Several Situations Affecting the Measurement Accuracy of Coating Thickness Gauge
1. Magnetic properties of base metal
The thickness measurement by magnetic method is affected by the magnetic change of the base metal (in practical applications, the change of the low carbon steel's magnetic properties can be considered to be slight). The standard sheet is used to calibrate the instrument; it can also be calibrated with the test piece to be coated.
2. Electrical properties of base metal
The conductivity of the base metal affects the measurement, and the conductivity of the base metal is related to its material composition and heat treatment method. The instrument is calibrated using a standard that has the same properties as the base metal of the test piece.
3. Base metal thickness
Every instrument has a critical thickness of the base metal. Above this thickness, the measurement is not affected by the thickness of the base metal.
4. Edge Effects
The instrument is sensitive to abrupt changes in the surface shape of the specimen. It is therefore unreliable to measure near the edge of the specimen or at the inner corner.
5. Curvature
The curvature of the specimen has an influence on the measurement. This effect always increases significantly as the radius of curvature decreases. Therefore, measurements on the surface of a curved specimen are unreliable.
6. Deformation of the test piece
The probe will deform soft-covered specimens, so reliable data cannot be measured on these specimens.
7. Surface roughness
The surface roughness of the base metal and capping layer affects the measurement. The roughness increases, the influence increases. Rough surfaces will cause systematic and accidental errors, and the number of measurements should be increased at different positions for each measurement to overcome such accidental errors. If the base metal is rough, it is also necessary to take several positions on the uncoated base metal specimen with similar roughness to calibrate the zero point of the instrument; zero.
8. Magnetic field
The strong magnetic field generated by the surrounding electrical equipment will seriously interfere with the magnetic thickness measurement.
9. Attachment substances
The instrument is sensitive to adhering substances that prevent the probe from being in close contact with the surface of the covering layer. Therefore, the adhering substances must be removed to ensure direct contact between the probe of the instrument and the surface of the test piece.
10. Probe pressure and side head orientation
The amount of pressure applied by the probe on the test piece will affect the measurement reading, so keep the pressure constant. How the probe is placed has an impact on the measurement. During the measurement, the probe should be kept perpendicular to the surface of the specimen.
