## 2 Materials and Methods
### Experimental Setup  
The research standing on which the measurements were carried out was a model of a belt conveyor, shown in Figure 5. Its supporting structure consists of four bearing units with self-aligning ball bearings, and two drums are mounted in the inner races: a drive drum and a return drum, on which strain gauges T1, T2, and T3 are located. Inside the return drum of the conveyor, there are elements of the measuring system, and on its surface, at a distance of lo = 100 mm from each other, as shown in Figure 6, three strain gauges are placed, which are the most important element of the measuring system. The return drum is mounted in two bearing units with self-aligning bearings, twisted in the same way as in the case of the drive drum. Pinstripe thin-film strain gauge sensors DFRobot RP-L-170 with a thickness of t\({}_{\text{t1}}\) = 0.35 mm, a width of \(w_{\text{t1}}\) = 15 mm, and a length of the measuring part \(l_{\text{t1}}\) = 170 mm were used. The operating principle of these sensors is based on resistance change. When pressure is applied to the active area of the sensor, a connection is made in the conductive circuit, leading to a change in its resistance. Crucially, the output signal, expressed in ADU (analog-to-digital units), exhibits an inverse relationship with the applied pressure: as pressure increases, the ADU value decreases. This inverse characteristic is a key aspect for accurate data interpretation and conversion to physical force units. Three strain gauges,  
Figure 5: General view of the research site [31]. designated T1, T2, and T3, are precisely attached to the outer surface of the tail drum. They are strategically positioned at an equal distance of lo=100 mm from each other. The measuring system includes an electronic circuit that converts analog data from one of the three strain gauge sensors, marked T1, T2, and T3, into a digital signal. The digital signal is sent via a Bluetooth module to the _Terminal_ program for communication and data recording. The electronic system consists of a printed circuit board powered by 4.5 V, which contains a microcontroller with a built-in analog-to-digital converter. The conveyor belt, the condition of which is to be monitored in real time on the test stand, is the most critical element of the conveyor. It rotates on two drums with a diameter of 60 mm, described above. The experimental studies utilized two-ply, single-sided, welded conveyor belts. These belts featured upper covers and an adhesive layer made of polyvinyl chloride (PVC), while the internal fabric layers, forming the core, were made of polyester. This specific material combination is highly relevant due to PVC's widespread industrial use, offering properties such as chemical resistance and mechanical strength, complemented by polyester's textile properties that provide tensile strength and structural integrity. The physical dimensions of the conveyor belt are as follows:  
* Thickness 2 mm,
* Total length of the belt loop 1875 mm,
* Nominal width of the conveyor belt 350 mm,
* Multi-layer structure: top cover, ply (textile layer), inter-ply layer (adhesive/elastomeric), and bottom cover. The mechanical properties and operating parameters are as follows:  
* Tensile force for 1% pre-tension 8 N/mm,
* Drum diameter 60 mm,
* Operating temperature \(-\)10 to 88 \({}^{\circ}\)C.  
The stand uses a controller that allows smooth adjustment of the motor's rotational speed, thanks to which three speed values were checked for research purposes. Notches and complete longitudinal and transverse cuts were made in the belt as stress concentrators, the presence of which causes crack propagation due to increased stress and belt destruction. In the research model, seven different damages were made on the conveyor belt (Figure 7). The description of the damages is included in Table 1.  
Figure 6: Strain gauges on the drum [31].