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Abstract

The present invention concerns the measuring of a silicon coating on paper or cardboard moving in the form of a continuous web and which may as fillers contain substances containing silicon such as kaolin, or aluminum silicate. By x-ray radiation from a primary radiation source (3) and passing through the web is excited the characteristic x-ray radiation of an element, in a secondary radiation source (7) on the silicon coating side of the paper web (1), having a higher ordinal number than silicon (Si). The exciting radiation is sent obliquely against the surface of the paper or cardboard, whereby the irradiation of the surface is accentuated and the characteristic x-ray radiation of the silicon in the silicon coating can be excited. The exciting radiation also partly excites the silicon in the filler, but in this case it will be accompanied by the characteristic x-ray radiation of the metal associated with the silicate, such as aluminum in the instance of kaolin. These two fluorescence radiations are measured using a semiconductor detector (9) with good energy discriminating capacity, the quantity of silicon coating being calculable from the silicon energy peak recorded in the spectrum from this detector when it is corrected, as in the exemplary case, to eliminate with the aid of the aluminum peak the contribution of the filler and when in the scattered energy peak measured from the spectrum the irradiation correction is taken into account. If there is coating on both sides, two measuring heads are placed one after the other in the web's direction of travel by which the surface fluorescence is recorded from different sides.

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First Claim