Monitoring of air quality – visibility and gases

Visibility and gas monitoring during normal operation is used to control the tunnel ventilation at normal operation. If and with how much power artificial ventilation by jet fans is operated depends on the measured visibility and gas concentration.

Visibility is expressed by the extinction coefficient, which describes the light attenuation caused by particles in the air.

The sensor extracts air from the tunnel by an integrated fan and feeds it into the measuring cell which detects the intensity of light scattered by this sample, sets it into relation with the light passing through and calculates the extinction coefficient.

Optional electrochemical gas sensor cells induce currents proportional to the prevailing gas concentration. With these currents and the measured temperature, the gas sensor modules calculate the gas concentrations.

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smart/AQM Air Quality Monitor

  • Smart IoT enables visibility and gas sensor
  • Scattered lightvisibility sensor
  • Dual beam method to compensate soiling and ageing
  • Optional up to 3 electrochemical gas sensor modules
  • Pre-calibrated gas sensor modules for different gases and measuring ranges, including CO, NO, NO2, SO2
  • Installation in-situ in the tunnel’s driving area or extractive with hose adapters
  • Active extraction of sample air by integrated fan
  • Integrated purge air system
  • Optional sample heater to eliminate fog from measurement
  • Stainless steel housing 1.4404 (AISI 316L)
  • Sensor protected against splashing of water and powerful water jets used for tunnel washing
  • IP rating IP69K
  • Optional LCD in housing cover
  • Integrated web server for visualisation, configuration, data logging, remote maintenance
  • Connection to tunnel control system by
    • MODBUS/TCP (Ethernet)
    • MODBUS RTU (RS-485)
    • Analogue and relay outputs (optional)
    • OPC UA (Ethernet)
  • Optional smart/HUB IoT operating and control unit with touch display


Data sheet DE (PDF)
Data sheet EN (PDF)