# Analysis of Uncertainty in Conveyor Belt Condition Assessment Using Time-Based Indicators
## 2 Materials and Methods  
This study was conducted at one of Poland's largest open-pit lignite mines, equipped with an extensive belt-conveyor system for transporting both lignite and overburden. The conveyors utilize steel-cord-reinforced belts (Type St) designed for heavy mass transport. The DiagBelt+ diagnostic system enables non-invasive, dynamic scanning of belt condition during normal conveyor operation. Data were collected from over 100 conveyor belt loops comprising various belt segments. A belt segment is defined as a continuous span between joints, supplied in a single spool (at Belchatow Mine, segments may reach up to \(\sim\)300 m). For each segment, the following were recorded: Material Type (l lignite, overburden, or mix), Belt Age (in months), Resurs (% of expected operating time), Segment Length (m), Loop Length (m), number of core defects, defect density (defects per meter), defect area (m\({}^{2}\)), and defect area density (m\({}^{2}\) per meter). Only segments that began their operation on the tested conveyor and had not undergone reconditioning were included: 274 segments (39 carrying lignite, 46 carrying mixed material, 189 carrying overburden). Figure 2 shows the length distribution by Material Type. Figure 3 depicts the distribution of belt age at the time of inspection per material type. All the analyzed belts were of the same construction: steel-cord belts with a strength class of 3150 kN/m and cover thicknesses of 14 mm (top) and 7 mm (bottom). Due to their uniform technical specification, these characteristics were not included as model variables. The DiagBelt+ system, developed at Wroclaw University of Technology, uses inductive magnetic methods to magnetize steel cords and register magnetic-field disturbances caused by internal core discontinuities--cord breaks, wire fractures, corrosion, or at belt joints. The system was deployed at Belchatow Lignite Mine under an NCBR project (PO-IR.01.01.01  
Figure 1: Ishikawa diagram showing factors affecting the wear of conveyor belts. 0-1194/19-00) and is routinely used for conveyor belt scanning. Prior to its introduction, only visual inspections were conducted, which limited detection to large surface defects. DiagBelt+ enables continuous monitoring of belt core condition during operation, without stopping or dismantling the belt--a significant innovation. Magnetic diagnostics reveal the state of the steel cords hidden beneath the rubber cover. Figure 4 illustrates the installation scheme on the conveyor belt. The belt core is magnetized by permanent-magnet bars, and a multi-channel inductive sensor array detects localized field disturbances indicating defects. The sensor head contains over 90 coils spaced 25 mm apart across the belt width. High spatial resolution (25 mm transversely and 2.5 mm longitudinally per 1 m/s belt speed, with 400 Hz sampling) allows detection of small defects--from single-cord cuts and wire fractures to advanced corrosion invisible from the outside. Signals from the coils are collected and processed by a dedicated data-collection unit and DiagBelt software (DiagBelt+ Data Analysis v. 1.0), synchronized to belt displacement (via a tachometer magnet on a pulley of known diameter). This enables localization of defects along the belt loop length and across its width. Detailed system operation is described in [29; 30]. The system also automatically recognizes belt-joint signals (displaying distinct magnetic polarity), enabling identification and localization of all joints in the loop, and thus segmentation of belt sections. During a single scanning cycle, DiagBelt+ can scan the entire conveyor loop--several kilometers long and comprising multiple belt segments--without disrupting conveyor operation. For instance, at the lignite mine, a 2.25 m wide, 3-4 km long belt running at ~56 m/s can be fully scanned within minutes. The DiagBelt+ system acquires inductive magnetic signals at a sampling frequency of 400 Hz, resulting in a longitudinal resolution of approximately 2.5 mm per 1 m/s of belt speed.