- 28 -
figure 6.1
6.3.2
If the thickness of the material is less than required thickness of 3×δ, the thickness
of the same material can be superposed to achieve the minimum thickness. In order to
achieve the true credibility of the measurement results, we should pay attention to the
following aspects:
①
In the premise of meeting the minimum thickness, the less the number of layers is more
reliable.
②
Between layer and layer should be treated clean, to reduce the error can not have dust
isolation,
③
The layer and layer should be compacted to reduce air gap, generally not more than
three layers.
6.4 Camber influence
Camber has a direct influence on measurement value. Conductivity calibration use
planar calibration testing block, the probe impedance changes only with material
conductivity. When the probe measures on the camber, the probe impedance changes not
only with the conductivity but also with the diameter of the material surface.According to
the following relationship established formula of curvature compensation.
)
(
)
(
φ
φ
η
σ
σ
σ
: the real conductivity value of material
σ(φ) : conductivity value of material with the curvature diameter φ
η(φ) is correction factor for curvature diameter , the user get the relation curve
for correction coefficient η(φ) and diameter according to the the same material
with different curvature diameter(with same conductivity).
Example 1: using diameter 14mm, conductivity values 60KHZ probe to measure the
conductivity of convex surface, the curvature diameter of work piece is 50mm, measuring
Summary of Contents for 2008 B1
Page 17: ... 14 ...