The exchangeable digital sensor PMU-P is equipped with the Mela humidity measuring element humidity measuring element FE09/4. Protected by a PTFE pocket filter, the measuring element measures the air humidity. The pocket filter consists of porous vapour-permeable material and protects the sensor element from most dirt, dust and pollutants. The electronics and the plug contacts on the back are ex- trusion-coated with plastic to make them watertight.