PSN-L Email List Message

Subject: Re: Did I get 12 second period ?
From: "Geoffrey" gmvoeth@...........
Date: Tue, 26 May 2009 06:18:50 -0700

You Lucky Devil being on bedrock of Granite or ??
I got to go 800 feet underground to get to bedrock.

Have you considered possibly static electric charges
as causing the attraction on your boom ?

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.

----- Original Message ----- 
From: "Jón Frímann" 
Sent: Monday, May 25, 2009 4:43 PM
Subject: Re: Did I get 12 second period ?

Hi all

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.

The setup is not much diffrent. But I did change about the legs, so
there is no soft spot under them any more.

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.

Jón Frímann.

On mán, 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.
> shows 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 AWAY 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.
>     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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