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TunnelTech 204

Visibility Only Monitor

The TunnelTech 204 Air Quality Monitor continuously monitors visibility and is an essential part of any road or rail tunnel safety system.


The TunnelTech 204 Air Quality Monitor is an essential part of any road or rail tunnel safety system. Firstly, it monitors the atmosphere within the tunnel and ensures that the tunnel ventilation system provides sufficient clean air to protect tunnel users health and for drivers to clearly see the road ahead.


The TunnelTech 204 analyser uses well proven optical attenuation technology to monitor visibility levels.


As there is only one moving part, reliability levels are very high and maintenance requirements are extremely low.

Features & Benefits

Related Products

TunnelTech 305 - Air Flow Monitor
TunnelTech 205 - N02 Monitor

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      TunnelTech 204 Specification

      Gas Species OptionsSingle or multi-gas measurements available: Visibility
      Measuring Unitsm-1 or m for visibility
      Response TimeVis 10s – 2min Selectable
      Ambient Temperature-20°C to +50°C
      Power Supply12 – 24V dc 1.5A
      ConstructionCorrosion resistant epoxy coated aluminum housing sealed to IP65
      Analogue Outputs3 x 4-20mA current outputs as standard, isolated, 500Ω maximum load, fully configurable
      through TunnelTech software
      Relay Outputs3 x volt-free SPCO contacts, 50V, 1A max, configurable as alarm contacts
      Serial DataFor local connection to laptop PC using RS232 or optional RS485 interface unit

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