This optical system covers extremely low concentrations of turbidity. The system consists of the transmitter Trb 8300 F/S and the InPro8400 and InPro8500 sensor series. These systems are designed for demanding applications in the chemical process, beverage and biopharmaceutical industries. The forward scattered light technique of the InPro8400 sensor series enables measurements even in liquids which appear clear to the human eye. The combined forward/90&#176 scattered light technique of the InPro8500 sensor series makes it possible to distinguish between turbidity caused by colloidal particles or larger particles. These are two requirements for reliable detection of particles in liquid streams for advanced process control and improved quality assurance measurements. With a wide variety of different process connections and line sizes, these flow-through sensors can be easily installed in main pipes or in a bypass line. The rugged sensor design allows installations even in harshest process conditions and in hazardous areas (Ex-proof). The Trb 8300 F/S transmitter enables quick start-up and operation with the full text menu guide in three selectable languages. Sensor diagnostic features provide information on sensor performance and consequently reduces maintenance time. Depending on specifications sensors are provided with application relevant certificates like CE, 3.1B, PED, 3A, ATEX and factory calibration certificates to satisfy safety requirements and to guarantee traceability.