Precautions for using platinum-rhodium thermocouples

If the platinum-rhodium thermocouple is improperly installed and used, it will not only increase the measurement error, but also reduce the service life of the platinum-rhodium thermocouple. Therefore, the platinum-rhodium thermocouple should be correctly installed and used reasonably according to the measured temperature range and working environment.
(1) A suitable installation location should be selected. Since the temperature distribution in the heating furnace is uneven, the platinum-rhodium thermocouple measures the temperature of a local area, so a suitable measurement point should be selected to place the platinum-rhodium thermocouple. Usually, the platinum-rhodium thermocouple can be installed in a position where the temperature is relatively uniform and can represent the temperature of the workpiece, but it should not be installed next to the furnace door or too close to the heating source.
(2) The location where the platinum-rhodium thermocouple is installed should be as far away from the strong electromagnetic field as possible to avoid the temperature measuring instrument introducing additional interference signals.
(3) The depth of the platinum-rhodium thermocouple inserted into the furnace should not be less than 8 to 10 times the outer diameter of the platinum-rhodium thermocouple protection tube, and the hot end should be as close to the workpiece as possible, but it must be ensured that the platinum-rhodium thermocouple is not damaged when loading and unloading the workpiece.
(4) The junction box of the platinum-rhodium thermocouple should not be close to the furnace wall to prevent the cold end temperature from being too high. Generally, it should be about 200mm away from the furnace wall.
(5) The platinum-rhodium thermocouple should be used vertically as much as possible to prevent the protective tube from deforming under high temperature. If it needs to be installed horizontally, the insertion depth should not be greater than 500mm, and the exposed part should be supported by a rack. After a period of use, it should be rotated 180°; to prevent the platinum-rhodium thermocouple junction box from overheating, a right-angle platinum-rhodium thermocouple can also be used.
(6) The gap between the platinum-rhodium 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 wiring hole of the junction box should also be tightly plugged with asbestos wire and pointed downward to prevent dirt from falling in.
(7) When measuring the furnace temperature with a platinum-rhodium thermocouple, avoid direct flame spray, because the temperature at the flame spray point is higher than the actual temperature in the furnace and is unstable.
(8) When measuring low temperatures, in order to reduce the thermal inertia of the platinum-rhodium thermocouple, a platinum-rhodium thermocouple with an open protection tube or without a protection tube can be used.
(9) During the service life of the platinum-rhodium thermocouple, the thermode and the protection tube should be checked regularly to see if they are in good condition. If pitting, stains, local diameter reduction or severe corrosion on the surface of the protection tube are found on the surface of the platinum-rhodium thermocouple, it should be stopped from use and repaired or replaced with a new platinum-rhodium thermocouple.