Shrouded or bandaged blades are increasingly being used in turbomachines of large capacity, mainly in steam turbines. To avoid accidents with extensive economic losses, there appears to be an urgent need to equip at least every stage of a low-pressure turbine (with respect to the dimensions of the installed blades) with a modern measuring system that would provide information of the loading of the blades in turbine operation, their damage and residual lifetime. This paper summarises the current approaches and methods, and highlights directions that are currently being addressed in the field of research and development. As a new research direction, the paper describes a method for monitoring the state of the moving blades from the standard signals of mounted relative rotor vibration sensors. The paper presents a unique way of using the relative rotor vibration sensors for measuring shaft vibration in journal bearings, compared to the standard method of non-contact vibration monitoring, often called blade tip-timing. A comparison of the blade oscillations using the two approaches described above in TG operation has resulted in the design of an algorithm for online monitoring of blade frequencies and blade vibration amplitude estimates.
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