Sistema scada de supervisorio, Manuais, Projetos, Pesquisas de Engenharia Elétrica

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AGENDA

• Introduction – Basics of Data Communication

• Serial Communication

• Ethernet Communication

• Modbus Protocol

• DNP Protocol

DATA C OMMUNICATION

Communication Link

• Symplex
• Half-Duplex
• Full-Duplex

Broadband

• Many different channels
• Ex: Home cable

Baseband

• Single channel
• Entire bandwidth of link transmits one bit

Character Encoding

• ASCII
  • Ex A = 00101000
• Hexadecimal
  • Base of 16
  • Digits 0-9 and letters A-F

SERIAL C OMMUNICATION

• Only 2 wires are required between transmitter and receiver
• 8 electrical on/off voltage signals are sent in a sequence w.r.t a time base
• Data transfer is done bit by bit arranged in a particular format - Baud Rate - A measure of how fast serial data is moving between devices per second - Data Packet - Characters transmitted one after the other in short bursts. - Contains address, data and error check

PARITY E RROR

• Errors inevitably occur in the transfer of data due to noise and timing errors
• Parity error checking is a very simple form of error detection
• Limited to detection of a single bit error
• User can use even or odd parity

NETWORKS

NETWORK TOPOLOGIES

• SCADA communication topologies classification:
  • Physical Topology: Physical connection of wires between the devices in a network.
  • Logical Topology: Refers to how the information is through the network among the devices.
  • In many instances, the logical topology is same as the physical topology.
• Physical topologies:
  • Point to point and multi-point (multi-drop)
  • Bus topology
  • Ring topology
  • Star topology
  • Mesh topology

NETWORK TOPOLOGIES

Bus topology

• Commonly used for master station communication
• Each node is connected to a single or redundant bus that carries the message
• Advantages: Cost effective, reliable and easy to expand
• Disadvantages: Bus failure and delay in message transmission during heavy traffic.

NETWORK TOPOLOGIES

• Ring topology
• All the nodes including the master form a ring

STANDARDS

• Need for a common set of rules

C OMPATIBILITY

• The pure physical connection standard
• The existence of complementary software standards used in conjunction with the physical standards
• Confirmability of physical connection and software to open system interconnected model

OPEN SYSTEM INTERCONNECTION

OPEN SYSTEM INTERCONNECTION

DATA L INK

• Provides service that allow communication between devices
• Framing or separation of messages
• Error detection
• Correction mechanism
• Addressing mechanism
• Direct exchange of frames among devices on a single

communications channel

OPEN SYSTEM INTERCONNECTION

N ETWORK

• Responsible for device-to-device data delivery and optimal routing across multiple data links

TRANSPORT

• Guaranteed-delivery messaging service ensuring data is error free and correctly sequenced
• Allowing process-to process communications between devices across a network or multiple networks

S ESSION

• Mechanism for the establishment of a communication session between applications running within the devise

RS 232/

• 1969: EIA developed and introduced RS 232
• Defined electrical and mechanical details of the interface for serial transfer of characters between Data Terminal Equipment such as printers and computers to Data Communication Equipment.
• A lot of flexibility open to the designer of the hardware regarding the rules of data exchange

RS 232/

FOR THE RECEIVER

• Logic one = - 3V to -25V
• Logic zero = +3V to +25V
• Undefined signal = > -3V and <+3V

SLEW RATE

• It will take sometime for the transmitter output to swing from +25V to -25V. This delay is called the slew rate
• Slew rate is one of the factors that limits the maximum transmission rate