Modern Vibration Monitoring Technology
Automation has become an essential tool for industry, delivering
benefits that include increased productivity, consistent quality
and cost reduction. Yet automation also brings a new set of challenges,
as more and more companies become increasingly dependent on physical
rather manual assets.
In particular, machinery has to be constantly available. Downtime
costs money, which, in turn, places ever greater emphasis on
the importance of effective maintenance.
One of the key tools for plant and equipment maintenance today
is vibration monitoring. In some circumstances where vibration
is carefully monitored it is possible to extend operating life
beyond recommended maintenance intervals, while in others a rapid
increase in vibration must be taken seriously if a catastrophic
failure is to be avoided.
The accelerometers used to measure levels of vibration are typically
easy to install and use; however, an accelerometer is only as
good as the engineer who is responsible for it. A poorly installed
or maintained accelerometer will not offer the precision or longevity
of which it is capable and so it is in everyone's interest to
apply best practice to managing their performance. To achieve
this, it is worth spending a little time considering what an
accelerometer is and how to effectively install one.
 The current array of sensors or
accelerometers for vibration monitoring offered by companies
such as Hansford Sensors can operate over a wide temperature
range, measuring both high and low frequencies with low hysteresis
characteristics and excellent levels of accuracy. These devices
also offer robust and reliable service, due to stainless steel
sensor housings that can prevent the ingress of moisture, dust,
oils and other contaminants.
There are two main categories: AC accelerometers, which are used
with a data collector for monitoring the condition of higher
value assets such as wind turbines, and 4-2OmA accelerometers,
which are used with a PLC to measure lower value assets such
as fans and pumps. Both are capable of detecting imbalance, bearing
condition and misalignment but AC accelerometers can also identify
cavitation, looseness, gear defects and belt problems.
 Accelerometers contain
a piezoelectric crystal element bonded to a mass. When the sensor
is subject to an accelerative force, the mass compresses the
crystal, causing it to produce an electrical signal that is proportional
to the level of force applied. The signal is then amplified and
conditioned using inbuilt electronics that create an output signal,
which is suitable for use by higher level data acquisition or
control systems. Output data from accelerometers mounted in key
locations can either be read periodically using sophisticated
hand-held data collectors, for immediate analysis or subsequent
downloading to a PC, or routed via switch boxes to a centralised
or higher level system for continuous monitoring.
To correctly specify an accelerometer, engineers need to consider
the vibration level and frequency range that is to be measured,
as well as environmental conditions, such as temperature and
whether corrosive chemicals are present.
Further considerations follow. For example, is the atmosphere
combustible? Are there weight constraints? Consultation with
a company that has experience in a wide range of sectors can
swiftly enable the right decisions to be made.
To correctly install an accelerometer, engineers should mount
the device directly onto the machine surface on a flat, smooth,
unpainted surface that is larger than the base of the accelerometer.
The surface should be free from grease and oil, as close as possible
to the source of vibration and at right angles to the axis of
rotation. By following these guidelines, you will have already
supported your accelerometer, and thus your maintenance regime,
by enabling the device to give the most accurate measurements
of vibration levels.
Once data has been collected in the most efficient manner, machine
reliability data can be effectively analysed and interpreted
and, with an efficient vibration monitoring system in place,
engineers can maximise machine performance, energy efficiency
and output.
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