DFX Doppler Ultrasonic Flow Meters

The DFX ultrasonic Doppler flow meter measures flows of liquids containing suspended particles or aerated liquids. Used with the DT9 clamp-on, non-intrusive transducers, the meter is suitable for sewage and mud slurries and can be used on most pipes constructed from metal or plastic. The DT9 transducer for the DFX meter is rated to Type 6 (IP-67) and has the ability to work with temperatures up to 400° F (200° C).
The DFX flow meter operates by transmitting ultrasonic sound from its transmitting transducer through the pipe wall into the flowing liquid. Each transducer contains piezoelectric crystals to transmit this signal. The sound will be reflected by useful sonic reflectors suspended within the liquid and recorded by the receiving transducer (see Figure 1). If the reflectors are moving within the sound transmission path, sound waves will be reflected at a frequency shifted (Doppler shift) from the transmitted frequency. The difference between the reflected frequencies and transmitted frequencies is directly proportional to the speed of the sonic reflectors, resulting in a liquid flow rate that is converted to various user defined measuring units.

Applications: Successful application of Doppler ultrasonic flow meters relies on three physical constraints:

  • The liquid flowing within the pipe must contain 100 ppm of useful sonic suspended reflectors. Dissolved solids do not generate reflections and are not relevant.
  • A significant portion of the ultrasound energy generated by the transducer must reach the sonic reflectors. The ultrasonic transducer must be acoustically coupled to the outside of a pipe (using grease or RTV couplant) and the pipe must permit ultrasound to pass without significant attenuation. Most pipes constructed of solid, homogenous materials meet this qualification. Pipes that cause application difficulty include concrete pressure pipes, woodstave pipes, Teflon®-lined pipes and fiberglass reinforced pipes.
  • The pipe must be completely filled with liquid when measurements are made. The DFX microprocessor assumes that the pipe is completely full when it calculates flow rate. Use on partially-filled pipes may result in inaccurate readings.


  • Minimal installation time: the DFX may be installed and fully operational within minutes. For most homogeneous pipe  materials, there is no need to break into pipelines.Sizes available for 1-1/2”, 2”, 3”, 4”, 6”, 8”, 10” and 12”
  • Minimal material costs: clamp-on sensor eliminates the need  for in-line flanges, pipe fittings, strainers or filters.
  • Reduced down-time: installation may be performed on full pipes and active systems. There is no need to shut down the process for installation or maintenance.
  • Lower maintenance costs: with no moving parts, there is nothing on the DFX to wear down.


  • Non-intrusive, clamp-on transducers for most pipes from 0.25 in. (6 mm) and above.
  • Wide velocity range: 0.15…30 fps (0.0…9 mps).
  • Accuracy ±2% full scale, over calibrated span.
  • Liquid Types Liquids containing a minimum of 100 ppm of useful sonic suspended reflectors greater than 35 micron size, and at least 25% of the overall particle volume is larger than 100 microns.
  • Flexibility: with automatic gain control and in-field linearization, the DFX will adapt to a wide variety of applications.