In order to permanently guarantee the purity of clean and clean rooms, specific measured variables must be controlled and monitored. Standards and guidelines such as DIN EN ISO 14644-3 require monitoring of temperature and air humidity with certain accuracies, in the case of relative humidity with a measurement uncertainty of +/- 2%. Furthermore, the standard requires monitoring of the overpressure in the cleanroom to prevent particles from entering the critical areas. The overpressure of the clean room in relation to a reference room must be between 5 and 20 Pa, and this should be monitored using suitable differential pressure measuring systems. Differential pressure transmitters are also used in cleanrooms for filter monitoring in order to permanently monitor the degree of filter contamination. Furthermore, the volume flows are measured in the supply and exhaust air