Factors Affecting the Measuring Precision
1. The magneic nature of metal base
Measuring the thickness with magnetic method can be affected by the change of base
metal’s magnetic field (in pratical application, the magnetic change of mild steel can
be considered as slight). To avoid the effect of heat treatment and cold processing, we
should calibrate the unit with the standard tablet which has the same magnetic nature
with base metal specimen.
2. The electric nature of metal base
The conductivity of base metal has the effect on measurement. And the conductivity
of base metal has connection with its composition and heat treatment method.
Calibrate the unit with the standard tablet which has the same electric nature with base
metal specimen.
3. The thickness of metal base
Every unit has a critical base metal thickness. If above this thickness, the
measurement will not be affected by the thickness of base metal.
4. Edge effect
The unit is sensitive to the specimen’s surface shape. Therefore, the result is
unreliable if approaching the specimen’s edge or inner corner.
5. Curvature
The curvature of the specimen has an effect on the measurement. And the effect is
always increasing obviously with the derease of curvature radius, Therefore, the measuremment is
not reliable for the flexible specimen.
6. Deformation of specimen
The detector can distort the specimen with soft coating. Therefore, the datum are unreliable that
measured from these specimens。
7. Surface roughness
The base metal and the surface roughness degree has effects on the measurement. The effect
increases as the roughness degree increases. The rough surface can cause the system error and
accidental error. When make every measurement, add the measuring times on different positions
to avoid the accidental error. If the base metal is rough, select several positions to calibrate the
unit’s zero point from the base metal which is uncoated and has the similar roughness, or calibrate
the unit’s zero point after using the liquor which has no corrosion to the base metal to dissolve the
coating