the industrial communication systems profibus and profinet 01

Applied Natural Sciences 2009 329

THE INDUSTRIAL COMMUNICATION SYSTEMS PROFIBUS AND PROFInet

IGOR BÉLAI, PETER DRAHOŠ

Institute of Control and Industrial Informatics, Faculty of Electrical Engineering and Information Technology STU, Ilkovičova 3, Bratislava, SK-812 19, Slovak Republic

([email protected], [email protected])

Abstract: PROFIBUS and PROFInet are open and vendor independent industrial communication systemsused in the area of control of the discrete and continuous processes. There are introduced the main PROFIBUS and PROFInet characteristics in the article. The application of these communication systems in the education on the Institute of Control and Industrial Informatics is introduced too. There are also the examples of both, the workplaces and the exercises, in the article. The exercises allow the following: 1. to understand the principles of the work with the smart sensors, 2. to master the communication on the basis of the PROFIdrive communication profile in the motion systems, 3. to handle the PROFIBUS diagnostics, 4. to master the communication configuration in the PROFInet CBA systems.

Key words: Fieldbus, Industrial Ethernet, PROFIBUS, PROFInet, PROFIdrive.

1. Introduction

The industrial automation systems can be very complex, and they are usually structured into several hierarchical levels. Each of these levels has an appropriate communication level, which poses different claims on the communication system of each level. The industrial communication systems is possible classify on different categories based on functionality: field-level networks, control-level networks and information-level networks. Hierarchy of an industrial automation system is on Fig.1 (DJIEV, 2009).

At the field level distributed devices such sensors, actuators, I/O modules, drive units, communicate with automation systems over a powerful, real-time communication system. Transmission of the data is cyclic and is characterized by short bus cycle. The real length of the bus cycle is application dependent. It varies from the tenth of microseconds to hundreds of milliseconds. Profibus DP and PROFInet IO fulfill these criteria and offer the universal solutions for both factory automation and process automation.

At the cell level programmable controllers such as PLCs and IPCs, communicate with each other and with IT systems of the office world using standards such as Ethernet, TCP/IP, Intranet and Internet. This information flow requires data packets and a range of powerful communication functions. As well as PROFIBUS, Ethernet based PROFInet offers a trendsetting solution for this purpose.


Fig.1: Hierarchy of an industrial automation system

The information level is the top level of a plant or an industrial automation system. The plant level controller gathers the management information from the area levels and manages the whole automation system. At the information level there exist large scale networks, e.g. Ethernet WANs for factory planning and management information exchange.

2. PROFIBUS and PROFInet

PROFIBUS and PROFInet respect ISO/OSI reference model. PROFIBUS uses OSI layers 1, 2 and 7 only (DRAHOŠ, 2008). PROFInet uses OSI layers 1, 2, 3, 4 a 7 (Ethernet, TCP/IP, UDP/IP, DCOM) (PNO, April, 2006).

PROFIBUS DP (Decentralized Periphery) is the simple, fast, cyclic and deterministic process data exchange between bus master end the assigned slave devices. The original version designed DP-V0, has been expanded to include versions DP-V1 and DP-V2. PROFIBUS DP is the main emphasis for factory automation, it uses RS485 transmission technology, one of the DP communication protocol versions and one or more application profiles. RS485 Transmission Technology is simple and primarily used for task that require high transmission rate. Shielded twisted pair


copper cable with one conductor pair is used. Various transmission rates can be selected between 9,6 kbit/s and 12 Mbit/s. Fiber optic transmission over fiber optic conductors is suitable in environments with very high electromagnetic interference or when particularly large distances need to be covered. Each PROFIBUS DP system is made up of 3 different device types (FRANEKOVÁ et al., 2007): 1. DP Master Class I is a central controller that cyclically exchanges information with the distributed stations (slaves) at a specified message cycle (e.g. programmable logic controller). 2. DP Master Class II is engineering, configuration or operating devices. 3. Slave is a peripheral device which reads in process information and/or uses output information to intervene in the process.

PROFIBUS PA (Process Automation) is the main emphasis for process automation, for smart sensors and actuators. Profibus PA uses MBP (Manchester Coded Bus Powered) transmission technology, typically MBP-IS (Intrinsically Safe), communications protocol version DP-V1 and the application profile “PA Devices“. PROFIBUS PA is named MBP (Manchester Coding and Bus Powered) too according IEC 61158-2. MBP is synchronous transmission with a defined transmission rate of 31,25 kbit/s and Manchester coding. This technology is frequently used in process automation as it satisfies the key demands of chemical and petrochemical industries for intrinsic safety and bus power using two-wire technology. This means that PROFIBUS can also be used in potentially explosive areas and be intrinsically safe.

PROFInet is based on Industrial Ethernet ISO/IEC 8802.3 (Full Duplex), IEEE802.1Q (Priority Tagging), always 100 Mbit/s and switched Ethernet. The PROFInet communications model defines a vendor-independent standard for communication on Ethernet with conventional IT mechanisms (runtime communications). It uses the most common standards of the PC world. It provides direct access from the office world to the automation level and vice versa (vertical automation). PROFInet has two basic orientations PROFInet IO and PROFInet CBA. PROFInet IO (Input, Output) is the simple, fast, cyclic and deterministic process data exchange between Controller and Decentralized Periphery such as PROFIBUS DP. PROFInet CBA (Component Based Automation) is a comprehensive automation concept that has emerged as a result of the trend in automation technology towards modular reusable machines and plants with distributed intelligence.

3. PROFIBUS and PROFInet systems at the Institute of Control and Industrial Informatics

The properties of the PROFIBUS systems are educated on several workplaces of the Institute of Control and Industrial Informatics. The control units of these workplaces are interconnected through PROFIBUS DP or/and PROFInet via built in communication processors. The SIMATIC S7-300 CPUs are used as the control units. The short description of these workplaces and their usage on the exercises from the subjects Industrial communication systems and Industrial buses are described thereinafter.

3.1 The PROFIBUS PA / HART communication with the smart sensors


This workplace allows the education of the configuration of the temperature and pressure sensors communicating via HART protocol or via PROFIBUS PA. The communication structure of the system is on Fig.2.

Fig. 2: The communication structure of the PROFIBUS PA/HART system

The control unit represented by PLC SIMATIC S7-300 communicates with four sensors. One HART device (Sitrans P pressure sensor equipped with HART transmitter) communicates through PROFIBUS DP and ET 200M remote I/O system with a built in analog HART module. The PROFIBUS PA devices are connected to two PROFIBUS PA segments created by PROFIBUS DP/PA link (IM 157 module). Two Sitrans T temperature sensors and one Sitrans P pressure sensor are connected to PROFIBUS PA. The parametrization, configuration and diagnostics of all four sensors are performed from five engineering stations (ES1 - ES5) via SIMATIC PDM software.

This system is exploited in the education on the exercises from the above mentioned subjects. The tasks solved by students are the following: 1. Study the principle of the work of the connected sensors. 2. Draw the overall communication diagram. 3. Study the software equipment – SIMATIC PDM. 4. Verify selected engineering activities (read the actual values, verify the parametrization of the device, change and download new parameters of the device). 5. Compare the alarm signaling in the pressure sensors PT 101 and PT 104.

The above mentioned tasks are solved via standard software SIMATIC Step 7 and SIMATIC PDM.

3.2 PROFIBUS DP communication in the motion systems

The motion systems workplace allows the education of the process values transfer principles via PROFIBUS DP and the PROFIdrive communication profile (described in: PNO, May, 2006). The communication structure of the system is on Fig. 3.


Fig. 3: The communication structure in the motion system exercise

The system is composed of the controller SIMATIC S7-300 (PLC), ET 200M remote I/O system (RIOS) with a counter module counting the impulses from the incremental encoder (IRC), P-Device represented by frequency inverter supplying an asynchronous motor (AM). Five engineering stations (ES1- ES5) make possible the configuration of PLC and they also serve as supervisors by PROFIdrive profile definition.

The tasks solved by students are the following: 1. Configure the PROFIBUS network and the controller for the communication with the frequency inverter. 2. Write a PLC program which will allows the frequency inverter control: Start, Stop, sending of the reference frequency and receiving of the actual frequency. 3. Verify your solution on the real system.

The above mentioned tasks are solved via standard software SIMATIC Step 7.

3.3 PROFIBUS diagnostics

The communication errors may be caused by physical layer malfunctions or by incorrect network settings. The PROFIBUS diagnostics can be performed during a PROFIBUS system installation, preventative on the working systems, or when the system malfunction happens. In the PLC systems, the basic diagnosis of the PROFIBUS networks is realizable via configuration software of the PLC. But the diagnostic possibilities of this software is limited and more profound diagnostics has to be performed by special software and/or hardware tools. We utilize two of such tools: BC-450 PROFIBUS protocol analyzer and PB-T3 PROFIBUS cable testerproduced by Softing AG.

The communication network of our system is on Fig. 4. The network consists of five PROFIBUS DP Masters Class I (programmable logic controllers PLC1- PLC4, PLC6), six PROFIBUS DP Masters Class II (engineering stations ES1 – ES6) , five PROFIBUS DP Slaves (one DP/PA link, two remote I/O systems ET 200M, two frequency inverters) and hardware error generator (ERR) which makes possible generation of some cabling errors. The following errors are possible to generate via


hardware error generator: line break, wrong cable type, damaged cable, high transition resistance, too many terminators.

Fig. 4: The PROFIBUS DP network in the Siemens laboratory of the Institute of Control and Industrial Informatics, FEI STU

The students learn to distinguish the symptoms of the errors generated by error generator and the way of their detection via PROFIBUS diagnostic tools.

3.4 PROFInet CBA system

The PROFINET component model sees its real use in distributed automation systems. It is ideally suited for intelligent field devices with programmable functionality as well as controllers. The component model describes autonomously acting partial units of machines or plants as technological modules. The engineering of distributed automation systems differentiates between the programming of the control logic of the individual technological modules (manufacturer- specific configuration tools) and the manufacturer independent configuration of the overall installation, in which the communications relationships between the technological modules are determined.

The communication network of our system is on Fig. 5. PROFInet CBA network consists of two technological modules and one engineering station (ES4). The technological module 1 is composed of the SIMATIC S7-300 PLC. The technological module 2 represents a motion system with SIMATIC S7-300 PLC, engineering station (ES6) and a frequency inverter supplying an asynchronous motor. Both PLCs have the PROFInet communication capabilities. The configuration of the PROFInet communication is performed via standard SIMATIC STEP 7 and SIMATIC iMAP software tools.


Fig. 5: The communication structure of the PROFInet CBA system

The students solve the following tasks: 1. Configure the PROFIBUS DP network of of the technological module 2. 2. Configure and program technological functions of both PLCs. The PLC of the technological module 1 shall send the commands to the technological module 2 via PROFInet CBA and on the contrary it shall receive the actual values from the technological module 2. 3. Generate the PROFInet components for both PLCs. 4. Generate PROFInet interconnections via SIMATIC iMAP software. 5. Verify your solution on the real system.

4 Conclusion

The basic informations about application of the both PROFIBUS and PROFInet industrial communication systems in education on Institute of Control and Industrial Informatics, are summarized in the paper. The above mentioned workplaces are located in the Laboratory of the Automation Technology Siemens.

The students, during the solution of the exercises, learn the following: 1. The elements of the SIMATIC S7-300 PLC programming and configuration. 2 The principles of configuration and diagnostics of the PROFIBUS PA field devices. 3. The principles of the communication with the drive units by PROFIdrive communication profile used in PROFIBUS and PROFInet networks. 4. The PROFIBUS error sources identification via advanced diagnose tools. 5. The configuration of the technology modules communication within the PROFInet CBA network.

This project is supported by the grant KEGA 3 / 5201 / 07.


References

PNO: PROFINET Technology and Application. PROFIBUS Nutzerorganisation e.V., Germany, April 2006.

PNO: Profile Drive Technology PROFIdrive, Technical Specification for PROFIBUS and PROFINET, Version 4.1. PROFIBUS Nutzerorganisation e.V., Germany, May 2006.

FRANEKOVÁ, M., KÁLLAY, F., PENIAK, P., VESTENICKÝ, P.: Komunikačná bezpečnosť priemyselných sietí (Communication safety of the industrial networks), Žilinská univerzita, Žilina, 2007, 271 pp.

DRAHOŠ, P.: Multivendor PROFIBUS. Proceedings of the 8th International Scientific - Technical Conference PROCESS CONTROL 2008. Kouty nad Ďesnou, Czech Republic, June 9-12, 2008.

DJIEV, S.: Industrial Networks for Communication and Control. http://anp.tu-sofia.bg/djiev/PDF%20files/Industrial%20Networks.pdf. Viewed on July 2009.

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