PLC learning experience - Solutions - Huaqiang Electronic Network

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

SMD aluminum electrolytic capacitor

L0504-Murata muRata common mode inductor 90Ω 150mA

The working process of plc is actually the same working principle as the lighting, except that the PLC drives the external load through a series of internal system programs. The PLC input signal must be sampled before it can be received, then executed, and finally output. ! It is such a working principle, the PLC absorbs the signal by diagnosing whether the command entered is wrong, and then can enter the sampling, enter the sampling and then the program execution, and finally the output processing, scanning phase: scan the input field signal to the input image register, Output image registers to drive external loads! The above is the whole work process, so it is not difficult to learn plc programming. Just understand the functions of the instructions and instructions, and familiarize yourself with the ladder diagram. That is to say, learning PLC programming must know the above basics. Although the book has a lot of text and some PLC components plus some internal system programs to introduce and explain, in fact, those are not the focus, it is just to let us fully familiar with the PLC, as for the part of learning programming is a bit Difficult, the most basic learning tools do not say to have a PLC, then at least there must be a computer, no computer can not complete this learning, familiar with the use and function of the instructions must understand, the best is someone pointing, if someone Pointing to learn PLC programming is not a problem, but you must first learn it yourself. If you don't understand it, ask if you don't seriously study it and ask others. It will definitely not learn! What kind of mentality has what kind of process, the result is determined from the process, we do not have to go to college to have a high education and high culture can also learn, the mentality will give you everything! So don't tell me how high you are and how smart you are. In fact, I didn't put you in the eye! Don't say that you didn't graduate from elementary school and you can't learn this thing, what you are stupid! In fact, as long as you have the ability to understand and understand the words you can do it, and there are no stupid people in the world, only those who do not want to brainstorm and refuse to work hard! Iron pillars can be ground into needles. What is this little thing?
The working principle of PLC and some related basic contents are very important in this learning process. A conclusion drawn from my personal learning experience is that the learning of the next program is to solve the problem and understand the function and application of the instruction familiar to it. The introduction and explanation, in fact, the working principle of PLC internal circuit is similar to the working principle of hardware. PLC has counter CNT and many soft relays or soft contacts of soft contacts. It is driven by some sensors or some switches to signal PLC. Then, the PLC receives the signal from the external hard circuit and passes the program of each stage step by step, and finally to the output! The fixed program will not be said, and those are manufacturers that use ROM to store the unchanged program! Regarding the backup battery, a lithium battery is generally used as a backup battery, and the life span is 5 to 10 years. If the load is often carried out for 2 to 5 years! There are three types of I/O points capacity for PLC: 256 points for minicomputers, 256 to 1024 points for medium-sized machines, and 1024 points or more for mainframes. The available resources for users are usually K-word KW, K-byte BK. Or K bit to indicate that 1K=1024, and some PLCs directly use the amount of program that can be stored. In some PLCs, the address unit of the program is step, each step occupies two bytes, one instruction is generally One step, the basic instructions and function instructions with complex functions often have several steps. The number of I/O points refers to the number of external I/O terminals, which determines the total number of input switch signals and output switch signals that the PLC can control! The input signal of the field passes through the optical coupler to the input data register and then to the CPU through the data bus. The input unit of the PLC usually has three types: DC 12 to 24V input, AC 100 to 120V or 200 to 240V input, AC DC 12 to 24V input, the external input switch is connected to the PLC through the input terminal! The load power of the output circuit is provided externally. The power supply voltage should be determined according to the output device type and load requirements. The output current is allowed to be 0 to 5 amps. The rated value is related to the load characteristics. The power supply unit converts the AC power into a PLC. The DC power supply required for the operation of the electronic circuit such as the central processing unit and the memory enables the PLC to work normally, and its quality directly affects the function and reliability of the PLC! PLC generally uses 220 volt AC power supply or 24 VDC power source. The internal switching power supply provides DC5V, positive and negative 12V, 24V and other DC power supplies for each module! The power supply that drives the PLC load is generally provided by the user! The PLC is a program that sequentially executes its internally stored program to complete a certain task. The input device of the program is called a programmer! The intelligent interface module is a stand-alone computer system. From the perspective of the module structure, it has its own CPU, system program, memory and interface circuit. It is connected with the CPU of the PLC through the system bus for data exchange and in the CPU. Working independently under the coordination of the modules! Work process: The completion of the PLC control task is realized by executing the user program reflecting the control requirements with the support of the hardware! The PLC determines the work task, loads the special program into a special machine, it uses the working mode of the cyclic scan, the system work task management and the execution of the user program are completed by the cyclic scan method! The working mechanism of the tour scan: initialization, first initialize the system after the PLC is powered on, clear the internal relay area, reset the timer, etc.! Communication service and self-diagnosis stage, at this stage, the CPU in the PLC completes some communication with the programmer or other external devices, completes the data receiving and sending tasks, responds to the commands entered by the programmer, updates the programmer display contents, and updates the clock. Working with special register contents, if the program syntax is wrong or abnormal, the CPU can generate prompt information according to the error type and program content, and even stop scanning or force STOP status! Execute the user program scanning phase: This phase includes three stages of input sampling, program execution, and output processing! Data I/O scanning phase: At this stage, the input field signal is scanned into the input image register, and the result of the output image register is driven to the production site! PLC working process: Under normal circumstances, a user program scanning cycle consists of 3 phases: input sampling phase, program execution phase, output processing phase, PLC core module CPU can not directly contact external terminal, send to PLC terminal The input signal is then subjected to a series of circuits such as level shifting, photoelectric isolation, and filtering processing to enter the buffer for sampling. Without the CPU sampling permission, the external signal cannot enter the memory, and there is a special storage I/ in the PLC memory. The area of ​​the O signal state is called the input image register and the output image register! Other programming components in the PLC ladder diagram also have corresponding image memory areas, which are called component image registers! In the input processing phase, the on/off status of all input devices such as buttons and speed relays on the PLC site is read into the input image register. When the contact of the external input device is turned on, the corresponding input image register is 1, in the ladder diagram. The moving contact of the corresponding input relay is turned on, and the breaking contact is opened. When the external input contact circuit is disconnected, the corresponding input image register is 0. The active contact of the corresponding input relay in the ladder diagram is disconnected, and the dynamic break contact is turned on! It is worth noting that only at the sampling time, the content in the input image register is consistent with the input signal, and the change of the input signal in other time ranges does not affect the content in the input image register, and the input signal changes state only. Can be read in the input processing phase of the next scan cycle! Therefore, if the input is a pulse signal, the degree of switching of the pulse signal must be greater than one scan period to ensure that the input can be read in any case! Program execution phase: The PLC user program consists of several instructions. The instructions are arranged in the order of the step numbers in the memory. According to the PLC ladder program scanning principle, the user program is scanned step by step according to the principle of first left, right, first up and down. Until the end of the user program! However, if a program jump instruction is encountered, the jump address of the program is determined according to whether the jump condition is satisfied! When the PLC executes the instruction program, the status of the input image register to be read is ON or OFF. The status of the programming element in the 1 or 0 and component image registers is ON or OFF. Both 1 or 0, the CPU performs logic according to the requirements given by the program. Operation and arithmetic operations, the operation result is stored in the corresponding component image register, and the signal to be outputted to the output image register is stored in the output image register and saved by the output latch! Output processing stage: In the output processing stage, the CPU turns ON or OFF the status of the output image register, and either 1 or 0 is transferred to the output latch. When the coil of an output relay in the ladder diagram is powered, the corresponding output image register is 1 state! After the signal is isolated and amplified by the output module, the coil of the corresponding hardware relay in the relay type output module is energized, and the moving contact is closed, so that the external load is energized! Waiting for the next scan cycle after one action will be refreshed, so that the second action can be performed, which is called centralized output mode! The input image area and the output image area are collectively referred to as the I/O image area. The size of the image area depends on the number of system I/O signals, which is determined by the number of I/O points! The I/O image area is set so that the signal state and execution result required by the computer to execute the user program are related to the I/O image area. The CPU reads from the actual input point only when the computer scans to the I/O service process. Enter the relevant signal status, store it in the input image area, and temporarily store the result of the operation in the output image area to the actual output point!