Re: Clock or anemometer?

John Haine

Thinking about this last night I realised that this kind of variation is not necessarily of the pendulum at all.  It is clear that there's a correlation between the period variance and wind speed, but another way to think about this is that the pendulum is actually providing a time reference which could be very stable, but what we are seeing is an artefact of the measurement system.  Essentially, vibration caused by the wind is shaking the sensor around its nominal position, but it sees this as a variation in the period because the bob is hardly affected.  The clock is perhaps working as a sensitive seismometer.

The plot  of my clock I showed over in another thread includes some odd, very rapid, variations in amplitude and period which seemed impossible for a high Q pendulum.  In fact, some further observations demonstrate that the variations are an artefact of the opto sensor, which had sunlight falling on it at a particular part of the day (more details to follow) (thanks to Tom van Baak and Bob Holmstrom for their analysis).

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