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Industrial Automation Automation Industrielle Industrielle Automation 3 Industrial Communication Systems 3.1Field Bus: principles Buses de terreno: principios.

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Presentation on theme: "Industrial Automation Automation Industrielle Industrielle Automation 3 Industrial Communication Systems 3.1Field Bus: principles Buses de terreno: principios."— Presentation transcript:

1 Industrial Automation Automation Industrielle Industrielle Automation 3 Industrial Communication Systems 3.1Field Bus: principles Buses de terreno: principios Bus de terrain: principes Feldbusse: Grundlagen CAN, DeviceNet, SDS, ASI-bus, Interbus-S Ethernet, ControlNet TCP - IP Ethernet Sensor Busses simple switches etc. Plant Network Office network Fieldbus intelligent field devices FF, PROFIBUS, MVB, LON

2 Field buses: principles 3.1 - 2 Industrial Automation 2013 Field bus: principles 3.1 Field bus principles 3.2 Field bus operation Centralized - Decentralized Cyclic and Event Driven Operation 3.3 Standard field busses

3 Field buses: principles 3.1 - 3 Industrial Automation 2013 Sensor/ Actor Bus Field bus Programmable Logic Controller Plant bus SCADA level Plant Level Field level File Edit Engineering Operator 2 12 2 33 23 4 Location of the field bus in the plant hierarchy direct I/O Sensor / Actor

4 Field buses: principles 3.1 - 4 Industrial Automation 2013 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)

5 Field buses: principles 3.1 - 5 Industrial Automation 2013 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

6 Field buses: principles 3.1 - 6 Industrial Automation 2013 The original idea: save wiring PLC But: the number of end-points remains the same ! energy must be supplied to smart devices field bus COM marshalling bar I/O PLC dumb devices (Rangierung, tableau de brassage (armoire de triage) tray capacity

7 Field buses: principles 3.1 - 7 Industrial Automation 2013 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)

8 Field buses: principles 3.1 - 8 Industrial Automation 2013 Different classes of field busses poll time, milliseconds 10 100 1000 10,000 10100100010,000 Sensor Bus Simple devices Low cost Bus powered Short messages (bits) Fixed configuration Not intrinsically safe Twisted pair Max distance 500m Low Speed Fieldbus Process instruments, valves Medium cost Bus-powered (2 wire) Messages: values, status Intrinsically safe Twisted pair (reuse 4-20 mA) Max distance 1200m High Speed Fieldbus PLC, DCS, remote I/O, motors Medium cost Not bus powered Messages: values, status Not intrinsically safe Shielded twisted pair Max distance 800m Data Networks Workstations, robots, PCs Higher cost Not bus powered Long messages (e-mail, files) Not intrinsically safe Coax cable, fiber Max distance miles One bus type cannot serve all applications and all device types efficiently... source: ABB frame size (bytes)

9 Field buses: principles 3.1 - 9 Industrial Automation 2013 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.

10 Field buses: principles 3.1 - 10 Industrial Automation 2013 Fieldbus over a wide area: example wastewater treatment Japan Malaysia Numerous analog inputs/outputs (AI/AO), low speed (37 kbit/s) segments (Hart) merged to 1 Mbit/s links (H1 Speed Fieldbus). source: Kaneka, Japan Junction Box Motor Control Center

11 Field buses: principles 3.1 - 11 Industrial Automation 2013 Fieldbus Application: locomotives and drives cockpit motorspower electronicsbrakes power line track signals Train Bus diagnosis radio data rate delay medium number of stations 1.5 Mbit/second 1 ms (16 ms for skip/slip control) twisted wire pair, optical fibers (EM disturbances) up to 255 programmable stations, 4096 simple I/O Vehicle Bus costengineering costs dominate integrityvery high (signaling tasks)

12 Field buses: principles 3.1 - 12 Industrial Automation 2013 Fieldbus Application: automobile - Electromechanical wheel brakes - Redundant Engine Control Units - Pedal simulator - Fault-tolerant 2-voltage on-board power supply - Diagnostic System

13 Field buses: principles 3.1 - 13 Industrial Automation 2013 Networking busses: Electricity Network Control: myriads of protocols low speed, long distance communication, may use power lines or telephone modems. Problem: diversity of protocols, data format, semantics...

14 Field buses: principles 3.1 - 14 Industrial Automation 2013 Engineering a fieldbus: consider data density (Example: Power Plants)  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. 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 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.

15 Field buses: principles 3.1 - 15 Industrial Automation 2013 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 ?

16 Industrial Automation Automation Industrielle Industrielle Automation 3.2Field bus operation Buses de terreno: modo de trabajo Bus de terrain: mode de travail Feldbus: Arbeitsweise 3 Industrial Communication Systems

17 Field buses: principles 3.1 - 17 Industrial Automation 2013 Fieldbus - Operation 3.1 Field bus principles 3.2 Field bus operation Data distribution Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

18 Field buses: principles 3.1 - 18 Industrial Automation 2013 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 (description) timequalityvaluesource description

19 Field buses: principles 3.1 - 19 Industrial Automation 2013 Data format 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 Field busses are slower (50kbit/s..12 Mbits/s) and thus more compact encodings are used. timequalityvaluesource description valuelengthtypeASN.1: (TLV) minimum

20 Field buses: principles 3.1 - 20 Industrial Automation 2013 Datasets wheel speed air pressure line voltage time stamp analog variables binary variables all door closed lights on heat on air condition on bit offset 163248064 6670 size 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 identifier dataset

21 Field buses: principles 3.1 - 21 Industrial Automation 2013 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: 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. dataset

22 Field buses: principles 3.1 - 22 Industrial Automation 2013 hierarchical or peer-to-peer communication AP all traffic passes by the master (PLC); adding an alternate master is difficult (it must be both master and slave) inputoutput PLCs may exchange data, share inputs and outputs allows redundancy and “distributed intelligence” devices talk directly to each other separate bus master from application master ! inputoutput PLC central master / slave: hierarchical peer-to-peer: distributed “slaves” “master” “slaves” “masters” alternate master AP Application

23 Field buses: principles 3.1 - 23 Industrial Automation 2013 application processor application processor Broadcasts Most variables are read in 1 to 3 different devices Broadcasting messages identified by their source (or contents) increases efficiency. … instances … = variable application processor plant image plant image plant image = distributed database The bus refreshes plant image in the background Each station snoops the bus and reads the variables it is interested in. Each device is subscribed as source or as sink for some process variables Only one device is source of a certain process variable (otherwise collision) The replicated traffic memories can be considered as "caches" of the plant state (similar to caches in a multiprocessor system), representing part of the plant image. bus plant image

24 Field buses: principles 3.1 - 24 Industrial Automation 2013 Transmission principle The previous operation modes made no assumption, how data are transmitted. The actual network can transmit data cyclically (time-driven) or on demand (event-driven), or a combination of both.

25 Field buses: principles 3.1 - 25 Industrial Automation 2013 Cyclic versus Event-Driven transmission event-driven: send when value change by more than x% of range limit update frequency !, limit hysteresis cyclic: send value strictly every xx milliseconds nevertheless transmit: - every xx as “I’m alive” sign - when data is internally updated - upon quality change (failure) misses the peak (Shannon-Nyquist!) always the same, why transmit ? how much hysteresis ? - coarse (bad accuracy) - fine (high frequency) time individual period hysteresis

26 Field buses: principles 3.1 - 26 Industrial Automation 2013 Fieldbus: Cyclic Operation mode 3.1 Field bus principles 3.2 Field bus operation Data distribution Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

27 Field buses: principles 3.1 - 27 Industrial Automation 2013 Traffic Memory: implementation Bus and Application are decoupled by shared memory, the Traffic Memory, (content addressed memory, CAM, also known as communication memory); process variables are directly accessible by application. Ports (holding a dataset) Application Processor Bus Controller Traffic Memory Associative memory two pages ensure that read and write can occur at the same time (no semaphores !) bus an associative memory decodes the addresses of the subscribed datasets

28 Field buses: principles 3.1 - 28 Industrial Automation 2013 Freshness supervision Applications tolerate an occasional loss of data, but no stale data, which are at best useless and at worst dangerous.  Data must be checked if are up-to-date, independently of a time-stamp (simple devices do not have time-stamping) How: Freshness counter for each port in the traffic memory -Reset by the bus or the application writing to that port -Otherwise incremented regularly, either by application processor or bus controller. -Applications always read the value of the counter before using port data and compare it with its tolerance level. The freshness supervision is evaluated by each reader independently, some readers may be more tolerant than others. Bus error interrupts in case of severe disturbances are not directed to the application, but to the device management.

29 Field buses: principles 3.1 - 29 Industrial Automation 2013 Example of Process Variable API (application programming interface) Simple access of the application to variables in traffic memory: ap_get (variable_name, variable value, variable_status, variable_freshness) ap_put (variable_name, variable value) Optimize: access by clusters (predefined groups of variables): ap_get (cluster_name) ap_put_cluster (cluster_name) Each cluster is a table containing the names and values of several variables. The clusters can correspond to "segments" in the function block programming.

30 Field buses: principles 3.1 - 30 Industrial Automation 2013 Cyclic Data Transmission address devices (slaves) Bus Master plant Principle: master polls addresses in fixed sequence (poll list) 123456 Poll List Individual period RTD N polls time [µs] read transfer time [ms] The duration of each poll is the sum of the transmission time of address and data (bit-rate dependent) and of the reply delayof the signals (independent of bit-rate). address (i) data (i) address (i+1) 10 µs/km 123456123456123456 Individual period 44 µs.. 296 µs Example Execution

31 Field buses: principles 3.1 - 31 Industrial Automation 2013 Round-trip delay of master-slave exchange The round-trip delay limits the extension of the bus master most remote data source repeater closest data sink Master Frame access delay propagation delay (t_pd = 6 µs/km) t_source distance next Master Frame t_ms Slave Frame T_m T_s T_m t_repeat (t_repeat < 3 µs) t_repeat t_sm t_mm

32 Field buses: principles 3.1 - 32 Industrial Automation 2013 Cyclic operation characteristics 2. The delivery delay (refresh rate) is deterministic and constant. 4. No explicit error recovery needed since fresh value will be transmitted in next cycle. To keep the poll time low, only small data items may be transmitted (< 256 bits) 3. The bus is under control of a central master (or distributed time-triggered algorithm). 1. Data are transmitted at fixed intervals, whether they changed or not. Consequence: cycle time limited by product of number of data transmitted and the duration of each poll (e.g. 100 µs / variable x 100 variables => 10 ms) The bus capacity must be configured beforehand. Determinism gets lost if the cycles are modified at run-time.

33 Field buses: principles 3.1 - 33 Industrial Automation 2013 Optimizing Cyclic Operation Problem: Cyclic operation uses fixed portion of the bus' time => Poll period increases with number of polled items => response time slows down Solution: introduce sub-cycles for less urgent periodic variables length: power of 2 multiple of the base period. Notes: The poll cycles should not be modified at run-time (non-determinism) A device exports many process variables with different priorities. If there is only one poll type per device, a device must be polled at the frequency required by its highest- priority data. To reduce bus load, the master polls the process data, not the devices group with period 1 ms time 4a81614b643 1 ms period (basic period) 2 ms period 24a 4 ms period 1 ms 1112

34 Field buses: principles 3.1 - 34 Industrial Automation 2013 Cyclic Transmission with Decoupled Application The bus master scans the identifiers at its own pace. The bus traffic and the application cycles are asynchronous to each other. Traffic Memory cyclic algorithms cyclic algorithms cyclic algorithms cyclic algorithms port address application 1 Ports application 2 4 source port sink port port data sink port cyclic poll bus controller bus master application 3 bus Periodic List Ports bus controller bus controller bus controller bus controller Deterministic behavior, at expense of reduced bandwidth and geographical extension.

35 Field buses: principles 3.1 - 35 Industrial Automation 2013 Example: delay requirement Worst-case delay for transmitting all time critical variables is the sum of: Source application cycle time Individual period of the variable on bus Sink application cycle time 8 ms 16 ms 8 ms = 32 ms subscribers application instances device publisher application instance bus instance device applications bus

36 Field buses: principles 3.1 - 36 Industrial Automation 2013 Fieldbus: Event-driven operation 3.1 Field bus types 3.2 Field bus operation Data distribution Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

37 Field buses: principles 3.1 - 37 Industrial Automation 2013 Event-driven Operation Detection of an event is an intelligent process: Not every change of a variable is an event, even for binary variables. Often, a combination of changes builds an event. Only the application can decide what is an event, since only the application programmer knows the meaning of the variables. Events cause transmission only when state changes. Bus load very low on average, but peaks under exceptional situations since transmissions are correlated by process (christmas-tree effect). event- reporting station event- reporting station event- reporting station plant intelligent stations sensors/ actors

38 Field buses: principles 3.1 - 38 Industrial Automation 2013 Bus interface for event-driven operation Application Processor Bus Controller message (circular) queues bus driver filter application Each transmission on bus causes an interrupt. Bus controller checks address and stores data in message queues. Driver is responsible for removing messages of queue memory and prevent overflow. Filter decides if message can be processed. interrupt

39 Field buses: principles 3.1 - 39 Industrial Automation 2013 Response of Event-driven operation Interruption of server device at any instant can disrupt a time-critical task. Buffering of events can cause unbounded delays Gateways introduce additional uncertainties Since events can occur anytime on any device, stations communicate by spontaneous transmission, leading to possible collisions Caller Application Called Application Transport software Transport software interrupt request indication confirm Bus time

40 Field buses: principles 3.1 - 40 Industrial Automation 2013 Determinism and Medium Access In Busses Although the moment an event occurs is not predictable, the bus should transmit the event in a finite time to guarantee the reaction delay. Events are necessarily announced spontaneously The time required to transmit the event depends on the medium access (arbitration) procedure of the bus. Medium access control methods are either deterministic or not. Non-deterministic Collision (CSMA/CA) Deterministic Central master, Token-passing (round-robin), Binary bisection (collision with winner)

41 Field buses: principles 3.1 - 41 Industrial Automation 2013 Events and Determinism Deterministic medium access is necessary to guarantee delivery time bound but it is not sufficient since events messages are queued in the devices. The average delivery time depends on the length of the queues, on the bus traffic and on the processing time at the destination. Often, the applications influence the event delay much more than the bus does. Real-time Control = Measurement + Transmission + Processing + Acting bus data packets acknowledgements input and output queues events producers & consumers

42 Field buses: principles 3.1 - 42 Industrial Automation 2013 Events Pros and Cons In an event-driven control system, there is only a transmission or an operation when an event occurs. Advantages: Drawbacks: Can treat a large number of events – but not all at the same time Supports a large number of stations System idle under steady - state conditions Better use of resources Uses write-only transfers, suitable for LANs with long propagation delays Suitable for standard (interrupt-driven) operating systems (Unix, Windows) Requires intelligent stations (event building) Needs shared access to resources (arbitration) No upper limit to access time if some component is not deterministic Response time difficult to estimate, requires analysis Limited by congestion effects: process correlated events A background cyclic operation is needed to check liveliness

43 Field buses: principles 3.1 - 43 Industrial Automation 2013 Summary: Cyclic vs Event-Driven Operation sending: application writes data into memory receiving: application reads data from memory the bus controller decides when to transmit bus and application are not synchronized application processor bus controller traffic memory (buffer) decoupled (asynchronous): sending: application inserts data into queue and triggers transmission, bus controller fetches data from queue receiving: bus controller inserts data into queue and interrupts application to fetch them, application retrieves data application processor bus controller queues coupled (with interrupts): events (interrupts)

44 Field buses: principles 3.1 - 44 Industrial Automation 2013 Fieldbus: real-time communication model 3.1 Field bus types 3.2 Field bus operation Centralized - Decentralized Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

45 Field buses: principles 3.1 - 45 Industrial Automation 2013 Mixed Data Traffic represent the state of the plantrepresent state changes of the plant -> Periodic Transmission of Process Variables short and urgent data items Since variables are refreshed periodically, no retransmission protocol is needed to recover from transmission error. -> Sporadic Transmission of Process Variables and Messages infrequent, sometimes long messages reporting events, for: System: initialisation, down-loading,... Since messages represent state changes, a protocol must recover lost data in case of transmission errors Users: set points, diagnostics, status Process DataMessage Data... motor current, axle speed, operator's commands, emergency stops,... periodic phase event sporadic phase time basic period sporadic phase

46 Field buses: principles 3.1 - 46 Industrial Automation 2013 Mixing Traffic is a configuration issue Cyclic broadcast of source-addressed variables is the standard solution in field busses for process control. Cyclic transmission takes a large share of the bus bandwidth and should be reserved for really critical variables. The decision to declare a variable as cyclic or event-driven can be taken late in a project, but cannot be changed on-the-fly in an operating device. A message transmission scheme must exist alongside the cyclic transmission to carry not-critical variables and long messages such as diagnostics or network management An industrial communication system should provide both transmission kinds.

47 Field buses: principles 3.1 - 47 Industrial Automation 2013 Real-Time communication stack The real-time communication model uses two stacks, one for time-critical variables and one for messages Logical Link Control time-critical process variables Management Interface time-benign messages Physical Link (Medium Access) Network (connectionless) Transport (connection-oriented) Session Presentation Application 7 6 Remote Procedure Call 5 4 3 2' 1 connectionless connection-oriented medium access implicit Logical Link Control 2" media common

48 Field buses: principles 3.1 - 48 Industrial Automation 2013 Application View Of Communication R4 Traffic Memory Periodic Tasks R3R2R1 Message Data (unicast) Process Data (Broadcast) E3E2E1 Event-driven Tasks bus Supervisory Data bus controller Message ServicesVariables Services Queues node

49 Field buses: principles 3.1 - 49 Industrial Automation 2013 Cyclic or Event-driven Operation For Real-time ? Data are transmitted at fixed intervals, whether they changed or not. Data are only transmitted when they change or upon explicit demand. cyclic operationevent-driven operation (aperiodic, demand-driven, sporadic)(periodic, round-robin) Worst Case is normal caseTypical Case works most of the time Non-deterministic: delivery time vary widelyDeterministic: delivery time is bound All resources are pre-allocatedBest use of resources message-oriented busobject-oriented bus Fieldbus Foundation, MVB, FIP,..Profibus, CAN, LON, ARCnet The operation mode of the communication exposes the main approach to conciliate real-time constrains and efficiency in a control systems.

50 Field buses: principles 3.1 - 50 Industrial Automation 2013 Fieldbus: Time distribution 3.1 Field bus types 3.2 Field bus operation Data distribution Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

51 Field buses: principles 3.1 - 51 Industrial Automation 2013 Time: TAI and UTC TAI (Temps Atomique International) is the scientific time scale. It is continuously incrementing and will never be reset or discontinued. It is the base of all other scales. UTC (Universal time coordinated) is the legal time. It is the base for the clocks of all countries. It indicates approximately 12:00:00 at solar noon in Greenwich at the Spring equinox (it was formerly called Greenwich Mean Time). The Bureau International des Poids et Mesures (BIPM), Paris, is responsible for the definition of UTC. Rate: UTC and TAI proceed at exactly the same rate; both were identical back in 1961. Leap Seconds: Since 1961, the earth rotation slightly slowed down, days became longer. When the difference between UTC and solar noon exceed 0,9 s, which happens after some years, the BIMP adjusts UTC by letting all clocks insert a leap second, so the last minute of a day lasts 61 seconds (the reverse case is also possible, but very unlikely). Leap seconds cannot be anticipated, since irregularities of the earth’s rotation are unpredictable. In 2011, UTC lagged behind TAI by 34 seconds: when TAI was 2011-02-04 12:00:00, UTC was 2011-02-04 11:59:26. One cannot deduce TAI time from UTC time without a table of all elapsed leap seconds, and UTC cannot be predicted for a given TAI, since the introduction of a leap second is a decision of the BIPM. The system of leap seconds is still subject to discussion and could be revised in the future – it could be abolished in 2015.

52 Field buses: principles 3.1 - 52 Industrial Automation 2013 Time-stamping and synchronisation In many applications, e.g. disturbance logging and sequence-of-events, the exact sampling time of a variable must be transmitted together with its value. => Devices equipped with clock recording creation time of value (not transmission time). To reconstruct events coming from several devices, clocks must be synchronized. considering transmission delays and failures. bus input processing t1t1 t2t2 t3t3 t4t4 t1t1 val 1

53 Field buses: principles 3.1 - 53 Industrial Automation 2013 Example: Phasor information Phasor transmission over the European grid: a phase error of 0,01 radian is allowed, corresponding to +/- 26 µs in a 60 Hz grid or 31 µs in a 50 Hz grid.

54 Field buses: principles 3.1 - 54 Industrial Automation 2013 Time distribution In master-slave busses, the master distribute the time as a bus frame. The slave can compensate for the path delays. Time is relative to the master In demanding systems, time is distributed over separate lines as relative time (e.g. PPS = one pulse per second) or absolute time (IRIG-B), with accuracy of 1 µs. In data networks, a reference clock (e.g. GPS or atomic clock) distributes the time. A protocol evaluates the path delays to compensate them. NTP (Network Time Protocol): about 1 ms is usually achieved. PTP (Precision Time Protocol, IEEE 1588), all network devices collaborate to estimate the delays, an accuracy below 1 µs can be achieved without need for separate cables (but hardware support for time stamping required). (Telecom networks typically do not distribute time, they only distribute frequency)

55 Field buses: principles 3.1 - 55 Industrial Automation 2013 NTP (Network Time Protocol) principle time request time response t1t1 t2t2 t3t3 t4t4 time request time response t’ 1 t’ 2 t’ 3 t’ 4 distance time  network delay servernetworkclient network delay  Measures delay end-to-end over the network (one calculation) Problem: asymmetry in the network delays, long network delays

56 Field buses: principles 3.1 - 56 Industrial Automation 2013 IEEE 1588 principle (PTP, Precision Time Protocol) Grand Master Clock Two calculations: residence time and peer delay All nodes measure delay to peer TC correct for residence time (HW support)

57 Field buses: principles 3.1 - 57 Industrial Automation 2013 IEEE 1588 – 1 step clocks Sync (contains all  + ) residence time Pdelay_Resp (contains t 3 – t 2 ) Pdelay_Req ordinary (slave) clock distance time Sync 1-step transparent clock grand master clock 1-step transparent clock residence time bridge  link delay t2t2 t3t3 Pdelay_Resp t1t1 t4t4 Pdelay_Req t2t2 t3t3 t1t1 t4t4 t2t2 t3t3 t1t1 t4t4 Sync Pdelay_Resp Pdelay_Req  t5t5  t5t5 t6t6 Grandmaster sends the time spontaneously. Each device computes the path delay to its neighbour and its residence time and corrects the time message before forwarding it residence time calculation peer delay calculation

58 Field buses: principles 3.1 - 58 Industrial Automation 2013 References To probe further http://www.ines.zhaw.ch/fileadmin/user_upload/engineering/_Institute_und_Zentr en/INES/IEEE1588/Dokumente/IEEE_1588_Tutorial_engl_250705.pdfhttp://www.ines.zhaw.ch/fileadmin/user_upload/engineering/_Institute_und_Zentr en/INES/IEEE1588/Dokumente/IEEE_1588_Tutorial_engl_250705.pdf http://blog.meinbergglobal.com/2013/11/22/ntp-vs-ptp-network-timing- smackdown/http://blog.meinbergglobal.com/2013/11/22/ntp-vs-ptp-network-timing- smackdown/ http://blog.meinbergglobal.com/2013/09/14/ieee-1588-accurate/

59 Field buses: principles 3.1 - 59 Industrial Automation 2013 Fieldbus: Networking 3.1 Field bus types 3.2 Field bus operation Data distribution Cyclic Operation Event Driven Operation Real-time communication model Time distribution Networking 3.3 Standard field busses

60 Field buses: principles 3.1 - 60 Industrial Automation 2013 Networking field busses Networking field busses is not done through bridges or routers, because normally, transition from one bus to another is associated with: - data reduction (processing, sum building, alarm building, multiplexing) - data marshalling (different position in the frames) - data transformation (different formats on different busses) Only system management messages could be threaded through from end to end, but due to lack of standardization, data conversion is not avoidable today.

61 Field buses: principles 3.1 - 61 Industrial Automation 2013 Networking: Printing Example B C D E PMLS PMLS PMLS PMLS MPS Section Control Line bus (AF100) Section Busses (AF100) Console, Section Supervision Reelstand bus (Arcnet) Reelstand-Gateways Operator bus (Ethernet) Plant-bus (Ethernet) Production Reelstands Printing Towers RPERPDRPCRPB SSCSSDSSESSB multiplicity of field busses with different tasks, often associated with units. main task of controllers: gateway, routing, filtering, processing data. most of the processing power of the controllers is used to route data MPS = Master Printing System LS = Leitstand (section supervision) PM = Print Master SS =Section Steuerung (section control)

62 Field buses: principles 3.1 - 62 Industrial Automation 2013 Assessment What is the difference between a centralized and a decentralized industrial bus ? What is the principle of source-addressed broadcast ? What is the difference between a time-stamp and a freshness counter ? Why is an associative memory used for source-addressed broadcast ? What are the advantages / disadvantages of event-driven communication ? What are the advantages / disadvantages of cyclic communication ? How is time transmitted ? How are field busses networked ?

63 Industrial Automation Automation Industrielle Industrielle Automation 3.3Field bus: standards Buses de terreno estándar Bus de terrain standard Standard-Feldbusse 3 Industrial Communication Systems

64 Field buses: principles 3.1 - 64 Industrial Automation 2013 Field busses: Standard field busses 3.1 Field bus types 3.2 Field bus operation Centralized - Decentralized Cyclic and Event Driven Operation 3.3 Field bus standards International standard(s) HART ASI Interbus-S CAN Profibus LON Ethernet Automotive Busses

65 Field buses: principles 3.1 - 65 Industrial Automation 2013 Different classes of field busses poll time, milliseconds 10 100 1000 10,000 10100100010,000 Sensor Bus Simple devices Low cost Bus powered Short messages (bits) Fixed configuration Not intrinsically safe Twisted pair Max distance 500m Low Speed Fieldbus Process instruments, valves Medium cost Bus-powered (2 wire) Messages: values, status Intrinsically safe Twisted pair (reuse 4-20 mA) Max distance 1200m High Speed Fieldbus PLC, DCS, remote I/O, motors Medium cost Not bus powered Messages: values, status Not intrinsically safe Shielded twisted pair Max distance 800m Data Networks Workstations, robots, PCs Higher cost Not bus powered Long messages (e-mail, files) Not intrinsically safe Coax cable, fiber Max distance miles One bus type cannot serve all applications and all device types efficiently... source: ABB frame size (bytes)

66 Field buses: principles 3.1 - 66 Industrial Automation 2013 Which field bus ? Bitbus FIP P14 P13/42 Profibus-DP MVB ZB10 Spabus MIL 1553 MB90 Arcnet Sigma-i DIN V 43322 IsiBus MODBUS J-1850 Master FB IEEE 1118 (Bitbus) LON Hart Sinec L1 ISP FAIS ISA SP50 * SERCOS ControlNet... Arinc 625 Profibus-FMS Fieldbus Foundation Suconet DIN 66348 (Meßbus) VAN IEC 61158 Partnerbus IHS Instabus EIB Interbus-S PDV Factor MAP Sinec H1 LAC J-1708 ASI Profibus-PA A-bus Batibus CAN SDS DeviceNet Ethernet * * WorldFIP * *

67 Field buses: principles 3.1 - 67 Industrial Automation 2013 Worldwide most popular field busses Interbus-S Profibus (3 kinds) LON Ethernet CANs ASI Manufacturing Process control Building systems Plant bus Automotive, Process control Building Systems Phoenix Contact Siemens, ABB Echelon, ABB all CiA, OVDA, Honeywell Siemens Modbusobsolete point-to-pointmany ControlNetplant busRockwell Fieldbus Foundation, HARTChemical IndustryFisher-Rosemount, ABB 7% 26% 6% 50% 25% 9% 22% 14% 7% Sum > 100%, since many companies use more than one bus BusApplicationSponsorUser* *source: ISA, Jim Pinto (1999) European market in 2002**: 199 Mio €, 16.6 % increase (Profibus: 1/3 market share) **source: Elektronik, Heft 7 2002

68 Field buses: principles 3.1 - 68 Industrial Automation 2013 Field device: example differential pressure transducer The device transmits its value by means of a current loop 4..20 mA current loop fluid

69 Field buses: principles 3.1 - 69 Industrial Automation 2013 4-20 mA loop - the conventional, analog standard (recall) The transducer limits the current to a value between 4 mA and 20 mA, proportional to the measured value, while 0 mA signals an error (wire break) The voltage drop along the cable and the number of readers induces no error. Simple devices are powered directly by the residual current (4mA), allowing to transmit signal and power through a single pair of wires. 4-20mA is basically a point-to-point communication (one source) The 4-20 mA is the most common analog transmission standard in industry transducerreader 1 2 i(t) = 0, 4..20 mA R1R2R3 sensor i(t) = f(v) voltage source 10V..24V R L4 conductor resistance R L2 R L3 R L4 R L1 flow

70 Field buses: principles 3.1 - 70 Industrial Automation 2013 3.3.2 HART Data over 4..20 mA loops

71 Field buses: principles 3.1 - 71 Industrial Automation 2013 HART - Principle HART (Highway Addressable Remote Transducer) was developed by Fisher-Rosemount to retrofit 4-to-20mA current loop transducers with digital data communication. HART modulates the 4-20mA current with a low-level frequency-shift-keyed (FSK) sine-wave signal, without affecting the average analogue signal. HART uses low frequencies (1200Hz and 2200 Hz) to deal with poor cabling, its rate is 1200 Bd - but sufficient. Transmission of device characteristics is normally not real-time critical

72 Field buses: principles 3.1 - 72 Industrial Automation 2013 HART - Protocol Hart communicates point-to-point, under the control of a master, e.g. a hand-held device preamblestartaddresscommandbytecount[status]data checksum 11..5 5..20 (xFF) 11 [2] (slave response) 0..25 (recommended) 1 Master Indication Slave Request Confirmation Response time-out command response Hart frame format (character-oriented, not bit-oriented):

73 Field buses: principles 3.1 - 73 Industrial Automation 2013 Universal commands (mandatory): identification, primary measured variable and unit (floating point format) loop current value (%) = same info as current loop read current and up to four predefined process variables write short polling address sensor serial number instrument manufacturer, model, tag, serial number, descriptor, range limits, … Common practice (optional) time constants, range, EEPROM control, diagnostics,… total: 44 standard commands, plus user-defined commands Transducer-specific (vendor-defined) calibration data, trimming,… HART - Commands

74 Field buses: principles 3.1 - 74 Industrial Automation 2013 HART - Importance Practically all 4..20mA devices come equipped with HART today About 40 Mio devices are sold per year. more info: http://www.thehartbook.com/default.asp http://www.hartcomm.org/

75 Field buses: principles 3.1 - 75 Industrial Automation 2013 3.3.5 CAN Automotive bus

76 Field buses: principles 3.1 - 76 Industrial Automation 2013 CAN (1) - Data Sheet SupportersAutomotive industry, Intel/Bosch, Honeywell, Allen-Bradley StandardSAE (automotive), ISO11898 (only drivers), IEC 61158-x (?) Mediumdominant-recessive (fibre, open collector), ISO 11898 Medium redundancynone Connectorunspecified Distance40m @ 1 Mb/s (A); 400m @ 100kb/s (B); 1000m @ 25kb/s (B) Repeatersunspecified (useless) EncodingNRZ, bit stuffing User bits in frame64 Mastershipmulti-master, 12-bit bisection, bit-wise arbitration Mastership redundancynone (use device redundancy) Link layer controlconnectionless (command/reply/acknowledgement) Upper layersno transport, no session, implicit presentation Application ProtocolsCAL, SDS, DeviceNet (profiles) Chipscomes free with processor (Intel: 82527, 8xC196CA; Philips: 82C200, 8xC592; Motorola: 68HC05X4, 68HC705X32; Siemens: SAB-C167

77 Field buses: principles 3.1 - 77 Industrial Automation 2013 CAN (2) - Analysis –interoperability questionable (too many different implementations) –small data size and limited number of registers in the chips. +strong market presence, Nr 1 in USA (> 12 Mio chips per year) +application layer definition –several incompatible application layers (CiA, DeviceNet, SDS) –strongly protected by patents (Bosch) +supported by user organisations ODVA, Honeywell... +application layer profiles –limited product distance x rate (40 m x Mbit/s) –sluggish real-time response (2.5 ms) +bus analyzers and configuration tools available ”Unix" of the fieldbus world. +numerous low cost chips, come free with many embedded controllers –non-deterministic medium access +Market: industrial automation, automobiles + - –no standard message services.

78 Field buses: principles 3.1 - 78 Industrial Automation 2013 3.3.8 Ethernet The universal bus To probe further: "Switched LANs", John J. Roese, McGrawHill, ISBN 0-07-053413-b "The Dawn of Fast Ethernet"

79 Field buses: principles 3.1 - 79 Industrial Automation 2013 Ethernet - another philosophy switch SCADA Fieldbus Ethernet SCADA simple devices PLC Soft-PLC Ethernet costlier field devices Soft-PLC as concentrators Event-driven operation cheap field devices decentralized I/O cyclic operation classical Ethernet + Fieldbus Ethernet as Fieldbus This is a different wiring philosophy. The bus must follow the control system structure, not the other way around

80 Field buses: principles 3.1 - 80 Industrial Automation 2013 The Ethernet consortia IAONA Europe (Industrial Automation Open Networking Alliance, ( www.iaona-eu.com ) ODVA (Open DeviceNet Vendors Association, www.adva.org ) CIP (Control and Information Protocol) DeviceNet, ControlNet Siemens ( www.ad.siemens.de ), PNO ( www.profibus.com ) « Industrial Ethernet » new cabling: 9-pin D-shell connectors « direct connection to Internet (!?) » Ethernet/IP (  Internet Protocol), Rockwell Automation www.rockwellautomation.com Hirschmann ( www.hirschmann.de ) M12 round IP67 connector ProfiNet Fieldbus Foundation ( www.fieldbus.org ): HSE FS 1.0 Schneider Electric, Rockwell, Yokogawa, Fisher Rosemount, ABB IDA (Interface for Distributed Automation, www.ida-group.org ) - Jetter, Kuka, AG.E, Phoenix Contact, RTI, Lenze, Schneider Electric, Sick www.jetter.de.. there are currently more than 25 standardized industrial Ethernets

81 Field bus standards 3.3 - 81 Industrial Automation 2013 The Ethernet „standards“ IEC SC65C „standardized“ 22 different, uncompatible "Industrial Ethernets“, driven by „market demand“. Compatibility: practically none Overlap: a lot 2EtherNet/IP(Rockwell. OVDA) 3Profibus, Profinet(Siemens, PNO) 4P-NET(Denmark) 6INTERBUS(Phoenix) 10Vnet/IP(Yokogawa, Japan) 11TCnet(Toshiba, Japan) 12Ethercat (Beckhoff, Baumüller) 13Powerlink(BR, AMK) 14EPA(China) 15Modbus-RTPS(Schneider, IDA) 16SERCOS(Bosch-Rexroth / Indramat) … In addition to Ethernets standardized in other committees: FF's HSE, (Emerson, E&H, FF) IEC61850(Substations) ARINC(Airbus, Boeing,..)

82 Field buses: principles 3.1 - 82 Industrial Automation 2013 The "real-time Ethernet" Method 1: Common clock synchronisation: return to cyclic. Method 2: IEEE 1588 (Agilent) PTP precision time protocol Method 3: Powerlink B&R, Kuka, Lenze, Technikum Winterthur www.hirschmann.de, www.br-automation.com, www.lenze.de, www.kuka.de Method 4: Siemens Profinet V3 synchronization in the switches Master clock The non-determinism of “normal” Ethernet makes it usuitable for the real-time world. Several improvements have been made, but this is not anymore a standard solution.

83 Field buses: principles 3.1 - 83 Industrial Automation 2013 Ethernet and fieldbus roles Traditionally, ethernet is used for the communication among the PLCs and for communication of the PLCs with the supervisory level and with the engineering tools Fieldbus is in charge of the connection with the decentralized I/O and for time-critical communication among the PLCs. Ethernet fieldbus local I/O CPU

84 Field buses: principles 3.1 - 84 Industrial Automation 2013 Future of field busses Non-time critical busses are being displaced by LANs (Ethernet) and cheap peripheral busses (Firewire, USB) These "cheap" solutions are being adapted to the industrial environment and become a proprietary solution (e.g. Siemens "Industrial Ethernet") The cost objective of field busses (less than 50$ per connection) is out of reach for LANs. The cabling objective of field busses (more than 32 devices over 400 m) is out of reach for the cheap peripheral busses such as Firewire and USB. Fieldbusses tend to live very long (10-20 years), contrarily to office products. There is no real incentive from the control system manufacturers to reduce the fieldbus diversity, since the fieldbus binds customers. The project of a single, interoperable field bus defined by users (Fieldbus Foundation) failed, both in the standardisation and on the market.

85 Field buses: principles 3.1 - 85 Industrial Automation 2013 Fieldbus Selection Criteria Installed base, devices availability: processors, input/output Interoperability (how likely is it to work with a product from another manufacturer Topology and wiring technology (layout) Connection costs per (input-output) point Response time Deterministic behavior Device and network configuration tools Bus monitor (baseline and application level) tools Integration in development environment Power distribution and galvanic separation (power over bus, potential differences)

86 Field buses: principles 3.1 - 86 Industrial Automation 2013 Assessment Which is the medium access and the link layer operation of CAN ? Which is the medium access and the link layer operation of Industrial Ethernet? Which are the selection criteria for a field bus ? What makes a field bus suited for hard-real-time operation ? How does the market influence the choice of the bus ?

87 Industrial Automation Automation Industrielle Industrielle Automation 3 Field busses 3.4 Industrial Wireless

88 Field buses: principles 3.1 - 88 Industrial Automation 2013 Motivation for Industrial Wireless Reduced installation and reconfiguration costs Easy access to machines (diagnostic or reprogramming) Improved factory floor coverage Eliminates damage of cabling Globally accepted standards (mass production)

89 Field buses: principles 3.1 - 89 Industrial Automation 2013 Wireless Landscape

90 Field buses: principles 3.1 - 90 Industrial Automation 2013 Wireless IEEE Numbers

91 Field buses: principles 3.1 - 91 Industrial Automation 2013 Requirements for Industrial Wireless

92 Field buses: principles 3.1 - 92 Industrial Automation 2013 Wireless for Non Real-Time Applications Remote Control: –Used for remote control of overhead cranes –High security requirements –Long code words to initiate remote control action Machine health monitoring: –Accurate information about status of a process –Local on demand access: PDA or laptop that connects to sensors or actuators –Control room: access point / gateway 92

93 Field buses: principles 3.1 - 93 Industrial Automation 2013 Wireless for Soft Real-Time Applications Measurements: –For physical process, timestamp values –Ability to reconstruct course of events –Requires clock synchronization; precision dictated by granularity of measurement –E.g. geological or industrial sensors collecting data and transmitting them to base station or control room Media: –Delay and loss rate constraints for user comfort –E.g. voice and video transfer Control loops: –Slow or non-critical operations –Low sample rate –Not affected by a few samples being lost –Delay constraint based on comfort demands –E.g. heat control and ventilation system

94 Field buses: principles 3.1 - 94 Industrial Automation 2013 Wireless Hard Real-Time Applications Late transmission cannot be tolerated E.g. control loops Assumes fault-free communication channel Wireless: –Error probability cannot be neglected –Sporadic and bursty errors

95 Field buses: principles 3.1 - 95 Industrial Automation 2013 Challenges and Spectrum of Solutions Wireless Challenges Attenuation Fading Multipath dispersion Interference High Bit Error rate Burst channel errors Application Requirements Reliable delivery Meet deadlines Support message priority Existing Solutions

96 Field buses: principles 3.1 - 96 Industrial Automation 2013 Radio wave interferes with surrounding environment creating multiple waves at receiver antenna, they are delayed with respect to each other. Concurrent transmissions cause interference too. => Bursts of errors Forward Error Correction (FEC): Encoding redundancy to overcome error bursts Automated Repeat ReQuest (ARQ): Retransmit entire packets when receiver cannot decode the packet (acknowledgements) Reliability for wireless channel

97 Field buses: principles 3.1 - 97 Industrial Automation 2013 Deadline Dependent Coding Uses FEC and ARQ to improve Bit Error Rate: –Re-transmissions before deadline –Different coding rate depending on remaining time to deadline –Tradeoff between throughput and how much redundancy is needed –Additional processing such as majority voting –Decoder keeps information for future use (efficiency)

98 Field buses: principles 3.1 - 98 Industrial Automation 2013 Existing protocols- comparison Feature802.11BluetoothZigbee / 802.15.4 Interference from other devices --Avoided using frequency hopping Dynamic channel selection possible Optimized forMultimedia, TCP/IP and high data rate applications Cable replacement technology for portable and fixed electronic devices. Low power low cost networking in residential and industrial environment. Energy ConsumptionHighLow (Large packets over small networks) Least (Small packets over large networks) Voice support/SecurityYes/Yes No/Yes Type of Network / Channel Access Mobile / CSMA/CA and polling Mobile & Static / PollingMostly static with infrequently used devices / CSMA and slotted CSMA/CA Bit error rateHighLow Real Time deadlines???

99 Field buses: principles 3.1 - 99 Industrial Automation 2013 Range 1 m 10 m 100 m 1 km 10 km 0 GHz2 GHz1GHz3 GHz5 GHz4 GHz6 GHz 802.11a UWB ZigBee Bluetooth ZigBee 802.11b,g 3G UWB

100 Field buses: principles 3.1 - 100 Industrial Automation 2013 Legal Frequencies www.fcc.gov

101 Field buses: principles 3.1 - 101 Industrial Automation 2013 Industrial Example: WirelessHART HART (Highway Addressable Remote Transducer) fieldbus protocol Supported by 200+ global companies Since 2007 Compatible WirelessHART extension Not part of exam 2015

102 Field buses: principles 3.1 - 102 Industrial Automation 2013 WirelessHART Networking Stack PHY: –2,4 GHz Industrial, Scientific, and Medical Band (ISM-Band) –Transmission power 0 - 10 dBm –250 kbit/s data rate MAC: –TDMA (10ms slots, static roles) –Collision and interference avoidance: Channel hopping and black lists Network layer: –Routing (graph/source routing) –Redundant paths –Sessions and broadcast encryption (AES) Not part of exam 2015

103 Field buses: principles 3.1 - 103 Industrial Automation 2013 WirelessHART Networking Stack Transport layer: –Segmentation, flatten network –Quality of Service (QoS): (Command, Process-Data, Normal, Alarm) Application layer: –Standard HART application layer –Device Description Language –Smart Data Publishing (lazy) –Timestamping –Events –Command aggregation Boot-strapping: –Gateway announcements (network ID and time sync) –Device sends join request –Authentication and configuration via network manager Not part of exam 2015

104 Field buses: principles 3.1 - 104 Industrial Automation 2013 Design Industrial Wireless Network Existing wireless in plant; frequencies used? Can the new system co-exist with existing? How close are you to potential interferences? What are uptime and availability requirements? Can system handle multiple hardware failures without performance degradation? What about energy source for wireless devices? Require deterministic power consumption to ensure predictable maintenance. Power management fitting alerting requirements and battery replacement goals

105 Field buses: principles 3.1 - 105 Industrial Automation 2013 Assessment Why is a different wireless system deployed in a factory than at home? What are the challenges of the wireless medium and how are they tackled? How can UWB offer both a costly and high bandwidth and a cheaper and high bandwidth services? Which methods are used to cope with the crowded ISM band? Why do we need bootstrapping in Wireless HART?

106 Field buses: principles 3.1 - 106 Industrial Automation 2013 References Wireless Communication in Industrial Networks, Kavitha Balasubramanian, Cpre 458/558: Real-Time Systems, www.class.ee.iastate.edu/cpre458/cpre558.F00/notes/rt-lan7.ppt WirelessHART, Christian Hildebrand, www.tu-cottbus.de/systeme, http://systems.ihp-microelectronics.com/uploads/downloads/ 2008_Seminar_EDS_Hildebrand.pdf WirelessHART TM Expanding the Possibilities, Wally Pratt HART Communication Foundation, www.isa.org/wsummit/.../RHelsonISA-Wireless-Summit-7-23-07.ppt Industrial Wireless Systems, Peter Fuhr, ISA, www.isa.org/Presentations_EXPO06/FUHR_IndustrialWirelessPresentation_EXPO06.ppt

107 Industrial Automation Automation Industrielle Industrielle Automation


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