Several factors affecting coating thickness gauge measurements
Magnetic method to measure the thickness of the base metal by the influence of the change in the nature of the base metal (in practice, the change in the magnetic properties of mild steel can be considered to be slight), in order to avoid the influence of heat treatment and cold processing factors, should be used with the specimen base metal has the same properties of the standard piece of the instrument for calibration; the conductivity of the base metal has an impact on the measurement of the base metal of the conductivity of the base metal and its material composition and heat treatment methods. Use a standard piece with the same properties as the base metal of the specimen to calibrate the instrument; each instrument has a critical thickness, greater than this thickness, the measurement is not affected by the thickness of the base metal; sensitive to the steep change in the shape of the surface of the specimen, and therefore measurements near the edges of the specimen or inside the corner are unreliable; the curvature of the specimen has an effect on the measurement, which increases significantly with the decrease of the radius of curvature, and therefore the Measurements on the surface of curved specimens are also unreliable; the probe deforms soft-coated specimens, so no reliable data can be measured on these specimens; the surface roughness of the base metal and coating has an effect on the measurement. Roughness increases, the impact increases, rough surfaces can cause systematic and accidental errors, each measurement should be increased in different positions to overcome this accidental error. If the substrate on the base metal roughness, but also must be in the uncoated roughness similar to the base metal specimen to take a few positions to calibrate the zero point of the instrument, or the base metal with no corrosion of the solution to dissolve the removal of the coating, and then calibrate the zero point of the instrument; around a variety of electrical equipment produced by a strong magnetic field, which can seriously interfere with the magnetic thickness work; those who hinder the probe and the surface of the coating closely in contact with the adhesion of the material must be cleared! In the measurement, it is necessary to keep the pressure constant and the probe perpendicular to the surface of the specimen in order to achieve accurate measurement.
