[time-nuts] Cesium Mechanical Chronometer

[Dana Whitlow]

I've been looking at M21 photos, trying to decide if it has a single
balance wheel, or a
pair of contra-rotating balance wheels.  I just can't tell.

If it's a single wheel, then gently rocking the M21 movement about an axis
parallel to that
of the balance wheel seems like it could be a viable way to injection lock
the M21 to an
external standard.  This should require no modification of the M21 in any
way.  And if done
in a thoughtful way the M21 could probably even be wound in-situ.

Dana     K8YUM

On Fri, Jan 31, 2020 at 11:51 AM Dan Kemppainen <dan at irtelemetrics.com>
wrote:

> Hi,
>
> I agree with tom, winding may be an issue.
>
> If that could be overcome, would it be possible to injection lock the
> clock with a piezo or other small mechanical actuator? Something mounted
> to the clock body that 'pings' it periodically may all that's needed to
> pull it where you want it to go.
>
> One would think it would be nice to do this project without having to
> modify the clock significantly, or risk damaging it.
>
> If you do succeed I'd be interested in reading the results. A fun
> project, in my opinion.
>
> Dan
>
>
>
>
> On 1/30/2020 3:18 PM, time-nuts-request at lists.febo.com wrote:
> > Message: 7
> > Date: Thu, 30 Jan 2020 10:35:11 -0800
> > From: Tom Van Baak<tvb at LeapSecond.com>
> > To:time-nuts at lists.febo.com
> > Subject: Re: [time-nuts] Cesium Mechanical Chronometer
> > Message-ID:<e775549d-4368-2ade-e338-7e208e07f09e at LeapSecond.com>
> > Content-Type: text/plain; charset=utf-8; format=flowed
> >
> > That would be a fun project. There are examples of measuring a M21 on
> > Bryan's site:
> >
> > https://www.bmumford.com/mset/tech/chrono/
> >
> > Here are phase and ADEV plots for my M21:
> >
> > http://leapsecond.com/pages/m21/
> >
> > That page also shows you a typical chronometer rate card, which provides
> > the key "paper clock" advantage over using the clock dial alone.
> >
> > I use a piezo pickup to extract timing pulses from the clock. The audio
> > waveform isn't pretty but you can form a low jitter 1PPS out of it.
> > Laser sensors give a cleaner signal but are more difficult to use with
> > an M21.
> >
> > Running a GPS/CSAC + M21 in a master/slave arrangement should be easy,
> > although I don't know how you'll handle the rate card corrections.
> >
> > Running them in phase lock will be much harder. You can probably
> > discipline the CSAC from the M21 using RS232 commands to the CSAC. But
> > to discipline the M21 from the CSAC requires that you have a way to
> > dynamically adjust the rate of the M21 at ppm levels. That's going to be
> > tricky, given that high-end compensated chronometers like this are
> > specifically designed to be as immune to internal and external changes
> > as possible. One avenue may be the winding interval: notice the slopes
> > of the phase plot.
> >
> > The biggest problem I had with long-term data collection was re-winding
> > the chronometer. If you design a non-invasive auto-winder as part of
> > your project, please contact me.
> >
> > /tvb
>
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