The design characteristics of a 320 kV microfocus X-ray set are presented; the high kV level necessitates a bipolar design, which requires special considerations in order to achieve unobstructed access around the beam port and a small minimum distance from the focal spot to the test object.

Probably the most important parameter of a microfocus X-ray set is the focal spot size, which it is difficult to measure at 320 kV. Measurements based on extrapolation of the principles set forth in BS 6932 are presented, and the uncertainties are analysed.