PSN-L Email List Message

Subject: Re: Geophone questions
From: "tchannel" tchannel@..............
Date: Mon, 28 May 2007 08:21:10 -0600

Hi Geoffrey,   This is a follow up question.
Which would create the most useful current, under these conditions:
The coil, being a donut, 1" hole, 3/4" thick.
The magnet inserted into the 1" hole, is a ring, 1/4" thick, 3/4" OD, with a 
1/4" hole in the center.

1  The N pole enters and exit the top 1/4" of the coil, in and out.  This 
results in only the N pole entering the coil.
2  The magnet, at rest, is now midway inserted into the coil.  This results 
in both the N and S poles actively engaging the coil. My thinking is that 
you would be getting a push/pull affect, as it moves in either direction.

Thanks, Ted

----- Original Message ----- 
From: "Geoffrey" 
Sent: Monday, May 28, 2007 4:22 AM
Subject: Re: Geophone questions

> 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 sides.
> 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 before.
> Coils and magnets are ancient history but that about all po-folk can play 
> with.
> ----- Original Message ----- 
> From: "tchannel" 
> To: 
> 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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