Worldwide Support
Over 25 distributors and support centres worldwide

Flexible maintenance contracts
Tailor made plant specific contracts with 24Hr Support

30 years experience
Developing, manufacturing and installing


TunnelTech 205

NO2 Monitor

The TunnelTech 205 Air Quality Monitor continuously monitors NO2 and is an essential part of any road or rail tunnel safety system.


The TunnelTech 205 NO2 Air Quality Monitor is a highly efficient transmissometer configured for the continuous measurement of Nitrogen Dioxide in road tunnel atmospheres.


This extremely stable and reliable monitor incorporates a high-power blue LED to utilise the capacity of nitrogen dioxide to absorb UV and blue light to provide accurate readings in parts per billion.


NO2 is produced naturally by the combustion processes within the internal combustion engine and is emitted from the exhausts of all types of vehicles.

Features & Benefits

Related Products

TunnelTech 305 - Air Flow Monitor
TunnelTech 201 - Gas Analyser

Brochure Download

    Looking for a manual?

    Please contact us below and we will be happy to help you.

    Ask a question

    For further information on any of our products, please complete our enquiry form and a member of staff will respond as soon as possible.

    You can also call: +44(0)1629 814351

      TunnelTech 205 Specification

      Gas Species OptionsSingle or multi-gas measurements available: NO2
      Measuring Unitsppb (Parts Per Billion)
      Response TimeLess than 200 seconds
      Ambient Temperature-20°C to +50°C
      Power SupplySupplied with 48V power supply which requires 100-240Vac 150VA
      ConstructionCorrosion resistant epoxy coated aluminum housing sealed to IP65
      Analogue Outputs2 x 4-20mA, 200V common mode isolation, maximum load 500Ω
      Relay Outputs2 x volt-free contacts SPCO, 0.25A @ 125V AC, 1A @30V DC, 0.25A @ 100V DC
      Serial DataVia CODEL serial digital data bus

      For a full product specification please download the product brochure below.