10
The dBm/dBc technique
The dBm/dBc technique has been successfully applied for more than 35 years and continues to be widely
used. It is well suited for industrial condition monitoring, because it works with few, easy to understand
in- and output data.
Even on a logarithmic scale, there is normally a large, distinct difference between the maximum values
from good and bad bearings. Thus, minor inaccuracies in the input data (rpm and shaft diameter) have
little effect on the evaluated measuring result.
Lubrication condition is indicated by the delta value, i.e. the difference between dBm and dBc. High read-
ings and a small delta value indicate poor lubrication or dry running. This is sufficient for maintenance
purposes.
dBm and dBc are measured in a fixed time window and automatically displayed.
The headphone is used to listen to the shock pulse pattern in case of suspect or high readings. This,
and the possibility to search for shock pulse sources with the probe transducer, are means to verify the
measuring result and its cause.
Life time