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Wanted: A Very Accurate Timer

Discussion in 'Electronic Repair' started by [email protected], Jun 24, 2005.

  1. 2.com

    2.com Guest

    Can I get recomendations for the most accurate electronic timer that I
    can buy?

    It must to be accurate to within 1/60th of a second over the course of
    6 hours.

    Is something like this commercially available, or will I have to build
    it, or have someone build it?

    Any advice would be appreciated.

    Thanks a lot.

    Darren Harris
    Staten Island, New York.
     
  2. Ian Stirling

    Ian Stirling Guest

    GPS recievers.
    I've seen some with an alarm function.
    However, 1/60th of a second in 6 hours isn't impossible to do otherwise.
     
  3. Jim Thompson

    Jim Thompson Guest

    An ordinary digital clock powered from the AC line is more accurate
    than that.

    ...Jim Thompson
     
  4. On the surface, shouldn't that be "as accurate as that"? In North America
    and other 60-Hz realms, at least.

    I have heard horror stories about short-term inaccuracies in the power
    system 60 Hz timing, that it is only guaranteed to be accurate within 1
    cycle per day, for instance.

    And I found this tidbit googling around for accurate clocks: "GPS time was
    zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds GPS is
    now ahead of UTC by 13 seconds."
     
  5. Jim Thompson

    Jim Thompson Guest

    As I understand it, for grid-power-hopping to work, the accuracy is
    _much_ better than that.
    I think that's nonsense.

    ...Jim Thompson
     
  6. EL

    EL Guest

    *** GASP!!!!!! ***

    An error of one part in 5,184,000??!?!?!?!?!

    How could anyone possibly tolerate that???!?!?!?!?!

    ;^)
     
  7. I recall working with a marketing guy a few years back who had a customer
    interested in a ruggedized PC that had timing accurate to 1 second/month,
    even when turned off. He thought the PC's real-time clock chip would be ok,
    because it has its own battery.
     
  8. DaveM

    DaveM Guest

    Dan,
    Sadly enough, there have been a number of replies to your question, but none
    have attempted to answer it directly.
    But, you didn't state the intended use or desired method of operation of the
    timer. Assuming that you are looking for a handheld timer suitable for
    tasks such as cooking or sunbathing, almost any of the common timers
    available at outlets such as Radio Shack, Target, Walmart, etc. should fill
    your bill. They are all crystal controlled, and although their accuracy
    isn't usually stated in the specs, they should easily meet your
    requirements.
    If you're looking for an industrial timer that can control other devices,
    then you need to specify what kind of equipment or the power requirements of
    the equipment.

    --
    Dave M
    MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
    the address)

    Never take a laxative and a sleeping pill at the same time!!
     
  9. You really need to say more about the enviroment.
    Crystals, can relatively easily get to 1ppm. (you need just slightly
    better than this), and with a crystal oven to control the temperature,
    accuracies better that 0.1ppm, are relatively easy. Omega offer off the
    shelf timing systems warranted to better than this.
    Some radio transmitters in most countries have warranted accuracies
    (usually on the long-wave), and a receiver, with a PLL locked onto this
    can give superb accuracies (some warrant 0.01ppm, and some go even
    further - in the UK, the 60KHz used for this, is maintained to better that
    2 parts in 10^12). In the US, WWVB, broadcasts a similar signal.
    These same transmitters are usually the ones carrying MSF time and date
    information, and the master source is usually now an atomic clock. Some of
    the receiver systems for these, have inputs for the distance to the
    transmitter, and give 'real time', compensated for this to mSec or better
    accuracies.
    The master clock for the GPS system, provides similar accuracies. A
    receiver, with local PLL, can be used again to get access to this clock.
    Mains provides good 'long term' accuracy, but in the short term is poor,
    and would not meet your requirements in this regard.
    So, if you have access to radio reception, look at using a local
    oscillator locked to the WWVB transmissions. Otherwise you will need to
    consider a high accuracy crystal, in a suitable oven. If internet
    connectivity is available, you could use a time server, and a local clock
    slaved to this (units to do this are off the sheld items).
    In the UK, one of th companies doing a range of products using these
    technologies, are:
    http://www.steatite.co.uk/downloads/time_freq_linecard.pdf

    Best Wishes
     
  10. Joerg

    Joerg Guest

    Hello Darren,
    This lets me assume that you need some kind of electronic triggering.
    1/60th of a second is to precise for a finger to push a button.
    Check out the sports markets. The devices for swimming relay contests
    may not quite offer 6 hours but equipment for marathons or triathlons
    should. It has been a while since I did competition swimming but I
    vaguely remember that the stuff mostly came from the major watch
    companies, usually from Switzerland.

    Regards, Joerg
     
  11. I had thought that maintaining an accumulated deviation of no greater
    than 1/60 sec in 6 hours is about like 24 seconds/year or 2 seconds a
    month. This is <1ppm drift. Without being temperature stable, this
    is not so easy, is it?

    Jon
     
  12. Mike Monett

    Mike Monett Guest

    Just checking the math: 1/(6*3600*60)=7.716E-7

    You are right. That may be difficult without an oven.

    Darren's spec may be a little tight. Normally, people who need to measure to
    that precision already know the methods and where to get the needed
    equipment.

    The next question : what is he measuring that is that stable? I don't know of
    anything that is expressed in seconds with <1ppm stability, except perhaps
    gps. But if it involved gps, he'd already have the answer to his question.

    Mike Monett
     
  13. Asimov

    Asimov Guest

    "2.com" bravely wrote to "All" (24 Jun 05 09:35:29)
    --- on the heady topic of "Wanted: A Very Accurate Timer"

    Se> From: 2.com
    Se> Xref: aeinews sci.electronics.design:24723
    Se> sci.electronics.repair:51346

    Se> Can I get recomendations for the most accurate electronic timer that I
    Se> can buy?

    Se> It must to be accurate to within 1/60th of a second over the course of
    Se> 6 hours.

    Se> Is something like this commercially available, or will I have to build
    Se> it, or have someone build it?

    Se> Any advice would be appreciated.

    Se> Thanks a lot.


    Darren,

    A typical lcd wrist watch with an alarm has quartz crystal precision.
    What sort of use are you in need of a timer for? Cooking eggs? What?

    A*s*i*m*o*v

    .... Acme Corp: Unlimited credit for disadvantaged coyotes.
     
  14. quietguy

    quietguy Guest

    In order to be sure of the accuracy that you are seeking, I presume the
    timer woul dhave to have a readout in the order of 1/100's of a second.

    Since this sort of accuracy is common in timing many sporting events (eg
    swimming, motor racing, running etc) a chat with the local swimming club
    etc might give you some leads to sources

    David
     
  15. NSM

    NSM Guest

    You can pick up a Radio Shack Model 100 from $5 and up on eBay. There is
    free software that will give you 8 separate accurate lap timers on that, one
    for each function key. It runs off 4 AA cells.

    N
     
  16. 6 hours would be 6 x 3600 x60 units = 1,296,000 or better than one part
    in 10^6.

    That is heading into TCXO crystal oven country.
    Or possibly locking to a NIST radio source such as WWV or WWVB.

    Or, at the very least, a calibration from a traceable source.

    Loosen your spec.

    --
    Many thanks,

    Don Lancaster
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    voice: (928)428-4073 email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  17. Jim Adney

    Jim Adney Guest

    It's about one part in 13 million, so, yes, this is pretty difficult.
    You won't do this with a straight crystal oscillator, and I don't know
    if any of the GPS units actually give out a clock signal that's fast
    enough to measure 1/60 of a second.

    HP makes a 10 MHz ovenized crystal oscillator which is much more
    stable than this, however. There is one on ebay now for about $85.
    That's about as cheap as you are likely to find for this level of
    precision.

    Do you really need this much precision?

    -
     
  18. Richard H.

    Richard H. Guest

    You will certainly find what you need here, though whether it is within
    your budget may be another matter. They have units that are far better
    than 1ppm accurate. http://www.symmttm.com/

    Or, have you considered a simple PC application that syncs its time from
    NIST via the Internet using an NTP client? Virtually free and accurate
    to <10ms, as long as you can tolerate a net-connected PC.

    Or, perhaps a PC / system connected to a GPS receiver via the serial
    port (though I understand the time via the serial port may only have
    1-second resolution for many units, so homework is in order).

    Richard
     
  19. mike

    mike Guest

    Once you have this precision, you need some way to reliably use it.

    I always get a chuckle out of "Star Trek". They've got massive
    computers calculating precise timing, trajectories etc.
    but they always initiate it with an imprecise verbal command, "ENGAGE".
    mike

    --
    Return address is VALID but some sites block emails
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    ..
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  20. I'm sitting here looking at my homebuilt digital clock that is counting
    120 zero crosses of the AC line as its 1 second time base. Motorola
    processor. Do you need the absolute accuracy or would counting
    2,592,000 AC zero crosses do the trick?
    GG
     
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