A wavelength dispersive detection system physically separates the X-Rays according to their wavelengths.
The x-rays are directed to a crystal, which diffracts the X-Rays in different directions according to their wavelengths (energies).
On a sequential system a detector is placed at a fixed position, and the crystal is rotated so that different wavelengths are picked up by the detector. The XRF spectrum is built up point by point. In a simultaneous system, a number of crystal/detector units are used, so that a range of elements can be detected simultaneously