What is the structure of PLC, please

1. Host. The host part includes the processor (CPU), system program memory, and user program and data memory. CPU is the core of PLC, which is used to run user programs, monitor the status of input and output interfaces, make logical judgments and carry out data processing, that is, read input variables, complete various operations specified by user instructions, send the results to the output end, and respond to requests from external devices (such as computers, printers, etc.) and make various internal judgments.

There are two types of internal memory of PLC, one is the system program memory, which mainly stores the system management and monitoring program and the program of compiling and processing the user program, and the system program has been fixed by the manufacturer and cannot be changed by the user; The other type is user program and data memory, which mainly stores user-compiled applications and various temporary data and intermediate results.

2. Input-output (IO) interface.

The IO interface is the part that connects the PLC to the input and output devices. The input interface accepts control signals from input devices such as buttons, sensors, contacts, travel switches, etc. The output interface is to drive the output equipment (such as contactor, solenoid valve, indicator light, etc.) through the power amplifier circuit after the processing of the host.

IO interfaces generally use opto-coupled circuits to reduce electromagnetic interference and thus improve reliability. The number of points is the number of input and output terminals is a major technical index of PLC, usually the small machine has dozens of points, the medium machine has hundreds of points, and the large machine will exceed 1,000 points.

3. Power supply. The power supply in the figure refers to the DC switching regulated power supply configured for the operation of internal electronic circuits such as CPU, memory, and I-O interface, and usually also provides DC power for input devices.

4. Programming. Programming is the use of external devices in PLC, which is used by users to input, check, modify, debug programs or monitor the working conditions of PLC. The PLC is connected to the PC via a dedicated PC PPI cable, and the computer is programmed and monitored using dedicated software.

5. Input and output expansion unit.

The io expansion interface is used to connect the expansion unit that expands the number of external input and output terminals with the base unit (i.e., the main unit).

6. External device interface.

This interface can connect external devices such as printers, barcode scanners, and inverters to the host computer to complete the corresponding operation.

The host model provided by the experimental setup is the CPU 224 (AC DC Relay) of the Siemens S7-200 series. The number of input points is 14, and the number of output points is 10; CPU226 (AC DC Relay), the number of input points is 26, and the number of output points is 14.

Because it is so widely used, you may need to consult the teacher to eat it thoroughly, I am now working in a factory, and it is also in this regard, I was a student of Dongxun before, and now I don't understand anything or I will go back to ask the teacher, the teacher will help me answer, I hope it can help you, thank you.

The PLC structure mainly includes power supply, CPU, expansion I-O module and some other special modules, such as communication module, analog module, motion control module and so on.

CPU Memory, IO Expansion Interface, and Communication Interface Power Supply.

PLC is composed of CPU, power supply, input interface, output interface, memory and communication interface circuit.

There are two types of memory in PLC: system memory and user memory. The system memory is used to store the system program of the PLC, and the user memory is used to store the user program of the PLC. PLCs generally use electrically erasable E2PROM memory as system memory and user memory.

The function of the input interface circuit of the PLC is to input the signals generated by buttons, travel switches or sensors into the CPU; The function of the output interface circuit of the PLC is to convert the signal output from the CPU into a signal that can drive the external actuator, so as to control the power on and off of electrical appliances such as contactor coils. The input and output interface circuits of PLC generally adopt opto-coupling isolation technology, which can effectively protect the internal circuits.

The output structure of the PLC

The input interface circuit of PLC can be divided into DC input circuit and AC input circuit. The delay time of the DC input circuit is relatively short, and it can be directly connected with electronic input devices such as proximity switches and photoelectric switches; The AC-closed commotion input circuit is suitable for use in harsh environments with oil mist and dust. The AC input circuit is similar to the DC input circuit, and the external input power supply is changed to 220V AC power supply.

There are generally 3 types of output interface circuits: relay output type, transistor output type, and thyristor output type. The output circuits of the relay output type, the transistor output type, and the thyristor output type are similar, except that the transistor or thyristor relays are used instead of relays to control the external load.

The PLC is composed of a processor CPU, memory, input and output interfaces, and a programmer.

1. The CPU of the processor is the core, and its role is to accept the input program and store the program, scan the input status of the site, execute the user program, and self-diagnose.

2. The memory is used to store programs and data.

3. The input interface collects the signal status of various switch contacts on the site, and converts it into a standard logic level, and the output interface uses the output electrical signal to control the object.

4. The programmer is used for the compilation, debugging, inspection and monitoring of user programs, and can also display various states of PLC.

a. Power supply. The power supply of the PLC plays a very important role in the whole system. It can't work properly without a good and reliable power supply system, so PLC manufacturers also attach great importance to the design and manufacture of power supplies.

Generally, the AC voltage fluctuates in the range of +10% (+15%), and the PLC can be connected directly to the AC grid without other measures.

b. ** Processing Unit (CPU).

**The processing unit (CPU) is the control center of the PLC. It receives and stores the user program and data typed from the programmer in accordance with the functions assigned by the PLC system program; Check the status of the power supply, memory compartment, IO, and alert timers, and diagnose syntax errors in user programs. When the PLC is put into operation, first it receives the status and data of each input device in the field in the form of scanning, and stores them in the IO image area respectively, then reads the user program from the user program memory one by one, and sends the result of the logic or arithmetic operation according to the provisions of the instruction into the IO image area or the data register after the command is interpreted.

After all the user programs have been executed, the output status of each output area or the data in the output register will be transmitted to the corresponding output device, and so on until the operation is stopped.

In order to further improve the reliability of PLCs, a redundant system with dual CPUs or a voting system with three CPUs is used for large PLCs. This way, even if one CPU fails, the entire system will still function normally.

c. Memory.

The memory that holds the system software is called system program memory.

The memory that holds the application software is called the user program memory.

d. Input and output interface circuits.

1. The field input interface circuit consists of the optocoupler circuit and the input interface circuit of the microcomputer, which is the input channel of the interface interface between the PLC and the field control.

2. The field output interface circuit is integrated by the output data register, the strobe circuit and the interrupt request circuit, and the PLC outputs the corresponding control signal to the execution component in the field through the field output interface circuit.

e. Functional module.

Such as counting, positioning and other functional modules.

f. Communication module.

Hope...

PLC is mainly composed of CPU, power supply, circuit, memory and input and output interfaces.

There are only two kinds of people who learn PLC, there is a foundation and there is no foundation. Electrician fundamentals are the first step, and their importance is self-evident. With the foundation of electrician, the first thing you have to face is the foundation of PLC programming and the setting of logic control sequence.

In fact, to put it bluntly, it is the basic knowledge of PLC introductory knowledge and PLC programming instruction knowledge.

Introduction to PLC programming, how to learn Siemens PLC.