Magnetic thickness gauges for non-destructive measurement of the thickness of coatings (paints, enamels, galvanizing, oxidations).
Non-destructive measurements of the coating thickness can be made on both magnetic steel surfaces and non-magnetic metal surfaces such as stainless steel or aluminum.
Electromagnetic induction is used for non-magnetic coatings on ferrous substrates such as steel, while the eddy current principle is used for non-conductive coatings on non-ferrous metal substrates.
- There are three different families of coating thickness gauges: coating thickness gauges that measure non-magnetic coatings on magnetic substrates (e.g. paint or zinc on iron), coating thickness gauges that are capable of measuring non-metallic coatings on non-magnetic substrates ( e.g. paint on aluminum) and coating thickness gauges that can measure non-metallic coatings on non-metallic substrates (e.g. paint on wood or concrete).
- The most common application is the measurement of non-magnetic coatings on magnetic (ferrous) substrates, e.g. measuring the thickness of paint on iron, zinc or thickness on iron. Analog thickness gauges use a magnet to test how much force is needed to detach the magnet from the material; the thicker the coating, the easier it is to detach the magnet from the wall. Digital feeler gauges use the magnetic induction principle to determine the distance between the coating thickness gauge and the magnetic metal substrate. This method of measurement can be very precise, especially when surfaces are flat.
- To measure non-metallic coatings on non-magnetic metals, the distance between the meter head and the metal substrate is measured using the eddy current principle. An example of this application is the measurement of the thickness of the paint on aluminum.
- Some models of coating thickness gauges are available with a double measurement function, both for ferrous and non-ferrous materials. These feeler gauges are supplied with a probe which is able to automatically determine whether the substrate is magnetic (ferrous) or non-magnetic (non-ferrous) and automatically select the correct operating mode.
- Measuring non-metallic coatings on non-metallic substrates, such as measuring paint on wood or concrete for example, can be done with an ultrasonic coating thickness gauge. This coating thickness gauge measures the coating only by sending an ultrasonic wave into the coating and measuring the time it takes to reflect the signal relative to the rear wall of the coating. This means that the coating and paint thickness can be measured on any substrate. Advanced models can also measure the thickness of individual layers of paint. When a surface has been painted 3 times the most advanced models of thickness gauges are able to determine the thickness of all the individual layers of paint.