PSN-L Email List Message

Subject: Best Overall Geophone to have.
From: "Geoffrey" gmvoeth@...........
Date: Sun, 26 Nov 2006 12:55:02 -0700

Hello Everyone on PSN;

I have realized after spending
maybe 10 years or more playing around
with seismic stuff that there is one
and only one sensor that an amateur
needs to receive teleseismic/regional/local
earthquakes and that is a single vertical sensor
with a free period of about 4(four) seconds.
That is a frequency of 0.25 Hertz.
A second runnerup would be a 2(two) Hertz
geophone which can easily be equalized by electronics
down to a period of four or so seconds.

This is the single most important instrument
of the entire system.

Why in heck dont the experts build a standard instrument
in these two ranges. All they have to do is give
us amatures a standard set of plans we can
build our own from ????

By expert I am talking about an experienced mechanical engineer.

All he has to do is keep in mind that
his design will be constructed from materials
that come from like Home Depot or some Internet
Supplier like a magnet shop or a copper wire dealer.

The pros do not need all the info for the EQS
from us amateurs. They really only want and need
what you call "first time of arrival".
The only thing we need is to watch the signals come in and tell roughly
the size and distance. All this can be met with a single
vertical sensor.

It is interested to note that they really like to
know if you were closest to the event and if you
felt the event physically.

Try buying borrowing stealing a vertical geophone that
has a free period of less than 2Hz.

You really must be somewhat gifted/ have your own machine shop/
be somewhat rich to buy a decent vertical sensor.

If you all could solve this sensor problem then all else seems to me would just fall into place.

There seems to be some kind of resistance to standardization
that I do not understand.

The frequency range is like 0.4 HZ to 2.4 HZ butterworth
with a gain of about 80 to 86 DBv at one hertz in frq or 1 second in period.

If you live close to human activity you will find
things get noisy during the day.

By having at least a 12 bit converter you can through
programming automatically lower the overall gain in steps
of two simply by dividing the results and summing in
an offset. You can do this automatically in your program
acording to the time of day. You always want a bit of
of noise showing on your graph.

You also want a modulo recorder like nine minutes of history
so that you will keep that 9 minutes of history in memory
until something triggers the rest of the recording.

You will also want a audible alarm to sound when
the recording has been triggered.

All these things I have actually done with the exception
of building a decent vertical sensor. To date I have only been able
to puchase a worthy sensor and even it is not in the right frequency range
to get easy flatness between 0.4Hz and 2 Hz.

There is no reason I can see in this day and age
a standard system can not exist as a kit or something
for people to simply put together and build.

I just wanted all you folks who love science and technology
over the arts to think of this awhile and respond with great verbosity.


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