# An OCARI-Based Wireless Sensor Network for Heat Measurements during Outdoor Fire Experiments
## 4 Results  
In our experiments, we compared signals gained by a wired datalogger and OCARI-based WSN in the same experimental conditions. Figures 8-11 show comparisons between wired (continuous lines) and wireless signals (symbol lines). In each figure, there is a temperature plot (top) and a heat flux plot to compare between LHFL and HHFL (bottom) in configurations 1 and 2, for 2, 4, and 8 kg/m\({}^{2}\). As shown in configuration 1, there are fires that display behaviour that is consistent with the usual observations as follows: The level of heat radiation is measured as 3.3 m in front of the edge of the plot and increases with the fuel load under low wind conditions (Table 1). In configuration 1, the heat flux density reaches 8, 10, and 20 kW/m\  
Figure 9: Comparison between the temperature and radiant heat flux acquired on the wired and OCARI wireless system during the 4 kg/m\({}^{2}\) fire (configuration 1). As shown in configuration 2, the wind flow can affect the expected behaviour of the fire observed at a field scale under low wind conditions. For example, the 8 kg/m\({}^{2}\) fuel load (Experiment C2 3 in Table 1) does not coincide with the stronger heat radiation because the wind is not conveniently oriented to sustain the development of a vertical flame front as the source of the heat radiation, which faces the HFMs, as shown in configuration 1. In the present case (i.e., 8 kg/m\({}^{2}\), configuration 2, Figure 11, the flame front is tilted in a transverse direction, and this reduces the view factor between the flame front and HFMs (see photograph in Figure 7). Thus, the horizontal component of heat radiation is lower than that in the case of 8 kg/m\({}^{2}\) in the first configuration (approximately 20 kW/m\({}^{2}\) in Figure 10). The influence of the unexpected local instantaneous aerology is valuable to test the wireless heat measurement system in outdoor conditions. Figure 10: Comparison between the temperature and radiant heat flux acquired on the wired and OCARI wireless system during the 8 kg/m\({}^{2}\) fir (configuration 1). We now compare the time evolutions of signals obtained with both wired and wireless solutions facing the fires. The first main difference between wired and wireless solutions involves the temporal resolution of the rapid increase and decrease in temperature and flux plots. For example, we consider the temperature profiles in configuration 1 at the top of Figure 8 for the 2 kg/m\({}^{2}\) fuel load, Figure 9 for the 4 kg/m\({}^{2}\), and Figure 10 for 8 kg/m\({}^{2}\). All plots exhibit a different time sampling between both wired and wireless data acquisitions with similar temperature signals. Specifically, the wired datalogger records digitised information from each thermocouple (TC) as sampled at 1 Hz. The wireless system works differently wherein it records data packaged in each message reaching the coordinator of the personal area network (CPAN) successfully. In each message, timestamping of the AD conversion exists at every note at the microcontroller level (Figure 5). Therefore, in each figure from Figures 8-11, we can see that the time evolution of the wireless system is not affected by the amount of time. Figure 11: Comparison between the wired _continuous_/wireless _symbols_ temperature and radiant heat flux during the 8 kg/m\({}^{2}\) fire (configuration 2). we observe data and the timestamp that was received by the CPAN from the WSN. This implies that the sampling of analogue signals on the WSN is observed a posteriori as the reconstruction of the couple timestamp-data in each validated message. Given the possible constant message losses in this type of a harsh environment (e.g., large fires), the WSN data rebuilt by the CPAN can correspond to nonregularly sampled data. Under the conditions, the OCARI based WSN sends-receives messages at a maximal rate of approximately 0.2 Hz. Therefore, it is not possible to resolve wireless temperature and heat flux signals with the same temporal accuracy as the wired ones.