Factors Affecting the Measurement Accuracy of Coating Thickness Gauges
1. Magnetic properties of the base metal
Magnetic thickness measurement is affected by changes in the magnetic properties of the base metal (in practical applications, changes in the magnetic properties of low carbon steel can be considered slight). To avoid the influence of heat treatment and cold working factors, standard plates with the same properties as the base metal of the specimen should be used to calibrate the instrument; Calibration can also be performed using the test piece to be coated.
2. Electrical properties of the base metal
The conductivity of the base metal has an impact on the measurement, and the conductivity of the base metal is related to its material composition and heat treatment method. Use standard plates with the same properties as the base metal of the specimen to calibrate the instrument.
3. Thickness of the base metal
Each instrument has a critical thickness of the base metal. Beyond this thickness, the measurement is not affected by the thickness of the base metal.
4. Edge effect
This instrument is sensitive to sudden changes in the surface shape of the specimen. Therefore, measuring near the edge or inner corner of the specimen is unreliable.
5. Curvature
The curvature of the specimen has an impact on the measurement. This effect always increases significantly with the decrease of curvature radius. Therefore, measuring on the surface of bent specimens is unreliable.
6. Deformation of the specimen
The probe will cause deformation of the soft cover layer specimen, so reliable data cannot be measured on these specimens.
7. Surface roughness
The surface roughness of the base metal and cover layer has an impact on the measurement. The increase in roughness leads to a greater impact. Rough surfaces can cause systematic and accidental errors, and the number of measurements should be increased at different positions during each measurement to overcome these accidental errors. If the base metal is rough, several positions must be taken on uncoated base metal specimens with similar roughness to calibrate the zero point of the instrument; Or dissolve and remove the covering layer with a solution that does not corrode the base metal, and then calibrate the zero point of the instrument.
8. Magnetic field
The strong magnetic field generated by various electrical equipment around can seriously interfere with magnetic thickness measurement work.
9. Adhesive substances
The instrument is sensitive to adhesion substances that hinder the close contact between the probe and the surface of the cover layer. Therefore, adhesion substances must be attached to ensure direct contact between the instrument probe and the surface of the tested object.
10. Probe pressure and side head orientation
The pressure applied by placing the probe on the specimen will affect the measured reading, therefore, it is necessary to maintain a constant pressure. The placement of the measuring head has an impact on the measurement. In measurement, the probe should be kept perpendicular to the surface of the sample.
