Regulations to be observed when using thickness gauges
1. Base metal properties
For the magnetic method, the magnetic properties and surface roughness of the base metal of the standard piece shall be similar to those of the test piece base metal.
For the eddy current method, the electrical properties of the base metal of the standard sheet shall be similar to those of the test piece base metal.
2. Base metal thickness
Check whether the base metal thickness exceeds the critical thickness, if not, use one of the methods in 3.3 to calibrate.
3. Edge effect
Measurements should not be made close to sudden changes in the test piece, such as edges, holes and inner corners.
4. Curvature
Measurements shall not be made on curved surfaces of test pieces.
5. Surface cleanliness
Before measurement, any attached substances on the surface should be removed, such as dust, grease and corrosion products, etc., but do not remove any covering substances
The thickness measurement by the magnetic method 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 sheet with the same properties as the base metal of the test piece; the test piece to be coated can also be used for calibration.
6. Number of readings
Often several readings must be taken within each measurement area since each reading from the instrument is not identical. Local variations in cover thickness also require multiple measurements in any given area, especially when the surface is rough.
