First atomic clock wristwatch (2003)

Add to that the gym membership you will need to get fit enough to carry it around... and the chiropractor bills for when you realize you weren't fit enough after all.

mikewarot3• 5 years ago

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.

tvb10• 5 years ago

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.

mikewarot3• 5 years ago

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?

Animats• 5 years ago

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...

avalys• 5 years ago

More like "armwatch" I'd say.

obilgic• 5 years ago

What are the current use cases for atomic clocks?

formerly_proven• 5 years ago

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.

SAI_Peregrinus• 5 years ago

Also GPS (and other GNSS system) satellites themselves have atomic clocks.

tyingq2• 5 years ago

Low latency time source for stuff like Spanner that appreciates times that are the same across disparate data centers?

jdsully• 5 years ago

They have applications in the database space, e.g. see Google's spanner: https://www.theverge.com/2012/11/26/3692392/google-spanner-a...

jdxcode• 5 years ago

how much does it weigh?

tvb10• 5 years ago

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• 5 years ago

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• 5 years ago

Less than the embarrassment of being the only person on your block without one.

mikepurvis3• 5 years ago

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/

systemvoltage• 5 years ago

I am realizing how ordinary my childhood was.

mikepurvis3• 5 years ago

I know! Three atomic clocks riding in the middle and the kids in the back playing on a GameCube.

serf• 5 years ago

as a track marshal that routinely denies track entry (probably every single event) due to inappropriate battery mounting and wire mismanagement, these pictures terrify me.

It's a cute experiment with the kids, and i'm glad they got away without injury -- but on the other hand i've witnessed first hand what a lead battery that is floating around the cabin can do during a wreck -- and what I witnessed was, sadly, deadly for the driver.

single orientation nylon straps that are strapping heavy square objects against foam cushioned seats and sandwiching the chaos with human meat on both sides. It's a recipe for disaster regardless of what vector the force of the impact comes from -- and that's ignoring the batteries.

Please folks , when you drive a vehicle the heavy stuff gets strapped behind a bulkhead at the front or rear of the car, or atop the car with appropriate and well-tested strapping & mounting equipment.

Don't risk your life for the sake of convenience.

throwaway0a5e• 5 years ago

Do you honestly expect these people to add proper tie down points to the floor of a minivan for a one time trip?

The batteries are behind a seat row, the stuff in the seat is strapped in, the loose stuff is in the pass front foot well per OSHA guidelines (I figure most here worship at that altar). It'll be fine. They're not tracking the minivan.

I know that every time something like this is posted everyone likes to swoop in and talk about how X or Y is unsafe and you need eye protection every time you pick up a screwdriver and fall protection every time you even glance sideways at a step ladder because that's a way to score easy virtue points but it just comes across as tone deaf posturing. They aren't driving the van around like this 40hr a week for an entire career likewise it is not reasonable to expect them to implement a tie down solution that scales to that level.

joshu• 5 years ago

i tapped a kwall in a drift car (as one does) and the battery detached and shattered.

that was fun.

dang• 5 years ago

If curious see also

2014 https://news.ycombinator.com/item?id=7596922

2010 https://news.ycombinator.com/item?id=1870559

tvb10• 5 years ago

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• 5 years ago

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).

xkeysc0re• 5 years ago

How hard are cesium clocks to maintain / repair? I've seen some listed online for ~1k with various startup errors and always thought it'd be fun to fix one up, but I'm very much an entry level atomic clock enthusiast!

7373737373• 5 years ago

Have you had any encounter with astronomical interferometers?

deanmen• 5 years ago

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• 5 years ago

Note that bathyshawaii.com is likely no longer owned by the maker, and it most certainly is NSFW (oh, keep scrolling).

Teknoman1172• 5 years ago

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• 5 years ago

Only $5,100.20 from Mouser

https://www.mouser.com/ProductDetail/Microchip-Technology/09...

hengheng• 5 years ago

It draws quite a lot of power. From what I remember, the lipo battery required for 16hrs w/ no display would be the same size as the already chunky module itself, requiring wristband integration. Better to have a quartz oven and fire up the CSAC only once per hour as a reference, still yielding one factor of 10 in precision.

All in all it's better suited for a nice pocket watch with a 10MHz out connector. Any takers at 15k$+?

peterfisher• 5 years ago

"When engineering doesn't involve product or design"

amenghra2• 5 years ago

Leaves car full of batteries and cables running in front of a lodge for two days. If this were 2020, every three letter agency would be surrounding the place.

tvb10• 5 years ago

I anticipated that, so I had relativity books and physics magazines with pictures of Einstein on the front seat just in case we got stopped and the officer wanted a quick lesson in the fun of measuring time dilation. It was 2005, the 50th anniversary of the first cesium clock, the 100th anniversary of the theory of relativity, so it was also a current news topic.

Actually, a three letter agency did ask me what was going on: NPS, the National Park Service! But they kindly allowed us to park in front of the Lodge for the weekend. The advice I was given by old timers was to refer to the electronics simply as accurate clocks instead of atomic clocks or cesium clocks because many people false trigger on words like cesium or atomic. You'll notice that the official name on the front panel of a 5071A is "Primary Frequency Standard".

amenghra2• 5 years ago

Love it!

What's the cheapest clock you can purchase (used or new) where you can still do a similar experiment (i.e. that's accurate enough to measure dilatation over a day/week/month period of time)?

mothsonasloth• 5 years ago

This is interesting, I would like to get an Atomic Clock (5071A Primary Frequency Standard), however I can't seem to find any in the UK (Ebay, LocalEbay or other places)

Are they a restricted item because of the radio-isotope?

fsh• 5 years ago

The Cesium isotope used in atomic clocks (133Cs) is not radioactive. This seems to be a common confusion between "atomic" and "radioactive".

tvb10• 5 years ago

Look for any vintage caesium clock made by National, Varian, Hewlett-Packard / Agilent / Symmetricom / Microsemi / Microchip, FEI, FTS / Austron / DATUM, Oscilloquartz, and maybe others. None of them are a restricted item because of a "radio-isotope". Again, cesium 133 is not a radioactive isotope. Atomic timekeeping is based on ultra-precise quantum mechanics, not random nuclear radioactive delay.

Just take your time. Some of us look for months and even years before we find one worth the eBay risk.

There is one fact to consider. I have heard that the 5071A clock is still ITAR classified. It's not because of "atomic" or "cesium", but because the internal design is so advanced that the US decided it was essentially like a military weapon.

If in doubt look for vintage models like 5060, 5061, 5062, or 4050, 4060, 4065 instead of the still current model 5071.

bjeds2• 5 years ago

Please tell me more about your atomic clock. Which one did you eventually buy, how much did it cost, and how do you use it?

Dirlewanger• 5 years ago

Do these "atomic" clocks that get synched by an external ER source account for the (minute) travel time of said ER source? I'm assuming they do.

xtiansimon• 5 years ago

Wolverine is your brother-in-law? Dude. You better be good to her.

First atomic clock wristwatch (2003)

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