[time-nuts] Measuring the accurcy of a wrist watch
df6jb at ulrich-bangert.de
Thu Apr 17 08:14:39 UTC 2014
many thanks for your help. Will give it a new try over Eastern!
> -----Ursprüngliche Nachricht-----
> Von: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] Im Auftrag von Tom Van Baak
> Gesendet: Mittwoch, 16. April 2014 19:44
> An: 'Discussion of precise time and frequency measurement'
> Betreff: Re: [time-nuts] Measuring the accurcy of a wrist watch
> > 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:
> > 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:
> output to scope: http://leapsecond.com/pages/Junghans/coil-aa.gif
> > I have made some basic tests with a coil coming from a
> > 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.
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