indoor machine in the refrigerator.
    >
    > RM


    Unfortunately, that is not practical given the particular constraints I have

  19. Re: How accurate will Sun clock be over 4 hours?

    On 2008-03-20, Dave wrote:
    > Rex Mottram wrote:
    >
    >> Put the indoor machine in the refrigerator.
    >>
    >> RM

    >
    > Unfortunately, that is not practical given the particular constraints I have


    Are the machines close enough together to connect a cable between them?


    --
    "Be thankful that you have a life, and forsake your vain
    and presumptuous desire for a second one."
    [email me at huge {at} huge (dot) org uk]

  20. Re: How accurate will Sun clock be over 4 hours?

    Huge wrote:
    > On 2008-03-20, Dave wrote:
    >> Rex Mottram wrote:
    >>
    >>> Put the indoor machine in the refrigerator.
    >>>
    >>> RM

    >> Unfortunately, that is not practical given the particular constraints I have

    >
    > Are the machines close enough together to connect a cable between them?
    >
    >


    No - otherwise it would be easy with NTP over ethernet.

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