Vacuum coating machine PLC usually consists of central processing unit, memory, input and output (I/O) channels, timer (T), counter (C) and other units. Sometimes external devices such as printers and CRT monitors are connected, and the control program is input by the programmer. The structure of PLC is similar to that of computer, and the functions of each component are:

       ①The central processing unit CPU of vacuum coating machine. It is the core component of PLC, which is composed of processor, intermediate variable memory, etc., similar to the CPU of microcomputer. Its function is to receive and store the user program and data input from the programmer according to the function given by the system program in the PLC; receive the status and data of the field input device by scanning, and store it in the human data register; diagnose the power supply and the internal circuit of the PLC Syntax errors in working status and programming process. When the PLC is running, read the user program one by one from the memory, and generate corresponding signals according to the tasks specified by the program to open and close the relevant circuits; time-sharing and channel-sharing to perform data access, transmission, combination and comparison And transformation, complete tasks such as logic control or calculation specified in the user program; according to the calculation result, update the status of the relevant flag bit or the relevant content in the data register to realize output control, tabulation and data communication.
       ②Program memory of vacuum coating machine. The system program memory is used to store system engineering programs (monitoring programs), functional subprograms and management programs. The user program memory is used to store the control algorithm coefficients (analog) and user-made programs. PLC user memory usually uses words (16 bits/word) as the unit to express the memory capacity. The memory type and capacity given in the PLC product documentation refer to user memory. Since the user memory is powered by a lithium battery, even if the power grid fails, the program in the user memory will not be lost.
       ③Vacuum coating machine input and output channel I/O. I/O is the connecting part between the CPU and the on-site vacuum device or other external equipment. PLC provides I/O for various purposes, various operating levels and drive capabilities for users to choose. I/O has level shifting, electrical isolation, string pie line switching, data transmission, error checking, A/D or D/A conversion and other functional control.