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 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) Image courtesy of Allen-Bradley, a Rockwell Automation business

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 Image courtesy of Allen-Bradley, a Rockwell Automation business

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 or 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 Image courtesy of Allen-Bradley, a Rockwell Automation business

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 Image courtesy of Allen-Bradley, a Rockwell Automation business

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 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 Image courtesy of Allen-Bradley, a Rockwell Automation business

Interface Cable Attachment to PCMK Card (1 of 2) Image courtesy of Allen-Bradley, a Rockwell Automation business

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 Image courtesy of Allen-Bradley, a Rockwell Automation business

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 Image courtesy of Allen-Bradley, a Rockwell Automation business

Connecting Industrial Mouse and Keyboard to the RAC 6181 Image courtesy of Allen-Bradley, a Rockwell Automation business

What Is the IEC ? 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 standard, have attracted the most attention internationally.

IEC 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