Fieldbus integrated in dcs three implementation methods - Database & Sql Blog Articles

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Industrial control has evolved from early local control and centralized control to current distributed control (dcs). In the past 20 years, the process industry has invested heavily in dcs systems and related instrumentation, and the application of dcs systems The result was affirmed by the user. The 4-20 mA signal is the most essential feature of the interconnection of dcs systems and field devices. This is a major advancement in the development of control systems and instrumentation.
However, nowadays, digitalization and networking have become the main direction of today's control network development. It is recognized that traditional analog signals can only provide raw measurement and control information, and the ability of smart transmitters to attach information over a 4-20 mA signal is limited by its low communication rate, so the mechanism of the entire process control system Digitalization and networking should be an inevitable trend in its development.
The fieldbus provides a fully digital, two-way, multi-node communication link between intelligent field devices and automation systems. The advent of fieldbus has facilitated the digitization and networking of field devices and has made field control more powerful. This improvement brings the openness of the process control system, making the system a comprehensive control network with measurement, control, execution and process diagnostics.
1 Fieldbus impact on traditional dcs The impact of fieldbus on traditional dcs comes from its technical characteristics superior to the dcs system. According to the definition of IEC and Fieldbus Foundation FF, fieldbus technology has the following five main features:
1 digital signal completely replaces 4-20mA analog signal;
2 to make the basic process control, alarm and calculation functions completely distributed on site;
3 to increase non-control information, such as self-diagnosis information, configuration information, and compensation information;
4 to achieve the unification of site management and control;
5 Realize system openness and interoperability.
Fieldbus technology is not only a communication technology, it actually integrates the essence of technologies such as intelligent instrumentation, computer networks and open system interconnection (OSI). All of these features make fieldbus control systems (FCS) based on fieldbus technology superior to traditional dcs systems:
1 system structure is greatly simplified, and the cost is significantly reduced;
2 On-site equipment autonomy is strengthened, and system performance is comprehensively improved;
3 improve the reliability and accuracy of signal transmission;
4 Realize a fully distributed, fully digital control network;
5 users always have system integration rights.
These advantages can be verified from the comparison of the network structure of dcs and fieldbus systems.
2 Fieldbus integration in the dcs system is the development trend of the current control network. Although users welcome the structural improvement of the control system, they do not want to make major changes to their existing instrumentation systems.
At the beginning of the development of fieldbus, most users are more inclined to gradually add and replace their existing instrumentation systems; on the other hand, the disappearance or complete replacement of dcs systems and their instruments, for cost or manpower It is also unreasonable. The most feasible solution at this stage is to consider how to make the fieldbus work as much as possible with the traditional dcs system. This integrated solution enables flexible system configuration for a wider range of practical applications.
3 Fieldbus integration on the dcs system I/0 bus In the dcs architecture, the top-down can be roughly divided into three layers: management layer, monitoring operation layer and I/O measurement and control layer. On the I/O bus of the I/O measurement and control layer, there are dcs controllers and various I/O cards. I/O cards are used to connect live 4-20mA devices, discrete or PIC and other live signals, dcs. The controller is responsible for on-site control.
The key to integrating the fieldbus on the I/O bus of the dcs system is to hang on the I/O bus of the dcs through a fieldbus interface card, and realize the mapping of the data information in the fieldbus system to the original dcs I/O bus. The corresponding data information, such as basic measured values, alarm values ​​or process settings, makes the fieldbus seen by the dcs controller as if it were from a traditional dcs device card. This enables fieldbus technology integration on the I/O bus.
This solution can be used mainly for small-scale applications where the dcs system has been installed and stable, and the fieldbus is first introduced into the system; this solution can also be applied to the plc system.
The advantage of this scheme is that the structure is relatively simple, and the disadvantage is that the integration scale is limited by the fieldbus interface card.
Fisher-Rosemount's dcs system DeltaV uses this integrated solution. The DeltaV system has specially developed an interface card designed with this function in its I/O card--fieldbus H1 communication module (31.25kbit/s), successfully integrating fieldbus technology into the DeltaV system, enabling Fieldbus instruments are connected to each other, which greatly saves installation, operation and maintenance costs. The same controller is compatible with H1 and traditional I/O modules, which facilitates the transition and transition from the traditional control mode to the fieldbus control mode.
A specific driver is provided in the fieldbus H1 communication module of the DeltaV system for mapping the fieldbus system data information with the corresponding information on the I/O bus.
4 Fieldbus integration in the network layer of the dcs system In addition to the integration scheme on the I/O bus, the fieldbus system can be integrated on the higher layer, the dcs network layer. In this scenario, the fieldbus interface card is not attached to the I/O bus of the dcs, but to the upper LAN of the dcs.
In this scenario, fieldbus control execution information, measurements, and field instrument control functions can all be viewed and modified at the dcs operator station. Its advantage is that some of the control and calculation functions that must have been done by the dcs host computer can now be decentralized to the field instrument implementation, and relevant parameters or data information can be obtained on the dcs operator interface; another advantage of this is that it is not required. Changes to the dcs control station have less impact on the original system.
This integration scheme is also used in engineering practice. For example, Smar's 302 series fieldbus products can integrate their fieldbus functions at the dcs system network layer.
5 Fieldbus is integrated with the dcs system through the gateway. If the dcs system and the fieldbus system are run in parallel in one factory, you can also connect the two through a gateway to install the gateway to complete the dcs system and the fieldbus high-speed network. Information transfer. In this configuration, the information of the dcs system can be obtained and displayed on the new operator interface. A large number of H1 low speed buses can be installed by using a throwing bridge. The fieldbus interface unit provides control coordination, alarm management and short-term trend collection.
Parallel integration of fieldbus and dcs completes the integration and control of the entire plant's control system and information system, and can interconnect the Infranet and Inernet through the Web server. The advantage of this scheme is that it enriches the information content of the network and facilitates the comprehensive advantages of data information and control information. In addition, in this integration scheme, the fieldbus system and the dcs system integrated through the gateway are independent of each other. .
6 Conclusion In summary, we believe that the fieldbus system will be widely used in process industry control. By making some necessary modifications to the process control system, the fieldbus technology will be introduced into dcs, which will bring a lot of users. On the other hand, even though most of the continuous control loops will be completed by the fieldbus system, the dcs system will still play an important role in many control situations such as real-time requirements. The coexistence of fieldbus and dcs systems at this stage will give users more choices to achieve a more reasonable control system.