Abstract:
This thesis describes an optical fibre sensor to detect and accurately measure
ammonia gas in the agricultural sector. Increases in ammonia emission especially
from the farming industry have created the need for a sensor that is capable of
measuring ammonia gas in the agricultural environment. The research of this
investigation is validated by measurement in a barn at a cattle farm and in the most
stringent weather condition. The optical fibre sensor system described in this thesis is based on an openpath spectral absorption gas cell addressed by optical fibres. A stainless steel hollow cylinder is used as the absorption cell and two Ultra Violet (circa 220 nm wavelength)optical fibres are used to transmit the light. The construction of the sensor uses robust material and is able to withstand the weather conditions encountered in this environment and is relatively low in cost. An Ultra Violet light source is used to avoid potential cross sensitivity problems with atmospheric gases. The optical sensor system uses a spectrometer as a detector and it is interfaced with a computer hosting data
capture and analysis software. A specially designed in-house program has been
developed using graphical programming software in order to monitor the ammonia
concentration in real time. Following optimisations for better performance, the
developed sensor system is capable of detecting ammonia gas at very low
concentration with a Lower Detection Limit of 0.39 ppm. This optical sensor system
also shows a fast response and recovery time being less than 4 s which is relatively
much faster than existing commercially available systems.
