## 2 Measurement System Architecture
### Development of Embedded Sensor Software  
This study uses LabVIEW to create a VI (virtual instrument) system that reads data and analyzes temperature and vibration signals. The program interface is user friendly, in terms of writing the program and building a user interface. Figure 5 shows a flowchart for the various specific functions for the VI. The VI system accepts two types of sensor signals, and measures vibration signals due to defects in the planetary gearbox structure. For a gear rotating at 7500 rpm, most defect-induced signals are distributed in the frequency band from 1.7 to 5000 Hz, as confirmed by analytical and experimental investigations. The signal also detects temperature variations within the planetary gearbox structure. These are typically low frequencies below 1 Hz. This study uses a multi-channel programmable data acquisition printed circuit board with a maximum sampling frequency of 10 kHz. The system samples signals from 0 to 5000 Hz without distortion. \begin{table}
\begin{tabular}{c c c} \hline  & **System Specification** & \\ \hline \multirow{4}{*}{Vibration Measurement} & Channel number & 3 axis \\  & Acceleration range & \(\pm\)10 g \\  & Sensitivity & 80 mV/g \\  & Sampling rate & 5 k Sps \\  & Resolution & 16 bits \\ \hline \multirow{4}{*}{Temperature Measurement} & Temperature range & \(-\)55\(-\)125 \({}^{\circ}\)C \\  & Measurement accuracy & \(\pm\)0.5 \({}^{\circ}\)C \\  & Sampling rate & 5 Sps \\ \hline \multirow{2}{*}{Others} & Input Power & 24 V DC \\  & WiFi & 802.11 standard protocol \\ \hline \end{tabular}
\end{table} 
Table 1: Prototype specification. Figure 4: Block diagram of the vibration sensor. A section of the VI main program is shown in Figure 6. Each module or icon in the diagram represents a function, such as data acquisition, signal display, spectrum display, Fourier transform analysis, calculation of root mean square values and data logging. The signal analysis module provides a time domain analysis, frequency analysis and calculates the root mean square for the vibration signal. The data are transferred to waveform data and shown in the time domain and are then processed using a Fourier transform to give a result in the frequency domain. The RMS result is calculated using these data. The raw data are logged into a file that contains three-axis acceleration data. The VI must offer an explicit graphical user interface that allows an observer to efficiently communicate with the gear monitoring system. Figure 7 shows the graphical user interface. Depending on the frequency of the signal, anti-aliasing and sampling rates for different gear operation modes are adjusted. The waveform display window in the upper middle left part of the menu shows the time domain for real-time gear signals. The frequency display window at the bottom center of the menu shows the spectrum of the real-time response signal from the Fourier transform analysis. The remaining functions of the menu include a real-time temperature display, and a data logging trigger, which is clicked one time to start recording the raw data and once to stop recording. Figure 5: Flowchart for the VI. Figure 6: Main program details of the VI system. To simulate interference in gearbox operation characteristic frequencies, LabVIEW's built-in noise and the sine wave simulation function are used. The sine wave has a frequency of 250 Hz and an amplitude of 5, and the noise factor has an amplitude of 10. Figure 8 shows that the simulation result is correct because the Fourier transform result for the sine wave with noise signal matches the frequency of 250 Hz. The result is quite close in the time domain to the real result. This tool produces simulated vibration signals that are similar to real signals. Using the Internet of Things (IoT), the vibration data are transmitted to the Internet database.