# Mechanical Fault Prognosis through Spectral Analysis of Vibration Signals
## 3 Test Platform and Software Flow
### System Structure  
As shown in Figure 1, the designed visualizable real-time vibration analyzer consists of vibration sensors, a data acquisition unit (DAU), an Raspberry Pi embedded system, a 5G industrial router, and an optional remote server. The piezoelectric acceleration sensors are attached to the pump motor, gearbox or water pipe by strong magnets to collect vibration acceleration signals. The DAU is connected to up to eight sensors of different types, such as vibration acceleration sensors, velocity sensors, eddy current displacement sensors, and inductive displacement sensors. Moreover, the DAU has an Ethernet interface, through which the sampled data are uploaded to a remote embedded system. Thus, the embedded system is cross-connected to the DAU via wired Ethernet, or directly connected to it via a switch/router. The 5G industrial router makes the data interaction between the machine equipment and the platform more efficient, and the 5G characteristics of ultra-high speed, ultra-large link, ultra-low latency, and secure transmission are highly desirable. The 5G industrial router can be used in harsh and complex factory environments. It contains high-performance industrial-grade 32-bit communication processors and industrial-grade wireless modules to ensure reliability for long-time communication between remote devices and a monitoring center in harsh environments. A vibration detection system using MEMS as an acceleration sensor was designed in [25]. However, the used YXS-8908 charge output piezoelectric acceleration sensor works on the piezoelectric effect of the piezoelectric crystal and adopts a unique isolated shear structure, which enables the sensor to have low strain on the mounting base, low transverse sensitivity, and performance stability. It is used in conjunction with a YX-ADV2 DAU with charge amplifier. Table 1 lists the dynamic performance parameters of the acceleration sensor. The YX-ADV2 DAU supports simultaneous input of multiple sensor types, such as vibration velocity sensor, acceleration sensor, eddy current displacement sensor, and inductive displacement sensor, with 8-channel, 16-bit A/D simultaneous acquisition with sampling rate of \(f_{s}=4\) KHz. The DAU encapsulates the collected raw data into a frame and sends it to the Raspberry Pi via TCP protocol (port number 8000). The communication protocol is customized by the company but is open to users. The vibration analysis application running on the Raspberry Pi parses the received packets according to the protocol to obtain the sample values of each sensor. The Raspberry Pi embedded system (controller) hardware includes an external power supply, an SD (Secure Digital) card, a keyboard, a mouse, and a display. The Raspberry Pi Model 3B+ uses a Qualcomm BCM2837 processor with a 64-bit quad-core processor running at 1.4 GHz. It has 1 GB of RAM, 2.4/5 GHz dual-band WiFi, Bluetooth 4.2, 300 Mbps Ethernet, 4 USB 2.0 ports, 40 GPIO pins, as well as audio and video interfaces, multimedia support, \begin{table}
\begin{tabular}{l l} \hline Measurement range (Peak) & \(\pm 5\) g (1 g \(\approx\) 9.8 m/s\({}^{2}\)) \\ Sensitivity (25\({}^{\circ}\)C) \(\pm\) 5\% & 100 mV/g (160 Hz) \\ Amplitude nonlinearity & \(\pm 1\%\) \\ Frequency response & 1\(\sim\)10,000 Hz (3 dB) \\ Transverse sensitivity ratio & \(\leq\)5\% \\ \hline \end{tabular}
\end{table} 
Table 1: Dynamic performance of YXS-8908 vibration acceleration sensor. Figure 1: Block diagram of the test platform. and more. The embedded system hardware, though having the size of a credit card, is powerful and has all the basic functions of a computer with the Debian Linux operating system. Raspberry Pi's operating system, applications, and data files are all on the SD card. In order to store the raw data of each sensor for a long period, a SanDisk 128 GB high-speed SD card with a read speed of 100 MB/s and a write speed of 10 MB/s was used.