PLC Parts Explained PDF

## Parts of a PLC 1.2 - The major parts of a PLC system are the central processing unit (CPU), the input/output (I/O) section, the power supply, and the programming device. ### Diagram of PLC System The diagram shows the following components of a PLC system: | Component | Description | |---|---...

## Parts of a PLC 1.2 - The major parts of a PLC system are the central processing unit (CPU), the input/output (I/O) section, the power supply, and the programming device. ### Diagram of PLC System The diagram shows the following components of a PLC system: | Component | Description | |---|---| | Input sensing devices | These devices provide data to the input module. | | Input module | This module receives signals from the input devices and sends them to the CPU. | | Processor module | This module contains the CPU, memory, and program data. | | Central Processing Unit (CPU) | This unit processes the program and controls the PLC. | | Memory | This component stores the PLC program and other data. | | Output module | This module receives data from the CPU and sends it to the output devices. | | Output load devices | These devices perform the actions commanded by the PLC. | | Power supply module | This module provides power to the entire PLC system. | | Optical isolation | This circuitry isolates the PLC from external interference, preserving signal integrity. | | Programming device | This device is used to program the PLC with instructions. | ### PLC Architecture - The term architecture can refer to PLC hardware, to PLC software, or to a combination of both. **Open Architecture Design** - An open architecture design allows the system to be connected easily to devices and programs made by other manufacturers. **Closed Architecture Design** - A system with a closed architecture is one whose design is proprietary, making it more difficult to connect to other systems. ### Fixed I/O - Fixed I/O is typical of small PLCs that come in one package with no separate, removable units. - The processor and I/O are packaged together. ### Modular I/O - Modular I/O is divided by compartments into which separate modules can be plugged. - This feature greatly increases your options and the unit's flexibility. ### Power Supply - The power supply provides DC power to all modules that plug into the rack. - For large PLC systems, this power supply does not normally supply power to the field devices. ### Processor (CPU) - The processor (CPU) consists of a microprocessor for implementing the logic and controlling the communications among the modules. - The processor requires memory for storing the results of the logical operations performed by the microprocessor as well as the operating system and the PLC program. ### PLC Program Execution - Scan - The PLC program is executed as part of a repetitive process referred to as a scan. - It begins by reading the status of all inputs from the input module and then proceeds to execute the program, updating the status of all outputs to the output module. - This 'scan' cycle is repeated continuously. ### I/O (Input/Output) System - The I/O (Input/Output) system forms the interface by which field devices are connected to the controller. **Input Devices** - Input devices, such as pushbuttons, limit switches, and sensors, are hardwired to the input module terminals. **Output Devices** - Output devices, such as motor starters, solenoid valves, and indicator lights, are hardwired to the output module terminals. ### Programming Device - A programming device is used to enter the desired program into the memory of the processor. **Hand-held Programming Device** - This device can be used to program the PLC using a simple, user-friendly interface. **Personal Computer (PC)** - A personal computer (PC) is the most commonly used programming device. - It offers a larger screen for showing program logic and can be used to develop more sophisticated program interfaces. ### PLC Program - A program is a series of instructions that directs the PLC to execute actions. - Individual instructions are contained within 'rungs,' which are arranged vertically in a ladder diagram. ### Relay Ladder Logic - Relay ladder logic, the standard programming language for PLCs, is based on electromagnetic relay control. - It offers a clear and intuitive method for representing program logic and is widely understood by electrical engineers.