@ Jón / Jack,

the clicking noise is barely audible and is not the from the mass hitting
the mechnical stop.
The noise forms when I move the mass slowly by hand with the period
adjustment rod.
It sounds like a noise from a spring but I can not tell whether it comes
from the period
adjustment spring outside of the housing or from the main leafspring inside.
Maybe the noise comes from the cause of the unlinearity...
My HS-10 has a locking screw for the mass for transportation.
There is no real centering indicator on my HS-10 but there is a threaded rod
that
comes from the inside and is connected to the mass. There is a spring
outside of the housing
whose force can be adjusted by a bushing on the rod. The mass can move 6 mm
up and  6 mm down.
The rest position of the mass is roughly in the center of the movement range
of the mass, so the
centering should be ok. When I reduce the drive current to 10 uA the seismic
noise is too high to evaluate the
form of the curve on the oscilloscope. I will try to build a simple filter
to reduce the high frequency
seismic noise and check the response with lower drive current at low
frequencies.
With about 30 uApp the movement of the adjustment screw/rod is about 1 mm.
I think the response should still be linear at a 1 mm movement but
the output voltage looks more like a triangle. Maybe I demand too much ...

Andreas

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