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Industrial Automation
Automation Industrielle
Industrielle Automation
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
3.1
Industrial Communication Systems
Field Bus: principles
Buses de terreno: principios
Bus de terrain: principes
Feldbusse: Grundlagen
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
Industrial Automation
2013
Field buses: principles 3.1 - 2
Location of the field bus in the plant hierarchy
File
Edit
SCADA level
Operator
23
2
4
33
12
2
Engineering
Plant bus
Programmable
Logic Controller
Plant Level
Field bus
Field level
Sensor/
Actor
Bus
Sensor /
Actor
direct I/O
Industrial Automation
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Field buses: principles 3.1 - 3
What is a field bus ?
A data network, interconnecting an automation system, characterized by:
- many small data items (process variables) with bounded delay (1ms..1s)
- transmission of non-real-time traffic for commissioning and diagnostics
- harsh environment (temperature, vibrations, EM-disturbances, water, salt,…)
- robust and easy installation by skilled people
- high integrity (no undetected errors) and high availability (redundant layout)
- clock synchronization (milliseconds to microseconds)
- low attachment costs ( € 5.- .. €50 / node)
- moderate data rates (50 kbit/s - 5 Mbit/s), large distance range (10m - 4 km)
Industrial Automation
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Field buses: principles 3.1 - 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
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Field buses: principles 3.1 - 5
The original idea: save wiring
tray
marshalling
dumb devices
capacity
bar
I/O
B
e
f
o
r
e
PLC
(Rangierung,
PLC
COM
tableau de brassage (armoire de triage)
field bus
But: the number of end-points remains the same !
energy must be supplied to smart devices
Industrial Automation
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A
f
t
e
r
Field buses: principles 3.1 - 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
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Field buses: principles 3.1 - 7
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 (e-mail, files)
Not intrinsically safe
Coax cable, fiber
Max distance miles
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 500m
Honeywell
PV 6000
SP 6000
AUTO
1
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
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 mA)
Max distance 1200m
1000
poll time, milliseconds
Industrial Automation
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10,000
source: ABB
Field buses: principles 3.1 - 8
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.
Industrial Automation
2013
Field buses: principles 3.1 - 9
Fieldbus over a wide area: example wastewater treatment
Control Room
Japan
source: Kaneka, Japan
LAS
Remote
Maintenance
System
SCADA
Malaysia
Bus Monitor
Ethernet
H1 Speed Fieldbus
JB
Segm ent 1
Sub Station
Segm ent 3 JB
AO
AI
AI
PID
AI
PID
AI
Junction
Box
JB
AI
AI
AI
AI
PID AO
AO
Segm ent 2
JB
Segm ent 4
Motor
Control
Center
Digital Input/Output
AI
AI
M.C.C.
DI
FB Protocol
Converter
AI
AI
AI
AO
PLC
AO
AI
S
PID AI PID
AO
AO
AI AI
AI
S
S
S
S
AI
Numerous analog inputs/outputs (AI/AO),
low speed (37 kbit/s) segments (Hart) merged to 1 Mbit/s links (H1 Speed Fieldbus).
Industrial Automation
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Field buses: principles 3.1 - 10
Fieldbus Application: locomotives and drives
power line
radio
cockpit
Train Bus
diagnosis
Vehicle Bus
brakes
data rate
delay
medium
number of stations
integrity
cost
Industrial Automation
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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
Field buses: principles 3.1 - 11
Fieldbus Application: automobile
- Electromechanical wheel brakes
- Redundant Engine Control Units
- Pedal simulator
- Fault-tolerant 2-voltage on-board power supply
- Diagnostic System
Industrial Automation
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Field buses: principles 3.1 - 12
Networking busses: Electricity Network Control: myriads of protocols
SCADA
control
center
IEC 870-6
control
center
IEC 870-5
Modicom
RTU
COM
Inter-Control Center Protocol
ICCP
DNP 3.0 Conitel
RTU
control
center
HV
High
Voltage
RP 570 serial links (telephone)
RTU
RTU
Remote Terminal Units
RTU
substation
substation
FSK, radio, DLC, cable, fiber,... RTU
houses
RTU
MV
Medium
Voltage
LV
Low
Voltage
RTU
RTU
low speed, long distance communication, may use power lines or telephone modems.
Problem: diversity of protocols, data format, semantics...
Industrial Automation
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Field buses: principles 3.1 - 13
Engineering a fieldbus: consider data density (Example: Power Plants)
Acceleration limiter and prime mover: 1 kbit in 5 ms
Burner Control: 2 kbit in 10 ms
For each 30 m of plant: 200 kbit/s
Fast controllers require at least 16 Mbit/s over distances of 2 m
 Data transmitted from periphery or from fast controllers to higher level
 Slower links to control level through field busses over distances of 1-2 km.
The control stations gather data at rates of about 200 kbit/s over distances
of 30 m.
The control room computers are interconnected by a bus of at least 10 Mbit/s,
over distances of several 100 m.
Field bus planning: estimate data density per unit of length or
surface, response time and throughput over each link.
Industrial Automation
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Field buses: principles 3.1 - 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
2013
Field buses: principles 3.1 - 15
Industrial Automation
Automation Industrielle
Industrielle Automation
3
Industrial Communication Systems
3.2
Field bus operation
Buses de terreno: modo de trabajo
Bus de terrain: mode de travail
Feldbus: Arbeitsweise
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
Industrial Automation
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Field buses: principles 3.1 - 17
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
Industrial Automation
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value
quality
time
description
Field buses: principles 3.1 - 18
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
ASN.1: (TLV)
type
length
value
Field busses are slower (50kbit/s ..12 Mbits/s) and thus more compact encodings are used.
Industrial Automation
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Field buses: principles 3.1 - 19
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
air
pressure
16
bit offset
Industrial Automation
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line
voltage
32
size
time
stamp
48
64 66
70
all door closed
lights on
heat on
air condition on
Field buses: principles 3.1 - 20
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
correct variable
error
undefined
variable value
check
0 1 0 1 1 1 0 0
0 1
0 0 0 0 0 0 0 0
0 0
1 1 1 1 1 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
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Field buses: principles 3.1 - 21
hierarchical or peer-to-peer communication
PLC
“master”
central master / slave: hierarchical
alternate
master
AP
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
PLC
AP
Industrial Automation
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“masters”
AP
input
separate bus master from application master !
output
PLC
AP
“slaves”
output
AP
Application
Field buses: principles 3.1 - 22
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
application
processor
plant
image
…
application
processor
instances
…
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)
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.
Industrial Automation
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Field buses: principles 3.1 - 23
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
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Field buses: principles 3.1 - 24
Cyclic versus Event-Driven transmission
cyclic: send value strictly every xx milliseconds
individual
period
misses the peak
(Shannon-Nyquist!)
always the same,
why transmit ?
time
hysteresis
event-driven: send when value change by more than x% of range
how much hysteresis ?
- coarse (bad accuracy)
- fine (high frequency)
Industrial Automation
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limit update
frequency !,
limit hysteresis
nevertheless transmit:
- every xx as “I’m alive” sign
- when data is internally updated
- upon quality change (failure)
Field buses: principles 3.1 - 25
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
Industrial Automation
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Field buses: principles 3.1 - 26
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
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Field buses: principles 3.1 - 27
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.
Industrial Automation
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Field buses: principles 3.1 - 28
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
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Field buses: principles 3.1 - 29
Cyclic Data Transmission
address
Bus
Master
1
2
3
4
5
devices
(slaves)
6
Poll
List
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
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Field buses: principles 3.1 - 30
Round-trip delay of master-slave exchange
master
closest data sink
repeater
T_m
most remote data source
repeater
t_repeat
t_repeat
The
round-trip
delay limits
the extension
of the bus
propagation delay
(t_pd = 6 µs/km)
T_m
t_source
t_mm
t_ms
access delay
(t_repeat < 3 µs)
T_s
t_repeat
t_sm
T_m
distance
Industrial Automation
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Field buses: principles 3.1 - 31
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
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Field buses: principles 3.1 - 32
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
1
2
4a
8
16
1 4b
4 ms period
1
2
3
64
1
4a
time
1 ms period
(basic period)
1 ms
1 ms
group with
period 1 ms
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 highestpriority data. To reduce bus load, the master polls the process data, not the devices
Industrial Automation
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Field buses: principles 3.1 - 33
Cyclic Transmission with Decoupled Application
cyclic
poll
cyclic
algorithms
cyclic
algorithms
cyclic
algorithms
cyclic
algorithms
application
1
application
2
application
3
application
4
bus
master
Periodic
List
source
port
Traffic
Memory
Ports
Ports
Ports
sink
port
bus
controller
bus
controller
Ports
sink
port
bus
controller
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
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Field buses: principles 3.1 - 34
Example: delay requirement
publisher
application instance
device
subscribers application instances
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
Industrial Automation
2013
Field buses: principles 3.1 - 35
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
Industrial Automation
2013
Field buses: principles 3.1 - 36
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
eventreporting
station
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
2013
Field buses: principles 3.1 - 37
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
2013
Field buses: principles 3.1 - 38
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
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Field buses: principles 3.1 - 39
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)
Industrial Automation
2013
Deterministic
Central master,
Token-passing (round-robin),
Binary bisection (collision with winner)
Field buses: principles 3.1 - 40
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
Industrial Automation
2013
Field buses: principles 3.1 - 41
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
2013
Field buses: principles 3.1 - 42
Summary: Cyclic vs Event-Driven Operation
decoupled (asynchronous):
coupled (with interrupts):
application
processor
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
Industrial Automation
2013
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
Field buses: principles 3.1 - 43
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
Industrial Automation
2013
Field buses: principles 3.1 - 44
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:
• Users: set points, diagnostics, status
• System: initialisation, down-loading, ...
... motor current, axle speed, operator's
commands, emergency stops,...
-> 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
Industrial Automation
2013
periodic
phase
sporadic
phase
periodic
phase
Field buses: principles 3.1 - 45
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.
Industrial Automation
2013
Field buses: principles 3.1 - 46
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
implicit
Logical Link
Control
connectionless
connectionless
common
Industrial Automation
2013
Management
Interface
Field buses: principles 3.1 - 47
Application View Of Communication
Periodic Tasks
R1
R2
R3
Event-driven Tasks
R4
E1
Variables Services
(Broadcast)
node
E3
Message Services
Traffic
Memory
Process Data
E2
Queues
Supervisory
Data
Message Data
(unicast)
bus controller
bus
Industrial Automation
2013
Field buses: principles 3.1 - 48
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,
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)
Best use of resources
(aperiodic, demand-driven, sporadic)
object-oriented bus
message-oriented bus
Fieldbus Foundation, MVB, FIP, ..
Profibus, CAN, LON, ARCnet
Industrial Automation
2013
Field buses: principles 3.1 - 49
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
Industrial Automation
2013
Field buses: principles 3.1 - 50
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.
t1
t2
processing
input
input
input
t3
t4
bus
t1 val1
Industrial Automation
2013
Field buses: principles 3.1 - 52
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
2013
Field buses: principles 3.1 - 53
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)
Industrial Automation
2013
Field buses: principles 3.1 - 54
NTP (Network Time Protocol) principle
client
t1
network
server
time request
t2
network
delay 
time response
t3
t4

time request
(t 4  t1 )  (t3  t 2 )
2
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
2013
Field buses: principles 3.1 - 55
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
OC
OC
Two calculations: residence time and peer delay
All nodes measure delay to peer
TC correct for residence time (HW support)
Industrial Automation
2013
Field buses: principles 3.1 - 56
IEEE 1588 – 1 step clocks
time
ordinary
(slave) clock
t1
peer delay
calculation
Pdelay_Req
bridge
bridge
1-step
transparent
clock
1-step
transparent
clock
t2
t1
link delay
 t4
t3
Pdelay_Resp
(contains t3 – t2)
Pdelay_Req
t1
Pdelay_Req
t2
Pdelay_Resp
t3
t4
grand
master clock
t2
Pdelay_Resp
t3
t4
Sync
residence

time
residence time
calculation

t5
residence 
time
Sync
t5
t6
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
2013
Field buses: principles 3.1 - 57
References
To probe further
• http://www.ines.zhaw.ch/fileadmin/user_upload/engineering/_Institute_und_Zentr
en/INES/IEEE1588/Dokumente/IEEE_1588_Tutorial_engl_250705.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
2013
Field buses: principles 3.1 - 58
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
Industrial Automation
2013
Field buses: principles 3.1 - 59
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.
Industrial Automation
2013
Field buses: principles 3.1 - 60
Networking: Printing Example
MPS = Master Printing System
LS = Leitstand
(section supervision)
PM = Print Master
SS =Section Steuerung
(section control)
MPS
Production
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
C
Section Control
E
D
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
Industrial Automation
2013
Field buses: principles 3.1 - 61
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
2013
Field buses: principles 3.1 - 62
Industrial Automation
Automation Industrielle
Industrielle Automation
3
3.3
Industrial Communication Systems
Field bus: standards
Buses de terreno estándar
Bus de terrain standard
Standard-Feldbusse
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
Industrial Automation
2013
Field buses: principles 3.1 - 64
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 (e-mail, files)
Not intrinsically safe
Coax cable, fiber
Max distance miles
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 500m
Honeywell
PV 6000
SP 6000
AUTO
1
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
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 mA)
Max distance 1200m
1000
poll time, milliseconds
Industrial Automation
2013
10,000
source: ABB
Field buses: principles 3.1 - 65
Which field bus ?
• A-bus
• Arcnet
• Arinc 625
• ASI
• Batibus
• Bitbus
* • CAN
• ControlNet
• DeviceNet
• DIN V 43322
• DIN 66348 (Meßbus)
• FAIS
• EIB
* • Ethernet
• Factor
• Fieldbus Foundation
• FIP
* • Hart
• IEC 61158
Industrial Automation
2013
• IEEE 1118 (Bitbus)
• Instabus
• Interbus-S
• ISA SP50
• IsiBus
• IHS
• ISP
• J-1708
• J-1850
• LAC
• LON
• MAP
• Master FB
• MB90
• MIL 1553
• MODBUS
• MVB
• P13/42
• P14
• Partnerbus
* • Profibus-FMS
• Profibus-PA
• Profibus-DP
• PDV
* • SERCOS
• SDS
• Sigma-i
• Sinec H1
• Sinec L1
• Spabus
• Suconet
• VAN
• WorldFIP
• ZB10
• ...
Field buses: principles 3.1 - 66
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
Building systems
Echelon, ABB
LON
6%
Ethernet
50%
Plant bus
Interbus-S
7%
Manufacturing
Fieldbus Foundation, HART
7%
Chemical Industry
ASI
9%
Building Systems
Modbus
22%
obsolete point-to-point
ControlNet
14%
plant bus
all
Phoenix Contact
Fisher-Rosemount, ABB
Siemens
many
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 7 2002
Industrial Automation
2013
Field buses: principles 3.1 - 67
Field device: example differential pressure transducer
4..20 mA current loop
fluid
The device transmits its value by means of a current loop
Industrial Automation
2013
Field buses: principles 3.1 - 68
4-20 mA loop - the conventional, analog standard (recall)
The 4-20 mA is the most common analog transmission standard in industry
sensor
flow
transducer
i(t) = f(v)
RL1
reader
reader
1
2
R1
i(t) = 0, 4..20 mA
RL2
RL4
R2
voltage
source
10V..24V
RL3
R3
RL4
conductor resistance
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)
Industrial Automation
2013
Field buses: principles 3.1 - 69
3.3.2 HART
•
Industrial Automation
2013
Data over 4..20 mA loops
Field buses: principles 3.1 - 70
HART - Principle
HART (Highway Addressable Remote Transducer) was developed by Fisher-Rosemount to
retrofit 4-to-20mA current loop transducers with digital data communication.
HART modulates the 4-20mA
current with a low-level
frequency-shift-keyed (FSK)
sine-wave signal, without
affecting the average analogue
signal.
HART uses low frequencies
(1200Hz and 2200 Hz) to deal
with poor cabling, its rate is
1200 Bd - but sufficient.
Transmission of device characteristics is normally not real-time critical
Industrial Automation
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Field buses: principles 3.1 - 71
HART - Protocol
Hart communicates point-to-point, under the control of a master, e.g. a hand-held device
Master
Slave
Indication
Request
time-out
Response
Confirmation
Hart frame format (character-oriented, not bit-oriented):
preamble
start
address
5..20
(xFF)
1
1..5
Industrial Automation
2013
command bytecount
1
1
[status]
data
data
[2]
0..25
(slave response) (recommended)
checksum
1
Field buses: principles 3.1 - 72
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
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Field buses: principles 3.1 - 73
HART - Importance
Practically all 4..20mA 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
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Field buses: principles 3.1 - 74
3.3.5 CAN
•
Industrial Automation
2013
Automotive bus
Field buses: principles 3.1 - 75
CAN (1) - Data Sheet
Supporters
Standard
Medium
Medium redundancy
Connector
Distance
Repeaters
Encoding
User bits in frame
Mastership
Mastership redundancy
Link layer control
Upper layers
Application Protocols
Chips
Industrial Automation
2013
Automotive industry, Intel/Bosch, Honeywell, Allen-Bradley
SAE (automotive), ISO11898 (only drivers), IEC 61158-x (?)
dominant-recessive (fibre, open collector), ISO 11898
none
unspecified
40m @ 1 Mb/s (A); 400m @ 100kb/s (B); 1000m @ 25kb/s (B)
unspecified (useless)
NRZ, bit stuffing
64
multi-master, 12-bit bisection, bit-wise arbitration
none (use device redundancy)
connectionless (command/reply/acknowledgement)
no transport, no session, implicit presentation
CAL, SDS, DeviceNet (profiles)
comes free with processor
(Intel: 82527, 8xC196CA; Philips: 82C200, 8xC592;
Motorola: 68HC05X4, 68HC705X32; Siemens: SAB-C167
Field buses: principles 3.1 - 76
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)
+ application layer profiles
– interoperability questionable (too many
different implementations)
+ bus analyzers and configuration tools
available
+ Market: industrial automation, automobiles
Industrial Automation
2013
– small data size and limited number of
registers in the chips.
– no standard message services.
Field buses: principles 3.1 - 77
3.3.8 Ethernet
•
The universal bus
To probe further: "Switched LANs", John J. Roese, McGrawHill, ISBN 0-07-053413-b
"The Dawn of Fast Ethernet"
Industrial Automation
2013
Field buses: principles 3.1 - 78
Ethernet - another philosophy
classical Ethernet + Fieldbus
SCADA
switch
Ethernet
PLC
cheap field devices
decentralized I/O
cyclic operation
PLC
PLC
Fieldbus
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
Industrial Automation
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Field buses: principles 3.1 - 79
The Ethernet consortia
Ethernet/IP (Internet Protocol), Rockwell Automation
www.rockwellautomation.com
IAONA Europe (Industrial Automation Open Networking Alliance, (www.iaona-eu.com)
ODVA (Open DeviceNet Vendors Association, www.adva.org)
CIP (Control and Information Protocol) DeviceNet, ControlNet
ProfiNet
Siemens (www.ad.siemens.de), PNO (www.profibus.com)
« Industrial Ethernet » new cabling: 9-pin D-shell connectors
« direct connection to Internet (!?) »
Hirschmann (www.hirschmann.de)
M12 round IP67 connector
Fieldbus Foundation (www.fieldbus.org): HSE FS 1.0
Schneider Electric, Rockwell, Yokogawa, Fisher Rosemount, ABB
IDA (Interface for Distributed Automation, www.ida-group.org) Jetter, Kuka, AG.E, Phoenix Contact, RTI, Lenze, Schneider Electric, Sick
www.jetter.de
.. there are currently more than 25 standardized industrial Ethernets
Industrial Automation
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Field buses: principles 3.1 - 80
The Ethernet „standards“
IEC SC65C „standardized“ 22 different, uncompatible "Industrial Ethernets“, driven by „market demand“.
2
3
4
6
10
11
12
13
14
15
16
…
EtherNet/IP
Profibus, Profinet
P-NET
INTERBUS
Vnet/IP
TCnet
Ethercat
Powerlink
EPA
Modbus-RTPS
SERCOS
(Rockwell. OVDA)
(Siemens, PNO)
(Denmark)
(Phoenix)
(Yokogawa, Japan)
(Toshiba, Japan)
(Beckhoff, Baumüller)
(BR, AMK)
(China)
(Schneider, IDA)
(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
Industrial Automation
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Field bus standards 3.3 - 81
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
www.hirschmann.de, www.br-automation.com, www.lenze.de, www.kuka.de
Method 4: Siemens Profinet V3
synchronization in the switches
Industrial Automation
2013
Field buses: principles 3.1 - 82
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
2013
Field buses: principles 3.1 - 83
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.
Industrial Automation
2013
Field buses: principles 3.1 - 84
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
2013
Field buses: principles 3.1 - 85
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 ?
Industrial Automation
2013
Field buses: principles 3.1 - 86
Industrial Automation
Automation Industrielle
Industrielle Automation
3
Field busses
3.4
Industrial Wireless
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
2013
Field buses: principles 3.1 - 88
Wireless Landscape
Industrial Automation
2013
Field buses: principles 3.1 - 89
Wireless IEEE Numbers
Industrial Automation
2013
Field buses: principles 3.1 - 90
Requirements for Industrial Wireless
Events Registration
Measurements
Media
- ti
al
Re
Remote Control
Machine Health Monitoring
System Configuration
Internet Connectivity
me
Soft Real - time
No
n
Wireless Industrial
Applications
Hard
im
Real - T
e
Control Loops
Machine-to-machine communication
Industrial Automation
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Field buses: principles 3.1 - 91
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
Industrial Automation
2013
92
Field buses: principles 3.1 - 92
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
Industrial Automation
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Field buses: principles 3.1 - 93
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
Industrial Automation
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Field buses: principles 3.1 - 94
Challenges and Spectrum of Solutions
Wireless Challenges
Attenuation
Fading
Multipath dispersion
Interference
High Bit Error rate
Burst channel errors
Existing
Solutions
Existing
Solutions
Antenna Redundancy
Cooperative diversity
ARQ
Application Requirements
Reliable delivery
Meet deadlines
Support message priority
Industrial Automation
2013
Error Correction Codes
Modulation Techniques
Transmitter Design
Field buses: principles 3.1 - 95
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)
Industrial Automation
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Field buses: principles 3.1 - 96
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)
Industrial Automation
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Field buses: principles 3.1 - 97
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
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
Low
Real Time deadlines
???
???
???
Industrial Automation
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Field buses: principles 3.1 - 98
Range
10 km
3G
1 km
100 m
802.11a
802.11b,g
10 m
ZigBee
Bluetooth
ZigBee
UWB
1m
0 GHz
1GHz
Industrial Automation
2013
UWB
2 GHz
3 GHz
4 GHz
5 GHz
6 GHz
Field buses: principles 3.1 - 99
Legal Frequencies
www.fcc.gov
Industrial Automation
2013
Field buses: principles 3.1 - 100
Industrial Example: WirelessHART
• HART (Highway Addressable Remote Transducer) fieldbus
protocol
• Supported by 200+ global companies
• Since 2007 Compatible WirelessHART extension
Industrial Automation
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Field buses: principles 3.1 - 101
WirelessHART Networking Stack
• PHY:
– 2,4 GHz Industrial, Scientific, and Medical Band (ISM-Band)
– Transmission power 0 - 10 dBm
– 250 kbit/s data rate
• MAC:
– TDMA (10ms slots, static roles)
– Collision and interference avoidance:
Channel hopping and black lists
• Network layer:
– Routing (graph/source routing)
– Redundant paths
– Sessions and broadcast encryption (AES)
Industrial Automation
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Field buses: principles 3.1 - 102
WirelessHART Networking Stack
• Transport layer:
– Segmentation, flatten network
– Quality of Service (QoS): (Command, Process-Data, Normal, Alarm)
• Application layer:
– Standard HART application layer
– Device Description Language
– Smart Data Publishing (lazy)
– Timestamping
– Events
– Command aggregation
• Boot-strapping:
– Gateway announcements (network ID and time sync)
– Device sends join request
– Authentication and configuration via network manager
Industrial Automation
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Field buses: principles 3.1 - 103
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
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Field buses: principles 3.1 - 104
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
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Field buses: principles 3.1 - 105
References
• Wireless Communication in Industrial Networks, Kavitha Balasubramanian, Cpre
458/558: Real-Time Systems,
www.class.ee.iastate.edu/cpre458/cpre558.F00/notes/rt-lan7.ppt
• WirelessHART, Christian Hildebrand, www.tu-cottbus.de/systeme,
http://systems.ihp-microelectronics.com/uploads/downloads/
2008_Seminar_EDS_Hildebrand.pdf
• WirelessHARTTM Expanding the Possibilities, Wally Pratt HART Communication
Foundation, www.isa.org/wsummit/.../RHelsonISA-Wireless-Summit-7-23-07.ppt
• Industrial Wireless Systems, Peter Fuhr, ISA,
www.isa.org/Presentations_EXPO06/FUHR_IndustrialWirelessPresentation_EXPO06
.ppt
Industrial Automation
2013
Field buses: principles 3.1 - 106
Industrial Automation
Automation Industrielle
Industrielle Automation