Is there something wrong with my oscilloscope? - Page 1
Forum section: electronics / beginners

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 12:47:04 am
content: Uhm, I wanted to ask something, but this might be a stupid question. I'm a newbie, I'm still learning and I just got my first oscilloscope (Hantek DSO5102B, it's a used unit not new), so please go easy on me.Let's suppose that I turn on the oscilloscope without any probes attached (actually the probes haven't arrived yet, still waiting for the mail).Now, if I set the oscilloscope to 20mV per division, I can see ground nose (I assume it's ground noise) of about 5.6mV dV.You can see that also in the "picture1" file I attached.Now, let's suppose that I set the oscilloscope to 5V per division, and I press the Run/Stop button.While the acquisition is stopped (Run/Stop button is red), if I turn the knob to adjust the vertical scale to a lower value (let's say 100mV), the waveform size increases and if I measure it I get a 604mV dV.You can see that also in the "picture2" file I attached.Is this normal behavior? Does this happens on most digital storage oscilloscopes?

author: c4757p
author_rank: Super Contributor
timestamp: April 19, 2014, 12:50:20 am
content: Completely normal. The analog-to-digital converter has only 8 bits (256 levels) of resolution, and when you zoom in on already-captured data, all the scope can do is expand it. It becomes pixellated just like a crappy image.It happens onallDSOs, not just most.

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 01:01:05 am
content: Quote from: c4757p on April 19, 2014, 12:50:20 amGreat, thank you for your reply.Then if I want the most accurate measurement I could get, I suppose I should set the volts/div to a value that the waveform occupies most of the grid/screen, before capturing data? Is that correct?

author: c4757p
author_rank: Super Contributor
timestamp: April 19, 2014, 01:05:54 am
content: Yes, for best resolution your waveform should fill the display.However, also note this: if the waveformexceedsthe display at all, even the visible part can sometimes distort (depends on the oscilloscope and how much it exceeds the display). So don't make one small part fill the display just so you can see it better, while chopping off something else. The best way to see the whole waveform, as accurately as possible, is for it toexactlyfill the display.

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 01:11:10 am
content: I see, interesting.Thanks for your help.

author: pickle9000
author_rank: Super Contributor
timestamp: April 19, 2014, 01:45:12 am
content: Don't forget to cal your scope, if you haven't already.

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 02:05:56 am
content: Quote from: pickle9000 on April 19, 2014, 01:45:12 amI assume you mean the self calibration procedure, right?When I received it, I loaded a newer firmware, I reset all settings to the defaults and performed a self calibration.

author: w2aew
author_rank: Super Contributor
timestamp: April 19, 2014, 02:50:08 am
content: Yes, completely normal. And also don't forget tocompensateyour probes when you get them!

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 03:02:26 am
content: Quote from: w2aew on April 19, 2014, 02:50:08 amYes, I will when I receive them.They are two P6100 probes (100MHz) from ebay. I suppose they are adequate.

author: Dave
author_rank: Super Contributor
timestamp: April 19, 2014, 03:32:25 am
content: What w2aew is trying to say is that you need to hook up the probe to your scope and connect it to the square wave output of the scope. You then need to use the screwdriver that came with the probes and tweak the variable cap to make the waveform on the display as square as possible. The variable cap is located on the BNC connector (it's a small screw - see picture below).

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 03:40:36 am
content: Quote from: Dave on April 19, 2014, 03:32:25 amYeah, I know the procedure (theoretically), thanks for reminding me.On these probes the variable cap is on the BNC connector (at least according the pictures I saw).Edit: By the way, what are the small blue/green "rings" and grey tips/shrouds (on the picture) used for?

author: w2aew
author_rank: Super Contributor
timestamp: April 19, 2014, 04:00:44 am
content: Quote from: astraios on April 19, 2014, 03:40:36 amThe little rings are simply identifiers. Put one at the probe end, and one at the scope end. It makes it easy to figure out which probe is connected to which channel when you've got multiple probes in use at the same time.

author: astraios
author_rank: Contributor
timestamp: April 19, 2014, 07:46:15 am
content: Quote from: w2aew on April 19, 2014, 04:00:44 amOh ok, good to know.