PSN-L Email List Message
Subject: Re: Anyone seen this MS thesis: Improving a Geophone
From: ChrisAtUpw@.......
Date: Mon, 4 Dec 2006 18:32:59 EST
In a message dated 2006/12/04, ivey@.......... writes:
> You can fit the geophone with a negative input impedance pre
> amplifier, which converts the 'dog leg' f^2 + the flat geophone responses into a
> much smaller straight line response proportional to f. You then put this through
> a low frequency bandpass filter set at your minimum frequency of interest.
> See the ARRL radio handbook. This removes the slope :f and you then amplify /
> filter the signal further. However, this does need an extremely low noise and
> specialised first amplifier. See
> http://www.lennartz-electronic.de/MamboV4.5.2/
Hi Jack,
Sorry about that! It worked for me.
Go to http://www.lennartz-electronic.de/MamboV4.5.2/
In the left hand column under Main Menu, click on downloads;
then click on PDF;
then click on Brochures;
then at the bottom of the page click on Seismometers Short Form and
click Download.
It is quite a large file ~1 MB and the relevant information is on P 13
& seq. It also has the reference on P 3 for the Erich Lippmann Patent No: DE
3307575 C2 as of 20/12/1984
Lennartz use both this method and the Roberts' boost amplifier method
in their seismometers. They produce 1 sec, 5 sec and 20 sec sensors.
I use a modification of the Roberts' method. I can get 0.5 Hz out of a
4.5 Hz geophone OK. Any further increase in period and you may start to see
1/f noise. With Lippmann's method, you may need a lower noise than ordinary
opamps can provide. I suspect that a x10 period gain may be easier to obtain with
2 Hz geophones. The mass is greater and internal noise is lower than on a 4.5
Hz geophone.
Regards,
Chris Chapman
In a me=
ssage dated 2006/12/04, ivey@.......... writes:
&=
nbsp; You can fit the geophone with a negative input impedance pre amplifier=
, which converts the 'dog leg' f^2 + the flat geophone responses into a much=
smaller straight line response proportional to f. You then put this through=
a low frequency bandpass filter set at your minimum frequency of interest.=20=
See the ARRL radio handbook. This removes the slope :f and you then amplify=20=
/ filter the signal further. However, this does need an extremely low noise=20=
and specialised first amplifier. See http://www.lennartz-electronic.de/Mambo=
V4.5.2/
Hi Jack,
Sorry about that! It worked for me.
Go to http://www.lennartz-electronic.de=
/MamboV4.5.2/
In the left hand column under Main Menu=
, click on downloads;
then click on PDF;
then click on Brochures;
then at the bottom of the page click on=
Seismometers Short Form and click Download.
It is quite a large file ~1 MB and the=20=
relevant information is on P 13 & seq. It also has the reference on P 3=20=
for the Erich Lippmann Patent No: DE 3307575 C2 as of 20/12/1984
Lennartz use both this method and the R=
oberts' boost amplifier method in their seismometers. They produce 1 sec, 5=20=
sec and 20 sec sensors.
I use a modification of the Roberts' me=
thod. I can get 0.5 Hz out of a 4.5 Hz geophone OK. Any further increase in=20=
period and you may start to see 1/f noise. With Lippmann's method, you may n=
eed a lower noise than ordinary opamps can provide. I suspect that a x10 per=
iod gain may be easier to obtain with 2 Hz geophones. The mass is greater an=
d internal noise is lower than on a 4.5 Hz geophone.
Regards,
Chris Chapman
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