Vibration Analysis

The most commonly used Condition Monitoring tool for rotating machines is vibration analysis. Vibration measurements can be taken on machine bearing casings with accelerometers (seismic or piezo-electric transducers) to measure the casing vibrations, and on the vast majority of critical machines, with eddy-current transducers that directly observe the rotating shafts to measure the radial (and axial) displacement of the shaft. The level of vibration can be compared with historical baseline values such as former start ups and shutdowns, and in some cases established standards such as load changes, to assess the severity.

Interpreting the vibration signal obtained is an elaborate procedure that requires specialized training and experience. One commonly employed technique is to examine the individual frequency components present in the signal. These frequencies correspond to certain mechanical components (for example, the various pieces that make up a rolling-element bearing) or certain malfunctions (such as shaft unbalance or misalignment). By examining these frequencies and their harmonics, the location and type of fault, and sometimes the root cause can be identified. Special analysis techniques and instrumentation can detect wear and fatigue weeks months or even years before failure, giving ample warning to schedule replacement before a failure which could cause a much longer down-time.

Handheld data collectors and analysers are commonly used for the measurement of vibration data from critical, non-critical and balance of plant machines. Critical equipment should be permanently monitored with on-line monitoring instrumentation and software. The use of permanent on-line vibration instrumentation for non-critical and Balance of Plant equipment cannot normally be economically justified. Permanent on-line monitoring / protection systems can be applied to heavy process industries such as pulp, paper, mining, petrochemical and power generation, shipping, transport, and manufacturing to list a few.