|
|
 |
 |
Programmable Logic Controllers(PLC) |
 |
| | |  |
Programmable Logic Controllers |
 |
Outline |
|
Conventional industrial machine controls use hard-wired relays, timers and counters. With this method, however, the functionality of the circuit cannot be tested until all wiring has been completed.
Any modification to the circuit will be time consuming and difficult. The greatest disadvantage of this type of system is that it requires frequent maintenance because
of the short service life of each component.
Programmable logic controllers were developed to solve such problems. Since the control process of programmable
logic controllers is created with programs, control elements can be changed in the programs. PLCs also
perform arithmetic operations and control high-speed lines, which cannot be performed using a combination of
relays, timers and counters. Since semiconductor devices and microcomputer technology have been
rapidly advancing in recent years, PLCs now have a much longer service life. Therefore, little maintenance is required. |
|
Configuration |
|
Programmable logic controllers are considered to be a large group of relays, timers and
counters. These elements are combined with various instructions to make sequential circuits. The sequential
circuits are software-based logic circuits, not hard-wired circuits such as electromagnetic relay circuits.
Although conventional systems require complicated physical wiring, programmable logic controllers create logic circuits through simple programming. |
|
Ladder program |
|
A ladder program is a program used for programmable logic controllers (PLCs).
A ladder program is based on a sequence diagram (electrical circuit diagram). It uses a programming
language that allows easy visualization of the relationship between input conditions and outputs.
A ladder program is written with a combination of an instruction word and a device. For example, the following
is the ladder program which turns on output relay 500 when both input relays 000 and 0001 are turned on (AND circuit). |
|
In a ladder program, instruction words are represented by symbols. A relay input is graphically shown as and a
relay output is graphically shown as . PLCs must convert the ladder program symbols to mnemonics which then can be processed. The ladder program above can be represented by the following mnemonic words. |
|
|
The ladder programming support software automatically performs the conversion from the ladder program to the mnemonic words. Users can write programs without any concern for the difference.
KEYENCE's KV Series Programmable Logic Controllers feature hundreds of instructions, enabling various types of control operations such as calculation and saving of data as well as turning output relays on or off. |
|
English
日本語
简体中文
Page Top
| Privacy |
Terms of Use |
Contact |
Produced by KEYENCE