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PLC编程和硬件基础英文文献和中文翻译

时间:2017-09-29 16:25来源:毕业论文
1. PLC PROGRAMMING AND HARDWARE FUNDAMENTALS Over recent years electronic programmable logic controllers (PLCs) have sprung up like mushrooms, and over three hundred different types and brands are now available. Electronic programmable logic
1. PLC PROGRAMMING AND HARDWARE FUNDAMENTALS Over recent years electronic programmable logic controllers (PLCs) have sprung up like mushrooms, and over three hundred different types and brands are now available. Electronic programmable logic controllers have undoubtedly become an indispensable feature of the ever advancing industrial automation.
These controllers evolved as industry sought more economical ways of automating production lines, particularly those involved in the manufacturing of equipment, consumer goods and heavy industry products. Thus the electronic programmable controller has replaced relay-based, hard-wired electrical systems, and more recently it has also made significant inroads into the traditional domain of pneumatic logic circuitry. This encroachment unfortunately has brought about some problems:13960
(1)    Programming difficulties caused through non-standardised and varying programming techniques.
(2)    Programming difficulties caused through the use of varied logic element names and element description for hardware and software components within the controller.
(3)    Demarcation problems in factories between electrical and metal worker unions when maintenance on machines with fluid power control and PLC control is required.
(4)    Extreme shortage of skilled personnel who can program and install such electronic PLC controllers and interface them with fluid power circuitry.
    PLCs operate by monitoring input signals from such sources as push-button switches, proximity sensors, heat sensors, liquid level sensors, limit switches, and pressure and flow rate sensors. When binary logic changes are detected from these input signals, the PLC reacts through a user-programmed, internal, highly sophisticated, logic switching network and produces appropriate output signals. These output signals may then be used to operate external loads and switching functions of the attached fluid power control system.

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PLCs eliminate much of the wiring and rewiring that was necessary with conventional relay-based systems.
    Instead, the programmed “logic” network replaces the previously “hard-wired” network. This logic network may be altered as required by simply deleting, inserting or changing certain sections in the PLC’s program. Thus, the automated processes of a production line or complex manufacturing machine can be controlled and modified at will for highly economical adaptability to a rapidly changing manufacturing environment.
Some people use the abbreviation PC for programmable logic controller, but PC normally stands for personal computer. To avoid confusion, therefore, throughout this book PLC is used for programmable logic controller.
WHAT IS AN ELECTRONIC PROGRAMMABLE LOGIC CONTROLLER?
Programmbale logic controllers are purpose-built computers. A typical PLC has four separate yet interlinked components. These are:
(1)    an input/output section, which connects the PLC to the outside world (the machine with its sensors, solenoid valves and switches, lamps,heaters and electric motors).
(2)    A central processing unit (CPU), which is microprocessor-based. This may be an octal or hexadecimal microprocessor.
(3)    A programming device, which may be a hand-held programming console, a special PLC desk-type programmer, similar to a lap-top computer, or a desk-top computer with monitor.
(4)    A power supply to power input sensors and output signals leading to lamps, motors, heaters and solenoids on the flaid power valves.
THE PLC’s INTERNAL ORGANISATION PROGRAM
When a programmable logic controller (PLC) operates, that is, when it executes its program to control an external system with, for example, fluid power valves, a series of operations are automatically performed within the CPU. These automatic operations are regarded as the PLC’s internal organization program. PLC编程和硬件基础英文文献和中文翻译:http://www.lwfree.cn/fanyi/20170929/14347.html
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