Key points for using platinum rhodium thermocouples

Platinum rhodium thermocouples belong to precious metal thermocouples. Due to its high price, one must be very careful when using it. If the platinum rhodium thermocouple is used improperly, it will not only increase measurement errors, but may also reduce the service life of the platinum rhodium thermocouple. Therefore, platinum rhodium thermocouples should be installed and used correctly and reasonably according to the measured temperature range and working environment.

1. Suitable installation locations should be selected. Due to the uneven temperature distribution inside the heating furnace and the fact that the platinum rhodium thermocouple measures the temperature in a local area, it is necessary to choose a suitable measurement point to place the platinum rhodium thermocouple. Usually, platinum rhodium thermocouples can be installed in locations where the temperature is relatively uniform and can represent the temperature of the workpiece, rather than near the furnace door or too close to the heating source.

2. The position for installing platinum rhodium thermocouples should be as far away from strong electromagnetic fields as possible to avoid additional interference signals introduced by temperature measuring instruments.

3. The depth of inserting the platinum rhodium thermocouple into the furnace should not be less than 8-10 times the outer diameter of the platinum rhodium thermocouple protection tube. 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 during loading and unloading of the workpiece.

4. The junction box of platinum rhodium thermocouples should not be placed 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. Platinum rhodium thermocouples should be used vertically as much as possible to prevent deformation of the protective tube at high temperatures. If horizontal installation is required, the insertion depth should not exceed 500mm, and the exposed part should be firmly supported by a rack. After a period of use, it should be rotated 180 °; To prevent the junction box temperature of the platinum rhodium thermocouple from being too high, a right angled platinum rhodium thermocouple can also be used.

6. The gap between the platinum rhodium thermocouple protection tube and the furnace wall should be tightly sealed with refractory materials to prevent air convection from affecting the accuracy of temperature measurement. The gap between the compensating wire and the junction box junction hole should also be plugged with asbestos wire, facing downwards to prevent dirt from falling in.

7. When measuring furnace temperature with platinum rhodium thermocouples, direct flame spraying should be avoided, as the temperature at the source of the flame spraying is higher and more unstable than the actual temperature inside the furnace.

8. When measuring low temperatures, to reduce the thermal inertia of platinum rhodium thermocouples, platinum rhodium thermocouples with open protective tubes or without protective tubes can be used.

9. During the service life of platinum rhodium thermocouples, the thermoelectric electrode and protective tube should be regularly checked for good condition. If any pitting, stains, local diameter reduction, or severe corrosion of the protective tube surface are found on the surface of the platinum rhodium thermocouple, it should be stopped from use and repaired or replaced with a new one.