Recent developments in the technology of odours have carried out the emergence of new devices mainly for odour monitoring. These systems were previously known as electronic noses or "e-noses", however this term in incorrect because these devices do not have a sense of smell, which is a human thing. A more correct term would be odorant sensor or o-sensor. In some cases the term "o-sensor" would be maybe too restrictive as it would exclude some other instruments for odour monitoring such as Gas Chromatograps for example.
The primary application of these instruments is to generate odour metrics that are relevant indicators for the presence and attributes of odour as would be perceived by human observers.
A benefit of instrumental odour monitoring systems is that they can be used for continuous measurement.
Odour monitoring systems are typically limited in their ability to mimic human olfaction and its very specific sensitivity to a large number of odorants. Human olfaction involves approximately 400 highly specific classes of olfactory receptor cells, from which the signals are aggregated in the brain to one odour perception. Odour monitoring systems are typically less evolved and therefore currently only give indicative results.
Odour sensors are often sensitive to both odour relevant molecules and also to odour irrelevant molecules. Odour sensors can also be subject to other interferences such as humidity and temperature. This can lead to both false positive and false negative sensor signals as far as odour relevance is concerned.
An o-sensor is usually a device with several sensors and equipped with a software that learn a sequence of electronic signs corresponding with a specific gas and memorizes it. In this manner an o-sensor gets an electronic pattern which is afterwards recognized whenever the same gas is presented to the sensors.
The operating mode of this sensors is relatively simple. The gas samples are compared with a built-up library and recognized as the "odour" when there is a coincidence with the pattern previously registered. With this technology it is possible a real-time recognition of the odours without the need of bringing the sample to the lab.
To date, the o-sensors cannot be used to measure odour concentration unless they have been calibrated before with a reference odour with the same chemical properties.
O-sensors are widely used in monitoring systems. For example in WWTPs or in refineries. In this case, a sample of the odorous gas is passed through a set of sensors and the pattern of the electric sign is registered. Afterwards, an alert-level is set and activated any time this level is exceeded.
Notes:
- See in our Directory section a list of several electronic noses available in the market
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Sampling is an essential and extremely important sub-step in the whole measurement procedure, and can be the most relevant cause for measurement errors. Thus, sampling must strictly follow appropriate standards suited for the respective measurement task.