Electromechanical NO2 monitor for tunnels

The ENOX is a compact electrochemical gas sensor suitable for continuous monitoring of Nitrogen Dioxide (NO2) within tunnel environments.


Special design
Designed for in-situ monitoring in tunnels or similar confined spaces
NO2 measurement
Electrochemical measurement of NO2
Gas detector
High accuracy intelligent gas detector with pre-calibrated sensing modules
Clear information
Backlit LCD display providing clear information and diagnostic data
Ingress protection
Rugged and reliable, with ingress protection toIP65
Compatible with BS EN 50545-1:2011

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The ENOX tunnel monitor measures the concentration of Nitrogen Dioxide (NO2) within an ambient environment such as road and rail tunnels or other industrial applications. These measurements can be used as part of an air quality management system for ventilation control.

The ENOX is a fixed sensor, which uses an electrochemical cell for NO2 detection. The ENOX consists of a Sender Unit and a ‘plug-in’ Sensor Module, which are mounted together on the wall or ceiling of the tunnel. The Sensor Module is pre-calibrated and stores all necessary data relating to type identification, sensing range and specific calibration. This data is automatically recognised by the Sender Unit when the module is fitted.


  • Cost effective fixed sensor solution
  • Rugged and reliable, with IP65 ingress protection
  • Easy to install, commission and operate
  • Plug-in sensor modules for quick and simple replacement
  • Compatible with BS EN 50545-1:2011

Tunnel diagram


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How works the ENOX?

Using an electrochemical cell means that the ENOX combines good sensitivity at low gas concentrations with high range capability and excellent stability. Electrochemical cells contain an electrolyte that is gradually consumed during use, influenced mostly by the duty cycle, ambient temperature and humidity. Therefore, the Sensor Module requires replacement / recalibration every 6 to 12 months to ensure accuracy of response. The sensor modules are pre-calibrated plug-in units which can be quickly and conveniently replaced, which means calibration gases are not required. Replacement sensor modules are available from Tunnel Sensors.

The ENOX is an intelligent sensor with 4-20 mA output and the option of RS485 serial communication protocols. It has two visual output alarm signals for GENERAL alarm and HIGH alarm. Default values are entered during manufacture and these can be adjusted to preferred values.

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