Technical Manual CODEL
2
The monitoring stations, Figure 1, provide all required measurements and outputs at each monitoring
location within the tunnel.
Figure 1 : Tunnel Tech 700 Series - Monitoring Station
CO, NO, NO², and Visibility Air Quality Monitor
The Air Quality Monitor (AQM), shown in Figure 2, uses visible light channels to measure visibility and
electrochemical cells. The AQM consists of a transceiver that projects visible beams to a reflector unit
mounted 3m away.
A high-powered modulated LED is used for the visible light source.
Optical visibility is measured by a silicon photo-detector that determines the attenuation of the light
beam, along the instrument sight path, due to the particulates in the tunnel atmosphere.
CO, NO and NO2 are measured using electrochemical cell technology. Once the zero level of the cell
is set and recorded in the instrument memory, the cell output is linear and proportional to the ppm or
ppb reading.
A serial data link via an RS485 interface allows communication directly with the AQM sensors.
CO/NO/NO²/VIS Air Quality
Monitor
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