Hi

The bedrock is made out of basalt, it is the most common rock in
Iceland. I live in a slope of a extint volcano and this is one of it's
older lave flows that I am top of.

I found out why the attraction was happeing. The boom is made out of
iron and in 15 second setup it is so sensitive that the magnet
attratching it when it is too close. I am going to fix that issue
tomorrow by replacing the boom the aluminum one that I have. I cannot
use it now, as I need to do minor changes to it so it works properly.

Regards.
J=F3n Fr=EDmann.

On =FEri, 2009-05-26 at 06:18 -0700, Geoffrey wrote:
> You Lucky Devil being on bedrock of Granite or ??
> I got to go 800 feet underground to get to bedrock.
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> Have you considered possibly static electric charges
> as causing the attraction on your boom ?
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> I have found when its very dry in the summer here
> in AZ my whole place is charged like a rubber balloon
> and until I grounded everything caused great problems
> with my amplifier giving me bogus signals. It was
> more like a proximity sensor than an EQ detector.
> Use high quality microphone cable ( 100% shielded )
> for all connections even power. Ground everything
> but prevent ground loops from forming by cutting the shield
> before it reaches the thing its going to from
> the amplifier. Ground loops are unwanted stray AC/DC currents
> circulating within the ground itself. Can be induced like in
> a transformer.
> Or so I understand.
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> ----- Original Message -----=20
> From: "J=F3n Fr=EDmann" 
> To: 
> Sent: Monday, May 25, 2009 4:43 PM
> Subject: Re: Did I get 12 second period ?
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> Hi all
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> After spending almost thee hours on the setup on the sensor. It appears
> that I have managed to get ~15 second period, at least that is what
> early resault tell me, I don't think I can get any better then that. I
> did solve the magent pull issue by incresing the distance between the
> coil and the magnet, it still gives signal. Everything that comes close
> to the magent is made out of non-magnetic stuff, but for some unkown
> reason there was magnetic pull.
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> The setup is not much diffrent. But I did change about the legs, so
> there is no soft spot under them any more.
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> Current housing build rules state that gravel must be put around basis
> of a house. The ground also only freezes 70 cm over the winter here in
> Iceland. The place where I live is build on a bedrock that goes down few
> km, I would guess.
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> Regards.
> J=F3n Fr=EDmann.
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> On m=E1n, 2009-05-25 at 18:23 -0400, ChrisAtUpw@....... wrote:
> > In a message dated 25/05/2009, gmvoeth@........... writes:
> >         The floor is level, this is the same floor where I keep my
> >         geophone, with any issues.
> >
> >         However, the lehman sensor appears to be this high so I can
> >         get 12 to 20
> >         second period. I am not sure why that is.
> > Hi Jon,
> >
> >     It is the angle between the local vertical and the line joining
> > the centres of rotation of the top and bottom bearings which
> > determines the period.
> >     http://www.jonfr.com/myndir/v/geology/lehman/p5100003.jpg.html show=
s the bottom bearing. You need to loosen the nuts and
> > unscrew them so that the head of the bolt is a few mm or more further A=
WAY from the bottom cross bar, towards the mass. The
> > tighten the nuts again. You will also have to adjust the top suspension=
.. Maybe adjust the top suspension so that the bolt head is
> > further away from the mass end?
> >         The only problem that I am dealing with now is that once I
> >         have setup the correct period. I sometimes find that the coil
> >         slides to the magnets and gets stuck there. I do not know why
> >         that movment happens.
> >     http://www.jonfr.com/myndir/v/geology/lehman/p5100005.jpg.html
> >
> >
> >
> >     You have a bolt through the centre of the coil and another
> > one suspending it from the arm. Are these bolts, nuts,
> > washers completely NON MAGNETIC? eg.Brass and not nickel plated? Can
> > you replace the metal bolt through the coil with a nylon bolt? Maybe
> > bolt or stick the coil to a sheet of fibreglass / plastic and attach
> > this to the arm?
> >     What metal is the plate supporting the magnet?
> >
> >     Regards,
> >
> >     Chris Chapman
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