Pharmaceutical products such as drugs and vaccines are held in batch filling holding tanks ready to be filled into injection vials under absolutely sterile conditions. After each batch, the holding tank has to be totally sterilized using an autoclaving procedure. During this process, the sensor is exposed to a pressure of 2.5 bar and a temperature of 130 °C for at least half an hour. The rapidly changing levels of the aqueous liquids are continuously monitored. The rapidly changing levels of the aqueous liquids require continuous and precise monitoring.