## 3 The Relay Experiment and Parameters Analysis
### Parameter Analysis  
Parameters describe the performance of a relay contact. The bounce time and contact resistance are commonly used. The bounce time includes the bounce time of the contact and the steady time of the contact in the dynamic process of closure. The contact causes grain fatigue on the contact surface and mechanical wear. The bounce time is changed by the wear of contact surface, thus the condition of contact wear is reflected by the bounce time. In the applied process of the relay, the contact resistance value also changes constantly owing to the phenomena of oxidation, electrochemical reaction, and wear. The contact failure occurs when the contact resistance value exceeds the limit. The dynamic contact resistance and static contact resistance are two important parameters of the performance of relay. However, it is not easy to measure the contact resistance directly. The contact resistance is expressed by measuring the contact voltage drop indirectly. The contact voltage drop is also divided into the dynamic contact voltage drop and static contact voltage drop. The dynamic contact voltage drop is the voltage drop from just touching the steady state of the intermediate process, which is always reflected by the dynamic contact voltage drop peak. The static contact voltage drop is the voltage drop after steady contact. The working environment of relay is complicated. The reliability of relay is related to the external environment. Temperature is an important parameter. High temperature causes the coil resistance to increase and accelerate the deformation of the insulating material. If the sealing is poor, the low temperature leads to the formation of frost between the contacts. Thus, temperature is a parameter that must be considered in the lifetime experiment of relay. The HH52P relay is taken as an example. The four parameters are taken as the measuring indexes which contain contact bounce time \(t_{\rm T}\), duration of dynamic contact resistance \(t_{\rm D}\), dynamic contact voltage drop peak, and static contact voltage drop \(V_{\rm C}\). Thirteen groups relay are taken to conduct lifetime experiment at \(-20\)\({}^{\circ}\)C, \(20\)\({}^{\circ}\)C and \(55\)\({}^{\circ}\)C. The experimental results are shown in Tables 2-4. \begin{table}
\begin{tabular}{c c c c c} \hline
**Temperature** & **Times** & **\(t_{\rm T}\) (ms)** & \(t_{\rm D}\) (ms) & \(V_{\rm m}\) (V) & \(V_{\rm C}\) (V)** \\
**(\({}^{\circ}\)C)** & **(Ten Thousands Times)** & **\(t_{\rm T}\)** (ms)** & **\(t_{\rm D}\)** (ms)** & **\(V_{\rm m}\) (V)** & \(V_{\rm C}\) (V)** \\ \hline \(-20\) & 10 & 0.71 & 0.20 & 1.12 & 0.88 \\ \(-20\) & 50 & 0.44 & 0.69 & 1.17  
The static contact voltage drop and the dynamic contact voltage drop peak are taken as examples, which can reflect the change law of different parameters with the increase of the number of lifetime experiment at different temperatures. The line graphs are as follows. There are some sharp points from the experimental data in Figures 3 and 4, which are due to the influence of the experimental environment and the material itself. To imitate the operating state of the relay under real conditions, these sharp points are retained in this paper. Figures 3 and 4 show that the static contact voltage drop of each relay at different temperatures is different. The static contact voltage drop at 20 \({}^{\circ}\)C is smaller than that at \(-\)20 \({}^{\circ}\)C and 55 \({}^{\circ}\)C. The static contact voltage drop at 20 \({}^{\circ}\)C is about 0.15-0.3 V, while the voltage drop is about 0.8-0.9 V at \(-\)20 \({}^{\circ}\)C and the voltage drop is about 0.9-1.1 V at 55 \({}^{\circ}\)C. The static contact voltage drop fluctuates greatly at 20 \({}^{\circ}\)C. The dynamic contact voltage drop is different at different temperatures. The dynamic contact voltage drop peak at 20 \({}^{\circ}\)C is lower than that at \(-\)20 \({}^{\circ}\)C and 55 \({}^{\circ}\)C. The performance of relay is different at different temperatures.