A crucial part of understanding relativistic heavy ion collisions is characterizing the geometry of the nucleus-nucleus interaction. This is done by assigning a collision “centrality” which presently in all heavy ion experiments is determined indirectly in model dependent way by relating collision events with similar bulk energy characteristics to a mean number of nucleons participating in the nucleus-nucleus interaction. Various assumptions associated with this model and particle production mechanism gives rise to large systematic error. Collider themselves being spectrometer provides the opportunity to detect and identify  spectator fragments species based on their different mass number to charge ratio by stations downstream from the interaction point and hence determining centrality in model independent way. Different stations located at the different positions along the beampipe will be measuring spectator species of certain mass number and charge ratio range. The concept of centrality detector alongwith the detailed simulation of the collisions and propagation of spectator following the interaction showing expected detector performance parameters will be shown.