Meredith
Thanks for the quick response to my question.  Living in New Jersey I don't 
see a great deal of seismic activity so I will stick to the normal S G 
construction. I've had my Lehman running since 1981 and have logged quite a 
few earthquakes.
Thanks again.
Al.


At 10:24 AM 11/8/99 -0800, you wrote:


>Al Frielink wrote:
>
> > To All
> > In making an S G Seismometer is there any reason why the coil/magnet
> > combination couldn't be used as the sensor used in my Lehman?
> >   I enjoy reading the e-mail from the PSN.
> > Thanks.
> > Al.
>
>Al,
>
>It would work for short period use, generally related to the
>period of your S-G, but I suspect the longer period phases
>would be greatly attenuated, due solely to the mechanical
>nature of the S-G compared to the mechanical "amplification"
>arrangement on the Lehman.
>
>Most S-G's use sensors with position displacement sensing and
>not coil and magnet induction; to sense the longer periods.
>
>On the other hand, it would make it interesting to try, as I've
>never heard of a coil and magnet induction S-G, as of this
>writing.  I would think its "range", would be much greater than
>a geophone due to its longer period....unless you get like a
>1hz geophone....in comparison to the "normal" 8-10-12-20 hz
>typical amateur geophone.
>
>If you live in a seismic area, the coil and magnet might be
>interesting to try; but if you don't, I would suggest trying other
>methods of sensing.  If you live in a city/town with or near alot
>of seismic noise sources, you will see alot of false triggers with
>coil & magnet sensing.   With a displacement sensor, and
>earthquakes "L" waves, real records will be much more obvious.
>
>Personally, I think the S-G's are the easiest route for amateurs,
>and with care in construction they can mimic the output of alot
>of coil & magnet horizontal instruments.   The "zeroing" factor
>is simple gravity for S-G's, and with its much smaller size, the
>tilt factor and leveling adjustments is alot less frequent than a
>"Lehman".  I use a linear (mostly) Hall sensor circuit myself,
>created by Robert Lamb, in two S-G's.
>
>Going further, one could even incorporate more than one type
>of sensor in a single S-G, with additional lead in wires
>compensation in construction.....you could try induction,
>capacitive, Hall,  optical light sensors or any other possible
>method combination.
>
>Take care,
>
>Meredith Lamb
>
>
>
>
>
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