Chapter 03 Programming a PLC

7/29/2019 Chapter 03 Programming a PLC

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Objectives

Describe the available options for programming aPLC.

Explain what online is in comparison to offline. List the advantages of software programming with apersonal computer over a hand-held programmingterminal.

Explain the differences when interfacing a notebookpersonal computer to a PLC.

Discuss open or soft PLC programming. Provide an overview of the IEC 1131-3 standard.


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PLC Run Mode (1 of 2)

The PLC can do nothing without someonedeveloping a program and loading it into the

PLC processors memory. Once the program has been loaded into PLC

memory, the processor is put into run mode.

While in run mode, the processor is solvingthe ladder program.


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PLC Run Mode (2 of 2)

While in run mode, the processor reads fielddevice input signals and stores them in

memory. There is one memory location for each input

screw terminals ON or OFF state.

Field device status information is stored inthe input status table.


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PLC Programming

The oldest programming method is the hand-held programmer.

Most popular programming method is IBM-compatible personal computer using eitherDOS or Windows software.

Higher-end PLCs can only be programmedusing software.


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Allen-Bradley SLC 500

Programming Options

Image courtesy of Allen-Bradley, a Rockwell Automation business


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Allen-Bradley SLC 500

Hand-held Terminal (HHT)



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Hand-held Programmer andSLC 500 Modular Processors

Hand-held are used only on fixed SLC 500,

5/01, and 5/02 processors. 5/03, 5/04, and 5/05 modular processors

allow software programming only.

MicroLogix 1000 PLC has own hand-heldprogrammer.


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Smart Hand-held Programming

Terminal Advantages Compact size Easy to use and learn, no software required

Low cost; cheaper than notebook computer Easy to transport a program to the field Easy to transfer PLC program to HHT for

editing or troubleshooting


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Smart Hand-held ProgrammingTerminal Disadvantages

Holds one program at a time Newer more complex processors do not

support Limited capability to display ladder rungs Documentation not displayed Many keystrokes needed to program or edit

ladder program Dead battery means program lost


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Software ProgrammingUsing PC Advantages

Newer software Windows-based

View or monitor multiple ladder rungs Documentation displayed Easy to scroll through rungs for troubleshooting Programs stored on computers hard drive Programs transferred to floppy or CD-ROM Easy editing and programming, drag and drop,

cut and paste, etc.


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Software ProgrammingDisadvantages

Maintenance personnel must learn Windows

programming software. Notebook computers are expensive. Interface cards are expensive.

Personal computers are not designed forfactory use. There are frequent software upgrades.


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Allen Bradley 1747-PIC Interface

1747-PIC communication box used tocommunicate from a PCs serial port to a

SLC 500 family data highway 485 PLC Connects to any PC with a serial port Communicates with fixed SLC 500, and 5/01,

5/02, and 5/03 modular processors


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AB 1747-PIC Interface

Converter Interface



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Connecting a GE RS-422/RS-485

to a RS-232 to a PC (1 of 2)

Image courtesy of GE Fanuc Automation


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Connecting a GE RS-422/RS-485to a RS-232 to a PC (2 of 2)

Easy connection between personal computerand Series 90-30 or 90-70 PLC

Connects to computer serial port Connects up to 50 feet away


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Desktop or IndustrialComputer Interface to PLC

Allen Bradley 1784-KTX interface card PC ISA expansion slot card Connects to data highway plus or data

highway 485 processors

Set up RSLinx software drivers tocommunicate


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Allen-Bradleys

1784-KTX Interface Card



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1784-KTX Card andNetwork Interface

Easy network connectivity between personalcomputer and up to 64 data highway plusPLC 5 or SLC 5/04 processors (nodes) onDH+ network

Up to 32 data highway-485 SLC 500 familyprocessors on network


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Node Addresses

Each device on the network will require aunique identifier called a node or station

address. Data highway plus network will support up to

64 nodes, using octal addresses.

Data highway-485 network will support up to32 nodes, using decimal addresses.


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Communicating to

Multiple SLC 500s



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Notebook PC Interface to PLC

Direct serial connection Hardware interface device such as 1747-PIC

PCMCIA card


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PCMCIA Interface Card

Notebook PCs do not have expansion slotsfor installation of KTX card.

PCMCIA card is a credit-card sized plug-ininterface card.

Allen-Bradleys PCMCIA card is called the

1784 PCMK card. 1784 PCMK card serves as an interfacebetween a PLC and a PC used as aprogramming terminal.


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1784 PCMK Card Installation

Interface between notebook PC and eitherDH+ or DH-485

Interface PLC 5 or SLC 500 familyprocessors

Insert card into notebook computer PCMCIA

slot


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PCMK Card Insertioninto a PCs PCMCIA Slot



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Interface Cable Attachment

to PCMK Card (1 of 2)



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Interface Cable Attachmentto PCMK Card (2 of 2)

One cable to communicate to SLC 500,

DH-485 processors One cable to communicate to SLC 5/04,

DH+processor

Same DH+ cable will communicate to PLC 5processors


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Interface Cable from

PCMK Card to PLC Processors



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Industrial Computers

Notebook and desktop personal computerswere not designed for continuous use in the

manufacturing environment.


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Industrial Computers

Are Designed to Withstand:

Dirt

Shock Vibration High temperatures

Wash downs


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Industrial Computer Features

Shock-mounted hard drives Air filters with air intake fans

Hazardous environment rating NEMA 12, 4, and 4X ratings Integrated mouse on front panel

Air-conditioned enclosure not required Modular for easy repair


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Two Styles of Industrial Computers

Panel-mount Computer and monitor built into one

integrated unit Rack-mount

Computer either separate componentmounted in standard 19-inch rack orembedded inside enclosure

Separate monitor or touchscreen display


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Rockwell Automations RAC 6181

Computer Connections



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Connecting Industrial Mouse and

Keyboard to the RAC 6181



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What Is the IEC 1131-3?

Standardize PLC programming A program developed on one system could be

used on other PLC platforms with minimummodification. Programming languages, Part 3 of the 1131-

3 standard, have attracted the most attentioninternationally.


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IEC 1131-3

Programming Standard Defines a consistent set of programming

languages for PLCs: Ladder diagram Function block diagram Instruction list Structured text Sequential function block


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Sequential Function Chart (1 of 2)

It is similar to flowchart programming. It consists of steps and transitions.

Each step is represented by a box thatcontains one or more major actions.

When actions in the box are satisfied, the box

is exited. Transition step must be true before next step.


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Sequential Function Chart (2 of 2)


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Sequential Function

Chart OR Logic


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Sequential Function Chart

Illustrating a Simultaneous Branch

Documents

Chapter 03 Programming a PLC