an x ray diffractometer device comprising an x ray source a collimator device for the source a sample support a collimator device for the beam reflected by the sample and a counter producing an output signal in the form of a voltage which is proportional to the number of photons reflected by the sample this device furthermore includes a motor drive for the sample support recording means for the signal y originating from the proportional counter as a function of the angle u03b8 between the plane of incidence of the sample and the incident beam denoted x mechanical means having a support for a plurality of filters having different coefficients of absorption and including a motor drive for this filter support data processing means for selecting one of the filters of the filter support and for controlling the motor drive of the sample support the motor drive of the filter support and the recording means respectively application_number US 73392591 A description in accordance with the invention the prior art apparatus is modified to render the measurement of large parameters d possible the value d of predetermined parameters being linked to u03b8 and u03bb the wavelength of the source by the relation on the one hand to obtain the measurement of ever larger parameters d the choice of the source is influenced that is to say the choice of u03bb to this effect the x ray source is chosen from among one of the sources specified in table i which shows the wavelengths u03bb in u00e5 1 10 nm as a function of the rays k u03b1 of several x ray metal sources on the other hand one opts for having the angle u03b8.