1 Scope

This document specifies a method for the measurement of effective focal spot dimensions > 0,2 µm of X-ray systems by means of the edge method applied to digital images taken from hole type or disk type test objects if no phase contrast is observed. The imaging quality and the resolution of X-ray images depends highly on the characteristics of the effective focal spot, in particular its size and two-dimensional intensity distribution as seen from the detector plane.

This document specifies procedures for determining the effective size (dimensions) of standard, mini and micro focal spots of industrial X-ray tubes for users in applications where the pin hole method according to ISO 32543‑1 is not applicable. The method specified in this document is applicable for measurement and long-term monitoring of focal spot sizes without a pin hole camera.

This document can be used by manufacturers, if special hole test objects manufactured with lower tolerances according to 6.2.1 are applied (see Figure 1). For measurements of the effective focal spot size, the accuracy of the method in this document is lower than the methods specified in ISO 32543‑1 (pin hole method) and ISO 32543‑3 (microfocus tubes) if using ASTM hole plate IQIs (see ASTM E1025, ASTM E1742), due to its manufacturing tolerance of ±10 %.