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Technical data are subject to change without notice.
ISO 9001 certified. © Copyright SPM 1996-9. 71519.Z
SPM Instrument AB
• Box 4 • S-645 21 Strängnäs • Sweden
Tel +46 152 22500 • Fax +46 152 15075 • [email protected] • www.spminstrument.se
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 meas-
urements indicate a need for action.
To be able to plan ahead and work efficiently, a main-
tenance department needs regular and easily inter-
preted information on all
significant
changes in ma-
chine 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 ma-
chine 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 “accept-
able“ 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 previ-
ous 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 dete-
rioration.
Each condition band consists of two steps. An in-
crease 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 vibra-
tion level is still “acceptable“.
Reporting changes in step is the simplest way of indi-
cating the extent and urgency of a maintenance prob-
lem. If needed, the supporting figures are on record.
Moreover, the method is flexible. As experience in-
creases, 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 VIB-
11 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 mainte-
nance 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
