The Greyline Instruments DFS 5.1 is a Doppler ultrasonic flow switch that provides accurate flow control from outside the pipe . It is specifically recommended for difficult liquids including wastewater, cooling water, slurries, sludge, chemicals, viscous liquids, and abrasives . The DFS 5.1 is ideal for pump protection or to activate flow/no-flow alarms .

The ultrasonic sensor mounts on the outside of any metal or plastic pipe from 1/2 to 180 inches ID and installs in minutes, with no need to cut into the pipe or shut down the system. The sensor injects high-frequency sound through the pipe wall into the moving fluid; acoustic pulses reflected from particles or bubbles are detected to determine flow. The control relay can be set to turn ON and OFF at any flow rate between 0.25 and 10 ft/sec (0.075 to 3 m/sec) .

The DFS 5.1 features an adjustable time delay from 0 to 80 seconds to prevent nuisance alarms and relay "chatter" in turbulent flow. It includes switch-selectable "normal" and "failsafe" operating modes. The compact, water-tight NEMA 4X (IP 67) polycarbonate enclosure includes adjustable controls with separate ON and OFF relay set-points, a time delay adjustment, an LED bargraph for flow rate, and relay status LEDs. A 5 Amp DPDT control relay is standard .