Reply To: Arduino Pendulum Clock Design – Comments Welcome

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Posted by John Haine on 24/10/2020 14:02:26:

No, Allan compares the test clock with itself. If you use the TimeLab package you just give it a big file list of successive period readings and it does the rest (IIRC).

Here is an Adev plot of my "Arduinome" clock I just generated to remind myself.

It takes the whole file of which only the first column are period measurements and ignores the rest. So far I haven't really worked out what it means but generally the trend is sort of diagonally downwards though with some flattening off. What the little wiggles result from I don't know. Good explanation here. If you explore that site you can read about Tom's adventures testing General Relativity on a camping trip.

John, you are my hero. I had the fixed idea Allan analysed phase differences between clocks and managed to spin my reading of the documentation to cement the misunderstanding. Might have taken me weeks to get back on track. Thanks to you sorting me out it's easy to to apply any of the methods provided in Python's Allantools module.

Interpreting the graphs is another walk in the dark, but I read your Arduinome chart thus:

• The line generally falls from left to right, which is good.
• The wave like wiggles in the first 100 seconds could be settling errors, maybe due to the pendulum vibrating after start-up, or the clock being bumped whilst the measurement was set up.
• Y axis values are small, which I think indicates good stability.

My clock's chart:

• The tick shaped line is bad – rising to the right indicates a consistent rate error. Sharp falls are characterised by Rowland as observation error. In my case, pretty certain the observations are OK, and the real cause is pendulum bounce due to restarting the clock from scratch for each test.
• Y-axis values are big, which I think indicates poor stability.

Could be wrong!

Meanwhile, I broke the pendulum rod again. I frayed the rod and made a brass clamp to hold the fibres OK but got clumsy reassembling the clock. Showstopper – looks like I've run out of 0.5mm rod and will have to order more.

Dave