Fundamental principle and standard of Eddy current coating thickness measuring

1. Fundamental principle and standard of Eddy current coating thickness measuring

Modern engineering material development and application practical shows ,aluminum,copper ,zinc and other nonferrous material and its alloy material in aviation ，building material,metallurgy,light industry,machine,instrument,chemical engineering has widely application,always with helps of oxidation file,oil paint,spraying plastics,rubber surface covering layer antiseptic protection。Extend its life。Applicable eddy current technique developed eddy current layer thickness meter ,is effective method that nondestructive measurement nonmagnetic metal  matrix non electric conduction overburden  thickness 。

Basic principle of  Eddy current coating thickness gauge:when measuring head touch sample, measuring head  device generates high frequency electromagnetic field ,and make metallic conductor produces eddy current，its amplitude and phase is nonconductive coating thickness that Between a conductor and probe ,namely the eddy current generates alternating electromagnetic field will change probe parameter，but probe parameter size depended on coated layer thickness。By testing probe parameter ,and transform and deal with this electrical signal ,then get a thickness value of being measured coating。

2.Eddy current coating thickness method standard profile

In domestic GB/T49557-85 《 nonmagnetic metallic matrix nonconductive covering layer thickness measures eddy current method》,has detailed explanation  on eddy current thickness gauge standard、operating procedure and factors that affect measurement precision and matters need attention。The term about affecting testing precision ,should be thought guidance document that eddy current coating thickness gauge developing and applying  must obey，these main factors that affects precision include:

1. Overburden thickness more than 25μm,its error  approximately in direct proportion to covering layer thickness

2.Conductivity of Base metal has effect on measurement,it is related to base metal material composition and heat treatment 

3.Any thickness gauge requires base metal has a critical thickness,only bigger than this thickness,measurement can not be affected by base metal thickness

4.Eddy current thickness gauge has fringe effect on sample measure,namely close to sample margin or inside nook  are unreliable

5.Curvature of Sample  has effect on measurement,this effect will be clearly enlarge with curvature  radial decreased

6.Surface roughness of Base metal and covering layer affect measuring precision ,roughness is increasing ,effect is increasing 

7.Eddy current thickness gauge is sensitive to attached  material that stop probe and covering layer surface touch closely，so before measuring ,it should clean probe and impurity on covering layer surface,when testing ,it be better to make probe keep constant voltage vertical touch with detected surface

Above main point,not only strictly regulate whole process quality of customer test thickness but also provide a design consideration of instrument developing for manufacturer ,so this strongly promote overall development of eddy current thickness measuring technique