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TunnelTech 205

NO2 Monitor

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.


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  • Continuous measurement of NO2 in road and rail tunnels
  • Class-leading Accuracy, Repeatability, and Resolution
  • Rugged, corrosion-resistant construction
  • Minimal maintenance requirements
  • Optional RS 485 (Modbus) Output
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
Series DataVia CODEL serial digital data bus


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