CONDITION MONITORING
Good vibes
When vibration exceeds a certain threshold, it may be an indication that the machine is deteriorating.
Therefore, vibration is a useful tool for investigating the status of rotating machinery, such as
electric motors, pumps and generators. Vibration analysis can locate a potential problem and provide
the opportunity to rectify it before it causes further damage to the equipment
By Chris Robson, sales director, Houghton International
bene ts for equipment owners, helping
them spot issues early on and plan repairs,
while minimising costs and reducing
downtime. Acceptable operational
vibration is prede ned either through
long-term utilisation, maintenance history
or through standards established by the
OEM. If this limit is breached, there is an
indication of a potential defect.
For instance, in the case of a roller
bearing outer race, if a crack develops,
it would constantly collide with the
bearing rollers. By analysing the vibration
frequency using the spectrum method,
engineers can determine the periodicity of
the collisions to detect a bearing fault.
Furthermore, vibration analysis
supports remote condition monitoring,
as it can be performed while the system is
running. If a fault is observed on one of the
components, repairs can be scheduled in
advance during non-productive times to
avoid costly downtime. As part of a robust
predictive maintenance strategy, vibration
analysis can also increase operational
safety.
The amount of vibration in
any machine depends on
a number of factors: the
exciting force, the closeness
of frequency of these
exciting forces to structural resonances
or their multiples (harmonics), and
the restraints the machine structure
imposes to vibration. Vibration analysis
is a non-intrusive, fast-response,
preventative maintenance solution that
measures the vibration characteristics in
rotating equipment based on three main
parameters: velocity, displacement and
acceleration.
It can detect changes in machinery
caused by imbalance, misalignment
or mechanical looseness. As part of a
predictive maintenance strategy, vibration
analysis can prove crucial to predicting
breakage, planning appropriate repair
and substituting damaged parts before
disaster strikes.
An accelerometer is used to collect
vibration readings, which are analysed by
software systems to detect anomalies
with the machine. When mounted, an
accelerometer proportionally converts
mechanical energy to electrical energy.
Its sensors are connected to the vibrating
structure and read the incoming electrical
voltage generated by the piezoelectric
crystal. The analysis can be conducted
on either the time waveform (amplitude
versus time) or on the frequency
spectrum (amplitude versus frequency) by
applying a Fourier transform on the time
waveforms or on both.
Time waveform analysis is e cient
for understanding when and how often
severe abnormal vibration happens. It
works by measuring the number of times
a complete motion cycle occurs during
a period of one second, but it does not
take into account the time duration and
the energy in the event. Thus, it is limited
to generating insights into the overall
condition of a machine.
However, a complex machine has
many components, each generating
its own vibration. Critical components
like bearings, impellers and shafts in
large rotating equipment require a
more in-depth evaluation. In this case, a
spectrum analysis is better to get a clearer
picture of the vibration frequency.
The data collected using either
of these methods is then recorded
using a vibration transducer at various
points around an electric motor, pump
or generator. A quali ed engineer will
then analyse the ndings, ag issues
and recommend actions to prevent
breakdown.
Vibration analysis yields massive
Winter 2021 www.operationsengineer.org.uk 65
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