Coating thickness gauges can be based on different measuring principles. The category of coating thickness gauges can be divided into three operation modes:
Coating thickness gauges for measuring non-magnetic and insulating coatings on magnetic substrates, for example plastic, lacquer or a zinc coating on iron. Often, these gauges are also referred to as a paint thickness gauges, as they are often used in the automotive industry to locate repainting works and repairs on car paint.
Measuring devices for determining the coating thickness of insulating coatings on non-magnetic metallic substrates.
Ultrasonic coating thickness gauges for measuring the coating thickness on non-metallic substrates such as paint on wood or concrete.
The most common application is the measurement of non-magnetic coatings on magnetic substrates. As already mentioned, these coating thickness gauges are frequently used in the automotive industry but also in surface finishing works and last but not least in industrial production. This method can again be divided into the analogue and digital coating thickness measurement: Analog gauges use a magnet for the measurement and measure how much force is necessary to release the magnet from the material. The thicker the coating, the easier it becomes to release the magnet. The result of the output is then indicated on the analogue scale.
Devices that use the digital method are based on the magnetic induction principle. These methods are characterized by their high accuracy, especially on flat surfaces.
For the measurement of insulating coatings on non-magnetic, metallic substrates, the distance between the coating thickness gauge and the metal substrate is measured by means of the eddy current principle. Among other things, the eddy current principle is used to measure the coating thickness of paint on aluminium. The digital measuring devices allow a very accurate determination of the coating thickness.
Combination devices that combine both measuring principles in a digital device are particularly convenient. A combination probe can use both measuring principles and automatically detects which material the substrate has and selects the appropriate measuring mode.
Finally, there are coatings such as plastic, paint and paint on non-metallic substrates such as wood or concrete. Here, none of the methods mentioned above are possible to used. Nevertheless, a coating thickness measuring device by means of ultrasound can be used. The measurement of the coating thickness via ultrasound works with the same principle as our wall thickness gauges: an ultrasonic wave is directed into the material and blasted straight back. The probe measures the reflection time of the ultrasonic wave from where the coating ends until it returns into the probe. Particularly noteworthy is here that we even have special solutions for the thickness measurement of several superimposed coatings. For example, if a workpiece has been painted three times, the coating thickness of each individual coating can be displayed.