## 3 Condition Monitoring of the Impedance Bonds
### Condition Monitoring Device and Sensors Used for Monitoring the Impedance Bonds  
Considering the above presented aspects about the necessity of impedance bond monitoring and diagnosing, for limiting the negative effects, both technical and economic--in the following sections are presented an experimental device that was developed for monitoring and diagnosing an impedance bond in real-time. The condition monitoring device was designed and realized from the need to monitor the parameters discussed above (currents, temperatures). The device role is to prevent possible faults in the operation of the railway signaling installations on the electrified lines in the traction power system, respectively, the avoidance of the return circuit interruption that will lead to delays in the circulation of the trains, and some technical and economic loses. The architecture of the device was designed specially to allow acquiring data in real-time and to intervene in case of anomalies appearance [35]. Figure 4 presents the block diagram of the hardware structure for the condition monitoring of the impedance bond. Figure 4: Condition monitoring device block diagram of the impedance bonds. The main elements of the condition monitoring device used to acquire and record the parameters on the impedance bond are:  
* ATmega644P microcontroller;
* two current transducers based on Hall effect of LEM LTS 6-NP type;
* two current transformers;
* four Negative Temperature Coefficient (NTC) temperature sensors;
* digital temperature sensor of DS18B20 type;
* power supply module of Tracopower TMLM 04105 type;
* communication interfaces with TTL/RS232 converter and TTL/USB converter;
* SD-card module of ROGUE uMMC type for local data storage;
* 2 \(\times\) 16-character liquid crystal display, for monitoring device configuration and data displaying;
* GSM modem. The electronic part of the impedance bond monitoring and diagnosis device was built around the ATmega644P microcontroller, an 8-bit microcontroller in Reduced Instruction Set Computing (RISC technology), which, by its flexible properties and low cost, offers an ideal solution for many applications in the engineering field. The microcontroller is characterized by: 10 bit Analog to Digital Converter (ADC); calibrated internal RC oscillator; internal and external interrupt sources; two programmable serial ports USART1, USART2; two serial interfaces; two SPI serial ports. Figure 5 shows the frontal image of the embedded system. Thus, the connection terminals, the configuration keys of the device, the local display, GSM modem, etc., can be observed. The hardware architecture of the device was designed for specific working conditions to 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. Among the characteristics of the device designed and performed:  
* direct supply from the operative voltage (230 V AC);
* displaying on LCD the temperatures acquired from each sensor of the impedance bond, as well as the traction current;  
Figure 5: Image with monitoring and diagnosis device of impedance bonds. * recording all the parameters on an SD-card;
* sending alarms via a communication interface (GSM) to an operator. During monitoring of the parameters from the impedance bond, the following data are acquired and stored:  
* the traction currents on the two railway tracks;
* the current imbalance between the two railway tracks;
* interrupting a connection cable to one of the railway tracks;
* the temperature on each terminal and the connection ropes;
* the temperature from the impedance bond housing. The device can be mounted in the relay cabinets at each railway sector, and the connection to the impedance bond is made by installing the temperature transducers on the terminals, respectively, the housing, and the current transformers on the connecting conductors between the railway tracks and impedance bond terminals.