In a message dated 23/03/2008, johnjan@........ writes:

My  understanding of a long period physical pendulum is that sensitivity to 
ground  motion is sacrificed in order to obtain the long  period. 


Hi Ted,
 
    That is NOT my understanding in general.
 
    But you are using a nearly balanced pendulum, with  a high moment of 
inertia but a small C of G to suspension distance, correct?  This type have a long 
period but a LOUSY sensitivity to  linear ground motion. They are however, 
sensitive to ground rotation. 
 
    Longer period pendulums like the Lehman  and the Romberg are very 
sensitive to linear ground motion and make good  seismometers.
 
    Regards,
 
    Chris Chapman



   






In a message dated 23/03/2008, johnjan@........ writes:
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  understanding of a long period physical pendulum is that sensitivity to gr=
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  motion is sacrificed in order to obtain the long=20
period. 

Hi Ted,
 
    That is NOT my understanding in general.
 
    But you are using a nearly balanced pendulum, w=
ith=20
a high moment of inertia but a small C of G to suspension distance, correct?=
=20
This type have a long period but a LOUSY sensitivity t=
o=20
linear ground motion. They are however, sensitive to ground rotation. 
 
    Longer period pendulums like the Lehman=20
and the Romberg are very sensitive to linear ground motion and make goo=
d=20
seismometers.
 
    Regards,
 
    Chris Chapman