D-FL 220T

Ultrasonic flow velocity monitor

Measuring system for continuous evaluation of flow velocity and flow direction in tunnels. Ultrasonic sensors for tunnel ventilation control system. Reliable measurement across the tunnel profile. Two identical sensors alternately transmit and receive ultrasonic pulses. The system evaluates the transition times dependant on direction and calculates flow speed. D-FL 220T requires extremely low maintenance.


  • stand-alone system, no control unit required
  • simple configuration
  • corrosion resistant against aggressive tunnel atmosphere
  • 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
  • minimized spare requirements
  • extremely low maintenance

Your benefit

  • Precise Air Speed and Volume flow Monitoring
    Ultrasonic technology allows precise measurement of the average air flow along the whole tunnel cross section
  • Easy system setup and autonomous Operation
    Measuring device does not require an additional operation unit. Measuring devices can be replaced quickly with no tools or re-alignment required
  • Long Lifetime and extremely low maintenance requirements
    No consumables and no moving parts stand for low maintenance costs and a long Lifetime
  • Robust Design for a wide range of environmental conditions
    High-quality, corrosion-free plastic housing and a wide ambient temperature range
  • Easy connection due to configurable interfaces
    Connection to tunnel control system either via freely adjustable analogue output, relay or RS-485 Modbus RTU
  • Field-tested in road- and railway-tunnels
    Long-standing experience in various tunnel applications including high-speed railway tunnels


suitable for flow measurement in

  • road tunnels
  • railway tunnels

provides signals for ventilation control system

  • to monitor the air flow speed
  • to allow control of flow speed in case of fire

Technical Data

measurementsflow speed, flow rate
flow direction
sample gasair
flow velocity-20 .. 20 / -10 .. 10 / 0 .. 10 / 0 .. 20 m/s
sample gas moisture0 - 100% relative humidity
ambient temperature-25 to 55 °C (system)
-40 to 70 °C (sensor)
conformityEN 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
remarkscorrosion resistant against agressive gases, withstands lavation process in tunnels
measuring principleevaluation of transition times of ultrasonic pulses dependant on direction and subsequent calculation of flow speed
measuring path1.2 - 25 m
orientation of measuring path30 - 60°C to tunnel axis, typically 45°
measuring range-40 to 40 m/s
any interval can be assigned to analog output
default: 0-20 m/s
response time> 1s … 180s, programmable
resolution0,1 m/s,
accuracy depends on: installation, path length, flow profile,
typ. < +- 0,2m/s bei 3m/s
ambient temperature-40 to 70 °C
MTBF> 170.000 h
within service life if used within specifications
measurement output1x 4-20mA, 400 Ohm, isolated, can be assigned by any measured component and output range
1x RS 485 Modbus RTU, bi-directional to control room
status output1x failure, relay NC
1x flow direction, relay NC
max. load: 48V, 0,5A
signal transfer1x Intercom RS 485 Master-Slave communication
service interfaceUSB 1.1
service softwareD-ESI 100, requires laptop with Windows 7 oder 8
check cycleinternal automated routines, self test
power supply24 VDC +- 10%, ca. 1 A
protectionIP 67
dimensions (h x w x d)270 x 130 x 95 mm
weight2,2 kg
material1.4571/316Ti, polyamide, ca. RAL5017
fire class: B1 (UL 94 V0)
weightca. 1,5 kg
material1.4571 / 316Ti
fixation4x bolt, od= 8 to 10mm
ambient temperature-25 to 55°C
power supply90 - 264 VAC, 48 - 62 Hz, 30 VA
includes 24VDC supply for D-FL 220T
dimensions (h x w x d)ca. 160 x 160 x 110 mm
protectionIP 66
weightca. 1,5 kg
materialpolycarbonate, ca. RAL 7035
fire class: B1 (UL 94 V0)
fixation4 x bolt od= 8 to 10 mm

* variants Subject to technical modifications!


Universal display and operating units

The universal operating unit  Opens internal link in new windowD-ISC 100 allows the connection of several DURAG devices. It allows parameterisation and maintenance of all connected devices via integrated keypad or a connected PC and also supports remote access via intranet or internet connection.


Our  Opens internal link in new windowD-ESI Service and Parameterisation Software  assists you to manage all your DURAG sensors connected in one network system via a uniform graphical Interface.


Please contact your sales representitive for more Information.

Supply unit

  • Opens internal link in new window D-TB x00 in various versions
  • for voltage supply of one DURAG sensor
  • different housings available

Please contact your sales representitive for more information.

We offer various accessories such as weather protection covers for your sensor, mounting flanges and so on to fit your application and to have all components from one source.

Please contact your sales representative for further information.