PSN-L Email List Message

Subject: Re: Round external coils and stacked internal magnets
From: ian ian@...........
Date: Fri, 16 May 2008 19:25:11 +0100


I too have a heretical arrangement: Round coil mounted on the ground and 
a single column horizontal stack of 7 10mm cubed neodymium magnets 
attached to the end of the pendulum, perpendicular to it, which moves 
back and forth inside and along the internal axis of the coil.

This non-optimum arrangement does simplify the mechanical design in that 
there are no signal wires coming off the pendulum.  It would be 
interesting to hear how much is lost by this non-optimum arrangement.  
Is it worth the modification?


meredith lamb wrote:
> Hi all,
> Am getting to the (shall we say a unqualified) opinion that with a 
> choice of round or square/rectangular coils
> with a magnet, that it seems like the round coil approach is the more 
> efficient route to take.  It just simply
> uses all the coil and not just a couple selected sides mainly.  Theres 
> obviously no heavy
> problem to making a round coil; versus the more construction work with 
> a square or rectangular coil. 
> The route you take with the round coil size/shape with the magnet/s 
> can be quite different than most now use.
> Having multi or multiple round (or ring) magnets stacked attracting, 
> with the coil on the outside centered
> seems to be a sensitive and quick approach.   One magnet can work, but 
> with 2 or more, it will increase
> the sensitivity, and, the coil will be normally centered down the 
> length of the magnet stack.  The magnets
> are still mounted on a metal plate.  It still works normally; i.e., 
> movement in one direction will still be + or -
> throughout its continued movement in that direction; and vice versa + 
> or - signal for the other direction.
> For home brew seismometers with a heavy mechanical boom/coil drift 
> problem; this approach would seem
> to be the best ideal design answer.
> Although I've not actually done it, one could also put a iron can 
> around and slightly away from
> such a coil/magnet assembly, and slightly increase the sensitivity, 
> while also providing a measure
> of limiting some magnetic or electro magnetic induction "noise" pickup 
> and air or thermal influence also.
> Tight and limited movement magnet coil assemblys are interesting to be 
> sure; but what the heck; your
> amplifier gain controls should easily take up any slack.
> Take care, Meredith Lamb

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