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6.1.2.3
“Automatic temperature compensation-manual entering temperature ” mode
This model without inserting an external temperature sensor to calibrate temperature of
testing block and the testing material , only need to input temperature T
A
manual when
calibrate (see 5.3.2.5), the other operation methods are the same as and mode 6.1.2.2. The
model applied to have known temperature of calibration testing block and the testing
material already.
6.2 Lift-off influence
The error influence of the conductivity measurement by distance between the testing
material and the probe.The lift-off compensation with a diameter of 14mm probe can be
about 500 μm and diameter of 8mm probe can be about 200μm of this serial product. The
practical application effect is when the non conducting layer (such as paint, plastic thin film,
dust, etc.) between the probe and the measured material is less than distance from the
lift-off compensation, the measuring conductivity value is correct. Beyond the distance
from the lift-off compensation, the measuring conductivity value will have a greater error.
6.3 Material thickness influence
If the actual material thickness is less than 3 times of the standard penetration depth of
the eddy current standard, the measurement accuracy can not be guaranteed. The standard
penetration depth is determined by the frequency and the conductivity. The flowing
relationship applies,
σ
f
δ
·
503
σ =conductivity in
MS/m
f
=
testing frequency in Hz
δ
=
standard penetration depth in mm
6.3.1
Figure 6.1 shows the dependence between the thickness of the material and the
conductivity and the test frequency, the minimum material thickness required by 3 times the
standard penetration depth (3 ×δ).
