Modern Instrumentation and Control

1
Chapter 1
INTRODUCTION
2
Topics

• Introduction
• Modern Instrumentation and Control
• OSI Model
• Protocols
• Standards

3
Introduction

• Transfer of Information From One Point to Another
• Transmitter/Receiver/Link
• Serial Links vs Parallel Links
• Digital Data vs Analog
• Mutual Agreement

4
Historical Background

• Telegraph System
• Morse Code
• Baudot Code

5
Three Themes

• Physical Standards
• Open Systems Interconnection
• Protocols

6
Standards

• EIA-232 Interface Standard
• EIA-485 Interface Standard

7
A Typical Serial Data Communications Link
8
Modern Instrumentation

• Distributed Control System (DCS)
• All Electronic tightly integrated system
• Programmable Logic Controller (PLC)
• Came from Relay Equipment
• SCADA System
• RTUs and Master Station - radio links
• Smart Instrumentation
• Intelligent Sensors on comms link
• Fieldbuses and Devicenets ( and HART)

9
Distributed Control System (DCS)

• Based Around a Data Highway
• Modular Distributed Integrated
• Each Module Performs Specific Dedicated Task
• Good on Analog Control
• Easy Connection to PLCs / supervisory Computer
  Interfaces

10
PLC

• Programmable Logic Controller
• Sequence Control and Interlocking
• On/Off Inputs/outputs
• Ladderlogic Type Programs

11
A Typical PLC System
12
SCADA

• Supervisory Control and Data Acquisition System
• RTUs to Master Station
• Radio Links /Landlines
• Also term used for SCADA Software package eg
  Citect

13
Smart Instrumentation

• Microprocessor Based Instrument
• Embedded Controllers
• Data Communications Capability
• RS- 232, RS 485 or Fiber Optic
• Ability to Multi-drop With Other Instruments on
  Same Highway
• Wave of the Future...Eg Fieldbus

14
OSI Model

• Developed by the ISO
• Universal Framework for Building A Communications
  Systems
• 7 Layer Model
• 3 Layer Model Very Common for Industry
• Missing the 8th Layer

15
Representation of the OSI Model
16
Standards Within A Communications System

• Code - Morse - Hex - ASCII
• Physical - 232 - 422 - 485
• Protocol - Modbus, Profibus, Hart, Foundation
  Fieldbus, Ethernet
• Open Systems Interconnection Model

17
Protocols

• Rules for Transmission of Data (Packets)
• Packet Can Include
• Sync Byte
• Destination Address
• Source Address
• Data
• Error Detection
• Modbus - Profibus - Canbus - Ethernet - TCP/IP
• HDLC - DH - HART - DNP3 - Interbus - FTP

18
Basic Structure of an Information Frame Defined

• SYNCHRONIZING BYTE Is Used To Synchronize The
  Receiver.
• DESTINATION ADDRESS Is Where The Packet Is
  Going.
• SOURCE ADDRESS Is Where The Packet Has Come
  From.
• DATA Is The Information Contained In The Packet.
• ERROR BYTE Is The Result Of The Error Correction
  Calculation.

19
Voltage Standards

• EIA/RS-232 Interface Standard
• Half / Full Duplex - Point to Point
• EIA/RS-485 Interface Standard
• Half Duplex - Multidrop

20
RS-232
21
Two Wire Multidrop RS-485
22
Fiber Optic Cable
23
Modbus Protocol Structure
24
Modbus Plus

• Builds on Modbus
• Token Passing and deterministic
• High Speed - minimum of 1Mbit/s

25
DH Protocol Structure
26
HART Protocol4 - 20 ma Communications
27
ASI Bus

• Idiot Proof
• 167kbps and fast for digitals
• 31 slaves and 124 I/O points with 5ms scan

28
The DeviceNet Model
29
ProfibusTypical Architecture of System
30
Foundation Fieldbus

• Newest Fieldbus
• H1 standard - 31.25kbit/s
• HSE - 100Mbit/s
• Three layers plus excellent User Layer

31
Ethernet 10BaseT
MAC Media Access Control
32
TCP/IP

• Internet Protocol (IP)
• Transmission Control Protocol (TCP)
• Application Layer
• Three Layer Model
• Derived from Internet

33
Wireless Communications