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RS485 Bus Systems up to 115 kbit/s (not suitable for PROFIBUS)



RS485 Bus Systems up to 115 kbit/s (not suitable for PROFIBUS)

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    The RS485 bus is a low-cost half-duplex communication bus, which, due to its relatively high interference immunity, is not only used for monitoring and control in industrial systems, but is now increasingly used for SCADA and protection applications by utilities in substations. Protocols, such as DIGSI, IEC 60870-5-103, DNP 3 and MODBUS up to 115 kbit/s, are used between a station master and up to 31 slave devices on shielded twisted-pair (STP)
    cable. In ideal conditions, the length of the bus may be up to 1000 m. This requires correct confi guration of the bus, use of suitable cables, and connector connectors, as well as correct termination of the bus. Devices with different termination methods require special adaptors to achieve the highest possible interference immunity. The RS485 bus systems 7XV5103 are optimized in this respect for our control and protection product range. With the ordering code 7XV5103, two different RS485 bus systems are available.

    When combining the required components for a RS485 bus, the corresponding application examples contained in this document can be of assistance.

    The bus system with 9-pin SUB-D connectors has long been applied in systems with SIPROTEC protection devices, 7XV5 converters, and master units. Connection to the individual devices is achieved directly with a special Y-cable or with a corresponding adapter cable to devices with different termination methods. The bus terminates in a 9-pin SUB-D bus terminating connector with an integrated 220-Ω resistor.

    On some SIPROTEC devices, the serial signals are routed to RJ45 female connectors on the communication module, as is the case, for example, with the redundant IEC 60870-5-103 module. There the bus is based on double-shielded CAT 5 patch cables. Connection of the individual devices to the two redundant buses is achieved via two special Y-adapter cables each. The buses each terminate with a RJ45 bus terminating connector with a 120-Ω resistor.

    A combination of the two bus systems and the different device interfaces or a combination of the two systems is also possible using the Y-adapter cable 7XV5103-2BA00.

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