Some comments;

I understand that the system also needs either a high / medium gain short
or long period device so that smaller or teleseismic events can be recorded
to keep up the interest. There are plenty of plans on the Internet on how
to make a long period device. For a short period device a new or used
geophone can be used. What is missing is a good simple design for a SM type
sensor. Also, to be used as a teaching device it should be rather large
(like the size of a geophone) with a clear case. This is one reason I would
like to stay away from a solid-state chip device like the one offered by
EGG. I also have some other reservations about them, but more about that
later.

I see the discussion quickly turned to the A/D and TCP/IP part of the
project. I see this as the easy part. The hard part, for me, is the actual
mechanical part of the sensor. After all, I already have an A/D card and
event files can be placed on the Internet using existing hardware and
software....So I would like to keep the discussion focused on the sensor.
If the sensor produces a voltage output, then any A/D converter can be
used. I see this like stereo equipment. Some people like the all in one
receiver, others like myself like to have each component separate so that
each part can be changed without replacing the whole thing.

Solid State devices like the EGG part; Heres some problems I have with
them. First they are expensive. In small numbers each component costs over
$100.00. Apparently they have temperature and calibration problems. EGG
also offers a calibrated and temp compensated unit, but I'm sure at a much
higher cost. From an email I read from John Evens at the USGS, who is using
the non compensated part, also records temperature and does some post
processing of the data. I just don't like this at all! Its hard enough to
deal with the data and this would be one more thing to worry about. 

The part would be only available from EGG. When I called them early this
year, lead times just to get a sample was over 6 weeks. I just don't have a
good feeling about them supply small numbers too use. I'm also not sure
what the overall dynamic range of the part is, since I haven't p[lay with
one. How much better are they over the ADXL type of parts from Analog Devices?

Besides the cost of the part there is still more electronics that would be
need to make the chip device into a real sensor. One still needs buffering,
filtering, power supply etc. Since some external electronics is needed, why
not also have all of the parts needed to make a complete sensor on it and
make the mechanical part? Maybe the device could also be sold as a kit, if
it's not to hard to make. In fact, if its too hard to make then it will
probably be hard to produce, so it needs to be as simple as possible. 

We have a lot of clever people out there I'm sure we can come up with
something....

Regards,
Larry Cochrane
Redwood City, PSN


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