How does wall-wart power supply break ground loops?

ariaaudio · Post by **ariaaudio** » Fri Mar 23, 2007 9:37 pm

I know that if the Picoscope is connected via USB to a computer that is AC-Mains powered and earthed, and the device I am testing is also earthed to Mains, I have a ground loop.

The manual says that the loop can be broken by using the wall-wart to power the Picoscope. I don't get how this breaks the loop -- the Picoscope is still connected to the earthed computer, and the device I am testing is also earthed.

ziko · Post by **ziko** » Mon Mar 26, 2007 2:19 pm

Hi and thank you for your post. The Power Adapter does not break the ground loop. It is important to note that the PicoScope is still referenced to ground. What the adapter does is stop the USB connection from supplying a voltage.

Hope this helps.

ariaaudio · Post by **ariaaudio** » Mon Mar 26, 2007 4:01 pm

Thank you.

Section 5.3 of the Picoscope User Guide (document ps3000044.pdf) discusses ground loops and suggests that if the computer is not floated from earth, using the wall wart to power the Picoscope will reduce noise. This then is not meant to suggest that using the external power supply will affect ground loop noise? It seems a bit confusing.