Optical sensor system on an apparatus for treating liquids.

An optical sensor system on an apparatus for treating liquids, with a device for projecting light (9, 10, 11) to at least one illumination position (12) in space, at least one device for imaging (11) the at least one illumination position on at least one photo detector (13) in order to supply a measurement signal depending on the received light, wherein the device for projecting (9, 10, 11) is a device for simultaneously projecting light to plural illumination positions and/or the device for projecting (9, 10, 11) is a device for simultaneously projecting light under different angles to the same illumination position (12), and/or plural photo detectors (13) are existent, and an analysing unit (21) connected to the at least one photo detector (13) for analysing the at least one measurement signal.