PSN-L Email List Message

Subject: Re: "P" ky "Slinky"
From: John Lahr johnjan@........
Date: Thu, 26 Jul 2007 09:43:57 -0700

Hi Ted,

Nice design!

How do you damp out horizontal, swinging motion of the slinky 
system?  What's the resonant period of this motion?


At 08:51 AM 7/26/2007, you wrote:
>Hi Folks,   In the past I have asked the group questions about 
>various designs.  I have made several sensors, some of no value and 
>some which work well for me in this location.   We all learn from 
>doing.  I really like the simplicity of the AS-1, but the cost keep 
>me from purchasing one, and started my efforts to make one from 
>items I could get locally.   I also wanted to get kids involved in a 
>project which would not require a machine shop.   My Grandkids in 
>Alaska enjoyed their project for a
>science class.
>One thing I could not do, was to build the Amp/Filter, I did try and 
>got the board working by not good enough.
>I solved that Big issue by purchasing Larry's board, which worked great.
>I think it was the sixth sensor I dubbed   "P" ky-"Slinky"   The 
>idea was to hang a long spring from the ceiling 7' overall.  On the 
>end of the spring a magnet moving in and out of a coil.   Add a 
>damper, and enclose it.
>A little like a very long geophone.
>I did a prototype and it worked.  So I built one for real,  I 
>started using 7'  which included the entire unit.  I later changed 
>it to 5'...........I thing the period is about 2.2 seconds.  I made 
>a few modification and it has been trouble free and recording 
>earthquakes from all over the world, and in greater numbers than my 
>Lehman.   Obviously not with all the phases, one would expect with a 
>longer period sensor.
>The spring, perhaps the one at the bottom of the list of appropriate 
>choices, is working just fine.   I see no temperature noise, 
>although it must be there, and since the spring is in a tube I don't 
>get air currents.   The only issue I had with the spring is that it 
>stretched about one inch over one month, and now has stopped.
>I did not keep track of the cost, but I think it was maybe $50 - $75 
>including everything for the sensor.   For a full station one would 
>need all the other things, like the Amp/Filter, AD converter, cables 
>Software and an old computer, etc.
>I am now operating this unit and posting the recordings as 
>TCIDzs  as z-vertical s-slinky.   At night time the noise level is 
>very low, during the day the noise level is high, due to road 
>construction.  On the week end the noise level is low.
>I have posted some picture here.  Just click on the album call "5' Slinky"
>and you can see 9 pictures,  I hope.  Notice one shows the tube 7' 
>tall and one 5' tall, after I modified it.
>This is an inexpressive unit, using simple materials, little machine 
>work, fun..........and I am please with its performance.
>Email me if you want to make one,  and I will give you details.  I 
>can sent or post .gif images of its recordings as well.
>It just a fun and easy 
>project.     tchannel1@............


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