Absolute beginners 101 - measuring my power supply output

• Absolute beginners 101 - measuring my power supply output
  Posted by 3PinFanHeader on 20 Apr, 2024 23:07
• Hi all, and thatnks for a wonderful forum.
  
  This is a totally 101 question, so bare with me.
  
  I have two scopes - my "old" FNIRSI 1014D and a Rigol MSO5072 upgraded to uhm, "the best"
  
  This is my setup:
  
  A power supply to be measured (I'm using + and - but not GND)
  A 2W 2Ω resistor
  A breadboard
  generic P6100 (100MHz) probe (connected to the FNIRSI)
  Rigol PVP350 350MHz probe (connected to the Rigol)
  
  My attempt is to see the spike on the scope induced by setting the power supply to 3.0V 0.3A and
  * Turn on the power supply output using the output button
  * Have the output on and hotplug the + to the resistor
  
  So I set both scopes to single and the trigger to 2.8V (ish).
  On the FNIRSI, I get a nice graph showing me that the power supply isn't exceeding its 3.0V on pushing the output on button, but on the Rigol, I just get a flat-line.
  
  On the Rigol it tends to trigger very fast with no important information visible other than noise.
  
  So, what is it that I might be doing incorrectly - and how might I do it better on the Rigol?
  
  Please keep in mind - the FNIRSI, simple as it is, really is dumbass-friendly (good for me) - but I still want to know how to use my Rigol properly. It's too expensive to be just a shelf-warmer
  
  Thanks all <3
  
  
• #1 Reply
  Posted by JustMeHere on 21 Apr, 2024 01:58
• Post photos/screenshots.
• #2 Reply
  Posted by Aldo22 on 21 Apr, 2024 07:51
• Quote from: 3PinFanHeader on 20 Apr, 2024 23:07

  On the FNIRSI, I get a nice graph showing me that the power supply isn't exceeding its 3.0V on pushing the output on button, but on the Rigol, I just get a flat-line.
  
  On the Rigol it tends to trigger very fast with no important information visible other than noise.
  

  
  Yes, hard to tell without screenshots.
  
  Have you checked the most basic settings?
  Coupling (AC/DC)
  Probe Attenuation (1x/10x). Do they match on the scope and the probe?
  Vertical Scale (V/div)?
  Horizontal Scale (s/div)?
  
  etc.
• #3 Reply
  Posted by radiolistener on 21 Apr, 2024 08:01
• its unclear what your'e using and what you get. Post photo of your circuit connections and oscilloscope screenshot.
  
  In general there are two notes:
  - don't use breadboard for such purposes, because it has high resistance unreliable contacts
  - don't use manual terminal connection during measurements, because it will lead to a lot of spikes and oscillations.
• #4 Reply
  Posted by shapirus on 21 Apr, 2024 08:08
• Solderless breadboards are just fine at these speeds (and much higher speeds too). Contact resistance has to be accounted for, that's right.
  
  In this case, since one of the scopes is showing an expected waveform and the other one doesn't, it's clear that there's something wrong in either wiring or scope settings. So yeah need to see how it's wired up and how the Rigol is set up.
• #5 Reply
  Posted by Aldo22 on 21 Apr, 2024 08:18
• Keep in mind that this Fnirsi has a really low/bad sensitivity (50mV according to the specs vs 500μV for the Rigol).
  The signal or noise might look different on the two scopes due to this fact, although I don't think that's the main problem here.
  
  
• #6 Reply
  Posted by 3PinFanHeader on 21 Apr, 2024 20:17
• Thanks all - of course I should have posted pictures (it was late and the beer telling me to go to bed )
  
  I re-did the experiment using my Owon PSU, skipped the breadboard (it _is_ solderless, but I'd thought it wouldn't matter for such a simple measurement).
  
  I also used a 22Ω 10W resistor - but if I understand the situation, the Owon did good? Although I feel that the noise should be something that ought to give me concern?
   
  I also did find my error - the timebase on the Rigol was set to way too fast and I just didn't notice 
  
  This is my Owon:
  
  
  This is the display on the Fnirsi (the one I expected and originally got)
  
  
  And this is the image I /finally/ got on my Rigol after realizing that I was just using the incorrect timebase...
  
  
  Thanks all for the comments -
  
  
• #7 Reply
  Posted by CaptDon on 22 Apr, 2024 01:56
• Still have any Trabants or LADA's running around Islands? My friend Ingimundur moved his antique truck out of the Grindavik area about 4 months back when the ground started breaking up. Good thing he did!! Skal i botn!!
  
• #8 Reply
  Posted by 3PinFanHeader on 23 Apr, 2024 18:52
• Quote from: CaptDon on 22 Apr, 2024 01:56

  Still have any Trabants or LADA's running around Islands? My friend Ingimundur moved his antique truck out of the Grindavik area about 4 months back when the ground started breaking up. Good thing he did!! Skal i botn!!
  

  
  There may be some - but most were I think sold as scrap for "a bottle of vodka" or some cigs to russians that needed cheap spares