Precautions For Using Thermocouple
If the thermocouple is installed and used improperly, it will not only increase the measurement error, but also reduce the service life of the thermocouple. Therefore, the thermocouple should be installed correctly and used reasonably according to the measured temperature range and working environment.
(1) Choose a suitable installation location. Because the temperature distribution in the heating furnace is not uniform, and the temperature measured by the thermocouple is the temperature of a local area, the appropriate measuring point should be selected to place the thermocouple. Generally, the thermocouple can be installed at a position where the temperature is relatively uniform and can represent the temperature of the workpiece, but cannot be installed near the furnace door or too close to the heating source.
(2) The location where the thermocouple is installed should be as far away from the strong electromagnetic field as possible to prevent the temperature measuring instrument from introducing additional interference signals.
(3) The depth of the thermocouple inserted into the furnace should not be less than 8-10 times the outer diameter of the thermocouple protection tube, and the hot end should be as close to the workpiece as possible, but it must be ensured that the thermocouple is not damaged when loading and unloading the workpiece.
(4) The junction box of the thermocouple should not be close to the furnace wall to prevent the temperature of the cold end from being too high. Generally, it should be about 200mm away from the furnace wall.
(5) The thermocouple should be used as vertically as possible to prevent deformation of the protective tube under high temperature. If you need to install it horizontally, the insertion depth should not be greater than 500mm, and the exposed part should be supported by the shelf. After a period of use, it should be rotated 180°; to prevent the thermocouple junction box from overheating, a right-angle thermocouple can also be used.
(6) The gap between the thermocouple protection tube and the furnace wall should be tightly blocked with refractory materials to prevent air convection from affecting the accuracy of temperature measurement. The gap between the compensation wire and the connection hole of the junction box should also be plugged tightly with asbestos thread, and make it face down to prevent dirt from falling into it.
(7) When using thermocouples to measure furnace temperature, direct flame injection should be avoided, because the temperature at which the flame sprays out is higher and unstable than the actual temperature in the furnace.
(8) When measuring low temperature, in order to reduce the thermal inertia of the thermocouple, a thermocouple with a protective tube opening or without a protective tube can be used.
(9) For thermocouples within the service life, check whether the hot electrode and protection tube are in good condition. If there are pitting, stains, local diameter reduction or serious corrosion on the surface of the protection tube on the surface of the thermocouple, stop using it, and Repair or replace with a new thermocouple.
