Transient test facilities offer the potential for the simultaneous study of turbine aerodynamic performance, unsteady flow phenomena and the heat transfer characteristics of a turbine stage. This paper describes the accurate measurement of the shaft power generated by the turbine in the Oxford Rotor Facility (ORF), one of the key requirements for aerodynamic performance testing. A high resolution encoder system has been developed for the accurate measurement of the turbine speed and acceleration. The desired accuracy and frequency response specifications of the system are outlined. The method that has been developed to characterise the error signature of the encoder disc and the signal processing used to remove it are also outlined. The measurement of the losses due to disc windage and bearing friction are also described.

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