Browsing by Author "Torvinen, Hannu"

The aim of this master’s thesis was to examine the influence of sample bulk density (5 density levels), volumetric moisture content, and the measurement frequency of capacitive moisture sensors on the results of capacitive moisture measurement of grass. A laboratory study was carried out in summer 2017 to be able to measure in controlled conditions. Literature study was also carried out to gather more information about the subject. The capacitive moisture sensors tested during the measurements were soil moisture sensors Decagon Devices 5TM, Delta-T Devices ThetaProbe ML2X, Soil Scout Hydra 100, bale moisture sensor Agreto PFM II and LCR meter R&S Hameg Lcr Bridge. The volumetric moisture contents were calculated based on the thermogravimetric moisture contents of the samples and the sample volumes that were calculated from sample thicknesses. The results of electric measurement devices were then compared to these volumetric moisture contents. Linear regression equations were utilized to determine the relationship between both thermogravimetric and calculated volumetric moisture contents and the results of the moisture sensors. The best coefficient of determination (corrected R2) for gravimetric moisture content (wet basis) was 0,54 and 0,67 for volumetric moisture content. The regression equations, which explained volumetric moisture content and had bulk density level as explanatory factor, produced the best results. It was concluded that the bulk density of grass samples and measurement frequencies of the sensors both influenced markedly the results of capacitive moisture measurement. Conductance and sensor geometry had also their own significance. Based on the results of these measurements, the continuous moisture measurement of grass yield is not possible by capacitive sensors. To be able to measure moisture content of grass precisely, one should know also the mass or volume flow passing the capacitive measurement device. One possibility is to combine capacitive sensors to other types of sensors.