## 4 Evaluation and Experiments
### Experiments
#### 4.2.3 Process and Analysis of Comparative Experiments  
In the first experiment, all sensor probes were fixed in one container that is full of water from group 3. The depth of the sensor probes during this trial was fixed at approximately 0.3 m beneath the water surface, which was similar to the deployment position in real lake water. To validate the proposed approach, different decision approaches were applied on the three monitoring nodes mentioned. Node 1 works continuously with a constant sampling interval of 30 s and communicating interval of 5 min. Node 2 uses a basic method to make the communication device sleep after a certain period to approximately suit the electric quantity of the battery. It has a constant sampling interval and communicating interval similar to that of Node 1. However, the communicating device enters a dormancy state for 0.5 h after working continually for 2 h. Node 3 adopts the approach proposed in this paper. It self-configures the sampling interval and communicating interval or enters a dormancy state with the decision of the reasoning engine which considers four rules mentioned in Section 3.3. The monitored water sample is the same as that of the three nodes. The comparison of the three nodes is shown in Table 3. \begin{table}
\begin{tabular}{c c} \hline
**Grade** & **Definition** \\ \hline Water\_I & Mainly applicable to the source water or national nature preserves. \\ \hline Water\_II & Mainly applicable to the first level of centralized drinking water source protection area, \\  & rare aquatic habitat, fish spawning grounds, larvae feeding _etc._ \\ \hline Water\_III & Mainly applicable to the second level of centralized drinking water source protection area, \\  & fish and shrimp overwintering grounds, swimming channel, aquaculture areas. \\ \hline Water\_IV & Mainly applicable to general industrial water district and the recreational \\  & water area with non-direct contact with human body. \\ \hline Water\_V & Mainly applicable to agricultural water district and the general requirement of landscape waters \\ \hline \end{tabular}
\end{table} 
Table 1: Definition of five grades of water quality in GB3838-2002. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Water Quality Item** & **Group 1** & **Group 2** & **Group 3** & **Group 4** & **Group 5** \\ \hline Water temperature (\({}^{\circ}\)C) & 24.5 & 24.5 & 24.5 & 24.5 & 24.5 \\ pH & 6.9 & 6.6 & 7.1 & 7.4 & 7.6 \\ Conductivity (us/cm) & 276 & 430 & 657 & 1543 & 2000 \\ DO (mg/L) & 7.3 & 5.9 & 4.7 & 2.85 & 1.2 \\ \hline \end{tabular}
\end{table} 
Table 2: Water quality data of five groups of water sample. The same types of battery as those mentioned were used to provide energy for three nodes. Thus, consumed energy is the total energy used by the monitoring nodes to perform sensing, transmission, and reception. Every battery was fully charged. Then, the monitoring nodes began to perform data collection and communication. Each of the four parameters (water temperature, pH, DO, and conductivity) were collected and transmitted. The dump energy of three battery groups were tested every 30 min until the battery power ran out. The test result was the average of three experiments. Figure 19 shows the dump power ratio of three monitoring nodes for the same battery consumption. Electric quantity (vertical) decreased with time (horizontal). Among the three nodes, Node 1 had the shortest duration. Node 2 had a longer duration than Node 1 for the same energy consumption. Node 3 conserved the most energy. These results show that because the communication device of Node 2 entered a dormancy state at a certain moment, it sustained a slightly longer duration than Node 1. For Node 3, the ontology middleware played a role in saving energy by deciding to reconfigure the monitoring node according to the energy rule. Therefore, Node 3 had the longest duration. The ontology middleware did not affect the accuracy of the water-quality data, but it effectively reduced the energy consumption of the WSN.