Oscilloscope Noise - Page 1
Forum section: electronics / beginners

author: Longhair
author_rank: Regular Contributor
timestamp: January 06, 2011, 01:18:49 pm
content: I have my oscilloscope plugged into the same outlet line (circuit breaker <--> wall outlets) as my computer, monitor, power supply, etc. and I happen to be getting what I feel like is a lot of noise. Doing the self calibration did not improve (or make worse) anything so now I am wondering what I would be able to do to clean up the noise from the AC outlet. Rewiring the house is not an option.I took a picture with nothing plugged in to the osilloscope. This is the Rigol DS1052E 50MHz (not hacked) that is very common on here.

author: Simon
author_rank: Unknown
timestamp: January 06, 2011, 05:28:21 pm
content: is this 200mV/Div the setting you took the measurement on ? if not (you have zoomed in) it is normal, if it is yes that is a bit much, I was a little disappointed with the noise on my scope but this is inherent in digital scopes.

author: Longhair
author_rank: Regular Contributor
timestamp: January 06, 2011, 05:51:47 pm
content: I just did another one (200mV / 200ns) and it doesn't look like that so I must have zoomed in.I guess that it is good to hear that it is normal - at least it isn't broken.Thanks for letting me know.

author: Simon
author_rank: Unknown
timestamp: January 06, 2011, 06:13:39 pm
content: looks just like mine with or without the hack, I suspect that SMPS is part of the problem, when I get around to screening the motherboard I'll let the forum know of the effect if any

author: cybergibbons
author_rank: Frequent Contributor
timestamp: January 06, 2011, 06:17:09 pm
content: Is the Rigol normally that bad? 0.8V PtP noise?You should really ground the probe when look for noise however.

author: Simon
author_rank: Unknown
timestamp: January 06, 2011, 06:27:54 pm
content: It seems to be a combination of the normal digital sampling issues you get on any digital scope (nature of the beast) and I beleive some power supply noise although that is disputed. I once made up an aluminium screen that helped a bit (I had to recalibrate as the trace was offset negatively) but ideally it should be steel which I'm yet to do.The noise has roughly a constant VDiv/Vnoise ratio however this does increase on the lowest 2 or 3 V/Div settings which is where i think the PSU noise is coming into play

author: Zero999
author_rank: Super Contributor
timestamp: January 06, 2011, 09:01:59 pm
content: The signal appears to be digital so it looks like the noise is within the sampling margin. In other words, suppose at 200mV/division and 8-bit per sample the full scale deflection is +/- 410mV, the quanta would be 410/127 = 3.228mV. If you zoom in 120 times you now have 1.5mV/div so each quanta now takes two squares so 2mV of random noise looks like a squarewave.

author: Simon
author_rank: Unknown
timestamp: January 06, 2011, 09:06:34 pm
content: on the lower 3 scales the noise is significant although it tend to stay within +/-1 pixel so yea pretty much sampling error, but at the lower scale it does creep up considerably so I think there is some pickup there although not a lot

author: chscholz
author_rank: Regular Contributor
timestamp: January 07, 2011, 01:20:53 am
content: Yes, around 0.8 Vpp amplitude noise??? That is HUGE!What happens if you terminate the inputs to ground?If the noise is still that high, I'd say the instrument is borderline useful.Quote from: cybergibbons on January 06, 2011, 06:17:09 pm

author: Unknown
author_rank: Unknown
timestamp: January 07, 2011, 03:24:56 pm
content: Quote from: chscholz on January 07, 2011, 01:20:53 amDepends on the settings. Assuming it was set for a 10x probe, the actual voltage is 80mV. If the scope was set to 1V/div (10V/div on display), +/- 40mV is about 1-bit. It certainly looks like +/- 1 bit to me.

author: chscholz
author_rank: Regular Contributor
timestamp: January 07, 2011, 03:47:58 pm
content: Not familiar with the GUI of this scope but it looked as if he was using 200 mV/div setting. I am also used to scopes auto-detecting probes, so yes, if there is a passive probe attached that might be all good or at least not so bad.To get a rough estimate of the scope noise one would certainly remove the probes, some would call this "baseline noise".Quote from: alm on January 07, 2011, 03:24:56 pm

author: Simon
author_rank: Unknown
timestamp: January 07, 2011, 03:53:36 pm
content: if you take a snap shot of the noise and then zoom in you will get that, the noise will be on the screen about the same size on all ranges as it is +/-1bit, so in effect the bigger the V/Div the higher the noise as it remain a constant percentage of the V/Div

author: Longhair
author_rank: Regular Contributor
timestamp: January 07, 2011, 04:30:34 pm
content: Just so there is no confusion, I just took a couple of pictures of the current noise. In the very first post, the noise was zoomed in but in the following 2 pictures below, this is how it looked like when I pressed the Run/Stop button.

author: Simon
author_rank: Unknown
timestamp: January 07, 2011, 04:38:50 pm
content: perfectly normal

author: sonicj
author_rank: Frequent Contributor
timestamp: January 10, 2011, 02:30:05 am
content: let me guess, either you took over your wife's sewing table or you're into scratch building rc airplanes...-sj

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 10, 2011, 09:20:58 am
content: Quote from: sonicj on January 10, 2011, 02:30:05 amboth!