Problems that should be paid attention to during the overall calibration of the muffle furnace system

(1) The installation and wiring of the standard thermocouple furnace are carried out when the resistance furnace is powered off. After the wiring is checked, the resistance furnace can be turned on to increase the temperature.

(2) The measuring end of the standard thermocouple should be placed near the sample analysis position, but the sample or the inner wall of the furnace should not be touched to prevent contamination or damage to the standard thermocouple.

(3) After the temperature reaches the temperature control point, in order to make the furnace temperature uniform and stable, it is necessary to control the temperature for 30 minutes before reading. Since the secondary meter of the resistance furnace is not synchronized with the millivolt meter display, the highest and lowest values ​​of the millivolt meter should be read for each round of reading, and the highest and lowest values ​​displayed by the secondary meter should be read accordingly.

(4) The measurement of furnace temperature uniformity must be carried out when it reaches a thermally stable state under no-load conditions. For resistance furnaces with fans, the fans must work normally during the measurement.

(5) If the indication error is too large, check whether the furnace is working properly. For example, in order to prevent the stainless steel protection tube of the thermocouple of the control instrument from being shorted to the furnace wire, an insulating porcelain tube is placed on the thermocouple of the control instrument. In this way, the insulating porcelain tube should be cut short to avoid the actual length of the thermocouple of the control instrument being exposed. It is shorter than 8-10 times of the thermocouple protection tube; the hole of the control instrument thermocouple on the furnace wall should be sealed tightly to prevent heat loss in the nearby area. In the actual situation, certain measures can be taken to reduce the furnace temperature field correction value with a larger absolute value of the indication error.

(6) After calibration, in order to avoid damaging the thermocouple or shortening the life of the thermocouple, the standard thermocouple cannot be taken out quickly, and the furnace door cannot be opened quickly because the rapid heat and cold will damage the furnace.