AVFM-II Area-Velocity Flow Monitor
  • For Open Channels and Pipes
  • Ultrasonic - Measures Velocity + Level to Calculate Flow
  • No Flume or Weir required
  • 3 Isolated 4-20mA Outputs (Flow, Level and Velocity)
  • Totalizer and 2 Programmable Control Relays
  • Simple 3-key Calibration - Password Protected
  • Optional Intrinsically Safe Sensor
  • Optional built-in 50,000 point Data Logger and Software

Monitor flow through open channels, partially full sewer pipes and surcharged pipes without a flume or weir. Ideal for stormwater, combined effluent, raw sewage, irrigation water and streams. 

The AVFM-II uses a submerged ultrasonic sensor to continuously measure both Velocity and Level in the channel. The sensor is a completely sealed ultrasonic unit with no orifices or ports. It mounts inside a pipe or at the bottom of a rectangular, trapezoid or egg-shaped channel. Calibration is simple: enter the pipe diameter or channel width and the AVFM-II computes the flow volume and displays the flow rate.

Standard features include:

  • QZ02L sensor – measures flow Velocity and Level
  • sensor cable – 25 ft / 7.6 m submersible, shielded 3-coaxial
  • enclosure - watertight, NEMA4X (IP66) polycarbonate
  • displays - Flow Rate - large 4-digit LCD
    - Totalizer/Menu/Status - 16-digit alphanumeric
  • calibration - built-in 3-key programmer
  • output – three isolated 4-20mA (1000 ohm), Flow, Level and Velocity
  • 2 control relays - 5 amp, SPDT - programmable for flow
    proportional pulse output, flow and/or level alarm
  • power input - 100-160VAC 50/60Hz
  • electrical surge protection and RFI filters - AC, sensor, 4-20mA
  • 1 Manual - Installation and Operation


SCOPE: This specification covers an ultrasonic, area-velocity flow monitor as manufactured by Greyline Instruments, Massena, New York / Long Sault, Ontario. The instrument shall provide for indicating, transmitting, totalizing of the flow rate through partially filled or surcharged round pipes or rectangular, trapezoidal and egg-shaped channels.


  1. Flow Monitor to consist of a submersible ultrasonic sensor, connecting cable, and remote enclosure with indicating, transmitting and controlling electronics. System shall have no moving parts.
  2. Level measurement accuracy shall be ±0.25% of Range. Velocity measurement accuracy shall be ±2% of reading.


  1. Ultrasonic sensor shall be designed for continuous submersion in liquids.
  2. Using the Doppler principle, the sensor shall measure fluid velocities from 0.1 to 20 ft/sec (0.03 to 6.2 m/sec).
  3. Using ultrasonic echo-ranging principle, the submerged sensor shall measure liquid level from 1" to 15 ft. (25.4 mm to 4.57 m). Minimum level shall not be greater than 1" (25.4 mm). Level sensing circuitry shall include a temperature sensor for automatic temperature compensation.
  4. Sensor shall be constructed of PVC and epoxy resin.
  5. Sensor operating temperature shall be 5°F to 150°F (-15°C to 65°C).


  1. Provide minimum length 25 ft (7.6 m) tri-coaxial cable with potted bond to the Sensor head. Sensor cable shall be waterproof and electrically shielded. Exposed material shall be polyurethane only.
  2. Extended sensor cable shall be shielded tri-coaxial to a maximum length of 500 ft (152m). Cable shall be spliced with screw terminal connections in manufacturer’s recommended steel NEMA4 Junction Box.


  1. The transmitter shall provide for field calibration to round pipes, rectangular, trapezoidal and egg-shaped channels.
  2. Calibration shall be via built-in 3-key calibration system with menu selection of parameters. Systems requiring calibration by Parameter codes, BCD switches or external calibrators shall not be accepted.
  3. Calibration data shall be password protected and permanently stored through power interruptions for a minimum of 12 months.
  4. Field calibration shall allow selection and automatic conversion of measurement units, measurement span, high/low flow alarm relay and flow proportional relay pulse rates.
  5. Transmitter shall permit field programmable damping to smooth output in turbulent flow conditions, and programmable rejection time to disregard false signals from rain, wind, floating objects and spurious echoes.
  6. Transmitter operating temperature shall be from -5° to 140°F (-20° to 60°C). Transmitter shall contain a thermostat-controlled enclosure heater for condensation protection below 30°F (-1°C).
  7. Transmitter shall have three isolated 4-20mA outputs rated for 1000 ohm maximum load. Outputs shall be configured to transmit level, velocity and flow.
  8. Provide two relay contacts rated 5 amp SPDT programmable for flow proportionate pulse to a remote totalizer or sampler, high-low flow, velocity and/or level alarm, echo loss alarm.
  9. Provide a 4-digit LCD display scaled in user-selected engineering units and visible without opening the Transmitter enclosure.
  10. Provide a 16-digit alphanumeric display for calibration menu, running totalizer, flow reports and operation messages.
  11. Transmitter shall be housed in a wall-mount, watertight NEMA4X (IP66) enclosure with hinged, clear cover. Mounting hardware shall be included.
  12. Transmitter Displays indicating flow rate, units of calibration, maximum flow rate and flow totalizer shall be visible without opening cover.
  13. Transmitter electronics shall be surge protected on AC power input, sensor and 4-20mA outputs.
  14. Transmitter power input shall be 115VAC 50/60Hz with power consumption of 8.5 watts or less.



  1. Have separate, submerged Doppler velocity sensor, plus a non-contacting ultrasonic level sensor mounted above the liquid. Doppler velocity sensor shall be designed for continuous submersion in liquids and rated for fluid velocities from 0.1 to 20 ft/sec (0.03 to 6.2 m/sec). Non-contacting ultrasonic level sensor shall be rated for measurement range from 8" to 12 ft. (203.2 mm to 3.66 m) and shall include integral temperature compensation.
  2. Sensor cable shall be 50 ft. (15 m) continuous length with potted bond to the Sensor head.
  3. Sensor cable shall be 100 ft. (30 m) continuous length with potted bond to the Sensor head.
  4. Separate length extended sensor cable shall be shielded tri-coaxial to a total maximum length of 500 ft (152m). Cable shall be spliced with screw terminal connections in manufacturers recommended steel NEMA4 Junction Box.
  5. Sensor and connecting cable shall be rated intrinsically safe to Class I,II,III, Div. I,II, Groups C,D,E,F,G for installation in hazardous locations.
  6. Sensor shall mount with manufacturer's stainless steel mounting band for specified pipe diameter from 6" to 72" (150 to 1800 mm).


  1. Have a built-in 50,000 point data logger, RS232 serial output and connecting cables. Data logger shall support time and date-stamped logging and generate formatted flow reports including total, average, minimum, maximum and times of occurrence. Include Windows software for data log retrieval, graphing and export.
  2. Have a thermostat controlled enclosure heater for Transmitter operation at temperatures below freezing.
  3. Have manufacturer's recommended enclosure sunscreen to permit Electronics enclosure mounting in direct sunlight.
  4. Transmitter power input shall be 200-260VAC 50/60Hz with maximum power consumption of 8.5 watts or less.
  5. Transmitter power input shall be 9-36VDC with minimum power consumption of 2.9 watts.


Area-Velocity Flow Monitor shall be Greyline Model AVFM-II and warranted against defects in materials and workmanship for one year.