Serial to USB and PH readings going crazy

[Primetime33]

I have my ACjr connected to my PC via a keyspan serial to USB port since I do not have a serial port on my PC. When connected my ph readings are way off. When I disconnect, ph readings on acjr are fine. Is this a known issue?

[schwaggs]

Yep. You are getting interference from a ground loop in the serial cable. Get yourself a Ground Isolated Serial Connector (SERIPC9) and the problem will go away.

[Primetime33]

Great!!! Thank you for the quick info :)