1. comparison of the DCS and FCS
As shown in Figure 7-28, FCS has broken the traditional DCS (distributed control system) structure. DCS in the field devices and controllers are located in the control room one physical connection. FCS uses a smart device, DCS in the control room of the original control modules, input/output modules in the field equipment and field device with communication capability and direct transmission of signals between the field devices and control system functions not dependent on computers or controllers in the control room, directly in the field to complete, thorough dispersion control is realized. In addition, FCS using digital signals instead of analog signals can be achieved on a pair of wires to transmit multiple signals, and power supply for multiple devices. In order to simplify the system, saving hardware device, saving the connection cable and create the conditions for various installation and maintenance costs. Comparison of the DCS and FCS are detailed in table 7-4.
Figure 7-28 comparison between DCS and FCS structure
Table 7-4 of DCS and FCS
2. features of fieldbus
Fieldbus system breaks the traditional structure of the control system, which technically has the following characteristics:
(1) open fieldbus system to build a unified plant floor networks of open systems. Users according to their needs, through fieldbus random products from different vendors of open interconnection systems.
(2) the interoperability and interoperability interoperability refers to the interconnection between devices, information transfer and communication among and interoperability means different manufacturer performance of similar devices can replace each other.
(3) equipment intelligent and functional autonomy of its sensing and compensation calculation, project processing and control functions to complete field equipment, alone to complete the basic functions of automatic control of field equipment and diagnostic equipment running at any time.
(4) the system structure is highly fragmented field bus constituted a new distributed control system–wide architecture, fundamentally changing the concentration and dispersion of DCS system, simplified the system structure, and improves reliability.
(5) the fieldbus environment adaptability is designed specially for the site, supports a variety of communication media, with strong anti-jamming ability, can use two–wire power and communications, and meet the essential safety requirements.
3. advantages of field bus
Due to the field bus system structure simplified, control system design, installation, commissioning of normal operation and maintenance, reflects the superiority. Advantages of field bus are as follows:
(1) save hardware number and investment due to dispersed in site of intelligent equipment can directly implementation variety sensing, and measurement, and control, and alarm and calculation function, thus can reduced variable sent device of number, no longer need separate of regulator, and calculation unit,, also no longer need DCS system of signal conditioning, and conversion, and isolation, function unit and complex wiring, also can with industrial PC machine as operation station, to save has a large hardware investment, and can reduced control room of accounted for to area.
(2) to save installation cost fieldbus control system wiring is simple, a pair of twisted or on a cable can usually hook up multiple devices and cables, terminal boxes, Qiao greatly reduced the amount of line design and proofing of joints workload is greatly reduced. When you need to increase the control equipment on site, without adding new cables, close the connection cable on the original, save investment, and reduce the workload of the design, installation. According to the information of typical test projects show that can save installation cost more than 60%.
(3) save maintenance cost control device with self diagnosis and simple troubleshooting skills, and relevant diagnostic information over the digital communications to the control room, users can query runs for all devices, diagnostic maintenance information for early analysis of the failures and remove, shorten maintenance downtime and simplify system structure, connection simple and reduces maintenance.
(4) users with a high degree of system integration initiative users are free to choose different vendor–supplied device integration system. Avoid selecting a brand range of products and limited selection of used equipment, not for the system integration of incompatible protocols, interfaces, and at a loss to make systems integration initiative in the process firmly in the hands of the user.
(5) improving the accuracy and reliability of the system of intelligent field devices, digital, compared with analog signals, and fundamentally improve the accuracy of measurement and control, reduced shipping errors. Simplified system structure, equipment and connection reduced internal function of field equipment, reduce round-trip transmissions of signals, improve the reliability of the system.
In addition, because of its standardization of equipment, function modules, which also has a simple design, easy refactoring and other advantages.