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

[Tim Shoppa]

It does not take a large pickup coil to pick up the magnetic field of a
quartz watch movement tick.

Radio Shack used to sell suction cup "telephone pick up coils" but I doubt
they have them anymore. These piggybacked on a phone receiver. They are
still out there,
http://www.elliottelectronicsupply.com/camera-security-equipment/listening/telephone-pickup-coil-suction-cup.html

Just as effective is any unshielded mH-range inductor. e.g.
http://www.mouser.com/ProductDetail/Murata-Power-Solutions/13R336C/?qs=gLyyx31KZaCXYrPIar3DqA==

I work with e.g. Rick Campbell's R2 series receivers, which do AF filtering
using inductors and these pick up the tick, tick, tick from my watch clear
as day from over a foot away. Back when I had a CRT computer monitor on my
desk, they picked up the flyback and deflection frequencies real well.

Tim.


On Wed, Apr 16, 2014 at 1:51 PM, Chris Albertson
<albertson.chris at gmail.com>wrote:

> The first sensor I'd think of if I wanted to measure a wrist watch would be
> a microphone.  Listen for the tick.  You'd need a good quality
> preamplifier.  Place the watch directly on top of the microphone then the
> mic in a closet with a blanket  on it.
>
> Good quality studio microphones are very, very sensitive.  At home with two
> doors shut my condenser mic picks of the motor in the fridge, wall clock
> ticks and the nearly silent fan motor in computer 20 feet away.    Then in
> post processing software I can find and identify the frequency components
> of each of those the remove most of the signal.   I'm not by any means an
> audio pro and I'm using entry level recording gear.   I'm making digital
> recording but for precision timing you'd need to use the analog signal
> after a pre-amplifier and apply a sharp bandpass analog filter.
>
> About using a coil, I'd assume they use one with many thousands of turns,
> maybe 100x more then a crossover coil.  and place the watch, coil and
> signal conditioning amplifier all in a faraday shield and apply a powerful
> analog filter.   But even if this works it needs a battery powered watch,
> it couldn't pick up a purely mechanical movement.
>
>
>
>
>
> I was all set to
>
>
> On Wed, Apr 16, 2014 at 6:21 AM, Ulrich Bangert <df6jb at ulrich-bangert.de
> >wrote:
>
> > Tom,
> >
> > can you explain what exactly you understand by "a large coil of wire"?
> >
> > Did you make the easurements on the Junghans with a DIY sensor or with
> one
> > of the commercially available?
> >
> > 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.
> >
> > Best regards
> >
> > Ulrich
> >
> > > -----Ursprungliche Nachricht-----
> > > Von: time-nuts-bounces at febo.com
> > > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Tom Van Baak
> > > Gesendet: Dienstag, 15. April 2014 15:53
> > > An: Discussion of precise time and frequency measurement
> > > Betreff: Re: [time-nuts] Measuring the accurcy of a wrist watch
> > >
> > >
> > > > Some research has shown that there is an comparable instrument for
> > > > ANALOG quarz watches. As far as I understand it does not
> > > try to detect
> > > > the quarz frequency but detects magnetic pulses from the
> > > step motors
> > > > that move the hands of the watch.
> > > >
> > > > Has anyone of you ever tried to do this in a time nuts laboratory?
> > >
> > > Ulrich,
> > >
> > > Yes, this works well, for both those with seconds hands (one
> > > magnetic pulse per second) and those with only minute/hour
> > > hands (one or two steps per minute). A large coil of wire is
> > > all you need. Have a look at the watch timing tools and
> > > sensors at http://www.bmumford.com/microset.html or
> > > http://www.bmumford.com/mset/modelwatch1.html
> > >
> > > Here's an example using a magnetic sensor:
> > > http://leapsecond.com/pages/Junghans/
> > >
> > > /tvb
> > >
> > > _______________________________________________
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>
>
> --
>
> Chris Albertson
> Redondo Beach, California
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