[time-nuts] Time Interval Counter(?) for high-precision watch measurement

Tue Sep 8 20:20:18 UTC 2020

I have seen, many years ago, a watch/clock tester that picked up the 32768
Hz signal with a ferrite coil and displayed beat frequency against its
internal standard by rotating a ring of LEDs. It was a cheap handheld
device : I can see similar devices online which are more expensive and are
equivalent to the microphone-based devices used for mechanical watches.

On Tue, Sep 8, 2020 at 9:11 PM Raven L <cuervamellori at gmail.com> wrote:

> The pickup I use (a Seiko DM-1) is inductive. It picks up the magnetic
> field from the motor impulse that drives the hands. It works very similarly
> to electric guitar pickups. I have used a piezo microphone (using the
> microphone from a commercial mechanical watch timer), but the precision is
> far worse - the "tick" sound is only localized to a couple of milliseconds
> at best, rather than tens of microseconds from the inductive pickup.
>
> Thanks to everyone for all the guidance so far!  I'm learning a lot very
> quickly - I have a long reading list already lined up for tonight.
>
> On Tue, Sep 8, 2020, 3:58 PM Warren Kumari <warren at kumari.net> wrote:
>
> > On Tue, Sep 8, 2020 at 3:15 PM djl <djl at montana.com> wrote:
> > >
> > > Sort of eavesdropping... you might try a piezoelectric pickup,
> available
> > > cheap on epay for guitars, etc. Looking at the actual motion kick of
> the
> > > hand(s)?
> >
> > I have one of these for mechanical watches:
> https://one-of.com/accuracy-2/
> >
> > It works nicely for tracking / accuracy of my mechanical watches - it
> > uses a piezo for pickup, and hooks up to an iPhone / iPad (presents
> > itself as a microphone). It reports on "accuracy" and amplitude, and
> > allows me to save a "library" of watches so I can monitor them over
> > time.
> > Of course, this of for mechanical watches, and so "accuracy" is fairly
> > relative ( COSC-certified chronometers must accurate to within -4/+6
> > seconds a day).
> >
> > I just tried it with a Citizen Eco-Drive quartz (hoping that it might
> > pick up the stepper "tick"), but it doesn't even detect that a watch
> > is on the sensor....
> >
> > W
> >
> > > Don
> > >
> > > On 2020-09-08 11:59, Raven L wrote:
> > > > Hi Bob, thanks very much for all the info!
> > > >
> > > > You're right that my input signal is pretty crummy - if anything you
> > > > overestimate it. Eyeballing it on the scope, the edge is not
> > > > particularly
> > > > defined at all - resolution better than a couple of microseconds just
> > > > isn't
> > > > possible. I've typically used gate times in the 10^4 to 10^5 seconds
> > > > range
> > > > (though typically collecting a measurement each second and doing the
> > > > gating
> > > > myself in software, as modern watches have multi-millisecond
> phenomenon
> > > > that are interesting to study in the 1 to 100 second range).  I have
> > > > tried
> > > > picking up electrical signals from the actual contacts going from the
> > > > IC to
> > > > the motor, but even then the cleaner edge I got wasn't worth the
> > > > trouble.
> > > >
> > > > I took an initial pass through the manuals of the models you
> mentioned,
> > > > I
> > > > really appreciate the guidance. (and the well-deserved correction on
> 2g
> > > > tipover for AT crystals - I'm not sure what I was thinking when I
> wrote
> > > > that but my notes confirm I was way off). I do hope to move up to a
> > > > basic
> > > > home lab running off CSAC and Rb standards in the next few years once
> > > > I've
> > > > seen all there is to see in wristwatches, but it looks like I have a
> > > > lot to
> > > > digest.
> > > >
> > > > One question if you know the answer on these 53131 and family models
> -
> > > > the
> > > > manual mentions that RS232 is talk-only to a printer. Are there
> > > > reasonable
> > > > tools out there for emulating a printer on a computer to pick up the
> > > > data?
> > > > Otherwise it looks like I would need to set up GPIB.
> > > >
> > > > On Tue, Sep 8, 2020, 1:12 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> > > >
> > > >> Hi
> > > >>
> > > >> First off, 0.001 seconds per year is ~ 3x10^-11. If you are talking
> > > >> about
> > > >> the 2G tip effect on a typical AT cut crystal that’s up around 2
> ppb.
> > > >>
> > > >> Next up, low frequency / small package crystals are (inevitably)
> > > >> relatively
> > > >> low Q devices. Low Q degrades ADEV performance / increases noise. If
> > > >> you *could* measure a high Q device to 3x10^-11 in one second, it’s
> a
> > > >> good bet that a low Q device will take 10X to 100X that amount of
> > > >> time.
> > > >>
> > > >> The stepper motor in a watch is a low frequency inductive device.
> The
> > > >> waveform out of it has a (very) limited bandwidth. Again another
> > > >> factor
> > > >> that
> > > >> will stretch out the time involved in the measurement. Your pickup
> > > >> coil
> > > >> likely
> > > >> also has some issues. ( That assumes the watch is still closed up. I
> > > >> would
> > > >> not
> > > >> recommend opening one up for testing …).
> > > >>
> > > >> So far, none of this is looking at the frequency counter. We’re just
> > > >> looking
> > > >> at the device you are trying to measure.
> > > >>
> > > >> Since there does not appear to be a need to get the data really
> > > >> quickly,
> > > >> none of this is a show stopper. It simply suggests that something
> out
> > > >> in
> > > >> the hundreds of seconds is likely to be the sort of gate time
> > > >> involved.
> > > >>
> > > >> If you are after 3x10^-11 on a 100 second gate, that comes out to a
> > > >> rather
> > > >> convenient 3 ns resolution. Better than that would be fine, but
> that’s
> > > >> roughly
> > > >> what you “need” to have.
> > > >>
> > > >> There are lots of low cost counters out there that will hit that
> sort
> > > >> of
> > > >> number.
> > > >> The HP 5334 and HP 5335 both come to mind. They should be available
> > > >> for
> > > >> < $200 (delivered). The TAPPR TIC would easily do the job for
> slightly
> > > >> more.
> > > >> The TIC probably would be easier to automate compared to running
> GPIB
> > > >> on the 5334 or 5335.
> > > >>
> > > >> Next step up would be something like a 53181 or 53131. They seem to
> > > >> start
> > > >> out around $300 (delivered). You now have an RS-232 serial I/O and a
> > > >> device
> > > >> that is about 10X better than your “need”.
> > > >>
> > > >> These are only a very small sample of the vast number of counters
> out
> > > >> there.
> > > >> The only reason for picking them is that they all are devices I have
> > > >> used
> > > >> a lot.
> > > >> They all (with some effort) can be used to do what you are trying to
> > > >> do.
> > > >>
> > > >> Fun !!!
> > > >>
> > > >> Bob
> > > >>
> > > >> > On Sep 7, 2020, at 6:23 PM, Raven L <cuervamellori at gmail.com>
> > wrote:
> > > >> >
> > > >> > Hello time nuts and greetings from the 10^-10 world of high
> > precision
> > > >> > wristwatches.
> > > >> >
> > > >> > I'm trying to set up a lab for automated watch measurement. I
> have a
> > > >> basic
> > > >> > GPSDO with a PPS and a 10MHz output. I use an inductive sensor to
> > pick up
> > > >> > the signal from the motor inside the watch.
> > > >> >
> > > >> > I've been using a basic digital oscilloscope to measure the
> interval
> > > >> > between the PPS and the watch signal.  The signal from the watch
> > has a
> > > >> > total rise time of about 10us to 40us, varying by watch, and rises
> > a few
> > > >> > volts above a noise floor of about 50mV. The oscilloscope does a
> > > >> > serviceable job but doesn't allow automated measurements and can't
> > be
> > > >> > driven by an external timebase. My goal is to make measurements
> > with a
> > > >> > precision of about 10us, with a goal of ultimately pinning down a
> > rate to
> > > >> > better than 0.001 seconds per year (initial testing shows this is
> > what I
> > > >> > need to resolve the effect of tipover on AT-cut MHz-range quartz
> > > >> crystals).
> > > >> >
> > > >> > Are there specific time interval counters or frequency counters
> that
> > > >> would
> > > >> > make this easier?  I've been looking at the SR620 as a candidate,
> > which
> > > >> > appears to be available used for around 2k USD, but wouldn't be
> > surprised
> > > >> > to learn if there was something that was a meaningfully better
> fit.
> > > >> Thanks!
> > > >> > _______________________________________________
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> > > >>
> > > >>
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> > >
> > > --
> > > Dr. Don Latham  AJ7LL
> > > PO Box 404, Frenchtown, MT, 59834
> > > VOX: 406-626-4304
> > >
> > >
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> >
> >
> >
> > --
> > I don't think the execution is relevant when it was obviously a bad
> > idea in the first place.
> > This is like putting rabid weasels in your pants, and later expressing
> > regret at having chosen those particular rabid weasels and that pair
> > of pants.
> >    ---maf
> >
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