Abstract: An apparatus provided with a measuring head for determining with the aid of X-ray fluorescence or X-ray absorption measuring techniques the surface weight of a measuring subject comprising coatings or surface-deposits or the concentration of basic substances in the subject to be measured, comprising liquid, slurries, powder or solid samples. The apparatus includes means for moving the measuring head (1) over the subject (5) to be measured and also over a reference sample (4), such as a sample or an empty sample-container, or vice versa. The measuring aperture provided in the measuring head (1) is covered with a protective film (7) for the purpose of preventing the ingress of particles from the subject (5) into the aperture. Means (3) are also provided for checking the dirt-coating on the protective film (7) regularly and for sending an order to a film-carrying device (8, 10, 11) to advance film when the dirt-coating is found unacceptable.

Abstract: When controlling and/or determining the thicknesses of layers or surface coatings there is chosen a coating composition that incorporates a fluorescing indicator substance, the proportions of which in the coating composition can be measured by X-ray fluorescence. The coating composition is applied to a substrate surface in solution, slurry or molten form and the thickness of the coating, or layer, is controlled and/or monitored in accordance with the intensity of the light which fluoresces from the coating.