Durag D-FL 220T ultrasonic flow velocity monitor for tunnels

The D-FL 220T continuously measures flow velocity and flow direction in tunnels. Its ultrasonic sensors provide reliable measurement across the tunnel profile for tunnel ventilation control systems.

Two identical sensors alternately transmit and receive ultrasonic pulses. The system evaluates the transition times dependent on direction and calculates flow speed.

Key Benefits

  • Extremely low maintenance
  • Reliable measurement across the tunnel profile
  • Stand-alone system, no control unit required
  • Simple configuration
  • Corrosion resistant against aggressive tunnel atmosphere
  • Withstands lavation process in tunnels
  • Sensors can be replaced quickly, no tools, no re-alignment required
  • Signal transmission
    – per 4-20mA analog signal and 2 relays
    – per RS 485 bus via MODBUS RTU protocol
  • Minimal spare requirements.


Slow measurement:

  • Road tunnels
  • Railway tunnels

 Signals for ventilation control system

  • Monitors air flow speed
  • Enables control of flow speed in case of fire

Download Specifications


Tunnel & Roads Transport


Measurements Flow speed

Flow rate


Measuring path 1.2 – 25 m
Orientation of measuring path 30 – 60°C to tunnel axis, typically 45°
Response time > 1s … 180s, programmable
Resolution 0,1 m/s,
accuracy depends on: installation, path length, flow profile,
typ. < +- 0,2m/s bei 3m/s
orientation of measuring path 30 – 60°C to tunnel axis, typically 45°
Sample Gas Air
Flow velocity -20 .. 20 / -10 .. 10 / 0 .. 10 / 0 .. 20 m/s
Sample gas moisture 0 – 100% relative humidity
Ambient temperature 25 to 55 °C
Standards conformity EN 61 326-1 (2006)
EN 61 010-1 (2001)
RABT 2006
ASTRA guideline ventilation of road tunnels – 2008, V2.01
RVS 09.02.22 2007


Dimensions 270 x 130 x 95 mm
Weight 2.2 kg
Material 1.4571/316Ti, polyamide, ca. RAL5017
fire class: B1 (UL 94 V0)
Weight ca. 1.5 kg/td>
Fixation 4x bolt, od= 8 to 10mm
Category Tag Brand:

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