The OPTISYS SLM 2100 is a sludge level measuring system for measurement of sludge blanket level and fluff levels as well as sedimentation profiles. Using an optical sensor which travels right down to the tank bottom, it detects all sludge phases, supplying precise concentration and level measurements. In this way, it is also able to measure the sludge blanket continuously (zone tracking) and hence monitor one specific "zone" (e.g. for controlling the pumps during de-pumping of the sludge). For an optimised process monitoring, an automatic measuring mode change is possible in which sedimentation profile measurements can be carried out in the meantime. Unlike with ultrasonic sludge level meters, there are no echo returns from tank walls or signal damping by fluff or floating sludge that can cause false measurements.