Faults in steel cords in the core are not visible during routine visual inspections. They can be identified using magnetic diagnostic systems. The article presents an analysis of the impact of the sensitivity threshold of the DiagBelt+ system, the diameter of cords in the core, and the belt speed on the quality of signals representing known damage: cutting of cords, their absence, and a reduction in the cross-section of the cord. The study focused on defects to cords across the belt, as they can weaken the belt's strength and lead to a complete belt failure. The proposed results and analyses contribute to the improvement of the methodology for magnetic examination of the core's condition and the developed diagnostic system DiagBelt+. Consequently, this enhances the reliability and safety of belt conveyors in various industries, including in brown coal mines, where it has been implemented (PGE GiEK SA KWB O/Bełchatów), as well as in coal, limestone, and copper ore mines, where it is used to assess the condition of belts with steel cords.