# An OCARI-Based Wireless Sensor Network for Heat Measurements during Outdoor Fire Experiments
## 4 Results
Specifically, the explanations provided to describe the differences in temperature signals remain valid for those observed in the heat flux measurements. The comparison of heat flux measurements (Figure 8-11 bottom) also explores a few other aspects while comparing the wired datalogger and WSN. We consider the impacts of HFM sensitivities to low-level heat flux (LLHF) and high-level heat flux (HLHF) on the signals gained with wired or wireless network technologies. To the best of the authors' knowledge, the aforementioned point was not explored in existing studies, including those with the Zigbee prototype. Specifically, we consider the impact of the heat radiation on vertical targets that can be observed on the HFM plots in Figure 8 for 2 kg/m\({}^{2}\), Figure 9 for 4 kg/m\({}^{2}\), and Figure 10 for 8 kg/m\({}^{2}\) in  
Figure 12: Comparison between the wired _continuous_/ wireless _symbols_ temperature and radiant heat flux during the 2 kg/m\({}^{2}\) fire (configuration 2). configuration C1. A couple of HFMs with the same sensitivities are represented with the same colour between wired (continuous lines) and wireless (symbol lines) systems. In configuration 1, with respect to the 2 kg/m\({}^{2}\) cases (Figure 8), low-level HFMs on the WSN (node 2 (red)/central top and node 3 (blue)/lateral) collapse in a single master curve with LLHF meters plugged on the wired datalogger. Departures from wired to wireless signals approximately correspond to 0.4 kW/m\({}^{2}\), i.e., lower than each confidence interval and scale the maximal measurement error of the radiant heat flux due to the heat flux Medtherm transducers. This difference from wired to wireless HFMs increases to 3 kW/m\({}^{2}\) in the 4 kg/m\({}^{2}\) case / configuration 1 (Figure 9) and reaches more than 2.5 kW/m\({}^{2}\) in the 8 kg/m\({}^{2}\) case (Figure 10). Thus, discrepancies are stronger between wired  
Figure 13: Comparison between the wired _continuous_/wireless _symbols_ temperature and radiant heat flux during the 4 kg/m\({}^{2}\) fire (configuration 2). and wireless HFMs that are calibrated for a high level of radiant heat fluxes (green (node 1--lateral) and black plots (node 1--central bottom). This begins from 0.43 kW/m\({}^{2}\) at 2 kg/m\({}^{2}\) and extends to more than 10 kW/m\({}^{2}\) in the 8 kg/m\({}^{2}\). This behaviour is confirmed in configuration C2, where the horizontal penetration of the heat radiation is investigated. Three fuel loads are examined in Figure 12 for 2 kg/m\({}^{2}\), Figure 13 for 4 kg/m\({}^{2}\), and Figure 11 for 8 kg/m\({}^{2}\) in C2. In this case, the profiles of LHFLs are black (node 1 in C2--lateral) and red coloured (node 2 in C2--front central), whereas HHFLs are blue (node 3--lateral) and green (node 4--back central). Thus, the difference between wired and wireless heat flux data is stronger than the calibration errors of the fluxmeters. Therefore, this is caused by the bit-resolution effect of each system: The wired one corresponds to a 16-bit architecture, while the wireless one only offers a 12-bits ADC on the data acquisition board. The second display of the bit-resolution effect indicates that an upgrade of the wireless systems towards the accuracy of the wired one requires a higher bit resolution of the ADC component on each wireless node. Specifically, the upgrade must be on purpose, keeping in mind the requirement to maintain a reasonably low cost of the WSN solution to remain consistent with the advantages of the microcontroller-based wireless technology. Finally, the proposed OCARI-WSN system fully solves the time-shift effect on temperature and heat flux signals as observed with the previous Zigbee-based measurement solution. The temporal plot of the WSN follows the relevant wired reference signal. The temperature and heat fluxes acquired on the WSN suffer from a difference in amplitude when compared to that acquired via the wired one. This is due to the measurement error relative to each sensor used and also due to the difference in bit resolution between both systems.