Rigol DHO804 not earth referenced? - Page 1
Forum section: electronics / testgear

author: i509VCB
author_rank: Contributor
timestamp: January 13, 2025, 03:16:20 am
content: As a result of watching Dave's video on how not to blow up your scope, I ended up checking if the DHO804 I own is earth referenced (since Dave said scopes are almost always earth referenced). It appears that from measuring with the Lite-On power brick that came in the box connected and nothing else, the scope is not actually earth referenced.The Lite-On power brick in question:When measuring from the BNC ground points to the earth pin of the power brick, it seems there is a 1MOhm resistance to earth. In Daves video what he measures from the scope to earth is a dead short to ground.The quick start guide mentions the scope is not isolated, so it should be earth referenced? Right?:QuoteThe DHO800 does come with a yellow-green cable that can be used to attach to a ground. Although the quick start manual just says that this exists and shows in chapter 5 to just plug the power brick into the wall and then into the scope. I just grabbed a banana jack outlet adapter so that I could use this in the future, since the scope should be grounded for safety reasons.Connecting the HDMI port to my monitor does earth reference the scope. Is there a reason why Rigol would choose to pick a power brick which ends up with the scope floating, but then its ports earth reference it? This kind of feels like lazy design?

author: tautech
author_rank: Super Contributor
timestamp: January 13, 2025, 07:40:43 am
content: Quote from: i509VCB on January 13, 2025, 03:16:20 amOne would need to know the design brief......Would an internal and properly shielded PSU compromise the intention of battery operation, compactness and light weight ?Protective Earth is normallyexpectedin a bench DSO as is Line triggering, both are missing by default when using a battery supply or power brick.Is there a spec for elevated floating voltage of the DHO ?Maybe capturing some of the portable scope market was also an intention.

author: ledtester
author_rank: Super Contributor
timestamp: January 13, 2025, 08:22:05 am
content: Quote from: i509VCB on January 13, 2025, 03:16:20 amAnother way to look at it is that they wanted you to be able to use any USB-C PD power supply. Additionally, users are going to try to use their own PD power supply, not necessarily the one that that came with the scope. And since not all USB PD supplies are earth referenced, the next best thing is to supply a grounding terminal.

author: coppercone2
author_rank: Super Contributor
timestamp: January 13, 2025, 08:42:25 am
content: or batteriesand I had to look for the source LOLhttps://www.youtube.com/shorts/ovZJzCWPePII think if you want the scope to work on batteries you basically have to design it to work without ground and meet all specifications.And USB ground is nuts.Will you get a ferrite bead? 4k7 + 100nF? just a cap? just a resistor? a open? a short to ground? Will the cable have a choke on it? WHO KNOWS

author: cte
author_rank: Regular Contributor
timestamp: January 13, 2025, 10:23:32 am
content: Yes, the scope is not earth referenced by the power supply (PSU). In fact, there is an high impedance resistor-capacitor network in the PSU between DC ground and protection ground that will blow up if mains voltage is applied - be it intentionally or unintentionally.There were already some discussions about it here:https://www.eevblog.com/forum/testgear/rigols-new-dho800-oscilloscope-unbox-teardown/msg5590693/#msg5590693https://www.eevblog.com/forum/testgear/hacking-the-rigol-dho800900-scope/msg5779617/#msg5779617Current conclusion is to ground the scope externally. Note that an connected ethernet cable will ground your scope through its grounded shielding, but I wouldn't rely on this connection being low-impedance enough to be of any relevance when it comes to electrical safety.

author: Fungus
author_rank: Super Contributor
timestamp: January 13, 2025, 12:24:40 pm
content: Quote from: i509VCB on January 13, 2025, 03:16:20 amI think it's so that it's really really easy to be able to power it. You can useanysuitable USB power supply, eg. have one at home and one at work so you don't have to carry power supplies around.Power supplies are always the biggest point of failure in these devices so these are easy to replace, too.Quote from: cte on January 13, 2025, 10:23:32 amOnly if you're poking at dangerous things, otherwise it works just fine.

author: Kean
author_rank: Unknown
timestamp: January 13, 2025, 08:40:11 pm
content: Non-isolated and earthed referenced have different meanings. You can have the former without the latter, as all the exposed metal will be connected, and thus could be at non-earth potential.Making equipment isolated can add a lot of cost, and doesn't on its own make it safer.