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3
used, the maintenance specialist must
have in-depth knowledge of the ma-
chine design and behavior and should
have service and operating experi-
ence. In Level 1 Monitoring, the fol-
lowing vibration values are moni-
tored for changes during operation
with the aim of avoiding sudden dam-
age and catastrophic failure [2]:
noise, vibration severity, peak-to-peak
shaft vibrations, axial displacements
and other vibration values.

In some industrial applications, the
characteristic overall values and the
warning and alarm values are stan-
dardized and grounded in specific
guidelines. For wind turbines, a spe-
cific guideline is currently under de-
velopment. To measure machine vi-
bration, non-contacting displacement
sensors are becoming an increasingly
popular tool in addition to the more
common accelerometers. Thus, for
example, valuable monitoring and di-
agnosis information is contained in
the axial displacement of a diesel
engine flywheel or in the radial or
axial displacement of a generator
with a journal bearing.

If the overall values of the machine
being monitored can be filtered out in
a frequency-selective or order-selec-
tive manner, and if these values can
be monitored permanently, cavitation
and imbalance can be detected and
eliminated early on in simple ma-
chines such as fans. However, most
machines have a complex vibration
pattern. Alternatively, small discrete
excitations can be analyzed to
achieve early damage protection us-
ing frequency and order analyses.

2.2 Diagnosing vibration
and drive conditions
(Level 2 Diagnosis)

A rotating machine is exhibiting a
change in its noise pattern, a guide
roller is vibrating excessively, the iron
content in gear lubricant has in-
creased, and generator bearings have
failed prematurely.

What is the cause? What is the
condition of the neighboring ma-
chines? Level 2 measurements are
required to diagnose the drive condi-
tion of a machine (Figure 4). In the
first step, vibration specialists identi-

fy the exciters of the raised vibration
levels using the frequency spectra,
search for unusual patterns in the
frequency spectra and look for vibra-
tion behavior that is atypical for the
affected machine. For example, if the
two-fold gear mesh frequency in a

simple bevel gear is dominant, this
indicates contact pattern wobble in
the bevel gear.

An example from the field will illus-
trate the usual procedure. The sud-

den change in noise and
vibration levels in a com-
pressor were examined
during a service call in a
paper mill. Mobile vibra-
tion measurements prior
to the service call had
revealed that the guide
vane was not balanced.
From experience it is
known that sudden
changes in vibration are
often linked to blade
tears. Therefore, a video-
endoscopic examination
was performed after di-
agnosis, which indeed re-
vealed a defective blade
in the compressor stage.

A prerequisite for this
kind of diagnosis mea-
surement is that mean-
ingful frequency and or-
der spectra are measured
under representative
conditions with sufficient
accuracy. This can be a
problem in variable
speed machines and sys-

tems, where production consider-
ations may make it impossible to run
the machine within the critical speed
range in which increased vibrations
appear on the measurement day. Or,
in the case of wind turbines, wind
speeds are usually too low on mea-

surement days. For these types of
operation-related limitations, testing
equipment that permanently mea-
sures condition data (online) is the
method of choice.

Figure 3: View of a fan after catastrophic failure and typi-
cal machine arrangement with measurement locations.

Figure 4: Mobile vibration measurement and alignment check

Page 5

5
erected and coupled in such a manner
that no additional forces act between
the coupled components at higher
speeds.

But what does this mean in prac-
tice? In the case of coupled machine
components, the shafts and not the
couplings should be aligned. Also, the
coupled drive components must be
aligned when the machine is warm,
not when it is cold. Design details of
the machine should be taken into
account as well.

Below are several examples of mis-
alignment which, while they resulted
in elevated vibration levels, could
only be verified using laser alignment
technology.

3. Improving geometric devia-
tions (straightness & flatness)
Examples of geometric deviations

are deviations in straightness and
flatness. Modern laser-based testing
technology lets you measure straight-
ness and flatness in the machine or
system with a resolution of 0.02 mm.

The LEVALIGN® measurement sys-
tem can be used with electromechani-
cal drive components to determine
the straightness of the X and Y axes
and the flatness of a surface or circle
with a distance or diameter of up to
40 meters. This will now be illustrat-
ed using a pump motor in a chemical
factory as an example.

A shaft in a motor with a journal
bearing cracked. After the rotor was
changed and the machine put back
into operation, the motor produced
unusual sounds and did not run

smoothly. Vibration measurements re-
vealed an increased level of axial
vibrations and indications of field
asymmetries in the stator caused by
foundation effects. Therefore, a level
measurement was requested for the
base frame. Several of the views and
results are shown in Figure 7. It was
found that one side of the base frame
on the free motor end was 4.2 mm
too low. This was the cause of the
vibrations and it was now clear how
to correct the situation. The base
frame was adjusted using suitably
manufactured shims. After the motor
was put back into operation, it ran
quietly and with low levels of vibration.

3.2 Improving the
geometric accuracy of

crankshaft bearings and axes
Machines with multiple bearings

like piston compressors and large ma-
chines demand high internal and ex-
ternal geometric axis accuracy as
their speed increases. The inner axis
positions can be improved by aligning
the bore holes with each other or by
mounting the crankshaft bearings
properly within tolerance as specified.

Figure 8 shows a piston pump on
which the crankshaft bearing is being
measured using the laser-optical
BORALIGN® measurement system.
The present condition of the new
compressor was determined by laser-
optical methods at the manufacturing
factory, as was the mounting accura-
cy. This ensured that the additional
dynamic strain and the erection-relat-
ed vibration would remain small.

For service companies, the aim of
inspections is not only to ensure that
the design-related mounting require-
ments and tolerances of the machines
are met, but also to verify this by
means of suitable testing methods.
This is illustrated in the following two
examples of service calls. During a
general overhaul of a water screw, the
lower, poorly accessible bearing had
to be realigned. The present condi-
tions were determined using a laser
alignment system (Fig. 9 a,b), the
mounting company was given clear
instructions on how to mount the
journal bearing and the achieved
alignment accuracy was documented.

3.3 Turbine alignment
Figure 9c shows the alignment of

steam turbines. PRÜFTECHNIK’s
unique alignment tool CENTRALIGN®

together with our expert teams from

Figure 8: View of the laser-optical alignment of
a compressor using BORALIGN®

Figure 9 a,b,c: Improving the inner machine alignment in special machines

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