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
  •     Sequencing.

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.

EIT Stock Image

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 terms

Abbreviations

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
  • Sequencing.
  • 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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