Detection and Control of Furnace Temperature

Temperature detection generally uses thermocouples, but the thermocouple used must correspond to the measured temperature. Under no circumstances should a nickel-chromium–nickel-silicon (K-type) thermocouple be used to measure furnace temperatures around 1200°C. Instead, a platinum-rhodium–platinum (S-type) or dual platinum-rhodium (B-type) thermocouple must be used. Otherwise, the service life of the thermocouple will be much shorter than that of silicon carbide rods, requiring frequent replacement of the thermocouple, which is detrimental to the use of silicon carbide rods. Additionally, the installation position of the thermocouple should avoid the silicon carbide rods, and the free end of the thermocouple should be at least 150mm above the furnace top to ensure accurate temperature measurement. Temperature control is often achieved by combining thermocouples with intelligent temperature control instruments. By adjusting the output voltage of the thyristor, the primary voltage of the transformer is regulated, thereby adjusting the heating power of the silicon carbide rods to achieve automatic constant temperature control of the furnace. As long as the control parameters (P, I, D) of the temperature controller are properly adjusted (some instruments come with self-tuning functions), the temperature control accuracy can fully meet process requirements, and manual control should be avoided whenever possible. Furthermore, the connection between the thermocouple and the temperature control instrument must use compensation wires with the same graduation as the thermocouple. Otherwise, the measurement error will be significant, far worse than using copper wires.