Magnetic induction, eddy current, ultrasonic pulse-echo, optical methods — how does a thickness gauge actually turn a physical response into a number? This section covers the mechanism, the applicable range and the failure conditions of each principle.
Magnetic induction uses a probe to generate a low-frequency magnetic field and reads how the ferrous substrate responds to it, deriving the thickness of the non-magnetic coating from that response.…
Eddy current testing drives a high-frequency coil to induce eddy currents in a conductive substrate and derives non-conductive coating thickness from the change in coil impedance. Defined by ISO 2360:2017,…
Choosing a principle comes down to one question: is the substrate ferromagnetic? If yes, use magnetic induction (Fe). If not, and the substrate is conductive, use eddy current (NFe). If…
An ultrasonic thickness gauge fires a sound pulse and times its round trip between the two surfaces of the part, converting that time with velocity × time ÷ 2. It…
Echo-Echo mode calculates wall thickness from the interval between successive back-wall echoes, automatically ignoring the coating on the surface. Painted, coated pipework and hulls can therefore be measured without damaging…
Coatings on concrete, wood, plastic, glass and fibreglass cannot be measured by magnetic induction or eddy current; they require ultrasonic coating thickness measurement to ASTM D6132-13(2022) or ISO 2808 Method…
ASTM D7091-22 and SSPC-PA 2-2022 sort coating thickness gauges into two types: Type 1 magnetic pull-off and Type 2 electronic. Type 2 gauges read electronically through magnetic induction or eddy…
Resolution is the smallest displayed step, accuracy is how far a reading can sit from the true value, and repeatability is how well repeated measurements at one spot agree. None…
The geometry of the part changes the reading systematically: a substrate that is too thin pulls the reading low, curvature changes the coupling between probe and substrate, and near an…
Transmittance measures the share of visible light that passes through a material (VLT), haze measures the scattered fraction of that transmitted light, and gloss measures the specular reflection at a…
