PSN-L Email List Message

Subject: Re: Geophone questions
From: "Geoffrey" gmvoeth@...........
Date: Mon, 28 May 2007 03:22:57 -0700

Ideally you want a uniform magnetic field through which the wire moves puhsing the electrons all in the same direction.
Take that idea and you will see that the B fields seems to need
to be n-s at one side and s-n at the other of any kind of coil
but I would imagine that a rectangular loop is better than a circular one so that the coil moves at right angle to the fiels on both 
The strength of the B field is ectremely important, the stronger the better.
I once saw an impressive demonstration of magnetic field strength at Arizona State University where an aluminum bar was dropped from 
vertical (hinged at one end) and was stopped cold by the magnetic field alone. but the magnet was absolutely huge. it was tapered to 
concentrate the magnetic lines of force.
You want a uniform field through which the wire moves. The current is dependent upon the B field strength and the voltage the number 
of loops.of wire I would think the same amount of energy is present no matter what the coil so if you could make an ideal current 
sensor that looks only at hole flow is really what you may want instead of lots of turns og 40ga wire. I can only imagine what the 
researchers are using today with technology being what it is and everything I suspect they have sensors we have never imagined 
Coils and magnets are ancient history but that about all po-folk can play with.

----- Original Message ----- 
From: "tchannel" 
Sent: Sunday, May 27, 2007 05:43
Subject: Geophone questions

I have a few questions about magnets and coils:

1  I have seen a cross section of a Geophone, magnet, spring and mass etc.  When used in a Seismic Sensor, how is it dampened, or is 
it do electronically?

2 I am making a new vertical sensor, and this question has to do with the coil and magnet.  The coil is a spool with a 1" dia. hole 
in the center.  The thickness of the coil is 3/4"   The value of the coil is 500ohms.   The magnet will be suspended from a rod and 
centered in this 1" hole. Left to Right and Top to Bottom.

I can choose from three magnets.  One magnet 1/4" thick x 3/4" dia. centered leaving 1/4" of coil above and below the 
magnet......... OR Two magnets 1/4" thick, together to equal 1/2" x 3/4", leaving 1/8" of coil above and below the two magnets when 
centered........... Lastly I could use One magnet 1/2" thick x 3/4" dia. leaving 1/8" above and below.

This is a basic question about the magnet's surface and the N/S poles,  I do not know the science, but just curious about just these 
three scenarios, which arrangement is the best?.....I could try all three and measure the result, but in theory is it better one way 
or the other?

Thanks, Ted 


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