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This is because the sensor’s relatively high operating frequency of 2kHz can generate eddy
currents within the conductor, which in turn can cause inaccuracies in the susceptibility
measurement. If a good conductor forms a conductive loop, is larger than the FWHM outline and
is more than 0.2mm thick, then apparent negative susceptibility values will be measured.
Note: For this reason cores cannot be measured in split aluminium cladding or trays.
8.2.3. 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 equal to 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 the calibration sample to high magnetising fields as these can alter
the calibration value. Keep the sample with the sensor at all times.
Note: The correct face of the calibration sample must be aligned with the MS2E sensor
face. This is its black face, which is the actual sample material.
Note: The black lines either side of the calibration sample label should be orientated with
the marks on the MS2E sensor head that indicate its long axis
Figure 9 shows the correct position of the calibration sample aligned with the MS2E sensor face.
The calibration label is uppermost so that the black sample face is aligned with the sensor face.
Figure 9. MS2E calibration sample: correct orientation.
Note: Figure 9 is for illustration of the sample orientation only, when the cable is attached
to the sensor it will be easier to measure with the MS2E held in a different position.
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