This document specifies a method for the measurement of effective focal spot dimensions above 0,1 mm of X-ray systems up to and including 1000 kV tube voltage by means of the pinhole camera method with digital evaluation. The tube voltage applied for this measurement is restricted to 200 kV for visual film evaluation and may be selected higher than 200 kV if digital detectors are used.
The imaging quality and the resolution of X-ray images depend highly on the characteristics of the effective focal spot, in particular the size and the two dimensional intensity distribution as seen from the detector plane. This method compared to the others in the EN 12543 series allows to obtain an image of the focal spot and to see the state of it (e.g. cratering of the anode).
This test method provides instructions for determining the effective size (dimensions) of standard (macro focal spots) and mini focal spots of industrial X-ray tubes. This determination is based on the measurement of an image of a focal spot that has been radiographically recorded with a "pinhole" technique and evaluated with a digital method.
For the characterization of commercial X-ray tube types (i.e. for advertising or trade) it is advised that the specific FS (Focal spot) values of Annex A are used.