How do I choose the right membrane cartridge for my sensor? Membrane Cartridge Selection If your sensor cathode looks like this Broadley James OxyProbe II Broadley James OxyProbe Broadley James OxyProbe Mettler Toledo® Ingold® Mettler Toledo® Ingold® Mettler Toledo® Ingold® Use this membrane cartridge model OxyProbe II OxyProbe (12mm) OxyProbe (25mm)