EPFL Spring 2017 3 Industrial Communication Networks Automation

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 Supervision level Engineering Operator 2 Control Bus programmable controllers Control level Fieldbus direct I/O micro. PLCs 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 (1 ms. . 1 s) - 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 (10 m - 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 I/O tray marshalling capacity bar dumb devices PLC B e f o r e PLC COM smart devices A f t e r field bus But: the number of end-points remains the same ! 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. . . 10, 000 1000 frame size (bytes) 100 Sensor Bus Simple devices Low cost Bus powered Short messages (bits) Fixed configuration Not intrinsically safe Twisted pair Max distance 500 m Data Networks Workstations, robots, PCs Higher cost Not bus powered Long messages (e-mail, files) Not intrinsically safe Coax cable, fiber Max distance miles 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 800 m 10 10 100 Low Speed Fieldbus Process instruments, valves Medium cost Bus-powered (2 wire) Messages: values, status Intrinsically safe Twisted pair (reuse 4 -20 m. A) Max distance 1200 m 1000 poll time, milliseconds 10, 000 source: ABB Industrial Automation | 2017 8

Fieldbus Application: locomotives and drives power line radio cockpit Train Bus diagnosis Vehicle Bus brakes data rate delay medium number of stations integrity cost power electronics motors track signals 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 very high (signaling tasks) engineering costs dominate Industrial Automation | 2017 9

Fieldbus Application: automobile ECU Monitoring and Diagnosis Board network ECU redundant board network 12 V und 48 V ECU c Brakes 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 control center IEC 870 -6 Modicom control center IEC 870 -5 RTU COM ICCP DNP 3. 0 Conitel RTU control center HV High Voltage RP 570 serial links (telephone) RTU Remote Terminal Units RTU substation FSK, radio, DLC, cable, fiber, . . . houses RTU MV Medium Voltage LV Low Voltage RTU 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 Þ Data transmitted from periphery or from fast controllers to higher level Þ 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 (50 kbit/s. . 12 Mbits/s) and thus more compact encodings are use 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 identifier wheel speed 0 bit offset air pressure 16 line voltage 32 size time stamp 48 64 66 70 all door closed 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 ANTIVALENT 2: dataset correct variable error undefined variable value check 0 1 1 1 0 0 0 0 1 1 1 1 1 chk_offset var_offset 00 = network error 01 = ok 10 = substituted 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 central master / slave: hierarchical AP “master” alternate master PLC AP all traffic passes by the master (PLC); adding an alternate master is difficult (it must be both master and slave) “slaves” input peer-to-peer: distributed PLCs may exchange data, share inputs and outputs allows redundancy and “distributed intelligence” devices talk directly to each other PLC AP separate bus master from application master ! AP input “slaves” output “masters” PLC AP output AP Application Industrial Automation | 2017 20

Broadcasts Most variables are read in 1 to 3 different devices Broadcasting messages identified by their source (or contents) increases efficiency. application processor plant image … instances … application processor plant image = = distributed variable database plant image bus 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) Bus refreshes plant image in the background 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. Each station snoops the bus and reads the variables it is interested in. Industrial Automation | 2017 21

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. Industrial Automation | 2017 22

Cyclic versus Event-Driven transmission cyclic: send value strictly every xx milliseconds misses the peak (Shannon-Nyquist!) always the same, why transmit ? time resolution individual period event-driven: send when value change by more than x% of range how much resolution? - coarse (bad accuracy) - fine (high frequency) limit update frequency!, limit resolution nevertheless transmit: - every xx as “I’m alive” sign - when data is internally updated - upon quality change (failure) Industrial Automation | 2017 23

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. Application Processor Traffic Memory Ports (holding a dataset) Associative memory an associative memory decodes the addresses of the subscribed datasets Bus Controller two pages ensure that read and write can occur at the same time (no semaphores !) bus Industrial Automation | 2017 24

Freshness supervision Applications tolerate an occasional loss of data, but no stale data, which are at best useless and at worst dangerous. Þ 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. Industrial Automation | 2017 25

Example of Process Variable API (application programming interface) Simple access of the application to variables in traffic memory: ap_put (variable_name, variable value) ap_get (variable_name, variable value, variable_status, variable_freshness) Optimize: access by clusters (predefined groups of variables): ap_put_cluster (cluster_name) ap_get (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. Industrial Automation | 2017 26

Cyclic Data Transmission address Bus Master 1 2 3 Poll List 4 5 devices (slaves) 6 plant Principle: master polls addresses in fixed sequence (poll list) Example Execution Individual period 1 2 3 4 5 Individual period 6 1 2 3 4 5 N polls 6 1 2 3 4 5 6 time [ms] RTD address 10 µs/km (i) read transfer data (i) address (i+1) time [µs] The duration of each poll is the sum of the transmission time of address and data (bit-rate dependent) and of the reply delay of the signals (independent of bit-rate). 44 µs. . 296 µs Industrial Automation | 2017 27

Round-trip delay of master-slave exchange master T_m closest data sink repeater Master Frame most remote data source repeater t_repeat The round-trip delay limits the extension of the bus propagation delay (t_pd = 6 µs/km) t_mm t_source (t_repeat < 3 µs) t_ms T_m access delay T_s t_repeat Slave Frame t_sm T_m next Mas ter Frame distance Industrial Automation | 2017 28

Cyclic operation characteristics 1. Data are transmitted at fixed intervals, whether they changed or not. 2. The delivery delay (refresh rate) is deterministic and constant. 3. The bus is under control of a central master (or distributed time-triggered algorithm). 4. No explicit error recovery needed since fresh value will be transmitted in next cycle. 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) To keep the poll time low, only small data items may be transmitted (< 256 bits) The bus capacity must be configured beforehand. Determinism gets lost if the cycles are modified at run-time. Industrial Automation | 2017 29

Optimizing Cyclic Operation Problem: fixed portion of the bus' time used => 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. 2 ms period 1 2 4 a 8 16 1 ms period (basic period) 1 4 b 4 ms period 1 2 3 64 1 4 a time 1 ms group with period 1 ms Notes: Poll cycles should not be modified at run-time (non-determinism) Industrial Automation | 2017 30

Cyclic Transmission with Decoupled Application cyclic poll cyclic algorithms application 1 application 2 application 3 application 4 bus master Periodic List Traffic Memory Ports source port Ports sink port bus controller bus controller bus port address port data The bus traffic and the application cycles are asynchronous to each other. The bus master scans the identifiers at its own pace. Deterministic behavior, at expense of reduced bandwidth and geographical extension. Industrial Automation | 2017 31

Example: delay requirement publisher application instance device subscribers application instances device applications bus instance Worst-case delay for transmitting all time critical variables is the sum of: Source application cycle time 8 ms Individual period of the variable on bus 16 ms Sink application cycle time 8 ms = 32 ms Industrial Automation | 2017 32

Event-driven Operation • 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). intelligent stations eventreporting station sensors/ actors plant 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. Industrial Automation | 2017 33

Bus interface for event-driven operation application filter driver Application Processor • 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. message (circular) queues interrupt Bus Controller bus Industrial Automation | 2017 34

Response of Event-driven operation Caller Application Transport software Bus Transport software Called Application request interrupt indication confirm time Since events can occur anytime on any device, stations communicate by spontaneous transmission, leading to possible collisions Interruption of server device at any instant can disrupt a time-critical task. Buffering of events can cause unbounded delays Gateways introduce additional uncertainties Industrial Automation | 2017 35

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) Industrial Automation | 2017 36

Events and Determinism Deterministic medium access necessary to guarantee delivery time bound but not sufficient since events messages are queued in the devices. events producers & consumers input and output queues bus acknowledgements data packets 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 Industrial Automation | 2017 37

Events Pros and Cons In an event-driven control system, there is only a transmission or an operation when an event occurs. Advantages: 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) Drawbacks: 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 Industrial Automation | 2017 38

Summary: Cyclic vs Event-Driven Operation decoupled (asynchronous): coupled (with interrupts): application processor events (interrupts) traffic memory (buffer) queues bus controller 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 bus controller 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 Industrial Automation | 2017 39

Mixed Data Traffic Process Data represent the state of the plant Message Data represent state changes of the plant short and urgent data items infrequent, sometimes long messages reporting events, for: . . . motor current, axle speed, operator's commands, emergency stops, . . . • Users: set points, diagnostics, status • System: initialisation, down-loading, . . . -> Periodic Transmission of Process Variables -> Sporadic Transmission of Process Variables and Messages Since variables are refreshed periodically, no retransmission protocol is needed to recover from transmission error. Since messages represent state changes, a protocol must recover lost data in case of transmission errors basic period event time sporadic phase periodic phase Industrial Automation | 2017 40

Mixing Traffic is a configuration issue Cyclic broadcast of source-addressed variables standard solution for process control. Cyclic transmission takes large share of bus bandwidth and should be reserved for really critical variables. 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. 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 modes. Industrial Automation | 2017 41

Real-Time communication stack The real-time communication model uses two stacks, one for time-critical variables and one for messages time-critical process variables time-benign messages 7 Application 6 Presentation Remote Procedure Call 5 Session connection-oriented 4 Transport (connection-oriented) 3 Network (connectionless) 2" Logical Link Control medium access 2' Link (Medium Access) media 1 Physical implicit Logical Link Control connectionless common Management Interface Industrial Automation | 2017 42

Cyclic or Event-driven Operation For Real-time ? cyclic operation event-driven operation Data are transmitted at fixed intervals, whether they changed or not. Data are only transmitted when they change or upon explicit demand. Deterministic: delivery time is bound Non-deterministic: delivery time vary widely Worst Case is normal case Typical Case works most of the time All resources are pre-allocated (periodic, round-robin) object-oriented bus Fieldbus Foundation, MVB, FIP, . . Best use of resources (aperiodic, demand-driven, sporadic) message-oriented bus Profibus, CAN, LON, ARCnet Industrial Automation | 2017 43

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. t 1 input t 2 input processing input t 3 t 4 bus t 1 val 1 Industrial Automation | 2017 44

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. Industrial Automation | 2017 45

Time distribution In master-slave busses, master distributes time as bus frame. Slave can compensate for path delays, time is relative to 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) Industrial Automation | 2017 46

NTP (Network Time Protocol) principle client t 1 network server time request t 2 network delay time response t 3 t 4 time request t’ 1 t’ 2 time response network delay t’ 4 t’ 3 distance time Measures delay end-to-end over the network (one calculation) Problem: asymmetry in the network delays, long network delays Industrial Automation | 2017 47

IEEE 1588 principle (PTP, Precision Time Protocol) Grand Master Clock residence time calculation peer delay calculation MC Pdelay-response TC Pdelay-request TC TC MC = master clock TC TC TC = transparent clock OC = ordinary clock OC OC Two calculations: residence time and peer delay All nodes measure delay to peer TC correct for residence time (HW support) Industrial Automation | 2017 48

IEEE 1588 – 1 step clocks time ordinary (slave) clock t 1 peer delay calculation link delay t 4 Pdelay_Req bridge 1 -step transparent clock t 2 t 3 Pdelay_Resp (contains t 3 – t 2) t 1 Pdelay_Req t 2 Pdelay_Resp t 3 t 4 grand master clock Pdelay_Resp t 4 t 2 t 3 Sync residence time residence time calculation t 5 residence time Sync t 5 t 6 Sync (contains all + ) distance 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 Industrial Automation | 2017 49

References To probe further • http: //www. ines. zhaw. ch/fileadmin/user_upload/engineering/_Institute_und_Zentr en/INES/IEEE 1588/Dokumente/IEEE_1588_Tutorial_engl_250705. pdf • http: //blog. meinbergglobal. com/2013/11/22/ntp-vs-ptp-network-timingsmackdown/ • http: //blog. meinbergglobal. com/2013/09/14/ieee-1588 -accurate/ Industrial Automation | 2017 50

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. Industrial Automation | 2017 51

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 ? Industrial Automation | 2017 52

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 53

Different classes of field busses One bus type cannot serve all applications and all device types efficiently. . . 10, 000 1000 frame size (bytes) 100 Sensor Bus Simple devices Low cost Bus powered Short messages (bits) Fixed configuration Not intrinsically safe Twisted pair Max distance 500 m Data Networks Workstations, robots, PCs Higher cost Not bus powered Long messages (e-mail, files) Not intrinsically safe Coax cable, fiber Max distance miles 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 800 m 10 10 100 Low Speed Fieldbus Process instruments, valves Medium cost Bus-powered (2 wire) Messages: values, status Intrinsically safe Twisted pair (reuse 4 -20 m. A) Max distance 1200 m 1000 poll time, milliseconds 10, 000 source: ABB Industrial Automation | 2017 54

Worldwide most popular field busses Market shares held by the leading fieldbus and industrial Ethernet systems Source: HMS Industrial Networks, 2016 Industrial Automation | 2017 55

Field device: example differential pressure transducer 4. . 20 m. A current loop fluid The device transmits value by means of a current loop Industrial Automation | 2017 56

4 -20 m. A loop - the conventional, analog standard The 4 -20 m. A is the most common analog transmission standard in industry sensor flow transducer i(t) = f(v) RL 1 reader 1 2 R 1 i(t) = 0, 4. . 20 m. A RL 2 R 2 voltage source 10 V. . 24 V RL 3 RL 4 conductor resistance The transducer limits the current to a value between 4 m. A and 20 m. A, proportional to the measured value, while 0 m. A 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 (4 m. A), allowing to transmit signal and power through a single pair of wires. 4 -20 m. A is basically a point-to-multipoint communication (one source) Industrial Automation | 2017 57

HART § Data over 4. . 20 m. A loops Industrial Automation | 2017 58

HART – Principle (1986) HART (Highway Addressable Remote Transducer) was developed by Fisher-Rosemount to retrofit 4 -to-20 m. A current loop transducers with digital data communication (not for closed-loop communication). HART modulates the 4 -20 m. A current with a low-level frequency-shift-keyed (FSK) sine-wave signal, without affecting the average analogue signal. HART uses low frequencies (1200 Hz 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 Industrial Automation | 2017 59

HART - Protocol Hart communicates point-to-point, under the control of a master, e. g. a hand-held device Master Slave comman d Request Indication time-out respons e Response Confirmation Hart frame format (character-oriented, not bit-oriented): preamble start address 5. . 20 (x. FF) 1 1. . 5 command bytecount 1 1 [status] data [2] 0. . 25 (slave response) (recommended) checksum 1 Industrial Automation | 2017 60

HART - Commands 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, … Industrial Automation | 2017 61

HART - Importance Practically all 4. . 20 m. A devices come equipped with HART today About 40 Mio devices are sold per year. more info: http: //www. hartcomm. org/ http: //www. thehartbook. com/default. asp Industrial Automation | 2017 62

Fieldbus Comparison Fieldbus BW 1. 5 -12 PROFIBU Mbit/s S (DP 31. 25 and PA) Kbits/s Device. Ne t 250 k. Bit/s Max Length 100 m – 24 km 1900 m Max Data Size Applicati on Max Nodes Factory Automatio 246 n bytes Process Automatio n Factory 500 m 8 bytes Automatio n Notes 127 32 Token passing, masterslave / P 2 P, operate sensors and actuators (DP), monitor measuring equipment (PA) 64 CSMA/CD, master-slave, multidrop, motors, drives, uses CAN Automobil 10 e, k. Bit/s - 25 -1000 CSMA, Ideal for small data CANopen 8 bytes Industrial 127 1 m and fast sync, uses CAN http: //www. bierlemartin. de/hengstler/training/fbcomp. htm Automatio Mbit/s http: //www. pacontrol. com/download/fieldbuscomp. pdf n Industrial Automation | 2017 63 http: //www. mtl. de/pdfs/news/open_fieldbus. pdf

CAN Mastership Link layer control Upper layers multi-master, 12 -bit bisection, bit-wise arbitration connectionless (command/reply/acknowledgement) no transport, no session, implicit presentation Industrial Automation | 2017 64

CAN - Analysis + + supported by user organisations ODVA, Honeywell. . . – limited product distance x rate (40 m x Mbit/s) – sluggish real-time response (2. 5 ms) + numerous low cost chips, come free with many embedded controllers – non-deterministic medium access + application layer definition – several incompatible application layers (Can. Open, Device. Net, SDS) + application layer profiles – strongly protected by patents (Bosch) + bus analyzers and configuration tools available – interoperability questionable (too many different implementations) + Market: industrial automation, automobiles – small data size and limited number of registers in the chips. – no standard message services. Industrial Automation | 2017 65

Ethernet Paradigms Classical Ethernet + Fieldbus SCADA switch Ethernet PLC cheap field devices decentralized I/O cyclic operation PLC Fieldbus simple devices Ethernet as Fieldbus SCADA switch Ethernet costlier field devices Soft-PLC as concentrators Event-driven operation Soft-PLC This is a different wiring philosophy. The bus must follow the control system structure, not the other way around Industrial Automation | 2017 66

The Ethernet „standards“ IEC SC 65 C „standardized“ 22 different, uncompatible "Industrial Ethernets“, driven by „market demand“. 2 3 4 6 10 11 12 13 14 15 16 … Ether. Net/IP (Rockwell. OVDA) Profibus, Profinet (Siemens, PNO) P-NET (Denmark) INTERBUS (Phoenix) Vnet/IP (Yokogawa, Japan) TCnet (Toshiba, Japan) Ethercat (Beckhoff, Baumüller) Powerlink (BR, AMK) EPA (China) Modbus-RTPS (Schneider, IDA) SERCOS (Bosch-Rexroth / Indramat) In addition to Ethernets standardized in other committees: FF's HSE, (Emerson, E&H, FF) IEC 61850(Substations) ARINC (Airbus, Boeing, . . ) Compatibility: practically none Overlap: a lot Industrial Automation | 2017 67

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. local I/O CPU fieldbus Ethernet Industrial Automation | 2017 68

Future of field busses Non-time critical busses are being displaced by LANs (Ethernet) and cheap peripheral busses (USB, …) These "cheap" solutions are being adapted to the industrial environment and become a proprietary solution (e. g. Siemens "Industrial Ethernet") The cabling objective of field busses (more than 32 devices over 400 m) is out of reach for cheap peripheral busses such as 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. Industrial Automation | 2017 69

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) Power distribution and galvanic separation (power over bus, potential differences) 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 Industrial Automation | 2017 70

Assessment Which are the selection criteria for a field bus ? Which is the medium access and the link layer operation of CAN ? What is the wiring philosophy of Industrial Ethernet? What makes a field bus suited for hard-real-time operation ? How does the market influence the choice of the bus ? Industrial Automation | 2017 71

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 72

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) Industrial Automation | 2017 73

Wireless Landscape Industrial Automation | 2017 74

Wireless IEEE Numbers Industrial Automation | 2017 75

Requirements for Industrial Wireless Industrial Automation | 2017 76

Challenges and Spectrum of Solutions Wireless Challenges Attenuation Fading Multipath dispersion Interference High Bit Error rate Burst channel errors Existing Solutions Application Requirements Reliable delivery Meet deadlines Support message priority Industrial Automation | 2017 77

Reliability for wireless channel 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 Re. Quest (ARQ): Retransmit entire packets when receiver cannot decode the packet (acknowledgements) Industrial Automation | 2017 78

Existing protocols- comparison Feature 802. 11 Bluetooth Zigbee / 802. 15. 4 Interference from other devices -- Avoided using frequency hopping Dynamic channel selection possible Optimized for Multimedia, 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 Consumption High Low (Large packets over small networks) Least (Small packets over large networks) Voice support/Security Yes/Yes No/Yes Type of Network / Channel Access Mobile / CSMA/CA and polling Mobile & Static / Polling Mostly static with infrequently used devices / CSMA and slotted CSMA/CA Bit error rate High Low Real Time deadlines ? ? ? Industrial Automation | 2017 79

Legal Frequencies www. fcc. gov Industrial Automation | 2017 80

Range vs Data Range 10 km 3 G 1 km 100 m 802. 11 a 802. 11 b, g 10 m Zig. Bee UWB 1 m 0 GHz 1 GHz Bluetooth Zig. Bee UWB 2 GHz 3 GHz 4 GHz 5 GHz 6 GHz Industrial Automation | 2017 81

Industrial Example: Wireless. HART § HART (Highway Addressable Remote Transducer) fieldbus protocol § Supported by 200+ global companies § Since 2007 Compatible Wireless. HART extension Industrial Automation | 2017 82

Wireless. HART Networking Stack § § § PHY: • 2, 4 GHz Industrial, Scientific, and Medical Band (ISMBand) • Transmission power 0 - 10 d. Bm • 250 kbit/s data rate MAC: • TDMA (10 ms slots, static roles) • Collision and interference avoidance: Channel hopping and black lists Network layer: • Routing (graph/source routing) • Redundant paths Industrial Automation | 2017 83

Wireless. HART Networking Stack § Transport layer: • § § May be replaced by 6 Ti. SCH? Quality of Service (Qo. S): (Command, Process-Data, Normal, Alarm) Application layer: • Standard HART application layer • Device Description Language • Timestamping Boot-strapping: • Gateway announcements (network ID and time sync) • Device sends join request • Authentication and configuration via network manager Industrial Automation | 2017 84

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 Industrial Automation | 2017 85

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? Industrial Automation | 2017 86

References • Wireless Communication in Industrial Networks, Kavitha Balasubramanian, Cpre 458/558: Real-Time Systems, www. class. ee. iastate. edu/cpre 458/cpre 558. F 00/notes/rt-lan 7. ppt • Wireless. HART, Christian Hildebrand, www. tu-cottbus. de/systeme, http: //systems. ihp-microelectronics. com/uploads/downloads/ 2008_Seminar_EDS_Hildebrand. pdf • Wireless. HARTTM Expanding the Possibilities, Wally Pratt HART Communication Foundation, www. isa. org/wsummit/. . . /RHelson. ISA-Wireless-Summit-7 -23 -07. ppt • Industrial Wireless Systems, Peter Fuhr, ISA, www. isa. org/Presentations_EXPO 06/FUHR_Industrial. Wireless. Presentation_EXPO 06. ppt Industrial Automation | 2017 87