Abstract: A turbidity sensor and a method for determining at least one physical, chemical and/or biological measured variable of process automation in a medium by means of at least one optical sensor, comprising the steps of sending transmission signals into the medium, wherein the transmission signals are converted into received signals by interaction with, especially by scattering from, the medium as a function of the measured variable; receiving the received signals; and converting the received signals into the measured variable as a function of environmental conditions at the location of installation and, adjusting the sensor based on a calibration graph corresponding to environmental conditions at the location of installation.