The Waterpilot FMX21 level sensor from Endress+Hauser has stainless steel housing and a flush-mounted process diaphragm, making it ideal for measuring the level of sludge and wastewater. It also can measure temperature with an optional Pt 100 sensor. A corrosion-resistant, coated version is available for use in aggressive environments. The sensor uses a ceramic cell to measure pressure. Pressure changes cause a change in capacitance, which the sensor’s electronics convert into a 4-20mA signal that is linear to the level of the liquid.