Appendix 5. Calculating Magnetic Susceptibility - Bartington MS2 Operation Manual

Appendix 5. Calculating Magnetic Susceptibility

The magnetic state of a specimen is generally described by the following equation:
B=µ (H+M) ... (1)
0
where:
B is the flux density of the specimen in T (Tesla). (B = µH)
µ is the permeability of free space in N A
0
H is the applied field strength in Am
M is the magnetisation of the specimen in Am
Dividing through by H we get:
µ= µ + µ c ... (2)
0 0 vol
where:
µ is the permeability of the specimen (in N A
k is the volume magnetic susceptibility of the specimen (dimensionless)
Rewriting, we get:
c
µ = µ - µ ... (2)
vol
0 0
The MS2/3 magnetic susceptibility system relies on the principle that any changes in the
permeability of a core will cause a change to the inductance of a wound inductor.
The sensors operate on the principle of AC induction. Power is supplied to the oscillator circuit
within the sensor, generating a low intensity alternating magnetic field.
The frequency of oscillation is determined by the inductance of the system. When the inductor
contains only air, the permeabilty µ
inside the inductor, the change in permeability also leads to a change in inductance.
The meter reads the frequency values for µ
inductance, and thus the magnetic permeability. The magnetic susceptibility is then calculated
using equation (2).
The value of µ is constant but the variable of interest is relatively small. Therefore any thermally
0
induced sensor drift needs to be eliminated by occasionally obtaining a new 'air' value, to re-
establish the µ reference.
0
BARTINGTON INSTRUMENTS
. This is a constant (4πx10
-2
.
-1
. (M = c
-1
)
-2
determines the inductance. When a sample is introduced
0
and µ, and uses them to calculate the change in
0
Page 80 of 82
)
-7
H)
vol
OM0408/49