Several situations that affect the measurement accuracy of coating thickness gauges
1. Magnetic properties of base metal
Thickness measurement by magnetic method is affected by changes in the magnetism of the base metal (in practical applications, the change in the magnetism of low carbon steel can be considered slight). In order to avoid the influence of heat treatment and cold working factors, a material with the same properties as the base metal of the specimen should be used. The standard sheet is used to calibrate the instrument; the specimen to be coated can also be used for calibration.
2. Electrical properties of 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 a standard piece with the same properties as the base metal of the specimen to calibrate the instrument.
3. Base metal thickness
Every instrument has a critical thickness of base metal. Above 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. Measurements near the edges or inside corners of the specimen are therefore unreliable.
5. Curvature
The curvature of the specimen affects the measurement. This effect always increases significantly with decreasing radius of curvature. Therefore, measurements on the surface of bent specimens are unreliable.
6. Deformation of specimen
The probe will deform the soft-covered specimens, so reliable data cannot be measured on these specimens.
7.Surface roughness
The surface roughness of the base metal and covering layer affects the measurement. As the roughness increases, the impact increases. Rough surfaces will cause systematic errors and accidental errors. For each measurement, the number of measurements should be increased at different positions to overcome such accidental errors. If the base metal is rough, you must also calibrate the zero point of the instrument by taking several positions on an uncoated base metal specimen with similar roughness; or use a solution that is not corrosive to the base metal to dissolve and remove the covering layer, and then calibrate the instrument. zero point.
8.Magnetic field
The strong magnetic field generated by various surrounding electrical equipment will seriously interfere with the magnetic thickness measurement work.
9. Attached substances
The instrument is sensitive to attached substances that prevent the probe from close contact with the surface of the covering layer. Therefore, the attached substances must be removed to ensure direct contact between the instrument probe and the surface of the test piece.
10. Probe pressure and side head orientation
The amount of pressure exerted by the probe on the test piece will affect the measured reading, so the pressure should be kept constant. The way the probe is placed affects the measurement. During measurement, the probe should be kept perpendicular to the surface of the sample.
