PSN-L Email List Message
Subject: RE: Lehman magnet/coil position
From: Richard Gagnon richg_1998@.........
Date: Thu, 3 Oct 2002 19:04:16 -0700 (PDT)
Ok. Sounds good. I have been monitoring the psn messages off and on and I
remember the recent discussion you had so I will go with the magnet on the
base. I have plenty of #30 wire wrap.
My area has occasional cars, school bus and a ups truck. It is a (I think)
fairly quiet area.
By the way, where do you find 1/4 inch copper for the damping? I have
everything but that. I do have 1/4 inch aluminum but I do not know if that will
work. Any ideas? Thank you.
--- "Jan D. Marshall" wrote:
> 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
> 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,
> 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
> 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?
> Chris Chapman
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