# Monitoring Perishable Commodities Using Cellular IoT:
## 3 Results and Discussion
### Field Test Results  
The results of the field test, recorded over a two-week period in a refrigerated truck with perishable products, are displayed in Figures 15 and 16. This test subjected the datalogger to real dynamic conditions, capturing temperature, relative humidity, CO\({}_{2}\) concentration, luminosity and vibrations (average, maximum and count), as well as battery level and geolocation data. The device operated reliably, logging and transmitting data continuously. When wireless connectivity was unavailable, the system successfully stored measurements locally in its flash memory and transmitted them once the connection was restored, demonstrating robustness in data retention. Figure 15: Field test results: (**a**) temperature; (**b**) relative humidity; (**c**) CO\({}_{2}\) concentration; (**d**) battery voltage; (**e**) luminosity; (**f**) average vibrations; (**g**) number of vibrations; (**h**) maximum vibrations. The data reflect distinct stages along the truck's route, providing insights into the environmental conditions and events that shaped each parameter trend. Initially, until day 51, the truck was stationary with doors open, exposing the datalogger to ambient conditions. This is evident in the temperature data, which show daily fluctuations corresponding to external day and night cycles, with daytime temperatures rising and nighttime temperatures falling. Humidity, in turn, varies inversely, with higher humidity levels when temperature drops, consistent with typical temperature-humidity relationships. Luminosity data further confirm the day-night cycle, with light levels peaking during daylight and dropping to zero at night due to ambient sunlight. Vibrations were minimal during this stationary period, as the truck was at rest. On day 51, the truck's refrigerated system was activated, and transportation began at a controlled temperature of 4 \({}^{\circ}\)C. The temperature quickly stabilized at this setpoint, while relative humidity reached around 80%, reflecting stable refrigeration conditions with minimal air exchange. CO\({}_{2}\) concentration gradually increased, likely due to limited ventilation and the accumulation of CO\({}_{2}\) from both product respiration and internal emissions within the closed truck. With the doors now closed, luminosity dropped to zero, indicating darkness within the cargo area. Vibrations increased with the truck's motion, as shown by oscillations in both average and maximum vibration levels, caused by road conditions and normal travel impact. During a brief unloading stop between days 53 and 54, a slight increase in temperature and humidity occurred when the truck doors opened, allowing external air to enter. These parameters returned to stable values of 4 \({}^{\circ}\)C and 80% once the doors were closed and refrigeration resumed. Day 55 marked the beginning of a frozen product delivery phase, during which the temperature was lowered to \(-19\)\({}^{\circ}\)C. The data show a rapid stabilization at this temperature, along with a reduction in relative humidity to around 40%, reflecting limited moisture retention at sub-zero temperatures. CO\({}_{2}\) concentration decreased during this period, likely due to the reduced metabolic activity of the products at the colder temperature, thereby lowering CO\({}_{2}\) generation. The closed-door condition continued, as indicated by zero luminosity, while vibrations maintained regular oscillations in response to the truck's travel. Following the completion of deliveries on day 56, the truck's refrigeration unit was turned off, and conditions returned to ambient temperature while stationary. The temperature and humidity gradually rose to approximate ambient levels, reaching around 20 \({}^{\circ}\)C and 90%, respectively. At the same time, CO\({}_{2}\) levels rose again, potentially due to increased  
Figure 16: Route followed by the refrigerated truck during the field test. air exchange or residual product emissions.