Implementacion de Una Completa Automatizacion Integrada Con Profibus

Implementation of Fully Integrated Automation with PROFIBUS

Chen Meicheng Fang YanjunDepartment of Automation Department of Automation

Wuhan University Wuhan UniversityWuhan, 430072 Wuhan, 430072

CHINA [email protected] [email protected]

Xu JunDepartment of Automation

Wuhan UniversityWuhan, 430072

[email protected]

Abstract –This paper presents an integrated approach for implementing fully automation with Profibus technology. We studied the frame of Profibus protocol and the communication model for Profinet components. A scheme for developing Profibus slave was proposed. Aiming at the interoperation between Profibus devices and other fieldbus devices, a scheme for designing fieldbus protocol conversion gateway was also presented. Other kinds of fieldbus devices can connect withProfibus network via the gateway. Profibus devices can be directly encapsulated in Profinet components, and through a gateway, other kinds of fieldbus devices can also be encapsulated with Profinet.

I. INTRODUCTION

Fieldbus technology enables the changeover from central to decentralized automation systems. Nowadays, due to the high commercial interests involved, there are many fieldbuses coexisting as Profibus, Hart, CAN and some others [1]. A modern enterprise is likely to adopt a few different kinds of fieldbus technologies in its control systems, which will lead to incompatible problems.. How to form an efficient solution for theses problems is a current hot spot in the research field on industrial automation.Today, Profibus International has more than 1100 active

members worldwide; many results have shown its reliability and high efficiency. Profibus technology is mainly used in manufacture and process automation. It includes three compatible editions: Profibus-DP (Decentralized Periphery) � Profibus-PA (Process Automation) and Profibus-FMS (Field Message Specification). Profibus-DP is mainly used in high-speed data communication between automatic control systems and dispersive I/Os or field intelligent devices. Profibus-DP protocol adopts the normative model of ISO/OSI; includes only the first, second layer and the user interface; it doesn’t include the third to the seventh layer, for the purpose of high-speed data communication. Other fieldbus devices can also be integrated in Profibus network through protocol conversion gateway and act as Profibus devices, so they can also be encapsulated in Profinet components.

II. DESIGN OF PROFIBUS MODULES

SIEMENTS Corporation provides development kits for Profibus modules design. In addition, kinds of protocol chips are available for implementation of different editions of Profibus protocol. With the development kit and the protocol chip, it is very convenient to design Profibus components.

A. Profibus-DP protocol

Profibus-DP protocol adopts the normative model of ISO/OSI; includes only the first, second layer and the user interface; it doesn’t include the third to the seventh layer, for the purpose of high-speed data communication.The physical layer of Profibus-DP is accord with the EIA criterion. Physically, Profibus is an electrical network based on a twisted pair or an optical network based on a fiber optic cable. The data link layer describes the normal formation, security mechanism and available communication services of data transmission messages. The only task of the Profibus-DP is to define how the user data transmit from one station to another through field bus, without the evaluation of the data. The direct data link map (DDLM) program supports the accessing right to the second layer. The user interface defines application functions of devices based on Profibus-DP and the characteristics of all kinds of systems or field devices. Architecture of Profibus protocol is shown as Fig.1.

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Fig. 1. Architecture of Profibus-DP Protocol

According to OSI normative model, the second layer defines the bus accessing control, the data transmission security, the management of communication protocol and messages. The second layer is called FDL (Field Data Link) layer and its services are shown in Fig.1as below. All of the services are executed the SAPs (Service Access Points)

4120-7803-9252-3/05/$20.00 ©2005 IEEE

through the upper protocol. Profibus-DP only uses the subclass of the services, namely SRD and SDN service. In Profibus-DP, every SAP is defined with a definite function.The default SAP is for data exchange.SRD is used for all the Profibus-DP functions that involve

data transmission between master and slaves, such as cyclic data exchange, diagnostic, parameterization, acyclic read and write, etc. SDN is a non-confirmed connectionless service that is used for issuing global control commands from master to slave. DDLM uses SDN service to implement the DDLM_global_control function and uses SRD service to implement other functions. SDN is the only FDL service that can address a group of stations.

B. Profibus slave design

Profibus is the network for the cell and field area in the open, heterogeneous communication systems. Profibus allows comprehensive networking of the management, cell and field levels along with Industrial Ethernet and the AS-Interface (AS-I). In actual use in field area, about 90% of the slaves are based on Profibus-DP. The DP masters communicate with DP slaves through a

series of messages. These messages include the services of SRD (send and require responsive data) and SDN (send no- responsive data). The DP master sends data to DP slaves and receives the data from DP Slaves within the DP polling cycle time. To increase the reliability of the data transmission process, there are mandatory services for the master class 1 and optional services for the master class 2.A Profibus slave can be divided into two parts, i.e. a

communication board for implementation of Profibus protocol and an I/O interface board for handling peripheral signals’input or output. The communication board and the I/O interface board can be connected through a flat cable. Frame of a Profibus slave is shown as Fig.4.

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Fig. 4. Frame of Profibus slave

The SPC3 is an intelligent communication chip for slave applications. It enables connection to the Profibus-DP field bus. The IM 183-1 interface module is implemented with the SPC3. The SPC3 has a 1.5Kbyte message frame memory. It can handle all communications tasks of the Profibus-DPprotocol completely independently. This accelerates protocol handling and reduces the scope of the software in the microprocessor of the interface module. Bus access is hardware driven. Data transfer takes place via a 1.5Kbyte RAM. The interface to the application is a data interface. Therefore, the data can be transferred independent of the bus circle. The maximum transmission rate is can reach 12Mbit/s.

The main board provides chip selecting signals, data bus, address bus, and some control signals for the slave board. The slave board can be easily connected to the main board through a flat cable, thus it can process the corresponding signals. This doing assures the convenience for the slave module’s future function extending. The I/O interface board is used for signal acquisition and

outputting. It can be designed with the corresponding functions according to practical requirements. Many chips can be selected to process peripheral signals. MAX197 can be used for analog signal sampling, and TLV5618 can be used for outputting analogsignals. 74LS244 and 74LS573 can handle the switch signal inputting and outputting respectively.

III. INTERCONNECTION OF HETEROGENEOUS FIELDBUS DEVICES

Interconnection of heterogeneous fieldbus devices is an excellent way to exert each fieldbus technology’s advantages. As most fieldbus are quite different from each other at the physical layer and the data link layer, the protocol conversion task can be fulfilled only through gateways.

A. Fieldbus protocol conversion model

As heterogeneous fieldbuses define quite different standards at each layer of their protocols, protocol conversion can be realized only through gateways [5]. In addition, adopting the compound protocol conversion method will optimize the design schemes. Fieldbus protocol defines a user interface above its application layer, thus the gateway must try to call the defined SAPs (Service Access Points) to transfer services from the upper entity to the lower entity. Fig.5 shows the communication model between fieldbus devices.

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Fig. 5. Communication model between fieldbus devices

B. Fieldbus gateway design

A good example of the fieldbus gateway design can be implemented between Modbus and Profibus-DP. Modbus is another widely used fieldbus technology, which is actually the standard for industry communication since 1979. Though Profibus-DP and Modbus both can use RS-485 bus at the physical layer, their data link layer and user interface/application layer are quite different from each other. Gateway must be adopted to implement the interconnection of the two different networks. Protocol conversion adopts layer-by-layer mode, namely from the lower layer to the upper layer. The lower layer supports the upper layer and the upper layer calls the services provided by the lower layer.

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Protocol chip SPC3 is adopted for the implementation of Profibus-DP protocol. Single chip processor 89C52 provides serial interface for Modbus and protocol chip SPC3 provides Profibus-DP with RS-485 interface. Fame of the gateway between Profibus-DP and Modbus is shown as Fig.6.

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Through the way, a Modbus device can implement all of thefunctions of Profibus-DP, and act as a node in the Profibus-DPnetwork. Similarly, gateway for protocol conversion between Profibus and other fieldbus can be designed.

III. PROFINET TECHNOLOGY

Profinet technology supports the modularization of plants and machines through the distribution of automation and intelligent field devices. This technological modularization is a key characteristic of distributed automation systems and simplifies the reuse and standardization of plant and machine parts.

A. Profinet component

The function of an automatic plant or machine is performedthrough the defined interaction of mechanical, electrical/electronics and control logic/software. Working on this principle, Profinet [6,7] defines the parts “mechanical”, “electrical/electronics” and “control logic/software” in functional terms to form a technological module. A simple Profibus-DP network with several masters and slaves can also be encapsulated in a Profinet device. A typical model of a Profinet component is shown as Fig.7.

It represents a technological module in the system-wide engineering. It encapsulates its automation functionality in a software component, and from the technological point of view, has an interface containing the variables required for interacting with other components.

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Fig. 7. Profinet component model

Profinet components are based on the open communicationCOM. The interfaces can be easily connected in the Profinet

connection editor. The component model enables objects of various origins through defined interfaces.

B. Engineering with Profinet

A Profinet component created and configured in Profinet Engineering will perform the automation functionality in runtime [8]. The component description must be created with the respective vender specific programming and configuration tools. Use of the vendor-specific tool presupposes that it includes the component generator, which enables the Profinet specific XML file of the Profinet components to be created. The concrete system is described through the configuration of ES-Autos. Component interconnection during configuration results in some major advantages compared to programming a system with functionality. The topological structure of the automation system, on the other hand, is created in the network view. The field devices and programmable controllers are assigned to communication or bus system and the device addresses are fixed in accordance with the rules of the underlying bus system.

C. Real-time performance analysis

The analysis of various TCP/IP implementations has revealed that considerable running times are needed with standard communication stacks to manage the data packets. It is possible to optimize these running times, but the required TCP/IP stack is no longer a standard product but a proprietary implementation [9]. The same is true when using UDP/IP implementations.An efficient solution is created in Profinet for real-time

applications which are typically found in production automation and whose update or response times are at least in the range of 5-10ms. The update time is created in a device application, is then send to a partner device through the communication systems, and is subsequently made availableto the application again at this partner device. Such a solution greatly minimizes throughout times in the communication stack and results in enhanced performance in terms of the update rate of automation data. On the one hand the elimination of several protocol levels reduces message length; on the other hand it takes less time before the data to be transmitted are ready for sending and the application is ready for processing.

IV. CONCLUSIONS

The scheme of adopting Profibus technology to implement fully integrated automation inside an enterprise is an efficientway to raise the efficiency and save the costs. A successfulapplication example has shown that the fully integrated automation with Profibus saves 15% of a system’s overall costs. Moreover, such a system-wide and vender-independent engineering project will provide the users with a high degree

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of clarity and transparency, thus it will finally contribute a lot to the improvement of the qualities of a intelligent control system. It can be foreseen that the application of Profibusfieldbus technology will become more attractive in the future.

V. REFERENCES

[1] Yang Xianhui, Filedbus Technology and Its Application, Beijing: Qinghua University Press, 1999, pp.101-103.

[2] A. N. Expert, A Book He Wrote, His Publisher, 1989.Yang Changkun. Fieldbus Technology Handbook on PROFIBUS, Chinese PROFIBUS Organization, 2001.

[3] Tang JiYang, Guidance of The Application of Profibu-, Chinese PROFIBUS Organization, 2001.

[4] Manfred Popp, Introduction to PROFIBUS on Industrial PC. SIEMENS AG, 1997.

[5] Cai Jianxin, Theory and application of HART modern HT2012.Electricaltechnologyapplication,1994(4),pp.43-46.

[6] Gu Hongjun, Industry Ethernet and Fieldbus Technology, Beijing: Renmin Youdian Press, 2002, pp.96-99.

[7] Geoff Brown, “Bring Together Drivers and Fieldbus Technology”, Control and Instrumentation, vol 8, pp. 35-37, May 2000.

[8] Geoff Brown, “Bring Together Drivers and Fieldbus Technology”, Control and Instrumentation, vol 8, pp. 35-37, May 2000.

[9] PADABIS, Plant Automation Based on Distributed system ,http://www.pabadis.org.

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Implementacion de Una Completa Automatizacion Integrada Con Profibus

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