EPFL, Spring 2017 3 Industrial Communication Networks Automation Overview
3 Industrial Communication Networks 3.1 Field bus principles 3.2 Field bus operation 3.3 Standard field busses 3.4 Industrial wireless communication Industrial Automation | 2017 2
Networks in Automation Hierarchy Engineering Operator Supervision level 2 Control Bus programmable Control level controllers Fieldbus microPLCs direct I/O Field level Sensor-Actuator Bus transducers / actors Course Hierarchy Industrial Automation | 2017 3
What is a field bus ? A data network, interconnecting an automation system, characterized by: - many small data items (process variables) with bounded delay (1ms..1s) - transmission of non-real-time traffic for commissioning and diagnostics - harsh environment (temperature, vibrations, EM- disturbances, water, salt,…) - robust and easy installation by skilled people - high integrity (no undetected errors) and high availability (redundant layout) - clock synchronization (milliseconds to microseconds) - low attachment costs ( € 5.- .. € 50 / node) - moderate data rates (50 kbit/s - 5 Mbit/s), large distance range (10m - 4 km) Industrial Automation | 2017 4
Expectations - reduce cabling - increased modularity of plant (each object comes with its computer) - easy fault location and maintenance - simplify commissioning ( mise en service , IBS = Inbetriebssetzung ) - simplify extension and retrofit - off-the- shelf standard products to build “Lego” -control systems Industrial Automation | 2017 5
The original idea: save wiring marshalling tray dumb devices I/O B bar capacity e f PLC o r e smart devices A COM PLC f field bus t e But: the number of end-points remains the same ! r energy must be supplied to smart devices Industrial Automation | 2017 6
Marshalling (Rangierschiene, Barre de rangement) The marshalling is the interface between the PLC people and the instrumentation people. The fieldbus replaces the marshalling bar or rather moves it piecewise to the process (intelligent concentrator / wiring) Industrial Automation | 2017 7
Different classes of field busses One bus type cannot serve all applications and all device types efficiently... Data Networks Workstations, robots, PCs 10,000 Higher cost Not bus powered Sensor Bus Long messages (e-mail, files) Simple devices Not intrinsically safe Low cost Coax cable, fiber 1000 Bus powered Max distance miles Short messages (bits) frame size Fixed configuration (bytes) Not intrinsically safe Twisted pair Honeywell 100 PV 6000 SP 6000 Max distance 500m AUTO 1 High Speed Fieldbus Low Speed Fieldbus PLC, DCS, remote I/O, motors Process instruments, valves Medium cost Medium cost 10 Not bus powered Bus-powered (2 wire) Messages: values, status Messages: values, status Not intrinsically safe Intrinsically safe Shielded twisted pair Twisted pair (reuse 4-20 mA) Max distance 800m Max distance 1200m 10 100 1000 10,000 source: ABB poll time, milliseconds Industrial Automation | 2017 8
Fieldbus Application: locomotives and drives power line radio cockpit Train Bus diagnosis Vehicle Bus brakes power electronics motors track signals data rate 1.5 Mbit/second delay 1 ms (16 ms for skip/slip control) medium twisted wire pair, optical fibers (EM disturbances) number of stations up to 255 programmable stations, 4096 simple I/O integrity very high (signaling tasks) cost engineering costs dominate Industrial Automation | 2017 9
Fieldbus Application: automobile redundant Monitoring redundant ECU board network and board network Board network ECU ECU Diagnosis 12V und 48V ECU c Brakes ECU ECU ECU 4 - Electromechanical wheel brakes - Redundant Engine Control Units - Pedal simulator - Fault-tolerant 2-voltage on-board power supply - Diagnostic System Industrial Automation | 2017 10
Networking busses: electricity network control: myriads of protocols Inter-Control Center Protocol SCADA IEC 870-6 ICCP High control control control HV Voltage center center center Modicom IEC 870-5 DNP 3.0 Conitel RP 570 serial links (telephone) RTU RTU RTU RTU Remote Terminal Units COM RTU substation substation Medium MV Voltage FSK, radio, DLC, cable, fiber,... RTU RTU RTU RTU houses Low LV Voltage low speed, long distance communication, may use power lines or telephone modems. Problem: diversity of protocols, data format, semantics... Industrial Automation | 2017 11
Fieldbus over a wide area: example wastewater treatment Pumps, gates, valves, motors, water level sensors, flow meters, temperature sensors, gas meters (CH 4 ), generators, etc are spread over an area of several km 2 . Some parts of the plant have to cope with explosives. Industrial Automation | 2017 12
Engineering a fieldbus: consider data density (Example: Power Plants) Acceleration limiter and prime mover: 1 kbit in 5 ms Burner Control: 2 kbit in 10 ms For each 30 m of plant: 200 kbit/s Fast controllers require at least 16 Mbit/s over distances of 2 m Data transmitted from periphery or from fast controllers to higher level Slower links to control level through field busses over distances of 1-2 km. The control stations gather data at rates of about 200 kbit/s over distances of 30 m. The control room computers are interconnected by a bus of at least 10 Mbit/s, over distances of several 100 m. Field bus planning : estimate data density per unit of length or surface, response time and throughput over each link. Industrial Automation | 2017 13
3 Industrial Communication Networks 3.1 Field bus principles 3.2 Field bus operation 3.3 Standard field busses 3.4 Industrial wireless communication Industrial Automation | 2017 14
Assessment • What is a field bus ? • Which of these qualities are required: 1 Gbit/s operation Frequent reconfiguration Plug and play Bound transmission delay Video streaming • How does a field bus support modularity ? • Which advantages are expected from a field bus ? Industrial Automation | 2017 15
Objective of the field bus Distribute process variables to all interested parties: • source identification: requires a naming scheme • accurate process value and units • quality indication: {good, bad, substituted} • time indication: how long ago was the value produced • (optional description) source value quality time description Industrial Automation | 2017 16
Data format minimum In principle, the bus could transmit the process variable in clear text (even using XML..) However, this is quite expensive and only considered when the communication network offers some 100 Mbit/s and a powerful processor is available to parse the message More compact ways such as ASN.1 have been used in the past with 10 Mbit/s Ethernet ASN.1: (TLV) type length value Field busses are slower (50kbit/s ..12 Mbits/s) and thus more compact encodings are used. Industrial Automation | 2017 17
Datasets Field busses devices have a low data rate and transmit always the same variables. It is economical to group variables of a device in the same frame as a dataset. A dataset is treated as a whole for communication and access. A variable is identified within a dataset by its offset and its size Variables may be of different types, types can be mixed. dataset binary variables analog variables dataset wheel air line time speed pressure voltage identifier stamp 0 16 32 48 64 66 70 all door closed bit offset size lights on heat on air condition on Industrial Automation | 2017 18
Dataset extension and quality To allow later extension, room is left in the datasets for additional variables. Since the type of these future data is unknown, unused fields are filled with '1". To signal that a variable is invalid, the producer overwrites the variable with "0". Since both an "all 1" and an "all 0" word can be a meaningful combination, each variable can be supervised by a check variable, of type ANTIVALENT2: dataset check variable value correct variable 0 1 0 1 1 1 0 0 0 1 error 0 0 0 0 0 0 0 0 0 0 undefined 1 1 1 1 1 1 1 1 1 1 00 = network error chk_offset 01 = ok 10 = substituted var_offset 11 = data undefined A variable and its check variable are treated indivisibly when reading or writing The check variable may be located anywhere in the same data set. Industrial Automation | 2017 19
Hierarchical or peer-to-peer communication PLC PLC alternate central master / slave: hierarchical AP “master” master AP all traffic passes by the master (PLC); adding an alternate master is difficult (it must be both master and slave) “slaves” input output PLC PLC peer-to-peer: distributed PLC “masters” AP AP AP PLCs may exchange data, share inputs and outputs allows redundancy and “distributed intelligence” devices talk directly to each other “slaves” input output AP Application separate bus master from application master ! Industrial Automation | 2017 20
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