Foxboro（福克斯波罗）：I/A Series系统，FBM全系列（现场输入/输出模块）
顺序控制、梯形逻辑控制、事故追忆处理、数模转换、输入/输出信号处理、
数据通信及处理等。
Westinghouse（西屋）：1C31系列DCS系统、CPU、OVATION系统、WDPF系统、
WEStation系统备件。
Triconex（英维思）:冗余容错控制系统、基于三重模件冗余（TMR）结构的现代化的容错控制器。
EMERSON（艾默生）:模块、卡件、驱动器等各类备件。
Nowadays, there are many kinds of PLC used in industry. For the low-end PLC, the ladder diagram instruction is similar. For the middle and high-end machine, many programs are compiled in language. Useful ladder diagram must be annotated with Chinese symbols, otherwise it is very difficult to read. If you can understand the equipment technology or operation process before reading ladder diagram, it seems relatively simple. If we analyze the electrical faults, we usually use the reverse search method or the reverse deduction method, that is, according to the corresponding table of input and output, we can find the corresponding PLC output relay from the fault point, and start the reverse search to satisfy the logical relationship of its action. Experience shows that if one question is found, the problem can be eliminated. Since there are two or more problems with the equipment at the same time, there are not many.
5. PLC fault identification
Generally speaking, PLC is an extremely reliable equipment with low failure rate, but it can also be damaged due to external factors.
(1) A proximity switch with 220 V working power supply shares a 4-core cable with the two lead wires of its input PLC signal contact and the 220 V power line of the proximity switch. The proximity switch is damaged at one time. When the electrician replaced it, he mistakenly adjusted the zero line of the power supply and the common line of the input PLC, resulting in burning out three PLC input points during power transmission.
