Narrow Band Vibration Monitoring of Gas Turbines

Industrial gas turbines

The use of accelerometers for vibration measurement on bearings, casings or structures is best practice on gas turbines. The measurements are often referred to as “absolute” vibration, to compare them against the “relative” measurement of displacement (which is preferred for the vibration measurement of journal bearings). In general, aeroderivative and lighter industrial gas turbines use exclusively absolute measurements, whereas heavy duty gas turbines employ relative measurements. However, the use of accelerometers on heavier machines at selected locations is quite common. When considering absolute measurements, there are three modes of signal evaluation, namely:

• Broadband or reduced band
• Dual path – two or more frequency bands
• Narrow band frequency with tracking filter

This application note discusses the narrow band implementation.