In a message dated 21/01/2008 18:32:46 GMT Standard Time, jonfr@.........  
writes:

I am  looking for specs for Lehman type sensor. As I can build a Lehman type 
sensor  in my school with help.

However, the specs I already aren't good, so I  need better ones. If someone 
has them ready. If no one has them, I need to  write them up my self.

I need the size and length in cm. I also need a  suggestion for the material 
needed for the mass, I was thinking about using  led. But I don't know how 
good idea that is. For the base of the sensor I was  thinking about using 
aluminum.

Please send this to my main email  address, jonfr [at] jonfr.com



Hi Jon,
 
    I use 3" x 1" U channel Al with 1/8" thick Al  corner plates for the 
frame. The arm is about 24" long overall.
    You want a natural pendulum length of at least 1.5  seconds, 22". If you 
make it shorter, you may have problems getting a final  20 second period. Have 
a look our school seismometer at 
_http://www.bgs.ac.uk/education/school_seismology/seismometer.html_ 
(http://www.bgs.ac.uk/education/school_seismology/seismometer.html)  and  _http://jclahr.com/science/psn/chapman/lehman/index.html_ 
(http://jclahr.com/science/psn/chapman/lehman/index.html)  This  latter design 
was modified using a rigid top tube and tungsten carbide rod  suspensions, 
from the SS balls and plates. 
    It is probably easier to use brass for the mass. I  make the arm out of 
15 mm SS water pipe, but you can also use Al tube.
    They seem to work well.
 
    Regards,
 
    Chris Chapman



   






In a message dated 21/01/2008 18:32:46 GMT Standard Time, jonfr@........
om=20
writes:
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  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I am=20
  looking for specs for Lehman type sensor. As I can build a Lehman type sen=
sor=20
  in my school with help.

However, the specs I already aren't good, s=
o I=20
  need better ones. If someone has them ready. If no one has them, I need to=
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  write them up my self.

I need the size and length in cm. I also nee=
d a=20
  suggestion for the material needed for the mass, I was thinking about usin=
g=20
  led. But I don't know how good idea that is. For the base of the sensor I=20=
was=20
  thinking about using aluminum.

Please send this to my main email=20
  address, jonfr [at] jonfr.com


Hi Jon,
 
    I use 3" x 1" U channel Al with 1/8" thick Al=20
corner plates for the frame. The arm is about 24" long overall.
    You want a natural pendulum length of at least=20=
1.5=20
seconds, 22". If you make it shorter, you may have problems getting a f=
inal=20
20 second period. Have a look our school seismometer at h=
ttp://www.bgs.ac.uk/education/school_seismology/seismometer.html an=
d=20
http://jcla=
hr.com/science/psn/chapman/lehman/index.html This=20
latter design was modified using a rigid top tube and tungsten carbide=20=
rod=20
suspensions, from the SS balls and plates. 
    It is probably easier to use brass for the mass=
.. I=20
make the arm out of 15 mm SS water pipe, but you can also use Al tube.
    They seem to work well.
 
    Regards,
 
    Chris Chapman