Ensuring reliability of measurement results of thickness of metal coatings with the Magneto-Inductive and Eddy-Current methods in the conditions of the Machine Industry

摘要

Article is devoted the analysis of the factors defining metrological characteristics Magneto-Inductive and Eddy-Current metal coating thickness gauges and reliability of results of measurements with their use in the conditions of the Machine Industry. In Russia it is traditionally paid much attention to questions of metrological ensuring of coating thickness measurements, including metal, the most part from which has high cost and small thickness: h = 2 ... 20 microns. In the domestic market the big nomenclature of domestic and foreign electromagnetic coating thickness is presented. In the operation manual for each transducer, which is a part of the device, it is necessary to stipulate types of controllable coatings and the bases, a limit of an allowed main absolute error of measurements, a range of measurements of h_(max), the minimum internal and external radiuses of products, diameter of a zone of measurement and an allowed roughness of R_(zmax bases) (coatings), a working temperature range. Now the majority of leading producers manufacture metal coatings thickness devices with a declared limit of an allowed main absolute error of measurement of Δh ≤ ±(0,01h + 1) μm in the field of small thicknesses. Thus it is meant that tests of devices carry out on the exemplary bases and working standards (calibration foils), identical subjects on which defined the calibration characteristic in normal conditions. It can mislead unprepared users concerning reliability of results of measurement under production conditions. Let's analyze compliance of declared and really provided (achievable) metrological characteristics of protective metal coatings thickness devices under production conditions. Metrological characteristics of coating thickness gauges are determined by a method of measurements, creation of the measuring transducer, used algorithms of transformation and h calculation by the calibration characteristics. Essential influence is rendered by the stirring parameters operating on measuring transducer in processes of graduation, calibration and measurement. Such geometrical parameters are: the base thickness (T), diameter of a zone of measurement (D), radius of curvature (r) and a roughness of a surface (R_z), gap between the transducer and a coating (Z). Physical stirring parameters include: electric conductance (σ_1, σ_2) and relative magnetic permeability (μ_1, μ_2) of coating and basis, temperature (t), external electromagnetic fields, etc.