I have to agree -- I JUST went through this same exercise -- I swapped the
magnet locations (from boom to base) and it made ALL the difference in the
world in the unit stability. (see the thread New Lehman on line (almost))

I was concerned about the wires too -- I used a pair of twisted #30 wire
wrap wires.  If you provide a nice loose coil/loop at the pivot end I don't
think you will see any problem.

Jan Marshall
jandmarshall@............
www.cableone.net/jandmarshall
Nampa, ID

  -----Original Message-----
  From: psn-l-request@.............. [mailto:psn-l-request@.................
Behalf Of ChrisAtUpw@.......
  Sent: Thursday, October 03, 2002 7:42 PM
  To: psn-l@..............
  Subject: Re: Lehman magnet/coil position


  In a message dated 03/10/02, richg_1998@......... writes:


    I am building a Lehman and I wonder if the coil on the boom is better
than the
    magnet on the boom or is it not an issue? From what I have seen,
building
    seismometers seems to be an art form.


  Hi Richard,

        Building seismometers may well be an art form. Getting them working
well maybe where the application of some science / technology is desirable.
Seismometers are designed to have the ability to detect extremely small
motions and forces. Otherwise they are of little use as seismometers. If you
are not in a very isolated and quiet location, putting a powerful U or bar
magnet on the arm will pick up small changes in the local magnetic field
from a wide variety of sources, a visit from the garbage truck, moving the
car, switching on the TV, magnetic storms, down to the steel in your belt
buckle. If your intention is to monitor the garbage truck, etc., that is
fine. If your desire is to only detect seismic vibrations, it is not so
good.

        It is magnetic fields which extend out from the apparatus which
enable it to interact strongly with outside events. If you enclose the
magnet in a screen, the interactions will be reduced. They will not be
eliminated, since you have to use ferromagnetic materials to make the
screen. This is done in some small modern seismometers, but they usually
have a magnetic screen provided. Putting an effective magnetic screen around
a 3 ft Lehman might be more difficult.

        If you have any doubts, why not download the PSN archives and do a
keyword search?

        Regards,

        Chris Chapman





I have=20
to agree -- I JUST went through this same exercise -- I swapped the =
magnet=20
locations (from boom to base) and it made ALL the difference in the =
world=20
in the unit stability. (see the thread New Lehman on line=20
(almost))
 
I was=20
concerned about the wires too -- I used a pair of twisted #30 wire wrap=20
wires.  If you provide a nice loose coil/loop at the pivot end I =
don't=20
think you will see any problem.
 
Jan=20
Marshall
jandmarshall@............
www.cableone.net/jandmarshallNampa,=20
ID 

  
-----Original Message-----
From: =
psn-l-request@.................
  [mailto:psn-l-request@...............On Behalf Of=20
  ChrisAtUpw@.......
Sent: Thursday, October 03, 2002 7:42 =

  PM
To: psn-l@..............
Subject: Re: Lehman=20
  magnet/coil position

In a message dated 03/10/02, richg_1998@......... writes: =



  I am building a Lehman and I wonder if the coil on the =
boom is=20
    better than the 
magnet on the boom or is it not an issue? From =
what I=20
    have seen, building 
seismometers seems to be an art =
form.


Hi Richard,=20
  

      Building =
seismometers may=20
  well be an art form. Getting them working well maybe =
where the=20
  application of some science / technology is desirable. Seismometers =
are=20
  designed to have the ability to detect extremely small motions =
and=20
  forces. Otherwise they are of little use as seismometers. If you are =
not in a=20
  very isolated and quiet location, putting a powerful U or bar magnet =
on the=20
  arm will pick up small changes in the local magnetic field from a wide =
variety=20
  of sources, a visit from the garbage truck, moving the car, switching =
on the=20
  TV, magnetic storms, down to the steel in your belt buckle. If your =
intention=20
  is to monitor the garbage truck, etc., that is fine. If your desire is =
to=20
  only detect seismic vibrations, it is not so good.=20
  

      It is magnetic fields =
which extend=20
  out from the apparatus which enable it to interact strongly with =
outside=20
  events. If you enclose the magnet in a screen, the interactions will =
be=20
  reduced. They will not be eliminated, since you have to use =
ferromagnetic=20
  materials to make the screen. This is done in some small modern =
seismometers,=20
  but they usually have a magnetic screen provided. Putting an effective =

  magnetic screen around a 3 ft Lehman might be more difficult.=20
  

      If you have any doubts, =
why not=20
  download the PSN archives and do a keyword search?=20
  

      Regards,=20
  

      Chris Chapman=20