Destructiveness measurement coated Film thickness

Coating Thickness Measuring Principle

Coatings and parts are coated with a coating for decorative and surface protection purposes, and the actual measurement of coating thickness for the applied material is very important. Phynix coating Thickness Gauges use two different methods for non-destructive thickness measurement: magnetic induction and eddy current principles:

For the non-destructive measurement of ferrous materials, i.e. ferromagnetic substrates, the principle of magnetic induction is used. The principle of magnetic induction is in models marked with F or FN (F = ferromagnetic) such as the suffix ®FN. Coatings need to be non-magnetic such as varnish, paint, enamel, plastic, glass, aluminum, lead, chrome, copper, brass, zinc, tin, etc.

The eddy current principle enables non-destructive measurements on non-magnetic metal substrates such as aluminum, aluminum alloys, lead, bronze, copper, brass, zinc, die-cast zinc, tin. The eddy current principle is used for marking or FN models (n = colored), such as the suffix ® easy i-fn. The coatings tested need to be electrically insulating, such as varnishes, paints, enamels, plastics, glass, anodized coatings and ceramics.

Typical applications for coating Thickness Gauges use magnetic induction and eddy current principles

All Surfix® models meet special international standards for thickness measurement:

• Method 1: ISO 2808
• Magnetic induction method: DIN EN ISO 2178, ASTM b499, ASTM open D7091
• Eddy current method: DIN EN ISO 2360, ASTM d7091
• Basic terms of measurement technology: DIN 1319, Part 1 and Part 3

functional sensor

The figure below shows the detection principle for magnetic induction measurement (eg model Surfix® F). For this purpose, an alternating magnetic field is generated in the two-pole space.

When a pole is close to the iron part, the magnetic field will be amplified. Then, a voltage is generated at the second coil (measuring coil). This voltage depends on the distance from the iron. By placing the iron core or measuring the coating of the sensor, the defined distance results in the relationship between the pole and the iron, thereby determining the coil voltage. This is evaluated electronically and digitally displayed as coating thickness.

Measurements according to the eddy current method use only a single coil (eg model suffix ®N), passing a high-frequency alternating current. This creates an alternating electromagnetic field around the coil.

When a non-ferrous metal approaches its alternating magnetic field coil, alternating currents – called eddy currents – are induced by this metal. This creates another electromagnetic alternating magnetic field in the opposite direction, weakening the original field. The effect of the coils is a changing induction, characteristic of each coil. Coil inductance is determined by measuring the relationship between the coating application of the sensor, defining the distance between the coil and the non-ferrous metal results. This will be evaluated electronically and digitally displayed as coating thickness.

In combination probes (such as model Suffix®FN), a two-coil system is placed on the measuring sensor, and the alternating magnetic field of the two coils – a low-frequency and a high-frequency alternating field – influences the sensor to the object being measured. The measurement signals of the two coils are automatically evaluated electronically and by a microprocessor, so that the corresponding program for the measurement of the basic material can be selected and the correct layer thickness will be displayed, regardless of the measurement taking place on ferrous and non-ferrous metals.