## 5 Conclusions  
The necessity of monitoring the impedance bonds increases due to their importance in ensuring the traction current return to the power supply, respectively, to the control and signaling of the railway vehicles to achieve the safety of railway traffic. A fault of the impedance bond will block the signaling circuit, which will lead to the interruption of the power supply system from electric traction, including the train movement in the respective sector.  
The monitoring and diagnosis of the impedance bonds will lead to the reduction of delays in the circulation of trains, delays caused by the failure of the signaling installations.  
Limiting the adverse effects of such an event, respectively, removing as much as possible of the occurrence of abnormal situations, can be achieved by knowing the essential parameters of the impedance bond that influence its operation.  
In this context, a device for monitoring and diagnosing of impedance bonds was designed and realized. The hardware architecture of the device was designed for working conditions specific to the electric traction, being made a compact and robust structure, suitable for insertion in housing that can be mounted on the omega rail, the rail commonly used in switchboards.  
The novelty character of the device is:  
Figure 11: Temperature variation from the contact area by different contact resistances.  
* knowing the currents through the two primary coils of the impedance bond, the temperatures on the contact terminals, on the metallic or non-metallic housing of the coil, and the ambient temperatures;
* impedance bond diagnosis (a higher temperature in the contact areas, a higher of the current imbalance through the two running rails, the interruption of the connecting conductors between the impedance bond terminals and railway track, etc.);
* real-time knowledge of the technical condition of the impedance bond by analyzing the acquired data and comparing it with previous records;
* the device has high flexibility, both at the hardware structure (the possibilities of extending of inputs number, respectively, possibly extending the storage capacity), and also to the software (upgrading the firmware at the device location).  
The monitoring and diagnosis of impedance must allow good knowledge of the technical condition of the impedance bonds to retain their behavior in the most varied situations, and it compared with a database of others of the same equipment type, but exposed under similar conditions.  
The thermal stresses of the return circuit from the electric railway traction are produced by the electrocaloric effect of the current flowing through them. Thus, an experimental test setup to determine the thermal stress level of the contact terminal area between the impedance bond terminals and connectors (of the connection ropes), through a condition monitoring device, and with an infrared device for validating the measurements, was realized.  
The experimental tests performed in the laboratory on the impedance bond tested with various modes of connection to the railway tracks, showed, on the one hand, a good functioning of the monitoring device, thus fulfilling the purpose for which it was designed and realized. On the other hand, the thermal stresses of the monitored impedance bonds were correctly highlighted. Those aspects are shown by comparing the values monitored with the experimental device and with the infrared thermographic investigation device.  
Based on the present achievements, future research will focus on developing a software application in LabVIEW for an easy interface with the operator.  
Finally, for future work, there will be a desire to realize the modeling and simulation of the ensemble with finite element analysis software, such as COMSOL Multiphysics.