Alphasense recently launched the new Electronic Diffusion Tube (EDT) in response to demand for low cost monitoring with the ability to monitor semi-continuously. “Diffusion tubes have provided low-cost air quality monitoring for decades,” explains Alphasense Director Arthur Burnley. “However, they only provide an average reading over several weeks, and results are generally delayed until after laboratory analysis.”
“The EDT resolves both of these issues whilst retaining the advantage of low cost. This is because the EDT contains an advanced electrochemical sensor that logs readings and transmits data via Bluetooth to an android tablet or mobile phone running the EDT App; making it ideal for recording air quality at congested junctions, construction sites, warehouses and offices for extended periods.”
The EDT is a single gas monitor and users can select from a range of gases at the time of ordering. These include NO2, NO2 + O3, SO2, H2S, NO, NH3 and CO, with relative humidity and ambient temperature also being recorded for every measurement. Typical applications include monitoring urban air quality, checking livestock welfare, and recording waste water treatment and other odour nuisances.
Capable of storing 500,000 data sets, the EDT can operate remotely for months, downloading when convenient. Users simply approach the EDT within 10 meters, and it will recognise their device and download on command from the EDT App. Data can be sent to the cloud for analysis or downloaded to the user’s laptop or network.
The instrument is powered for up to eight months by two replaceable Lithium AA cells, and users are able to set any logging interval from one second to three days. The EDT can be used as either a hand-held unit or fixed to a wall or post, using the protective mounting bracket.
Odour Monitoring Application
Following complaints of nuisance odours, a major UK water company sought a cost-effective method for monitoring trace (ppb) levels of hydrogen sulphide (H2S), a toxic gas characterised by a ‘bad egg’ smell. This gas was chosen for measurement because it is usually the predominant component of a cocktail of gases that can contribute to odour at wastewater plants. Hydrogen sulphide is therefore commonly used as an indicator gas where odours arise from wastewater.
The human nose is highly sensitive to H2S, with most individuals able to detect at two to three ppb levels, so monitoring equipment must be able to monitor H2S at these low levels.
In order to respond effectively to the odour complaint, the water company needed to be able to monitor at a location with no mains power between its pumping station and the residential development. It also needed to monitor continuously so that
the effects of different plant processes could be correlated with H2S levels.
The Alphasense EDT is ideal for this application and was supplied pre-calibrated and set to record concentrations every two minutes. Mounted in the protective bracket, the EDT was quickly and easily mounted on a fence in an ideal location, running on internal batteries and logging data to an internal SD-card.
Bluetooth communications enabled the water company staff to collect data regularly over a 3 month period. As a result, it was possible to identify the processes that resulted in H2S spikes, and to thereby implement process changes to minimise the release of odorous gases. The EDT therefore enabled the water company staff to respond to the complaint in a professional manner, resolving odour issues to the satisfaction of the local residents.