The TunnelTech 101 Visibility Monitor (VIS), is an essential part of any road or rail tunnel safety system. It monitors the Visibility within the tunnel and ensures that the tunnel ventilation system provides sufficient clean air for drivers to clearly see the road ahead.
The TunnelTech 102 Cold smoke monitor (CSM detects smoke from a fire to rapidly warn the operator of the hazard. Secondly, used in combination with other TunnelTech 101 VIS monitors, the operator can quickly detect the locus of the fire if it is also equipped with the optional PT 101 temperature sensor to accurately measure ambient air temperature in a range of -15 to 1050C.
The TunnelTech 200 series are primarily gas monitors with optional Visibility capability. Most use Infra-red absorption technology to monitor gaseous pollutants and those with a visibility channel use optical attenuation for that application. All TunnelTech 200 analysers except the TunnelTech 205 use the same rugged corrosion resistant enclosures and have an optional Data Display unit. As there is only one moving part so reliability levels are very high and maintenance levels very low.
There are four versions of the TunnelTech 200 series
The CODEL 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.
In some areas the use of electrochemical cells predominates, this is because they are a lower cost option to infra-red analysers. However, their use in road tunnels does present some issues as the cells require changing at regular intervals and this takes some planning so as to coincide with planned tunnel maintenance. Secondly their use in tunnels where the airflow exceed 5 metres/second is not recommended as the diffusion mechanism loses significant efficiency.
Despite these caveats, these gas sensors can give good service where the right conditions exist. CODEL offer the following electrochemical sensors:-
Tunnel Air Flow
Tunnel ventilation systems are designed to enable a sufficient throughput of air to be maintained to ensure a safe operating environment for users. These systems consume large amounts of power and need to be operated as efficiently as possible. To do this it is necessary to know the effectiveness of the system in terms of air flow and direction developed within the tunnel.
The TunnelTech 301 is a single point ultrasonic flow monitor that is unaffected by traffic flow and sound reflections. It is designed to withstand the harsh tunnel environment and has a working range of 0-20 metres/second in both directions.
In some countries they do not allow tunnel atmosphere monitors to be mounted on the tunnel wall; also, where there is a single bore it is very difficult to gain access for maintenance purposes. The TunnelTech 400 series are extractive gaseous pollutant and visibility monitors and extract a gas and dust sample from the tunnel bore and carry to a remote analyser. This allows maintenance to take place without affecting tunnel traffic flow.
The NO2 analyser 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. Visibility is monitored in the same sampling chamber using a standard opacity technique. The other optional gases are monitored using electrochemical cells.
One advantage of extractive analysers is that they can be regularly calibrated using bottled audit gases. There are four versions of the TunnelTech 400 series:-
According to the International Committee on Illumination CIE recommendations, luminance should be monitored as the luminance contained within in a conical field of view, subtending an angle of 20º. It is recommended that a luminance photometer is mounted in the tunnel approach road approximately 120 - 200 metres from the portal, depending on the approach speed of the vehicles and their stopping distance.
The purpose of monitoring the luminance at the portal is to adjust the level of light intensity inside the road tunnel to the light intensity outside so that drivers do not have to adjust their eyes quickly or become affected by the “black hole” effect where they decelerate rapidly and become a hazard to other road users.
CODEL offer the TunnelTech 601 luminance photometer for this application; it calibrated over a range of 0-6500 cd/m2 using standard traceable to the UK National Physical Laboratory. It has a thermostatically controlled heater to prevent condensation on the window and has an optional automatic window cleaning system.
In order to ensure that the light levels within the tunnel match those outside, Illuminance monitors are sited down the tunnel to control the tunnel lighting. Secondly, once inside the tunnel, as the driver's vision becomes adapted to lower lighting levels, the artificial lighting levels can be reduced in intensity as the distance travelled within the tunnel increases, a relationship known as the “Luminance Reduction Curve.
The TunnelTech 602 Illuminance photometers monitor the lighting levels along the length of the tunnel and ensure the levels are regulated in line with “Luminance Reduction Curve”.