Design of PLC-based Measuring and Controlling System for Polysilicon Crystallization Holding Furnaces

A measuring and controlling system based on PLC is designed for groups of holding furnaces that are used for purification of polysilicon by crystallization. By this system, crystallization temperature curve of any holding furnace can be independently controlled at the same time, polysilicon purification which is above 4N (99.99%) and batch produce can be realized. This system uses Programmable Logic Controller (PLC) as the primary controller, R-type thermocouples as temperature sensor units. The PLC outputting PID switching-values can control the Double Solenoid Valves System to affect the flow of air, and meet the requirements of temperature control precision of polysilicon crystallization. Configuration supervision system is developed on the host link computer to implement remote control, real-time data recording, error alert, crystallization temperature curves setting, etc.