The Greyline Instruments, by Pulsar Measurement, DFM 6.1 doppler flow meter is a simple, non-contact meter designed for applications that would defeat regular contacting flow meters. Because the sensor is mounted on the outside of the pipe, it is unaffected by abrasives or harsh chemicals making it ideal for wastewater, slurries, sludge, chemicals, viscous liquids and abrasives. There is no obstruction to flow and no pressure drop. The DFM 6.1 is recommended for full pipes and any fluid that contains solids or bubbles .

The DFM 6.1 clamp-on sensor is mounted on the outside of any pipe 1/2in / 12.7mm diameter or larger. To measure velocity an acoustic signal is reflected back to the sensor from moving particles or gas bubbles suspended in the fluid. Flow is calculated based on configured pipe ID. Flow rate range is ±0.1 to 40 ft/sec (±0.03 to 12.2 m/sec) with ±2% accuracy requiring solids or bubbles of at least 100 microns and 75ppm concentration .

The DFM 6.1 includes an ultrasonic sensor, an easy to use 5-key calibration system, a large digital flow rate display with totalizer, isolated 4-20mA output (1000 ohm load max), 26 million point data logger, and two programmable control relays. The sensor is classified as non-incendive and an intrinsically safe sensor is optional. Additional features include reverse flow measurement, ±0.1% repeatability, and ±0.5% linearity .