# Evaluation of the Variability of Vibration Measurement Results in Rolling Bearing Quality Control
## 5 Conclusions  
The research presented in this paper aimed to present the most common phenomena of variation in results, which are not intuitive and are not taken into account in the acceptance quality control of rolling bearings. The results demonstrate the extent to which a result obtained for the same object, measured in the same manner but on a different test station, can be ambiguous. It must be noted that the extent of result difference between different systems can also substantially depend on the bearing's condition, i.e., on the general vibration level generated by the bearing. For properly crafted, undamaged bearings operating in a predictable manner, the differences in the results obtained for different systems can be minor and can change in narrow ranges. Imperfections and damage of tested objects can affect the systems' operation and result in a change in the proportions of the results obtained for undamaged bearings. The repeatability values are mainly related to the correct operation of the clamp that applies an axial load. It must be noted that the clamp's operation affect each measurement, thereby affecting reproducibility (repeatability is related to reproducibility). On the other hand, reproducibility is related to the natural result variation. This variation results from the dynamic nature of a bearing's operation and is caused by the fact that the bearing can be \"positioned\" differently during each fitting to a certain degree, thereby making it operate \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Bearing No.**} & \multirow{2}{*}{**Bearing Type**} & \multirow{2}{*}{**Defect Location**} & \multicolumn{4}{c}{**Spread, And**} \\ \cline{3-5}  & & & **50–300 Hz** & **300–1800 Hz** & **1800–10,000 Hz** \\ \hline
1 & 6206 & none & 2.1 & 2.4 & 1.6 \\
2 & 6206 & none & 1.9 & 2.3 & 2.9 \\
3 & 6204 & none & 2.2 & 1.6 & 1.2 \\
4 & 6204 & none & 2.7 & 1.4 & 2.2 \\
5 & 6205 & inner ring & 6.6 & 3.2 & 5.1 \\
6 & 6205 & inner ring & 5.7 & 4.9 & 6.5 \\
7 & 6304 & inner ring & 3.5 & 3.2 & 3.6 \\
8 & 6304 & inner ring & 4.9 & 6.8 & 5.1 \\
9 & 6205 & outer ring & 15.1 & 1 & 1.6 \\
10 & 6205 & outer ring & 2.8 & 5.7 & 8.1 \\
11 & 6305 & outer ring & 9.6 & 2.4 & 1.4 \\
12 & 6305 & outer ring & 3.8 & 8.4 & 10.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Range of vibration measurement results obtained for the system 1 in eight evenly spaced points on the tested bearings’ outer rings. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Range, And**} \\ \hline Bearing 6206 & LB & MB & HB \\
1.8 & 0.9 & 1.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Range of a series of 20 vibration measurements, obtained for the same sensor application point on the tested bearing’s outer ring. differently after each fitting. A change in the balls' rotation axis also substantially affects a system's reproducibility result. After removal and repeated fitting, a bearing's balls can roll in completely different planes. Additional result demonstrates that omission of the fact of obtaining different (occasionally substantially different) results depending on the sensor's application point in scientific testing prevents one from obtaining a relevant result, while in quality control of manufacturing plants can result in the sale of defective bearings. The research presented here shows how ambiguous the result of a vibration measurement can be. The result depends both on the measuring system, on the place of application of the sensor, and also varies on its own (be difficult to repeat and difficult to reproduce). The drive for continuous improvement in rolling bearings necessitates changes in the measuring systems used for acceptance checks.