Chapter 7 Vibration monitoring 7.1 Introduction The use of vibration data from rotating machinery to determine machine health has a long history. Traditionally the shop foreman would press the end of a screwdriver against a bearing housing and the handle against his ear, and in this way conduct the pure vibration signal from the bearing to be analysed in his brain. This proved so reliable over many decades that it was attempted to develop instruments which performed the same function but whose performance was reproducible and could function independently of the individual operator's skill and experience (Angelo, 1987). Initially vibration meters, reading an overall rms level of velocity, were introduced. Later on integration of accelerometer signals was introduced. This enabled rms estimates of acceleration, velocity and displacement to take place. The use of peak value and crest factor were also introduced. These estimates proved valuable but experienced operators could still identify incipient faults long before they were detected by these basic vibration meters(Angelo, 1987). The development of the FFT algorithm and affordable, portable, robust battery- powered FFT analysers, allowed the use of much more of the information embedded in the vibration signal and obtaining far more advanced and useful analyses. Today condition-based vibration monitoring has established itself as a reliable and cost effective technique for monitoring and diagnosing machinery faults before leading to irreversible damage, deterioration or unsafe catastrophic breakdowns. It renders signifi- cant benefits, including decreased maintenance costs, increased availability of machinery, reduced spare part stock holdings and improved safety. Condition monitoring involves the continuous or periodic assessment of the condition of a plant or a machine component while it is running, or of a structural component while in service. The maintenance interval is determined by the condition of a machine. This is quite different to a scheduled maintenance programme where a machine is serviced at a specific period in time irrespective of its condition, and a breakdown maintenance programme where a machine is run until it fails. Noise and vibration analysis is one of several condition monitoring techniques (albeit certainly the most widely applied). Other techniques include temperature monitoring, current and voltage monitoring, metallurgical failure analysis, and wear debris analysis. 1