Area-Velocity Flow Monitor AVFM 6.1

  • No flume or weir required – submersible ultrasonic sensor measures velocity and level simultaneously to calculate flow. No moving parts to wear, foul, or clog.
  • Built-in 5-button keypad, intuitive menu, and large backlit LCD display make the AVFM 6.1 the most operator-friendly area velocity flow meter on the market.
  • Fast, simple, installation and setup.
  • Improved performance in a wider range of operating conditions.
  • At a glance, view flow rate, velocity, level, totalizer, relay status, and important diagnostic information on the LCD display.
  • Three isolated 4-20mA outputs for flow rate, velocity, and level, and two relay outputs for pulse output or alarm.
  • 6.5 million point data logger for greater flexibility of data monitoring, control, and reporting.
  • Min, Max, and Total Flow data from the last 365 days is available on the LCD display, or download directly to a USB for easy reporting.
  • Monitors flow rate, volume total, run hours, and diagnostic information through only two wires with the optional Modbus RTU serial communication output.
  • Description
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  • Specifications
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Product Description

Measure flow through partially filled pipes, channels, canals and turnouts without a flume or weir. Ideal for wastewater, stormwater, effluent, industrial wastewater and irrigation water. Configuration is simple: enter the pipe diameter or channel shape and the AVFM 6.1 computes the flow volume and displays the flow rate. Measure forward and reverse flow and calibrate to channels of any shape.

  • Waste water
  • Combined sewers
  • Stormwater Channels
  • Industrial Effluent
  • Natural streams
  • Irrigation water


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


  1. Flow meter to consist of a submersible ultrasonic sensor, connecting cable, and remote enclosure with indicating, logging, totalizing, transmitting and controlling electronics. System shall have no moving parts.
  2. Level measurement accuracy shall be ±0.25% of reading or ±0.08”, whichever is greater. Repeatability & Linearity 0.1%. Velocity measurement accuracy shall be ±2% of reading or ±0.04 ft/sec, whichever is greater. Requires solids or bubbles minimum size of 100 microns, minimum concentration 75ppm. Repeatability & Linearity 0.5%.


  1. Ultrasonic sensor shall be rated for continuous submersion up to 15 feet (4.57 meters).
  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) and reverse flow to -5 ft/sec (-1.5 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).
  4. Level sensing circuitry shall include a temperature sensor for automatic temperature compensation.
  5. Sensor shall be constructed of 316 stainless steel and epoxy resin.
  6. Sensor operating temperature shall be 5°F to 175°F (-15°C to 80°C).
  7. Shall include manufacturer's recommended stainless steel sensor mounting bracket.


  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 only be polyurethane.
  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 configuration to round pipes and open channels of any shape.
  2. Configuration shall be via built-in 5-key calibration system with menu selection of parameters. Systems requiring calibration by Parameter codes, BCD switches or external calibrators shall not be accepted.
  3. Configuration data shall be password protected and permanently stored through power interruptions for a minimum of 12 months.
  4. Field configuration 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 independent field programmable damping of both the level and velocity to smooth output in turbulent flow conditions.
  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 with menu-selectable 0-5VDC alternative. 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 or low flow alarm, velocity and/or level alarm, and echo loss alarm.
  9. Provide a white, backlit matrix LCD display indicating flow rate, level, velocity, relay states, 14-digit totalizer in user-selected engineering units and multiplier, logger status, and sensor status.
  10. Transmitter display indicating flow rate, units of calibration, totalizer, relay states, logger status, and sensor status shall be visible without opening cover.
  11. Have a built-in 26 million point data logger with USB output to flash drives or mass storage devices. 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 graphing and export.
  12. Meter shall store the minimum, maximum, and daily total flow for the last 365 days. This data can be downloaded directly to flash drives or mass storage devices for easy reporting.
  13. Configuration parameters can be downloaded by invoking menu selection. Parameters download directly to flash drive or mass storage device.
  14. Level and Doppler signals can be downloaded to flash drive or mass storage device, for diagnostic purposes, by invoking menu selection.
  15. Transmitter shall be housed in a wall-mount, watertight NEMA4X (IP66) enclosure with hinged, clear cover. Mounting hardware shall be included.
  16. Transmitter electronics shall be surge protected on AC power input, sensor, and 4-20mA outputs.
  17. Transmitter power input shall be 100-240VAC 50-60Hz with power consumption of 10VA or less.
  18. The transmitter shall permit plug-in field installation and auto-detection of optional accessories including alternative sensor configurations, serial communications, and additional control relays.



  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) and reverse flow to -5 ft/sec (-1.5 m/sec). Non-contacting ultrasonic level sensor shall be rated for measurement range from 8" to 15 ft. (203.2 mm to 4.57 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. 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. 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 thermostat controlled enclosure heater for Transmitter operation at temperatures below freezing.
  2. Have manufacturer's recommended enclosure sunscreen to permit Electronics enclosure mounting in direct sunlight.
  3. Transmitter power input shall be 9-32VDC with minimum power consumption of 10 Watts max.


Area-Velocity Flow Meter shall be Greyline Model AVFM 6.1 and warranted against defects in materials and workmanship for one year.

Specifications are subject to change without notice.

Please contact  Aktek  if you need more information or for advice in your application. We can provide quotations and refer you to the Greyline sales representative in your area.



Area-Velocity Flow

Measure open channel flow without a flume or weir
An Area-Velocity Flow Meter continuously measures both Level and Velocity to calculate flow volume in an open channel or pipe.

The ultrasonic sensor is installed at the bottom of a pipe or channel. To measure water level the sensor transmits ultrasonic pulses that travel through the water and reflect off the liquid surface. The instrument precisely measures the time it takes for echoes to return to the sensor. Based on the speed of sound in water, the level is measured with accuracy of ±0.25%.

Flow velocity is measured with an ultrasonic Doppler signal continuously injected into the water. This high frequency sound (1.28MHz) is reflected back to the sensor from particles or bubbles suspended in the liquid. If the fluid is in motion, the echoes return at an altered frequency proportionate to flow velocity. With this technique the instrument measures flow velocity with accuracy of ±2%.

Area-Velocity Flow Meters work in partially full and surcharged pipes, rectangular, trapezoid and egg-shaped channels.

Optional - Separate Level and Velocity Sensors

A separate down-looking ultrasonic sensor can be used for highly aerated or turbulent flow applications. It measures level by transmitting ultrasonic pulses through the air to the liquid surface with accuracy of ±0.25%. Along with the level sensor, a submerged Doppler velocity sensor is used to measure the water velocity.