Brett,
I found the following statement by Erhard W. in his online publicati=
on, in the Velocity broadband seismometers section of "Seismic sensors a=
nd their calibration":
As far as the response is concerned, a force-balance circuit as described h=
ere may be seen as a means to convert a moderately stable short- to medium-=
period suspension into a stable electronic long-period or very-long-period =
seismometer. The corner period may be increased by a large factor, for exam=
ple 24-fold (from 5 to 120 sec) in the Streckeisen STS2 seismometer or even=
200-fold (from 0.6 to 120 sec) in a version of the Guralp CMG3. But this f=
actor is not necessarily a figure of merit. Feedback does not reduce the in=
strumental noise; according to section 3.2, short-period suspensions m=
ust be combined with extremely sensitive transducers for a satisfactory sen=
sitivity at long periods.
Assuming the comments you just posted are (mostly) correct, and that this q=
uote of his is also correct-then does not this imply that a good 'soft' spr=
ing is an important part of making a user-friendly-for-construction instrum=
ent? I interpret his statement to mean that 'herculean' efforts in the re=
alm of sensor/transducer and electronics would be necessary for the Mettler=
balance to ever work as desired for seismic purposes.
Randall
Brett,
I found the =
following statement by Erhard W. in his online publication, in the Velocity broa=
dband seismometers section of “Seismic sensors a=
nd their calibration”:
=
As far as the response is concerned, a force-balance circuit =
as described here may be seen as a means to convert a moderately stable sho=
rt- to medium-period suspension into a stable electronic long-period or ver=
y-long-period seismometer. The corner period may be increased by a large fa=
ctor, for example 24-fold (from 5 to 120 sec) in the Streckeisen STS2 seism=
ometer or even 200-fold (from 0.6 to 120 sec) in a version of the Guralp CM=
G3. But this factor is not necessarily a figure of merit. Feedback does not=
reduce the instrumental noise; according to section =
3.2, short-period suspensions =
must be combined with extremely sensitive transducers for a satisfactory se=
nsitivity at long periods.
<=
/o:p>
Assuming the comments you just posted are (most=
ly) correct, and that this quote of his is also correct—then does not=
this imply that a good ‘soft’ spring is an important part of m=
aking a user-friendly-for-construction instrument? I interpret his statement to mean that &=
#8216;herculean’ efforts in the realm of sensor/transducer and electr=
onics would be necessary for the Mettler balance to ever work as desired fo=
r seismic purposes.
Randall
=