The Greyline DFM 5.1 is designed for “difficult liquids” that would damage regular flow meters such as wastewater, slurries, sludge, chemicals, viscous liquids and abrasives. There is no obstruction to flow and no pressure drop because the device measures flow from outside a pipe. The non-intrusive, clamp-on ultrasonic sensor fits any pipe 1/2” (12.5 mm) inside diameter or larger. The electronics/display enclosure can be mounted nearby. The DFM 5.1 includes a new digital signal processor to filter background noise and interference, and to measure flow rates accurately in liquids containing gas bubbles or solids particles.