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BASICS OF SENSOR NETWORKS
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Sensor Networks © 2014: Dr. H. K. Verma
Dr. H. K. Verma
Distinguished Professor (EEE)
Sharda University, Greater Noida
(Formerly: Deputy Director and Professor of Instrumentation
Indian Institute of Technology Roorkee)
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CONTENTS
Sensor Networks © 2014: Dr. H. K. Verma
1. Industrial Data Networks
2. LAN Topologies
3.
Device Level Networks
4. 7-Layer OSI Model of Communication System
5.
Networking of Sensors
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Sensor Networks © 2014: Dr. H. K. Verma
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!
Communication among computers/ servers/ work-
stations
! Communication between computer and peripherals
!
Communication between computer and intelligent
instruments
! Communication among field devices (Factory-floor or
field communications) using: " Transducer networks or Sensor networks, or" Field-device networks or Device-level networks, or
" Sensor and actuator networks, or" Factory-wide networks
Industrial Data Communications
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Sensor Networks © 2014: Dr. H. K. Verma
Hierarchy of Industrial Data Networks
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FD FD FD FD
ServerPC
Enterprise – levelnetwork
(LAN / WAN)Control Terminal Control Terminal
Device-level network(LAN/PAN)
FD: Field Device (Sensor / Actuator/etc.)
Control – levelnetwork
(LAN)Industrial Controller/PLC/RTU
Workstation
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Sensor Networks © 2014: Dr. H. K. Verma
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Data Networks in Industry
!
Enterprise NetworkNetwork of the PCs, workstations and servers in Offices
and the control terminals (PCs) in Control Room.
!
Control-Level Network Network of the control-terminals (PCs) and industrial
controllers (PLCs), which are either in Control Room oron Factory Floor.
! Device-Level Network
Network of a controller/PLC/RTU in Control Room with
its field devices (Sensors, Actuators, etc.) on FactoryFloor.
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Sensor Networks © 2014: Dr. H. K. Verma
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LAN Topologies
! Basic Topologies
1. Point-to-Point2. Multipoint
! Multipoint Topologies
1. Bus2. Ring
3.
Star4. Tree5. Mesh
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Bus (or Multidrop)Topology
S t a t i o n
s
BusData flow
T
Tap
!
Bus is a linear transmission medium
! Data flow is bidirectional
! Stations connected through taps taken from bus
! Terminator (T) absorbs signal, thus avoids echos
T
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Ring (or Loop)Topology
!
Nodes (computers) are connected in tandem (series) to form closed loop! Data flows through nodes (computers)
! Data flow is unidirectional
! Each node acts as a repeater
! It receives a data on one link and transmits bit-by-bit on other link
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Star Topology
! Network comprised of many point-to-point circuits! Central node: Hub or switch! Hub: Operates in broadcasting mode! Switch: Operates as frame-switching device
Central node
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Tree Topology
Headend
Branches
Data flow
T
Tap
! Generalization of bus topology
! Each branch may have further branches
T
T
Data flow
Data flow
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Mesh (or Fully Connected) Topology
! Each station has a bidirectional link to every other station
! Less traffic problems, high reliability, high security
! Large no. of links: n(n-1)/2 links for n nodes
! Each station must have n-1 I/O ports
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Device–Level Wired Network
FD: Field Device (Sensor / Actuator/etc.)
Control – level network
(Ethernet)
FD FD FD FD
Device-level network
Industrial Controller/PLC/RTU
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FD FD FD
Device–Level Wireless Network
FD: Field Device (Sensor / Actuator/etc.)
Device-level network
Control – level network
(Ethernet)
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Industrial Controller/PLC/RTU
Access Point
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Special Requirements of Device Level Networks
!
Low latency or small end-to-end delay
! Low bandwidth or data rate
! High data security
!
High network security
! Low power consumption or long battery life(for wireless networks only)
T h l i /P t l
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Technologies/Protocolsfor Device-Level Networks
Technologies/Protocolsfor Wired Networks
! RS422
! RSR485
!
MODbus
! Foundation Fieldbus
! HART
! CAN
! LON
! BACNet
Technologies/Protocolsfor Wireless Networks
! Zigbee
!
Wi-Fi
! Bluetooth
! Wireless Fieldbus
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7-Layer OSI Model of Communication Systems
! Open System Interconnection model
! Prepared and issued by International Standards Organization
! Reference model of communication systems
! Defines functions of a communication system in 7 layers
!
For use as reference or model to identify and classify the
various functions of a given communication system
! Not a standard or set of prescriptions for a communication
system to adhere to
! For any communication system, layers 1 and 7 are
essential, while some middle layers may be absent
! A communication protocol or standard may not define all
the 7 layers, it may define as few as one layer.
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Data Transfer Between Systems
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-Link Layer
Physical Layer
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-Link Layer
Physical Layer
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Functions of Seven Layers
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data-Link Layer
Physical Layer
Signal
Application Programs
Data Presentation(Encryption, Compression, Data Formatting)
Inter-Application Dialogues
Addressing
Network Routing
Medium Access Control, Frame Format
Comm. Medium, Connectors,Data-to-Signal Conversion,
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Networking of Sensors
Four Situations:
Situation A – Ordinary Sensor + SC + MPU + Interface
Situation B – Network Sensor
Situation C – Smart Sensor + Custom Interface
Situation D – Smart Sensor + IEEE 1451 Interface
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Situation A: Ordinary Sensor+SC+MPU+Interface
Ordinarysensor
Network
SC ADC !pComm.
interface
Advantage ! Flexibility
Disadvantages ! Cumbersome
! Only expert can do! Expensive
Comm.port
ROM
RAM
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Situation B: Network Sensor
Smartnetwork
sensor
Network
Comm. port
Advantages ! Simple
! Fast! No expertise required
Disadvantage ! No flexibility of network protocol
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Situation C: Smart Sensor + Custom Interface
Smart
sensorNetworkADC MPU
Customcom
interface
Comm.
port
Advantage ! No SC required
Disadvantages ! Cumbersome
! Only expert can do
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S N k © 2014 D H K V
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Situation D: Smart Sensor + IEEE1451 Interface
Smartsensor
NetworkSTIM NCAP
IEEE 1451–Compliant
Advantages ! No SC required
! Flexibility of network protocol
Disadvantage ! Needs STIM & NCAP