A PLC consists of a CPU, power supply, input circuits, output circuits, most of the memory, and communication interface circuits. The CPU module is the core memory (RAM/ROM) of the controller. The input module is the CPU interface circuit that connects to field devices. The output module transmits the PLC's logic operation results to peripheral actuators and programmers; it writes user programs into designated memory; and the special function module provides power to the controller. The power supply module provides power to the PLC's internal circuitry, which is independently developed for special applications. What are the main components of a PLC?
1. CPU module
The CPU module mainly consists of a microprocessor (chip) and memory. Like a machine, a PC is analogous to the brain and heart of a human. It aggregates and analyzes information collected by other modules and finally delivers the calculation results to the output system. The main function of the CPU is to execute user programs. Programmers can implement various functions by writing user programs. Memory is used to store programs and data, similar to the memory module in a home PC. The CPU module is also called the CPU.
2. Input/Output Module
The output interface circuit acts as a bridge between the PLC and external loads. PLC output signals can be converted into control signals to drive external circuits, controlling the energization and de-energization of contactor coils and other electrical appliances. Digital output modules are mainly used to control relays, contactors, solenoid valves, indicator lights, and other devices that operate in only two on/off states. Analog output modules are used to control devices requiring continuous adjustment, such as regulating valves and frequency converters. Digital signals: have only two states, ON and OFF; digital devices use signals composed of 0s and 1s. This signal is discontinuous, with only two opposite states. Analog signals: continuous voltage, current, etc., with signal ranges varying over time. The CPU's operating voltage is typically 5V, while the circuit voltage of PLC peripheral devices is generally higher. There are two main control voltages: DC24V and AC220V for the control cabinet. Introducing such high voltages will damage the CPU. Optocouplers and photothyristors are used in I/O modules. Small relays are isolated before being input to the PLC for isolation protection. Therefore, the main function of the I/O module is signal transmission and level conversion isolation. The CPU module of a small PLC is usually integrated with the I/O module. When integrated I/O is insufficient, dedicated I/O modules can be added. Most medium and large PLCs have independent CPU modules, and the corresponding I/O modules are configured according to the actual number of points.
3. Programmer
The primary function of a programmer is to generate user programs for editing, checking, modifying, and monitoring. Programmers were primarily used in the early days of the PC era.
Currently, PLC programming, debugging, and monitoring primarily rely on programming software installed directly on a computer. Siemens S7-200 programming software is STEP7Micro/WIN. Ladder diagrams can be written on the computer, and switching between different programming languages is possible.
Programming software can compile programs and download them to the PLC programming software, or upload PLC user programs to a computer.
4. Special function modules
As the name suggests, special function modules are special modules used in special occasions, such as weighing modules, communication modules, and high-speed counting modules.
5. Power Module
The PLC power module can process external input power and convert it into DC power required by the PLC's internal circuits such as CPU, memory, and input/output interfaces.
What are the components of a PLC? What are its main components? A PL/DC power supply uses a DC regulated switching power supply, which can provide multiple independent internal voltages and also power external inputs (such as sensors). Depending on the PLC model, some use a single AC power supply, typically 220V, while others use a DC power supply, typically 24V.
