Combined CO, NO, NO² and Visibility Monitorfor Tunnels

The VICONOX tunnel atmosphere monitor is a single sensor solution for measuring toxic gases, visibility and temperature within harsh tunnel environments.


In-situ measurement
Direct in-situ measurement of NO2, NO, (NOx), CO, Visibility and Temperature (or combinations thereof)
NO2 measurement
Direct optical measurement of nitrogen dioxide (NO2) using differential absorption
Visibility measurement
Visibility measurement using an accepted light transmission opacity technique
Infrared spectroscopy
Proven infrared spectroscopy technique for NO and CO measurement
Quick lock plug and socket cable connection enabling simple installation
RS485 communication (Modbus RTU), Digital Relays and Analogue outputs
Extended warranty
Optional extended warranty and 5 year refurbishment programs are available

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Tunnel atmosphere monitor

The VICONOX tunnel atmosphere monitor is a single sensor solution for measuring NO2, NO, (NOx), CO, visibility and temperature (or combinations of) within a road traffic tunnel, rail tunnel or other confined space. These measurements can be used as part of an air quality management system for ventilation control and / or secondary smoke detection.


  • Pre-aligned quick release TX and RX heads enabling easy installation and maintenance
  • Up to 6 measurement parameters in one unit minimises capital cost but also minimises the requirements for cabling, installation and commissioning
  • Temperature and humidity compensated measurements to ensure stable readings across all conditions
  • Rugged design to withstand corrosive atmospheres and regular tunnel washing
  • High quality 316 stainless steel construction ensuring a long service life
  • IP67 rated external enclosure with quick release dust protection tubes

VICONOX calibration kit

Tunnel Sensors offer six variants of the VICONOX tunnel air quality monitor. All VICONOX AQMs measure visibility along with a combination of gases including CO, NO, NO2 and NOx. To complement the monitors, six calibration / audit kits are now available to purchase for the specific variant of VICONOX installed.

All six kits comprise of three calibrated opacity filters to confirm the accuracy of the visibility readings. We also offer sealed gas check cells for both CO and NO and a filter to check NO2 readings. All kits are issued with calibration certificates to confirm performance and expected measured values.

The filters and gas check cells are supplied in a robust case with precision cut foam inserts to keep your calibrations tools safe when not in use. There’s also a documentation area to store instructions and calibration certificates.

The kit is suitable for tunnel operators who maintain their own instrumentation and service and maintenance contractors that support tunnel sensors equipment.

Discover the Viconox calibration kit

Harsh tunnel environments

The VICONOX has been designed for harsh tunnel environments with a high quality, IP67 rated stainless steel enclosure. Wall mounted alignment bracketry, quick release heads and quick lock cable connections make installation and future servicing easy and simple. The VICONOX’s intelligent heads have RS485 (Modbus RTU), Digital Relays and Analogue Outputs as standard for connection to a PLC / SCADA system.

The VICONOX tunnel atmosphere monitor

The VICONOX tunnel monitor is a single sensor solution for measuring NO2, NO, (NOX), CO, visibility and temperature within a traffic tunnel, rail tunnel or other confined space.

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