Basic Concept of PLC


Implementation of automated machines and automatic processing in industry field is a must to facilitate and streamline industrial processes. Because electromechanical control system has many weaknesses. Some of them are easy to wear out because of heating and burnt contact and also it took a large cost when the installation, maintenance and modification process.

To make the automatic processing we can use PLC programming. The PLC programming can integrate the components of stand alone to be a controlled system in an integrated manner.

Programmable Logic Controller (PLC) is a special computer that serves for regulation of industrial processes. The PLC works y programs (software) stored in the processor PLC. PLC programming is using a special program language called ladder diagrams.

The working concept of PLC as the name suggest is as follows:
Programmable is showing its ability that can be easily changed according to the program made.
Logic is showing its ability in processing the input of arithmetic (ALU) which compares the operation, add, multiply, divide, subtract, and negation.
Controller is showing its ability to control and manage the process to produce the desired output.

The PLC consists of:
Central Processing Unit (CPU) which contains the application program memory (a RAM and ROM) PLC. CPU is much variation depending on the brand and its type.
Interface module Input/Output (I/O) is connected directly to the input (switches, sensors) and output (motor, solenoid, lamps).
Digital Input Point
- DC 24 V input
- DC 5 V input / TTL (Transistors Logic)
- AC / DC 24 V input
- AC 110 V input
- AC 220 V input

Analog input
Analog input Point Linear
- 0 to 10 V DC
- DC 10 V - 10 V DC
- 4 to 20 mA DC

Output unit
Digital Output: Digital Output Point 1
- Relay Output
- 110 V AC output
- 220 V AC output
- DC 24 V output, the type of PNP and NPN types.

Output analog: Output Point Linear
- 0 to 1 V DC
- 10 V DC - 10 V DC
- 4 to 20 mA DC

Besides that PLC also has additional peripheral called programming console, it is to transfer the PLC program. PLC programming can also be done with special software. Programming console is a panel that contains RAM (Ramdom Access Memory) that functions as a semi-permanent storage in a program that was created or modified.

PLC programming is written into the console must be in the mnemonic form. This device can be connected directly to the CPU by using extention cables, it can be installed or removed at any time. If the execution of the program has gone through one cycle the programming console can be lifted and moved to another CPU. While the first CPU can still run the program, but it must be in RUN or MONITOR mode.


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