Sonar type sludge level detectors do not work in very thin sludges, or in the Dissolved Air Flotation (DAF) process, according to Markland Specialty Engineering, which says that its patented laser-like beam can easily monitor thin floc and DAF sludge levels. The microprocessor-based instrument is housed in a NEMA-4x enclosure with an LCD local readout, 4-20 ma output, two set-point relays and an RS 232/485 serial port. An advanced self-diagnostic system simplifies debugging. Depth ranges are 1.22 m. Fixed installation and portable models are available.