Feb 19, 2026
Rolling bearing characteristic frequencies are a cornerstone of vibration-based condition monitoring in rotating machinery. Defects on bearing components generate periodic impacts that excite vibrations at characteristic frequencies related to bearing kinematics and shaft speed. Since these frequencies are deterministic, they serve as reliable indicators for early fault detection.
Five fundamental rolling bearing characteristic frequencies are commonly considered. The Fundamental Train Frequency (FTF) corresponds to the rotational speed of the cage. The Ball Spin Frequency (BSF) represents the spin of the rolling elements around their own axes and is typically associated with rolling element defects. The Ball Pass Frequency of the Inner race (BPFI) and the Ball Pass Frequency of the Outer race (BPFO) describe how often rolling elements pass a fixed point on the inner or outer race. The Ball Pass Frequency (BPF) can be interpreted as the frequency at which a rolling element enters and exits the load zone of both the inner and outer ring, reflecting load-related interactions within the bearing.
The accurate calculation of these frequencies depends strongly on bearing geometry, including the number and diameter of rolling elements, pitch diameter, and contact angle. In practical applications, pure rolling conditions rarely exist. Sliding effects, as well as excitation from imbalance, misalignment, or gear meshing, can shift or modulate bearing characteristic frequencies, often producing diagnostically relevant sidebands.
In KISSsoft®, the bearing characteristic frequencies are computed within the shaft calculation module. The KISSsoft System Module further enables advanced frequency analysis of shafts, gears, and bearings, including the evaluation of sidebands, supporting more reliable vibration diagnostics and system-level assessments.
Trainings
The coming weeks offer a wide range of training courses covering various topics and skill levels, available in both English and German.
Build and strengthen your skills in the KISSsoft System Module, Cylindrical Gears, Shafts and Bearings, with hands-on training sessions guided by our experts.
In addition, a 3-day Gearbox Calculation training in German will take place in Austria this March, providing an in-depth learning experience for engineers seeking advanced knowledge.
Service Pack
KISSsoft Release 2025 SP3 is now available, bringing new improvements that enhance efficiency and support your engineering design workflow.