Meaning and purpose
4.1 – most commonly coating thickness gauge does not apply to all the combination of base material thickness and material. The limitations of a particular instrument is usually described by their manufacturers. In choosing to use the instrument and the required accuracy of measurement, should be examined to measure the substrate material and coating combination and the change of substrate and coating.

4.2 Magnetic – The magnetic type measuring instrument measures the magnetic force between the magnet and the coating or its substrate, or the reluctance of the magnetic flux path through the coating and the substrate. These thickness gauges are designed to measure the thickness of non-magnetic coatings on magnetic substrates. Some of them will also measure the thickness of nickel coatings on magnetic or non-magnetic substrates. 6

4.3 Eddy Current – The eddy current type thickness gauge is an electronic instrument used to measure the impedance change of the eddy current induction coil caused by the change of coating thickness. Only when the electrical conductivity of the coatings and the conductivity of the substrate is obviously not at the same time, in order to use them.

4.4 Precision – The accuracy of the measurement depends on the instrument, the foil, its calibration and standardization, and the operating conditions. Accuracy is also affected by the interference of listed in section 5, such as part geometry (curvature), magnetic permeability and electric conductivity, and surface roughness.

Note 2: Under ideal conditions, the coating thickness can be determined to within ±10% of its true thickness or ±2.5μm (or ±0.0001 in), whichever is greater. See Appendix X2 for exceptions.

Determination of Coating Thickness by Magnetic Field Method or Eddy Current Method (Electric Field Method)

Scope of
1.1 this practice include the use of magnetic and type eddy current thickness instrument (gauge) of the coating on metal (i.e., conductive) substrate nondestructive thickness measurement. The substrate can be ferrous or non-ferrous metal. The coating or plating under test can be conductive or insulating, ferrous or non-ferrous metals.

1.2 The more specific use of these instruments is covered by Practice D7091 and the following test methods published by ASTM: Test Methods B244, B499 and B530.

1.3 units – values in SI units shall be deemed to be standard. Values given in the brackets are inches – pound unit mathematical transformation, for reference only, not be regarded as standard.

1.4 according to the practice of measurement to accord with the requirement of printing of ISO 2178 in 1982.

1.5 this standard is not intended to solve is related to its use of all safety issues (if any). It is the responsibility of the user of this standard to establish appropriate safety, health and environmental practices and to determine the applicability of regulatory restrictions prior to use.

1.6 this international standard is the technical barriers to trade, according to the world trade organization committee issued “about setting international standards, guidelines and recommendations of the decision of the principle of” the establishment of the internationally recognized principles of standardization.