[HN Gopher] First atomic clock wristwatch (2003)
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First atomic clock wristwatch (2003)
Author : dddddaviddddd
Score : 83 points
Date : 2021-01-25 20:45 UTC (2 hours ago)
(HTM) web link (leapsecond.com)
(TXT) w3m dump (leapsecond.com)
| avalys wrote:
| More like "armwatch" I'd say.
| obilgic wrote:
| What are the current use cases for atomic clocks?
| formerly_proven wrote:
| Adjusting clocks that aren't atomic.
|
| Cellular base stations used to have rubidium sources
| disciplined to GPS as a reference frequency for synthesis.
| AIUI, put the expensive, precise part in the base station, have
| the cheap handset lock onto that. Free accuracy. Not sure if
| they still do it that way. That's where all the cheap used
| rubidium sources on eBay come from.
| tyingq wrote:
| Low latency time source for stuff like Spanner that appreciates
| times that are the same across disparate data centers?
| notum wrote:
| Real men demand real time. Technology. Elegance. Tradition.
|
| HP Cesium line, the man's watch.
| tyingq wrote:
| For as little as $47,500 USD. https://www.ebay.com/itm/HP-
| Agilent-Keysight-5071A-US3930164...
| hinkley wrote:
| Warranty void if product is submerged in water over 100m deep,
| travels at greater than 30,000 km/s, or is taken into outer
| space.
| botto wrote:
| What about if approaching a super dense point where space-
| time warps?
| hinkley wrote:
| We can certainly add that clause.
|
| But might we suggest that if you do encounter such a
| scenario within the earth's atmosphere, that you should
| address that situation immediately? Otherwise there may
| soon be no circuit court judges available to hear your
| case.
| notum wrote:
| Spacetime anomalies are covered only from the observer's
| reference point. Doh!
| deanmen wrote:
| There is an actual atomic clock watch on the market that is a
| little bit smaller:
|
| https://www.hodinkee.com/articles/introducing-the-bathys-ces...
| mikestew wrote:
| Note that bathyshawaii.com is likely no longer owned by the
| maker, and it most certainly is NSFW (oh, keep scrolling).
| Teknoman117 wrote:
| These days it's not as complicated. Microchip has a line of
| "chip scale" atomic clock modules you could use to make one.
| Not sure what the pricing is.
|
| https://www.microsemi.com/product-directory/clocks-frequency...
| sjruckle wrote:
| [Only $5,100.20 from
| Mouser](https://www.mouser.com/ProductDetail/Microchip-
| Technology/09...)
| jdxcode wrote:
| how much does it weigh?
| tvb wrote:
| About 70 lbs (30 kg), so not difficult to lift or carry with
| two hands. But it took a real man (my brother-in-law,
| construction worker) to hold it outstretched like you see in
| the photo.
| nullc wrote:
| And all this time I felt like a total wimp for finding that
| photo really daunting. 5071a is lighter with the batteries
| out, but not that light! :)
| stakkur wrote:
| Less than the embarrassment of being the only person on your
| block without one.
| mikewarot wrote:
| Cesium beam atomic clocks rely on an internal supply of cesium
| metal contained in an oven. This supply usually lasts 5-10 years,
| after which the tube containing the physics package needs to be
| replaced. They are interesting to work on, once you get the hang
| of it, you can diagnose them in an hour or two.
|
| Rubidium cell atomic clocks, on the other hand have a vapor cell
| which is a closed tube, and doesn't get expended. Thus Rubidium
| clocks have far longer service lives. You can find them surplus
| on Ebay for less than $200. The stability is slightly less, but
| still far more accurate than most electronics technicians need to
| do adjustments and calibrations.
|
| [Update - Far more than you ever thought you wanted to know about
| atomic clocks] The main difference between an atomic clock and a
| quartz crystal oscillator is that in a crystal oscillator, you
| have a continuous signal that is generated from the circuitry and
| passed through the crystal, and amplified in a feedback loop. A
| crystal oscillator can be made with a single transistor and a few
| passive components.
|
| In an atomic clock, there is a stabilized quartz oscillator,
| which actually keeps time, but it is then steered up or down in
| frequency slightly by using a harmonic of that frequency, along
| with a very slight amount of frequency modulation, to inject into
| a cavity containing the atom of interest.
|
| In Cesium (Caesium outside the US) beam clocks, the physics
| package is all packed inside a large vacuum tube. Inside the tube
| is an oven with microscopic holes in the top containing cesium
| metal, the oven is heated to about 200 degrees. A small stream of
| individual atoms exit. Those atoms pass through a magnetic field
| which diverts them according to spin. The atoms then drift
| through a microwave chamber where there is a 9.129 Ghz signal
| imparted. If the frequency of the signal exactly matches the
| natural resonance frequency of the cesium atom, its spin will
| flip.
|
| On the other side of the drift chamber, a second magnet selects
| only those atoms which have flipped state, all other atoms are
| diverted and trapped. Then the atoms encounter a hot wire with
| high voltage where they are ionized, them passed through another
| magnetic field which is a mass spectrometer, this serves to
| filter out impurities and contaminant that are present in the
| tube. There is a fine slit that allows entrance only to the
| cesium beams (now regardless of their spin), and they imping upon
| a plate in a photomultiplier.
|
| The net result of all this physics is that if you have exactly
| the correct frequency, there is a DC current of a microampere or
| so output, too high or too low, and the output drops quickly. The
| line width is on the order of a few hertz.
|
| To sample against this, the quartz oscillator is multiplied in
| frequency the appropriate amount using multipliers and phase
| locked loops, and combined with a very small amount of frequency
| modulation at 137 hertz.
|
| The DC output of the tube varies with the modulation... if it
| increases with increasing frequency, the reference clock is too
| slow... if it is out of phase, the reference clock is too fast,
| and if you get a 274 hz second harmonic, you are right on
| frequency.
|
| They take about 10-20 minutes to warm up and lock.
|
| There are some adjustments, and it is possible to have them
| locked on the wrong frequency if you aren't careful.
|
| Cesium clocks, used, are on the order of $5000
|
| --
|
| Rubidium clocks are easier to use... they are also quartz
| oscillators probing with FM signals, but instead of a stream of
| atoms, there is a lamp with one isotope of rubidium which is then
| passed through a chamber with microwaves and the other isotope of
| rubidium... if the frequency is just right, the light
| transmission dips by 1%, and this is used to lock the oscillator.
|
| Rubidium standards are about 10 times less stable, but have far
| longer service lives, and can be had used for about $200.
| tvb wrote:
| Cesium beam atomic clocks are available on the surplus market,
| though not nearly as common or as cheap as Rubidium. The clock
| in the photo is model hp 5071A and I got it on eBay 20 years
| ago. The tube will last on the order of 7 to 20 years with
| continuous use, depending on which type of tube is installed.
|
| This was one of the atomic clocks I used for the time dilation
| / relativity experiment linked at the bottom of the page.
| mikewarot wrote:
| I loved that story back then... with the advent of optical
| lattice clocks, and smaller sources, etc... have you done an
| update to the experiment?
| tvb wrote:
| Yes, the original Mt Rainier experiment in 2005 caught the
| attention of Stephen Hawking and I was asked to repeat the
| experiment for his PBS/BBC TV series in 2016. It was mid-
| winter up here in PNW so we used Mt Lemmon in Arizona
| instead:
|
| http://www.leapsecond.com/great2016a/
|
| And in 2018 I was asked to be part of a "time travel"
| episode on a History channel show. We used Palomar Mountain
| in California:
|
| http://www.leapsecond.com/great2018a/
|
| Each experiment was a little different; different
| combination of clocks, different audience, different
| mountain, different elevations, different latitude, etc.
| Animats wrote:
| You can get a rubidium time standard in an IC package.[1] It's
| about 50mm square, comparable to a CPU chip. Talks USB. Error
| is under 100ns/day. Time servers should have one.
|
| [1] https://www.mouser.com/new/microchip/microchip-
| macsa5x-atomi...
| mikepurvis wrote:
| Don't miss a previously-featured-on-HN article from the same site
| about taking an atomic clock up Mt. Rainier to check if you would
| actually gain billionths of a second as predicted by GR:
| http://www.leapsecond.com/great2005/
|
| And pictures: http://www.leapsecond.com/great2005/tour/
| dang wrote:
| If curious see also
|
| 2014 https://news.ycombinator.com/item?id=7596922
|
| 2010 https://news.ycombinator.com/item?id=1870559
| tvb wrote:
| Thanks, DanG. Author here. I happen to be reading HN right now
| if anyone has questions about cesium clocks or using them to
| demonstrate relativistic effects. This is just a DIY hobby of
| mine.
| ajford wrote:
| It's a bit melancholy now with the collapse and all, but just
| wanted you to know a paper copy of that image was taped up on
| the Clock Room wall at Arecibo Observatory when I left
| (somewhere in 2015).
| [deleted]
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