Non-hazardous ultrasound can replace nuclear type density meters. The sonic transducers fit flush with the pipe wall, so there are no intrusions into the flow which avoids fouling with stringy sewage sludge. The Markland #502 has an LCD local readout of percent solids; 4-20ma output; two set-point relays and RS-232/485 SERIAL PORT. The microprocessor is housed in a NEMA-4X enclosure and features advanced diagnostics, push button simplified calibration and dynamic damping.