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) 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 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 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. • 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 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 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.