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

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 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

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

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

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

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

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

Profisafe Mittuniversitetet

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

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

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

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

Real Time Ethernet (RTE) Mittuniversitetet

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

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

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

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

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

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

ETHERCAT Mittuniversitetet

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

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

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

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

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

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