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

2. 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. Location of the field bus in the plant hierarchy2 12 33 23 4
File
Edit
Engineering
SCADA level
Operator
Plant bus
Programmable
Logic Controller
Plant Level
Field bus
fieldbus interconnects field devices and PLCs. In particular the data of IOs which are not directly attached to a PLC are transported to the PLCs with a fieldbus.
Field level
Sensor/
Actor
Bus
Sensor / Actor
direct I/O

4. - robust and easy installation by skilled people
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 ( € €50 / node)
- moderate data rates (50 kbit/s - 5 Mbit/s), large distance range (10m - 4 km)
requirements from PLCs carry over to the field bus as well (real-time constraints, harsh environments, high integrity and availability). In addition synchronization is necessary to assign precise timestamps to data, attachment cost should be kept low. While data rates are moderate, large distances need to be covered (depending on plant type).

5. - increased modularity of plant (each object comes with its computer)
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. The original idea: save wiring
marshalling
bar
I/O
PLC
dumb devices
(Rangierung,
tableau de brassage (armoire de triage)
tray
capacity
Before
After
PLC
COM
Marshalling: connects primary and secondary equipment
field bus
But: the number of end-points remains the same !
energy must be supplied to smart devices

7. 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. Different classes of field busses
One bus type cannot serve
all applications and all device types efficiently...
Data Networks
Workstations, robots, PCs
Higher cost
Not bus powered
Long messages ( , files)
Not intrinsically safe
Coax cable, fiber
Max distance miles 10
100
1000
10,000
Sensor Bus
Simple devices
Low cost
Bus powered
Short messages (bits)
Fixed configuration
Not intrinsically safe
Twisted pair
Max distance 500m
frame size
(bytes)
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
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 10
100
1000
10,000
source: ABB
poll time, milliseconds

9. Fieldbus over a wide area: example wastewater treatment
Pumps, gates, valves, motors, water level sensors, flow meters, temperature sensors, gas meters (CH4), generators, etc are spread over an area of several km2. Some parts of the plant have to cope with explosives.
Wiring is traditionally mA => long threads of cable (several 100 km).

10. Fieldbus over a wide area: example wastewater treatment
Japan
source: Kaneka, Japan
Malaysia
Motor Control
Center
Junction
Box
plant has demanding requirements with respect to large distances and need cope with explosives. A hierarchical structure with H1 Speed Fieldbus on the high level and Hart Fieldbus on the lower levels is used for the water treatment part. The lower levels and higher level are combined with junction box gateways. On the other hand the electrical grid part (substation) uses Ethernet. For the interconnecting of these two parts fieldbus protocol converters are used.
Numerous analog inputs/outputs (AI/AO),
low speed (37 kbit/s) segments (Hart) merged to 1 Mbit/s links (H1 Speed Fieldbus).

11. Fieldbus Application: locomotives and drives
power line
radio
cockpit
Train Bus
diagnosis
Vehicle Bus
brakes
power electronics
motors
track signals
data rate
1.5 Mbit/second
delay
. Each car of a train has its own vehicle bus to control the brakes, power electronics and motors and gather track signals. In addition there is a train bus that connects the different cars.
1 ms (16 ms for skip/slip control)
medium
twisted wire pair, optical fibers (EM disturbances)
number of stations
up to 255 programmable stations, 4096 simple I/O
integrity
very high (signaling tasks)
cost
engineering costs dominate

12. Fieldbus Application: automobile
- Electromechanical wheel brakes
- Redundant Engine Control Units
- Pedal simulator
- Fault-tolerant 2-voltage on-board power supply - Diagnostic System
The communication network of a car is redundant, there are several engine control units and separate cables connecting them. This allows a highly available and safe operation.

13. Networking busses: Electricity Network Control: myriads of protocols
houses
substation
Modicom
ICCP
control
center
Inter-Control Center Protocol
IEC 870-6 HV MV LV
High
Voltage
Medium
Low
SCADA
FSK, radio, DLC, cable, fiber,...
RTU
COM
Remote Terminal Units
IEC 870-5
DNP 3.0
Conitel
RP 570
serial links (telephone)
large number of different fieldbus protocols which need to be interconnected with gateways which convert from one protocol to another. Note that High, Medium and Low Voltage parts have different requirements and thus use different fieldbus protocols
low speed, long distance communication, may use power lines or telephone modems.
Problem: diversity of protocols, data format, semantics...

14. Engineering a fieldbus: consider data density (Example: Power Plants)
Acceleration limiter and prime mover: 1 kbit in 5 ms
Burner Control: 2 kbit in 10 ms
For each 30 m of plant: 200 kbit/s
Fast controllers require at least 16 Mbit/s over distances of 2 m
Data transmitted from periphery or from fast controllers to higher level
Slower links to control level through field busses over distances of 1-2 km. The control stations gather data at rates of about 200 kbit/s over distances of 30 m.
The control room computers are interconnected by a bus of at least 10 Mbit/s, over distances of several 100 m.
plant might require more than one kind of fieldbus. Where which fieldbus protocol is used depends mainly on data density and distances.
Field bus planning: estimate data density per unit of length or surface, response time and throughput over each link.

15. How does a field bus support modularity ?
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. 3 Industrial Communication Systems
3.2 Field bus operation
Buses de terreno: modo de trabajo
Bus de terrain: mode de travail
Feldbus: Arbeitsweise
3 Industrial Communication Systems

17. 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. 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)
source
value
quality
time
description

19. Data format
source
value
quality
time
description
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
Field busses are slower (50kbit/s ..12 Mbits/s) and thus more compact encodings are used.
ASN.1: (TLV)
type
length
value

20. Variables may be of different types, types can be mixed.
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
analog variables
binary variables
dataset
identifier
wheel
air
line
time
stamp
speed
pressure
voltage
Inflexible, but plants change rarely 16 32 48 64
all door closed
lights on
heat on
air condition on 66 70
bit offset
size

21. Dataset extension and quality
To allow later extension, room is left in the datasets for additional variables.
Since the type of these future data is unknown, unused fields are filled with '1".
To signal that a variable is invalid, the producer overwrites the variable with "0".
Since both an "all 1" and an "all 0" word can be a meaningful combination, each variable can be supervised by a check variable, of type ANTIVALENT2:
dataset 1
check
correct variable
error
undefined
variable value
var_offset
chk_offset
10 = substituted
00 = network error
01 = ok
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.

22. hierarchical or peer-to-peer communication
PLC
alternate master
PLC
central master / slave: hierarchical
“master” AP AP
all traffic passes by the master (PLC);
adding an alternate master is difficult
(it must be both master and slave)
“slaves”
input
output
peer-to-peer: distributed
PLC
PLC
PLC
“masters” AP AP AP
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 !
“slaves”
input
output AP
Application

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

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

26. 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. 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
Content-addressable memory (CAM) is a special type of computer memory used in certain very high speed searching applications.
Unlike standard computer memory (random access memory or RAM) in which the user supplies a memory address and the RAM returns the data word stored at that address, a CAM is designed such that the user supplies a data word and the CAM searches its entire memory to see if that data word is stored anywhere in it. If the data word is found, the CAM returns a list of one or more storage addresses where the word was found (and in some architectures, it also returns the data word, or other associated pieces of data). Thus, a CAM is the hardware embodiment of what in software terms would be called a map (java) or dictionary (python)
Because a CAM is designed to search its entire memory in a single operation, it is much faster than RAM in virtually all search applications, but more expensive.
an associative memory decodes
the addresses of the subscribed
datasets
two pages ensure that read and write can occur at the same time
(no semaphores !)
Bus Controller
bus

28. 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.
Independent of time stamping (simple devices)
Freshness counter
Reset by bus or app, incremented regularly
App reads value of counter before using data
Some readers more tolerant than others

29. 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.

30. Cyclic Data Transmission
address
Bus
devices
(slaves) 1 2 3 4 5 6
Master
Poll
List
plant
Principle: master polls addresses in fixed sequence (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 delay
of the signals
(independent of bit-rate).
address
(i)
data
(i+1)
10 µs/km 1 2 3 4 5 6
44 µs µs
Example Execution

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

32. 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.

33. 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.
2 ms period
4 ms period 1 2 4a 8 16 1 4b 1 2 3 64 1 4a
time
1 ms period
1 ms
1 ms
group with
period 1 ms
(basic 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

34. Cyclic Transmission with Decoupled Application
algorithms
algorithms
algorithms
algorithms
cyclic
application
application
application
application
poll 1 2 3 4
bus
source
master
port
Ports
Ports
Ports
Ports
Traffic
Periodic
List
Memory
sink
sink
port
port
bus
bus
bus
bus
bus
controller
controller
controller
controller
controller
bus
Bus and applications are decoupled by a shared memory, the traffic memory,
which acts as distributed database updated by the network.
The principle of cyclic operation, combined with source-addressed broadcast, has been adopted by most modern field busses.
It is currently used for power plant control, rail vehicles, aircrafts, etc...
The poll scan list located in the central master (which may be duplicated for availability purposes) determines the behavior of the bus. It is configured for a specific project by a single tool, which takes into account the applications’ requirements. This guarantees that no application can occupy more than its share of the bus bandwidth and gives control to the project leader.
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.

35. Example: delay requirement
publisher
application instance
subscribers application instances
device
device
device
applications
bus
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

36. 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. 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
event-
event-
event-
stations
reporting
reporting
reporting
station
station
station
sensors/
actors
plant
Transmission when state changes
Load low on averge, correlation leads to high peaks
Detection needs intelligence (combination of changes, application based, meaning)
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.

38. Bus interface for event-driven operation
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.
application
filter
driver
Application
Processor
message (circular) queues
interrupt
Bus
Controller
bus

39. Response of Event-driven operation
Caller
Transport
Bus
Transport
Called
Application
software
software
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

40. 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
Deterministic
Central master,
Collision
Token-passing (round-robin),
(CSMA/CA)
Binary bisection (collision with winner)

41. 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.
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

42. 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

43. Summary: Cyclic vs Event-Driven Operation
decoupled (asynchronous):
coupled (with interrupts):
application
processor
application
processor
events
(interrupts)
traffic
memory
(buffer)
queues
bus
controller
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
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

44. 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. represent the state of the plant represent state changes of the plant
Mixed Data Traffic
Process Data
Message Data
represent the state of the plant
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
basic period
event
time
sporadic
phase
periodic phase
sporadic
phase
periodic phase

46. 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.
Broadcast source-addressed variables is standard
Cyclic only for REALLY critical variables
Decide before deployment
Provide both traffic types

47. 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
Management
Interface 7
Application
implicit
implicit 6
Presentation
Remote Procedure Call 5
Session
Logical Link Control
connection-oriented 4
Transport (connection-oriented)
connectionless 3
Network (connectionless)
connectionless
2"
Logical Link Control
medium access 2'
Link (Medium Access)
common
media 1
Physical

48. Application View Of Communication
Periodic Tasks
Event-driven Tasks R1 R2 R3 R4 E1 E2 E3
Variables Services
Message Services
Traffic Memory
Queues
Process Data
Supervisory
Message Data
Data
(Broadcast)
(unicast)
node
bus controller
bus

49. Cyclic or Event-driven Operation For Real-time ?
The operation mode of the communication exposes the main approach to
conciliate real-time constrains and efficiency in a control systems.
cyclic operation
event-driven operation
Data are transmitted at fixed intervals,
Data are only transmitted when they
whether they changed or not.
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
Best use of resources
(periodic, round-robin)
(aperiodic, demand-driven, sporadic)
C: controlled by a central master (redundant for availability), number of participants limited by maximum period, call/reply in one bus transfer
(fetch principle), cheap connection, dumb devices, limited geographical range
E: multi-master arbitration, large number of participants, costly connection, intelligent devices, open systems, bring principle
object-oriented bus
message-oriented bus
Fieldbus Foundation, MVB, FIP, ..
Profibus, CAN, LON, ARCnet

50. 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. 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 :00:00, UTC was :59: 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.
Time expressed in digital form is counted in number of seconds after a reference date, called an epoch.
Unix counts seconds since its epoch of 1st January h0s with a signed 32 bits counter which will wrap around in 2038 (Unix Millenium Bug). Unix time is based on Coordinated Universal Time (UTC) and is subject to leap seconds.
In IEEE 1588 (PTP) uses the same epoch as Unix, but PTP is based on International Atomic Time (TAI) and moves forward monotonically.
GPS uses an epoch of January 6, 1980.
Therefore, epoch and time reference are independent.

52. 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.
input
input
input
processing t1 t2 t3 t4
bus t1
val1

53. 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. 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. NTP (Network Time Protocol) principle
client
network
server
time t1
time request t2
network delay
time response t3  t4
time request
t’1
t’2
time response
t’3
network delay 
t’4
distance
Measures delay end-to-end over the network (one calculation)
Problem: asymmetry in the network delays, long network delays

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

57. peer delay calculation residence time calculation
IEEE 1588 – 1 step clocks
bridge
bridge
time
1-step transparent clock
1-step transparent clock
ordinary (slave) clock
grand master clock t1
Pdelay_Req t2
Pdelay_Req t1
Pdelay_Req t2
peer delay calculation t1 t2
Pdelay_Resp
link delay  t3 t4
Pdelay_Resp t4 t3
Pdelay_Resp (contains t3 – t2) t4 t3
Sync
residence time  t5
residence time calculation 
residence time
Sync t6  t5
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

58. References
To probe further

59. 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. 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. Networking: Printing Example
MPS = Master Printing System
LS = Leitstand (section supervision)
PM = Print Master
SS =Section Steuerung
(section control)
Production
MPS
Plant-bus (Ethernet)
Operator bus (Ethernet)
Console, Section Supervision LS LS LS PM LS LS LS PM LS LS LS PM LS LS LS PM
Printing Towers
Section Busses (AF100) B E C D
Section Control
SSB
SSC
SSD
SSE
Line bus (AF100)
Reelstand-Gateways
RPB
RPC
RPD
RPE
Reelstand bus (Arcnet)
Reelstands
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

62. 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. 3 Industrial Communication Systems
3.3 Field bus: standards Buses de terreno estándar Bus de terrain standard
Standard-Feldbusse

64. 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. Different classes of field busses
One bus type cannot serve
all applications and all device types efficiently...
Data Networks
Workstations, robots, PCs
Higher cost
Not bus powered
Long messages ( , files)
Not intrinsically safe
Coax cable, fiber
Max distance miles 10
100
1000
10,000
Sensor Bus
Simple devices
Low cost
Bus powered
Short messages (bits)
Fixed configuration
Not intrinsically safe
Twisted pair
Max distance 500m
frame size
(bytes)
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
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 10
100
1000
10,000
source: ABB
poll time, milliseconds

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

67. Worldwide most popular field busses
*source: ISA, Jim Pinto (1999)
Bus
User*
Application
Sponsor
CANs
25%
Automotive, Process control
CiA, OVDA, Honeywell
Profibus (3 kinds)
26%
Process control
Siemens, ABB
LON 6%
Building systems
Echelon, ABB
Ethernet
50%
Plant bus
all
Interbus-S 7%
Manufacturing
Phoenix Contact
Fieldbus Foundation, HART 7%
Chemical Industry
Fisher-Rosemount, ABB
ASI 9%
Building Systems
Siemens
Modbus
22%
obsolete point-to-point
many
ControlNet
14%
plant bus
Rockwell
Sum > 100%, since many companies use more than one bus
European market in 2002**: 199 Mio €, 16.6 % increase (Profibus: 1/3 market share)
**source: Elektronik, Heft

68. Field device: example differential pressure transducer
4..20 mA current loop
fluid
The device transmits its value by means of a current loop

69. 4-20 mA loop - the conventional, analog standard (recall)
The 4-20 mA is the most common analog transmission standard in industry
sensor
transducer
reader
reader
voltage source
10V..24V 1 2
i(t) = f(v)
flow
RL1 R1
RL2 R2
RL3 R3
RL4
RL4 conductor resistance
i(t) = 0, mA
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)

70. 3.3.2 HART
Data over mA loops

71. 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.
HART uses Bell 202 modem technology, ADSL technology was not available in 1989 (when HART was designed)
Transmission of device characteristics is normally not real-time critical

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

73. total: 44 standard commands, plus user-defined commands
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,…

74. HART - Importance
Practically all 4..20mA devices come equipped with HART today
About 40 Mio devices are sold per year.
more info:

75. 3.3.5 CAN
Automotive bus

76. CAN (1) - Data Sheet
Supporters Automotive industry, Intel/Bosch, Honeywell, Allen-Bradley
Standard SAE (automotive), ISO11898 (only drivers), IEC x (?)
Medium dominant-recessive (fibre, open collector), ISO 11898
Medium redundancy none
Connector unspecified
Distance 1 Mb/s (A); 100kb/s (B); 25kb/s (B)
Repeaters unspecified (useless)
Encoding NRZ, bit stuffing
User bits in frame 64
Mastership multi-master, 12-bit bisection, bit-wise arbitration
Mastership redundancy none (use device redundancy)
Link layer control connectionless (command/reply/acknowledgement)
Upper layers no transport, no session, implicit presentation
Application Protocols CAL, SDS, DeviceNet (profiles)
Chips comes free with processor (Intel: 82527, 8xC196CA; Philips: 82C200, 8xC592; Motorola: 68HC05X4, 68HC705X32; Siemens: SAB-C167

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

78. "The Dawn of Fast Ethernet"
The universal bus
To probe further: "Switched LANs", John J. Roese, McGrawHill, ISBN b
"The Dawn of Fast Ethernet"

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

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

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

82. The "real-time Ethernet"
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.
Method 1: Common clock synchronisation: return to cyclic.
Master clock
Method 2: IEEE 1588 (Agilent)
PTP precision time protocol
Method 3: Powerlink
B&R, Kuka, Lenze, Technikum Winterthur
Method 4: Siemens Profinet V3
synchronization in the switches

83. 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

84. 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. 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

86. Which are the selection criteria for a field bus ?
Assessment
Which are the selection criteria for a field bus ?
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?
What makes a field bus suited for hard-real-time operation ?
How does the market influence the choice of the bus ?

87. 3 Field busses 3.4 Industrial Wireless

88. 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)
Wireless technology is increasingly being used in several fields because of the tremendous advantages it is capable of offering. Even for industrial networks, its usage can offer numerous benefits such as reduced installation, reconfiguration and maintenance costs. avoiding adverse effects due to damage of cables and providing improved coverage of the factory floor
Standards leading to mass production and reduced prices

89. Wireless Landscape
There are many frequencies and protocols for a number of good reasons. There are many different application requirements for wireless. Some requirements are for high bandwidth – and long distance other are for low power short range…. These different needs dictate different technologies.

90. Wireless IEEE Numbers
Wireless communications is hardly new. Here are a few examples.

91. Requirements for Industrial Wireless
An application is said to be real-time if the total correctness of an operation depends not only upon its logical correctness, but also upon the time in which it is performed.
Based on this, Industrial applications can be classified into three different categories namely non real-time, soft real-time and hard real-time. In case of hard real-time applications such as control loops, tasks need to completed within the deadline, if not, it could lead to a critical failure of the complete system. A soft real-time application on the other hand will tolerate such lateness but may respond with decreased service quality (e.g., dropping frames while displaying a video). By contrast, a non-real time application is one for which there is no deadline, even if fast response or high performance is desired or even preferred.

92. 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

93. 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. 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. 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
face inherent characteristics of the wireless medium that conflict with the application requirements
Properties hamper the reliable delivery and stringent deadline requirements demanded by industrial applications.
A number of schemes have been developed to that
exploit the spatial and temporal diversity of the wireless channel to overcome the bursty error conditions.
Antenna redundancy uses multiple spatially seperated antennas to overcome the bursty channel error conditions
co-operative diversity scheme uses other nodes in the medium to provide efficient delivery of messages.
Several error correction codes are also being used to improve the reliability of the wireless medium.

96. 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 ReQuest (ARQ): Retransmit entire packets when receiver cannot decode the packet (acknowledgements)

97. 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. Existing protocols- comparison
Feature
802.11
Bluetooth
Zigbee /
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
Low
Real Time deadlines
???
This slide shows the comparison between the different wireless standards contrasting different characteristics such as the applications type each is optimized for
their but error rate, energy consumption and their mode of channel access.
As you can see, none of these standards provide hard real-time guarantees as required by industrial applications. Hence there arises a need to develop protocols specifically targeted towards the message characteristics and requirements of industrial applications

99. 10 km 3G 1 km 100 m 802.11b,g 802.11a Bluetooth 10 m ZigBee ZigBee UWB
Range
10 km 3G
1 km
100 m
802.11b,g
802.11a
Bluetooth
10 m
ZigBee
ZigBee
UWB
1 m
UWB
0 GHz
1GHz
2 GHz
3 GHz
4 GHz
5 GHz
6 GHz

100. Legal Frequencies www.fcc.gov
In each country organizations similar to the FCC exist and establish which EM frequencies can be used for communication. Some bands require a license, others are for everyone’s use.

101. Industrial Example: WirelessHART
Not part of exam 2015
HART (Highway Addressable Remote Transducer) fieldbus protocol
Supported by 200+ global companies
Since 2007 Compatible WirelessHART extension

102. WirelessHART Networking Stack
Not part of exam 2015
PHY:
2,4 GHz Industrial, Scientific, and Medical Band (ISM-Band)
Transmission power 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)
eine TDMA genutzt. Dazu wird die zur Verfügung stehende Zeit in
Für die Steuerung des Zugriffverfahrens auf das Medium wird
Kommunikationsbeziehung zugeordnet. Dazu werden zwei
jeweils 10ms Slots eingeteilt und jeder
Senke.
Geräten feste Rollen zugewiesen. Eines als Quelle und eines als
Quelle mit dem Senden einer Nachricht nach einer definiertes Zeit
Empfänger Synchron auf das Medium zugreifen. Dazu beginnt die
Um eine Kommunikation zu gewährleisten müssen Sender und
nach dem Start des Slots. Daraus kann sich die Senke den
übermittelt.
Ein Sonderfall ist der Broadcast, bei diesem wird kein ACK
Slotstart errechnen und darauf einstellen und antwortet mit ACK.
Da WirelessHART nicht nur in dem ISM-Band sendet und andere
Teilnehmer stören kann, sondern auch in diesem Band Empfängt
Verfügung stehenden Kanäle gemacht. Wenn auf Kanälen zu
werden. Um dieses zu minimieren wird ein Hopping über die zur
kann die Kommunikation von anderen Teilnehmern gestört
dauerhaften Störungen kommt oder diese nicht genutzt werden
werden beim Hopping ausgelassen.
sollen können diese auf Blacklisten eingetragen werden und
16 channels
jeden Teilnehmer dass er nicht nur Quelle wie auch Senke sein kann
Da WirelessHART als Mesh-Netzwerk betrieben wird bedeutet das für
redundante Pfade vorgehalten um so das Routing gegenüber den Ausfall
Zur Sicherung der Netzwerkinfrastruktur werden im Netz meistens
sondern auch die jeweiligen Pakete weiter routen muss.
eines oder mehrerer Konten zu sichern. Dieses kann eher mit Knoten in
eine Sterntopologie dabei ist jeder Knoten einen Hop vom Gateway
dienen und meist mehr beansprucht werden. Eine mögliche Alternative ist
der Nähe des Gateways passieren da diese als Dienstzugangspunkt
entfernt, was die Kommunikation sehr beschleunigt. Jedoch ist der große
Nachteil, dass es nur zu einer geringen räumlichen Ausdehnung des
Verfügung. Bei dem Graph-Routing für den Austausch von alarms,
Als Routing-Verfahren stehen das Graph- und das Source-Routing zur
Netzes kommt.
request/reponse, publishing, etc. kennt jedes Gerät einen Ausschnitt des
Information über das Routing hinzugefügt. Dies hat zur Folge das die
Bei dem Source-Routing wird in dem zu übertragenden Paket die
Netzwerkes, damit ist ein redundante und sichere Kommunikation möglich.
Redundanz möglich ist. Diese Verfahren wird nur beim Routentest der
Routing-Liste durch die Konten abgearbeitet wird und bei Fehlern keine
Jedes Gerät hat mindestens zwei Sessions mit dem Netwerk Manager
Die End-zu-End Kommunikation wird mit Hilfe von Sessions gesichert.
Fehlersuche und dem Aufbau einer Ad-Hoc-Verbindung genutzt.
eine für die paarweise Kommunikation und eine für den Broadcast.
Nachbar welche es weiter gibt. Für die Wahrung der Redundanz wird das
Dazu führt jedes Gerät Statistiken über die Kommunikation mit dem
Die Netzwerkperformance wird kontinuierlich beobachtet und angepasst.
Energieverbrauch zu senken wird versucht das Netzwerk möglichst .flach.
Netzwerk regelmäßig durch den Netzwerk Manager aktualisiert. Um den
Zur Steuerung des Datenflusses wurde dieser in 4 Kategorien eingeteilt. Die
zu halten.
Command-Pakete enthalten Payload zur Netzwerk-Diagnose, Konfiguration
den Prozess-Daten und Netzwerk-Statistiken. Jedoch werden diese
und Kontroll-Informationen. Die Process-Data-Pakete enthalten Payload zu
ist. Von Alarm-Pakete die Alarme und Events enthalten wird nur eines
Informationen verworfen wenn schon ¾ des Buffers eines Gerätes belegt
gebuffert. Alle Pakete die in keiner der drei Kategorien passen werden als
halber Buffer beim Feldgeräte zur Verfügung steht. Sind verschiedene
Normale-Pakete bezeichnet und werden solange gebuffert wie noch ein
Priorität der höchsten im Paket enthaltenen Priorität gegeben. Um die
Befehle verschiedener Priorität in einem Paket so wird dem Paket die
Als Erweiterung dieser Priorisierung wird vorgeschrieben das Keep-Alive,
Schwellenwerte anpassen.
Flusssteuerung fein granularer zu gestalten kann der Netzwerk Manager die
einem ACK beantwortet werden. Für das Empfangen und Weiterleiten von
Advertise und Disconnect Pakete empfangen werden müssen und mit
Command-Paketen sollte immer Buffer zur Verfügung stehen.

103. WirelessHART Networking Stack
Not part of exam 2015
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
Die Netzwerkperformance wird kontinuierlich beobachtet und angepasst.
Dazu führt jedes Gerät Statistiken über die Kommunikation mit dem
Nachbar welche es weiter gibt. Für die Wahrung der Redundanz wird das
Netzwerk regelmäßig durch den Netzwerk Manager aktualisiert. Um den
Energieverbrauch zu senken wird versucht das Netzwerk möglichst .flach.
zu halten.
Zur Steuerung des Datenflusses wurde dieser in 4 Kategorien eingeteilt. Die
Command-Pakete enthalten Payload zur Netzwerk-Diagnose, Konfiguration
und Kontroll-Informationen. Die Process-Data-Pakete enthalten Payload zu
den Prozess-Daten und Netzwerk-Statistiken. Jedoch werden diese
Informationen verworfen wenn schon ¾ des Buffers eines Gerätes belegt
ist. Von Alarm-Pakete die Alarme und Events enthalten wird nur eines
gebuffert. Alle Pakete die in keiner der drei Kategorien passen werden als
Normale-Pakete bezeichnet und werden solange gebuffert wie noch ein
halber Buffer beim Feldgeräte zur Verfügung steht. Sind verschiedene
Befehle verschiedener Priorität in einem Paket so wird dem Paket die
Priorität der höchsten im Paket enthaltenen Priorität gegeben. Um die
Flusssteuerung fein granularer zu gestalten kann der Netzwerk Manager die
Schwellenwerte anpassen.
Als Erweiterung dieser Priorisierung wird vorgeschrieben das Keep-Alive,
Advertise und Disconnect Pakete empfangen werden müssen und mit
einem ACK beantwortet werden. Für das Empfangen und Weiterleiten von
Command-Paketen sollte immer Buffer zur Verfügung stehen.
Zur Sicherung der Abwärtskompatibilität nutzt WirelessHART den Standard
HART-Application Layer. Mit der Device Description Language können
Transmitter, Steuerventile und analyse Instrumenten die entsprechenden
Paramter übergeben und Funktionen aufgerufen werden.
Zur Verbesserung Kommunikation in HART7 und zur Erweiterung zu
WiredHART wurde das .Smart Data Publishing. eingeführt. Dabei werden
Daten erst übertragen wenn sie gebraucht werden oder ein bestimmter
Schwellenwert erreicht wurde. Da durch die Latenz im Netzwerk
unterschiedliche Pakete unterschiedlich lange bei der Übertragung
benötigen können, wurde ein Zeitstempel eingeführt, um zu verhindern das
Latenz die Messergebnisse beeinflussen kann. Da Messungen nicht
kontinuierlich laufen müssen sondern nur wenn sich bestimmte
Umwelteinflüssen ändern soll es möglich sein Messungen zum Beispiel bei
bestimmten Vibrationen zu starten.
Für die Beschleunigung der Lese-Kommandos ist es möglich diese
zusammen zu fassen um diese so schneller hoch zu laden.
Um ein Netzwerk aufzubauen gibt der Netzwerk Manager dem
Gateway ein Netzwerk bekannt zu machen, zu annoncieren.
Dazu sendet der Gateway regelmäßig Informationen über die
Netzwerk-ID und die Zeitsynchronisation aus. Im späteren Verlauf
wird dieses auch durch die Teilnehmer gemacht um Feldgeräte zu
erreichen die außerhalb des Empfangsradius des Gateways
liegen zu erreichen. Diese Phase wird als Annoncierungs-Zyklus
bezeichnet.
Das Gerät hört die Netzwerk-ID und sendet über den Gateway
eine Anfrage zur Teilnahme an den Netzwerk Manager. Zur
Authentifizierung des Feldgerätes nutzt dieser den Security
Manager. Wenn das Feldgerät von diesen authentifiziert wird
sendet der Netzwerk Manager ein Aktivierungsdatenpaket und
definiert die Route zum Feldgerät. Abschließend werden die
Konfigurationsparameter, z.B. wie oft Prozessdaten gesendet
werden, ausgelesen und im Superframe eingetrage

104. 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
Availability is uptime assurance - maximizing uptime so you can access the information when you need it, especially in abnormal situations.
Reliability is message delivery assurance - are my messages consistently getting through when needed. that they’re accurate when they arrive.
Analogy of airline – availability is like having a private jet – it’s always there. Reliability is that it always get you there – but not guaranteeing a time window.

105. Why is a different wireless system deployed in a factory than at home?
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. References
Wireless Communication in Industrial Networks, Kavitha Balasubramanian, Cpre 458/558: Real-Time Systems,
WirelessHART, Christian Hildebrand, _Seminar_EDS_Hildebrand.pdf
WirelessHARTTM Expanding the Possibilities, Wally Pratt HART Communication Foundation,
Industrial Wireless Systems, Peter Fuhr, ISA,