## 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

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

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