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


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!

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