# Mechanical Design and Testing of Mobile Monitoring Units for Security Systems
## 3 Results
\begin{table}
\begin{tabular}{c c} \hline \hline
**Mobile Monitoring Unit Version** & **Frequency** \\  & **(Hz)** \\ \hline Long legs & \\ Without tensioning wire ropes & 3.86 \\ Temperature 25 \({}^{\circ}\)C & \\ Long legs & \\ With tensioning wire ropes & 6.31 \\ Temperature 25 \({}^{\circ}\)C & \\ Short legs & 3.74 \\ Without tension wire ropes & 3.74 \\ Temperature 25 \({}^{\circ}\)C & \\ Short legs & \\ With tension wire ropes & 6.37 \\ Temperature 25 \({}^{\circ}\)C & \\ Long legs & \\ Without tensioning wire ropes & 3.85 \\ Temperature 37 \({}^{\circ}\)C & \\ Long legs & \\ With tensioning wire ropes & 6.34 \\ Temperature 37 \({}^{\circ}\)C & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dynamic frequency analysis results’ overview. Figure 13: Comparison of the measured dynamic frequency analysis results of the mobile monitoring units without and with the tensioning steel wire ropes. the base of the mobile monitoring unit was only 30 \({}^{\circ}\)C, and the construction itself was not overheated; this result was also confirmed by the measured frequency. The frequency was calculated as the average value of three measurements for every mobile monitoring unit version, and, as can be seen, the measured frequencies varied only in tenths or hundredths of Hz, which is a negligible difference and relates to the uncertainty of the measurements. The most significant difference was observed in the utilization of the tensioning wire cables. However, the difference was not only in the measured frequency, but also, as can be seen in Figure 13, the time needed for the mobile monitoring unit to enter into a steady state. For the version with the tensioning wire cables, it was 16.47 s for the version with the long legs and 14.78 s for the version with the short legs. As the steady state, a state with deviation of \(\pm\)5% from the average value was considered. Considering the versions without tensioning wire cables, the time required to get back into the steady state greatly exceeded one minute. The simulations were performed for mobile monitoring units with short and long legs at the temperatures overviewed in Table 1. Also in these cases, the differences between the frequencies obtained by the measurements and the simulations were only in tenths of a Hertz. Therefore, it can be concluded that the simulation models were of high quality, as the results of the simulations and of the measurements are very similar. In addition to the presented measurement results and their comparison with the simulation results, whole sets of simulations for the different mobile monitoring unit versions were performed. For example, from the results of simulation analyses performed on the mobile monitoring unit with long legs, the natural frequency change was only 0.307\(\cdot\)10\({}^{-3}\) Hz when the temperature increased from 20 \({}^{\circ}\)C to 30 \({}^{\circ}\)C, and 0.352\(\cdot\)10\({}^{-3}\) Hz when the temperature decreased from 20 \({}^{\circ}\)C to 10 \({}^{\circ}\)C. The additional cooling to -10 \({}^{\circ}\)C resulted in a difference in the natural frequency of only 0.976\(\cdot\)10\({}^{-3}\) Hz. Therefore, it can be concluded that the influence of the temperature is very small, and from this point of view, the overall mechanical design is appropriate for this application.