Turbine Diagnostics
Turbines often exhibit a strong component at the so-called blade rate, which is the number of turbine blades times the RPM of the rotor. The magnitude of this component is dependent on the internal geometry of the unit. If this changes, as for instance by a cracked, warped, or pitted blade, the blade pass component in the vibration signature will change, usually for the worse.
If the turbine blades wear uniformly, the blade pass frequency is quite uniform, but if a portion of the rotor is damaged, such as a broken blade, the blade pass component will be modulated by the RPM of the rotor or by the number of nozzles in the turbine times the RPM, causing sidebands in the spectrum.
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