OPTIMUM FOCUSING IN AN ELECTRON BEAM WELDING MACHINE

摘要

Apparatus for determining optimum focusing of an electron beam at the site of a weld wherein the electron beam is directed onto a sample and the intensity of the infra-red radiation emitted at the point of incidence between the beam and the sample is measured by means of a photoelectric cell. A radiation chopper is placed between the photoelectric cell and the samples in such a manner that particles displaced from the workpiece are deflected away from the photoelectric cell. The focus is adjusted in dependence upon the intensity of the infra-red radiation.