D-R 220T

Visibility monitor

Visibility Monitor for road tunnels using optical transmission principle. Sensor for ventilation control system or fire alarm system. Reliable measurement parallel to the tunnel axis.


  • measurement parallel to tunnel axis, continuous measurement
  • measurement along a distance of 10m, no spot measurement
  • corrosion resistant against tunnel atmosphere
  • determination and correction of the pollution of optical surfaces
  • measuring head and reflector can be exchanged quickly N
    – no tools required
    – no re-alignment required
  • signal transfer
    – per analog signal and relay outputs
    – per RS485 Modbus RTU
  • hermetically sealed housing - no gas diffusion to optics or electronics
  • dust protection tube prevents contamination of the optics
  • long maintenance intervals
  • quick and easy startup with or without PC

Your benefit

  • Precise visibility monitoring
    Transmission principle with compensation of pollution of the optical surfaces allows stable and precise measurement of the visibility
  • 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
    Use of durable components 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-tunnels
    Long-standing experience in various tunnel applications


suitable to measure visibility

  • in road tunnels
  • in factories

suitable for early fire detection

  • in road tunnels

suitable to measure dust concentration

  • in factories

Technical Data

sample gasair
0 - 95 % rel. humidity (not condensing)
measurementsextinction coefficient K in km-1
opacity as an option
extinction coefficient
K [km-1] (typically)
0 - 15 km-1
measuring pathdistance measuring head - reflector: 9.5-11m,
path length 19-22m
orientation parallel to tunnel axis,
ambient temperature-20 to +50 °C, dT/t < 10°C/h
measuring principlemeasuring the optical transmission of visible light which passed a measuring path twice
light sourceLED White, 530 nm
measuring ranges0 - 15 (...150) km-1 K extinction coefficient
0 - 97,5 % opacity
output rangeany interval of any measured value can be assigned to analog output, for example
extinction coefficient K in km-1
opacity in %
Modbus RTU allows access to the a.m. values
measurement outputs1 x 4-20mA, 400 Ohm, isolated
1 x RS 485 Modbus RTU
status output2 x relay NO, programmable, max load 48V, 0,5A
service interfaceUSB
service softwareD-ESI 100
power supply24 VDC, +- 10%, 0,4A
protectionIP 65
dimensions (h x w x d)ca. 150 x 220 x 140 mm
weightca. 2,7 kg
materialpolyamide, ca. RAL5017
fire class: B1 (UL 94 V0)
typeoptical retroreflector, optimized for 9.5 to 11m distance to measuring head
protectionIP 65
dimensions (h x w x d)ca. 150 x 110 x 140 mm
weightca. 1,6 kg
materialpolyamide, ca. RAL5017
fire class: B1 (UL 94 V0)
dimensions (h x w x d)ca. 280 x 110 x 110 mm
weightca. 3 kg
dimensions (h x w x d)160 x 280 x 190 mm
weight4 kg
fixation4x bolt d= 8 to 10mm
power supply90 - 264 VAC, 48 - 62 Hz, 30 VA
includes 24VDC supply for D-R 220T M
dimensions (h x w x d)ca. 160 x 160 x 110 mm
ambient temperature-25 to 55°C
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.

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