AS 3894.10:2002 pdf free.Site testing of protective coatings Method 3: Determination of dry film thickness.
3A Secondary standards
Standards that are referenced to the primary standards and are used in the field.
4 TEST METHODS
The coating film thickness may be measured using magnetic pull-off gauges (see clause 9), or by eddy current or magneti.c induction type instruments (see clause 10) of the type generally described in. Table 1.:
NOTES
1. Owing to the inherent inaccuracies of some inagaetic pull-off gauges, they are recoinrn ended only for process control operatious.. where accurate and reproducible measurements are not required.
2. Appendix C providcs a mcthod for dc:tcrminiiig the wet ifini thickness during application of a coating, which will assist applicators in achieving the required dry filni thickness.
5 PRICAUT1ONS
The accuracy of measurement of a coating thickness may be affected by a number of factors. The. following precautions should be observed:
(a) Calibration The instrument should be calibrated in accordance with Appendix D prior to use, re-calibrated after each hour and rechecked at the end of the work period.
(b) Substrate thickness For each instrument, there is a critical thickness of metal substrate below which the accuracy of the instrument cannot be assured. Since this thickness depends on both the measuring frequency of the probe system and the electrical conductivity or the magnetic permeability of the substrate, its value should be determined experimentally, unless it is specified by the manufacturer of the test instrument.
(c) Edge jfecIs Measurements should not be taken close to an edge, hole or inside corner of a test. specimen unless the instrument, is calibrated for such measurements.
(d) Curvature Measurements are affected. by the curvature of the specimen. The influence of curvature varies considerably, depending on the make and type of instrument, but always becomes more pronounced as the radius of curvature decreases. Measurements made on curved test specimens will therefore not be valid unless the instrument is specifically calibrated for such measurements.
(e) Sui face prçfile and roughness Measurements are influenced by the surface topography of the substrate and of the coating. Rough surfaces and the anchor pattern of a surface profile can cause both systematic and random errors.
(f) Foreign particles The probes of the coating thickness gauge need to make contact with the test surface. The instruments are therefore sensitive to an.y foreign, material that prevents intimate, contact between the probe and surface. of the coating. The probe tip should be checked periodically for cleanliness and foreign particles removed using piasticine or similar materiaLAS 3894.10 pdf download.