DFS-II Doppler Flow Switch
  • Non-Contacting Ultrasonic Sensor
  • Easy Calibration
  • Accurate and Repeatable
  • 5 amp DPDT Control Relay
  • Adjustable ON/OFF Set-Points
  • Adjustable Time Delay
  • Relay Status LED
  • Intrinsic Safety Option

Control Flow from outside a pipe. Recommended for "difficult liquids" including wastewater, slurries, sludge, chemicals, viscous liquids and abrasives. The Greyline DFS-II is ideal for pump protection or to activate flow/no-flow alarms.

The DFS-II strap-on Sensor mounts on any pipe over 1/2" diameter without cutting the pipe or shutting down flow. It installs in minutes and requires no maintenance. Includes one 5 amp DPDT control relay with 0-60 second adjustable time delay. Bright LED indicators show relay status and signal strength. Electronics are housed in a watertight enclosure and Sensor cable is shielded and can be extended up to 500 ft. (152 m).

Standard features include:

  • sensor - strap-on, single head ultrasonic
  • sensor cable - 20ft (6m) shielded coaxial pair
  • installation - sensor compound kit and stainless steel pipe clamp
  • enclosure - watertight NEMA4X (IP67) polycarbonate
  • 1 relay - 5 amp DPDT
  • set point - ON/OFF adjustment 0.25 to 10 ft/sec (0.076 to 3 m/sec)
  • failsafe mode - switch selectable
  • indication - relays and signal strength LED's
  • sensitivity - adjustable
  • time delay - adjustable, 0-60 seconds
  • power input - 120VAC 50/60Hz
  • electrical surge protection
  • 1 manual - Installation and Operation


SCOPE: This specification covers a non-intrusive, ultrasonic Doppler-type flow switch as manufactured by Greyline Instruments Inc., Massena, New York / Long Sault, Ontario. The instrument shall provide for flow control at adjustable flow velocities.


  1. The flow switch shall operate with a strap-on flow sensor mounted externally on carbon steel, stainless steel, ductile iron, copper, FRP, PVC, ABS, or cement lined pipe, and on liquids with entrained particles or gases of 100 microns or larger and minimum concentrations of 75 ppm.
  2. The control ON and OFF set-points shall be independently adjustable for flow rates between 0.25 ft/sec (0.076 m/sec) and 10 ft/sec (3 m/sec), in pipes 1/2" (12.5 mm) ID or larger.


  1. The flow sensor shall be single-head, ultrasonic in a stainless steel housing. It shall be installed on the outside of a pipe without interrupting flow. The sensor shall be capable of continuous operation at temperatures from -40°F to 200°F (-40°C to 93°C), and to withstand accidental submersion pressures to 10 psi. Manufacturer's recommended coupling compound and stainless steel pipe clamp shall be included.
  2. Shall include 20 ft (6m) shielded coaxial cable pair with waterproof, potted bond to the Sensor head.
  3. Shall be capable of extending sensor cable up to 500 ft (152m), without adjustment, and with no reduction in performance or signal strength.
  4. Shall be designed for Maximum RFI rejection, and include automatic high voltage bleeds for nearby lightning strikes.


  1. Shall include one 5 ampere DPDT control relay with separate ON/OFF set points individually adjustable between 1 and 10 ft/sec (0.3 to 3 m/sec).
  2. Shall be housed in a wall-mount watertight, dust tight NEMA4X (IP 66) fiberglass enclosure with a gasketed shatter proof window.
  3. The controller shall include separate dial adjustments for sensitivity and for damping.
  4. The controller shall include a signal strength LED light to indicate Doppler signal threshold, and a relay LED light to indicate relay status.
  5. The controller shall include relay time delay ON and OFF adjustment from 0 to 60 seconds.
  6. The controller shall include switch selectable Normal and Failsafe operating modes.
  7. The flow switch electronics/controller shall operate at temperatures from -5° to 140°F (-20° to 60°C).


  1. Sensor, connecting cable and junction boxes shall be rated intrinsically safe to Class I,II,III, Div. I,II, Groups C,D,E,F,G.
  2. Have a High Temperature Sensor for operating temperatures from -40° to 302°F (-40° to 150°C)
  3. Have a power input of 220-240VAC 50/60Hz.
  4. Have a power input of 24VDC.
  5. Have 50 ft (15 m) length shielded coaxial pair sensor cable.
  6. Have a Cable Junction Box and up to 500 ft (152m) extra Sensor cable that shall be shielded coaxial pair installed in conduit for mechanical protection.


The flow switch shall be a Model DFS-II Doppler Flow Switch as manufactured by Greyline Instruments Inc., and warranted against defects in materials and workmanship for one year.