The clock was measured and observed free running for few months. I might not be here in 158 million years to check if it had drifted by the mentioned one second. In this case the aim was to transfer the long term stability. Nevertheless, locking two oscillators makes the locked one inherit some of the properties of the master one. Hobby project, where one learns about PLL dynamics, system modelling, using noisy signals, design of control loops for non-linear systems, optimise the dynamics to profit the best from performance of each oscillator and many other. I guess reading through the article makes it clear. I think that was the height of mechanical clock making before electronics took over. The “master pendulum” is just free swinging (maybe for half an hour or so) and when it looses amplitude and needs some boost, then it does receive it, but the phase difference is then compared with and corrected for with another pendulum, which is freely swinging at that time. They have multiple pendulums swinging in vacuum, and they don’t get excited during most of the time. I also remember having read about the most accurate pendulum clocks ever made. It’s something with the cesium leaking out of the tube or some recombination, and when that happens, the only remedy is to replace the tube. When I read something about “one second in who knows how many years” of accuracy, I always have to think back to: Those clocks from the ’70-ties are being sold on Ebay for some time now, and they rarely work at all. It also feels like sacrilege to put a paper basket and some chain on such a vintage clock, but it all looks reversible so no real harm done. The first graph with “Pendulum period error ” has some noise, which is understandable, but it also has some systematic deviation and those all have nearly the same amplitude. I also see some weirdness in the logged data. And as long as that clock is enslaved, it won’t drift a second, not even in “158 million years” from that other clock. Posted in clock hacks Tagged arduino, cern, cesium, chain, invar, pendulum, phase-locked loop, PLL, stepper Post navigationĮnslaving a clock to another more accurate standard does not make the clock itself more accurate. Again, we’ll take his word for it, but it’s a wonderfully ad hoc approach to tuning the clock, and we appreciate its simplicity. It seems like is claiming that his chain-corrected clock won’t drift more than a second from the cesium clock for 158 million years. The change in mass changes the pendulum’s center of gravity, which changes its effective length, and allows the clock to be tuned a couple of seconds per day. Good guess on the PLL, but the trimming method is a little cruder - uses a stepper motor attached to the clock’s frame to pay out or retract a length of fine chain into a cardboard dish attached to the pendulum’s rod. Now, we know what you’re thinking - he must have used some kind of PLL to give an electromagnetic “kick” to the bob to trim the pendulum’s period. With access to a 10-MHz timebase from a cesium fountain atomic clock - no less a clock than the one that’s used to define the SI second, by the way - looked for ways to sync the clock up to it. ![]() This ensures the pendulum doesn’t change length with temperature, but it still only brings the clock into the 0.1 second/day range.Ĭlearly that’s not good enough for a clock at CERN, the European Laboratory for Nuclear Research, where works as an RF engineer. The pendulum of this mid-century beauty is made of the alloy invar, selected for its exceptionally low coefficient of thermal expansion. ![]() While we’re in no position to judge ’s claim, we’re certainly inclined to believe him, mainly because the 1950s-era Czechoslovakian pendulum clock his project was based on, the Elektročas HH3, was built specifically as a master clock for labs, power plants, and broadcast use. Unless, of course, you work at CERN and built “the most accurate pendulum clock on the planet.” ![]() That big grandfather clock in the library might be an impressive piece of mechanical ingenuity, and an even better example of fine cabinetry, but we’d expect that the accuracy of a pendulum timepiece would be limited to a sizable fraction of a minute per day.
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