Nondestructive evaluation and monitoring of vibration characteristics of equipment by MEMS sensors

Abstract

The practical application of MEMS sensors in the nondestructive testing of equipment is presented in the paper. The prospects of application and research are described. Among the existing methods of nondestructive testing (magnetic, thermal, eddy current, ultrasonic, radiation, visual, optical, acoustic emission control), vibration diagnostics is a complementary method for evaluating the functioning of mechanical systems. Monitoring and control of the vibration characteristics of equipment at the site of operation is necessary for ensuring the safe operation of complex engineering structures and facilities. When applying the method of vibration diagnostics at frequencies from 1 Hz to 30 Hz, the method of free and forced oscillations is used. The method of free and forced oscillations is applied to determine the natural resonant frequencies of the investigated equipment and damping decrement of this equipment at resonant frequencies. It is known that the frequency of seismic events from 3 to 12 degrees on the Medvedev–Sponheuer–Karnik scale (MSK 64) is in the range from 1 Hz to 30 Hz. This method has successfully proven itself in the testing of equipment weighing up to 100 kg. Important vibrational characteristics of complex engineering facilities and structures are their natural frequencies and damping decrement. The natural frequencies and damping decrement of the equipment can be determined by the free oscillation method. The free oscillation method (FOM) is to analyze the damping acoustic oscillations excited in the test equipment. The method has successfully proven itself in the testing of equipment that does not have a rigid attachment to the building structure (floor, wall, ceiling), does not require expensive materials for surface preparation. For a long time, FOM was mainly used in fault analyzers for layered media. Until recently, the available acoustic-to-electrical signal transducers, analog spectral analyzers, indicators of measurement results did not provide the necessary accuracy of measurements and did not allow to distinguish a stable informative component in the complex signal obtained by the transducing of the damped wave. The development of modern vibration sensor technologies, in particular, based on Micro-Electro Mechanical Systems (MEMS), has made it possible to use FOM with greater efficiency. Free oscillations were created by means of a basket with weights or by tension through a system of steel cables to a dynamometer. Forced oscillations (sinusoidal mechanical oscillations) were created by the portable generator BM-100, which excited sinusoidal mechanical oscillations in the specified coordinate areas of the equipment. Measurements of the accelerations of the specified coordinate areas of the equipment weighting up to 100 kg were performed by the MEMS sensor with the software-technical complex developed in the NSC “Institute of Metrology”. The processing of the obtained information was in determining the resonant frequencies, the relative power levels of the equipment oscillations, and their corresponding damping decrements. The prospective areas of application of accelerometers, developed on the basis of MEMS technology, are the works on the study and calculation of vibration state of systems of main steam lines of turbine-generators with determination of measures for reduction of vibration; use in systems of vibration diagnostics at nondestructive testing.