Several Factors Affecting the Coating Thickness Gauge's Measurement Accuracy
1. Magnetic properties of the base metal
The magnetic thickness measurement is affected by the magnetic change of the base metal (in practical applications, the magnetic change of low carbon steel can be considered slight). In order to avoid the influence of heat treatment and cold working factors, the instrument should be calibrated with a standard piece that has the same properties as the base metal of the test piece; the test piece to be coated can also be used for calibration.
2. Electrical properties of the 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 sheet having 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 test piece. It is therefore unreliable to measure near the edge or inside corners of the test piece.
5. Curvature
The curvature of the test piece has an effect on the measurement. This effect always increases significantly with decreasing radius of curvature. Therefore, measurements on the surface of curved test pieces are not reliable.
6. Deformation of the test piece
The probe can distort soft-covered specimens, so reliable data cannot be obtained on these specimens.
7. Surface roughness
The surface roughness of the base metal and the coating has an effect on the measurement. The greater the roughness, the greater the impact. Rough surface will cause systematic error and accidental error, and the number of measurements should be increased at different positions for each measurement to overcome this accidental error. If the base metal is rough, it is necessary to take several positions on the uncoated base metal test piece with similar roughness to calibrate the zero point of the instrument; or use a solution that does not corrode the base metal to dissolve and remove the covering layer, and then calibrate the zero point of the instrument.
8. Magnetic field
The strong magnetic field generated by various electrical equipment around will seriously interfere with the magnetic thickness measurement work.
9. Attached substances
The instrument is sensitive to the attachment substances that prevent the close contact between the probe and the surface of the covering layer. Therefore, it is necessary to attach substances to ensure that the probe of the instrument is in direct contact with the surface of the test piece.
10. Probe pressure and lateral head orientation
The amount of pressure exerted by the probe on the test piece will affect the reading of the measurement, so the pressure should be kept constant. The way the probe is placed has an effect on the measurement. During the measurement, the probe should be kept perpendicular to the surface of the sample.
