# An Internet of Things (IoT) Application on Volcano Monitoring
## 4 Results and Discussion
### Data Records
T1, T2, T3, T6, and T8 thermometers are powered by non-rechargeable 3.6-V batteries, and thermometers T4, T5, and T7 are powered by Li-ion rechargeable 3.7-V batteries. Except thermometer T5, whose recorded values where erroneous (Figure 16, blue line in area B) due to a hardware problem with the voltage divider that allows to measure the value of the battery, it can be seen that most of the curves displayed are fairly constant with a very slow battery discharge. Figure 13: Temperature records. Grey dashed rectangles point out temporally interruptions in communications due to adverse weather conditions. Red dashed rectangles highlight malfunctions in thermometers T2 and T8. Figure 14: Detail of the temperature record when interruptions in the network operation (grey dashed rectangle) take place due to adverse weather conditions. Figure 15: Battery records. The red rectangle highlights the T2 battery drain due to overheating. Besides the commented transmission issues between the gateway and the repeater, Figure 15 also shows problems related to batteries and the temperature operation. When designing the thermometer, it was assumed that the PVC tube would be able to act as a protection and insulator of the electronics against the corrosive gases and the high soil temperature. It was also thought that the part of the tube that was not buried would act as heat sink, since it was in contact with the air. While thermometers were tested in the laboratory, no problems related to batteries arose, since temperature values measured did not exceed 30 \({}^{\circ}\)C. However, once the network was deployed in the selected area, it was found that measures used to dissipate the heat inside the tube did not work as expected, and the temperature inside the tube probably exceeded what was recommended for the battery (Table 4). Analyzing capacity versus current curves depending on the temperature of operation provided by the manufacturer [88], it can be seen that the capacity of the battery is greatly reduced as the temperature increased, even though consumption is minimal, as in the case of thermometers. As a result, some batteries were completely drained out, as can be observed in Figure 15 for thermometer T2 (red rectangle) and consequently, the thermometers associated stopped working (red dashed rectangles in Figure 13). Regarding thermometer T8, on 8 November 2018, it was checked in situ that the battery was completely discharged. The most plausible explanation was that the battery drained out due to inefficient heat dissipation inside the T8 tube. The discharge record was not acquired as in T2, since during the first days of the network operation, the weather conditions did not allow proper communication among the network devices. The overheating problem affected not only the integrity of the batteries, but also the capacity, and therefore, the battery life. Taking the current values and the time in hours from the battery discharge curve provided by the manufacturer [88], a fitted curve has been drawn (Figure 16). Starting from the values shown in Section 3.3, the average consumption of a thermometer is 0.0939 mA. Taking this value and the discharge fitted curve shown above, the estimated battery-life value assuming an 80% maximum discharge level is 2.34 years, which is a very similar value to the one theoretically calculated (Section 3.3). However, taking the capacity versus current curves depending on the temperature of operation provided by the manufacturer [88], for the temperature ranges in which the network works, the capacity of the battery is reduced to 1400 mAh, and thus, 1.46 years would be a more accurate value for the battery life of the device. Figure 16: Fitted curve for battery life versus current consumption. Blue points highlight values obtained from the discharge curves provided by the manufacturer. The red point highlight the value corresponding to this work. Analyzing the overheating batteries issue, it was necessary to ensure that they did not exceed the operating temperature range as far as possible.