# Investigation of a Precise Control Scheme for Rice Quality
## 3 Results and Discussion
### Process Reference Chart for Quality
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Parametric Setting**} & \multicolumn{4}{c}{**Net Drying Time (min)**} & \multicolumn{4}{c}{**Total Drying Time (min)**} \\ \cline{2-10}
**Run** & **T (°C)** & **RH (\%)** & **MC (\%)** & **V (m/s)** & **TR** & **Predicted** & **Measured** & **Discrepancy** & **Predicted** & **Measured** & **Discrepancy** \\ \hline
1 & 37 & 45 & 27 & 0.7 & 2.4 & 2.29 & 2.67 & 16.50\% & 71.57 & 71.2 & \(-\)0.52\% \\
2 & 52 & 45 & 23 & 0.8 & 1.5 & 6.4 & 6 & \(-\)6.25\% & 68.54 & 68.1 & \(-\)0.64\% \\
3 & 42 & 35 & 27 & 0.75 & 2 & 3.94 & 4.33 & 9.90\% & 69.78 & 71.2 & 2.03\% \\
4 & 44 & 48 & 22 & 0.6 & 1.3 & 2.45 & 2.5 & 2.04\% & 70.21 & 69.1 & \(-\)1.58\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Predicted and measured values of milling quality. where desired responses could be achieved. According to the National Standards of the People's Republic of China, the ACP should not exceed 3%. For the net drying time, a moderate value of 200 min was selected based on the experimental results. The preferred area is where ACP \(\leq\) 3% and DT \(\leq\) 200 min achieve a suitable tradeoff at a specific relative humidity level. Figure 10a illustrates that the preferred area is enclosed by the DT at 40% RH, the ACP at 40% RH, and the \(X\)-axis and \(Y\)-axis at 40% RH. Assuming an initial moisture content of 24%, a chart search indicates that drying temperatures ranging from 40.9 \({}^{\circ}\)C to 45.3 \({}^{\circ}\)C are suitable options for the drying process design. However, in some exceptional cases, it may not be possible to establish the preferred areas to obtain this information. As depicted in Figure 11a, achieving a net drying time of less than 200 min at 50% relative humidity proves to be challenging. Under such circumstances, extending the drying duration is necessary to ensure optimal drying quality. Additionally, providing guidance for rice with an extremely high or low moisture content within the most favorable range presents difficulties. For high-moisture rice, we can reduce the moisture content to meet technological requirements through natural drying based on the reference chart in order to ensure compliance with the quality standards. However, when dealing with rice with an extremely low moisture content, adjusting the moisture level is not feasible and may lead to exceeding the ACP limits during drying. Fortunately, early indica rice varieties are widely cultivated in southern China and typically have higher levels of moisture. In addition to being correlated with the drying time and quality indices, milling indices can also be correlated with multiple simultaneously selected quality indices. Figure 12 illustrates the reference process charts for both ACP and HRY. Unlike the trend of ACP, the HRV exhibits higher values in the region near the bottom left on both charts. The contour lines of the HRV are consistently linear within the parameter ranges due to the insignificant interactions between the factors, resulting in each factor independently affecting the HRV. As rice is often graded based on its HRV level, it becomes necessary to limit the value of HRV. Based on China's national standards for high-quality early indica rice, the first-grade, high-quality early indica rice standard was combined with the experimental data to establish a limit of HRV greater than 70%. The preferred high-quality area was divided in the same manner as shown in Figure 10 (ACP \(\leq\) 3% and HRV \(\geq\) 70%). The preferred regions vary under different relative humidity conditions. As shown in Figure 11a, when the relative humidity is at 30%, all areas where ACP \(\leq\) 3% are within the range of HRV \(\geq\) 70%. This suggests that the ACP serves as the primary control index under low relative humidity levels. With an RH below 40%, the coupling area is nearly identical to the region where the HRV exceeds 70%, and the process adjustments primarily focus on the HRV.