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The clicking of valves, high pressure steam flow, mechanical rubbing, damaged or badly adjusted gears,
and load shocks from machine operation can cause a general high shock level on the machine frame. This
interference can mask the bearing signal in cases where he shock level measured outside of the bearing
housings is as high or higher than the shock level on the bearing housings.
Remove sources of interference
In most cases, interference is the result of bad machine condition. For example – cavitation in a pump is
due to flow conditions for which the pump was not designed. Cavitation does more than interfere with
bearing monitoring – it slowly erodes the material of the pump.
Monitoring the bearings is pointless if the machine breaks down or requires frequent repairs because of
other poorly maintained parts or badly adjusted operating parameters. Therefore, do not accept interfer-
ence – try to remove the cause.
Coping with interference
If the source of interference cannot be removed, there are several possibilities:
•
If it is intermittent, measure while there is no interference.
If interference is persistent, measure its shock pulse level with the same dBi setting as the bearing and
compare it with the condition zones:
•
If interference masks the green zone, you can get true bearing condition readings in the yellow and
red zone.
•
If interference masks the yellow zone, you can get true bearing condition readings in the red zone,
i.e. find a damaged bearing.
If the interference level is persistently higher than the shock level that would be caused by bad bearing
condition (35 to 40 dB above the dBi), do not try to monitor the bearing.
Alignment
Scraping,
alignment
Cavitation
Gear tooth
damage
No interference
Low level interference
High level interference
Creating acceptable measuring conditions