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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