PLC uses system memory (flash memory technology is mainly used at present) for process control system. Put aside the form. The operating system also includes a user program that translates the ladder diagram into binary form. The contents of the flash memory can only be changed if the user program is changed. In the early days, PLC controller was used to replace PLASH memory, and EPROM memory was used to replace flash memory, which had to be erased by UV lamp and programmed on the programmer. With the use of flash memory technology, this process is greatly shortened. Reprogramming the program memory is accomplished through the serial cable in the application development program.
User memory is divided into blocks with special functions. Some parts of the memory are used to store input and output states. The actual state of the input is stored in a specific memory bit in the form of "1" or "0"/each input or output has a corresponding bit in the memory. The other part of the memory is used to store the variable contents of the variables in the program used. For example, a time value or a counter value will be stored in this part of the memory.
The PLC controller can be reprogrammed by computer (usually) or by manual programmer (console). This actually means that if you have the necessary software for programming, every PLC controller can be programmed by computer. Today's transmission computer is an ideal choice for reprogramming PLC controllers in factories. This is very important for industry. Once the system is corrected, it is also important to read the correct program into PLC again. It is also beneficial to check whether the program in PLC has not changed from time to time. This helps to avoid dangerous situations in the factory floor (some automobile manufacturers have established a communication network, which regularly checks the programs in the PL C controller to ensure that only good programs are executed).
Almost every program used to program PLC controller has various useful options, such as forced switch of system input/output (I/O line), real-time program tracking and chart recording. This kind of record is necessary for understanding and defining faults and failures. Pro grammer can add comments, names of input or output devices, and useful comments when looking for errors or maintaining the system. Adding notes and remarks can make any technician (not just the person who develops the system) understand the ladder diagram immediately. If replacement is needed, comments and remarks can even accurately quote the part number. This will speed up the repair of any problems caused by bad parts. The old method was that a person who developed the system protected the program, so no one except this person could understand how it was done. A properly recorded ladder diagram allows any technician to thoroughly understand how the system works.
The power supply is used to transmit electric energy to the central processor. Most PLC controllers work under 24 volts DC or 220 volts AC. On some PLC controllers, you will find that the power supply is an independent module. These are usually larger PLC controllers, while small and medium-sized series already contain power modules. The user must determine how much current to draw from the I/ O module to ensure that the power supply provides the appropriate amount of current. Different types of modules use different amounts of current.
This power supply is usually not used to start external input or output. Users must provide a separate power supply when starting the input of PLC controller, because this can ensure the so-called "pure" power supply of PLC controller. For pure power supply, we refer to the power supply that will not be seriously affected by the industrial environment. Some smaller PLC controllers provide voltage to their inputs from a small power supply that has been incorporated into the PLC.
Structurally, PLC can be divided into fixed and modular. Fixed PLC includes CPU board, I/O board, display panel, memory block, power supply, etc. These elements are combined into an inseparable whole. Modular PLC includes CPU module, I/O module, memory, power module, backplane or rack, which can be combined and configured according to certain rules.
In the eyes of users, it is not necessary to analyze the internal circuit of CPU in detail, but it is necessary to fully understand the working mechanism of each part. The controller of CPU controls the work of CPU, which reads, interprets and executes instructions. But the working rhythm is controlled by the oscillation signal. The arithmetic unit is used for digital or logical operations and works under the command of the controller. The register participates in the operation and stores the intermediate result of the operation, and it also works under the command of the controller. CPU speed and memory capacity are important parameters of PLC, which determine the working speed, IO number and software capacity of PLC, thus limiting the control scale.
PLC uses system memory (flash technology is mostly used now) for process control system. In addition to this operating system, it also includes a user program translated from ladder diagram into binary form. The contents of the FLASH memory can only be changed when the user program changes. PLC controller was used earlier than flash memory, and EPROM memory was also used earlier than flash memory. Flash memory must be erased with ultraviolet light and programmed on the programmer. Due to the application of flash memory technology, this process is greatly shortened. In application development, program memory can be reprogrammed through serial cable.
User memory is divided into blocks with special functions. A part of the memory is used to store input and output states. The actual state of the input is stored in a dedicated memory bit, that is, "1" or "0". Each input and output has a corresponding bit in the memory. Another part of the memory is used to store the contents of variables in the user program. For example, a timer value or a counter value is stored in this part of the memory.
The PLC controller can be reprogrammed by the computer (usually), but it can also be programmed by the console of the manual programmer 9. In fact, this means that if you have the necessary software for programming, the early PLC controller can be programmed through a computer. Today's transmission computer is an ideal device for reprogramming the PLC controller itself in the factory. This is very important for industrial enterprises. Once the system modification is completed, it is also very important to re-read the correct program into the PLC controller. It is very good to regularly check whether the program in PLC has changed. This helps to avoid dangerous situations in the workshop (some automobile manufacturers have established communication networks, which can regularly check the programs in PLC to ensure the correct operation procedures).
Almost all programs used to program PLC controllers have various options, such as forced switching of system input/output (I/O lines), real-time tracking of programs and chart verification. Chart verification is necessary to understand and define faults and errors. Programmers can add labels, book dates and output device names, as well as notes to help find errors or system maintenance. Adding comments and labels can make technicians (not just developers) understand ladder diagrams quickly. If parts need to be replaced, notes and marks can even accurately indicate the part number. This will speed up the repair of any problems caused by damaged parts. The old response is that the person who develops the system must protect the program, and no one around knows how the system is completed. Correct ladder diagram with supporting documents enables any technician to thoroughly understand the functions of the system.
The power supply supplies power to the central processing unit. The working voltage of most PLC controllers is 24VDC or 220VAC. On some PLC controllers, you can treat the power supply as an independent module. The user must determine how much current to draw from the I/O module to ensure that the power supply provides the appropriate current. Different modules use different amounts of current.
This power supply is usually not used to start external input or output. Users must provide independent power supply to start the input and output of PLC controller, because this can ensure the so-called "pure power supply" of PLC controller. The use of pure electricity means that the power supply in the industrial environment will not seriously affect it. Some smaller PLC controllers provide voltage sources for their inputs from small power sources integrated with PLC controllers.