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very accurate timer

Discussion in 'Electronic Design' started by fragget, Oct 12, 2006.

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  1. fragget

    fragget Guest

    Hello, this is my first post here so here it goes...

    I'm looking for a highly accurate timer, I need one that could measure a time in nanoseconds

    if possible. I figured this would not be impossible since the clockspeed of a modern

    computer is 3 Ghz, which means measuring a time up to a third of a nanosecond would be

    possible. However a nanosecond is also fine by me;P
    I really hope someone can help me out here on how to get such a component or how to make one;)

    Thanks in Advance;)

    Dave


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  2. Just buy one:
    http://www.thinksrs.com/products/SR620.htm
    Will cost you $5000 though, but if this is for work tell'em it'll cost
    you more than that to dick around trying to build something suitable.

    Dave :)
     
  3. Just waiting for Bill S to jump in with an ECL problem solver
    answer....


    martin
     
  4. John Larkin

    John Larkin Guest

    What are you trying to measure?

    John
     
  5. Guest

    ECL will get you a 500MHz clock. When I did it for real, we actually
    used Gigabit Logic's GaAs and an 800MHz clock, then interpolated
    between clock edges with analog ramps to get down to 10psec resolution
    - the jitter on our clock was about 60psec so the 10psec was entirely
    theoretical.

    The version I designed a few years later using ECLinPS and a 500MHz
    clock was to have used a 500MHz Vectron crystal oscillator with around
    1psec of jitter.

    John Larkin now sells stuff to do the job.

    http://www.highlandtechnology.com/DSS/V660DS.html
     
  6. Joerg

    Joerg Guest

    Hello Dave,

    Bill mentioned the digital + analog method which is what I'd do. If you
    feel uncomfortable around blazingly fast analog stuff either get help or:

    Run several fast counters in parallel but shift their clocks. For
    example, if your ECL counter runs 500MHz but you want a 500psec
    granularity you run four in parallel. #1 gets the straight clock. #2
    gets the clock delayed by 500psec, #3 delayed by 1nsec and #4 delayed by
    1.5nsec.

    They all receive the same start and stop signal. Of course, you'll have
    to look into the setup and hold stuff so you don't accidentally choke a
    counter. Now your PC needs to read the results of all four and then
    determine the exact timings by looking at which one started first, how
    many clock cycles it did, which one stopped last and how many cycles
    that one did. The readout process can be slow because now the counters
    are stopped.
     
  7. John Larkin

    John Larkin Guest

    You could now do EclipsLite to 2 GHz at least.
    That one interpolates a 40 Mhz clock! I just sold 8 of them to a guy
    who's going to shine a laser beam through turbine blades, time the
    interruptions, and figure out blade vibration modes.

    John
     
  8. Guest

    Frequency counters have gating circuits so that you can measure a pulse
    time.

    The HP5340A cost me $300 a decade ago. No idea what they go for today,
    but it should be less.
     
  9. Dave,

    before you start up to construct something on your own which is by FAR not
    trivial go out and buy one of the following devices:

    Racal Dana 1991 or Racal Dana 1992 or Racal Dana 1996 counters.

    These have a nominal 1 ns resolution for single shot time interval
    measurements. If you use their IEEE488 you get out some digits more and you
    can see that the rms jitter of the counter itself is in the order of 300 ps.
    These devices are no more build today but can be bought surplus at very
    cheap prices. Most of them are equipped with a high quality OCXO timebase.

    If you are out for a bit more resolution and want to spend some dollars
    more, go out and get yourself a HP/Agilent 53131 counter which has a nominal
    500 ps resolution. If you want even more resolution and spend more $s buy
    the HP/Agilent 53132 with nominal 150 ps resolution. Both models are from
    the current program.

    If you need to get better, choices start to get rare: A surplus HP5370A/B
    (no more build today) will give you a 20 ps resolution for single shots at a
    reasonable price. A Stanford Research SR620 will give you the same
    resolution but be prepared for a smaller shock when looking at the price
    tag.

    If you can avoid DON'T build something on your own. There are hundreds of
    ways to perform sub-ns timing measurement but you can spend months to years
    in order to learn the tricks that are necessary to make simple sounding
    theory work in reality.

    Best regards
    Ulrich Bangert
     
  10. Mike Monett

    Mike Monett Guest

    Hi Dave,

    If you can use averaging, you can count an accurate clock several
    thousand times and average the counts. This is how at least one of
    the HP counters worked. The rms error decreases with the square of
    the number of counts. This places a practical limit on the minimum
    error you can achieve before you run out of time, or the signal
    drifts.

    If you can use averaging, you can also use the Binary Sampling
    technique descibed below. This bypasses the square root averaging
    barrier. The example shown is a 1MHz square wave, and using this
    technique gave 1 picosecond rms jitter in one second.

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
     
  11. Guest

    This is good advice, but while we spent three years getting our
    prototype working, the interpolation system only needed a month or so
    of work.

    Our biggest single problem was caused by the printed circuit
    department, who "knew" that the ordering of the inner layers of a
    printed circuit board didn't matter, so had a six layer board made with
    the ground planes on layers 3 and 4, rather than 2 and 5 as I'd
    carefully specified in my release note to the printed circuit
    department.

    It took us months to work out why the board wouldn't work - every time
    I looked in on the engineer who was working on the board (nominally my
    boss at that point) I'd point out to him that he had the board layers
    stacked up wrong in his pile of documentation, but it took about six
    weeks before he drilled down through the board to check. Once the penny
    dropped, he sort of got the board working by replacing all the critical
    tracks with lengths of sub-minature coax (50VMTX, still stocked by
    Farnell) but we had to get another batch of boards made before we had
    anything that looked like a prototype.

    The two outer layers of the board weren't FR4 epoxy glass, but Teflon
    cloth bonded with isocynate resin, and the board were biggish - triple
    extended Eurocards, largely to accomodate mixed DIN41612 connectors
    with coax inserts - and they cost us about $1500 each. Populating them
    cost as much again.

    They'd be a lot cheaper today and - as John Larkin has pointed out -
    appreciably faster.
     
  12. Glen Walpert

    Glen Walpert Guest

    Another interesting option for better, from the "47uF capacitor"
    thread:

    http://www.acam.de/index.php?id=23&L=0

    Just buy an evaluation system rather than try to build a system on a 2
    layer board like the 47uF cap OP foolishly thinks he wants to do.
     
  13. On 13 Oct 2006 02:25:45 -0700,
    Really? 50vmtx didn't turn up anything useful at Farnell.

    robert
     
  14. Guest

    Try order code 157-284 or manufacturer's list number 5633JZZD - it's on
    page 59 of volume 2 of my Farnell catalogue.
     
  15. Guest

    There is a cuter variation on this called the vernier chronotron. See

    http://scitation.aip.org/getabs/ser...00030000003000159000001&idtype=cvips&gifs=yes

    which points to an article of that name in Review of Scientific
    Instruments -- March 1959 -- Volume 30, Issue 3, pp. 159-166 by Harlan
    W. Lefevre and James T. Russell of the Hanford Laboratories Operation,
    General Electric Company, Richland, Washington.

    I got to hear about it in 1970, when one of my colleagues at Plessey
    Pacific got talking about his Ph.D. project which involved building a
    similar instrument with bistables built with pairs of tunnel diodes.

    I'd known him - vaguely - when we were both Ph.D, students at
    Melbourne, both using the university mainframe for our - very different
    - projects. He was simulating his tunnel diode bistables and thought
    that he had proved that he'd made them designable. They were certainly
    very fast.
     
  16. John Larkin

    John Larkin Guest


    A 5370A or B can be had on ebay or from a broker for under $1000. They
    have 20 ps single-shot resolution and around 30 ps RMS jitter,
    typically.

    My friend Bernard did this one...

    http://www.greenfieldtechnology.com/datasheet/GFT2002.pdf

    John
     
  17. Joerg

    Joerg Guest

    Hello Bill,
    I like that term "millimicrosecond region". That must have driven the
    physicists among the readers crazy. Can't read the full paper, I wish
    they would make these public domain after such a long time.

    Ah, Plessey. Good old company. Before things folded I stocked up on
    their famous mixer SL6440. It has a dynamic range from here to the
    Klondike yet doesn't need a lot of L.O. power. It's a pity no other
    company bought the rights and kept producing it.
     
  18. Joerg

    Joerg Guest

    Hello John,
    Even rather mundane test equipment could possibly be capable after some
    mods. When I repaired the HP4191 here in the lab I found that it had two
    very nice 300psec timed samplers in there, plus triggered ramp
    generators with remarkable precision. Milled module enclosures, rigid
    coax and all the good stuff.

    Very pretty design! Did he have a pro do that enclosure? The only thing
    I wouldn't like is the buttons. Those tend to wear out quickly.
     
  19. Mike Monett

    Mike Monett Guest

    Resolution : 1ps
    Jitter : 30ps rms

    Why claim 1ps when the system jitter is so large? You are paying for
    useless digits. Averaging to improve the SNR would take forever, and the
    system would probably drift before the rms error got close to 1ps. So the
    resolution spec is meaningless. IMHO, the resolution spec should be >= rms
    jitter.

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
     
  20. Joerg

    Joerg Guest

    Hello Mike,
    That had me puzzled as well :)
     
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