The Siemens SIMATIC series PLC was born in 1958 and has gone through the C3, S3, S5, and S7 series, becoming a widely used programmable controller.   1. Siemens' product was first launched in 1975 as the SIMATIC S3, which is actually a binary controller with a simple operating interface.   2. In 1979, the S3 system was replaced by the SIMATIC S5, which widely used microprocessors.   3. In the early 1980s, the S5 system was further upgraded - the U-series PLC, with commonly used models including S5-90U, 95U, 100U, 115U, 135U, and 155U.   4. In April 1994, the S7 series was born, which has advantages such as more internationalization, higher performance level, smaller installation space, and better Windows user interface. Its models are: S7-200, 300, 400.   5. In 1996, Siemens proposed the concept of PCS7 (Process Control System 7) in the field of process control, integrating its advantages of WINCC (Windows compatible operating interface), PROFIBUS (industrial fieldbus), COROS (monitoring system), SINEC (Siemens industrial network), and control technology.   6. Siemens proposed the concept of TIA (Total Integrated Automation), which is a fully integrated automation system that integrates PLC technology into all automation fields.   The S3 and S5 series PLCs have gradually withdrawn from the market and ceased production. The S7 series PLCs have developed into the control core of Siemens automation systems, while the TDC system continues to use the SIMADYN D technology core, which is a further upgrade to the S7 series products. It is the most cutting-edge and powerful programmable controller in Siemens automation systems.