Air Monitoring 29
Sensitivity and precision
A new generation of electrochemical sensors has been specifically designed for high precision monitoring in air quality applications. Traditionally, electrochemical sensors have not been suitable for this type of monitoring as they have not had enough sensitivity or precision. As well as a variety of other proprietary technology advances, the new type of sensor used has an additional fourth electrode which is used to provide this stability and help combat long term drift, along with a number of other new developments
including optimised catalyst loading and improved stack structures for stable operation at low concentrations.
By continuously measuring the status and performance within a monitoring device such as the AQMesh, correction factors can be applied to the measured data from the sensors. Information specific to each sensor used in AQMesh is recorded at the time of manufacture and uploaded to the Geotech cloud computing network for data processing.
To maintain detection levels in low parts per billion (ppb), careful electronics design is needed to ensure that the level of electronic noise in the circuit is very low. The AQMesh maintains this precision with noise levels less than a few ppb within the circuit, allowing the low detection limits needed in air quality monitoring. This vital element is an important challenge to overcome in order to achieve an acceptable level of sensitivity.
Graph 1 – NO data from two co-located AQMesh pods and calibrated reference-type analysers located in Leamington Spa, UK.
Graph 2 – NO2 data from two co-located AQMesh pods and calibrated reference-type analysers located in Leamington Spa, UK.
Wireless, low power design
For any compact air quality system to achieve such ease of deployment, two further design considerations become important: • It must communicate without hardwiring.
• It must be powered without the need for a mains power connection.
Both could limit how easy the device is to install and initialise, and where it is possible to locate a monitor.
Wireless communications can be achieved via the use of mobile GPRS technology. Although limited to where a signal can be accessed, this gives great scope for deployment in most urban and industrial areas. Where necessary, modern telecom networks will allow roaming to access a suitably strong signal and transmit data to a centralised cloud-based server. Data can then be accessed at any time from any location with suitable connectivity.
Graph 3 – O3 data from two co-located AQMesh pods and calibrated reference-type analysers located in Leamington Spa, UK.
The use of wireless technology can often be relatively intensive in terms of power usage. Sophisticated GPRS management techniques can be used to take a trickle charge from the batteries and is then used to give the short bursts of power needed to connect the wireless GPRS link for data transmission. This avoids taking large peaks of current from the battery which would shorten its life. Combining this approach with the use of high capacity cells means that a battery powered air quality monitor
can be deployed with a lifespan of up to two years before batteries need to be replaced.
Innovations in data processing
Traditionally most monitoring instruments perform data processing on-board. This can require high power, high capacity
www.envirotech-online.com AET Annual Buyers’ Guide 2013
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