What is the working principle of the PLC control cabinet?
Release time:
2022/09/26 20:23
What is the principle of cabinet making?
The cabinet can be integrated into the industrial production automation machinery site of various specifications and enterprise scale. Widely used in power installation engineering, metallurgical industry, chemical enterprises, paper industry, ecological environment protection sewage treatment and other fields. What is the principle of PLC control cabinet?
What is the principle of cabinet making?
After the programmable logic control board is started, the steps can be generally divided into three stages: key sampling, client program execution and damage update. Performing the above three steps is called the scanner cycle time. The CPU of the programmable logic control module repeats the above three steps at a specific scanner speed during all operating periods.
Type a sampling session
In the input sampling phase, the programmable logic control board loads all input states and data in a scanning manner and stores them in the corresponding modules in the I/O projection area. Upon completion of typing sampling, the Run and Injury Update section of the executable program will be entered. In these two links, even if the input state and data change, the situation and data of the corresponding machine in the I/O projection will not change. Thus, in the case of a differential signal, in order to be able to reliably load the key at any time, the spacing of the differential signal must exceed 1 scanner period.
executable program execution phase
In the process of user program execution, the programmable logic control board can execute the program (subroutine) from top to bottom. During the subroutine of the scanner, the control line composed of the contacts on the left of the subroutine is used to carry out logical functions on the control line composed of the contacts first left, then right, then first, and then successively. According to the result of the logical function, the system software RAM storage of the logical coil is formed or the matching position of the export coil in the I/O projection area is upgraded. Or, determining whether the execution of the subroutine requires a special function instruction.
In the execution of the executable program, only the input point state and data in the I/O image area do not change, and other export points and soft device states and data in the I/O image area and the system software RAM storage area may also change. Sorting the above subprograms indicates that the program flow is reversed, and the subprograms arranged below, it only plays a role in the program flow in the updated logic coil situation and data sorting before the next scanner cycle time.
The use of just-in-time I/O instructions during program execution enables direct access to I/O points. In other words, the application I/O instruction does not easily upgrade the values entered in the process image memory, the program flow obtains the values directly from the I/O control module, and the export process image memory is immediately updated. It's a little different than typing right away.
Damage Update Link
After the scanner executable program is completed, the programmable logic control board proceeds to the export update link. During this time, the CPU updates all the derived latched power supply circuits according to the corresponding state and data in the I/O image area, and pushes the corresponding external devices through the derived power supply circuits. At this time, it is the real export of the programmable logic control board.
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