44
Measure FERITSCOPE® DMP30
8.3 Parameters that influence the Delta-ferrite content measurement
The following factors influence the readings of a -ferrite content measurement:
Specimen curvature
The influence takes effect from following curvature diameters:
- diameters less than 50 mm (1.97 ") for convex curvatures,
- diameters less than 80 mm (3.15 ") for concave curvatures.
As a general rule: The smaller the curvature diameter of the specimen, the
greater the measurement error. Use the following equation for correction the
measured value:
Fe
T
= Fe
m
· k
Use the diagrams from page 45 and 46 to read the correction factor for convex
curved specimens, suitable for the used measurement unit. Observe our limita-
tion of liability on Page 5.
Specimen thickness
The influence takes effect from a specimen thickness less than 2 mm (0.08 ").
As a general rule: The thinner the thickness of the specimen, the greater the
measurement error. Note: For very small
-ferrite contents, determine the
thickness influence in test measurements.
Cladding thickness
The influence takes effect from a cladding thickness less than 2 mm (0.08 "). As
a general rule: The thinner the cladding thickness, the greater the measure-
ment error.
Edge distance of the measurement location
The influence takes effect if the distance of the measurement location from the
edge is less than 2 mm (0.08 "). As a general rule: The smaller the edge
distance, the greater the measurement error.
Surface roughness
However, the surface roughness is strongly dependent on the -ferrite content
and the influence cannot be stated quantitatively. The influence is relatively
small for -ferrite contents of < 10 Fe% (< ca. 10 FN). It rises with an increasing
-ferrite content and can be reduced best by combining a sufficient number of
single readings to one meaningful mean value.
Fe
T
: Ferrite content within the trueness from the probe data
sheet
Fe
m
: Measured ferrite content
k: Correction factor read from the diagram
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