Technical data are subject to change without notice.
© Copyright SPM 2002-04. 71650.B
SPM Instrument AB • Box 504 • S-645 25 Strängnäs • Sweden
Tel +46 152 225 00 • Fax +46 152 15075 • info@spminstrument.se • www.spminstrument.se
Create acceptable measuring conditions
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 interference – 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.
No interference
Low level interference
High level interference
Alignment
Scraping,
alignment
Cavitation
Gear
tooth
damage
26 General remarks on SPM measurement
To Next Page
Loading...
