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

DaveH info at blackmountainforge.com
Thu Apr 17 12:37:27 EDT 2014


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 
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
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> 
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