Hi Meredith,

Just one other point . The free period can be adjusted easily by =
changing the spring length from fairly short periods to infinite period =
and over  to the negative period region where the spring mass system is =
unstable.

The free period is usually set to about 3 seconds. The free period in a =
closed loop system is relatively unimportant as long as it is somewhere =
in the 1 second and longer region. The Guralp sensors have a free period =
of only 1/2 second and a 360 second long period response.

Dave=20









 Hi Meredith,
 
Just one other point . The free period =
can be=20
adjusted easily by changing the spring length from fairly short =
periods to=20
infinite period and over  to the negative period region where the =
spring=20
mass system is unstable.
 
The free period is usually set to =
about 3=20
seconds. The free period in a closed loop system is relatively =
unimportant=20
as long as it is somewhere in the 1 second and longer region. The Guralp =
sensors=20
have a free period of only 1/2 second and a 360 second long period=20
response.
 
Dave