Grounded vs Ungrounded Thermocouples for Tube-Skin Temperature Measurement

[gball]

Hello All,

We are experimenting with a flame tube design (quite literally, a flame within a tube). We are looking to get a temperature profile along this tube. So, we will need multiple thermocouples along this tube. I'm wondering whether it will be necessary to go to ungrounded (isolated) thermocouples for this since grounded thermocouples (junction connected to sheath) would all be electrically connected to each other since they are all on the same tube. Would this present a 'ground loop' problem?

Would this be a problem? Would there be interference between the thermocouples? I would really appreciate any input.

Thanks in advance,

gball

 

[0xDEADBEEF]

I think they would interfere. But it depends on your read out method. If you use an instrumentation amplifier you might be fine. But if you tie one leg of the thermocouple to ground at the read out circuit you will produce another thermocouple: "grounded leg of thermocouple 1 - contact at temperature 1 with pipe - pipe - contact at temperature 2 with pipe - grounded leg of thermocouple 2". This will shift your voltage I think.

 

[gball]

I think they would interfere. But it depends on your read out method. If you use an instrumentation amplifier you might be fine. But if you tie one leg of the thermocouple to ground at the read out circuit you will produce another thermocouple: "grounded leg of thermocouple 1 - contact at temperature 1 with pipe - pipe - contact at temperature 2 with pipe - grounded leg of thermocouple 2". This will shift your voltage I think.

Many thanks! I can see what you mean now. No common ground!