## PSN-L Email List Message

Subject: Re: Geophone questions
From: ChrisAtUpw@.......
Date: Mon, 28 May 2007 11:11:57 EDT

```In a message dated 2007/05/28, tchannel@.............. writes:

> 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.
> or
> 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.

Hi Geoff, Ted,

1 gives the max output

In 2 you DO get a push pull effect, but since the movement direction
and the winding direction are all constant, the induced voltages tend to CANCEL
!

If you want to use a single magnet like this, you need to wind two
coils on the same former, end to end but connected serially in the opposite
sense. The overall coil length might be 3x the magnet length, or a bit more.

Regards,

Chris Chapman
In a me=
ssage dated 2007/05/28, tchannel@.............. writes:

Hi Geoffrey,   This i=
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.&nbs=
p; This
results in only the N pole entering the coil.
or
2  The magnet, at rest, is now midway inserted into the coil.  Thi=
s 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.

Hi Geoff, Ted,

1 gives the max output

In 2 you DO get a push pull effect, but=
since the movement direction and the winding direction are all constant, th=
e induced voltages tend to CANCEL !

If you want to use a single magnet like=
this, you need to wind two coils on the same former, end to end but connect=
ed serially in the opposite sense. The overall coil length might be 3x the m=
agnet length, or a bit more.

Regards,

Chris Chapman
```