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Siglent SDS804/814X HD or Rigol HDO914S for Mechatronics student

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Antonio90:

--- Quote from: Jack359 on September 25, 2024, 04:28:11 pm ---In it is mentioned that not grounding the oscilloscope is actually workaround if I want to measure grounded circuits but it is not recommended. Didn't get why..
I read that DHO804 is made to run of power bank as well, so I guess it is safe to use it not grounded ?

--- End quote ---

As per why it is not recommended, as the video explains, if you probe a mains ground-referenced circuit, the probe ground has to be connected to the circuit ground. If you clip your probe on, say, 220V, it will be shorted to ground with very low impedance. That will blow either the circuit, the probe, the oscilloscope or all of them.

On the other hand, if you do that with a floating oscilloscope, the grounding on the probe, the bnc inputs, chassis, etc, will all be at 220V potential with respect to ground, and you might very well be the path of least resistance to earth ground.

Floating the scope allows you to make a differential measurement (only one, all the BNC grounds are at the same potential), as opposed to single-ended with respect to earth ground. I don't think it is worth it, but to each its own. If you find yourself needing that often, look for a differential probe, either used or Micsig.

Jack359:

--- Quote ---On the other hand, if you do that with a floating oscilloscope, the grounding on the probe, the bnc inputs, chassis, etc, will all be at 220V potential with respect to ground, and you might very well be the path of least resistance to earth ground.

--- End quote ---

I'm wondering if the power adapter of the DHO804 has a fuse and can prevent short to the ground when used as floating scope ?

Antonio90:

--- Quote from: Jack359 on September 25, 2024, 05:40:58 pm ---
--- Quote ---On the other hand, if you do that with a floating oscilloscope, the grounding on the probe, the bnc inputs, chassis, etc, will all be at 220V potential with respect to ground, and you might very well be the path of least resistance to earth ground.

--- End quote ---

I'm wondering if the power adapter of the DHO804 has a fuse and can prevent short to the ground when used as floating scope ?

--- End quote ---

Hello, no, ground connections are not fused. The fuse could silently fail, or break due to mechanical shock, manufacturing defect or whatever, and you would be left with floating device without knowing it.
EDIT: also, when floating, the problem is not shorting to ground, but dangerous voltages on the probes, connectors and outer case. The danger in that case isn't so much for the scope as it is for you touching the oscilloscope or the probes.

Jack359:

--- Quote ---Hello, no, ground connections are not fused. The fuse could silently fail, or break due to mechanical shock, manufacturing defect or whatever, and you would be left with floating device without knowing it.
EDIT: also, when floating, the problem is not shorting to ground, but dangerous voltages on the probes, connectors and outer case. The danger in that case isn't so much for the scope as it is for you touching the oscilloscope or the probes.

--- End quote ---

Doesn't it make any difference that the oscilloscope is  powered by USB-C and AC/DC power adapter rated to max 20V/3A which is connected to the power socket? Is it still as potentially deadly when floating?
I will not use it to measure my mains or circuits with 220V in them.

Antonio90:
The dangerous voltages come from outside the oscilloscope, DSOs which connect directly to mains have a similar PSU on the inside.
If you only work with low voltages and isolated circuits, maybe, but really, just ground your oscilloscope.
You will have time later on to float it perfectly knowing that you should not do it in most cases.

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