Factors affecting measured values and solutions
The use of thickness gauges and the use of other instruments, both to master the performance of the instrument, but also need to understand the test conditions. The use of magnetic principle and eddy current principle of the cladding thickness gauge are based on the measured substrate electrical and magnetic properties and the distance from the probe to measure the thickness of the cladding, so the measured substrate electromagnetic physical properties and physical dimensions have to affect the size of the magnetic flux and eddy current. That is, it affects the reliability of the measured value, the following is an introduction to this aspect of the problem.
1. Boundary spacing
If the probe and the measured body boundaries, holes, cavities, other cross-section changes in the spacing is less than the specified boundary spacing, due to magnetic flux or eddy current carrier cross-section is not enough will lead to measurement errors. If the cladding thickness at this point must be measured, it can only be measured if it is pre-calibrated on a cladding-free surface in the same conditions. (Note: Our products have a unique feature of calibration through the cladding to achieve an accuracy of 3 to 10%).
2. Substrate surface curvature
Calibrate an initial value on a flat comparison specimen and then subtract this initial value after measuring the cladding thickness. Or refer to the following article.
3. zui Minimum Thickness of Base Metal
The base metal must have a given minimum thickness so that the electromagnetic field of the probe can be completely contained in the base metal. The minimum thickness is related to the performance of the measuring instrument and the nature of the metal substrate, and just above this thickness the measurement can be made without correction of the measured value. The effect of insufficient thickness of the substrate can be eliminated by placing a piece of the same material immediately below the substrate. If it is difficult or impossible to add a substrate, the difference from the rated value can be determined by comparing with a specimen with a known cladding thickness. This is taken into account in the measurement and the measured value is corrected accordingly or in accordance with Article 2. For those instruments that can be calibrated, an accurate direct reading of the thickness can be obtained by adjusting a knob or key. Conversely, the use of the thickness is too small to produce the impact of the development of direct measurement of copper foil thickness gauge, as mentioned above.
4. Surface roughness and surface cleanliness
In the roughness of the surface in order to obtain a representative average measurement value must be measured several times. Obviously, the rougher the surface, whether it is the substrate or the cladding, the less reliable the measurement. To obtain reliable data, the average roughness Ra of the substrate should be less than 5 per cent of the cladding thickness. As for surface impurities, they should be removed. Some instruments have upper and lower limits to eliminate those "flying spots". 5.
5. Probe measurement force
Probe measurement force should be constant. And should be as small as possible, so as not to cause deformation of the soft cladding, resulting in a drop in the measured value or large fluctuations. If necessary, a hard, non-conductive film of a certain thickness can be placed between the two. In this way, by subtracting the thickness of the film can be properly obtained residual magnetism.
6. External constant magnetic fields, electromagnetic fields and remanent magnetisation of the substrate
Measurements near external magnetic fields with disturbing effects should be avoided. Residual magnetism can lead to more or less measurement errors depending on the performance of the detector, but this is generally not the case for e.g. structural steels, deep-drawn formed steel plates etc.
7. Ferromagnetic and conductive components of the cladding material
