Siglent sds1104x-e Power cord ground disconnected schuko. - Page 1
Forum section: electronics / beginners

author: diegooo1972
author_rank: Newbie
timestamp: July 30, 2019, 10:22:15 pm
content: Hi allAfter tons of reading I decided for the Siglent sds1104x-e. Already unlocked it to 200mhz.I was fooling around with graetz bridge to see the ripple but when I tried to use the scope 2 led went down.I understood that I was grounding them through the osc ground.I used a normal cable for PC already connected with ground.But I had a doubt about that cable.In fact inside the siglent box there's a cable with ground not connected. I tested it with dmm.With that cable I'm able to see my ripple without grounding problem.Now the questions.Is this normal ? Can i have some trouble using a cable without ground ? Cause in that way, as ignorant as I am, I think also that burning out probe and equipments fooling around is not a problem anymore.Is that right ? How can it be so simple to avoid osc isolators that are quite expensive ?The osc seems to work fine without ground with original cable.I think this question can be too simple for this forum but I have found just another thread about that but after discussions the cable on that oscilloscope did had the ground.I'm absolutely sure after measured the cable that the ground is disconnected measuring with multimeter. In no place around or under the plug I have continuity.The plug is absolutely without ground.Only in a web page outside eevblog I found someone that say no ground in oscilloscope to avoid grounding problem lead to other problem such that if something went wrong inside the osc i may have max current in every metal component of the scope. But i'm working with low voltage simple circuit and in that case I think I can work without ground.But I feel as I'm missing something cause I'm sure differential probe and ground isolator are usefull in many cases.Just trying to understand if in my case with low voltage circuits I can go on safely without ground on the cable.Please be patient. I'm sure I just miss a consideration and that ain't help me to find the solution.Forgive meJust trying to learn.

author: mlefe
author_rank: Regular Contributor
timestamp: August 11, 2019, 04:42:59 pm
content: Hi Diegooo1972, your message is a bit confusing, but let me see if I can help you to clarify your questions so the people that actually know about this stuff can help you out.I see two things here:1) EARTH GROUNDYou CAN use a cable with no ground in your oscilloscope but it's not recommended unless you know EXACTLY what you're doing.If the cable that provides power doesn't have a ground pin (or you avoid it using an adapter) you will leave your oscilloscope "floating" so it could be at a different potential from you.If you're messing with low voltage electronics, it shouldn't be a problem (as the risk of getting shocked is low) but could put you in a path were you feel confident that it's always safe to do that.Additionally, I see very few scenarios where this is really needed --> in a nutshell, you should understand that it's not a good idea and avoid it.2) How to connect the probe leadsWhen you use the cable with the 3rd pin to power your oscilloscope, there's definitely a connection between EARTH ground and the ground in your probes.In general that's not a problem (it only sets the "zero" level for the whole system) the REAL problems occur when you forget that:a) All probes share the same ground, all channels in your oscilloscope are connected to each other through there.b) if you connect any probe's ground to the power rail in your device and you have one of the probes connected to the "negative" side of your device, you will be shorting that rail.I hope this will help you getting this thread going and some answers for you.In any case, there's a very good video from Dave (EEVBLOG) where he explains all of this in detail... I recommend that you look for it in YouTube and then come back with some more questions