# IoT-Ready Temperature Probe for Smart Monitoring of Forest Roads
## 3 Simulation Model and Experimental Measurement Proposal  
For numerical simulation of the heat transfer from the environment and experimental verification of obtained results, two experimental probes were proposed. Both probes are 250 mm long and the sensors are placed on the printed circuit boards with a 50 mm distance. The experimental probes in Figure 7 differ in the applied housing material, dimensions and the number of sensors used for proposed experiments. The decision regarding the housing material was made based on its availability on the market considering mainly its environmental resistance. Considering this, PPR and HDPE plastic materials were selected. These plastic materials offer high abrasion and corrosion resistance to soil chemicals. Both materials are also suitable in terms of operating temperature, as the experimental setup is supposed to be installed in the forest, not in a laboratory environment. Another reason is the appropriate thickness of the available plastic tubes. This property affects the heat transfer from the environment to probes attached inside the housing. In case of probe 1 (PPR probe in Figure 7a), the probe housing is a polypropylene plastic tube with a diameter of 20 mm and a wall thickness of 3.2 mm. Sensors marked 100, 110, 120 are placed in the body of the probe with an offset of 4.5 mm from the printed circuit board, with a location corresponding to the thermometers 00, 10, 20. Sensors marked 01, 02, 03 are placed on the body of the probe with the location corresponding to the thermometers 00, 10, 20. The sensor marked 04 is, as in the case of probe 1, an auxiliary thermometer for measuring the ambient temperature. The base construction of the probe 2 (HDPE probe in Figure 7b) uses thermoplastic polymer (HDPE material) as a tube housing material with a diameter of 10 mm and a wall thickness of 1 mm. Sensors DS18B20 marked 00, 05, 10, 15, 20, 25 are in the body of the probe with a polyurethane sealant. Sensors marked 01, 02, 03 are placed on the body surface of the probe with the location corresponding to the thermometers 00, 10, 20. The sensor marked 04 is an auxiliary sensor for measuring the ambient temperature. Figure 6: System architecture block diagram. There are sensors inside the tube, as we have already mentioned. These probes are encapsulated using two components consisting of a resin and curing agent. PUR sealant is used to isolate electric components from the surrounding environment to prevent damage caused by water, air humidity. Equally important, dissipation factor using PUR sealant is acceptable. The proposed experiments covered two basic types of measurements:  
1. Measurement in a water bath to verify the measurement procedure during a step temperature change. 1. The measurement starts at ambient temperature. 2. The probe is immersed in a water bath at a temperature approximately 55 \({}^{\circ}\)C (domestic hot water). 3. The measurement is completed after approaching the temperatures measured by sensors 00, 05, 10, 15, 20, 25 and the auxiliary thermometer 04. The measurement is repeated at different values of the water bath temperature (30 \({}^{\circ}\)C and 10 \({}^{\circ}\)C). The time resolution of the measurement is assumed to be \(\sim\)1 s.
2. Measurement in a climate chamber to verify the measurement procedure in case of gradual temperature change. 1. The probe is placed into the climate chamber and the measurement starts. 2. The temperature increases by 10 \({}^{\circ}\)C comparing the initial temperature is adjusted in the climate chamber, followed by a dwell time of approximately 6-8 min at maximum temperature. Then the climate chamber is switched off [34]. 3. The measurement is completed after approaching the temperatures measured by sensors 00, 05, 10, 15, 20, 25 and auxiliary thermometer 04. The measurement is repeated at different maximum temperatures of the climate chamber (plus 15 \({}^{\circ}\)C and 25 \({}^{\circ}\)C).