## 1 Introduction
Furthermore, a comparison of measured values with specified ones from the manufacturer, or with previously determined values, are included in condition monitoring [11; 12]. Moreover, the introduction of artificial intelligence in faults diagnosis will obtain high accuracy in detecting some problems in the incipient phase to improve the availability and safety of the train operation [1; 13; 14]. Presently, no reports regarding impedance bond monitoring and diagnosis are presented in the literature; however, some patents close to this field of research [15; 16; 17; 18; 19] can be mentioned. Thus, the patent [15] related a system and method for detecting a broken rail and occupied track from a railway vehicle. The authors of [16] have developed an onboard measurement system for railway vehicle wheel flange wear. [PERSON] et al. in [17; 18; 19] have developed and implemented an in-service condition monitoring device, which is applicable for long-term condition monitoring of tracks being composed of: a compact device, data collection, and remote data collection via cellular phone. The onboard device was made for track fault detection by measuring the acceleration of bogies. In previous years, railway infrastructure monitoring has been based more on wireless sensor networks [6; 7; 8; 20; 21; 22; 23; 24; 25; 26]. Thus, in [6; 7; 8], the authors present wireless devices and sensors, which can be used in railway infrastructure to assist in decision-making processes for improving maintenance activities through real-time monitoring. In [20], a wireless network technology is presented for railway bridge monitoring from the railway infrastructures. The wireless network collects information (vibration, temperature, material deformation) for knowing the structural health and behavior of infrastructure when a train moves over. Moreover, the paper [21] describes the wireless network for monitoring structural monitoring of tunnels. The aim of [22] is to present an early warning system, based on a wireless network, for railway infrastructure monitoring and environmental security monitoring against natural hazards and intentional threats (earthquakes, fire, explosions, etc.). In [23] are shown aspects of the optimal energy resources allocation method of wireless sensor networks for railway status monitoring. [PERSON] et al. [24, 25] presented wireless sensor nodes with the Zigbee protocol, and self-powered for railway condition monitoring. Thus, in this paper, a condition monitoring system that uses an online device and sensors for acquiring some electrical parameters from railway infrastructure is described. It was developed and applied for faults detection and the diagnosis of impedance bonds. Moreover, for understanding the role of the impedance bond in railway infrastructure, the power supply system from the electric railway traction is presented. Furthermore, aspects of the impedance bond (as a component of the return circuit from railway infrastructure) is presented. The necessity for monitoring and diagnosis of the impedance bond and the parameters, which must be monitored to detect incipient faults, are discussed. Furthermore, with the condition monitoring system and thermal camera, a thermal analysis of the electrical contacts between the impedance bond and railway tracks (from the return circuit of electric traction) was made. The laboratory experiment consists of the obtained results analyses in different situations that could occur in exploitation. Four cases were analyzed for the connection between impedance bond and railway tracks. These connections were performed through cables made from different materials and with different cross-sections. Aspects about the Impedance Bond of the Return Circuit from the Power Supply System of Railway Infrastructure  
A power supply system from electric traction represents the assembly of the installations used to transform, transmit, and consume the electrical energy necessary for people and cargo railway transport.