## 3 Results and Discussion
Figures 12 and 13 show the results of analysis of the wrong indications of the piezoelectric sensor depending on the dosing tube tilt angle and the exit hole end shape obtained from the experimental and simulation tests using DEM. Both in computer simulation and in experimental tests the largest error of the sensor indication was found for a tilt angle equal to 15\({}^{\circ}\), whereas the smallest one for a tilt angle equal to 0\({}^{\circ}\). It is also noticeable that the sensor indication error increases along with the tilt angle increase in the straight system which is confirmed by the results of a correlation analysis (Tables 3 and 4). No distinct tendency was observed for the diagonal system in the experimental tests which in turn appeared in the simulation tests (Tables 3 and 4 and Figures 12 and 13). For a straight system, the simulation and experimental tests show a similar tendency of the indication error to increase along with an increase in tilt angle. Based on the results, it can be said that tilt in the range of 0-5\({}^{\circ}\) will provide the grain with single impact against the sensor surface, thereby the least number of wrong indications of all the analyzed configurations. Due to the lower values of error, it would be better to use an exit hole with a straight end. Low values of the sensor indication errors (up to 10%), particularly for small tilt angles (0\({}^{\circ}\) and 5\({}^{\circ}\)) prove its high grain detection efficiency, comparable with other sensors used in sowing systems e.g., photoelectric [46], fiber [47], or infrared sensors [48]. The whole chamber of \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of Exit Hole** & **Factor** & \(\mathbf{X}\) & \(\mathbf{Y}\) & \(\mathbf{X_{0}}\) & **Relative Error** \\ \hline \multirow{2}{*}{Straight exit hole} & Pearson Corr. & 0.755 & \(-\)0.786 & 0.752 & 0.867 \\  & \(p\)-value & 0.245 & 0.214 & 0.248 & 0.133 \\ \multirow{2}{*}{Diagonal exit hole} & Pearson Corr. & \(-\)0.701 & \(-\)0.958 * & 0.933 * & 0.058 \\  & \(p\)-value & 0.299 & 0.042 & 0.067 & 0.942 \\ \hline \hline \end{tabular} \({}^{*}\)statistically significant correlation for \(p<0.1\).  
\end{table} 
Table 3: Analysis results of correlation between tilt angle of the exit hole and the grain collision point coordinates and sensor indication error in experimental tests. Figure 11: Final position of grain \(X_{0}\) after collision for different tilt angles during experimental and simulation tests. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Type of Exit Hole** & **Factor** & \(\mathbf{X}\) & \(\mathbf{Y}\) & \(\mathbf{X_{0}}\) & **Relative Error** \\ \hline \multirow{2}{*}{Straight exit hole} & Pearson Corr. & 0.905 * & \(-\)0.873 & 0.685 & 1.000 * \\  & \(p\)-value & 0.095 & 0.127 & 0.315 & - \\ \multirow{2}{*}{Diagonal exit hole} & Pearson Corr. & \(-\)0.183 & \(-\)0.667 & \(-\)0.894 & 0.944 * \\  & \(p\)-value & 0.817 & 0.333 & 0.106 & 0.056 \\ \hline \hline \end{tabular} \({}^{*}\)statistically significant correlation for \(p<0.1\).  
\end{table} 
Table 4: Analysis results of correlation between tilt angle of the exit hole and coordinates of the grain collision point and the sensor indication error in simulation tests. a piezoelectric sensor and the end of the exit tube were carried out by fast prototyping methods (3D printing), which again were found to be the best solution in construction of prototype units and elements [49; 50]. An advantage of the presented grain detection system with a piezoelectric sensor in the sowing unit is the resistance of its indications to dust while sowing, which may occur when using photoelectric sensors, whereas the accuracy is comparable or higher (the piezoelectric sensor accuracy range in this study for all tilt angles is 70-95% compared to that of the photoelectric sensor described in [46] which is 47-63%). In addition, in this type of sensor the accuracy is independent of the temperature increase, which is observed for fiber sensors [46].