Rigol DS 4024 noise problem or may not, help me  - Page 1
Forum section: electronics / testgear

author: flywind
author_rank: Newbie
timestamp: October 05, 2013, 10:53:49 am
content: Hi, before i start i must warning you, my english may hurt your eyes ! Sorry !I try to play with my New Rigol DS4024 a couple weeks...Now I found some noise problem on it , please help me to verifind is that the faulty or I use it in wrong way (I am not family with so high resolution digital Scope.. )First Thing I found some noise pulse at 60Hz and around 100mV Vpp. i try to change the power source , then I solve it . like playfsx wrote in Rigol DS 2072 noise problempost. (https://www.eevblog.com/forum/testgear/rigol-ds-2072-noise-problem/) . looks like Rigol haven real solve this problem in DS4000 Serious..Ok . Next I found a Background Noise in my unit also ...It is about 15mv -25mv (some time go high to 100mv), no matter i plug the probe or not ....So I have done some testing .1. Unplug all Probes . the Noise will show every channel. and the Channel 1 is quit different ...like a self general pulse ...(see Video 2 ).2. When Unplug , the Noise Vpp is around 1.05mV at 1mv level (X1) . you can see in video 1 01:08, and at 2ns , it show a pulse ..3. when I plug the probe , the Noise Vpp go to 15mV,...that make sense , since my probe is X10 ..4. when I apply BW limit on Channel 1 . at 20Mhz , the noise go to low ..most like correct .500uV .it is said in DS4000 specification .5. when i connect the probe tip to it Clip , the noise still there , and both tip and clip connect to testing ground, noise still there .6. In the Video 2 , you can see all channel got same noise . the Channel 1 is quit special...

author: AndyC_772
author_rank: Super Contributor
timestamp: October 05, 2013, 11:50:16 am
content: I've not sat and watched both your videos all the way through, so apologies if I've missed something, but:It looks as though you're always triggering on ch 1, so the display has all the greatest peaks that (randomly) occur on ch1 overlaid on top of each other, giving the impression that ch1 is worse than it really is. Look at the noise amplitude away from the trigger point and you can clearly see it's the same on all four channels.The noise is reduced when you switch on bandwidth limiting, because the scope is applying a low pass filter to the signal. Look up "noise bandwidth" and have a good read... it's a really important factor to take into account when measuring noise levels. To put it simply, there's going to be less noise in the frequency band from DC-20 MHz than there is from DC-200 MHz.Trigger on the other channels and see if the "fault" moves. Also try setting the trigger level well away from 0V and put the scope into Auto trigger mode, so it's not actually triggering on any channel but simply free-running. I reckon you'll see all four traces exactly the same, and all perfectly OK.

author: flywind
author_rank: Newbie
timestamp: October 05, 2013, 12:33:21 pm
content: Quote from: AndyC_772 on October 05, 2013, 11:50:16 amOh .OMG...i think my brain has been block by something through Friday ....i got your meaning ........that pulse it cause by trigger ...Also after i upload the video , I have done more testing again . look the Ground Noise is about 15mV at 10mV with 10X probe . and without the probe , the noise is about 1mV-to 1.5mv ....it looks Fine ..but When i read the Specification of DS4000 . it said the noise should be 500uV ... is that mean My unit got a little bit error , or is Ok ?for the BW limit. i got an idea how is working, it that mean the DS4000 has a larger Ground Noise above 20Mhz?

author: Unknown
author_rank: Unknown
timestamp: October 05, 2013, 12:51:22 pm
content: Quote from: flywind on October 05, 2013, 12:33:21 pmNo, the trigger just highlights it. Similar pulses on other channels get lost in the noise.Quote from: flywind on October 05, 2013, 12:33:21 pmAll vertical scales are multiplied by ten if you attach a 10x probe to compensate for the attenuation, so that explains the difference. Are those peak-to-peak (Vpp) or root mean square (Vrms) that you measure and quote from the datasheet? If you measured Vpp and they specified Vrms, then it sounds like the scope is within spec.Quote from: flywind on October 05, 2013, 12:33:21 pmRead this again:Quote from: AndyC_772 on October 05, 2013, 11:50:16 amDave also discussed this extensively in this recent video (though that may be more details than you bargained for):