Today`s demand for growing productivity of combine harvesters obliges a rise of automation. Market-available grain loss sensors cannot meet the accuracy requirements. Hence, a new approach to identify the working quality of combine harvester cleaning devices is tested at the chair of agricultural systems and technology. An optical sensor is used to detect grain flow in combination with a hot film sensor to detect air flow velocity. Multiple sensors are arranged in the sieve and chaffer area to capture the longitudinal and lateral distribution of grain separation and air velocity. This paper presents the results of preliminary studies of both measurement systems. The investigations carried out so far are very promising and suggest a much higher benefit compared to conventional measurement systems for grain loss. It also represents the new approach to measure process characteristics rather than process outputs in order to combine model based control algorithms with real process measurements.