[time-nuts] Cesium Mechanical Chronometer

[Bob kb8tq]

Hi

If the idea is to generate a rate card and keep it up to date ….. I think that
can be done with just the GPS. The CSAC really does not add a lot that
I can see to that case. 

Of course I may have (yet again) missed something ….

======

The very standard  / “old school” approach for this is a microphone on the case
of the M21. These days feed the mic preamp output into a cheap micro along
with the GPS info and away you go.  Spit the results out to a little OLED display
maybe …..

Bob

> On Feb 1, 2020, at 1:39 PM, Tom Bales <tob.starhouse at gmail.com> wrote:
> 
>> 
>> Many thanks for everyone's response on my cesium-synchronized mechanical
>> chronometer project.  I'll keep the group informed of progress.  Some
>> responses to your questions and suggestions:
> 
> 
>   - My current plan is to use a chronometer that has been adjusted for
>   rate and is close to dead-on.  Of course, they're never dead-on, and that's
>   why keeping track of the rate is important.  I haven't dismissed the idea
>   of actually disciplining the chrono from the CSAC, but since this chrono's
>   rate adjustment involves screws on the balance wheel (it has a free-sprung
>   helical balance spring without any means of adjustment), that would be a
>   great challenge.  Perhaps the best would be for the CSAC system to maintain
>   a "rate card" of the chronometer, so that when all the electronics fail,
>   and the user is left with only the chrono, at least they would have a
>   really good knowledge of its rate and variation.  Doing so would require a
>   feedback signal from the chrono, which could be acoustic or photoelectric.
>   The electronic rate card could be updated now and then by turning off the
>   sync impulse to the chrono and listening for the ticks to move relative to
>   the 1pps.
>   -  The chrono would need a bigger box in order to incorporate the
>   CSAC/GPS system, microcontroller, and--the biggest part--backup batteries.
>   That's part of the fun, and I'm thinking to mount the gimballed chrono in a
>   purpose-built enclosure that will hold everything.  Connections to the
>   chrono will have to be very flexible FFC or silicone wire.
>   - I thiink auto-winding is a definite requirement.  The engineering
>   challenge is to couple a small gearmotor to the winding system without
>   disabling the manual-winding system that uses a ratcheted key.  Winding
>   noise should be short in duration, so it probably won't affect the time
>   sync.  People have wound chronos by turning them upside down in the gimbals
>   and poking a key through a hole for a long time without any  big issues.
>   - Coupling to the chrono balance and escapement might be difficult, or
>   it might be easy.  If it takes hours or days to synchronize, that's OK, I
>   think.  My guess is that anything that generates a slight impulse in the
>   direction of the escapement detent or a torque pulse to couple to the
>   balance will work well enough--a tiny little linear or rotary
>   electromagnetic actuator should work.  We'll see.
>   - The Hamilton M21 chrono beats at 2Hz, so driving it with a 1pps signal
>   will probably work fine.
>   - The idea that TVB suggests of disciplining the CSAC to match the
>   chrono is fascinating, indeed.  Hadn't thought of that one.  It would be
>   the easiest way to keep the chrono and CSAC in sync, and it would still use
>   the traditional rate-card method of keeping track of the actual time.
>   Hmmmm.
>   - Yes, the CSAC modules are expensive!  Over $5k currently.  It seems
>   like during the evaluation period the company sold them "at a discount" in
>   order to build applications and sales (or so the court documents say).  Let
>   me know if anyone sees a gyneesium one on *bay.  I thought long and hard
>   before buying it, but idle hands are the devil's cash register.  (Oh,
>   oh!--now I have an excuse to buy an HP 53230!)  In my initial measurements
>   of rate (after GPS disciplining for 24 hours) the CSAC freewheels within
>   1.7ms/yr.  Probably good enough.  Needs longer testing.
>   - The M21 has a single balance wheel consisting of an Invar spoke and a
>   stainless steel ring (it was Hamilton's magical way of doing temperature
>   compensation to match the balance spring.  The Russian knock-offs have a
>   standard bi-metal split balance wheel.  The Hamiltons beat just about
>   anything in performance.  Besides, "Murica!".
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