As the output voltage of the induction sensors varies with the speed, a static calibration is not possible and the use of sensors at varying speed is limited. These sensors have an order of magnitude lower frequency range, a lower accuracy and a higher sensitivity to disturbances. Induction sensors give a signal, the magnitude of which is proportional to the velocity of the blade movement. The advantage of this feature is that the sensors can be calibrated statically, for example using a positioning facility. The most favourable properties of the group of magneto-electric sensors have highlighted the magneto-resistive sensors, which are characterized by a high accuracy and sensitivity to a displacement, wide frequency bandwidth (0 to 300 kHz) and a very important feature, which is the independence of the sensor output voltage magnitude on the speed of a blade passage. ![]() Using permanent magnets as the source of the magnetic field has simplified the sensor construction and increased its reliability. The sensors are designed for a long-term temperature resistance of 200☌ and a short-term temperature resistance of 250☌. The BVMS system is orientated on magneto-electric sensors that have proven successful in all installations. Comprehensive research of non-contact methods and sensors preceded to the deployment of the system in service. The BVMS system has been successfully put into operation at the power plant Prunerov II and the nuclear power plant Temelin. Vaněk, in 10th International Conference on Vibrations in Rotating Machinery, 2012 4 CONCLUSIONSĪ non-contact system for turbine blade vibration measurement and monitoring has been developed in the Institute of Thermomechanics of the Czech Academy of Sciences. Stresses within blades are increased along with the amplitude of vibrations which during long flight may lead to initiation and propagation of fatigue cracks in the blades roots. The blades resonance vibrations are heavily amplified / Fig. In this case a part of the blades which has previously had only weak resonance is subjected to heavy fluctuation of forces /synchronous with rotational speed/. It was investigated that gentle blade vibrations /and stresses/picture observed within the whole speed range is disturbed by ingested foreign objects found on the stator blades /eg. At the and of acceleration phase synchronous blade vibrations /of the first flexural mode/caused by second harmonic of rotational speed can be seen within the range from 11000 to 14500 rpm blades vibrations are minimal. Within the speed range from 8000 to 8500 rpm blade resonance caused by third harmonic of rotational speed is visible. At the beginning of engine acceleration vibrations asynchronous with rotational speed are visible /stall blade vibrations/. ![]() Typical vibration picture of compressor first stage blades taken by MDPh device during engine acceleration from idling to n = n max is presented on figure 1. Their essential advantage is that vibrations of all blades of the stage may be examined simultanously. ![]() compressor blade vibrations caused by rotating stalls/. These devices are suitable for investigation of blade vibrations both synchronous and asynchronous with engine rotational speed /eg. Considerable development of devices functioning according to MDPh principle is noted down in professional literature. In this case the noninterference discrete-phase method /MDPh/ is very useful /references 1,2,3/. Such method is useless for diagnostics of compressor blade vibration state. channels drilling for installation of gauges. Investigations of blade vibration dynamics are conducted as a rule by strain gauging which demands previous engine preparation i.e.
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