When using thermocouples to measure the same temperature, why is there a difference of nearly one hundred degrees?
Thread Content
This post was last edited by zyz8438 on 2010-11-6 at 12:21. The S-type armored thermocouples installed on the conversion drum in our factory are used to measure the same temperature; why is there a difference of nearly 100 degrees between the readings?
Try swapping the positions of the two thermocouples and see. If the difference in temperature is still over 100 degrees even after swapping them, then it’s a wiring issue; it’s possible that one of the thermocouples isn’t connected to a compensation wire； It could also be that there is a problem inside the steam drum, resulting in different temperatures. If the temperature of the thermocouple remains unchanged after changing its position, there is a problem with the thermocouple.
Verify whether the internal parameter settings of the DCS are consistent
First, check whether the compensation wire is connected reversely； Additionally, the cold end of the thermocouple and the wiring terminals of the display instrument can be shorted together to see if the display shows the temperature of the shorted point. After ruling out problems with the display instrument and the compensation wires, it is either a problem with the thermocouple or the temperature displayed is accurate (a problem with the equipment)~~~
Reply to 1# shl86125: Is the insertion depth the same?
First, confirm with the process technicians whether the internal temperatures are consistent. If the temperatures are the same, then check whether there is a problem with the wiring; if that doesn’t work, replace the thermocouple and take another measurement to see if it’s the thermocouple that is damaged.
First, check the process to ensure that the temperature is consistent. Next, verify that the thermocouples and the display instruments are compatible with each other. Finally, check whether there are any quality issues with the thermocouples and display instruments, as products available on the market sometimes have such problems. :)
Judge step by step: 1. Measure the voltage at the site; if it matches, the thermocouple is in good condition; if not, the actual temperature in the process is different； If the values are different for the hollow part, then measure the voltage in front of the safety barrier; if those values are not consistent, it indicates that there is a problem with the compensation wire or its connection. If the values are consistent, then measure it in front of the input card ； If it’s consistent, it’s likely a problem with the configuration or the card; if it’s inconsistent, it’s related to the wiring – similar issues should be checked step by step
Near high temperatures, compensation wires tend to age easily; if there are no regular problems, try replacing them with new compensation wires of the same length. Another alternative fault is the accumulation of water inside the temperature protection sleeve. In such cases, it is necessary to remove the thermocouple core slowly, while carefully checking to see if there are any signs of damage to the protection sleeve. If there is no damage, simply drain the water and that’s it. If there are signs of damage, stop further removal and contact the technical team to repair the issue, or have a professional handle the sealing under pressure.
Reply to 9# bawanglang: Thank you. We seem to agree on one thing – it’s water getting into the casing. I try using an air blower to dry it out, but the readings still remain the same; yet before this issue arose, the readings were normal
Our factory dealt with a similar issue not long ago: two thermocouples spaced about 10 cm apart had a temperature difference of around 50 degrees. The solution was to remove the thermocouples, dry out the water inside their protective tubes, and then reinstall them, after which everything worked normally again.