9 ms·
Chip Scale Atomic Clock (CSAC)
- avsteele 5y agoThey put a tiny Cs vapor cell in there? That's pretty neat.
- denton-scratch 5y agoIs it Caesium? I thought Rubidium fountains were easier to minaturise. I can't see where I can find out how the device is made - there's not much detail. Ah - you're right, it's Caesium. https://ww1.microchip.com/downloads/en/DeviceDoc/A3405FE2-C1F7-435A-A90FD2DC0403621B.pdf https://ww1.microchip.com/downloads/en/DeviceDoc/A3405FE2-C1... I used to run an NTP server, in the pool. But it was stratum 2; it would stroke my ego to run a stratum 1 server. But 3.5 kilodollars: I'll wait.
- mikewarot 5y agoRubidium fountains actually launch ions up against gravity so that they are in free fall (in a vacuum, with magnetic fields nulled out) during their sample period. That's not something I can see being miniaturized, or put in use on a moving platform.
- fsh 5y agoAtomic fountains use neutral atoms. It is almost impossible to see the effect of gravity on ions since a single stray electron anywhere in your system creates a way larger Coulomb force. Fountains need to have a minimum size in order to achieve a sufficient flight time when throwing the atoms up on a ballistic trajectory. Obviously, they also have to be very carefully aligned with respect to gravity.
- makomk 5y agoYeah, though apparently they have a tendency to slowly leak and cause the parts to fail - very limited lifespan.
- fsh 5y agoNo, the CSAC is a Rubidium standard. It measures the ~6.8 GHz ground-state hyperfine splitting in 87Rb using coherent population trapping with a modulated 780 nm diode laser. This signal is used to lock the local oscillator to the atomic transition frequency. And all that in a tiny package with 120 mW power consumption. Pretty cool stuff! Edit: At second glance, it seems liks they are actually using Cesium now (some other demonstrators use Rubidium). The principle is the same, but the hyperfine splitting is 9.192631770 GHz (by definition) and the laser wavelength is 894 nm.
- Workaccount2 5y agoThis is borderline retro encabulator talk.
- avsteele 5y agogreat thanks
- exabrial 5y agoIf atomic clocks coyote be miniaturized/commoditized that has some pretty big implications in solving distributed transaction problems.
- BiteCode_dev 5y agoHere it is, next to a coin, for scale: https://www.microchip.com/en-us/products/clock-and-timing/atomic-clocks/_jcr_content/root/responsivegrid/container/cardgrid/card1/image.coreimg.png/1606931390716/r1-v1-200106-ftd-graph-csac-fig1.png https://www.microchip.com/en-us/products/clock-and-timing/at...
- wrmwrm 5y agoMore details for those who are interested. The physics package is about the size of a grain of rice. https://www.nist.gov/system/files/documents/2017/05/09/VCAT-NIST-CSADemo.pdf https://www.nist.gov/system/files/documents/2017/05/09/VCAT-... Many teams around the world are actively developing improvements on this technology. https://www.nist.gov/news-events/news/2019/05/nist-team-demonstrates-heart-next-generation-chip-scale-atomic-clock https://www.nist.gov/news-events/news/2019/05/nist-team-demo...
- geenew 5y agoThese can help against GPS spoofing / jamming by identifying false signals and allowing rapid resynchronization: https://www.army.mil/article/88361/Miniaturized_atomic_clock_to_support_Soldiers_in_absence_of_GPS/ https://www.army.mil/article/88361/Miniaturized_atomic_clock... Also related, NASA has a spaceborne atomic clock in testing that, if it works, will make space navigation much more efficient: https://www.nasa.gov/mission_pages/tdm/clock/index.html https://www.nasa.gov/mission_pages/tdm/clock/index.html
- KirillPanov 5y ago> These can help against GPS spoofing / jamming by identifying false signals Hrm, it would definitely stop a spoofer from misleading you about what time it is. If you care about your position: given the fact that GPS satellites are so far away and the signal is so weak, I don't see how it provides any defense against jamming specifically. If you can't hear the satellites, you can't hear them. Regarding spoofing, it really only defends against spoofed signals emanating from other satellites. This is a big concern for the military. For everybody else "spoofing" means spoofed signals from other land-based or atmospheric transmitters, which once again are close enough to easily drown out the true signal completely. TL;DR: useful if threat model includes attacker-controlled satellites.
- geenew 5y agoI'm not sure how much you know about GPS, but position in GPS is intrinsically linked to time. You know a satellite's orbit from its orbital elements, so, a given moment in time, you know where it is. The satellite emits signals with its internal time. You receive the signal sometime later. The difference between those times gives you the distance to the satellite at that frame[0]. When you have three or more measurements, you can triangulate your position in 3D. In terms of spoofing, one method is to emit signals from ground based transmitters that match the signal from the actual satellite, but with offset times, and at higher power levels than the actual satellite[1]. This gives the receiver a false location.[2] If you have a source of time-truth, you can reject these signals. In terms of jamming, you'll note that it allows rapid resynchronization after jamming. During jamming, you don't know where you are. After jamming, without a highly precise clock, you need to solve for the actual time by integrating signals from >=4 satellites. With a highly precise clock, this step is removed. [0] There are confounding factors, like refraction in the ionosphere, but a rough approximation is that the signal is travelling at c [1] Higher power is trivial because the signals from the satellites are very weak [2] This is a classic example: https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incident https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid... TL;DR: useful for existing ground/air based threats.
- rubicks 5y agoIf there are any current (or ex-) Symmetricom employees reading this, then I'd love to hear about your work. I have a profound interest in the domain of high-precision timekeeping.
- voxadam 5y agoI've never worked for Symmetricom but if you're interested in timekeeping be sure to check out the excellent Time-Nuts mailing list.[1] [1] http://leapsecond.com/time-nuts.htm http://leapsecond.com/time-nuts.htm
- Honga 5y agoI used to sell the microsemi line of clocks. Was always interesting to have to import caesium into Australia.
- numpad0 5y agoWhat would it be useful for, apart from all the practical purposes? i.e. putting one in a centrifuge and one next to it?
- Certified 5y agoOne application I am familiar with is their use in ocean bottom hydrophone and geophone recording nodes for reflection seismology. Land based, transition zone, and boat tethered systems can be synced to GPS time. Battery powered ocean bottom nodes have to maintain an independent clock with a limit on the maximum amount of clock PPS drift from the moment they are deployed. The longer you want it to operate usefully on the ocean bottom, the more accurate your timekeeping clock has to be. I don't know if I would say this is a non-practical purpose, but anything I can think of to do with a highly accurate clock would have some practicality
- cmos 5y agoYes, we use these in ocean bottom and subsurface buoys. However only for audio and seismic activity do we need this kind of accuracy. The cost is high, they don't always work perfect, and they consume a fair amount of power for long deployments. Overall we try to avoid them if possible.
- cryptonector 5y ago{Small, cheap, low-power} x {SpaceX launch capacity} == highly redundant and very resilient GPS equivalent? This thing is sufficiently small, low-power, and low-cost to use in something like StarLink sats, and it's accuracy is advertised as "±5.0E-11 accuracy at shipment", compared to about ~3e-15 or so for cesium clocks. With 30k+ StarLink sats in orbit one might be able to see enough sats overhead to provide comparable accuracy on the ground as GPS (but I've not done the math).
- jmpman 5y agoIf someone had a celestial database, and a telescope, how accurately could one determine their position on earth using this device? Assuming no GPS satellites are available.
- canadianfella 5y agoWild guess, but probably about as accurate as a telescope and timex watch. I imagine it’s like measuring speed using an hourglass and a camera.
- mnw21cam 5y agoThe telescope and timing part of this problem are actually relatively easy. You can align a fairly cheap telescope towards a star with an accuracy of about an arcsecond, which is a distance of about 30 metres on the earth's surface. Beyond that, the turbulence in the atmosphere tends to blur the view, so it is hard to get much more accurate. One of those arcseconds passes by approximately 15 times a second, so using an atomic clock for that is way overkill - any time source more accurate than 1/15 of a second is unnecessary. The main problem is that once you have aligned your telescope, now what you are trying to do is measure the direction of gravity, compared to the direction you're pointing the telescope, and that's a lot harder. Partly because that's a mechanical angle measurement (you need a pendulum that can freely swing and rest with minimal friction pointing directly in the direction of gravity, and then you need to measure angle). But then also, you need to take account of the fact that the gravitational field on the Earth is lumpy. If you're sitting next to a mountain, the gravitational field will be deflected slightly from pointing directly downwards - and in fact that was used a while back to measure the density of the Earth. But theoretically, if you can solve the angle measurement bit, you could determine your location on Earth with an error of around 30m.
- amelius 5y agoWould you still need to measure gravity if you used multiple celestial bodies as a reference?
- 5y ago
- hatsunearu 5y ago4.95 grand a pop, move along folks
- wmf 5y agoLet's attach one to a RPi.
- hatsunearu 5y agoI was thinking of putting it in my nixie tube clock, guess not
- 1-6 5y agoI did a double take. At first I thought you said ~$5, not ~$5K.
- cryptonector 5y agoFor some applications that's not that much. Imagine SpaceX putting one of these in each StarLink satellite and providing their own GPS-like service. I'm not sure if this clock would be good enough for GPS. It's 3 orders of magnitude less accurate than a cesium clock. But with so many StarLink sats overhead, and synchronizing with more accurate ground clocks, might make up for that.
- mikewarot 5y agoInstead of a beam of Cesium atoms being sensed with microwaves, this has a vapor cell sensed with microwave modulated light. This eliminates the finite lifespan previously associated with Cesium Beam atomic clocks. Unlike Rubidium references, the light is supplied by a solid state laser, eliminating another huge power sink. I expect these devices have a practically infinite life. What an amazing set of innovations.
- ginko 5y agoNot quite the size to fit into a wristwatch yet.
- jmwilson 5y agoSomebody already made one - Hoptroff, a London-based watchmaker produced a pair of wristwatches based on the CSAC a few years ago. Don't bother searching for a price or where to buy; they've since pivoted from making watches to being a time-as-a-service software company. IMO it was a bit of gimmick. Apart from being a little too chunky for a wristwatch, just because it's an "atomic clock" doesn't mean it's "atomic powered". IIRC the CSAC uses about 1/8 W which is really pushing it for a low-power device like a watch. It might lose "one second per millennium" as advertised but good luck keeping it continuously operating anywhere near a thousand years.
- hatsunearu 5y agoYeah, if you want something like that, you'd get a quartz radio watch that synchronizes with the free radio-based timekeeping service.
- pabl8k 5y agoI'm reminded of this delightful site featuring an HP brand atomic watch with nylon band: http://leapsecond.com/pages/atomic-bill/ http://leapsecond.com/pages/atomic-bill/
- sephamorr 5y agoWe looked at using these in a previous job that had a very tight tolerance on RF frequency tolerance. Vibration tolerance makes the use of crystals difficult. Unfortunately, the phase noise of this device wasn't good enough to be the frequency source for the radio itself, so we would have had to use the CSAC to discipline a tcxo. By the time we did that, it really wasn't that advantageous. It looks like they have a low-noise option that includes a tcxo now, but (no surprise), it doesn't appear to have a operating vibration spec.
- mikewarot 5y agoAt the heart of any atomic clock is a quartz crystal clock that is steered to match the resonance dip of the atom. It is that oscillator that actually outputs the 10Mhz, gets divided to 1PPS, etc. Perhaps it would be possible to have a pair of identical crystals tied together but electrically opposite in phase so that external vibrations tended to cancel. (Like a differential signaling pair in a cable)