Method and device for measuring the thickness of thin layers over large-area surfaces to be measured

#The invention relates to a method and a device for measuring the thickness of thin layers over large-area surfaces to be measured, such as the hulls of ships.

#The measurement of the thickness of thin layers using a measuring probe which comprises at least one sensor element and at least one contact spherical cap assigned to the sensor element is known for example from DE 10 2005 054 593 A1. As a result of such a measuring probe measurements can be taken in accordance with the magnetic induction method or in accordance with the eddy current method depending on the base material and the coating. For example, such measuring probes are applied manually to a surface to be measured so as to measure the layer thickness. Such a method is not adapted, for example, for the measurement and inspection of large-area coatings and surfaces to be measured, such as the hull of a ship or the wing of an aircraft.

#The problem addressed by the invention is to propose a method and a device for measuring the thickness of thin layers, whereby the surface to be measured and inspected is measured comprehensively in a simple manner.

#The invention as well as further advantageous embodiments and developments thereof will be described and explained hereinafter in greater detail with reference to the examples illustrated in the drawings. The features to be inferred from the description and the drawings may be applied, in accordance with the invention, either individually or in any combination. In the drawings:

#FIG. 1 is a schematic side view of a ship with a coated hull, the coating of which is subdivided as a surface to be measured into partial areas;

#FIG. 2 shows a partial area with a matrix of measurement points;

#FIG. 1 shows a schematic view of a ship 11. A coating on the hull of a ship forms, for example, a large-area surface to be measured 12. Owing to increased safety requirements and in order to avoid corrosion, the quality of the coating on the hulls of ships is of great importance, particularly since damage to the ship can thus be prevented. Such coatings must therefore comprise a minimum value of layer thickness for a coating. It can only be ensured that such minimum values are observed if a mean value of the layer thickness is sufficiently greater than the minimum value. The necessary gap between the mean value and the minimum value of the layer thickness depends on the dispersion immanent to the coating process. The coefficient of variation V is expediently used as a measure for the dispersion. This is the ratio of the standard deviation s to the mean value x of the measured layer thickness values. From these coefficients of variation it is possible to draw a conclusion regarding the quality of the coating, and more specifically as to whether the minimum layer thickness is present completely, partly, or not at all to the required extent. The coefficient of variation ascertained can be compared with an assessment chart which is compiled on the basis of evaluated process results and is categorised into different statements. For example, the statement may be “excellent”, “good”, “adequate” or “often inadequate” and a maximum upper limit of the percentage value of the coefficients of variation is allocated to each of these statements. A quick statement regarding the quality of the coating can thus be made by comparing evaluated process results with the assessment chart based on the individual measured values obtained of the coefficients of variation calculated therefrom.

#For rational assessment the surface to be measured 12 is to be subdivided, for large-area coatings, into individual partial areas 40 which are many times smaller than the surface to be measured 12. The surface to be measured is preferably subdivided into partial areas 40 of equal size.

#Such a partial area 40 of the large-area surface to be measured 12 is shown enlarged in FIG. 2. This partial area 40 comprises a matrix of measurement points 16 which are provided at equidistant distances Δ·lh along a row 17. The rows 17 are in turn preferably arranged parallel to one another at equal distances Δ·lv, in such a way that a matrix of measurement points 16 or a network of measurement points 16 is distributed uniformly over the partial area 14. It is thus possible to come to an adequate conclusion regarding the layer thickness or progress of layer thickness for this partial area 14 without the need to measure the layer thickness over the entire surface.