An introduction to vibration monitoring

Learn all about modern vibration monitoring technology and how to install and use accelerometers to maximise machine time and enhance efficiency

 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.  In the current economic climate, with pressures on operating costs looking set to continue for the coming year, an efficient maintenance strategy is critical.

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 specify the best accelerometers and apply the best practice in managing their performance.  In order 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 market leaders 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, thanks 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 4-20mA 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 the temperature and whether there are any corrosive chemicals present.  A series of further considerations follow on from there - for example, is the atmosphere combustible? Are there weight constraints? – however, consultation with a market leader 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 installer should ensure that the surface is 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 appropriate and efficient manner, machine reliability data can be effectively analysed and interpreted and, with an efficient vibration monitoring system now in place, engineers can truly maximise machine performance, energy efficiency and output.


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Date: 21/02/2012