GE Multilin SR750-P5-G5-S5-HI-A20-R Protection Relay


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The 750/760 is equipped with three standard serial communications ports, one RS232 located in the front panel, and two RS485/RS422 in the rear of the relay. A rear Ethernet port is also available as an optional feature. The front panel port allows easy local computer access. The rear ports provide remote communications or connection to a DCS, SCADA, or PLC. The baud rate of all the serial ports is variable from 300 to 19,200 bps. The optional Ethernet port can be used to connect the 750/760 to 10 Mbps Ethernet networks.

The 750/760 supports ModBus® RTU, DNP3.0 Level 2, and ModBus RTU TCP/IP protocols. The three serial ports support ModBus RTU protocol, while any one of the two rear ports but not both can be configured to support DNP 3.0 Level 2. The optional Ethernet port supports ModBus RTU via TCP/IP protocol. The communication system of the 750/760 is designed to allow simultaneous communication via all ports. Using Ethernet as the physical media to integrate the 750/760 to Local.


The new control strategy and network structure based on fieldbus technology will have a revolutionary impact on existing instruments and control systems. This paper analyzes the impact of fieldbus technology on traditional distributed control system DCS based on its essential characteristics, and proposes three implementation methods for integrating fieldbus into dcs based on the network structure characteristics of dcs.

Industrial control has evolved from early local control and centralized control to current distributed control (DCS). Over the past 20 years, the process industry has invested heavily in DCS systems and related instrumentation, and the application results of DCS systems have been recognized by users. The 4-20mA signal is the most essential feature of the interconnection between dcs systems and on-site equipment, which is a major progress in the development of control systems and instrumentation.

However, digitization and networking have become the main directions for the development of control networks today. People realize that traditional analog signals can only provide raw measurement and control information, and the ability of intelligent transmitters to add information above 4-20mA signals is constrained by their low communication rate. Therefore, digitizing and networking the mechanism of the entire process control system should be an inevitable trend in its development.

Fieldbus provides a fully digital, bidirectional, and multi node communication link between intelligent field devices and automation systems. The emergence of fieldbus has promoted the digitization and networking of field devices, and made the functions of field control more powerful. This improvement brings openness to the process control system, making it a control network with comprehensive capabilities for measurement, control, execution, and process diagnosis.

The Impact of Fieldbus on Traditional DCS
The impact of fieldbus on traditional dcs comes from its essentially superior technical characteristics over dcs systems. According to the definitions of the International Electrotechnical Commission IEC and the Fieldbus Foundation FF, fieldbus technology has the following five main characteristics:
① Digital signals completely replace 4-20mA analog signals;
② Complete the distribution of basic process control, alarm, and calculation functions on site;
③ Add non control information to the device, such as self diagnostic information, configuration information, and compensation information;
④ Realize the unity of on-site management and control;
⑤ Truly achieve system openness and interoperability.

Fieldbus technology is not only a communication technology, but actually incorporates the essence of technologies such as intelligent instruments, computer networks, and Open Systems Interconnection (OSI). All of these characteristics make the fieldbus control system (FCS) based on fieldbus technology have significant advantages over traditional dcs systems:
① The system structure is greatly simplified, and the cost is significantly reduced;
② Strengthen the autonomy of on-site equipment and comprehensively improve system performance;
③ Improved the reliability and accuracy of signal transmission;
④ Truly achieving a fully decentralized and fully digital control network;
⑤ Users always have system integration rights.
These advantages can be verified by comparing the network structures of dcs and fieldbus systems.

TRICONEX 9761-210
SAFT 063F 380