## 3 Experiments
During testing, cold food items were introduced into the microwave to replicate typical food-heating scenarios found in household kitchens. These tests were conducted in a specially designed cubic, replicating the dimensions of a standard household kitchen to maximize ecological validity. Throughout the experimental process, the microwave oven was operated at three distinct settings: low, medium, and high. Electrical signals corresponding to each setting were meticulously recorded. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Brand** & **Product Model** & \
\begin{tabular}{c} **Rated Voltage** \\ **/Frequency** \\ \end{tabular} & **Rated Input Power** & **Output Power** &
\begin{tabular}{c} **Rated Microwave** \\ **Frequency** \\ \end{tabular} & **Efficiency Value** \\ \hline Midea & M1-L202B & 220 V/50 Hz & 1150 W & 700 W & 2450 MHz & 56\% \\ Galanz & P70D20 TIL-D4 & 220 V/50 Hz & 1180 W & 700 W & 2450 MHz & 52\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Detail of two tested microwave ovens. Figure 5: The experiment equipment. Following the acquisition of operational electrical signals from a Galanz microwave oven, the sampled signals were analyzed to determine power values, fundamental current signals, and odd harmonics, specifically the 1 st, 3 rd, 5 th, and 7 th harmonics. Power trend graphs facilitated the segmentation and determination of operational events within the microwave oven's working cycle. For three different operating modes, microwave oven operation events were segmented based on the power figures below, allowing for the determination of the start and end times of each event. As illustrated in Figure 7 below, the segments between points A and B and C and D in each power graph represent sub-events within the microwave oven's operation. After the event identification, an analysis of the electrical current signals was conducted during the operational process, focusing on identifying the central clusters for the 1 st, 3 rd, 5 th, and 7 th harmonics. For the Galanz microwave oven operating at low, medium, and high settings, the central cluster positions for these harmonics are detailed in the figures in Appendix A, Figures A1-A3, shown below. The central cluster positions for these harmonics are detailed in Table 2, shown below. A Bayesian network model with inhibitory nodes was then constructed based on the current signal characteristics, as shown in Figure 8. The upper layer of the model identifies the appliance type, in this case, a microwave oven, while the lower layer comprises signal characteristic nodes, including total power and current harmonics for the 1 st, 3 rd, 5 th, and 7 th harmonics. Inhibitory and leak nodes in the model are utilized for calculation purposes and are not explicitly shown in the diagram. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multicolumn{2}{c}{**1 st Harmonic**} & \multicolumn{2}{c}{**3 rd Harmonic**} & \multicolumn{2}{c}{**5 th Harmonic**} & \multicolumn{2}{c}{**7 th Harmonic**} \\ \hline  & **I/A** & **U/V** & **I/A** & **U/V** & **I/A** & **U/V** & **I/A** & **U/V** \\ \hline \multirow{3}{*}{Low mode} & 0.1038 & 220.2 & 0.005785 & 220.2 & 0.001145 & 220.2 & 0.003154 & 220.2 \\  & 2.322 & 220 & 0.9144 & 220.1 & 0.3653 & 220 & 0.1101 & 219.8 \\  & 4.946 & 219.6 & 1.737 & 219.6 & 0.4702 & 219.6 & 0.1299 & 219.5 \\ \hline \multirow{3}{*}{Medium mode} & 0.07578 & 220.2 & 0.003182 & 220.2 & 0.0004261 & 220.2 & 0.0004261 & 220.2 \\  & 2.004 & 220.1 & 0.8767 & 220.1 & 0.362 & 220.1 & 0.074 & 220.1 \\  & 4.962 & 219.5 & 1.727 & 219.5 & 0.4772 & 219.5 & 0.1329 & 219.5 \\ \hline \multirow{3}{*}{High mode} & 0.007 & 220.2 & 0 & 220.2 & 0 & 220.2 & 0.0006484 & 220.2 \\  & 2.363 & 219.9 & 0.925 & 219.9 & 0.402 & 220 & 0.109 & 219.9 \\ \cline{1-1}  & 4.887 & 219.5 & 1.623 & 219.5 & 0.4644 & 219.5 & 0.1379 & 219.5 \\ \hline \end{tabular}
\end{table} 
Table 2: Central cluster positions of harmonics of Galanz microwave oven. Figure 6: The data acquisition of microwave oven.