Systems integration using Siemens' PC based automation technology

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Systems integration using Siemens' PC based

automation technology

Adwait Palsule

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Systems

Integration

Using

Siemens'

PC

Based

Automation

Technology

Adwait Arvind Palsule

M.S. (Computer Integrated

Manufacturing)

Thesis

submitted

in

partial

fulfillment

oftherequirements

for

the

Master

of

Science in

department

of

Manufacturing Engineering Technology

in

the

College

ofApplied

Science

and

Technology

ofthe

Rochester Institute

of

Technology

COLLEGE OF APPLIED SCIENCE & TECHNOLOGY

ROCHESTER INSTITUTE OF TECHNOLOGY

ROCHESTER, NEW YORK

CERTIFICATE OF APPROVAL

MASTER OF SCIENCE DEGREE THESIS

The M.S. Degree Thesis of Adwait Arvind Palsule has been examined and

approved by the thesis committee as satisfactory for the Thesis requirement

for the Master of Science Degree in Computer Integrated Manufacturing

Dr. Sudhakar R. Paidy

Dept. of Industrial and Systems Engineering

Kate Gleason College of Engineering

Prof. S. Manian Ramkumar

Dept. of Manufacturing Engineering Technology

Permission granted

Systems Integration Using Siemens'

PC Based Automation Technology

I, Adwait Arvind Palsule, hereby grant the permission to the

Wallace Library of the Rochester Institute of Technology to

reproduce my thesis in whole or part. Any reproduction will not be

for commercial use or profit.

Dedication

To my

parents and

family,

Acknowledgement

Throughout

the time

I

have been

working

in

this

applied research

study,

many

people

have

assisted me.

It

is impossible

to

acknowledge

them

all.

Nevertheless,

I

would

like

to

specifically

thank the

following

individuals:

Dr.

Sudhakar

Paidy,

for

all

the time

he

dedicated

to

my

research work and

for

the

knowledge he

shared with me

throughout the

course of

this

study.

This

thesis

wouldnot

have

been

possible without

his help.

Prof.

S.

Manian

Ramkumar,

for his

continuous support and valuable

comments on

my

work.

Mr. Dennis

Wilk,

Mr.

Barry

Hawley,

and

Mr. Peter

Stansky

of Siemens'

Energy

and

Automation

for

their

constant

help

and

technical

support.

To Prakash

Gandhi,

fellow

graduate research

assistant,

for his

support,

advice and comments

throughout the

course of

this

study.

To

all

my

friends

who

helped

me

from

the

beginning

of

my

thesis

for giving

valuable support and comments and

those

who

helped

me

to

prepare

for

the

Table

of

Contents

Sections

Page No

Abstract

1

Introduction

1

2

Data Communication for Process Control

4

2.1

Introduction

4

2.2

Data Transfer Modes

4

2.3

Serial Communication Standards

5

2.4

Parallel Communication Standard

7

2.5

Network

Interfaces

8

2.6

ISO OSI

seven

layer

model

10

2.7

Topology

of

Simatic NET Profibus

network used

in CAMCELL

12

2.8

Glossary

of

Terms

13

3

Programming

Languages

for Process Control

16

3.1

Introduction

16

3.2

Graphical

Programming

Languages

16

3.3

Statement Lists

19

3.4

Sequential

Programming

Languages

20

3.5

Structured Control Language

23

4

Simatic PC Based Automation System

25

4.1

Introduction

25

4.2

General Architecture

of

Simatic Automation System

25

4.4

Simatic NET

26

4.5

Simatic

Distributed I/Os

27

4.6

Simatic HMIs

27

4.7

Step7 Software

27

5

Description

ofthe

CAMCELL Architecture

39

5.1

Description

of

CAMCELL

39

5.2

Manufacturing

and

Material

Handling

System

39

5.3

Product/Process Flow

40

5.4

Computer Hardware Architecture

40

6

Control

ofthe

CAMCELL Material

Handling

System

43

6.1

Introduction

43

6.2

Components

ofthe

Material

Handling

System

43

6.3

Control

ofthe

CAMCELL Material

Handling

System

44

7

CAMCELL Automation

50

7.1

Introduction

50

7.2

Simulation

of a

Flexible

Manufacturing

System

50

7.3

WTNCC

tagsused

in

the

CAMCELL

Control Software

51

7.4

Inquire

52

7.5

Pallet Controller

54

8

Conclusions

57

List

of

Figures

Fig

No.

Name

of

Figure

Page No.

2

Data Communication for Process Control

6

2. 1

Structure

of a shielded

2-core Profibus Cable

6

2.2

Profibus

Access

Techniques

7

2.3

Star

Topology

8

2.4

Ring Topology

9

2.5

ISO OSI Seven-Layer

model

1

1

2.6

Simatic NET

topology

asused

in

the

CAMCELL

application

12

3

Programming

Languages

for Process Control

16

3.1

A rung in

a

ladder logic

program

1

6

3

.2

An

example of a

rung in

a

LAD

program

1 7

3.3

An

exampleofa

block

in

a

Functional Block Diagram

18

3.4

An

example of

STL instruction

1 9

3.5

Grafcet Program

20

3.6

A Graph

program

22

3.7

A function block in SCL

23

4

Simatic PC Based Automation System

25

4.1

Components/architecture

ofthe

Simatic Automation System

25

4.2

Using

Step7

tocombinethe

hardware

withthesoftware

28

4.3

Basic

tasks

in

an automation project

using

Step

7

29

4.4

Basic

architecture

in

control application

in

Siemens'

Technology

30

4.5

Project

Structure

within

Simatic Manager

3 1

4.6

Components

of

WinLC

32

4.7

Absolute

Addressing

33

4.8

Project

Structure

within

WTNCC Explorer

35

Fig

No.

Name

of

Figure

Page No.

5

Description

ofthe

CAMCELL

architecture

39

5.1

CAMCELL

Hardware

Architecture

41

6

Control

ofthe

CAMCELL Material

Handling

System

43

6. 1

Schematic

ofthe

CAMCELL Material

Handling

System

43

6.2

List

of

Inputs

used

in

thecontrol program

45

6.3

List

of

Flags

used

in

thecontrol program

45

6.4

List

of outputs used

in

thecontrol program

46

6.5

List

ofregisters used

in

thecontrol program

48

6.6

List

ofpassthroughoutputs

49

6.7

List

of passthrough

inputs

49

7

CAMCELL Automation

50

7. 1

Schematic

of

OPC Client-Server Architecture

used

in CAMCELL

5 1

7.2

WTNCC Screen for

the

Inquire

module

53

Appendices

No.

Appendix

A

Siemens'

Software Installation

B

Hardware Configuration

C

Communicating

Step7

with

WTNCC

D

Accessing

the

WTNCC

tagsviathe

OPC

channel

E

Quickstep

program

for

theconveyor control

F

Symbols

tableused

in

the

Step7

G

LAD

program

for

the

Inquire

and

Pallet Controller

module

Abstract

Manufacturing

Systems Integration is theprogressive

linking

and combination ofthevarious components

ofthe systemto merge their functional and technicalcharacteristics into a comprehensive interoperable

unit.Itrequires onetowork withdifferenthardwareand software.Thereare a number of vendors_providing alargenumber of products.

Integrating

thesevarieties of products provides a greater valuethan thesum of thevalue provided

by

theindividualproducts. Whathinderstheeffectiveintegration ofthese components

isthe

diversity

inthedesignandtheuse oftheseproducts.Systems Integration iseased

by

well-established

standards in data communication, programming

languages,

application development environments and computer_operating systems.

Many

vendors have attemptedto come _upwith standardsthatare_relatively open.

However,

when one has to _{integrate data among} multiple

vendors'

architecture, a new set of

challenges emerge.

The Siemens'

PC-based automation

technology

is an_emerging

technology

thatappears to provide robust

architecture for

integrating

all elements ofthe _{manufacturing} environment. _{Applications ranging from} simple controlto distributedcontrol andfull-fledged

Manufacturing

ExecutionSystems canbe developed

using

Siemens'

architecture. _{The primary focus}ofthisapplied research workisto

develop

a

Manufacturing

Execution System to control a _{flexible manufacturing} system _using Siemens PC-based automation technology. This_technology is implemented ina Flexible

Manufacturing

cell namedtheCAMCELL. The CAMCELLconsists oftwo_{CNC machiningcenters,assemblyrobots,} and a vision_system,all of which are

interlinked

by

a material

handling

system.Thesoftware architecture oftheCAMCELL is basedonNIST's five level

hierarchy,

discussed

briefly

in the report.

Specifically

it contains functionalmodules for order entry, schedulingand routing. Inadditionto these functionalmodules, thereare various support modules such as order_entrymodule, scheduler,routeretc, twoof which namedtheInquireandthePallet Controller

that are implemented in this study. Siemens'

Step

7 and WTNCC software are used forthe control and

Section

1.

Introduction

A systemis defined as a collection of elements or components thatare organizedtogetherfor a common purpose. [1]

Manufacturing

Systems Integrationis theprogressive

linking

and combination ofthe various components ofthe system to merge their functional and technical characteristics into a comprehensive interoperable unit. [2] System Integrationrequires us towork withdifferenthardware and software.There

are a number of vendors _providing a large number of products.

Integrating

these varieties of products provides a greater valuethan the sum ofthe value provided

by

theindividual products. Whathindersthe effective integration of these components is the

diversity

in the design and the use ofthese products.

Computersystems are_{continuouslyevolving,operating}systems are_{rapidly changing}andthe_programming languagesare_gettingmore and more object oriented.

Systems Integration is eased

by

well-established standards in data communication, programming

languages,

application development environments and computer _operating systems.

Many

vendors have attemptedto come_upwith standardsthatare_relativelyopen.Forexample, theSimatic PCS 7 isa process control systembasedon standardtechnologiesandthusoffers openness and also allowsitto_{be linked up}to systems made

by

other manufacturers. Ithas a flexible architecture that facilitates horizontal integration among the processes as well as vertical integration in the company-wide information network and

integration to field engineering. [3]

Industrial17

Solutions from ABB are designed to perform as a

fully

integrated set of solutions across common

hardware,

_software, engineering, spare _parts, project management,

training

and service components.

They

are scaleable and open andhenceyou canimplement

only what you require now, and add

functionality

over _time, as needs evolve. [41 The Westinghouse

Distributed

Processing Family

(WDPF)

distributedcontrol andinformationsystem provides_modulating

control, sequentialcontrol, and data acquisition fora wide _variety of process applications. Ithas a dual

network architecture thatprovides effective and reliable communications and a deterministic networkfor real-time process control data and anopenEthernet Information

Highway

for file transfer, remote_access, and enterprise integration. It also offers the

flexibility

to

fully

integrate plant process _control, local and wide area SCADA _systems, PLC networks, and maintenance management and

laboratory

computer systemsin asingle,unified architecture. [5]IBM's SiView

Standard,

an advanced_{manufacturing} execution systemforsemiconductormanufacturers,provides a complete open, multi-platform environment with the

industry's richest

functionality

andlargestrangeof

Manufacturing

ExecutionSystems

(MES)

_{applications,}

including

material management, equipment and process _management, schedule _management, process control,and

factory

automation. SiView Standardintegrateswith a_varietyof_third-partysoftware to offer an end-to-end MES solution. [6]

However,

when one has to _{integrate data among} multiple

vendors'

architecture,a new set of challenges emerge.

The Siemens' PC-basedautomation_technology is an_emerging

technology

that appears toprovide robust architecture for

integrating

all elements ofthe _{manufacturing} environment. Applications _{ranging from} simple controltodistributedcontrolandfull-fledged MEScanbe developed_usingSiemens'

The primaryfocus ofthis thesis isapplied research

leading

is tounderstandand

develop

a

Manufacturing

Execution System to control a _{manufacturing} cell named the CAMCELL. CAMCELL is a flexible

manufacturingsystem_containingtwo_{CNC machining}centers,assemblyrobots,anda vision_system,all of which areinterlinked

by

a material

handling

system.Thesoftware architecture oftheCAMCELLis based

on

NIST'

fivelevel

hierarchy

[7]

Specifically

itcontainsfunctionalmodulesfororderentry,schedulingand

routing. Inadditiontothesefunctional_modules, there are various support modules(order entry, scheduler, router_etc.)twoof which namedtheInquireandthePalletControllerareimplemented inthisstudy.

This study aims to evaluate the Siemens' Automation System in terms ofits important features in the

context of Systems Integration. There are many communication standards that govern the data communication within a _{manufacturing} cell. Such communication standards range fromdevice-to-device standardsliketheRS-232serial communication standardtoadistributednetwork communication standards like Industrial Ethernet.

Similarly,

there are varieties ofprogramminglanguagesstandards thatare popular in the process control field. Fromsimple graphical_{programming languages like} the Ladder Logic or the

functional block diagramtoSequential

Programming

languagesand complexStructuredControl

languages,

thereare a number of_{programming languages}thata control solutiondevelopercan chosefrom. Thesetwo

aspects ofSystems Integration inaddition to other problems faced inthe multi-vendor integrationare a

huge challenge to

bring

about effective _{Systems Integration. This study} aims at _studying the Siemens' AutomationSystemthrough theseperspectives.

In section number _two, we discussthe data communication standards popular within the process control field. Suchstandardsinclude Serial Communicationstandardslike

RS-232, RS-422,

RS-485,

andProfibus

networks communication _standards, Parallel Communication standards like IEEE-488 communication standardanddistributednetwork communication standardslike EthernetandTCP-IP.

Here,

we alsodiscuss

the ISO OSI 7-layer model, which specifies the functions that are to be fulfilled at each level in communication systems. Inthissection we alsodescribetheSimatic NET Profibusnetworkthatisusedin

theCAMCELL.

In section numberthree, we discuss the _programming languages _{currently in}use in the process control field. Such languages include Graphical

Programming

languages like the Ladder Logic

(LAD)

and the

Functional Block Diagram

(FBD),

Textual

Programming

language like the Statement Lists

(STL),

Sequential

Programming

languagesliketheGrafcetand

Graph,

and alsoStructured Control languages.

In section number

four,

we describe the General Architecture of the Siemens' Simatic PC-based Automation System. The various components ofthis architecture are Simatic

Controllers,

Simatic

HMIs,

Distributed

I/Os,

the Simatic NETcommunication networkandthe

Step

7configurationand_programming

software. Inthis section, we alsodescribethe Simatic Managerarchitecture. SimaticManager isthebasic applicationfor configuringthehardwareand_programminglogicina control application.Maincomponents in this architecture are the Simatic PC

Station,

Operator

Station, WinLC,

which is the logic controller,

Automation system. This section contains a brief descriptionofthese components ofthe overall Simatic

system architecture as well astheSimaticManagerarchitecture.

In section number

five,

we describe the CAMCELL through three different perspectives viz. the

Manufacturing

and Material

Handling

perspective, Product/Process flow perspective and the Computer

hardware

hierarchy

perspective.

Insection number_six,wedescribethematerial

handling

system ofthe

CAMCELL,

itscomponents andits

functions. We also describe the control program that runs the material

handling

system written in the

Quickstep

programminglanguage.

In section number _seven, we describe the CAMCELL automation system. Here we describe the actual implementation of the Siemens' automation

technology

in the CAMCELL. Here we describe the implementationoftwofunctionalmodules oftheCAMCELLviz.theInquireandthePallet Controller.

References:

[llhttp://searchwin2000.techtarget.com/sDefinition/0sidl_gci213083,00.html

[21www.its.bldrdoc.gov/fs-1037/dir-036/_5625.htm

[3]

http://www.sea.siemens.com/process/product/pa7ovrvw.html

[4]

http://www.abb.com/global/

[5]

http://www.westinghousepc.corn/wdpf-control/descriptions.cfm

[6]

www.ibm.com

Section

2.

Data Communication for Process Control

2.1 Introduction

Inthis_section,we willfocuson various communication standards that arerelativelymore popularinthe

process control field. Communication standards are an agreed upon set of rules and guidelines that

govern communication between two

devices,

or two systems. There are two aspects to _any

communication_standard, viz. the hardware aspect and the software aspect. The hardware aspect ofa

communication standard deals with such things as physical characteristics, electrical characteristics,

types of connectors and so on. On the other

hand,

the software aspect deals with the ways in which

information ispackagedandtransferred.Inthis section we willdescribe boththeseaspectsofthevarious

communication standards

leading

tothediscussionoftheSimatic NET Profibusnetwork,whichis a part

oftheSiemens' SystemandisusedintheCAMCELLapplication.

2.2 Data Transfer Modes

m

Therearetwodifferent kindsofdatatransfer modes,

1. Serialtransfer mode,or serialcommunication,

2. Parallel_{transfer mode,}or parallel communication.

2.2.1. Serial Communication

In Serial

Communication,

data istransferredfromsender toreceiver onebit at atimethrough a single

line or circuit.Thenameserial communication comesfromthefactthatthe serial porttakes

8,

16or32

parallel bits from a computer bus and converts it as an

8,

16 or 32 bit serial stream. Each bit of

information istransferredin seriesfromone locationto another. Eachstream ofbits_{is broken up}to8

bitscalled words.Serialcommunicationisoftwo types.

Synchronous Serial Communication

Inthis typeof serialcommunication, thesending and_receivingends ofthecommunication are

synchronizedusinga clockthat_preciselytimes theperiod_separatingeachbit.

Asynchronous Serial Communication

By

introducing

a startbitthatindicatesthestart ofa shortdata stream, theposition of eachbit

canbe determined

by

timing

thebitsat regularintervals. Thetwosystems thendon'thavetobe

synchronized

by

a clock signal.Whenthe_receivingend ofthecommunication receivesthestart

bit itstartsashort-termtimer.

By

keeping

streamsshort, there'snot enoughtimeforthe timer to

get out of sync. This method is known as asynchronous communication because the _sending

2.2.2. ParallelCommunication

Simultaneous transmission of the eight bit-voltages that constitute a byte is referred to as "parallel transfer".Whenbitshavetobemoved about withinthecomputer

itself,

_theyaretransmitted_alongwires. If the data to be transmitted is in 8-bits format

bytes,

then eight separate, discrete wires must

simultaneously carrytheeight representative electrical voltagesbetweenthetwopoints.Paralleltransfer, then, is done byte-by-byte. Sinceall eightbitsarrive attheirdestinationatthe same

instant,

paralleldata transfercanbeaccomplished at_extremelyhighspeeds.

2.3 Serial Communication Standards

|21 Themost popular serial communication standardsare,

1. RS 232communication_standard, 2. RS 485communication_standard, 3. RS422communicationstandard,and 4. Profibusnetworks

2.3.1. RS 232communication standard

RS-232communication standard wasintroduced in 1960

by

theElectronic Industries Association

(EIA),

and _{is currently} the most _widely used communication protocol. It is simple and inexpensive to implement. Even though_{relatively slow,} it is adequate for most simple serial communication devices such as keyboards and mice. RS-232 is a single-ended datatransmission system, which means that it uses a single wirefor datatransmission. Sinceuseful communication_{is generallytwo ways,} atwo-wire systemis employed, one to transmitand oneto receive. Because signals

traveling

this single wire are vulnerable to

degradation,

RS-232 systems are recommended for communication over short distances

(up

to 50

feet)

and at _relativelyslowdata rates

(up

to 20 kbps). RS-232 is usedto connect_onlytwo systems.'I2'

2.3.2. RS 422communicationstandard

RS-422 (EIA RS-422-A

Standard)

is a serial communication standard used on Apple Macintosh computers. RS-422 uses adifferential electrical signal, as opposedtounbalanced signals referenced to ground with the RS-232. Differential_{transmission,} which uses twolines each to transmit and receive signals,results ingreater noise

immunity

andlongerdistances as comparedto theRS-232. Thegreater noise

immunity

and distance are

big

advantages in industries.

RS-422,

like RS-232 is also used to connecttwosystems.[1 ]

2.3.3. RS485communicationstandard

PC or other controller for data collection,

HMI,

or other operations. RS-485 is a superset of

RS-422;

thus, all RS-422 devices may be controlled

by

_{RS-485. RS-485 hardware may be} used for serial communication_{for up}to4000feetof cable.

2.3.4. Profibus|9'

2.3.4.1 OverviewofProfibus Network

Profibus is an acronymfor "Process Field Bus". It isa modified version of the RS 485 standard and followstheinternationalstandards EN

50170,

EN 50254andIEC 61158[10]. It is a vendor-independent

standarddocumentedin thevolume 2ofEN 50170. Thetransmissionmediumis either a coppercable networkbasedon a shielded2-corecable or afiber-opticcable network as showninfigure2.1.

PVCouter sheath

Cores,solidcopper _s^-f-^^Z^

'V^CX

Copper braidshield

Aluminum foil

Plastic foil Cellular PE insulation

Filler

Fig

2.1 Structureof a shielded2-core ProfibusCable

Thetransmissionspeeddeterminesthelengthofthecable within a segment.Themaximumlengthatthe highest transmission speed (12

Mbit/sec)

is 100m and the minimum cable length at the lowest transmissionspeed(9

kbit/sec)

is 1000m.Thenetwork canbeexpanded with repeaters.

The Profibus supports the exchangeofinformation between field devicesand with systems at a higher

system level. It is mainlyused to transfer small to medium quantities ofdata. Itoffers a standardized

interface forthe transferof process inputand process output data between Simatic S7 stations andthe field devices.

2.3.4.2 Accesstechniques

Thenetwork access techniquefor PROFIBUS corresponds to the"Tokenbus"

Matterftto* assignment

Fig

2.2. Profibus Access Technique

When a station receives the token (addressed to

it),

it has permission to send telegrams. The time

allowed is specified

by

the so-called token

holding

time. Once this has elapsed, the station _{is only} permitted to send one more

high-priority

message. Ifthe station is not _waiting to send a message, it

passesthe tokenontothenext station inthelogical

ring

_{immediately. The corresponding} token timers

("maximum token

holding

time",

_etc.) are configured for all active stations. Ifan active stationis in

possession ofthe token and connections to passive stations are configured for it (master/slave

links),

thesepassive stationsare queried(e.g. variables are_read) ordatais sentto them(e.g.set point values).

Passivestations never receivethe token.Thisaccesstechnique allows stationstobeadded and removed under_operatingconditions.

2.4

Parallel

Communication

Standards

Parallelcommunicationis characterized

by

multiplebitstransfer thatleadstohigher datatransfer rates,

over_relativelyshorterdistances.

Theparallel communication _{greatly increases} transfer speeds

by

_using an eight-wire _connector, which

transmitstheeightbits inabyteofdatasimultaneously, thussendingan entirebyteofdata inthe timeit

takes to send a single bit in a serial system. This byte of data is supplemented

by

several other

handshaking

signals,eachsent onitsown_wire,which ensurethatdatatransfer takesplace_smoothly[3]

2.4.1. IEEE488

(GPIB)

'4|

The IEEE-488bus was developedto connectand control programmable

instruments,

andtoprovide a standard interface for communication between instruments from different sources. Hewlett-Packard

originally developedthe

interfacing

technique, and calledit HP-IB. Sincetheinterfacewas so_versatile,

thattheIEEE committee renameditasGPIB (General Purpose Interface Bus). The IEEE-488 interface

systemconsists of16 signallines and 8 groundlines. The 16 signallines are dividedinto 3 groups(8 data

lines,

3 handshake

lines,

and 5 interfacemanagementlines). ThestandardIEEE-488 cablehas both

The IEEE-488 bus specifies a maximumtotal cable lengthof20 meters with no morethan20 devices connected to the bus and at least two-thirds ofthe devices powered on. Amaximum separation of4 metersbetween devicesand an average separation of2meters overthefull busshouldbe followed.

2.5 Network Interfaces

2.5.1. Network Topologies

Therearetwo_widelyused networktopologies

Star

Topology

Ring Topology

2.5.1.1. Star

Topology

'5|

Star

topology

isa network configurationinwhichthereisa central pointtowhichagroupof systemsare [image:20.545.202.390.310.476.2]

directly

connected.Withthestar_topology,alltransmissionsfromone systemtoanother passthroughthe central _point, which _may consist of a device that plays a role _{in managing} and _controlling communications.

Fig. 2.3 Star

Topology

2.5.1.2.

Ring Topology

|6'

A ring is a network

topology

or circuit arrangementin which each device is attached _alongthe same signal pathto two other

devices,

forming

a path inthe shape of a ring. Eachdevice inthe _ringhas a unique address. Information flowisunidirectional anda _controllingdevice intercepts and managesthe

gi

Ring

Network

Topology

'I'rrmriJl

Fig

2.4

Ring Topology

2.5.2 TCP/IP

TCPandIPweredeveloped

by

aDepartmentofDefense

(DOD)

research projecttoconnect a number of

differentnetworks designed

by

differentvendors into a network of networks (the "Internet"). Several

computersina smalldepartmentcan useTCP/IP

(along

with other_protocols) on a singleLAN. The IP

component provides _{routing from}the departmentto theenterprise _{network, then to}regional_networks, and

finally

to the global Internet. As with all other communications _protocol, TCP/IP is composed of

layers:

IP - is_responsiblefor moving_{packet of}data from_nodeto_node.IP forwards_{each packet}based onafour-byte destinationaddress(the IPnumber).

TCP- is_responsible

for verifyingthecorrect

delivery

ofdata fromclienttoserver.Datacanbe lost intheintermediatenetwork.TCP isused

by

applicationsthatrequire reliabledatadelivery. TCPuses a check-sum withthedata sentthat theTCPlayerattheother end usesto_verifythat the data arrived undamaged. If the data checks _out, the _{receiving TCP} layer sends an

acknowledgment back to the sender. Ifit arrives

damaged,

the receiver discards it and the sender,afteran appropriate_{time-out period,}resendsit.

But beforedata is transmitted,the twohostsexchange a

three-way

handshake. Thesender sends a signal

telling

the receiverit wantsto set_upa connection andhowthe datawillbe sequenced. _{The receiving}

host sends a signal back acknowledging receiving the signal. _{The sending} host sends a signal back

acknowledging the acknowledgement and begins data transmission. The connection at the end ofthe

[image:21.545.137.457.50.305.2]

2.5.3 Ethernet

Ethernet is a local area network

(LAN)

technology

that transmits information between computers at

speeds of10and100millionbitsper second(Mbps).

Currently

themost_widelyused version ofEthernet

technology

isthe 10-Mbpstwisted-pairvariety.

The 10-MbpsEthernetmedia varietiesincludetheoriginalthickcoaxialsystem,as well asthin_coaxial,

twisted-pair, andfiberoptic systems.Themost recentEthernetstandarddefinesthe new 100-Mbps Fast

Ethernetsystems,which operates overtwisted-pairandfiberoptic media.

Each Ethernet-equipped computer, alsoknownas a _station, operates

independently

of all other stations

onthenetwork andthere isno central controller. Allstations attachedtoanEthernetare connectedtoa

shared _{signalingsystem,} also calledthe medium. Ethernetsignals are transmitted serially, onebitat a

time, overthe shared signal channelto _everyattached station. To senddataa stationfirstlistensto the

channel, and whenthechannelis idlethestationtransmitsits data intheformof anEthernet

frame,

or

packet.

After each frame transmission, all stations on the network must contend _{equally for} the next frame

transmission opportunity. This ensures that access to the network channel is

fair,

and that no single

station canlockouttheother stations.Accesstotheshared channelisdetermined

by

themedium access

control

(MAC)

mechanism embedded in the Ethernet interface located in each station. The medium

access control mechanismis based on a system called Carrier Sense Multiple Access with Collision

Detection (CSMA/CD).

2.6. ISO OSI Seven-Layer Model

[8]

The Open Systems Interconnection

(OSI)

7 Layer Model is the product of years of work

by

_many

organizations.The InternationalStandards Organization

(ISO)

hascompiled alltheresults.Thisstandard is called a reference model. It specifies the functions that are to be fulfilled at each level in

communicationbetweentelephone systems, or computers. These 7 layersarethought tobe adequateto

encompass all communicationsfunctions.

Layer 1: The Physical Layer is concerned with

transmitting

raw

bits,

electrical

impulses, tight,

and

radio signals over a communications medium. _{The primary} concern of a designer for this layer is

mechanical, electrical, or optical matters. Specifications for wave _{shapes, signaling rates,} cables and

connectorsareinvolvedinthislayer

Layer 2: The Data Link Layertakes the bitspassed

by

the physicallayerand creates and recognizes

frame

boundaries;

by

this techniqueittransfersunitsofinformationto theother end ofthephysicallink

It also contains the rulesgoverning access to thenetworkcable,Media Access Control

(MAC)

which

Network

mi

m\

mm mini

in

mini

Telephone Switches And _Routers

Working

at Layer2

Data Link

Network

DataLink

Network

Data Link

Transport

Network

Data Link

F,

Physical *- * _Physical *- ? _{Physical ? Physical}

Intornotworkinq

Fig

2.5 OSI ISO 7 layermodel

Layer3: The Network Layercontrols operations of sub networks that mightintervene betweenthe two

communicationdevices.This layerroutes_{information among different}networks.

Layer 4: The Transport Layersplits_{up information into}appropriate sizes(segments

information)

soit

willfit intopackets oftherightsizeforthe networks

being

used._{In manycases,}itensures allthepackets

arrive attheother end with errors and assembledinorder and withoutduplication.

Therefore,

itprovides

end-to-enddata

integrity

and_qualityof service.

Layer 5: The Session Layercontrolstheestablishment and continuation of a particularcommunication

between devices. Itcoordinates interaction betweenend-application_processes,

keeping

thetwodevices

talking

toeach other and_maintaininga connection.

Layer 6: The Presentation Layerperforms conversions oninformation. These include conversionof

code _{sets, encryption, text compression,} andprotocol conversion for virtual terminal communication.

Thislayermayalsotranslatefile formatsthatdiffer betweendevices.

[image:23.545.98.467.50.423.2]

Layer 7: The Application Layercontainsthefinalparticularsrequiredforprogramsto communicate. This layer establishes means _{for making} the network appear transparent to user

devices,

joining

the

communications streamtotheindividual device.

2.7

Topology

of

Simatic NET Profibus

network used

in

the

CAMCELL

2.7.1.OverviewoftheSIMATICNETsystem

SIMATIC NET is the name ofthe communication networks _{connecting SIEMENS} programmable

controllers,hostcomputers,workstations and personal computers. SIMATIC NETincludesthefollowing:

The communication network _consisting of transmission _media, network attachment and

transmissioncomponents andthe_{corresponding}transmission techniques Protocolsand services usedto transferdata betweenthedevices

The modules oftheprogrammable controller or computerthatprovide the connectionto the

communications processors.

To handle a _variety of tasks in automation _engineering, SIMATIC NET provides different

communication networkstosuittheparticular situation.The

topology

ofrooms,

buildings, factories,

and complete _companycomplexes andtheprevalent environmental conditions meandifferentrequirements. Thenetworked automation components also makedifferentdemandsonthecommunication system. The communication network used in the CAMCELL application is the Profibus network, which was discussedearlierinthissection.

TheSIMATIC NET

topology

usedintheCAMCELLapplicationisshownbelow inthefigure 2.6

DPrnoBtef

v.iih

PRORBUS

PC

CPSS13

(CP5613)

>lipki

tf- _;las

(ET

200M)

3V

^K

JTK fb>

I

WWW,

. ,

|

Proust-Pr.*

I

(Field

Devices)

Fig

2.6 SIMATIC NET

topology

as usedintheCAMCELLApplication.[nl

2.7.2CP 5613 Communication Processor

In any SIMATIC S7 application, aCommunicationProcessor

(CP)

is always requiredfortheProfibus

The CP 5613 is aPCI card with a microprocessorthatallows connection of a SIMATICprogramming

device to Profibus under Windows NT 4.0 or Windows 2000. The CP 5613 can also be used to

implementcontroltaskson a

PC,

thus

facilitating

PC basedcontrol.

The CP 5613 card is a short PCI card with a 9-pin sub D socket for connection to Profibus. It has

diagnostic LEDs for installation and _{commissioning} and

during

operation ofthe module. Inorder to

provide access to theprocess

data,

the CP 5613 operates as theProfibus master module

buffering

the process image (input/output and diagnostic

data)

in the DP RAM

(memory

area on the CP). High performancedatacommunicationsishandledautonomously

by

theCP 5613 hardware. Theprocessdata from the slaves are always consistent as

they

all originate from one and the same DP (decentralized

peripheral)cycle.

2.7.3 ET 200 M distributed I/Omodule

The ET 200-M is a modularI/O station. It is the passive station ofthe Profibus field bus and has a

maximumdatatransferrate of12Mbit/s. AtypicalET 200Mstation consistsof:

Power

Supply

IM 153 interfacemodule

Up

to 8 I/Omodules

No specific slots are assigned tothe I/O modules.

Any

combination of modules is possible. The ET

200M isconnectedto thePROFTBUS-DPvia anIM 153 interfacemodule.The inputsand outputsofthe

modularET 200M I/Ostation canbeaccessedfromtheuser programinthePLC inthesame manneras

theinputsand outputs ofthecentral controller.

Communicationviathebussystemis handled completely

by

themasterinterfacemodule inthe central

controller andtheTM 153 interfacemodule.

2.8

Glossary

of

Terms

Data bits: Data bit is a measurement ofthe actualdata bits ina transmission. Standardvalues for

the datapackets are

5, 7,

and 8 bits. A packet refersto a single bytetransfer,

including

start/stop

bits,

data

bits,

and parity.Sincethe number of actualbits dependsontheprotocol_{selected, the term}

packetisusedtocover allinstances

Stopbits:

Stop

bits are usedtosignaltheend of communicationfora single packet.Typicalvalues

are

1,

1.5,

and2 bits. Morethebitsusedfor stop

bits,

greateristhe leniencein _{synchronizing}the differentclocks,butslowerthedatatransmissionrate.

Parity:

Parity

is a simple form of error_checkingthat is used inserial communication. Thereare

fourtypesof parity: even, odd, marked, and spaced.Theoption of_usingno_parityisalso available.

Foreven and oddparity,the serial port sets the_{parity bit (the}last bitafterthedata

bits)

toa valueto

ensure thatthetransmissionhas aneven or odd number oflogic highbits. Ifthe_{parity is}odd, then

the_{parity bit is}

1,

_{resulting in 3 logic-high bits. Marked}and spaced_paritydoesnot_actuallycheck the data

bits,

but simply sets the _{parity bit high for}marked_parity or low for spaced parity. This

allowsthe_receiving device toknowthestate of a bitto enablethedevice to determine ifnoiseis

corruptingthedataorifthe

transmitting

and_{receiving device}clocks are out of sync.

Baudrate: Baudrate is a measurement of speedforcommunication. It indicatesthenumberofbit

transfers per second. _{For example, 300} baud is 300 bits per second. Common baud rates for

telephone lines are

14400, 28800,

and33600. Baudrates greaterthanthese arepossible, butthese

rates reducethedistance

by

whichdevicescanbeseparated.

Bus: In a computer, bus is the data path on the computers'

motherboard that interconnects the

microprocessor with attachmentsto the motherboard inexpansion slots. Suchattachments_may be hard disk

drives,

CD-ROM drives etc. Ona_network, abus is atransmissionpathon which signals

aredroppedoff or picked_upat_everydeviceattachedto theline.

Only

thedevicesaddressed

by

the signals_payattentionto

them,

theothersdiscardthe signals.Thereare varioustypesofbusavailable such asISA

bus,

PCI

bus,

EISA

bus,

IDE

bus,

ETDE

bus,

VMEbusetc.

Port: On computer and telecommunication

devices,

a port _{is generally}a specific place for

being

physicallyconnectedto some other

device,

_usuallywith asocket and_plugof somekind.

Typically,

a personal computer is provided with one or more serial ports and_usually one parallel port. The serial port supports_sequential,onebit-at-a-timetransmission toperipheraldevicessuchas scanners andthe parallel port supports multiple-bit-at-a-timetransmission todevicessuch as printers.

Standard: Anagreed upon set of rules and guidelines.

Many

standards are evolvedfrompopular

methods while others are crafted

by

professionalgroups

(ANSI, ISO,

_etc.)

LAN: A local area network

(LAN)

is a _group of computers and associated devices that share a

common communications line and

typically

share the resources of a single processor or server within a small geographic area(forexample,withinan officebuilding).

WAN: A computer network that spans a _{relatively large} geographical area.

Typically,

a WAN

consistsoftwoor morelocal-areanetworks(LANs). The largest WAN inexistenceistheInternet. Firewall:Firewallisa systemdesignedtoprevent unauthorized accesstoorfroma private network. Firewalls canbe implemented in both hardware and _software, or a combination ofboth.Firewalls

are

frequently

used to prevent unauthorized Internet users _{from accessing} private networks connected to the

Internet,

_{especially intranets. All} messages _entering or

leaving

the intranetpass

through the

firewall,

whichexamines each message andblocksthosethatdo not meetthespecified

securitycriteria.

Router: Router isa network devicethat sends and receivesNetworkprotocol-data units

(packets)

and relays packetsfromonedevicetoanotherthroughthenetwork.

Hub: Hub is localarea networkequipmentthatallows multiple networkdevicestobeconnectedto

the_{LAN cabling}systemthrougha central point.

Token Ring: Token ring is a LAN data linktechnology, in which systems are connectedto one

another_using a point-to-point twisted

-pair cable segments to forma _ring structure.A systemis allowedto transmit_onlywhenit hasthe_token,whichispassedfromonesystemtoanother around

thering.

References:

[1]

http://www.rad.com/networks/1995/rs232/rs232.htm

[2]

http://www.quatech.com/Application Obiects/FAQs/comm-over-rs-232.htrn

[3]

http://www.quatech.com/Application_Obiects/FAQs/cornm-over-parallel.htm

[4]

http://www.techsoft.de/htbasic/tutgpib.htm

[5]

http://fcit.coedu.usf.edu/network

{6]

http://hs.stcloudstate.edu/cirn/courses/im644/ring.html

[7]

http://www.ots.utexas.edu/ethernet/

[8]

http://web.singnet.com.sg/~psylence/c3p03.htm

[9] Berger,

Hans.

Automating

withSIMATIC. SIEMENS 2000.

[10]

http://www.profibus.com/profibus.html

[11]

http://www.sea.siemens.com/autogen/docs/net/pfb/man/DP Base Program Interface for 5613.pdf

[12]

http://www.synchrotech.com/support/serial_standards.html

Section 3.

Programming

Languages for Process

Control

3.1 Introduction

Inthissection we shalldiscuss the various_{programming languages}usedto writecontrollogicforprocess

control.There are various_programminglanguagesavailablefor writingcontrollogic. Thevarious typesof

programming languages include graphical _programming

languages,

statement

lists,

sequential

programming

languages,

and structured Control Languages.

First,

we describe these _programming languages and also discuss programming languages within each category.

Next,

we describe the Ladder Logic (abbreviated asLAD inthe Siemens'

Technology)

andtheFunctional Block Diagram (abbreviated

asFBD in the Siemens'

Technology),

which are graphical_{programming languages} and Statement

Lists,

which is a textual _{programming language.}

Next,

we will discuss the

Grafcet, Graph,

and the HiGraph programming

languages,

which are sequential _programming languages.

Next,

we will discuss the Structured Control Language. We shall discusstheimportant features of each_{programming language}and

alsodiscusstheiradvantages anddisadvantages.

3.2 Graphical

Programming

Languages

Graphical programminglanguagesmake use of symbols andicons inordertobuildcontrollogic. Graphical

programming languagesare _especiallysuitable _{for representing bit}

logic,

ina formeither modeled on a

relay ladder logic diagram

(LAD)

or_resemblingan electronic circuitdiagram (FBD). 3.2.1 Ladder Logic

(LAD)

Ladderlogic_{programming is}a graphical representation oftheprogramdesignedto_{look like relay logic.}[4) In

LAD,

user writes the program for the control application

by

_arranging graphical program elements.

Thesegraphical program elements consist ofcontacts,coils and

boxes,

which arelinkedtogetherinaform resembling a _{relay ladder logic diagram. In}

LAD,

the entire program is containedinnetworks. ^Each

network consists of onerung, thatisalogic operating ina coil orbox. Each rung isa combination ofinput

conditions

(symbols)

connectedfrom leftto

right,

withthe symbols that represent the output atthefar right. Thesymbolsthatarerepresentedasinputsare connectedinseries, parallel,or some combination ofthe two

toobtainthedesired logic.t2)

itacts

Run

3.2.1.1 Contactsin LAD

Contacts are usedin_{LAD programming} language to checkthe states of

binary

_addresses, such as inputs.

By

arrangingthecontactsin series orparallel, logic operations canbeperformed. There aretwo typesof

contact;

Normally

OpenContacts and

Normally

Closed Contacts. Ina_normallyopencontact, the input is

checkedforahighstate, thecontact closesiftheinputturnshigh. Ina_normallyclosedcontact,theinput is

checkedforalowstate,thecontact closesiftheinputturnslow. 3.2.1.2 Coils in LAD

Coilsare usedin LADprogramstoset or resetbitaddresses such as outputs.Coilsenergizes thebitaddress

when the power flows through_{the coil,} and de-energizes the bitaddress whenthe power stops

flowing

through it. Coils are also used to control timer and counter

functions,

call blocks without parameters,

performjumpstoadifferentplaceinthe_program,and so on. 3.2.1.3 Exampleof an_{LAD rung}

Fig

3.2 Anexample of a_{rung in}aLADprogram|S1

Inthe aboveexample,an outputS isenergized orturned

ON,

when eitherinput SIorinput S2 isenergized

orturnedON.

3.2.1.4 AdvantagesofLAD

The Ladder Logic

Programming

offers_manyadvantages.Someoftheadvantages are as

follows,

1. The LAD programming language is a part ofInternational Electrotechnical Commission

(IEC)

61131-3standardfor Industrial Control Programming.[6]

2. It isthemost_popularlyused_{programming language for}control_programming

3. Itis reasonably

intuitive,

especially fortechnicianswithrelaylogicexperience [21

4. It is particularlyeffective inan on-line _mode,whenthe_{PLC is actually performing}control. The

operationofthelogic isapparentfromthe

highlighting

of the various_relaycontacts and coils on the screen,whichidentifiesthelogicstateinrealtime.[2]

5. Itissimple and_easytouse

3.2.1.5 DisadvantagesofLAD

Ladder

Programming

hasbecomeone ofthemost popular graphical_{languages for programming PLCs but}

unfortunatelyhasa number of problems.[7]

1. The laddersymbolsvary between different PLCproducts.

2. Poor facilities forstructured orhierarchicalprogramdecomposition

3. _{Poor facilities for addressing}and_{manipulating data}structures,

4. Limitedfacilities for

building

complexsequences, 5. Limitedcontrol over programexecution,

6. Facilities forarithmetic operations are cumbersome.

3.2.2 Functional Block Diagram

(FBD)

Functional Block Diagramisanother graphical

language,

popularin Europe. FBDprogram elements appear asblocks that are "wired" _together, analogous to circuitdiagrams. It iswell suited for representingbatch control applications.[91In

FBD,

control programs are created

by

interconnecting

ANDandORboxes.FBD

providesfunction boxes _{for performing} logic operations on signal_states, simple_{boxes for processing}the

result oflogicoperations and complex_{boxes for non-binary functions.}

3.2.2.1 Boxes in FBD

There aretwo types ofboxes in FBD. Simple boxesoperate onbit addresses,likeoutputs. These usually

only have oneinputand _maycontain additionalletters or symbols. Thereare simple boxes for settingor

resetting bitaddresses,evaluatingsignaledges, settingor_resettingtimerand counteraddresses, and so on.

Complexboxesare usedforprogram elements with_{non-binary functions.}

3.2.2.2

Binary

Functions in FBD

Binary

functions are usedin FBD to checkthe signal states ofbit addresses, such as

inputs,

and perform

logic operations onthem. Thefunctions available are

AND, OR,

and XOR. Allthese functions canhave

more thantwoinputs. The function boxes canbe interconnectedto program complex logic operationsin one network.

3.2.2.3 Exampleof anFBD Block

1.1 ,=-i

Q4.D

Fig

3.3 Anexample of ablock in Functional Block Diagram

Intheaboveexample, theoutputSturns

ON,

when eithertheinput 1 1.1 or11.3turnsON.

3.2.2.4 AdvantagesofFBD|8]

The Functional Block Diagramoffersthe

following

_advantages,

1. Simultaneous programmingand

documenting (overview,

comments, reliability,information

flow)

2. _{Universal applicability (Signal}processing, numeric, arithmetic,

integer,

floating

point)

3. Structured programming (defineand callsubroutines)

4. Standardizedset ofFunctionsandFunctionBlocks

3.2.2.5 DisadvantagesofFBD

Following

arethedisadvantagesoftheFunctional Block Diagram

1. Poor facilities forstructuredorhierarchicalprogramdecomposition

2. Limitedcontrolover program execution

3.3 Statement List

(STL)

STL is a text-oriented language in which thecontrol task canbe described in the formof a list. _{It very}

muchlooks liketheshort and simplelinesof_assemblycodes. [U1Thusthecontrol programiswritteninthe

form of a series of statements. Each statement contains an instructionthat defines what is to be done.

Depending

on thetype of

instruction,

this_maybefollowed

by

an address thatdefineswhat actionistobe

doneto. The elements ofthe statement lists _closelyresemble the mnemonics of microprocessor_assembly

languages.[11)

3.3.1 Exampleof anSTLprogram

NETWORK

1

LD

10.0

A

10.1

=

QO.O

NETWORK 2

LD

I0.4

0

I0.5

=

Q0.1

Fig

3.4 Anexample ofSTL instruction

Astatementlistprovides another view of a set of_{instructions. The operation,} whatistobe

done,

is shown

onthe left. Theoperand, the itemtobe operated on

by

_{the operation,}is shown ontheright. Inthe above

figure,

in network

1,

outputQO.O turns highwhenthe inputs 10. 0 and 10. 1 both turnhigh. Onthe other

hand,

theoutputQ0. 1 turns

high,

when eithertheinput 10.4or10.5turnshigh.[12]

3.3.2 AdvantagesofSTL programming

Statement Listsofferthe

following

advantages,[13]

1. STLis verysimilartoanassemblycode,hencethecode canbe easilyread

by

everyone

2. STL'sgenericalgorithms allow algorithmstobeappliedto_{many different}structures

3. _{STL is easy}tolearn.The

library

isquite small_owingtothehighdegreeof generality.

4. STLcontainersare_veryclosetothe_efficiencyof

hand-coded,

type-specificcontainers.

3.3.3 DisadvantagesofSTL programming

Following

arethedisadvantagesoftheFunctional Block

Diagram,

[13]

1. _{Error checking is difficult in STL. This}meansthatifthe programmer makes an_error,an error_may

or_maynotoccur whentheerroneousinstruction ismade,but itwill puttheprograminan unstable

state(e.g.

Writing

offtheend of an array).

2. Accesstothe exact sourcethatone uses_{may be}

difficult,

soiftheuser needs specific_information

aboutcode

details, they

_maynotbeaccessible.

3.4 Sequential

Programming

Language

Sequential

Programming

Language is a method of_representing the

key

elements of a sequential _process,

i.e. conditions required for_{passing from}one stateto another, andthe effects present while ina particular

state.[10]

Insequential control_systems,unlike logiccontrol_{systems, the}static assignment oftheinputsignalsto the

outputs is not ofimportance. It's the chronological sequence ofthese assignments that is important. The

control processesthatare executed one aftertheother aredivided into individualsteps. _{A step}consists of one or more actions.

Only

theaction inan active _step

(step

_currently

being

_{executed) is} performed. The

next_stepcannotbeprocessed untilthe transitionconditionsare met.Thetransitioncanbedependentonthe process,or canbe dependenton atimefactor.tl]

3.4.1Grafcet

Grafcet is aninternational standardforsequentialfunctionchartsthatwas released

by

theIEC in 1988.[17] It is atype offlowchart representationspecifically developed forthe needs ofindustrialcontrol systems.

Sequentialoperationsare representedin Grafcetasa series of steps.Theconditions requiredtomovefrom

one_stepto thenext are referredtoastransitionconditions.Thesteps are represented

by

numberedsquares, wherethe _step comprises of one or more on-off or _analogtype actions. ['9]A_transition, which separates

steps, andisrepresented

by

ahorizontal

hash,

containsthelogicconditionfor

terminating

theexecution of thestep.^ ' Themethod canbeusedas adesigntoolforwhatever

technology

is

being

usedtocontrolthe system

-relays,pneumatic

logic,

orPLCs.[18] 3.4.1.1 Exampleof aGrafcetprogram

Open_Gnp

~~\~ _Start

2 + Arm_on_level_l

Grip_closed

4 __

Arm_on_leve1_2

5

Fig

3.5 Grafcet Program

In the above example, there are steps and transitions

taking

place in sequence. The steps are shown in

squares andtransitionsare shownin horizontal hashes. 3.4.1.2 AdvantagesofGrafcet

Following

aretheadvantages of

Grafcet,

1. Grafcetissupported

by

theIECstandard [l7]

2. _{In executing}the

Grafcet,

the PLCneed_onlyscantheactive steps andthe _succeedingtransitions.

Hencescantimesare reduced withGrafcet.[I8]

3.

Being

developed for sequential processes, Grafcet has outstanding features such as parallel

processing.

4. Grafcet application can be transferred into different controllers. With the

help

of software like

Cadepa [l91 the standard Grafcet code can be converted into machine code formost brands of

PLCs. Itcanbetransferredinto ladder logic for Allen

Bradley

PLC-5,

Modicon

984,

Siemens S5

and others. [1?1

3.4.1.3 DisadvantagesofGrafcet

Following

arethedisadvantagesofGrafcet

1. Notaverypopularlanguage

3.4.2 Graph

Graph isa sequentialprogrammingmethodforsequential control systems.tl]Usercan writetheconditions

enablingtransitionsfromone_stepto thenextin LAD orSTL. Alternativeor parallel

branching

extend the scope ofthe linearexecution of consecutive steps.With

Graph,

operations within a process are configured

and programmedina standardized

display

mode(incompliance withIEC 61131-3). Theprocess(e.g. the manufacture of a _{component) is divided into} sequential or simultaneous steps. This division makes the

structureofthePLCprogram easiertounderstand and also easierto analyzeintheevent of a malfunction. Thisis particularlyuseful_{in manufacturing}toavoid_{costly downtimes.}tl4]

3.4.2.1 Exampleof a programin Graph

In the operation sequences, the individual steps of a process and the transitions to the next steps are

representedas rectangles andlines as shownin figure 3.6.

Qualifiers,

withinthe_steps, caninitiateactions. (E.g. time-delay).

If,

forexample,theoperatingsequencedescribes a

drilling

_process,the "lowerthedrill"

willbe a_stepandthe"motorON"

willbean action. Thetransitions describethe conditions under which a transitionto thenext_step shouldoccur.

Moreover,

interlocking

and_monitoringconditions canbe defined

for everystep.An interlockcanbeusedtopreventthe execution of actions.

Monitoring

conditions enable

the recognition of operational faults. All conditions

(transitions,

interlocking

or _monitoring) can be

programmed eitherin LADorFBD.

Wl GRAPH:Proaramminqs7SequentialControlSystems- _Drill\..

&"

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Fig

3.6 A Graphprogram

3.4.2.2 AdvantagesofGraph

Following

aretheadvantagesofthe_{Graph programming}

language,

[15]

1. Graphenables clearconfiguringoftheprocessintheplanningphase

2. Graphprovidesclear graphic representation oftheprocess_usingsequence_{chains,resulting in easy}

maintenanceand adaptation of programs

3.

Easy

troubleshooting

with internal diagnostics

functions,

_{resulting in minimizing} of expensive

3.4.2.3DisadvantagesofGraph

Following

are thedisadvantagesofthe_{Graph programming}

language,

1. Graphissuitableonly forsequential control.Logiccontrol cannotbeprogrammed

by

Graph. [15]

2. The transitions and steps needto beprogrammedineitherLADorFBD.Hence Graph is notan

independent language likeLADorFBD.

3.5 Structured Control Language

Structured Control Language

(SCL)

is a PASCAL-like high-level language optimized for programmable

controllers. SCL is in compliance with IEC61

131-3,

and is especially suited to the _programming of complex algorithms orfor data processingprojects.[141

Apartfromtraditional control tasks, structured control language assists in performing data management

tasksand complex mathematical operations.tl6]

SCL statements consist of_expressions, controlstatements, functions and blockcalls. Expressions assign

values, which can also be result of arithmetic and logic operations or comparison functions. Control

statements executetheprogrambranchesor repeat sections of a program.

FUNCTI0N_BL0CK FB27 UAR INPUT

SIG SEL : INT = ₀

GRP1 SEL : BOOL = ₀

GRP2 SEL : BOOL = ₀

GRP3 SEL : BOOL = ₀

ENDJJAR

UAR OUTPUT

SEL OUT : INT = ₀

GRP1 OUT : BOOL = ₀

GRP2 OUT : BOOL = ₀

GRP3 OUT : BOOL = ₀

ENDUAR

UAR

SELECT : INT;

MAX : INT;

ENDJJAR

BEGIN

SELECT = _{SIG SE}

L;

MAX =

3; IF SELECT < 0 THEN

SELECT = -SELEt_T;

END IF;

IF SELECT > MAX THEhI

SELECT =

MAX; END _IF;

SEL OUT = _SELEC1

GRP1 OUT = _{GRP1 S}

EL;

GRP2 OUT = _{GRP2 S}

EL;

GRP3 OUT = _{GRP3 SEL;}

//make it positiue

//limit to MAX

END FUNCTION BLOCK

Fig

3.7 A function block in SCL [image:35.545.116.271.324.675.2]

3.5.1 AdvantagesofStructured Control Language

Following

are the advantages ofStructuredControl Language

1. SCLenables simple andfastprogramdevelopment forthe user,

by

theapplication of powerful

languageelements such asIF.. THEN.. ELSE.[15]

2. Programswrittenin SCLhave improvedcomprehensibilityandimprovedstructure.[15]

3. SCLprograms are programmed asASCIIsources and aretherefore_easytoimportand export.[15]

3.5.2 DisadvantagesofStructured Control Language

Following

arethedisadvantagesofStructured Control

Language,

1. SCLrequirestheknowledgeofbasic high level programminglanguageandhencenot popular

withtechnicians

2. SCL isnot a suitableforsimplelogiccontrols.

References:

[1]

Berger,

Hans.

Automating

withSIMATIC.

SIEMENS,

2000.

[2]

Petruzella,

Frank. Programmable Logic Controllers. Glencoe

McGraw-Hill,

1996.

[3]

http://xtronics.com/toshiba/llp.pdf,

1999.

[4] Gary

A. Mintchell.

http://www.controleng.com/archives/1998/ctl0402.98/04ebas.htm,

1998.

[5] Step

7-_{Ladder Logic for S7-300andS7-400. Siemens}

Help

Manual,

2000.

[6]

http://www.plcopen.org/,

2000.

[7]

http://www.searcheng.co.uk/selection/control/Articles/IEC61

131/main.htm,

2001.

[8]

http://www.plcopen.org/tiaining_education/FBD2520Tutorial.ppt,

1999.

[9] http://www.controleng.com/archives/1996/02/issues/na/02cl54.htm,

2001.

[10]

N.J.Nelson.

http://boumemouth.ac.uk/forth/euro/efDO/nelsonOOb.pdf,

2000.

[11]

www.pcbasedautomation.com,2001.

[12]

http://www.sea.siemens.com/step/pdfs/plc_l.pdf,

2000.

[13] http://www.exciton.cs.rice.edu/comp410/STL/STL_Overview.htm,

2001.

[14]

http://wwwmc.cem.chTndCtiyGUAPI/Siemens_Step7Technique.html,

2001.

[15]

http://www.sea.siemens.com/sw/docs/s7pro.pdf,

2001.

[16]

Structured Control Language for

Step

7.Siemens

Help

Manual,

2000.

[17]

Johnson,

Hugh.Grafcet/Sequential Function

Charts,

1992

[18]

Lloyd,

Michael. Grafcet Addssequencedimensiontoladder

language,

1989

Section 4. Simatic

PC Based Automation System

4.1 Introduction

In this section, we shall discuss the Simatic Automation System. We shall discuss aboutthe various components of the system and then describe them in brief. We shall discuss the various Simatic Controllers and Distributed I/Osand theHMIs.

Next,

we shall describe the

Step

7 softwarein details. The

Step

7 software is the centraldevelopmenttool inthe Simatic Automation System.

Next,

we shall discuss the general architecture oftheprojects usedinthe Siemens' PC basedautomationtechnology. We shall present an overview of the project structure anddiscussthemainelements ofthestructurein detail. The main elementsinthis architecture are theSIMATIC

Manager,

theHardware configuration, the Organization

blocks,

the symbols _table, the operator _stations, WINCC

Explorer,

and the

WINLC,

whichisthePC-basedlogiccontrollerinthe

family

ofS7controllers.Weshalldiscusstheseelementsin briefand also discussthe variousprogramming languagesavailable inthe Simatic Automation System environment.

4.2 The

General Architecture

ofthe

Simatic Automation System

The Simatic Automation system is a range of coordinated components with uniform methods of

configuring,datamanagement anddatatransmission.[l]

4.2.1 Various Components/Generalarchitecture oftheSimatic Automation System

Simatic

S7, M7,

C7

Simatic

WinAC

Simatic Controllers

controlthemachine or plant

ttLi

Simatic

DP

DistributedBOsextendtheinterface between PLCandmachine/plant

Operator Controland_Monitoringof

theplant in operation

Simatic HMIs

==>

Simatic NET

Networkingfortheexchange ofdata

andprogrammingat a central point

Step

7

BasicSoftwarefoi

configuringand

programming.

[image:37.545.110.444.397.676.2]

TheentireSimatic Automationsystem consists offivemajorcomponents,viz.

Simatic Controllers

SimaticDistributed I/Os

(DP)

Simatic HMI

SimaticNET

Step7

The Simatic Controllers control the machine or the plant. The Simatic Distributed I/Os provide the

interface between the PLC and the machine or plant

being

controlled. Simatic NET provides the

networkingfortheexchange ofdata and_programmingat a central point. Simatic HMIsare usedforthe

operator control and_monitoringoftheplantinoperation.

Finally,

Step

7isthe centraldevelopmenttool

intheSimatic Automationsystem,consistingof thebasicsoftware_{for configuring}and programming.

4.3 Simatic Controllers

[1'

Simatic Controllers formthecore of the automation system and

help

_{in controlling}productionmachines,

manufacturingplants orindustrialprocesses.

There are three main families of controllers in the Simatic Automation

System,

viz. Simatic S7

controllers,Simatic M7controllers andtheSimatic C7controllers

Simatic S7 programmable logic controllers form thebasis ofthe automation system. There are three

typesofPLCs inthis

family,

S7-200 Micro

PLC,

S7-300modular mini

PLC,

for low-endan mid-range applications

S7-400 forhigh-endtop-levelperformance requirements

PLCs consist ofthe _{CPU (central processing unit)} and the I/O modules. The CPU stores the user

program writtenin one ofthe_{PLC programming languages. The I/O}modules providetheconnectionto

themachineortheplanttobecontrolled.

The M7 familiesof controllers areAT-compatiblecomputermodules,which expandtheSimaticsystem

by

providingan open software platformforstandard software products.

The C7 complete units are designed for machine control and offer PLC performance in a co