## PSN-L Email List Message

Subject: Re: Sensor and Damping magnets
From: Bobhelenmcclure@.......
Date: Tue, 28 Mar 2006 16:54:23 EST

```Hi Chris,

Take a look at

_http://www.jclahr.com/science/psn/mcclure/horiz.html_
(http://www.jclahr.com/science/psn/mcclure/horiz.html)

for my magnet design. This page shows different sized magnets, but 2" by 3"
by 1/4" steel plates for the Gaussboys blk18 magnets work ok, with only slight
saturation.

I have no problems with sensitivity vs damping. My coil resistance  is 340
ohms, and critical damping is achieved with ~25,000 ohms shunt  resistance.

Regarding output sensitivity, the formula is V=BLnv, where B is  magnetic
field in Teslas, L is the effective length of wire per turn (in meters)
cutting the magnetic field lines, n is the number of turns, and v is the  velocity,
in meters per second.

The L per turn is twice the length of the Gaussboys magnets , so  L=0.1m.
Let n=1100, B=0.8T, and v=1.0 m/s. This gives a sensitivity of  88v-s/m.

The biggest problem I have with this design is the diamagnetism of  the
copper wire. Having a core of acrylic plastic for the coil and an outer  plate of
acrylic plastic helps to reduce net diamagnetic force on the coil  assembly,
since the plastic is also diamagnetic.

Bob

Hi Chris,

Take a look at

http://www.jcl=
ahr.com/science/psn/mcclure/horiz.html

for my magnet design. This page shows different sized magnets, but 2" b=
y 3"=20
by 1/4" steel plates for the Gaussboys blk18 magnets work ok, with only slig=
ht=20
saturation.

I have no problems with sensitivity vs damping. My coil resistan=
ce=20
is 340 ohms, and critical damping is achieved with ~25,000 ohms shunt=20
resistance.

Regarding output sensitivity, the formula is V=3DBLnv, where B i=
s=20
magnetic field in Teslas, L is the effective length of wire per turn (in met=
ers)=20
cutting the magnetic field lines, n is the number of turns, and v is the=20
velocity, in meters per second.

The L per turn is twice the length of the Gaussboys magnets , so=
=20
L=3D0.1m. Let n=3D1100, B=3D0.8T, and v=3D1.0 m/s. This gives a sensitivity=20=
of=20
88v-s/m.

The biggest problem I have with this design is the diamagnetism=20=
of=20
the copper wire. Having a core of acrylic plastic for the coil and an outer=20
plate of acrylic plastic helps to reduce net diamagnetic force on the coil=20
assembly, since the plastic is also diamagnetic.

Bob
```