Noisy Oscilloscope - Page 1
Forum section: electronics / beginners

author: george.okpe.james
author_rank: Newbie
timestamp: June 05, 2020, 11:58:31 am
content: I am a beginner in electronics and I recently got an oscilloscope but the oscilloscope shows a lot of noise even without being connected to anything. I set the attenuator to 10x but that did not change much. When checking for low signal I can't even tell what I am looking at.I have two coils and I am trying to simulate the effect of induced emf in a second coil and want to measure the changes of voltage across it. Even when just trying to get the value of a constant voltage source It shows flickering lines.Is this normal, or how do I fix it.The first two images show the reading when no signal is applied.The third image shows when I connect it to a 5VDC source and set to 1v/div------------Modified:Original post contained only the last image repeated three times, this has been updated to the correct images, sorry

author: capacitor_explosion
author_rank: Contributor
timestamp: June 05, 2020, 12:18:33 pm
content: Just for information can you show us what do you get on the scope ?What are you probing , if you are probing something ? Give details . One thing you can do is short the tip of the scope to the ground of the scope probe u should observe a flat line . Check your voltage per division tab , you maybe at 20mV/dev. Try to measure something like a double AA battery 1.5V.

author: george.okpe.james
author_rank: Newbie
timestamp: June 05, 2020, 03:41:45 pm
content: I have added some description and images to show the readings I get

author: ogden
author_rank: Super Contributor
timestamp: June 05, 2020, 03:50:00 pm
content: Quote from: george.okpe.james on June 05, 2020, 11:58:31 amIn all three images we see same scope screen that has not been updated between takes. Look at images - they are similar down to individual noise spikes. Set vertical resolution to something sensible like 1V/div, short your probe as advised andtriggeryour scope again.

author: capacitor_explosion
author_rank: Contributor
timestamp: June 05, 2020, 04:33:26 pm
content: As ogden mentioned the pictures are identical . But lets analyze the picture , you have set the voltage per devision at 20mV/d , which way too low .The only reason to be at this setting is to measure ripple of power supplies , AC content of DC signals , or just small signals in general . The noise you see on the scope is due to all the electronic devises emit some kind of Electro magnetic interference in the enviroment . The picture is perfectly normal to me . If you have time I advice you to read the manual , you will be suprised how many interesting information and handy guide there is .- Best way to check functionality is to use the reference generator on the scope . Just hook up your probes , click autoset button , and you have to see a square wave signal 1V 1khz or similiar.

author: george.okpe.james
author_rank: Newbie
timestamp: June 05, 2020, 07:53:05 pm
content: Thank you and sorry for the mistake.I have updated the images, if you take a look at the third image you will see that it is set to 1V per division and connected to a 5V DC source yet it shows ripples instead of a straight line.

author: StillTrying
author_rank: Super Contributor
timestamp: June 05, 2020, 08:02:17 pm
content: Put the Trigger on Auto so that the trace is always updating. It looks like the trigger level is set at-4mV on some of them,+0.5V would make more sense.Some of the previous looked like the input was in the 50R mode, don't use that mode with probes or for measuring DC."The third image shows when I connect it to a 5VDC source and set to 1v/div"You'll never see the 5V level on only 4 divisions of height @ 1V/div.

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 05, 2020, 08:05:29 pm
content: When you don't use a proper ground connection you can get large "ghost" voltages as the lead is acting like an antenna, especially when the positive lead is held by you or near something like a steel object. Common signals to see are an ugly 50 or 60 Hz sinewave coming from the mains grid and more spiky signals in the 25 kHz to 100 kHz range, which is where many switchers do their thing. The somewhat triangular signal in your picture might be coming from mains power though I'm not sure. Try stopping the oscilloscope and getting a cursor reading of the frequency as noise may be throwing the frequency counter off. That's a nice oscilloscope for a beginner, by the way!

author: ogden
author_rank: Super Contributor
timestamp: June 06, 2020, 04:38:39 am
content: Quote from: george.okpe.james on June 05, 2020, 07:53:05 pmThird image does not make any sense. Do you connect probe ground clip to ground of your 5VDC source as well? Do you measure 5VDC supply at the output capacitor? I am not sure. Start from very beginning - with probe compensation. Open manual of the scope, read chapter about probe compensation carefully and completely, perform it for at least single probe. Take picture of the calibration waveform after compensation is done, show us. Leave 20mV/div with 10x probe and 5VDC supply alone for a moment.