4.1 Conformable Eddy Current Sensors—Conformable, eddy current sensors can be used on both flat and curved surfaces, including fillets, cylindrical surfaces, etc. When used with models for predicting the sensor response and appropriate algorithms, these sensors can measure variations in physical properties, such as electrical conductivity and/or magnetic permeability, as well as thickness of conductive coatings on any substrate and nonconductive coatings on conductive substrates or on a conducting coating. These property variations can be used to detect and characterize heterogeneous regions within the conductive coatings, for example, regions of locally higher porosity.
4.2 Sensors and Sensor Arrays—Depending on the application, either a single-sensing element sensor or a sensor array can be used for coating characterization. A sensor array would provide a better capability to map spatial variations in coating thickness and/or conductivity (reflecting, for example, porosity variations) and provide better throughput for scanning large areas. The size of the sensor footprint and the size and number of sensing elements within an array depend on the application requirements and constraints, and the nonconductive (for example, ceramic) coating thickness.
4.3 Coating Thickness Range—The conductive coating thickness range over which a sensor performs best depends on the difference between the electrical conductivity of the substrate and conductive coating and available frequency range. For example, a specific sensor geometry with a specific frequency range for impedance measurements may provide acceptable performance for an MCrAlY coating over a nickel-alloy substrate for a relatively wide range of conductive coating thickness, for example, from 75 to 400 μm (0.003 to 0.016 in.). Yet, for another conductive coating-substrate combination, this range may be 10 to 100 μm (0.0004 to 0.004 in.). The coating characterization performance may also depend on the thickness of a nonconductive topcoat. For any coating system, performance verification on representative coated specimens is critical to establishing the range of optimum performance. For nonconductive coatings, such as ceramic coatings, the thickness measurement range increases with an increase of the spatial wavelength of the sensor (for example, thicker coatings can be measured with larger sensor winding spatial wavelength). For nonconductive coatings, when roughness of the coating may have a significant effect on the thickness measurement, independent measurements of the nonconductive coating roughness, for example, by profilometry may provide a correction for the roughness effects.
4.4 Process-Affected Zone—For some processes, for example, shot peening, the process-affected zone can be represented by an effective layer thickness and conductivity. These values can in turn be used to assess process quality. A strong correlation must be demonstrated between these “effective coating” properties and process quality.
4.5 Three-Unknown Algorithm—Use of multi-frequency impedance measurements and a three-unknown algorithm permits independent determination of three unknowns:
N代表Non- ferrous非铁磁性基体，N型的涂层测厚仪采用电涡流原理；来测量用涡流传感器测量铜、铝、锌、锡等基体上的珐琅、橡胶、油漆、塑料层等。FN型的涂层测厚仪既采用电磁感应原理，又采用采用电涡流原理，是F型和N型的二合一型涂层测厚仪。...
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两用测厚仪： 专业测量金属材料表面涂镀层覆盖层物体厚度的专业无损检测仪器。它根据金属基体不同使用以下不同的测量方法。同时具备涡流测厚方法和磁性测厚方法。 ...
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