New firmware, new noise, is it possible?   Rigol DS2072A - Page 1
Forum section: electronics / testgear

author: MattFL
author_rank: Contributor
timestamp: September 26, 2015, 01:50:06 am
content: I updated the firmware on my Rigol DS2072A scope tonight, and now suddenly I get a pile of noise with my probe just sitting on the bench (no loops), ground floating. It's 205mVpp at around 60Hz, which I thought was pretty big amplitude and probably related to my wall power here. With the probe clipped to its own ground I'm getting just over 8mV of noise, though up in the 100MHz range. See the attached images.I don't recall having this much noise before the firmware update, and nothing else on my bench has changed that I'm aware of. Am I crazy thinking that the firmware update may have contributed to this?

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: September 26, 2015, 03:11:42 am
content: I have been thru 3 or 4 firmwares on my DS2072A since I got it and there were some days where that would happen. At least on mine its not related to the firmware, because all of them would have the issue, especially the 60Hz. The first couple of times it happened I thought I had got a bad scope, but I started noticing on days that it was happening both of my DMMs would be jumping around when not connected to anything. For me I am clearly picking up some stray noise from somewhere in the house, when its happening it doesn't seem to matter where in the house I am plugged in. It seemed like it happened more frequently when it was colder, but as far as how strong the noise was, it was always pretty consistent.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 26, 2015, 03:30:46 am
content: The top trace looks pretty much identical to what I get from an ungrounded probe on my DS1054z (unlocked to 100Mhz bw) at the same settings. Mine's a little fuzzier but the same shape and frequency.I get about 11-13 mV p-p noise at most and no regular peaks when I try to duplicate the second trace with probe clipped to its own ground, at 5 ns/div and 10 mV/div.

author: MattFL
author_rank: Contributor
timestamp: September 26, 2015, 03:34:24 am
content: Thanks for replying! Just to clarify, you see this some days with your scope, but not every day? I've only had this scope a few weeks so that would validate my observation that it suddenly started. Are your DMM's bench type plugged into the mains, or on battery?It's definitely coming through the probes. If I disconnect the probes from the scope, the noise drops to almost nothing. But I wonder where it's coming from? I tried turning off everything in my office and it didn't make any difference.I'm wondering if it's related to the ground. The mains ground is directly connected to the probe ground, so it runs the length of the probe wire. When I unplugged my UPS from the wall so the scope is running on the UPS battery, the noise changed significantly (see the attachments). At this point the scope was basically ungrounded, but it's also getting a stepped sine approximation for power instead of a true sine wave, so I'm not sure if that's the cause of the noise change. Maybe I need to dig out my true sine wave inverter and see what happens when it's completely isolated from the mains ground. Hmm...

author: Bud
author_rank: Super Contributor
timestamp: September 26, 2015, 04:08:40 am
content: Try putting a snap-on ferrite choke on the probe lead at the scope BNC end.

author: CustomEngineerer
author_rank: Frequent Contributor
timestamp: September 26, 2015, 05:38:29 am
content: Quote from: MattFL on September 26, 2015, 03:34:24 amCorrect about only seeing it some days. The DMMs are both battery powered handhelds. When its happening disconnecting the probes (both scope and meters) reduces the amplitude some, but the noise is still there. On the scope it will still show even when measuring an actual signal if I zoom in enough.

author: Timur Born
author_rank: Regular Contributor
timestamp: September 26, 2015, 01:54:00 pm
content: I got this with three different DMMs here, including more expensive ones like Fluke 289 and Keysight U1272A. On the 289 the amplitude increases considerably the closer I put my hand towards the lower right corner, closer to the red V/Ohm probe port. I assumed these devices where better shielded, but obviously they are not. The probes seem to work like antennas, but it happens with or without probes.Interestingly it keeps happening after turning off all fuses of my apartment, but placement of the DMM/probes can affects this. With the VC890 I had it could happen when the DMM lay flat on the table, but not when the stand was used. Holding the DMM close to an open chassis of a running desktop PC could make it happen, placing more distance in between helped. With the 289 I get it pretty much all the time in all places, though.Frequency can increase when I hold the DMM closer to a power-saving bulb (including Philips Hue).At one point I planed to start a thread asking for the background and explanations of this phenomena. So if someone knowledgeable comes around, I am all curious and ears.

author: MattFL
author_rank: Contributor
timestamp: September 30, 2015, 01:18:47 pm
content: Quote from: Bud on September 26, 2015, 04:08:40 amWon't that also attenuate the signal that I'm trying to measure? I'll have to get my hands on one and give it a try just to see what happens.