How to determine the constant temperature zone of the muffle furnace?

Insert a thermocouple into the muffle furnace so that its hot junction is located in the center of the furnace as a reference, and insert another or several thermocouples into the furnace as a measuring couple. Heat the muffle furnace to the operating temperature (900°C or 815°C), and use the temperature controller to stabilize the furnace temperature at this temperature according to the reference galvanic couple. , Move in the downward direction, the moving distance depends on the temperature gradient of the muffle furnace, the distance can be larger when the gradient is small, and the distance is smaller when the gradient is large. Generally, each movement is 1-50px, and each movement is kept at a predetermined temperature for 3 to 5 minutes. , Read the temperature indicated by the measuring galvanic millivoltmeter, and finally find out the constant temperature zone in the muffle furnace according to the temperature of each measuring point.