A coating thickness gauge(also known as a film thickness gauge)is used to measure dry film thickness.Controlling dry film thickness is an extremely important part of the coatings industry.Because the dry film thickness affects the coating process, the quality and cost.Dry film thickness measurements can be used to assess the expected life of the coating,the appearance and performance of the product.
Dry film thickness (DFT)can be measured using two methods:destructive thickness measurement, using a cutter to cut the coating onto the substrate.Non-destructive coating thickness measurement,the coating surface will not be damaged during the measurement.For example, magnetic induction and eddy current thickness measurement methods.
Non-destructive coating thickness measurements can be made on magnetic metal surfaces or non-magnetic metal surfaces such as stainless steel or aluminum.Digital coating thickness gauges are ideal for measuring the coating thickness on metal substrates.Electromagnetic induction is used for the measurement of the non-magnetic coating thickness on ferromagnetic metal substrates,while the principle of eddy currents is used for the measurement of the non-conductive coating thickness on non-magnetic metals.
1)Magnetic coating thickness gauge
The magnetic coating thickness gauge used to measure the coating thickness on the magnetic metal substrate with the principle of electromagnetic induction.Using a three-coil probe system,the center coil is powered by the instrument.The other two coils (on both sides of the center coil) detect the generated magnetic field. The signal produced by the instrument is a sine wave,so an alternating magnetic field is generated around the central coil.
When no magnetic material affects the probe,the magnetic field will cut evenly into the other two coils.As the probe approaches the uncoated substrate, the magnetic field becomes unbalanced,more magnetic fields cut the nearest coil.And further coils are cut less.This creates a net voltage between the two coils, which is the distance to the substrate (coating thickness).
2)Eddy current coating thickness gauge
In the case of the eddy current principle,a single coil probe with a relatively high frequency signal (several megahertz) is used to create an alternating magnetic field in the non-ferrous metal under the coating.The resulting magnetic field causes the eddy current to circulate in the substrate,which in turn has an associated magnetic field. These magnetic fields affect the coating thickness probe and cause variations in the coil electrical impedance.These changes depend on the coating thickness.