PSN-L Email List Message
Subject: Re: C-Spring Sensor - 5/6 Second Period
From: RSparks rsparks@..........
Date: Thu, 20 Jan 2011 06:40:07 -0800
Good Morning Richard and list members,
I guess it is time to comment on the C-Spring seismometer. Nothing like
the internet to expand local news into international "fame"!
The C-Spring is easy and inexpensive to build, stable and easy to
adjust. I did grind off the teeth and no cracks appeared over about 3
years of use. Some may object to the inclined boom which does make the
maximum sensitivity occur at about a 20 degree angle to vertical, which
is done to extend the period making the seismometer much more sensitive
to low frequency waves.
The picture in the article is the new replacement seismometer which is
more sensitive to higher frequency waves, about the same period for
sensitivity to low frequency and avoids the oil damper. It is a lot
more difficult to build!
The spring is key to this seismometer. You see it in the picture as a
straight, very thin, plane. This has a great advantage over the curved
hacksaw blades because it is stable in the horizontal, right angle to
the beam, direction. The C-Spring is very sensitive in this direction,
which is a real weakness if a close tolerance damper like magnetic
damping is to be used. Not a problem for detecting as the magnetic
detector is not very sensitive in this sideways direction.
The straight spring is made from a 12 inch wide blue steel dry wall
knife blade. The blade is cut diagonally to form a tapered spring
designed to bend equally at all distances from the fulcrum which
distributes the energy from bending throughout the length of the
spring. After cutting and smoothing the outside edges of the spring,
bend it into a circle which is not too easy to do. The final resting
curled spring size is about 3 inches in diameter. Next, anneal the
spring in an oven for maybe an hour. Use the self clean heat setting of
an electric oven which I guess is about 600 degrees Fahrenheit. Without
the annealing, the bent spring would have lots of stored micro stressed
points that would relieve over time, making the spring unstable.
Finally, unroll the spring and attach the boom.
The damper is from Chris Chapman's design (thanks Chris).
The magnet is made from neodymium magnets attached to a soft iron frame
to make a large but powerful horseshoe magnet.
The adjusting weights are made from stainless steel washers found at the
local hardware store. There are no ferromagnetic materials on the boom.
I tried to balance the expected forces from the damper and sensor so
that they would act through the center of gravity of the boom, not
including the spring. This to minimize rotation of the boom due to
vertical motion.
I will try to, over the course of the next several days, to make a new
web page describing the new seismometer with more details.
I frequently post on the PSN site using the station ID ebgz or ebgzx.
Everything posted is from this straight spring seismometer.
Thanks for your interest and good luck,
Roger
On 01-19-2011 12:01 AM, psnlist-digest-request@.............. wrote:
> .------ ------ ------ ------ ------ ------ ------ ------ ------ ------.
> | Message 1 |
> '------ ------ ------ ------ ------ ------ ------ ------ ------ ------'
> Subject: Re: C-Spring Sensor - 5/6 Second Period
> From: Richard Schneider
> Date: Tue, 18 Jan 2011 10:56:26 -0800
>
> --0016367f9dc429d857049a2375c0
> Content-Type: text/plain; charset=ISO-8859-1
>
> Thanks Bob, I plan to contact Roger. Meanwhile I found this fairly recent
> article about him and what looks to be the new design you mentioned.
>
> http://dailyrecordnews.com/news/article_e99e7742-5159-11df-b578-001cc4c002e0.html
>
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