On ground loop while connecting a Logic Analyzer - Page 1
Forum section: electronics / beginners

author: mindentropy
author_rank: Contributor
timestamp: April 25, 2024, 06:23:03 pm
content: Hi,While reading through safety page of Saleae Logic Analyzer I found the common ways a ground loop can exist in this page:https://support.saleae.com/user-guide/safety-and-warranty#common-ways-a-ground-loop-can-existIn there I find the two points:QuoteI have a DUT which is connected to my laptop USB port and also my Saleae LA. Does this mean that both of these will be connected to the common ground of the PC? If yes, would this mean that a ground loop is formed? Will my laptop provide an isolation due to the battery connected? If I have connected the DUT to a PC would it have a common ground then?In the section on Common ways damages can occur here ->https://support.saleae.com/user-guide/safety-and-warranty#common-ways-damage-can-occurQuoteWhy nothing happens "If there are no other ground paths between the DUT and the PC"? Is it because there is no return path from the DUT power supply to the LA connected to the PC and finally to the ground of another PC?

author: aliarifat794
author_rank: Regular Contributor
timestamp: April 27, 2024, 03:22:03 pm
content: If you have a DUT connected to both your laptop's USB port and the Saleae Logic Analyzer (LA), then yes, both devices would typically share a common ground through the laptop's power system.

author: mindentropy
author_rank: Contributor
timestamp: April 28, 2024, 03:21:01 am
content: In the below statement:QuoteMy another confusion is won't this also cause a short if the DUT is powered by an external power supply and take out the DUT and the LA? Won't this also cause damage to the USB ports where the Saleae LA is connected?

author: m k
author_rank: Super Contributor
timestamp: May 01, 2024, 04:37:33 pm
content: Energy through a brushed connection is many times pretty low.It can usually damage only the source of that 5V.If wire is very thin it can only damage its self.

author: Retirednerd2020
author_rank: Regular Contributor
timestamp: May 02, 2024, 04:46:11 pm
content: I often use a USB isolator for circuits I have concern about. My personal policy is always use (USB/SERIAL) isolation if I'm dealing with DUT with circuits over 5V. I don't count on the power supply isolation of a laptop for equipment or personal safety. This may be a bit overkill but isolators don't cost much and generally don't get in the way.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 02, 2024, 11:16:38 pm
content: If you're nervous, run the laptop from battery when testing.

author: mindentropy
author_rank: Contributor
timestamp: May 04, 2024, 07:53:51 pm
content: Quote from: m k on May 01, 2024, 04:37:33 pmIf it is powered by an external source with Over Current Protection, wouldn't that be much better safety?

author: m k
author_rank: Super Contributor
timestamp: May 05, 2024, 08:26:43 am
content: Of course.But keep in mind that you can short everything else also, and those others may be much less tolerant.An output of a single OpAmp can be one, but it can be internally protected also.So better learn a habit that everything stay put when power is on.USB is a hot plug type connector, it can be disconnected anytime.If you think a Windows message telling that it's now safe to disconnect, it's different.Old Windows versions used delayed write style, so it's a software based message.