I am working on a palm oil mill project in Indonesia. We use the clarifier tank to separate the crude palm oil from the sludge. The efficiency for this separation process depends on the operator's observation on the liquid oil that is skimmed out via a skimmer valve. If the sludge oil is seen skimmed out from the skimmer than, the skimmer valve height is increased. The operator's activity is subjective, and the yield of separation varies from each shifts. We plan to automate this operation. The skimmer valve can be adjusted easily using servomotor or pneumatic diagphram actuating valves. But my problem is the level sensing of multiple liquid composition. i.e., the oil, sludge and sediments. How do you do that? My concept of the automation does not only skim out the first layer of the oil but also involve draining of the sludge oil for secondary recovery process and at the same time the capability of draining the sediments for bigger head space - to avoid upstream process interuption via level control and higher retention time in the tank for heating, thus better separation and yield. I need your helps and suggestion. Thank you.