PLC(Programmable Logic Controller)
                      Author: Nuttaphong(www.try-plc.com)


PLC: Programmable Logic Controller originated from the United States. A controller in industrial automation that can be programmable. Was created and developed to replace relay circuit. Due to the demand would be low cost controller can use Work with purpose. And can learn the easy to use.

                                           PLC Story Background.

When Year 1969 PLC was first developed by Bedford Associates under the name of Modular Digital Controller (Modicon) to a car plant in the U.S. company General Motors Hydramatic Division Allen-Bradley. Proposed control system under the name of PLC.
            Later developed the G PLC is processed by the faster. Changes. Microprocessor. The ability to communicate data between the PLC and PLC's Modicon Modbus system first started using the input / output signals to Analog. And efforts to standardize the communication of the PLC by General Motor Company has called a protocol. manufacturing automation protocal (MAP) the size of the PLC gradually reduced production software programmable PLC language symbolic can program through a personal computer instead of the program through a handheld or programing terminal current efforts to be made. language used to program the PLC using the same standard standard IEC1131-3. Programmable PLC with.
                    - IL (Instruction List).
                    - LD (Ladder Diagrams).
                    - FBD (Function Block Diagrams).
                    - SFC (Sequential Function Chart).
                    - ST (Structured Text.

1. The processor (CPU).
          A page that calculates เเ per person. Sueng like the brain of the PLC logic circuits include multiple microprocessors and bass (Micro Processor Based) Class replacement relay. Counter / timer's. And CK Trophy. So that users can design circuits using Relay Ladder Diagram the CPU will accept input data from various devices. It then processes and stores data using the program from memory After that will send the appropriate information and to correct the output device.

2. Memory (Memory Unit).
          Functions and data storage applications in the works. The size of the memory is divided into bits of information (Data Bit) in the memory a bit it will be the state of logic 0 or a different depending on the command that PLC contains two memory types. ROM and RAM.
          RAM storage functions. User program and data used in the performance of the PLC memory types will have a small battery. The party in power to the data when the power failure. Reading and writing data into RAM therefore very easy to contract work during treatment machines have been changed. Programs are often
          ROM for program storage functions in the operation of the PLC user program. ROM memory can be divided into EPROM, which will require special equipment to write and delete programs. Suitable for jobs that do not want to change the program. It also has an EEPROM memory, this section does not require special tools to write and delete programs. Can be used as RAM, but does not require battery backup. But the price is more expensive because of ROM and RAM and features together.

3. Public input - output. (Input-Output Unit).
          Unit to receive input signals from external devices and then converted into a signal and send the appropriate signals to the processor next
          Unit output. To receive data from the processor and send the data to control external devices such as motors and lighting control valves etc.

4. Power supply (Power Supply).
          Functions and maintain power voltage direct current to CPU Unit memory unit and input / output.

5. Connected with (Peripheral Devices).