Insert a thermocouple into the muffle furnace so that its thermal junction is at the center of the muffle furnace as a reference, and insert a thermocouple or tree into the furnace as a measuring appliance. Heat the muffle furnace to the operating temperature (900 ℃ or 815 ℃), and use the temperature controller to stabilize the furnace temperature at this temperature according to the instructions of the reference galvanic couple, and move the measuring couple in the front, back, left, right, and up and down directions. The distance depends on the temperature gradient of the muffle furnace. When the gradient is small, the distance can be larger. When the gradient is large, the distance is smaller. Generally, it moves 1 to 2 cm each time. After each movement, the temperature is kept at the predetermined temperature for 3 to 5 min. The temperature indicated by millivolt, and finally find out the constant temperature zone of the muffle furnace according to the temperature of each measuring point.
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