Platinum rhodium thermocouple common problem knowledge Q&A column

Platinum rhodium thermocouple is a traditional temperature measuring element with stable thermoelectric performance and strong oxidation resistance, suitable for continuous use in oxidizing and inert atmospheres. The long-term usage temperature is 1600 ℃, and the short-term usage temperature is 1800 ℃.

1, How to identify faults caused by the input of platinum rhodium thermocouples?
1. Connect the wires correctly according to the instrument wiring diagram. If the digital display on the upper row of the instrument shows negative values after the instrument is powered on, it indicates that the thermocouple "+" and "-" connected to the instrument are connected incorrectly. Just swap it again.
2. When the instrument is running with correct wiring, the temperature displayed on the digital display on the instrument panel differs from the actual measured temperature by 30oC~60oC. Even greater differences indicate that the scale of the instrument is incorrect compared to the scale of the thermocouple. According to the corresponding relationship between the temperature (oC) and millivolt (MV) values of thermocouples with scale marks B, S, K, E, etc., under the same temperature (oC), the resulting millivolt (MV) values are small for scale marks B, small for scale marks S, large for scale marks K, and large for scale marks E. Based on this principle, discrimination can be made.
3. After correctly wiring and powering on according to the instrument wiring diagram, the instrument first displays the thermocouple index number of the instrument, then displays the instrument range, and then the digital tube in the lower row of the instrument displays the set temperature, and the digital tube in the upper row of the instrument displays the measured temperature. If the digital display on the instrument panel shows "OVER", "0000" or "000" instead of the temperature of the heating element, it indicates that there is a fault in the input part of the instrument, and the following tests should be conducted:
a) Remove the thermocouple from the input end of the instrument thermocouple and short-circuit the input end of the instrument thermocouple with any wire. When powered on, if the digital display on the instrument panel shows a value of about room temperature, it indicates that the internal wiring of the thermocouple is open and should be replaced with a thermocouple of the same type. If the above situation persists, it indicates that the input end of the instrument was damaged during transportation and needs to be replaced.
b) Remove the thermocouple from the faulty instrument mentioned above and replace it with a thermocouple connected to a nearby instrument with the same calibration number that is running normally. After powering on, if the digital display on the upper row of the faulty instrument shows the temperature of the heating element, it indicates that the internal wiring of the thermocouple is open. Replace it with a thermocouple of the same type. If the above situation persists, it indicates that the input end of the instrument was damaged during transportation and needs to be replaced.
c) Remove the faulty thermocouple from the instrument and place it in the ohm (R) * 1 range using a multimeter. Use two multimeter sticks to measure the two ends of the thermocouple. If the resistance value displayed on the multimeter is high, it indicates an open circuit in the internal connection of the thermocouple. Replace it with a thermocouple of the same type. Otherwise, if there is a certain resistance value, it indicates that there is a problem with the input terminal of the instrument and the instrument should be replaced.
2, How to prevent interference during temperature measurement?
When using the reference terminal grounding method, one end of the output terminal of the platinum rhodium thermocouple (or compensating wire) is grounded through a sufficiently large capacitor (the larger the capacitor, the better if conditions permit). The measurement end grounding method is to ground the measurement end of the thermocouple, which means that a metal wire is led out from the measurement end of the thermocouple and grounded. This method has a good preventive effect on high-temperature leakage interference. When selecting metal wires, high temperature resistant and harmless metal wires should be chosen for thermocouple electrodes.
During the use of thermocouples, there are always many situations that interfere with our measurement accuracy, which is a very tricky problem. We need to be prepared to prevent interference when using thermocouples. With the improvement of current industrial production level, the usage rate of thermocouples is very high, so the measurement accuracy of thermocouples is a very important thing to pay attention to!
3, How to deal with interference encountered during the use of thermocouples?
Shielding method: Thread the compensating wire of the thermocouple into an iron pipe or other metal shielding material for shielding. This can prevent electromagnetic interference and interference from high-voltage electric fields. When using this method, the iron pipes and shielding materials should be well grounded, and the compensating wires should be twisted together.
Isolation method: The thermocouple is suspended and installed so that it does not come into contact with the refractory bricks on the furnace wall. Insulation is also used to isolate the thermocouple from the support. This method can effectively prevent high-temperature leakage interference.
Grounding method: This method involves grounding the measurement circuit and introducing interference into the ground to ensure the accuracy of the instrument measurement. There are two forms of this method: the thermocouple reference terminal is grounded, and the second is the thermocouple measurement terminal grounded.
Based on different temperature measurement and usage environments, the specific methods used for prevention are ultimately aimed at minimizing interference and achieving accurate temperature measurement. Therefore, in the process of prevention, attention must be paid to how to deal with relevant interference.