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Technical data are subject to change without notice.
ISO 9001 certified. © Copyright SPM 2003-10. 71679.Z
SPM Instrument AB • Box 4 • SE-645 21 Strängnäs • Sweden
Tel +46 152 22500 • Fax +46 152 15075 • info@spminstrument.se • www.spminstrument.com
Maintenance Based on Vibration Records
The purpose of regular vibration measurements is to
collect data for “condition based maintenance“, i.e.
maintenance carried out whenever condition measurements indicate a need for action.
To be able to plan ahead and work efficiently, a maintenance department needs regular and easily interpreted information on all significant changes in machine condition.
The flow chart opposite provides general rules for the
interpretation of vibration data. The diagram above
shows an example of how maintenance information
can be reduced to a few simple facts, which are passed
easily through one department to another.
Establish Norm Values
Usually, when vibration measurements start, the machine is in good condition. If its vibration class is
correctly chosen, the initial readings taken after a
running-in period should be in the “good“ or “acceptable“ range. Record these values and use them as a
standard of reference for this particular machine.
Provided the vibration level at all measuring points
remains stable, the subsequent readings are a matter
of routine. Small fluctuations of the values on the
follow-up forms are to be expected. They will hardly
show up on the graphs and the actual figures are
unimportant from a maintenance point of view.
Report Significant Changes
A one step change in the vibration level is generally
regarded as significant and should be reported. One
step is the space between two lines on the follow-up
form. For all machine classes at any level, it repre-
sents a 1.6 times increase (decrease) from the previous reading or, if the change is gradual, from the
original norm value.
For maintenance, it is a first warning that machine
condition is getting worse. At this stage, tightening a
few bolts or adjusting a belt may be sufficient to get
rid of the excess vibration and prevent further deterioration.
Each condition band consists of two steps. An increase from a starting point in the “good“ range to a
corresponding point in the next range means that
vibration has gone up 2.5 times. A large change like
that should be investigated, even though the vibration level is still “acceptable“.
Reporting changes in step is the simplest way of indicating the extent and urgency of a maintenance problem. If needed, the supporting figures are on record.
Moreover, the method is flexible. As experience increases, individual alarm levels and in-house limits can
be easily marked on the recording forms.
Basic Fault Analysis
It should be clearly understood that Vibrameter VIB11 is not intended to supply data for detailed fault
analysis. However, readings from several measuring
points in three directions can usually give a good
indication of the nature and location of the maintenance problem. Again, the flow chart may serve as a
general guide.
Notice where on the machine and in what direction
the measured value changes most. A simple report
(“motor bearing, up two steps, axial + radial“) gives a
repair crew a starting point and can save them a lot of
trouble.
Vibration
Measurement
(Shutdown)
Effect repairs
Plan major
overhaul
Inspection
minor repairs
Routine
maintenance
(lubrication, etc.)
Report dangerous increase
Report large increase
Report change
+ 4 steps
+ 3 steps
+ 2 steps
+ 1 step
Normal
Vibration severity Breakdown
Maintenance
Activities