WDS Wavelength dispersive X-ray spectroscopy (WDS), like energy dispersive X-ray spectroscopy (EDS), measures the energy distribution of X-rays emitted from a sample irradiated with an electron beam. The principle by which the X-rays are generated is the same as for EDS (read more on the EDS page). The difference between the two techniques is in how the X-rays are collected and analysed. In EDS, X-ray counts for the full range of energies are collected simultaneously. In WDS, the position of the detecting crystal (and at certain intervals the type of detecting crystal) is changed to collect X-ray counts at different wavelengths and the spectrum is built up in a sequential manner. This makes WDS a slower but more sensitive technique compared with EDS.