BARTINGTON INSTRUMENTS
Page 49 of 82 OM0408/49
Figure 18. MS2K depth response
14.2.2. Conductivity Effects
A low operating frequency, f, and the ability to be positioned at the point of interest make
the MS2K sensor a good choice for the measurement of the magnetic properties of poorly
conducting metals, e.g. stainless steel.
The resistivity,
r
, and relative permeability of the specimen,
m
r
, will also determine the depth of
penetration of the sensor’s magnetic field where:
Depth S = √ (
r
/
πm
f) where
m = m
0
m
r
and is defined as that depth at which the flux diminishes by a factor of
1
/e (0.37). From the examples
given below it is apparent that at a frequency of 1kHz the skin depth for stainless steel is compatible
with measurements performed using the MS2K sensor:
Cu, Ag
S = approx. 2mm
Fe
S = approx. 0.2mm
Stainless steel
S = approx. 14mm
Note that for Fe the high value of mr = 500 accounts for the significantly low value of S, as does
the low resistivity of Cu and Ag.
14.2.3. Calibration
The sensor is calibrated to read true volume susceptibility where the sample is effectively
infinitely large. The value
c
vol
displayed on the MS2 on the x1 and CGS range is therefore
equivalent to that which would be obtained for 1cc, and is therefore
c
vol
x 10
-6
CGS.
For further guidance on dimensional systems, refer to
MS2B Dual Frequency Sensor
.
A calibration sample is provided and should be used periodically to check that the sensor is
working correctly.
Note:
Never expose this calibration sample to high magnetising fields as these can alter
the calibration value. Keep the sample with the sensor at all times.
14.3. Operating Instructions
14.3.1. Connecting Up
Connect the MS2K sensor to the MS2 meter via the supplied TNC-TNC coaxial cable. Select the
desired operating range on the MS2 meter and, after a few minutes warm-up time, the sensor
will be ready to take measurements.
