DHO804 Bug or my function generator issue - Page 1
Forum section: electronics / beginners

author: mkosett
author_rank: Contributor
timestamp: February 20, 2024, 05:27:03 pm
content: Please refer the video i took:https://youtu.be/3nrgByC7fEs.Some context before this: Made a beginner mistake of connecting ground of two different channels at two different nodes and hence shorting the function generator. Then wanted to check if function generator was working properly( Im hoping nothing happens to the oscope at low voltages, 5V i was playing with . Please let me know if im right or wrong). And then function generator output on oscope gives like this where wave suddenly degenerates. But this happens only if i zoom in 50mV/div onwards which makes me think it could be a oscope bug ( hoping that the oscope wasnt affected by my beginner mistake). Please help me.My firmare version 00.01.02 build 2023/11/09 android.build 2023/11/16.Also my function generator had 50ohm impedence cable while using it which makes me think it shouldnt be a problem to short it as (5V/50 ohm = 100mAmps is fine. Please let me know if this is right or wrong).

author: wasedadoc
author_rank: Super Contributor
timestamp: February 20, 2024, 05:48:18 pm
content: Looks like user error. Scope triggering not adjusted appropriately.

author: mkosett
author_rank: Contributor
timestamp: February 20, 2024, 06:30:09 pm
content: Tried playing with the trigger, no luck. Trigger on edge mode and between the graph.

author: shapirus
author_rank: Super Contributor
timestamp: February 20, 2024, 06:42:38 pm
content: Is the signal too noisy? Try to turn on averaging (in the acquisition settings), also there's a noise reduction or something like that in the trigger menu.

author: Aldo22
author_rank: Super Contributor
timestamp: February 20, 2024, 09:31:40 pm
content: Quote from: shapirus on February 20, 2024, 06:42:38 pmI believe that too.I think it's the cable with the crocodile clips.I also have one of these, which is not properly shielded. My Hantek has also trouble triggering with the noise/spikes.Try a more direct oder better connection. It helps here.Bandwidth limitation may also help.

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 05:44:03 am
content: Do you think I could have shorted the function generator? Or damaged the oscope due to the ground loop error I made?

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 08:40:22 am
content: Didnt not work effect still exists

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 08:41:28 am
content: tried bandwidth limit still no luck.

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2024, 09:11:42 am
content: Other frequencies? Other waveforms? Damaging the generator by shorting it doesn't seem likely, and the scope... You mentioned 5V output at the time -- was this amplitude, p-p, or RMS?

author: Aldo22
author_rank: Super Contributor
timestamp: February 21, 2024, 09:22:06 am
content: You don't say what you've already tried.Have you tried different channels? Both with the signal generator and the scope?In the video you have 300mV output. That brings noise into play with your cables.Have you tried with a higher amplitude?Did you switch the probe 1x or 10x?

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 12:38:59 pm
content: 5V peak to peak.Can this affect the oscope?The effect is not changing when i increase or decrease frequency. The effect is similar for all sinusoidal type waveforms. For square wave there is no problem.Also here is a list of things ive done:1) Factory reset both oscope and function gen2) Tried different channels on both function gen and oscope3) Tried noise reject option in trigger, average acquisition, changing trigger level, types.4) Tried different amplitudes and frequenciesAnd none of these things have shown a positive result.But two things showed a positive result:1) Changing waveshape to square, ( All sinusoidal looking graphs still have problem) doesnt show any problem2) Changing the cables from the function generator cable to The oscilloscope probe cable at 1x. This removed the problem at 50mV and upto 30mV. At 20mV the same issue happens as seen in the video.I have posted a video on the same. :https://youtu.be/Y4RDemFyExoPlease consider the video, thanks and really sorry for my broken English.

author: Aldo22
author_rank: Super Contributor
timestamp: February 21, 2024, 12:57:15 pm
content: In my opinion, this is normal.At 20mV and this connection, it is simply noise.Try with a BNC to BNC cable.

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 01:12:03 pm
content: ok i will do that, right now im low on budget. when i get some money ill get a bnc to bnc. Thanks.Also in general is it possible that function generator can be damaged if its output is shorted through the bnc cable. Wont the bnc cable have 50ohm impedance and hence limit current always?Also is it ever possible to damage an oscilloscope by the kind of grounding loop error or any error for say like this ( I have watched some videos and wasn't able to get a definitive answer).

author: shapirus
author_rank: Super Contributor
timestamp: February 21, 2024, 01:22:05 pm
content: Quote from: mkosett on February 21, 2024, 12:38:59 pmSounds very unlikely to me. That's 5V/(2*sqrt(2)) ~= 1.77 V RMS, meaning only ~35 mA RMS max., if the generator's output resistance is 50 Ohm (which it should normally be), and that's not counting the resistance of the connecting cables etc., so the real current would be lower. I don't think that this can damage anything between the BNC grounds in the scope. I may be wrong -- someone correct me if I am!

author: Aldo22
author_rank: Super Contributor
timestamp: February 21, 2024, 01:27:15 pm
content: Quote from: mkosett on February 21, 2024, 01:12:03 pmYes, the probes can act like an antenna.Quote from: mkosett on February 21, 2024, 01:12:03 pmIsn't that written in your manual?I have the cheapest AWG (FY3224s) and the manual says: "All channels can operate for longer than 60 seconds when the load is shorted."Quote from: mkosett on February 21, 2024, 01:12:03 pmNormally you have to apply at least 30 or 40 volts to the probe with 1x setting for anything to happen.Check the manual.

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 01:43:08 pm
content: Thank you so much for your help

author: mkosett
author_rank: Contributor
timestamp: February 21, 2024, 01:44:08 pm
content: Can't comment on that hopefully someone does. Thanks a lot for your help

author: Aldo22
author_rank: Super Contributor
timestamp: February 22, 2024, 10:34:07 am
content: Quote from: mkosett on February 21, 2024, 01:12:03 pmBy the way, it doesn't cost a fortune.These are probably not the best quality, but certainly better than your wiring.The shorter, the better.https://www.aliexpress.com/item/1005005368020239.html

author: mkosett
author_rank: Contributor
timestamp: February 24, 2024, 03:18:29 am
content: Thank youuu