In a message dated 2006/10/04, jonfr500@......... writes:

> I also plan to build a Lehman seismometer, if I can keep it small enough. 
> But I need a suggestion for material and some mesurements and proper drawings 
> before I can start. I also want to keep the frequency of the Lehman 
> seismometer around 1Hz.

Hi Jon, 

       The  whole point about a Lehman type seismometer is that you take a 
pedulum which would have a period of about 1.3 to 1.5 sec if mounted vertically 
and extend the period to maybe 20 sec. The sensor will respond from 20 sec to 
the 10 Hz of your amplifier filter. I suspect that an arm of between 45 and 60 
cm would be fine for you. Don't try to make it smaller. This should pick up 
your seismic signals very well.

       I make a T / L frame with U channel Al with 5 mm Al plate for the 
corner supports. I don't know what materials are available to you. You can use 50 
x 25 mm, but I prefer 75 x 25 mm section.

       Regards,

       Chris Chapman 
In a me=
ssage dated 2006/10/04, jonfr500@......... writes:



I also plan to build a Lehman s=
eismometer, if I can keep it small enough. But I need a suggestion for mater=
ial and some mesurements and proper drawings before I can start. I also want=
 to keep the frequency of the Lehman seismometer around 1Hz.



Hi Jon, 



       The  whole point about a Lehman ty=
pe seismometer is that you take a pedulum which would have a period of about=
 1.3 to 1.5 sec if mounted vertically and extend the period to maybe 20 sec.=
 The sensor will respond from 20 sec to the 10 Hz of your amplifier filter.=20=
I suspect that an arm of between 45 and 60 cm would be fine for you. Don't t=
ry to make it smaller. This should pick up your seismic signals very well.


       I make a T / L frame with U channel Al=20=
with 5 mm Al plate for the corner supports. I don't know what materials are=20=
available to you. You can use 50 x 25 mm, but I prefer 75 x 25 mm section.


       Regards,



       Chris Chapman