PSI - Issue 44

Mauro Mazzei et al. / Procedia Structural Integrity 44 (2023) 1212–1219 Mauro Mazzei et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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important factors that enticed us to design a device suitable for the signal detection under study and as low-cost as possible for these specific needs. 3. Accelerometer specifications Vibration sensors are widely used in products, whether a mobile car, aircraft, circuit board, suspension bridge or building, for vibration measurements and to study the dynamic behavior of a structure, including defined modal analysis. The accelerometer is a vibration sensor used to evaluate the response to external stresses, verify modal models used in simulation programs, or to predict the response to different operating conditions. In the industrial and civil sectors, monitoring using vibration sensors is now the most widely used technique for monitoring the health of machines and large industrial and civil structures. Examination of vibration trends over time makes it possible to predict the onset of deterioration and to intervene in time before failure. This type of continuous or periodic monitoring of the service condition of a plant is also known as “Predictive Maintenance”. The principle of the accelerometer is essentially based on sensing the inertia of a mass subjected to acceleration. The mass is suspended by an elastic element, while some type of sensor detects its displacement relative to the fixed structure of the device. In the presence of acceleration, the mass having its own inertia moves from its rest position in proportion to the detected acceleration. The sensor transforms this displacement into an electrical signal that can be acquired by modern measurement systems. Based on this, different types of sensors have been developed. 3.1. MEMS capacitive accelerometers MEMS-based capacitive accelerometers are the cheapest, most common and smallest sensors of their kind. The principle of operation exploits the positioning of a weight installed on springs. One end of the springs is attached to the plates of the comb capacitor, the other end to the weight. The force acting on the sensor causes the weight to move over the springs, so the distance between the capacitive element and the mass varies, and there is a change in capacitance. 3.2. Strain gauge accelerometer The strain gauge bridge accelerometer uses the same sensing principle as load cells, namely, the change in resistance of a strain gauge due to the change in its length. In these devices, a mass is suspended on thin plates, on which are fixed strain gauges connected to the Wheatstone bridge. 3.3. Piezoelectric accelerometer This device is one of the most commonly used sensors for measuring vibration levels. For this reason, piezoelectric accelerometers are commonly used in industrial applications for diagnostics or control. Its operation is similar to the working principle of piezoresistive accelerometers. Under the influence of acceleration, their resistance does not vary and they generate an electrical voltage of a predetermined value. 3.4. LVDT accelerometer The LVDT accelerometer uses an LVDT (Linear Variable Differential Transformer) sensor built into the accelerometer structure as the principle for detecting mass displacement. In these devices, the mass itself forms the ferromagnetic core of the LVDT sensor, and it slides within a channel, around which coils designed to detect the position of the mass are wound. A dedicated circuit detects the position of the core relative to the coils and generates an electrical signal proportional to the displacement from the rest position.