I am a new subscriber to PSN-L and look forward to learning from, and
perhaps, contributing to the group.

I am an electrical engineer residing in the Shenandoah valley in
central Virginia.  Analog circuit design is my forte, but I have not
been using it much for the last 20 something years of my career as an
industrial maintenance and control consultant.  I have been interested
in geology, volcanism and earthquakes for a long time.  After
discussing seismometer amplifiers with someone, recently, in
sci.electronics.design, I started searching the web for home built
seismometer and sensor designs.  

One thing that struck me about many of the sensor designs is their
lack of optimization and sophistication.  Either this means that the
sensor is not the limiting part of most designs or else it means that
considerable improvement is possible.

After puzzling a bit over how I might design an inductive sensor that
would improve upon the simple solenoidal coil and horse shoe magnet
approach, I think I have come up with a more sensitive design that
also has noise canceling capability that will help it reject line
generated fields (AC hum), variations in the Earth's magnetic field
caused by the solar wind and lightning magnetic fields.  This is based
on making two similar coils that produce equal and opposite signals
when exposed to large, common, external fields, but produce equal and
aiding signals when exposed to the relative movement between the coils
and magnet structure.  The magnet structure also has no net external
field to interact with the geo field that might interact with the
seismometer boom.

I have purchased a batch of NeFeB magnets on EBAY and am awaiting a
quote for construction of the 6 iron pole pieces to make one of these
fist sized sensors.  I will make the coil forms and wind the coils,
myself.  I will also make the signal amplifier and filter.  If that
all comes together, I will take a shot at building a Lehman type
horizontal, long period pendulum.  I also have a DATAQ DI-194-RS to
hook it up to a computer but no software other than what came with
that unit.

Eventually I want to add an optical beam sensor that will make the
unit act as a tilt meter (true DC operation, similar to the
differential capacitive bridge type pickup, but with much simpler
support circuits) and allow experiments with feedback using the
original inductive sensor as a linear motor.  This should keep me busy
for a year or more.

I am looking forward to not only seeing signals from world wide
seismic events, but seeing what local signals come through.  Train
traffic passes a few miles away in two directions.

Your suggestions, questions, advice and comments are certainly
welcome.
   
-- 
John Popelish
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