[time-nuts] Cesium Mechanical Chronometer

[Bob kb8tq]

Hi

Keep in mind that these particular chronometers were designed (as best as
was possible) to be impervious to outside influences. Mag fields, rocking back
and forth, orientation changes all should have whatever the lowest impact you
could make them have.

Bob

> On Feb 1, 2020, at 9:58 PM, Ben Bradley <ben.pi.bradley at gmail.com> wrote:
> 
> I'm wondering about the balance wheel, if it's ferromagnetic (has iron
> or steel in it, which would probably make this idea not work), or if
> it's perhaps all aluminum or similar non-magnetic material. Adding a
> constant magnetic field from a coil and electric current source would
> provide a magnetic induction-induced drag on the balance wheel and
> slow it down (hopefully not so much that it stops). Setting the
> chronometer to normally run slightly fast would allow it to be slowed
> down and regulated by the strength of the magnetic field on the
> balance wheel.
> 
> On Sat, Feb 1, 2020 at 3:06 PM Bob kb8tq <kb8tq at n1k.org> wrote:
>> 
>> 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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>> 
>> 
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