[time-nuts] Measuring the accurcy of a wrist watch

Thu Apr 17 22:07:45 UTC 2014

Hello,

I've seen that on a forum (in french sorry) :
http://www.forum-mdp.com/t16731-un-chronocomparateur-pour-petit-budget

It's an application for iPhone called "Kello", look at the picture and you will understand. The most difficult part seems to find the right position of the microphone. 

Claude

On Thursday, 17 April 2014, 19:55, DaveH <info at blackmountainforge.com> wrote:

Something to consider is that most pickups are biased with a fairly strong
magnetic field.

Don't know if this would cause any damage or changes in operation of a
mechanical watch but something to consider...

http://www.guitarnuts.com/wiring/pickups.php

Dave

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Ulrich Bangert
> Sent: Thursday, April 17, 2014 01:15
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] Measuring the accurcy of a wrist watch
> 
> Chris,
> 
> I do not own a guitar with single coil pickups but I will 
> surely give it a
> try to find out whether the humbuckers of my Gibson Firebird 
> & SG Standard
> will also do the trick!
> 
> Best regards
> 
> Ulrich
> 
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com 
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Chris Albertson
> > Gesendet: Mittwoch, 16. April 2014 20:56
> > An: Tom Van Baak; Discussion of precise time and frequency 
> measurement
> > Betreff: Re: [time-nuts] Measuring the accurcy of a wrist watch
> > 
> > 
> > I just did an experiment.  Place a simple quartz movement 
> > wrist watch on top of a Fender Stratocaster guitar.  I get a 
> > very strong and easy to detect signal.  A loud and sharpt 
> > "ping" once per second.  More then 1 volt
> > peak to peak.   I can cancel almost all the background hum 
> > and hiss in the
> > normal way by using the selector switch on the guitar.
> > 
> > The guitar has a pickup coil with many thousands of turns of 
> > #40 wire.  With the selector with at #2 position there is a 
> > second coil some inches away that is wound in the opposite 
> > direction and the two are added canceling any field that is 
> > filing the room.
> > 
> > I tried the same with a wall clock and all I had to do was 
> > hold the clock an inch away.  The wrist watch was placed on 
> > top of the strings a few mm above the bridge PU.
> > 
> > These is likely about 3 oz of #40 magnet wire on a guitar PU. 
> >  If I were building a sensor I'd do it just like the guitar.  
> > one coil to pick up the signal and another identical coil 
> > some inches away to to pick up ambient "noise" and then wire 
> > the two in parallel but in anti-phase.
> > 
> > If yu happen to have a guitar around, you have a watch sensor.
> > 
> > 
> > On Wed, Apr 16, 2014 at 10:43 AM, Tom Van Baak 
> > <tvb at leapsecond.com> wrote:
> > 
> > > > Tom,
> > > >
> > > > can you explain what exactly you understand by "a large coil of 
> > > > wire"?
> > >
> > > Sorry, by large I meant a large number of turns; the coil 
> itself is 
> > > quite small. Rather the winding one myself I just used the 
> > pickup coil 
> > > from an old cheap plastic self-impulsed pendulum clock. 
> The wire is 
> > > extremely fine and there must be thousands of turns since 
> the spool 
> > > diameter is only 15-20mm and the net resistance is 3.5k. 
> > Here are some 
> > > iPhone photos I just
> > > took:
> > >
> > > http://leapsecond.com/pages/Junghans/coil.htm
> > >
> > > > Did you make the easurements on the Junghans with a DIY 
> sensor or 
> > > > with
> > > one
> > > > of the commercially available?
> > >
> > > Both. The commercial ones sold by Bryan Mumford are 
> excellent; his 
> > > instrument includes signal conditioning, adjustable high 
> gain, and 
> > > other useful features. It's meant for watchmaker types with no 
> > > electronics background. It works perfectly out of the box.
> > >
> > > The Junghans wristwatch is extremely well engineered for 
> > long-life and 
> > > the leaked magnetic signal is the weakest of any watch I've 
> > measured. 
> > > Still, it can be measured. The placement of the pickup 
> coil on the 
> > > watch face needs to be optimized for best "reception", or any 
> > > reception at all for that matter.
> > >
> > > By contrast, a typical AAA-battery desk/wall quartz clock 
> movement 
> > > generates a huge magnetic signal. It is so clean that you 
> > can clearly 
> > > see both the start (+) of the impulse and the end (-) of 
> > the impulse 
> > > about 30 ms later. In fact I suspect it's actually 31.25 
> > ms, or 1/32 
> > > s, since that's 1024 cycles of a 32.768 kHz oscillator. See:
> > >
> > > sensor placement: 
> > > http://leapsecond.com/pages/Junghans/quartz-clock.jpg
> > > output to scope: http://leapsecond.com/pages/Junghans/coil-aa.gif
> > >
> > > > I have made some basic tests with a coil coming from a 
> > loudspeaker's
> > > cross
> > > > over network. It has a few hundred windings, R=1.3 Ohms, 
> > 2.3 mH, but 
> > > > the only thing i receive with this coil is a strong 10 Mhz 
> > > > signal...perhaps
> > > no
> > > > real surprise in a time nuts laboratory.
> > >
> > > I suspect your 1.3 ohms means the number of turns is far 
> too low. I 
> > > don't see any RF here, nor even very much 50/60 Hz.
> > >
> > > /tvb
> > > _______________________________________________
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> > >
> > 
> > 
> > 
> > -- 
> > 
> > Chris Albertson
> > Redondo Beach, California 

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