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ABB DSQC604 3HAC12928-1 Digital input card

ABB DSQC604 3HAC12928-1 Digital input card

ABB DSQC604 3HAC12928-1 Digital input card

The difference between the three control systems

2.1 Differences

2.1.1DCS or PLC

The structure difference between PLC system and DCS system is not much, but the difference in the focus of function, DCS focuses on closed-loop control and data processing. PLC focuses on logic control and switching quantity control, and can also achieve analog quantity control.

The key to a DCS or PLC system is communication. It can also be said that the data highway is the backbone of distributed control systems DCS and PLC. Since its mission is to provide a communication network between all the components of the system, the design of the data highway itself determines overall flexibility and security. The media of the data highway can be: a pair of stranded, coaxial, or fiber optic cables.

DCS is characterized by: (1) strong control function. It can realize complex control laws, such as cascade, feedforward, decoupling, adaptive, optimal and nonlinear control. Sequence control is also possible. (2) High system reliability. (3) The CRT operation station has a good man-machine interface. (4) The software and hardware adopt modular building block structure. (5) The system is easy to develop. (6) With configuration software, programming is simple, easy to operate. (7) Good cost performance.

Through the design parameters of the data highway, you can basically understand the relative strengths and weaknesses of a particular DCS or PLC system.

(1) How much I/O information the system can process.

(2) How much control loop information related to control can be processed by the system.

(3) How many users and devices can be adapted (CRT, control station, etc.).

(4) How thoroughly the integrity of the transmitted data is checked.

(5) What is the maximum allowable length of the data highway?

(6) How many branches the data highway can support.

(7) Whether the data highway can support hardware produced by other manufacturers (programmable controllers, computers, data recording devices, etc.). In order to ensure the integrity of communication, most DCS or PLC manufacturers can provide redundant data highways.

In order to ensure the security of the system, complex communication protocols and error detection techniques are used. A communication protocol is a set of rules to ensure that the transmitted data is received and sent.

At present, two types of communication means are generally used in DCS and PLC systems, that is, synchronous and asynchronous, synchronous communication relies on a clock signal to regulate the transmission and reception of data, and asynchronous network uses a reporting system without a clock.

2.1.2 FCS

FCS has (1) good openness, interoperability and interchangeability. (2) Full digital communication. (3) Intelligence and functional autonomy. (4) Highly dispersed. (5) Strong applicability.

There are three key points of FCS:

(1) The core of FCS system is the bus protocol, that is, the bus standard.

The use of twisted pair, optical cable or radio transmission of digital signals, reduce a large number of wires, improve reliability and anti-interference ability. FCS is always a digital signal, from sensors to transmitters to regulators, which makes it easy to process more complex and precise signals, while the error function of digital communication detects errors in transmission.

FCS can completely decentralize PID control to the FieldDevice. FCS based on fieldbus is a new generation of fully decentralized, fully digital, fully open and interoperable production process automation system, which will replace the on-site one-to-one 4 ~ 20mA analog signal line, bringing revolutionary changes to the traditional industrial automation control system architecture.

According to the definition of IEC61158, fieldbus is a digital, bidirectional transmission, multi-branch communication network between the field device installed in the manufacturing or process area and the automatic control device in the control room. Fieldbus enables measurement and control equipment with digital computing and digital communication capabilities, improves the measurement, transmission and control accuracy of signals, and improves the function and performance of the system and equipment. The SC65C/WG6 working group of IEC/TC65 began to work on the introduction of the world's single fieldbus standard in 1984, and went through a difficult process of 16 years, and launched IEC61158-2 in 1993, after which the standard development was in chaos. There are eight subsets of IEC61158 fieldbus international standards published in early 2000, which are:

① Type 1IEC Technical Report (FFH1); Type 2Control-NET (Rockwell support); Type 3Profibus (supported by Siemens, Germany); Type 4P-NET (supported by ProcessData, Denmark); Type 5FFHSE (formerly FFH2) high-speed Ethernet (USA FisherRosemount company support); ⑥ Type 6 SWIFT-NET (supported by Boeing); ⑦ Type 7WorldFIP (supported by French Alsto company); ⑧ Type 8Interbus (supported by PhoenixContact).

In addition to the eight fieldbuses of IEC61158, IECTC17B has passed three bus standards: SDS (SmartDistributedSystem); ASI (ActuatorSensorInterface); DeviceNET. In addition, ISO published the ISO11898CAN standard. DeviceNET was approved as a national standard by China on October 8, 2002, and was implemented on April 1, 2003.

Therefore, to achieve compatibility and interoperability of these bus types is almost impossible in its current state. Open fieldbuses control the interoperability of systems, as far as a particular type of fieldbus is concerned, as long as the bus protocol follows the same type of fieldbus, its products are open and interoperable. In other words, no matter what manufacturer's product is not a product of the fieldbus company, as long as it follows the bus protocol of the same type of bus, the products are open and have interoperability, the bus network can be formed.

In addition, the FCS can also be connected to the upper management network of the enterprise through the gateway, so that managers have first-hand information and provide a basis for decision-making. Therefore, fieldbus has many outstanding characteristics, such as openness, interoperability, highly decentralized system structure, flexible network topology, high intelligence of field equipment, and high adaptability to the environment.

(2) The foundation of the FCS system is the digital intelligent field device

The control function is transferred to the field instrument, and the instrument device in the control room mainly completes the functions of data processing, supervision control, optimization control, coordination control and management automation.

Digital intelligent field device is the hardware support and foundation of FCS system. The reason is very simple, FCS system is the implementation of two-way digital communication fieldbus signal system between the automatic control device and the field device. The field device must follow the unified bus protocol, that is, the relevant communication protocol, have the digital communication function, and can realize the two-way digital communication. Moreover, a major feature of the fieldbus is to increase the field level control function.

(3) The essence of FCS system is on-site information processing

For a control system, whether using DCS or fieldbus, the system needs to process at least the same amount of information. In fact, after the fieldbus is used, it can be obtained from the field.

ABB DSQC604 3HAC12928-1 Digital input card