Measuring Total Coating Thickness on Plastics, Concrete, Wood & more Using Max Thick Mode on the PosiTector 200

Measurement Principle

The PosiTector 200 probe emits an ultrasonic sound pulse that travels into the coating and reflects/echoes from any interface that is different in density, such as the substrate. It measures the time it takes for the sound pulse to travel from the probe to the coating/substrate interface and back. By multiplying this travel time by the velocity of sound through the coating (which is similar for most polymer coatings), the thickness of coating(s) can be calculated.


While there is almost always a density change at the coating-substrate interface that the PosiTector 200 can detect, density changes between coating layers can also be identified. PosiTector 200 Advanced models can often detect the interface between layers of different or identical coatings, as long as the initial layer is allowed to fully cure before application of the subsequent layer. Typically, the loudest ultrasonic echo represents the coating-substrate interface, with smaller echoes representing individual layer thicknesses.

Default Mode

The default measurement mode on the PosiTector 200 has been successfully utilized for decades to measure coating thickness on a wide variety of coatings and substrates. The PosiTector 200 searches for the loudest ultrasonic echo within its measurement range, and reports it as the coating thickness. In multi-layer mode, the thicknesses associated with the loudest echoes (depending on the number of layers selected) were reported as individual layer thicknesses. For most measurement applications, and particularly when measuring smooth, polymer coatings, this method provided accurate readings of the total coating thickness and individual layers, without any setup or adjustment required.

Applications with surface roughness or many loud echoes near the surface of the coating were sometimes challenging to measure with the PosiTector 200, because those conditions generated loud, unwanted echoes, often larger and louder than the desired echo form the coating-substrate interface. While increasing the instrument's Lo Range would ignore these unwanted echoes, it is time consuming and is sometimes difficult to make an adjustment that would ignore the unwanted surface echoes, while still measuring thinner areas of applied coating.


 

Max Thick Mode

When increasing the Lo Range requires an adjustment too close to the expected coating thickness or if a user simply does not want to adjust the range, the NEW Max Thick Mode is optimal.

When Max Thick Mode is enabled, the PosiTector 200 searches for the deepest significant echo instead of the loudest echo. This means that any loud echoes near the surface (typically caused by surface roughness or a 'noisy' coating system) are ignored. This mode is often more effective at reporting the total coating thickness at the substrate interface, and eliminates the need to adjust the instrument's preset Lo Range. Since there will inevitably be some small echoes from within the substrate, only echoes above a pre-set loudness will be reported. On PosiTector 200 Advanced models, this threshold can be adjusted from the Graphic Display mode.

While Max Thick Mode is enabled and when multiple layers are selected (PosiTector 200 Advanced only), the layer thicknesses associated with the deepest ultrasonic echoes are reported.

Note: Max Thick Mode is not recommended for use with thin metal substrates or composites such as carbon fiber or fiberglass.
 

Conclusion

The PosiTector 200 Ultrasonic Coating Thickness Gage measures coating thickness on non-metals including wood, concrete, plastic and more. For most applications, the NEW Max Thick Mode will give the most accurate readings while eliminating the need to adjust the Lo Range to ignore incoming surface reflections.

A simple gage update adds this functionality to existing PosiTector Standard (serial numbers 795,375+) and Advanced (serial numbers 784,000+) models.