Non-Contacting Ultrasonic Sensor Accurate and Verifiable Built-in 2-million point Data Logger and Windows Software USB Outputs to Flash Memory Sticks Isolated 4-20mA/0-5V Output 2 Programmable Control Relays Simple 5-key Calibration with Language Selection Measure flow from outside a pipe. The Greyline DFM 5.1 is designed for "difficult liquids" that would damage regular flow meters - wastewater, slurries, sludge, chemicals, viscous liquids and abrasives. There is no obstruction to flow and no pressure drop. 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. Use the isolated 4-20mA to transmit flow to remote displays, recorders or controllers. The programmable relays can be used for flow control, pump protection or flow proportionate pulse. Calibration is easy with the built-in 5-key calibrator. Display and totalize flow in your choice of engineering units (gallons, liters etc.)