Résumé : A liquid-differential Cerenkov counter built to separate protons from kaons between 2 GeV/c and 9.5 GeV/c or kaons from pions up to 5 GeV/c is described. This counter has a 20 cm diameter useful cross-area. It can accept a ±7% momentum bite around its nominal setting. A resolution Δβ β better than 3% is achieved in the vicinity of β = 1. © 1978.