I am logging oven temperatures witk K-type elements and a Medion PC witn Win7.
During logging, when I attach the external power supply to the PC, the logged temperatures for the two thermoelemnts drop by about 30%, while the cold junction is unaffected. When external power is disconnected, the temperatures jump back up. Please see attached screen dump.
Starting the software and logging with or without external power gives the same result, and the use of a powered usb hub does not change the issue.
However, after I dipped the two thermoelements (with uninsulated tips) in a glass of tap water, the temperature jump disappeared!
Is it an issue of common (ground) potential for the thermoelements? And how is this fixed when measuring in air?
I am running version 5.22.8 of the logger software.
Any suggestions for a cure, please?