In a message dated 11/20/02 2:51:37 AM GMT Standard Time, Kplblange@....... 
writes:


> I had a Lehman working some years ago and know what a time 
> it is to have it stay in neutral.  I wonder if I should have make a 
> vertical 
> one and have plans in an old Scientific American. The problem is that it 
> needs springs that best would be make by a machine shop. They are not coil 
> springs but flat pieces of metal.
> 
> Ken from Gardena, CA

Hi Ken,

A good flat spring is the one Sean-Thomas used in his leaf spring 
seismometer. I bought one of these, a plasterer's 14" spackling trowel for 
about $20 at Home Depot and removed the handle by drilling out the rivets. 
This gave me a 0.025" thick flat spring 4" by 14" which I mounted vertically 
and bent over 90 degrees with a lead weight so the free end was horizontal. 
An outrigger carried a coil from a 120-Volt relay that dipped between the 
poles of a big Alnico magnet to generate a signal voltage. A flat sheet of 
copper 4" X 4" farther out on the outrigger sandwiched between eight flat 
ceramic magnets provided critical damping and enough additional weight to 
give a period of about 1 1/4 seconds. With one of Dave Saum's amp/filters 
there was more than enough sensitivity to record microseisims continuously 
even on quiet days. 

Cap
(Casper Hossfield)
In a message dated 11/20/02 2:51:37 AM GMT Standard Time, Kplblange@....... writes:





I had a Lehman working some years ago and know what a time 

it is to have it stay in neutral.  I wonder if I should have make a vertical 

one and have plans in an old Scientific American. The problem is that it 

needs springs that best would be make by a machine shop. They are not coil 

springs but flat pieces of metal.



Ken from Gardena, CA




Hi Ken,



A good flat spring is the one Sean-Thomas used in his leaf spring seismometer. I bought one of these, a plasterer's 14" spackling trowel for about $20 at Home Depot and removed the handle by drilling out the rivets. This gave me a 0.025" thick flat spring 4" by 14" which I mounted vertically and bent over 90 degrees with a lead weight so the free end was horizontal. An outrigger carried a coil from a 120-Volt relay that dipped between the poles of a big Alnico magnet to generate a signal voltage. A flat sheet of copper 4" X 4" farther out on the outrigger sandwiched between eight flat ceramic magnets provided critical damping and enough additional weight to give a period of about 1 1/4 seconds. With one of Dave Saum's amp/filters there was more than enough sensitivity to record microseisims continuously even on quiet days. 



Cap

(Casper Hossfield)