Hello,

i might suggest to use the spring in a triangle
configuration with a vertical axis and horizontal
moving axis that sustain the mass.
The priciple is called "Lacoste suspension"
you can have a look here.
http://mariottim.interfree.it/doc02v_i.htm#lacoste

this is a very rude seismometer but it has a
free period of 1.2 seconds.

It is not so big.
The same sensor can be built in wood
(i have made one for a scientific exibition)
I have some pictures but not in a web site
if you want i can send them to the interested people.

As transducer i used a powerful magnet from the
SuperMag kids toy and the coils is stolen by
a old relay. Such instrument can induce enough current
to drive (not much) a microampmeter.
kids like it very much.
Using a small preamplifier you can get a huge signal.
Damping was made using a plastic polycarbonate strip
bended at U like a springleaf and made stiffy with
electric tape.

wooden axis can be made that can be easily
assembled and disassembled without any tool

i hope it helps

regards
mauro

At 23:10 2006/11/28, you wrote:
>Hi Folks,  Some discussion on a simple vertical seismometer got me 
>to thinking about a possible school project for the kids.  At one 
>time, I found a simple vertical sensor on the internet, it used pvc 
>pipe and a small 9"? spring.  I built it but never tested it because 
>I had an idea the coil and magnet were just too undersized.  It 
>probably works but would require some strong amplification, further 
>more, I have no idea what the period would be.
>
>I wonder if one could use a "Slinky"  a toy spring used by kids? 
>They are about 3" in dia. and collapsed about 5" tall.  I think I 
>will get one and suspend it vertically, to check its suspended 
>length and its natural resonance.  I have no idea how long the 
>spring would expand under its own weight?   But let's say under 8 
>feet. If so, maybe it could be hung from the ceiling and the coil 
>and mass would be near the floor?
>
>It just might be something kids would enjoy.
>Q. 1.  If I pull down on a spring and release it, it will move up 
>and down, until it come to rest, if each cycle is 1 sec, (say a very 
>long spring), is that its natural period?
>Q. 2. If I put a mass on the end of the spring, will it move 
>slower?   If so, is that, now its period?  Maybe 2 or 3 seconds?
>Q. 3. If I could work out the construction details, what period 
>should I target for a vertical sensor?
>Q. 4. Are there any websites or information on using long vertical 
>springs?   Many thanks, Ted

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