In a message dated 2008/10/03, tchannel1@............ writes:

> My question is:  Does a Damper, oil or magnetic, not act the same as hinge 
> friction?, in that, the signal must, first, overcome the resistance of the 
> Damper?

Hi Ted,

       Forget oil damping. Magnetic damping is easy to use, not expensive and 
clean.

       To stop the arm oscillating, you want to generate a retarding force 
accurately proportional to the velocity. You DON'T want ANY static friction

> Is an undamper sensor  more sensitive than a dampered sensor? 
> 
       An undamped arm will oscillate at it's natural frequency and be very 
sensitive, but the amplitude will form a wavy line over time as signals 
continue to roll in. However, you want a response which is FLAT with frequency, say 
at all periods from 20 seconds to 5 Hz and changes as the incoming signal level 
changes, NOT a response which just has a peak at 20 seconds.

       It is possible to use an underdamped sensor, but you need to do some 
complicated maths analysis on it to extract the original ground motion from the 
quake. There is no problem getting a high enough sensitivity from 
semiconductor amplifiers. What limits your detection level is the ambient noise in the 
ground from road traffic, wind noise from trees, wave noise from the oceans, 
noise from weather systems......

       Regards,

       Chris Chapman
   
In a me=
ssage dated 2008/10/03, tchannel1@............ writes:



My question is:  Does a Da=
mper, oil or magnetic, not act the same as hinge friction?, in that, the sig=
nal must, first, overcome the resistance of the Damper?




Hi Ted,



       Forget oil damping. Magnetic damping is=
 easy to use, not expensive and clean.



       To stop the arm oscillating, you want t=
o generate a retarding force accurately proportional to the velocity. You DO=
N'T want ANY static friction



Is an undamper sensor  mo=
re sensitive than a dampered sensor? 



       An undamped arm will oscillate at it's=
 natural frequency and be very sensitive, but the amplitude will form a wavy=
 line over time as signals continue to roll in. However, you want a response=
 which is FLAT with frequency, say at all periods from 20 seconds to 5 Hz an=
d changes as the incoming signal level changes, NOT a response which just ha=
s a peak at 20 seconds.



       It is possible to use an underdamped se=
nsor, but you need to do some complicated maths analysis on it to extract th=
e original ground motion from the quake. There is no problem getting a high=20=
enough sensitivity from semiconductor amplifiers. What limits your detection=
 level is the ambient noise in the ground from road traffic, wind noise from=
 trees, wave noise from the oceans, noise from weather systems......



       Regards,



       Chris Chapman