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Jonahan Hare's Diary

Day 16: Seismograph

Photo: seismographThe seismograph seems to be working well apart from the fact that the pendulum can easily fall off the base, especially if the base is slightly off from the flat. We put the device onto the bridge and it seems to log the cars quite well. Unfortunately the bridge tends to move a lot vertically but there is little horizontal movement which is really where our seismograph has greatest sensitivity!! - it shows the Rough Science principles though.

Photo: Kathy and Jonathan on the bridgeWe build an electronic addition which consists of a magnet attached to the weight and a coil of wire mounted below it on the base. The wire ends from the coil go to a simple 1-transistor amp and this boosts the signal so that the output is easy to see on a meter. Even quite small motions can be detected by this modification. Because the coil and magnet records the change of movement then this device make the position sensitive seismograph (distance) into a motion (velocity) detector. Steve Evanson asked me if we can drop the electronics however as they think it would be too complex (“a mystery”) to explain on TV.

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Photo: Jonathan Hare
Metal Detector Interactive