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PROFIBUS PA Mittuniversitetet Profibus PA is the same protocol as - PowerPoint PPT Presentation

Aug 22, 2023 •396 likes •912 views

PROFIBUS PA Mittuniversitetet Profibus PA is the same protocol as Profibus DP. The physical medium is different with reduced voltage and current levels to meet the requirements of intrinsically safe areas. Profibus PA is designed to

  1. PROFIBUS PA Mittuniversitetet

  2. • Profibus PA is the same protocol as Profibus DP. • The physical medium is different with reduced voltage and current levels to meet the requirements of intrinsically safe areas. • Profibus PA is designed to operate in hazardous areas. • Devices that operate in this environments have to follow European directive ATEX • An equipment (Europe) is marked with “Ex” if its approved under ATEX directive • Profibus PA transmission techniques are described in IEC 61158-2. Mittuniversitetet Industriell Datakommunikation - Fieldbus 2

  3. The physical layer MBP-IS • Twisted cable • Fixed Baudrate of 31.25 kbit/s • Maximum distance 1900 m • Between 10 and 32 devices per segments • Power Supply directly from the bus • Each device has a current consumption of minimum 10 mA • The maximum device number depends on the current consumption per device. (typ. 10-20) Mittuniversitetet Industriell Datakommunikation - Fieldbus 3

  4. The role of a coupler in Profibus-PA Mittuniversitetet Industriell Datakommunikation - Fieldbus 4

  5. A “ coupler ” adapts a Profibus -PA network as a DP device: • electrical isolation • power supply of the bus and adaptation between RS485 and IEC61158-2 • baud-rate adaptation (DP to 31.25kbit/s voltage mode) • conversion between UART telegram and 8-bit synchronous telegram. Mittuniversitetet Industriell Datakommunikation - Fieldbus 5

  6. The couplers are relative simple devices. To work correctly the maximum speed of the Profibus DP segment must be decreased to 45.45 kbit/s. A “ DP/PA Link ” acts as a slave DP and a master PA. It is not required to decrease the DP segment datarate. Mittuniversitetet Industriell Datakommunikation - Fieldbus 6

  7. Reference • Official Website • PROFIBUS System Description • Practical Industrial Data Communications - Ch. 14a • Industrial Communication Systems - Ch. 32 Mittuniversitetet Industriell Datakommunikation - Fieldbus 7

  8. Profisafe Mittuniversitetet

  9. Profisafe is an application profile that can operate within any Profibus-DP or Pronifet network. Profisafe is based around the concept of “black channel”. • The safety services of Profisafe are independent of the characteristics of the transmission system. • Safety data are encapsulated inside Profinet and Profibus frames. Mittuniversitetet Industriell Datakommunikation - Fieldbus 9

  10. These safety measures include: • The consecutive numbering of the PROFIsafe messages ("sign-of- life") • A time expectation with acknowledgement ("watch-dog") • A codename between sender and receiver ("F-Address") • Data integrity checks (CRC = cyclic redundancy check) Profisafe message format: To keep track of the “Consecutive Number”, both sender and receiver use a counter that is synchronized via the Control Byte and Status Byte . Mittuniversitetet Industriell Datakommunikation - Fieldbus 10

  11. PROFIsafe compliant devices must have a set of parameters for the safety layer defined in the GSD file. The GSD files are protected from data corruption with a special CRC signature on storage media. Example of parameters: • F_WD_Time specifies a number of milliseconds for a watchdog timer. This timer monitors the reception of the next valid PROFIsafe message. • F_SIL indicates the SIL expected by the user form the particular F_Device. It is compared with the locally stored manufacturer information. • F_iPar_CRC is a signature across all the iParameters within the technology of the F-Device. • F_Par_CRC is a signature across all the F-Parameters which is used to ensure correct delivery of the F-Parameters. Mittuniversitetet Industriell Datakommunikation - Fieldbus 11

  12. Reference • Official Website • PROFIsafe System Description Mittuniversitetet Industriell Datakommunikation - Fieldbus 12

  13. Real Time Ethernet (RTE) Mittuniversitetet

  14. Advantages of Ethernet • Simple interfacing with higher levels (supporting of TCP/IP traffic) • Standard technology that is widespread, updated and supported by PC • 10Base5 → 10BaseT → 100BaseT → GigaEthernet • Hardware costs are decreasing • Availability of IT communication instruments • PC-based analyzers (Es. Wireshark -Ethereal-); • Simulators • Network analyzers with high performance. • Emerging nodes and controllers use web and java technologies • Soft-PLC, web-sensor,... • Support of related technologies (optical fiber, wireless 802.11 WiFi) • couplers, bridges vs. subnetworks Mittuniversitetet Industriell Datakommunikation - Fieldbus 14

  15. Ethernet is just a transportation medium, what matters are the higher layers. Mittuniversitetet Industriell Datakommunikation - Fieldbus 15

  16. Different approaches are possible for Ethernet in industry: • Tunneling of Fieldbus protocol over UDP/TCP/IP • Definition of a new real-time protocol • Modification of the standard 802.3 MAC layer • Tunneling of TCP/IP over an existing fieldbus Tunneling TCP/IP stack over same physical layers Example: TCP/IP over Interbus Segmentation of IP packets Mittuniversitetet Industriell Datakommunikation - Fieldbus 16

  17. Example: Modbus over TCP Physical layer: Ethernet 10/100 Mbit/s Characteristics: One master, 247 slaves (like Modbus) Overhead of 54 Bytes Mittuniversitetet Industriell Datakommunikation - Fieldbus 17

  18. REAL TIME ETHERNET Ethernet for real time applications Characteristics: • Determinism • Synchronization of communication, I/O and applications (e.g. IEEE1588) • Simple protocol stack (TCP/IP is too complicated for a sensor) • Compatibility with TCP/IP traffic (same infrastructure) - a part of the bandwidth is reserved for TCP/IP - router or gateway (proxy, firewall) for TCP/IP traffic • Difficult coexistence among different RTEs Approaches: • Full -software • Hardware/software Mittuniversitetet Industriell Datakommunikation - Fieldbus 18

  19. Full Ethernet (Modbus/TCP, Ethernet/IP, Profinet IO RT, FFHSE) • Standard Ethernet IEEE802.3, switched and full-duplex, with priority and VLAN • + coexistence, COTS network devices (cost, technology) • - No guarantee of deterministic services Ethernet compatible, but using specific devices (Profinet IO IRT) • Special switches with time slicing (mandatory, no other switches allowed) • + coexistence, deterministic guaranties, priorization of flow • - Uses specific network devices New fieldbus and Ethernet Links (EtherCAT, Sercos III) • Different MAC layer to provide real-time, use of specific devices, gateway • + deterministic, short cycle time, QoS guaranteed (all data in a single frame) • - Specific network devices Mittuniversitetet Industriell Datakommunikation - Fieldbus 19

  20. ETHERCAT Mittuniversitetet

  21. Ethernet for Control Automation Technology (EtherCAT) • Introduced by Beckoff in 2002, sponsored by the open source organization Ethercat in 2003 • A single Ethernet Frame is sent by the unique controller (master) and read or modified by the slaves “on -the- fly” • Not-EtherCAT frames are passed through (coexistence) • Software-based Master, Hardware-based Slaves • Many topologies supported (linear, ring, tree ,…) • Support CAN application protocol CANopen. Mittuniversitetet Industriell Datakommunikation - Fieldbus 21

  22. EtherCAT: the stack Layer ISO/OSI Model ETHERCAT Cyclic Data Exchange 7 Application Acyclic Data Exchange 6 - 3 Fast frame forwarding Mailbox handling 2 Data link IEEE 802.3 MAC 1 100Base-TX 100Base-FX Physical The EtherCAT commands are transported in the data area of an Ethernet telegram and can either be coded via a special Ether type or via UDP/IP. Mittuniversitetet Industriell Datakommunikation 22

  23. EtherCAT: characteristics • Hard Real -Time • Fast Cycle Times within µs • Precise Synchronization • Protocol is processed in hardware • Flexible Topology • Line, Tree, Star, Daisy Chain … • Standard Ethernet Cabling, Cost Effective Components • Master-Slave & Slave-Slave Communication Mittuniversitetet Industriell Datakommunikation 23

  24. EtherCAT: the Hardware Master • EtherCAT master can be implemented on any equipment controller that provides an Ethernet interface. Slave • All the time critical functions (communication) are implemented on FPGA or ASIC • Up to 65 535 devices Transmission medium • No switches or Hub • Ethernet • 100BASE-TX (up to 100m between two nodes) • 100BASE-FX (Fiber - up to 20km between two nodes) • E-bus (LVSD – Low Voltage Differential Signaling) • Short range communication (10 m) • 100 Mbps Mittuniversitetet Industriell Datakommunikation - Fieldbus 24

  25. EtherCAT operating principle • The slaves manipulate the Ethernet frame “on the fly” • Typically only one Ethernet Frame per Cycle • Allows for asynchronous event triggered communication • Switches are not necessary (decreased delay) Mittuniversitetet Industriell Datakommunikation - Fieldbus 25

  26. EtherCAT Frame Ethernet Frame Payload FCS Header EtherCAT … Datagram 1 Datagram n Header Datagram Datagram Data WKC Data WKC Header Header Ethernet Frame • Ethernet Header (14 bytes) • Payload • FCS (4 bytes) Frame Check Sequence EtherCAT Frame • EtherCAT Header (2 bytes) • Datagram • Datagram Header (10 bytes) • Data (0 to 1486 bytes) • WKC (2 bytes) Working Counter Mittuniversitetet Industriell Datakommunikation - Fieldbus 26

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