The partial pressure sensor consists of a measuring head with light wave conducting fibers communicating with it. The measuring head is couplable and decouplable with the light wave conducting fibers across a fiber connecting flange (9). The measuring head has a housing (1), in which a sensor (3) is fixed pressure tight. The sensor (3) consists of a substrate (4) provided with an optical layer system. In addition a tempering element (8) and a thermometer probe (7) are provided, communicating with the substrate. The optical layer system consists of a reflection system (6) and a function layer (5) lying over this.
