Question

I am considering building a force balance seismometer. I have some
questions>

(1) The recommended position sensor is a capacitive bridge, the details are
on the Uni-Stuttgart geophysics page. Has anyone on the list done this? If
so what problems, or more importantly, what solutions, ;) , evolved.

(2) How important is linearity of the spring? My daughter asked me why we
didn't float a beam using opposing magnets. That is a F = k(r^3) force to
distance relationship and the perfect seismometer spring would have F =
k(r). For vanishingly small displacements do the problems go away?

(3) I seem to remember someone has a source of material for zero  force
hinges.  Is it still available and who has it?

Thanks
Tom Schmitt
tschmitt@..............

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