PSN-L Email List Message

Subject: Re: Mini Lehman Damping
From: "meredith lamb" paleoartifact@.........
Date: Fri, 13 Jun 2008 19:54:49 -0600


Hi all,

Magnetic dampening on iron can be quite more adjustable than the coil pickup
assembly.  One can put on additional neodymium
magnets and in whatever (limited) quanity, varible rating, to make it work
with your seismo.  The "key" or strongest dampening area is simply
the joints (edges) between the mounted magnets as it is here where the
"magnetic arching crossover" field is the strongest, and hence the eddy
current.  Another way of putting it is that its not the center/broad area of
the individual magnets where the very strongest eddy current is induced in
your aluminum/copper; its the area immediately near the (crossover) joints
thereof.

I put up another brief web page for this subject, see:

http://seismometer.googlepages.com/magnetdampening

Take care, Meredith Lamb

On Fri, Jun 13, 2008 at 6:12 PM, Connie & Jim Lehman 
wrote:

>  *  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 -----
>  *From:* JAMES RIDOUT 
> *To:* PSN-L@..............
> *Sent:* Thursday, June 12, 2008 1:55 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
> of scrap aluminium
>       from work. It has a NeFe 3/4" x 1.5" magnet inside a coil of 6000
> turns of 0.18mm
> 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=7080078
>
>
>
>
Hi all,

Magnetic dampening on iron can be quite more adjustable than the coil pickup assembly.  One can put on additional neodymium
magnets and in whatever (limited) quanity, varible rating, to make it work with your seismo.  The "key" or strongest dampening area is simply
the joints (edges) between the mounted magnets as it is here where the "magnetic arching crossover" field is the strongest, and hence the eddy
current.  Another way of putting it is that its not the center/broad area of the individual magnets where the very strongest eddy current is induced in
your aluminum/copper; its the area immediately near the (crossover) joints thereof. 

I put up another brief web page for this subject, see:

http://seismometer.googlepages.com/magnetdampening

Take care, Meredith Lamb

On Fri, Jun 13, 2008 at 6:12 PM, Connie & Jim Lehman <lehmancj@...........> wrote:
  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 -----
From: JAMES RIDOUT
Sent: Thursday, June 12, 2008 1:55 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 of scrap aluminium
      from work. It has a NeFe 3/4" x 1.5" magnet inside a coil of 6000 turns of 0.18mm
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


[ Top ] [ Back ] [ Home Page ]