## 3 Design and Development of the Measuring System
### Hardware Design of the System  
According to the measuring principle, the size of vibration isolators, and the practical application demand, we designed and developed the measuring system, including a sensor array component and an integrated controlling component. The sensor array component  
Figure 5: General framework of the system. mainly contains multiple sensors and a mounting frame. And the controlling component is composed of other related parts. For the sensor array component, the ML33-25-00-02 eddy current displacement sensor, produced by China MIRAN Technology (Shenzhen Miran Technology Co., Ltd., Shenzhen, China), has been chosen. This type has a measurement range of 20 mm, a resolution of 1.0 \(\upmu\)m, and a signal output using the RS485 communication mode (see Table 2). Figure 6 gives a photograph of the eddy current sensor. The probe is for detecting displacement. The preprocessor is the signal processing center of the whole sensor system. On the one hand, the preprocessor would provide a high-frequency AC excitation current to the probe coil and make the probe work. On the other hand, through a special circuit, the preprocessor could sense the gap between the probe and the metal conductor to be measured. After processing, the electric output signal will be outputted, which changes linearly with the gap. Since the installation size of the vibration isolators is about 600 \(\times\) 600 \(\times\) 300 mm, \(11\) groups of sensors in total are set with a staggered layout, and the distance between each of them is at least 100 mm, which could avoid the cross interference on electromagnetism from the adjacent probe. Furthermore, based on the considerations of installation space and the probe size, the main dimensions of the frame are designed as 550 \(\times\) 450 \(\times\) 215 mm. The supporting frame for the sensors should have reliable stiffness and stability to guarantee the measured results. Moreover, it should be lightweight; only in this way can it be handled easily and conveniently. Consequently, unlike a traditional assembly, one-piece 3D printing technology was employed to make the mounting bracket by using non-metallic polymeric materials. To be specific, nylon plastic is applied. Figure 7a gives the structure model of the component in which a mounting frame accounts for the main part. Advanced computer aided technology has been applied in developing the mounting frame. In order to make sure the light-weighted frame structure has good rigidity and little deformation, finite element analysis has been employed to explore the deformation situation under different loaded conditions. The simulations have been carried out using \begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Item** & **Value** \\ \hline
1 & Sensor range & 20 mm \\
2 & Probe diameter & 40 mm \\
3 & Liner error & \(\leq\)\(\pm\)1\%FS \\
4 & Resolution & 1.0 \(\upmu\)m \\
5 & Probe weight & 0.20 kg \\
6 & Preprocessor weight & 0.35 kg \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Related specifications of the sensor used. Figure 6: A photograph of an eddy current sensor applied in this work. commercial software package ANSYS 2022 Release 1.0. Following the normal analysis work flow, the geometry model is designed first and then imported into the computing platform. Since the frame is small and the structure is not complex, there is no need for great computing power and the free meshing method is employed. Control the maximum element size, then the model is meshed, as shown in Figure 7b, which was experienced through a grid independence check. The boundary conditions are loaded including all the probe weights and the frame gravity for simplification. The four corners near the bolt holes are set with fixed condition, since they would be locked by bolts in the real installed status. Figure 7c,d display the frame at horizontal and vertical positions, respectively. It could be found that the deformations are as expected.