# Monitoring of Liquid Viscosity for Viscous Dampers through a Wireless Impedance Measurement System
## 3 Experimental Set Up  
The viscous damper is a type of passive velocity-related damper that operates by generating a damping force through the interaction of a viscous medium with structural parts of the damper. Viscous dampers are generally composed of a cylinder, a piston, a damping hole, damping medium (viscous fluid), and a guide rod. In order to simulate the real monitoring environment, the experimental specimen of the damper is made cylindrical in appearance. The physical and structural diagram of the damper cylinder test piece is shown in Figure 6.  
The damping medium consisted of methyl silicone oil, which has stable performance and is not affected by temperature. The damping medium will change during use. In order to simulate the viscosity of the damping medium at different stages, high temperature resistant dimethyl silicone oil (Liansheng Dow Corning Silicone Oil Sales, Shenzhen, China and Beijing Haibeisi Company, Beijing, China) is used. Ten different viscosity grades of dimethylsilicone oil are tested, and the viscosity of ten different samples are listed in Table 1 and the physical picture is shown in Figure 7. The samples of damping liquid are odorless and non-toxic, transparent and viscous in appearance, with good chemical stability. The density of these samples is 0.97 g/cm\({}^{3}\), and their viscosities are listed in Table 1. A PZT patch (model PZT-5) with the size of 50 mm \(\times\) 12 mm \(\times\) 1 mm is bonded inside the specimen, as shown in Figure 8.  
Figure 4: NB260 functional block diagram. Figure 5: Photos of wireless impedance measurement system. The experimental setup for wireless, impedance-based damping fluid viscosity monitoring includes a wireless impedance measurement system, computer, damper cylinder specimen and PZT sensor, as shown in Figures 6-9. The wireless impedance measurement system was developed by the authors. The device has a frequency measurement range of 10-100 kHz and an impedance measurement range of 100 \(\Omega\)-10 M\(\Omega\), with a measurement error of less than 5%. The wireless impedance system measures the electrical impedance of the PZT sensor and sends the data to the PC for storage and processing. Firstly, a wide range of frequency scanning is carried out to determine the appropriate frequency scanning interval. The frequency scanning interval selected in this paper is 70-100 kHz, because the formant is in this interval. The formant is more sensitive to the change of liquid viscosity. Therefore, this frequency range is selected to measure the viscosity of the liquid in the damper specimen. Applying a sinusoidal sweep signal to the piezoelectric transducer mounted on the damper structure causes the piezoelectric sensor to vibrate and interrogate the assembly. The propagation and analysis of vibrations allows the impedance characteristics of the damping fluid viscosity to be measured and expressed in terms of the impedance characteristics of the piezoelectric sensor. By comparing the impedance signals of the piezoelectric transducer at different viscosities, the monitoring of the damping fluid viscosity can be realized. \begin{table}
\begin{tabular}{c c c c} \hline
**Test No.** & **Viocousity (cSt)** & **Test No.** & **Viscousity (cSt)** \\ \hline
1 & 5000 & 6 & 200,000 \\ \hline
2 & 10,000 & 7 & 500,000 \\ \hline
3 & 20,000 & 8 & 1,000,000 \\ \hline
4 & 50,000 & 9 & 2,000,000 \\ \hline
5 & 100,000 & 10 & 5,000,000 \\ \hline \end{tabular}
\end{table} 
Table 1: Damping fluid samples with ten different viscosities. Figure 6: Photos of damper cylinder specimen. (**a**) Schematic diagram (**b**) physical diagram. Figure 8: PZT transducer. Figure 7: Photos of ten samples of damping fluids with different viscosities. (**a**) packages of damping fluid samples. (**b**) damping fluid samples inside packages. The maximum value of impedance curve is 83.53 kHz (Figure 10).