The calibration critically determines the quality of the absolute thickness measurement. Two topics will be discussed below, the making of samples and the referencing. By means of the calibration, a direct correlation between the measuring signal and the actual coating thickness is determined. For this, the coating thickness is usually measured using a reference measuring device, or known reference samples are used. The calibration is made by applying a coating which is then measured both with the PaintChecker and with the reference device. The calibration software supports the user with this and calculates the calibration function. The best calibration precision is achieved, if a tapering or step-shaped coating structure is created and then a multi-point calibration is carried out.

Sample creation

The calibration samples must be made very carefully and they should include the coating thickness range which is to be measured later. The sample sheets should have a smooth substrate and, in the case of multi-layer systems, a uniform basic structure. The uniformity of the basic structure can be checked using the reference tool. A small standard deviation indicates a uniform coating. The actual coating layer thickness should ideally be made using the same coating process and under identical production conditions, in order to achieve the best possible calibration sample. This ensures that the same conditions are present as during use in the production process. In exceptional cases, other methods for making the samples are possible. We will be pleased to assist you with the production of your calibration samples.

Referencing

Using an alternative measuring method, usually the eddy current method, the referencing determines a direct correlation with the actual coating thickness. To do this, conventional measuring tools are used, which also have limited measuring precision. The precision of the reference measuring tool has an important influence on the result of the calibration. No better measuring precision can be achieved than that of the reference measuring tool. For this reason, the reference measuring tool should have an adequate measuring precision and itself be calibrated before every measurement. The standard deviation is a good measure for assessing the sample quality . Non-metal substrates are often used for which eddy current measuring tools are not suitable. In such cases, specially prepared samples must be used onto which metal platelets are applied. Alternatively, a different measuring method can be used. In critical cases, destructive measuring methods, such as measuring a ground cross-section can be deployed, however these should only be performed in specialist laboratories.

For companies which do not wish to utilise additional reference technology, we can offer the production of standard calibration samples as a service. Using the standard calibration samples, the calibration can be carried out without a reference measuring tool. Then no coating substrate combination can be measured other than that of the standard calibration sample.

The measuring system capability can be verified by means of the special PTB certified reference sample.