© Brooke Clarke 2005 - 2013

## Background

## Shoplifting prevention tags

## Fluxgate

## Fluxmeter

## Links

Magnetometers measure magnetic
fields. There are scalar types that measure the total
field and there are vector types that measure the field
strength only along one axis. Some applications use 2 or
3 of the vector type sensors. There are AC only units
and more capable units that measure both DC and AC
fields. There quite a number of different sensor
technologies but this page is aimed at home built
magnetometers.

The shoplifting prevention tags
used on many products contain strips of thin magnetic
materials, one of which can be used as the basis of a home
built magnetic flux gate type field sensor. The common
U.S. drinking straw has an O.D. of about 9 mm (0.238 inches)
and will contain the sensor strip.

The Fluxgate (see my Fluxgate patents web page) is the
most sensitive of the different sensor types. It's used
for satellite applications, sonobuoys, laboratory instruments
and many other applications. A fluxgate has two
operational states:

### Toroid Equations

- The core is saturated by a drive coil. In this
state the magnetic field lines are undisturbed by the core
as if there was no core.

- The core is not saturated. In this state the
magnetic field lines are concentrated into the core.
The higher the permeability the more the flux lines are
concentrated into the core, so supermalloy or similar
material is good.

These are in cgs units, but
there are other units used making magnetic calculations
complicated since the MKS units all have different names.

B = (E * 1E8) / (4 * A * N *
f)

where:

B is Flux Density in Gauss

E is RMS Voltage across coil

A is Core cross section area in cm^2

N is the number of turns

f is the frequency in Hz

H = (0.4 * PI * N * I) / L

Where:

H is the magnetic field strength in Oersted

PI is 3.14159...

N is the number of turns

I is the current in Amps

L is the magnetic path length in cm

where:

B is Flux Density in Gauss

E is RMS Voltage across coil

A is Core cross section area in cm^2

N is the number of turns

f is the frequency in Hz

H = (0.4 * PI * N * I) / L

Where:

H is the magnetic field strength in Oersted

PI is 3.14159...

N is the number of turns

I is the current in Amps

L is the magnetic path length in cm

The fluxmeter is a device that integrates the magnetic lines to come of with the total strength of a magnet.

Handbook_for_Electrical_Engineers 1917 edited by Harold Pender - dead beat galvanometer

Electricity and Magnetism for Advanced Students 1920 by Sydney George Starling - equations for ballistic galvo fluxmeter.

Producing wound components -

International Coil Winding Association - mostly transformer related, but a couple of Strip Would Core suppliers.

Permag Ltd -

Wiltan Ltd. -

Telcon UK - Strip Wound Toroidal Cores -

Magnetics -

Publications at the Space Magnetometer Group, IAU-DTU

Back to Brooke's: PRC68, Products for Sale, Magents, DC
PM Motors, F.W. Bell Gaussmeter,
Walker Gaussmeter, Inductors, LoopstickInternational Coil Winding Association - mostly transformer related, but a couple of Strip Would Core suppliers.

Permag Ltd -

Wiltan Ltd. -

Telcon UK - Strip Wound Toroidal Cores -

Magnetics -

Publications at the Space Magnetometer Group, IAU-DTU