In this paper, the efficient implementation of a reliable measurement device to measure the angular velocity vibrations of rotating shafts is discussed. The solution is particularly suitable to be fit in measurement embedded systems equipped with field-programmable gate arrays (FPGAs). The proposed measurement method is analyzed from a theoretical point of view, focusing the study on the frequency response of the technique. On the basis of the theoretical results, a reliable and low-complexity design of the measurement device has been proposed. In the adopted solution, the high clock rates of FPGAs are exploited to increase the accuracy of the zero-crossing times estimation, for a given A/D acquisition frequency, using an upsampling approach. The experimental results confirm the validity of the technique. The upsampling method allows an increase of the measurement accuracy and an improvement of about 10 dB for the output signal-to-noise ratio over a wide range of vibration frequencies

In this paper, the authors discuss a measurement method, based on the zero-crossing demodulation technique of FM signals, to estimate the angular velocity vibrations of a rotating shaft. The demodulation algorithm is applied without any filtering to the direct voltage output issued by some probes sensing the passages of arbitrarily shaped targets installed on the rotating shaft. The authors discuss a theoretical approach to analyze the measurement problem taking into account the chief nonidealities related to the measurement setup, i.e., they have investigated the effects of both the shaft side vibrations and the irregular shape of the targets. On the basis of the theoretical results, the authors propose a measurement method that can reject the effects of these mentioned nonidealities, exploiting the measurements of two or more probes properly positioned around the shaft

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Nowadays the wide diffusion of the electrical machines, used for power generation, or as driver/helper in Oil&Gas applications, have amplified the problematic related to train torsional excitation. The standard instrumentation installed on the train does not permit to monitor and analyze this kind of stress; therefore to define criteria to screen torsional alternating stress by lateral vibrations becomes extremely important. This paper describes the experience achieved by the authors in the study of rotordynamic behavior of some geared train with the goal to define a methodology to analyze torsional stresses adopting industrial proximity probes (installed in the gear) or a non intrusive measurement system (optical probes). In order to confirm the last technology, an additional classic strain gage torsional measurement has been adopted obtaining similar results. An extensive part of this paper is dedicated to illustrate several test campaigns performed in different site where customers highlighted abnormal vibration levels. Finally, a wide description of data post processing and consequent conclusions are offered.

To enhance the Steam Turbine product line rotating speed and efficiency, GE Company has developed a new generation of high rotating speed Steam Turbine Low Pressure (LP) Sections named HS family (see also Cosi at al., [1.]). The master component of the family, and its smallest size, is the 4-stage LP section HS8, capable of variable speed operation up to 11250 rpm. The aeromechanical validation of HS8 was carried out in two steps: a full-scale rotating test in a vacuum chamber (so called wheel Box Test, WBT) and a full-size test vehicle campaign in steam (Low Pressure Development Turbine, LPDT). During both tests the 4-stage rotors were equipped with a reliable system of strain gages and thermocouples. Aim of the present paper is to present an overview of the experimental results and post-processed data from both tests. Measured blades modes frequencies, responses and quality factors from both WBT and LPDT are described and compared, and the behavior of these parameters at different mass-flows and backpressures is explored. Then, interesting results from the comparison of damping (or Q factors), in WBT and LPDT test are presented. Finally, a methodology for nodal diameter configuration identification is described. To the best of authors’ knowledge the present paper is the deepest investigation about damping in WBT and prototypical test for steam turbine last stage blades.