ISO 21968 standard, which establishes a method for the measurement of the thickness of nonmagnetic metallic coatings on metals and Non-metallic substrates. The standard uses the phase-sensitive eddy current method, also known as the phase-sensitive eddy current method, which is a non-Destructiveness Measuring method. The phase-sensitive eddy current method can measure coatings on various metals and Non-metallic materials, including aluminum, nickel, mg, zinc, and Miscellaneous nonmagnetic metals. The method calculates the thickness of the coating by measuring the phase difference and amplitude of the eddy current signal. Phase sensitive eddy current method has the advantages of high speed, high accuracy, simple operation and no special preparation, so it has been widely used in industry and laboratory.