Chapter 3 Programming a Programmable Controller. Objectives Describe the available options for programming a PLC. Explain what online is in comparison

Chapter 3

Programming a Programmable Controller

Objectives

• Describe the available options for programming a PLC.

• Explain what online is in comparison to offline.

• List the advantages of software programming with a personal computer over a hand-held programming terminal.

• Explain the differences when interfacing a notebook personal computer to a PLC.

• Discuss open or soft PLC programming.

• Provide an overview of the IEC 1131-3 standard.

PLC Run Mode (1 of 2)

• The PLC can do nothing without someone developing a program and loading it into the PLC processor’s memory.

• Once the program has been loaded into PLC memory, the processor is put into run mode.

• While in run mode, the processor is solving the ladder program.

PLC Run Mode (2 of 2)

• While in run mode, the processor reads field device input signals and stores them in memory.

• There is one memory location for each input screw terminal’s ON or OFF state.

• Field device status information is stored in the input status table.

PLC Programming

• The oldest programming method is the hand-held programmer.

• Most popular programming method is IBM-compatible personal computer using either DOS or Windows software.

• Higher-end PLCs can only be programmed using software.

Allen-Bradley SLC 500 Programming Options

Image courtesy of Allen-Bradley, a Rockwell Automation business

Allen-Bradley SLC 500 Hand-held Terminal (HHT)


Hand-held Programmer and SLC 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-held programmer.

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

Smart Hand-held Programming Terminal 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

Software Programming Using PC Advantages

• Newer software Windows-based• View or monitor multiple ladder rungs• Documentation displayed• Easy to scroll through rungs for troubleshooting• Programs stored on computer’s hard drive• Programs transferred to floppy or CD-ROM• Easy editing and programming, drag and drop,

cut and paste, etc.

Software Programming Disadvantages

• Maintenance personnel must learn Windows programming software.

• Notebook computers are expensive.

• Interface cards are expensive.

• Personal computers are not designed for factory use.

• There are frequent software upgrades.

Allen Bradley 1747-PIC Interface

• 1747-PIC communication box used to communicate from a PC’s 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

AB 1747-PIC Interface Converter Interface


Connecting a GE RS-422/RS-485 to a RS-232 to a PC (1 of 2)

Image courtesy of GE Fanuc Automation

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

• Easy connection between personal computer and Series 90-30 or 90-70 PLC

• Connects to computer serial port

• Connects up to 50 feet away

Desktop or Industrial Computer 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 to communicate

Allen-Bradley’s 1784-KTX Interface Card


1784-KTX Card and Network Interface

• Easy network connectivity between personal computer and up to 64 data highway plus PLC 5 or SLC 5/04 processors (nodes) on DH+ network

• Up to 32 data highway-485 SLC 500 family processors on network

Node Addresses

• Each device on the network will require a unique 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 to 32 nodes, using decimal addresses.

Communicating to Multiple SLC 500s


Notebook PC Interface to PLC

• Direct serial connection

• Hardware interface device such as 1747-PIC

• PCMCIA card

PCMCIA Interface Card

• Notebook PCs do not have expansion slots for installation of KTX card.

• PCMCIA card is a credit-card sized plug-in interface card.

• Allen-Bradley’s PCMCIA card is called the 1784 PCMK card.

• 1784 PCMK card serves as an interface between a PLC and a PC used as a programming terminal.

1784 PCMK Card Installation

• Interface between notebook PC and either DH+ or DH-485

• Interface PLC 5 or SLC 500 family processors

• Insert card into notebook computer PCMCIA slot

PCMK Card Insertion into a PC’s PCMCIA Slot


Interface Cable Attachment to PCMK Card (1 of 2)


Interface Cable Attachment to 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 5 processors

Interface Cable from PCMK Card to PLC Processors


Industrial Computers

• Notebook and desktop personal computers were not designed for continuous use in the manufacturing environment.

Industrial Computers Are Designed to Withstand:

• Dirt

• Shock

• Vibration

• High temperatures

• Wash downs

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

Two Styles of Industrial Computers

• Panel-mount– Computer and monitor built into one

integrated unit

• Rack-mount– Computer either separate component

mounted in standard 19-inch rack or embedded inside enclosure

– Separate monitor or touchscreen display

Rockwell Automation’s RAC 6181 Computer Connections


Connecting Industrial Mouse and Keyboard to the RAC 6181


What Is the IEC 1131-3?

• Standardize PLC programming– A program developed on one system could be

used on other PLC platforms with minimum modification.

• Programming languages, Part 3 of the 1131-3 standard, have attracted the most attention internationally.

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

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 that contains one or more major actions.

• When actions in the box are satisfied, the box is exited.

• Transition step must be true before next step.

Sequential Function Chart (2 of 2)

Sequential Function Chart OR Logic

Sequential Function Chart Illustrating a Simultaneous Branch

Documents

Chapter 3 Programming a Programmable Controller. Objectives Describe the available options for programming a PLC. Explain what online is in comparison