Technical data are subject to change without notice.
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Evaluation, why and when
Evaluation simply means that you make sure that the information you pass on to the maintenance
personnel is as correct as possible and as detailed as necessary. Always remember that
• some machines can contain many types of shock pulse sources other than the bearing, and
• there can be a number of different causes for bad bearing condition other than damage.
Evaluation requires only normal care and common sense. Use the peak indicator, the probe
transducer, and the earphone, and also use your senses: look, touch, listen. By being thorough you
can avoid raising false alarms or missing damaged bearings.
Initial readings and changes
There are only two situations where an evaluation is necessary. The first is when you start with
bearing monitoring:
• Always evaluate the first readings on new measuring points and newly installed bearings.
The purpose is to establish a reliable base for routine measurements. You want to be quite sure
that you are measuring shock pulses from the bearing and that the reading itself is correct. If you
find that bearing condition is good, you do not have to evaluate the following readings on that
measuring point as long as there is no significant change.
The other situation is when you notice a change in the readings (or get high readings from the
start):
• Investigate any significant increase or decrease of the shock pulse level.
Again, you want to be quite sure that you are measuring shock pulses from the bearing and that
the reading itself is correct.
If you find that bearing condition is not good, you have to distinguish between bad installation,
poor lubrication, overload and damage, in order to decide what kind of maintenance work is
needed. If you are getting an interference signal, it is probably caused by machine faults which
have to be reported and repaired.
Machine Bearing Bearing Bearing
alignment lubrication installation damage
High maximum value
Interference
Cross talk from
other bearings
Interference from
mechanical shocks
1 Reading Correct ? Check!
Measuring point? Installation ?
dBi ? dBm?
Look, feel, check data. Measure
with peak indicator.
2 Shock Pulse Source? Search!
Bearing ? Interference? Signal
pattern?
Look, listen. Use probe
transducer, earphone.
3 Bearing Fault? Analyse!
Lubrication? Alignment? Installation?
Bearing damage?
Identify shock pulse pattern.
Check trend. Test lubrication.
Operating condition not good
Evaluation of SPM measurements 31
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