## 3 Results and Discussion
### Effect of Porosity on Moisture Content Measurement  
A total of 22 sets of experimental data in the calibration experiment were obtained after drying, as shown in Table 1. The data were fitted with the capacitance and temperature of corn measured by the online moisture content measurement device at the same time according to a previous study [14], and Equation (23) was obtained. The results of the variance evaluation are also provided in Table 2. Table 2 shows that, for the obtained model, the sum of squares (\(SS\)) was 161.604, the mean square (\(MS\)) was 32.318, the statistic \(F\) was 40730.27, and the corresponding confidence level \(P\) was less than 0.001. Based on the above data, the mathematical model established had strong significance. Thus, this equation can be used as a standard algorithm for online corn moisture content measurement. \[ \begin{array}{c}MC=0.3453C^{2}+0.01908 Tg+0.1295 Tg\times C-\\ 3.08C-1.386 Tg+38.25\end{array}  \tag{23}\]  
where \(C\) is the capacitance, \(MC\) is the moisture content, in wet basis, \(T_{\mathcal{G}}\) is the paddy temperature. Figure 6: The structure and size of the designed sensor. At room temperature (25 \({}^{\circ}\)C), the measured capacitance of the corn samples with a moisture content of 14.7%, 18.2%, 21.5%, 24.3%, and 26.4% w.b. at different porosities were substituted into Equation (23). The corn was filled into the online measurement device, and the calculated value and measured moisture content were recorded separately. The calculated moisture content was compared to the actual measured moisture content, and the calculated moisture content deviation is shown in Figure 7. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Drying Time** & **Moisture** & **Temperature** & **Capacitance** & **Drying Time** & **Moisture** & **Temperature** & **Capacitance** \\
**(min)** & **(\%w.b.)** & **(\({}^{\circ}\)C)** & **(pF)** & **(min)** & **(\%w.b.)** & **(\({}^{\circ}\)C)** & **(pF)** \\ \hline
0 & 22.42 & 21.2 & 4.31 & 330 & 18.39 & 28.2 & 2.68 \\
30 & 21.84 & 21.6 & 4.09 & 360 & 18.33 & 28.8 & 2.66 \\
60 & 20.89 & 22.4 & 3.67 & 390 & 17.43 & 29.2 & 2.26 \\
90 & 23.58 & 22.7 & 4.7 & 420 & 17.64 & 29.4 & 2.36 \\
120 & 22.56 & 23.5 & 4.33 & 450 & 16.81 & 29.9 & 1.98 \\
150 & 23.22 & 23.7 & 4.56 & 480 & 16.04 & 30.1 & 1.61 \\
180 & 22.45 & 24.5 & 4.29 & 510 & 16.18 & 30.4 & 1.68 \\
210 & 19.85 & 24.9 & 3.31 & 540 & 16.51 & 31.5 & 1.83 \\
240 & 19.2 & 26.2 & 3.04 & 570 & 15.85 & 31.9 & 1.51 \\
270 & 19.93 & 27.5 & 3.32 & 600 & 15.61 & 32.3 & 1.39 \\
300 & 19.56 & 27.5 & 3.18 & 630 & 14.67 & 32.8 & 0.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental values of response variables for the calibration experiment. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Df** & **SS** & **MS** & **F** & \(p\) \\ \hline \(C\) & 1 & 0.004 & 0.0037 & 4.63 & 0.047 \\ \(Tg\) & 1 & 0.008 & 0.0079 & 9.92 & 0.006 \\ \(C^{2}\) & 1 & 0.023 & 0.0226 & 28.52 & \textless{}0.001 \\ \(Tg^{2}\) & 1 & 0.008 & 0.0076 & 9.62 & 0.007 \\ \(C\)-\(Tg\) & 1 & 0.008 & 0.0085 & 10.66 & 0.005 \\ _Model_ & 5 & 161.591 & 32.318 & 40,730.27 & \textless{}0.001 \\ _Error_ & 16 & 0.013 & \textless{}0.001 & & \\ _Total_ & 21 & 161.604 & & & \\ \(R^{2}\) & 0.99 & & & & \\ _Adj-\(R^{2}\)_ & 0.99 & & & & \\ _Pre-\(R^{2}\)_ & 0.98 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the variance evaluation. Figure 7: The moisture content deviation under different porosities. Note: LE, ME, and HE represent a low, medium, and high degree of extrusion, respectively. Figure 7 shows that the porosity change in the cavity, caused by different extrusion pressures, will significantly interfere with the moisture content measurement. For corn with the same moisture content, the measurement absolute error was larger when the extrusion force was larger. For example, when corn with 21.5% w.b. moisture content was filled into the cavity through free falling (porosity was 42.5%), the measured value of moisture content was 21.4% w.b.