Programmable controllers produced by Siemens (SIEMENS) Company of Germany are also widely used in our country, in metallurgy, chemical industry, printing lines and other fields. Siemens (SIEMENS) PLC products include LOGO, S7-200, S7-1200, S7-300, S7-400, S7-1500 and so on. Siemens S7 series PLC is small, fast, standardized, with network communication capability, stronger functions and high reliability.S7 series PLC products can be divided into micro PLC (such as S7-200), small-scale performance requirements of the PLC (such as S7-300) and medium- and high-performance requirements of the PLC (such as S7-400) and so on.