>> Lunar/Solar Tides and Pendulum Clocks (part 1) >> http://www.leapsecond.com/hsn2006/ch1.htm > > Nice. Thanks. Did you ever write chapter 2?
In progress. I'll let you know when it's done. >... > Or a digital camera: take a sequence of pictures and interpolate as to when > it crosses the center. > > The hardware used for bar code scanners might be a useful starting place. I > assume you would have to hack the firmware/whatever to output time/position > info rather than bar code data. You have lots of good ideas; I'm sure some been tried but I don't have references for you. From what I remember many modern attempts at super pendulum clocks end up using optical sensors. But you can save weeks of prototype work with a few minutes of calculation. For example, given the length of the pendulum and the half-angle amplitude you can calculate the velocity at center swing. Then knowing the geometry of the optical gate gives you the rise-time. If the IR emitter/transistor pair have a circular aperture instead of slit then you're getting a slower rise time as the pendulum crosses the circular beam, etc. One could do a series of experiments to obtain the most precise signal. Or the most stable swing-to-swing samples. But that's only part of the problem... I would also worry about long-term stability of any optical emitter and sensor pair. Any decline in light output over time might appear in the data as a phase shift which could affect amplitude or period stability. Then there's any tempco or voltco issues to consider with optoelectronic elements. By the way, a really nice technical paper on a precision pendulum clock is this 1996 paper by De Marchi: A Measurement of the Period Stability of a Free Pendulum http://www.leapsecond.com/history/1996-DeMarchi-Pendulum-Stability.pdf Clever solution. His optical gap is something like 5 microns. /tvb _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts