Hi,

I was reading the manual about thermocouples. It mentioned ground loops, so I'm curious if one is measuring three thermocouples would the negative (-) terminals be commonly connected to each to maintain a reference point between the three thermocouples?

This is in reference to type T unshielded thermocouples.

Thanks!
DT800 User

Good morning Qacer,

Ground loops occur when the ground of the input voltage exceeds the common mode range of the logger.

To explain further; Voltage is a relative measurement. We measure the potential difference between two different points. Because we are measuring multiple voltages we can end up with multiple grounds all at different voltages. If these grounds are outside the common mode range then you will note be able to read the the voltages.

For example. If your data acquisition unit has a common mode range of +/- 13 VDC . If you are using bare tipped thermocouple and place it on a conductor that is at 10 volts above the ground of the data acquisition unit then you will be able to measure the temperature because the total voltage is less than the common mode range.

If you then connect another thermocouple to the acquisition system and place it on another surface which ground is at -15 VDC with respect to the acquisition system ground then you won't be able to read the thermocouple because you are outside the common mode range.

In this case you will need to remove the differences in the two grounds. This is usually done by connecting the two grounds together.

Cheers,
Roger