Transcript Fieldbus

FIELDBUS
Industriell datakommunikation
Luca Beltramelli
Mittuniversitetet
Email: [email protected]
References
Book:
Practical Industrial Data Communications
by Reynders, Deon
Mackay, Steve
Wright, Edwin
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Program
02/05/2016
• Seminar I:
• Intro to Fielbus and Industrial Automation
• Overview of fieldbus technologies (Part 1)
03/05/2016
• Seminar II:
• Overview of fieldbus technologies (Part 2)
04/05/2016
• LAB:
• Simulating Fieldbus using Matlab and TrueTime
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What is a Fieldbus?
Fieldbuses are real-time networks for sensors and actuators.
Used for the communication among sensors, actuators and controllers
Data and
Nodes
Management
Fieldbus
include
Safety and
Security
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Diagnostic
and
Integration
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The Automation Pyramid
Office Network: TCP IP,
Ethernet
Plant Network: Ethernet,
ControlNet
Fieldbus: FF,
PROFIBUS PA, LON
Simple fieldbus or
Sensor Bus:
CAN, DeviceNet, SDS, ASI-bus,
Interbus-S
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Fieldbuses: the beginning
Traditionally in industries the communication was completly analog
Moving to digital communication brings many benefits:
• Immunity to noise;
• Less cabling;
• Better Diagnostic;
Q: Why 4-20 mA?
20
[mA]
Fieldbus replace the traditional
4 – 20 mA analog technology.
4
Measurement Range
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4-20 mA vs Fieldbus
4-20 mA
Information
Signal Integrity
Communication
Layer
Diagnostic
Fieldbus
Analog
Digital
Low (EMI,
Attenuation, ...)
High
Phyisical Physical, Data Link,
Application
Minimal
Extensive
Installation cost
High
Low
Cost per device
Low
High
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Fieldbuses: field devices
One of the key requirements for the adoption of fieldbus is
the distribuited intelligence.
To access the fieldbus sensors and actuators are required
to implement a communication stack.
Smart Sensors:
• Computetion capabilities;
• Communicate in a digital way;
• They use a communication standard (at least layers 1 and 2 of
ISO/OSI);
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Fieldbus Evolution
From the first proprietary solutions (’80) to the actually used standard (’90)
Predecessors
1969
Proprietary solutions
International
Standards
1991 … 1996
1979
First PLC
(Modicon 084)
MODBUS
CAN
HART
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Profibus FMS/DP/PA
FOUNDATION fieldbus
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Fieldbus Evolution
From the first proprietary solutions (’80) to the actually used standard (’90)
Industrial Ethernet
2001 … 2006
Wireless Networks
2007
2009
2010
EtherCAT (2003)
Eth/IP (2001)
Profinet (2004)
SafetyNET (2006)
…
Release of
WirelessHART
Release of
ISA100.11a
Introduction
of IO-Link
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Fieldbus and the OSI Model
Layer
ISO/OSI Model
Layer
ISO/OSI Model
7
6
5
4
3
Application
Presentation
Session
Transport
Network
7
Application
2
Data link
2
Data link + MAC
1
Physical
1
Physical
OSI Model
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Implementation Model
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Fieldbus: the applications
Factory
Automation
Process
Automation
FIELDBUS
Automative
Home
Automation
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FIELDBUS FOR AUTOMOTIVE
Safety
• Redundancy, Check codes, very low data error rate
Determinism
• Synchronized communications, TDMA
Wireless networks are considered unreliable and, up to now, are used for
entertainment and extravehicular communications
IEEE 802.11p for data exchange between high-speed vehicles (V2V) in
the licensed ITS band of 5.9 GHz (5.85-5.925 GHz).
Examples:
LIN – very simple protocol (e.g. window automation)
CAN – CAN version with TDMA (e.g. ABS)
FlexRay – New (BMW, Audi, Mercedes …), increases baud rate with
respect to CAN (up to 10Mbytes/s) and adopts a TDMA with dynamic
slots assignment.
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FIELDBUS FOR HOME AUTOMATION
The low-cost is mandatory, non-invasive and mobile sensors
could be the future (wireless fieldbuses)
Primary needs: low-cost, simple installation, auto-configuration
There are a lot of proprietary solutions:
•
•
•
CAN – based solutions (different application layers)
Some emerging Ethernet-based solutions (security and costs problems)
EIB, EHS and Batibus converge into Konnex (KNX) (ISO/IEC 145433,EN50090)
• European Standard (Siemens, ABB, Bticino, Vimar, etc.)
• Wired and wireless
•
LONWorks
• Widespread in USA
• Supported by electronic devices (Neuron Chips produced by
Toshiba, Freescale, Cypress)
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FIELDBUS FOR PROCESS AUTOMATION
• Safety is mandatory (particularly in chemical, oil, industries,…)
• High availability (redundant system)
• Reduce wiring (long distances) - the bus also powers the devices
• Speed is not important
• Cycle time are in the order of several hundreds of ms
• Timestamp is important in case of fault (resolution ~ 100 ms)
There are only two big players:
• PROFIBUS PA
• FIELDBUS FOUNDATION (it has local loop control between devices)
They use the same physical layer (Manchester, powered, 31.25kbaud)
but they are totally different at the data layer.
Wireless can be used for non critical processes, as it reduce wiring and
allow a range extension by suitable network topologies (mesh)
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FIELDBUS FOR FACTORY AUTOMATION
The main goals are:
• Fast and low-cost
• High rejection to noise
• Safety (e.g.protection of human operator)
Speed can be very important
• Reduced communication times means more products, i.e.
higher gain…
• Motion control (motor drives) need isochronous
communication
More than 20 fieldbuses for Factory Automation
• PROFIBUS DP is the most diffused but holds only the 15%
of the market (RS485, max 12Mbit/s)
• DeviceNet, CANOpen, use CANbus (max 1Mbit/s) Factory
environment is hostile for wireless technology (metal,
walls,…)
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The Ideal Fieldbus: some characteristics
• Transfers a “big number” of small length values;
• Supports real-time traffic (Upper bounded response times, ex. 1ms..1s);
• Operates in hazardous environments (high temperature, vibrations, etc.);
• Is robust and easy to install;
• Has high availability (e.g. redundant architectures);
• Has continuous supervision and diagnostic;
• Manages long distances (100m .. 4 km);
• Has good data transmission rate (e.g. 50 kbit/s … 5 Mbit/s);
• Supports clock synchronization (e.g. milliseconds up to microseconds);
• Manages non real-time traffic for maintenance and diagnosis.
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Fieldbus: the topology
Fieldbus daisy chain topology
Tree topology
• Flexibility of the hardware of the measurement system
• Cables reduction
• Every node can share information with other nodes
•More “powerful” sensors (HW & FW costs)
•Different delays from node to the measurement
system
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Fieldbus: distributed measurements
In Industry to ensure good control and monitoring actions, sensor nodes
should…
A. Be synchronized
• Synchronization protocols
• Delay
• Jitter
B. Be identified and localized
• Identifier for each sensor
• Localization of moving sensor
C. Be qualified
• Uncertainty measurement
• Status report
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Fieldbus: Measurement and Control
Measurement
• Data require a time reference
(timestamp)
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Loop Control
• Delay must be limited
(deterministic transmission)
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Fieldbus: Networked Control System (NCS)
Process
Actuator
Sensor
Communication Network
Controller
Close loops in Process Automation
Close loops in Factory Automation
• Process (temperature, humidity,…Tcycle > 1s)
• Motion (positioning, speed, torque… Tcycle < 1 ms)
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Fieldbus: a complex scenario
Ethernet
Seriplex
Profibus-FMS
CAN
Batibus
WorldFIP
ProfibusPA
Profibus-DP
PROFInet
CANOpen
FlexRay
EtherLink
AND MANY OTHERS
FieldBus
Sercos
Foundation
BacNET
!!!
ControlFIP
Hart
IEEE 802.11
ModBus-RTPS
Modbus
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DeviceNet
Profisafe
ControlNet
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M-Bus
Ethercat
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HART
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HART (Highway Addressable Remote Transducer)
• Developed in 1980, from 1990 is an open communication technology
for process automation.
• Enables the transmission of digital information superimposed on
analog 4-20 mA communication.
• The 4-20 mA is used for transmitting the analog data from sensor in
the field.
ISO/OSI
Model
Application
HART Commands
2
Data link
HART Protocol Rules
1
Physical
Bell 202 (FSK modulation)
Layer
7
HART
6-3
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“Analog” for sensing information, digital for diagnostics
FSK modulation
‘0’ – 2200 Hz
‘1’ – 1200 Hz
The average value of the Frequency Shift Keying (FSK) modulation is
zero, the analog communication is unaffected by it.
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HART: Point to Point communication
HART: Multi-point communication
Q: can we use analog
communication?
NOT HERE
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HART Telegram
Three classes of commands:
•
Universal Commands
•
Common Practice Commands;
•
Device-Specific Commands.
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Reference
• Official Website
• Practical Industrial Data Communications - Ch. 18a
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MODBUS
RTU and ASCII
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• Application layer (Layer 7) messaging protocol
• Developed by Modicon in 1980
• Mainly Used in SCADA system
• Master-slave protocol
• Communication is initiated by the Master (Client)
• Slaves (Server) communicate only to the Master
• One communication at the time (Unicast or Multicast)
• Peer-to-peer
• UART (RS232, RS485)
• 1 master, <248 slaves
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Modbus message Frame
Communication based around a
Query-Response cycle
The function code in the query tells
the addressed slave device the
action to perform.
(ex. read Input Registers, Force
Single Coil, Read Coil Status )
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• Two serial transmission mode (no coexistence):
• ASCII mode
• 1 byte -> 2 char (0-9, A-F)
• Error Check -> LRC
• Bits per Byte:
• RTU mode
• 1byte -> 8 bit (0 … 255)
• Error Check -> CRC
• Bits per Byte:
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Reference
• Modbus over serial line
• Reference Guide
• Official Website
• Practical Industrial Data Communications - Ch. 8a
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CANbus
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Controller Area Network (CAN)
Developed in ’85 by Bosch for automotive
• Random access bus (32 users, 1Mbaud @ 40m)
• Multi-master bus
• CSMA/CA
• Asynchronous Serial Bus
• 4 frames: DATA (data exchange), REMOTE (request to send
data), ERROR (error signaling, OVERLOAD (temporary
unavailable)
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The CAN standard includes:
• Physical layer
• Data-link layer
• Some message types
• Arbitration rules for bus access
• Methods for fault detection and fault confinement
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Phy layer
• Maximum bitrate 1Mb/s.
• The bitrate depend on the bus length.
• The bitrate is limited to sense the collision between distant nodes.
• Twisted pair cable, differential transmission
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• Bit Coding: NRZ (does not ensure enough edges for synchronization)
• Bit Stuffing
(CAN,…)
(Profibus, Ethernet…)
• “open-collector like”, that is “0” level wins
• Automatic bus release if collision occurs and retransmission
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The Arbitration Field
contains a 11-bit identifier
for the data.
Data with higher priority
have the MSBs at ´0´ and
win the arbitration.
Higher Layer Protocols
•
•
•
•
CANOPEN
DEVICENET
CAN Kingdom
…
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Reference
• Official Website
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PROFIBUS
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PROFIBUS (Process Field Bus)
Three versions of the standard:
• Profibus FMS (1991)
• PLC-PLC, PLC-SCADA, PLC-Field device (complex, obsolete)
• Profibus DP (1994)
• Simpler than FMS, normally 1 master (PLC), several slaves (field
devices)
• Market leader
• Profibus PA (1995)
• Different and more robust physical layer (IEC 61158-2)
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ISO/OSI
Model
Layer
FMS
DP
DP - Profiles
User
7
FMS Devices Profiles
Application
PA
PA - Profiles
DP - Acyclic Part
DP - Cyclic Part
Fieldbus Message Specification
(FMS)
6-3
2
Data link
(Fieldbus Data Link (FDL)
1
Physical
RS-485 Fiber Optic
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IEC Interface
IEC 61158-2 (Manchester
Encoded Power Bus)
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Profibus: the actors
• DPM1 (Master Class 1):central controller which exchanges data
with the connected I/O devices (slaves).
• Determines the baudrate.
• Handles the Token;
• Several class1 masters are permitted, typical devices are
PLC, PC.
• DPM2 (Master Class 2): diagnostic and startup tool, typically a
configuration tool, can control one slave at a time.
• Slave: passive station which acknowledges messages or
answers per request
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• At least one master is mandatory.
• Profibus networks allow for multiple masters.
• In total 127 stations can be addressed
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Master-Slave Communication
The master with the token can make use of
communications to address any other stations
(masters and slaves).
DP Slave State Machine
The slave is in one of four possible states:
• Power_ON / Reset
• Wait for Parameters
• Wait for Configuration
• Data Exchange
Cyclic data exchange between a Class 1
master and a DP slave can only take place if
the DP slave is in the data-exchange state
(DXCHG).
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Master-Master Communication
A device can consist of multiple functions:
•
a simple master master communication
via the master - slave combination;
•
whenever one master has the token the
other PLC can be a slave to this
master.
Using a DP-DP gateway:
•
combination of two mono master
systems;
•
simple data exchange between the
two masters up to 244 byte.
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Profibus transmission media
 RS-485




Twisted cable
Baudrate 9.6 kbit/s to 12 Mbit/s
Maximum 32 devices
Distance can be extended by means of repeaters
• 12 Mbit/s @ 100 m
• 187.5 kbit/s @ 1000 m
 Fiber Optic
 Single and Multi Mode
 Baudrate 9.6 kbit/s to 12 Mbit/s
 Distance can be extended by means of repeater to 100 km
 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
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Fieldbus Data Link
• 4 types of frames
• Identified by the value of the first byte (Start Delimiter)
SYN:
SD1
SD2
SD3
SD4
10h
68h
A2h
DCh
33 bits at 1
01101000
10100010
00010000
11011100
Hamming Distance equals
to 4
Note: SD3 practically unused
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Message SD2 (data exchange)
SD2 Start Delimiter (68H)
LE Information length (from 4 to 249)
LEr Information length repeated (Hamming distance = 4)
DA Destination address
SA Source address
FC Frame Control
DATA UNIT Data field (max length 246)
FCS Frame Check Sequence
ED End Delimiter (16H)
L Information length (L = from 4 to 249)
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Message SD1 (data request or Ack)
SD1 Start Delimiter (10H)
DA Destination address
SA Source address
FC Frame Control
FCS Frame Check Sequence
ED End Delimiter (16H)
L Information length (L = 3)
Message SD4 (token transfer)
SD4 Start Delimiter (DCH)
DA Destination address
SA Source address
Message SC (short Ack)
SC Short acknowledgment (E5H)
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GSD file (General Station Description)
• each slave or master class 1 device on PROFIBUS needs to have a
device description file, the characteristic of each PROFIBUS device is
described in the GSD-File;
• the GSD-file contains all device specific parameters e.g.:
•
•
•
•
•
Supported Baudrate
Supported Message Length
Number of input / output data
Meaning of diagnostic messages
Options for modular devices e.g. which are available
• text file (ASCII-format);
• each configuration tool relates to the GSD information.
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PROFIBUS PA
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• 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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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
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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 “Link” can reduce the DP baud rate acting as a slave DP and a
master PA.
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Reference
• Official Website
• PROFIBUS System Description
• Practical Industrial Data Communications - Ch. 14a
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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-oflife")
• 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 .
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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
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.
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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 basically just a transportation medium, what matters are
the upper layers.
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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
Q: Which of the bus we have seen
so far can be more easily
encapsulated in TCP/IP?
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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
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.
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EtherCAT: the stack
Layer
ISO/OSI Model
ETHERCAT
7
Application
Cyclic Data Exchange
Acyclic Data Exchange
6-3
2
Data link
1
Physical
Fast frame forwarding
Mailbox handling
IEEE 802.3 MAC
100Base-TX 100Base-FX
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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EtherCAT: characteristics
• Hard Real-Time
• Fast Cycle Times within µs
• Precise Synchronization
• Protocol is processed in hardware
• Fast Cycle Times (<100ns)
• 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)
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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)
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EtherCAT Frame
Ethernet
Header
Frame Payload
EtherCAT
Header
…
Datagram 1
Datagram
Header
Data
FCS
WKC
Datagram n
Datagram
Header
Data
WKC
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.
Physical Addressing
• Position address (incremental
addressing)
• Used during start-up to assign
a fixed address
• Every telegram is addressed
to a single slave
32 bit
Address
16 bit
16 bit
Position
Offset
Configuration Address
Offset
Logical Address
Logical Addressing
• 32-bit field address (4GByte address space with bit-wise capability)
• A table is used to convert logical address into physical address
• Improve the efficiency in the use of the Datagram
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Redundancy
• The ring structure
In case of a Node/Cable failure,
the slaves can close the loop
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The master requires only an
addition Ethernet port
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Reference
• Official Website
• Introduction
• Introduction 2
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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
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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3 TYPES OF TRAFFIC
1 TCP/IP TRAFFIC
Configuration and Diagnostic Data
Initialization Procedures
2 REAL TIME TRAFFIC
Event Triggered Data
Cyclic Data
3 ISOCHRONOUS REAL TIME TRAFFIC
High performance (jitter < 1μs)
Isochronous Data
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Profinet IO: Data exchange
Every data exchange is embedded into an AR (Application Relation)
Within the AR, CRs (Communication Relations) specify the
data explicitly.
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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
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Wireless Industrial Networks
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Wired vs Wireless
Wired
Wireless
Cost
Steady
Decreasing
Security
Internet
Open medium
Determinism
Good
Medium is unreliable
Maintenance
Cable replacement
Batteries
(Energy Harvesting)
Limited
Extensive
Good
Reduced by batteries
Mobility
Compactness
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93
Different Wireless technologies compared
IR
Frequency
802.11
802.15.1
802.15.4
UWB
NFC
800-900 nm
2.4/5 GHz
2.4 Ghz
868-902 MHz,
2.4 GHz
3.1-10.6
GHz
13.56 MHz
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
10-10 m
<10m
20 cm
Power
Consumption
Typ. 10 mW
1W
300 mW
100 mW
100 mW
Low
Remote control,
Short range
transmission
WLAN
Cable
Replacing
Control and
Automation
Localization
Short range
transmission
Data Rate
Application
ZigBee
WirelessHART
ISA 100.11a
WIA-PA
…
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94
Wireless Sensor Network (WSN)
Is a wireless network consisting of autonomous devices that
communicate monitoring information from the environment
What is important?
• Reliability
• Security
• Self-healing and Self-organizing capabilities
• Low Energy Consumption
WSN with mesh topology
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Reliability and use in industrial environment
• 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.
Six classes of application have been
defined.
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WirelessHART
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Extension of HART that uses wireless communication.
First release in 2007
Developed for the Process Automation
7
6
5
4
ISO/OSI
Model
Application
Presentation
Session
Transport
3
Network
2
Data link
1
Physical
Layer
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HART
WirelessHART
Command Oriented
Auto-Segmented transfer of Large Data Set
Redundant Path, Self Healing
Wireless Mesh Network
Mechanical/electrical connection,
TDMA/CSMA,
Transmits raw bit stream
Frequency Agile
2.4 GHz wireless,
4-20 mA copper wiring
802.15.4 Phy
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98
Analog Wiring vs WirelessHART
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Industriell Datakommunikation
99
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;
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
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Reference
• Official Website
• wirelessHART tech notes
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