In a message dated 2007/07/23, Paulc@........ writes:

> If I depress the arm say 3/4" on my sensor, the arm will return to zero 
> position overshoot about 1/2 cycle and return to rest at zero.

Hi Paul,
       
       The damping need to set so that if you displace the arm by 10 mm, it 
just swings back through the zero position by ~0.5 mm.

> However the suspension spring rings, resonates at a rate of a few hertz, 
> imparting its resonance on top of the  4 sec period of the sensor.
>  This is what I need to stop.

       Maybe increase the spring tension so that it resonates at >10 Hz and 
set the low pass filter to reject everything above 5 Hz?

> If the suspension spring on the AS-1 is plucked does it not vibrate at some 
> frequency and impart that noise into the machine?

       Certainly it will resonate if you do that, but are you really planning 
for >M6 local quakes? I would be surprised if you ever saw significant spring 
resonance effects. The whole system would need to be shaken at the resonant 
frequency, or by a seismic signal which has a rise time shorter than this. High 
frequency movements are severely damped. You can attach tiny cubic NdFeB 
magnets at points on a spring and mount a copper plate or tube close to them. This 
is sometimes done for leaf springs. 

       Regards,

       Chris Chapman   
In a me=
ssage dated 2007/07/23, Paulc@........ writes:



If I depress the arm say 3/4"=20=
on my sensor, the arm will return to zero position overshoot about 1/2 cycle=
 and return to rest at zero.




Hi Paul,

       

       The damping need to set so that if you=20=
displace the arm by 10 mm, it just swings back through the zero position by=20=
~0.5 mm.



However the suspension spring=20=
rings, resonates at a rate of a few hertz, imparting its resonance on top of=
 the  4 sec period of the sensor.

 This is what I need to stop.




       Maybe increase the spring tension so t=
hat it resonates at >10 Hz and set the low pass filter to reject everythi=
ng above 5 Hz?



If the suspension spring on th=
e AS-1 is plucked does it not vibrate at some frequency and impart that nois=
e into the machine?




       Certainly it will resonate if you do th=
at, but are you really planning for >M6 local quakes? I would be surprise=
d if you ever saw significant spring resonance effects. The whole system wou=
ld need to be shaken at the resonant frequency, or by a seismic signal which=
 has a rise time shorter than this. High frequency movements are severely da=
mped. You can attach tiny cubic NdFeB magnets at points on a spring and moun=
t a copper plate or tube close to them. This is sometimes done for leaf spri=
ngs. 



       Regards,



       Chris Chapman