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Aug 22, 2023 396 likes •914 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

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Mittuniversitetet

PROFIBUS PA

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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.

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Mittuniversitetet 3 Industriell Datakommunikation - Fieldbus

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)

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The role of a coupler in Profibus-PA

Industriell Datakommunikation - Fieldbus

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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.

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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.

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Reference

  • Official Website
  • PROFIBUS System Description
  • Practical Industrial Data Communications - Ch. 14a
  • Industrial Communication Systems - Ch. 32

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Profisafe

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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.

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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)

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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 .

Industriell Datakommunikation - Fieldbus

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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
  • f 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.

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Reference

  • Official Website
  • PROFIsafe System Description

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Real Time Ethernet (RTE)

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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

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Ethernet is just a transportation medium, what matters are the higher layers.

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Tunneling

TCP/IP stack over same physical layers Example: TCP/IP over Interbus Segmentation of IP packets 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

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Example: Modbus over TCP Physical layer: Ethernet 10/100 Mbit/s Characteristics: One master, 247 slaves (like Modbus) Overhead of 54 Bytes

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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

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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

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ETHERCAT

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Ethernet for Control Automation Technology (EtherCAT)

  • Introduced by Beckoff in 2002, sponsored by the open source
  • rganization 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.

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Mittuniversitetet Industriell Datakommunikation 22 Layer ISO/OSI Model ETHERCAT 7 Application Cyclic Data Exchange Acyclic Data Exchange 6 - 3 2 Data link Fast frame forwarding Mailbox handling IEEE 802.3 MAC 1 Physical 100Base-TX 100Base-FX

EtherCAT: the stack 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.

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Mittuniversitetet Industriell Datakommunikation 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
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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

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  • 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)

EtherCAT operating principle

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EtherCAT Frame

Ethernet Header FCS Frame Payload EtherCAT Header Datagram 1 Datagram n … Datagram Header WKC Data Datagram Header WKC Data

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

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Addressing

Datagram headers contain a 32 bit address which can be used either for logical or physical addressing.

Address Position Offset Configuration Address Offset Logical Address

32 bit 16 bit 16 bit

Physical Addressing

  • Position address (incremental

addressing)

  • Used during start-up to assign

a fixed address

  • Every telegram is addressed

to a single slave Logical Addressing

  • 32-bit field address (4GByte address space with bit-wise capability)
  • A table in the slave devices is used to convert logical address into

physical address

  • Improve the utilization ratio of the Datagram

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Redundancy

  • The ring structure

In case of a Node/Cable failure, the slaves can close the loop The master requires only an addition Ethernet port

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Reference

  • Official Website
  • Introduction
  • Introduction 2
  • Industrial Communication Systems - Ch. 38

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PROFINET IO

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PROFINET requirements for the Phy Layer

  • At least 100 Mbps (100 Base-TX, 100 Base-FX);
  • Switches (Hub cannot be used)
  • Switches have to be designed to operate with fast Ethernet (100 Mb)
  • Switches should support prioritized telegrams according to IEEE 802.1Q
  • Link distance < 100 m

PROFINET allows the use of proxy to integrate existing fieldbus systems

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The PROFINET IO-System

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PROFINET IO-Controller: Exhange Data to and from the IO-Device associated; Runs the user control program PROFINET IO-Device: Field device connected to the IO-Controller PROFINET IO-Supervisor: HMI and Diagnostic

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1 2 3 3 TYPES OF TRAFFIC

TCP/IP TRAFFIC REAL TIME TRAFFIC ISOCHRONOUS REAL TIME TRAFFIC

High performance (jitter < 1μs) Isochronous Data Event Triggered Data Cyclic Data Configuration and Diagnostic Data Initialization Procedures

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Mittuniversitetet Industriell Datakommunikation 34

Every data exchange is embedded into an AR (Application Relation) Within the AR, CRs (Communication Relations) specify the data explicitly. Profinet IO: Data exchange

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Mittuniversitetet 35 Industriell Datakommunikation - Fieldbus

Isochronous real time data use the channel in different time from standard TCP/IP communications.

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Similarly to Profibus, every device is described by a xml-based GSD

  • file. This contains all the information useful for the configuration of

the device in to the network. Profinet similarly to Profibus PA/DP supports application specific

  • profiles. (e.g. Profisafe)

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Reference

  • Official Website
  • PROFINET System Description
  • Industrial Communication Systems - Ch. 40

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Wireless Industrial Networks

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Mittuniversitetet Industriell Datakommunikation 39

Wired Wireless Cost Steady Decreasing Security Internet Open medium Determinism Good Medium is unreliable Maintenance Cable replacement Batteries (Energy Harvesting) Mobility Limited Extensive Compactness Good Reduced by batteries Wired vs Wireless

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Mittuniversitetet Industriell Datakommunikation 40

Different Wireless technologies compared

IR 802.11 802.15.1 802.15.4 UWB NFC Frequency 800-900 nm 2.4/5 GHz 2.4 Ghz 868-902 MHz, 2.4 GHz 3.1-10.6 GHz 13.56 MHz Data Rate 20 kbps - 16Mbps 11-54 Mbps 1 Mbps 20-250 kbps 100-500 Mbps 106-424 kbps Transmission Distance 1-9 m (LOS) 50-100 m 10 m 10 m <10m 20 cm Power Consumption

  • Typ. 10 mW

1 W 300 mW 100 mW 100 mW Low Application Remote control, Short range transmission WLAN Cable Replacing Control and Automation Localization Short range transmission

ZigBee WirelessHART ISA 100.11a WIA-PA

…

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Mittuniversitetet Industriell Datakommunikation 41

Wireless Sensor Network (WSN) What is important?

  • Reliability
  • Security
  • Self-healing and Self-organizing capabilities
  • Low Energy Consumption

WSN Is a wireless network consisting of autonomous devices that communicate monitoring information from the environment

WSN with mesh topology

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Mittuniversitetet Industriell Datakommunikation 42

  • The reliability of a data transmission is

defined in Bit Error Rate (BER).

  • BER is calculated as the number of bits

that are not transmitted correctly over the total number of transmitted bits.

  • The better the BER, the better the

reliability of the data transmission. Reliability and use in industrial environment Six classes of applications have been defined.

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WirelessHART

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Extension of HART that uses wireless communication. First release in 2007

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Layer ISO/OSI Model HART WirelessHART 7 Application Command Oriented 6 Presentation 5 Session 4 Transport Auto-Segmented transfer of Large Data Set 3 Network Redundant Path, Self Healing Wireless Mesh Network 2 Data link Mechanical/electrical connection, Transmits raw bit stream TDMA/CSMA, Frequency Agile 1 Physical 4-20 mA copper wiring 2.4 GHz wireless, 802.15.4 Phy

Developed for the Process Automation

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Mittuniversitetet Industriell Datakommunikation 45

Analog Wiring vs WirelessHART

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WirelessHART: Physical Layer Based around the IEEE 802.15.4-2006 Phy layer

  • Communication in the ISM band (2.4GHz) with DSSS modulation;
  • Co-existence problem with other technologies;

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Channel hop to avoid busy channels (15 channels)

  • Assess channels before use;
  • Blacklist “bad” channels;
  • Transmit for a short period of time

(good neighbor);

  • Vary transmit power (security benefit

too);

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WirelessHART: Topologies

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WirelessHART: Time Division Multiple Access

Dedicated time slots

  • Allocated based upon

data transfer needs

  • Data is time stamped

Shared time slots

  • Acyclic data transfer for

Asset Management

  • Process (valve)

signatures

  • Alarm reporting

Industriell Datakommunikation - Fieldbus

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Reference

  • Official Website
  • Industrial Communication Systems - Ch. 53

49 Industriell Datakommunikation - Fieldbus

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Labs

  • Lab1

May 17 –L109-

  • Lab2

May 18 –L109-

  • Lab3

May 28 –L109- MatlabR2012a or later and Simulink are required.

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