Reasons for the temperature deviation measured by thermocouples in the same pipeline
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Hello everyone, I would like to ask some questions regarding thermocouples. #The temperature from the outlet of the #2 high-temperature heater to the inlet of the #1 high-temperature heater is measured at points approximately 20 CM away from each inlet and outlet along the same pipeline; the measured temperature is lower at the inlet and higher at the outlet. The operators reported that there are no heating devices on the pipeline, and the temperature from the outlet of the #2 high-temperature heater to the inlet of the #1 high-temperature heater did not decrease but instead increased, which is contrary to common sense – this suggests that there may be defects in the temperature measurement points. What causes this phenomenon? How should it be explained whether a deviation of around 6°C is considered a normal one, and how can this deviation be explained? I’d like to hear the details. I am seeking help from kind people.
The sampling points are inconsistent, or there is a problem with the thermocouple itself.
It’s not clear what medium it is, what material the pipes are made of, what equipment the outlet belongs to, and what’s inside those pipes. First, measure the thermocouple voltage to check if the temperature is abnormal; if it is normal, swap the two thermocouples.
There could be several possibilities: 1. Circuit errors, such as faults with the thermocouple itself, incorrect models of compensation wires, issues related to the temperature range or the DCS measurement range. 2. The thermocouple is not inserted at the same depth in the pipe. 3. There are differences in heat loss at two different points along the pipe; for example, one point may be insulated while the other is not. Cross-swapping tests help to identify issues quickly
I have seen cases where the temperature at the same level in the reactor varied, with one system using hard wiring and another using a bus system. Three degrees positive and three degrees negative make 6 degrees in total. You can try it based on the suggestions from netizens.