In a message dated 2007/08/31, ciburch@........... writes:

> Being new to the home-built seismograph business I wonder about the 
> advantages / disadvantages of the "swinging gate" vs. the folded pendulum 
> designs 
> for horizontal component seismometers.  The swinging gate appears to have 
> the 
> advantage of simplicity requiring just two pivots while the FP requires 
> eight.
> 
> Chuck I. Burch

Hi Chuck,

       The swinging gate type is probably quite a bit easier to make and 
likely requires less skill to set up. The setup tilt sensitivities are the same. 

       You are aiming for a sensor with a 15 to 30 second period, to bring in 
the long period Love and Rayleigh waves at ~20 sec.

       I suggest that you use either ball on a plane or a crossed roller 
design of hinge for a swinging gate, but you can also use a single fine piano wire 
in tension.

       The T frame can be made out of 3" x1" U channel Aluminum with 1/8" 
thick corner plates. Make the whole seismometer as 'one item'. This is very much 
easier to set up and adjust. Use NdFeB magnet + Copper plate damping. I use SS 
nuts washers and bolts from a boat / marine chandler. They are a bit more 
expensive, but they are OK with Al and they don't rust. Ordinary steel rusts when 
in contact with Al. 

       You will need a thermally insulated enclosure to protect it from air 
movements / drafts. We usually use 2" thick Celotex, gaffer taped and stuck 
together with foam grouting, both from a builder's merchant. You can make widows 
with two sheets of mylar transparency film for laser printers. You want to be 
able to visually check the lateral balance of the seismometer, which may drift 
with time, without removing the cover.

       You can also make a horizontal sensor using a water manometer and 
plastic tube, but you will have to solder your own electronics to a prepared 
design.

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/08/31, ciburch@........... writes:



Being new to the home-built sei=
smograph business I wonder about the 

advantages / disadvantages of the "swinging gate" vs. the folded pendulum de=
signs 

for horizontal component seismometers.  The swinging gate appears to ha=
ve the 

advantage of simplicity requiring just two pivots while the FP requires eigh=
t.



Chuck I. Burch




Hi Chuck,



       The swinging gate type is probably quit=
e a bit easier to make and likely requires less skill to set up. The setup t=
ilt sensitivities are the same. 



       You are aiming for a sensor with a 15 t=
o 30 second period, to bring in the long period Love and Rayleigh waves at ~=
20 sec.



       I suggest that you use either ball on a=
 plane or a crossed roller design of hinge for a swinging gate, but you can=20=
also use a single fine piano wire in tension.



       The T frame can be made out of 3" x1" U=
 channel Aluminum with 1/8" thick corner plates. Make the whole seismomet=
er as 'one item'. This is very much easier to set up and adjust. Use NdF=
eB magnet + Copper plate damping. I use SS nuts washers and bolts from a boa=
t / marine chandler. They are a bit more expensive, but they are OK with Al=20=
and they don't rust. Ordinary steel rusts when in contact with Al. 



       You will need a thermally insulated enc=
losure to protect it from air movements / drafts. We usually use 2" thick Ce=
lotex, gaffer taped and stuck together with foam grouting, both from a build=
er's merchant. You can make widows with two sheets of mylar transparency fil=
m for laser printers. You want to be able to visually check the lateral bala=
nce of the seismometer, which may drift with time, without removing the cove=
r.



       You can also make a horizontal sensor u=
sing a water manometer and plastic tube, but you will have to solder your ow=
n electronics to a prepared design.



       Regards,



       Chris Chapman