James--a very interesting design-working into a chart recorder =
directly.  This reminds me of the early days of working with the =
system--before building an amplifier with two 741 op amps.  With liquid =
damping--it is easy to be overdamped.  Go magnetic damping as =
suggested--you will be able to "tune" easily for optimum performance.  =
As for filtering--there is alot of ideas out there--I only filtered the =
mechanical frequencies, and AC--40 to 60 cycles with a passive =
filter---let the microseisms come through--their changes were =
entertaining between events!!
   Keep up the good work,   Jim Lehman
  ----- Original Message -----=20
  From: JAMES RIDOUT=20
  To: PSN-L@.................
  Sent: Thursday, June 12, 2008 1:55 AM
  Subject: Re: Mini Lehman Damping


  Hi,=20
  This is a link to a picture of my mini lehman, It is one I made from =
bits of scrap aluminium=20
        from work. It has a NeFe 3/4" x 1.5" magnet inside a coil of =
6000 turns of 0.18mm=20
  enamelled copper wire, coupled directly to a chart recorder on the =
50Mv setting NO amplification or filters ( is this wrong????). I pick up =
constant microseisisms all the time
   at about 5 secs period. The unit I have managed to tune to 15 =
seconds, and still be
  quite stable.
                         James
  =
http://www.freewebs.com/jridout/apps/photos/photo.jsp?photoID=3D7080078


   =20







  James--a very =
interesting=20
design-working into a chart recorder directly.  This reminds me of =
the=20
early days of working with the system--before building an amplifier with =
two 741=20
op amps.  With liquid damping--it is easy to be overdamped.  =
Go=20
magnetic damping as suggested--you will be able to "tune" easily for =
optimum=20
performance.  As for filtering--there is alot of ideas out there--I =
only=20
filtered the mechanical frequencies, and AC--40 to 60 cycles with a =
passive=20
filter---let the microseisms come through--their changes were =
entertaining=20
between events!!
   Keep up the good=20
work,   Jim Lehman

  
----- Original Message ----- 
  From:=20
  JAMES RIDOUT 
  
To: PSN-L@.............. 
  
Sent: Thursday, June 12, 2008 =
1:55=20
  AM
  
Subject: Re: Mini Lehman =
Damping
  


  
Hi, 
  
This is a link to a picture of my mini lehman, It is one I made =
from bits=20
  of scrap aluminium 
  
      from work. It has a NeFe 3/4" x =
1.5"=20
  magnet inside a coil of 6000 turns of 0.18mm 
  
enamelled copper wire, coupled directly to a chart =
recorder on the=20
  50Mv setting NO amplification or filters ( is this wrong????). I pick =
up=20
  constant microseisisms all the time
  
 at about 5 secs period. The unit I have managed to tune to =
15=20
  seconds, and still be
  
quite stable.
  =
           &n=
bsp;          =20
  James
  
http://www.freewebs.com/jridout/apps/photos/photo.jsp?photoID=3D7=
080078


  
 =20