# Accuracy Characterization of a MEMS Accelerometer for Vibration Monitoring in a Rotating Framework
## 1 Introduction
For these reasons, the identification of the vibrations of the blades involves highly demanding data processing software, but the hardware cannot always comply with the requirements of the processing algorithms [30]. Currently, this technology still remains immature for its practical implementation in gas turbines. Other recent studies reported new contactless vibration measurement systems based on laser scanning and ground-based radars [31; 32; 33], but they can only be used for detecting large vibration amplitudes in operating blades. The recent development of MEMS-based fabrication techniques has provided an alternative for designers owing to their cost-effective and lightweight features that make them particularly attractive for the vibration monitoring in rotating structures. Notably, analog or digital signals of MEMS accelerometers can be easily acquired, even with inexpensive microcontrollers. This represents the major advantage over traditional ICP accelerometers which are more accurate and reliable, but would require wired data transmission, such as slip rings or expensive and bulky integrated charge amplifiers and wireless data transmission modules. In the last decade, several studies have been performed on the on-rotor acceleration measurement by means of MEMS accelerometers [34]. [PERSON] et al. [35] deployed a MEMS accelerometer on a rotating shaft to measure the shaft misalignments and compared the results with those measured by an optical encoder, and an excellent agreement was found. A lightweight MEMS accelerometer was successfully exploited by [PERSON]. [36] for studying a shaft's critical speeds during the start-up of a machine and the instantaneous torque measurement in induction motors [37]. [PERSON] [38] explored the viability of using a high-range (9810 m/s\({}^{2}\)) and low-sensitivity MEMS accelerometer to measure the centrifugal acceleration on a five-blades rotor fan disk. The outcomes demonstrated the potential for MEMS accelerometers implementation in fan and compressor rotor blades for structural health monitoring and vibration monitoring. A spectrum analyser using the Raspberry Pi and a tri-axial digital MEMS accelerometer for vibration monitoring in rotating machinery was also developed by [PERSON]. [39]. A disadvantage of employing digital output MEMS accelerometers lies in the evaluation of the amplitude and phase of vibration, since a frequency shift in the sample clock affects the accuracy of the sensor [40]; although, a theoretical model was proposed by [PERSON] [41] to resample the acceleration data and compensate the frequency shift error. However, the recent optimization and refinement of MEMS-based manufacturing technologies allowed to improve the performance of such sensors without significantly increasing their fabrication cost [42]. This paper explores the possibility of using a commercial MEMS to monitor vibration. A wireless system is developed for real-time rotating blades vibration monitoring by exploiting a commercial MEMS analog accelerometer. Its characterization was carried out by comparing the simultaneously acquired data with a more accurate and reliable reference system, based on an ICP accelerometer, that has been adapted to operate on rotating structures. Both the accelerometers were mounted on the tip of the blade, and the first four blade resonances were excited by means of piezoelectric actuators with the aim of replicating the most severe loading conditions. The frequency and amplitude of acceleration, simultaneously measured with both reference and wireless systems, were compared with each other in order to investigate the viability and accuracy of the proposed system. The data acquisitions were repeated six times for each considered resonance, and the measurement error was estimated by calculating the Mean Absolute Percentage Error (MAPE). It has been seen that this is always less than 5%, indicating a fair accuracy of the proposed wireless setup.