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

Tue Sep 8 20:27:52 UTC 2020

Hi

Back … umm … errr…. a while ago ( = 1974) the standard approach was to
use an ultrasonic microphone to pick up the 32.768 KHz “audio” from the
crystal. We used Racal computing counters on the production line to “process”
the results.

Bob

> On Sep 8, 2020, at 4:02 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!
>>>>>> _______________________________________________
>>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>>> To unsubscribe, go to
>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>>> and follow the instructions there.
>>>>> 
>>>>> 
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>>> To unsubscribe, go to
>>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>>> and follow the instructions there.
>>>>> 
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>>> To unsubscribe, go to
>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>>> and follow the instructions there.
>>> 
>>> --
>>> Dr. Don Latham  AJ7LL
>>> PO Box 404, Frenchtown, MT, 59834
>>> VOX: 406-626-4304
>>> 
>>> 
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at lists.febo.com
>>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>>> and follow the instructions there.
>> 
>> 
>> 
>> --
>> 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
>> 
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at lists.febo.com
>> To unsubscribe, go to
>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
>> and follow the instructions there.
>> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at lists.febo.com
> To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
> and follow the instructions there.