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FC-E - Design of Industrial Automation

Functional Specifications for PLCs, DCSs and
SCADA Systems

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Short Description
This manual will be useful to both specifiers and implementers providing a
theoretical grounding for preparing a control system functional specification for
implementation on Industrial control systems consisting of PLC (Programmable
Logic Controllers), HMI (Human Machine Interfaces / SCADA devices) or DCS
(Distributed Control Systems).

Description
This manual will be useful to both specifiers and implementers providing a
theoretical grounding for preparing a control system functional specification for
implementation on Industrial control systems consisting of PLC (Programmable
Logic Controllers), HMI (Human Machine Interfaces / SCADA devices) or DCS
(Distributed Control Systems).

Table of Contents
Download Chapter List

Table of Contents
First Chapter
Design of Industrial Automation Functional Specifications for PLCs, DCSs
and SCADA Systems - Function Design Specifications (FDS)

1 Functional Design Specifications (FDS)

In this chapter a brief overview of control system FDS is given. The important
industrial terms and naming conventions are discussed and the standards are
highlighted.

Learning objectives

You will learn about:

Overview of control system FDS

Essential industry terms and abbreviations used in the FDS
Naming conventions and standards
Control philosophy needed in guiding the FDS

1.1 Overview of control system FDS

Any Supervisory Control and Data Acquisition (SCADA) project will be successful
if, and only if, the creating, understanding and execution of the functional
specifications are executed perfectly. These technical specifications are
important in the overall development and designing of control systems which
contain the technical details that lead to the success of the project. These
functions are as important as that of the mechanical sections.

For example, consider piping. The complete description of the valves, pumps,
chillers, piping specialties and other components used to construct the piping
system are given in piping specifications. Designers will not submit a project
without this important information for the piping system. In general, this kind of
thorough information is not included for control systems. The lack of proper
technical specifications for control systems may lead to difficulty in meeting the
project’s design objectives. The design process is said to be successful if it
contains descriptions of maintenance, operation and commissioning
requirements. This leads to efficient building, and ensures the operation runs
smoothly.

A functional specification defines what the system should do and what functions
and facilities are to be provided. It provides a list of design objectives for the
system.
A standard specification of the project should consider what is generally available
in the market and what can reasonably be called upon for options. It is of no use
to specify aspects which suppliers cannot provide at a reasonable cost and within
a sensible time frame. The aim is to match what the manufacturer can offer,
within their standard range of equipment. An efficient approach, by the
purchaser, is to select standard equipment which is suitable for the manufacturer
and then design the power system around the equipment to be purchased. In
general, this approach will reduce the amount of time needed to design the
power system.

Functional aspects of the specification should be considered carefully. The

function of basic equipment such as generators, motors and switchgear will be
understood easily. But, in order to gain an understanding of what is required, it is
essential to pay attention to the design and performance details. Functionality
implies a more interrelated type of existence, as is the case with systems of
equipment rather than individual items of equipment.

Functional specifications in the area of process control systems cover the

following:

SCADA systems
Power management control system
System computer
Measuring devices
Controller set points
Switchgear
Rotating machines.

The entire system should be defined functionally and all the elements should be
compatible from the conceptual stage of the specification.

Control System Engineers analyze the following, to develop the design and
functional specifications of automation systems:

User requirements
Procedures
Design process
Mechanical equipment
Problems to identify the system components.

The automation system helps the equipment to function in a required manner.

The interface between the hardware and software development, for the
automation system, is the responsibility of Control System Engineers.

A FDS is the most important stage in the design of any control system. It
provides details of the solution to be implemented, to meet user requirements. It
should be accepted by the user and should form the basis of the design for both
hardware and software. An excellent FDS clearly specifies the following which
are associated with the system:

Functions
Operator interactions control

Therefore, before the system is developed, the user must confirm whether the
proposed solution fully meets the specified requirements or not. A FDS is
considered as the basis for the design of the system. It is used during testing to
verify and validate the system, to ensure whether all the required functions are
present and that they operate correctly.

A FDS has all the information associated with the control system including:

Details of how each area of the plant operates under automatic control
(control philosophy)
Details of the SCADA system i.e. screen layouts, navigation charts, alarm
handling, trending and reporting
Details of the Network architecture
Details of any local operator interfaces.

Figure 1.1

Control system design

The FDS should cover:

Control Modules such as PID Loops, indicators etc

HMI Graphic displays
Equipment Basic Control
Phase Logic
Operations
Unit Procedures
SCADA Recipes
 The Inputs and Outputs of the systems with cards and channels assigned
to them.

1.1.1 Benefits of using a FDS

There are numerous benefits provided by a complete and coherent FDS which
include time savings of approximately 50% of total time and a saving of
resources and money of approximately 25%. These benefits are achieved only
after everyone is involved in designing, developing, testing, approving of an
application, signing the document containing an ordered list of all design and
functional requirements.

By using a FDS (Functional Design Specification):

The manufacturer knows exactly what to develop & deliver

The system integrators know exactly what they are working with
Quality Assurance knows exactly what to test
The client knows exactly what they will be getting.

1.2 Essential industry terms and abbreviations used in the FDS

Technical terms and abbreviations are easily understood by professionals in one

field whereas they may be confusing to others from another field, and may be
misunderstood. Therefore, it is necessary to understand the abbreviations and
some of the terms that are used in the text and elsewhere in the industry.

The following are the essential industry terms and relevant abbreviations used in
functional design specifications:

Table 1.2

Industrial terms and their abbreviations

Industry Abbreviations
terms
AGC Automatic Generation Control
API Application Programming Interface
CORBA Common Object Request Broker Architecture
C&I Control and Instrumentation
CPU Central Processing Unit
CRC16 16-bit Cyclic Redundancy Check
CSMA/CD Carrier Sense Multiple Access/Collision Detection
CT Current Transformer
DC Direct Current
DCS Distributed Control System
DMS Distributed Management System
DNP Distributed Network Protocol
DOD Department of Defense
DOE Department of Energy
DISCO Distribution Company
DNP/DNP3 Distributed Network Protocol, version 3.0
DPI Double-Point Information
EMS Energy Management System
EMC Electromagnetic Compatibility
EMI Electromagnetic Interference
EPROM Erasable Programmable Read-Only Memory
FTP File Transfer Protocol
FDS Functional Design Specification
FS Functional Specification
FAT Factory Acceptance test
FMEA Failure Modes and Effect Analysis
FPGA Field Programmable Gate Array
GUI Graphical User Interface
GAMP Good Automated Manufacturing Practice
GAL Generic Array Logic
GENCO Generation Company
GPR Ground Potential Rise
HMI Human Machine Interface
HDS Hardware Design Specifications
I/O Input/Output
IED Intelligent Electronic Devices
ICCP Intercontrol Centre Communications Protocol
IEEE Institute of Electrical and Electronics Engineers
INEEL Idaho National Engineering and Environmental Laboratory
ISO Independent System Operator or International Organization for
Standardization
IRIG-B Inter Range Instrumentation Group format B
ISA Instrumentation Systems and Automation Society
IT Information Technology
ITU International Telecommunication Union
LCD Liquid Crystal Display
LED Light Emitting Diode
LAN Local Area Network
MMI Man Machine Interface
MTBF Mean Time Between Failure
MTTR Mean Time To Repair
NIM Network Interface Module
NISAC National Infrastructure Simulation and Analysis Centre
NRC Nuclear Regulatory Commission
NTP Network Time Protocol
OASIS Open Access Same - Time Information System
ODBC Open Database Connectivity
PID Proportional, Integral and derivative controller
POSIX Portable Operating System Interface
PLC Programmable logic Controller
P & ID Process & Instrumentation Diagram
PSU Power Supply Unit
PCS Process Control System
PROM Programmable Read-Only Memory
PSTN Public Switched Telephone Network
PT Potential Transformer
RTU Remote Terminal Unit
REA Rural Electric Association
RTO Regional Transmission Organization
RAID Redundant Array of Inexpensive Disks or Redundant Array of
Independent Disks
ROM Read-Only Memory
SCADA Supervisory Control and Data Acquisition
SAT Site acceptance test
SOE Sequence of Events
SNTP Simple Network Time Protocol
SPI Single-Point Information
SQL Structured Query Language
SWC Surge Withstand Capability
TASE Telecontrol Application Service Element
TRANSCO Transmission Company
TCP/IP Transmission Control Protocol/Internet Protocol
T&D Transmission and Distribution
UHF Ultra High Frequency
UPS Uninterruptible Power Supply
UTP Unshielded Twisted Pair
VDU Video Display Unit
WAN Wide Area Network
1.3 Naming conventions and standards

The General Design Principles (GDP) defines the number of conventions to be

used.

For example, consider the standard color scheme. In one division of the plant a
device is colored red, meaning 'stopped', and in another part of the plant the
same type of motor is colored red, meaning 'dangerous condition'. This may lead
to disaster, but by following naming conventions, such risks will be reduced.

Adopting a standardized reliable naming convention for devices controlled by the

system, will be favorable for scalable and maintainable systems in the long run.
In some cases, the naming conventions used are forced on the system by
external influences. Therefore, they should be properly documented in the GDP.

Examples of tagging and naming conventions are:

Graphic symbols
Instrumentation naming.

Naming conventions and standards are explained in further detail in the next
chapter.

1.4 Control philosophy in guiding FDS

Philosophy is a belief or a system of beliefs, accepted as authoritative by some

groups. Control philosophy is a guideline for a FDS which describes the basic
dos and don'ts and requirements of a FDS from the point of view of the end user.
It should describe the following:

Level of process automation

Information handling needs
Operational requirements
Requirement of flexibility
Level of control intervention
Operators work and skill
Management skills for both organization and data communication
Level of management needed
Extent of manual control required
Extent of the physical area the system is covering
Type of communication system
Level of security needed for communication
Type of control processing.

1.5 Summary
 This chapter summarizes the following:

A functional specification defines what the system should do and what

functions and facilities are to be provided.
An excellent FDS clearly specifies the following associated with the
system:
Functions
Operator interactions control

There are numerous benefits provided by a complete and coherent FDS,

which include time savings of approximately 50% of total time and a
saving of resources and money of approximately 25%.
It is necessary to understand the abbreviations and some of the terms
that are used in the text and elsewhere in the industry.
Technical terms and abbreviations are easily understood by professionals
in one field whereas it may be confusing to others and may be
misunderstood
Adopting a standardized reliable naming convention for devices,
controlled by the system, will be favorable for scalable and maintainable
systems in the long run
Control philosophy is a guideline for a FDS, which describes the basic
dos and don'ts and basic requirements of a FDS, from the point of view of
the end user.

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