50Hz signal on oscilloscope probe - Page 1
Forum section: electronics / beginners

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 02, 2016, 07:28:50 pm
content: Where does it come from?Newly bought Rigol DS1052E arrived today and when I tested it out one of the probes that came with it (but not the second one) is picking up this signal from somewhere. Any idea why or how I can get rid of it?

author: WaveyDipole
author_rank: Frequent Contributor
timestamp: November 02, 2016, 08:36:09 pm
content: In the UK, AC mains has a frequency of 50hz so I would guess that your probe has a problem with its shielding and is simply picking up EMI from the mains. If the shielding is not earthed properly all the way down to the tip, the wire will act a bit like an antenna and pick up all manner of stray EMI. Do you get continuity from the metal plug up to the outer shielding at the tip of the probe?From reading some of the threads on Rigol scopes (I'm thinking of getting a DS1054Z myself) I understand that occasionally probes supplied with Rigol scopes have been found to be faulty. However, Rigol, will usually replace them.

author: w2aew
author_rank: Super Contributor
timestamp: November 02, 2016, 09:06:17 pm
content: Quote from: NottheDan on November 02, 2016, 07:28:50 pmAssuming that you haven't connected the probe to anything (other than the scope), then this is normal - just picking up mains radiation. It's just acting as an antenna.If you connect the scope ground lead to the probe tip, it should go away. Similarly, if you connect to a circuit you're testing, making sure to connect the ground lead also, the 50Hz signal shouldn't be there.

author: Brumby
author_rank: Unknown
timestamp: November 02, 2016, 10:18:19 pm
content: I notice it is a fairly low level signal and even shorting the earth clip to the probe tip can still pick up stray EMF. This is because the earth lead will form a loop - basically a one turn secondary of an air-cored transformer to the rest of the world (or a loop antenna - choose your poison). This is actually a very important aspect of scope measurement and you need to be aware of this - and how to minimise the problem - as it will happen with even the best of probes. It's a function of the physics even a $1,000 probe must obey.The other thing I've noticed is that the signal has clear departures from the traditional sine wave profile and this indicates to me that there's some type of switching power control somewhere nearby. You can check if it's in your lab or nearby by having this display up on the scope and switching off equipment one by one.

author: danadak
author_rank: Super Contributor
timestamp: November 03, 2016, 02:02:10 am
content: Fluorescent lights ?Regards, Dana.

author: StillTrying
author_rank: Super Contributor
timestamp: November 03, 2016, 03:33:05 am
content: Why does the OP's 400mV p-p look like it's done on a 4 bit ADC.

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 03, 2016, 05:04:11 am
content: Quote from: StillTrying on November 03, 2016, 03:33:05 amBecause I just fiddled with the knobs until I got it in picture and otherwise the DSO is straight out of the box and I don't really know what I am doing?Quote from: Brumby on November 02, 2016, 10:18:19 pmBut the thing is, only one of the probes picks it up. That's what surprised me about it.Quote from: danadak on November 03, 2016, 02:02:10 amDon't use any here. LED lighting. Nextdoor has CFL but I don't know whether they were on or not.

author: tautech
author_rank: Super Contributor
timestamp: November 03, 2016, 06:56:13 am
content: Quote from: NottheDan on November 03, 2016, 05:04:11 amThe one set to 1:1 will be the most sensitive, the other is probably set at 10: 1.It's just EMI, RFI etc, quite normal for an unconnected probe.

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 03, 2016, 11:24:39 am
content: Quote from: tautech on November 03, 2016, 06:56:13 amThey were both set to 10:1. That was one thing I remembered to make sure of.

author: StuUK
author_rank: Frequent Contributor
timestamp: November 03, 2016, 11:32:29 am
content: I wouldn't suspect anything wrong at all, does it disappear when connected to something? I see this on my scope and the waveform will change will I switch off my CFL/Fluorescent light but it's not a problem when connected to a circuit.

author: StillTrying
author_rank: Super Contributor
timestamp: November 03, 2016, 12:23:19 pm
content: Use the 1khz square test signal on the front of the scope to test/set both probes up.Is it 'Brand new and high quality' or 'pre-loved'?

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 03, 2016, 12:50:00 pm
content: Quote from: StillTrying on November 03, 2016, 12:23:19 pmas far as I can tell it is new. It was advertised as unused and all the printed documents were in Chinese. So I guess it was someone's grey import.

author: StillTrying
author_rank: Super Contributor
timestamp: November 03, 2016, 02:24:22 pm
content: I hope you got it for aVERYgood price, after looking at some screen shots in old threads on here my only explanation for the steps in your noise is that it is.https://www.eevblog.com/forum/blog/rigol-ds1052e-nasty-surprise!https://www.eevblog.com/forum/blog/changing-the-rigol-ds1052e-to-ds1102e-using-usb-the-dummy-guideOr maybe not.https://www.eevblog.com/forum/testgear/rigol-ds-2072-noise-problem/msg195218/#msg195218

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 03, 2016, 10:23:10 pm
content: Quote from: StillTrying on November 03, 2016, 02:24:22 pmI dunno. To me £160 seemed to be quite a good price. Did I overpay?

author: StillTrying
author_rank: Super Contributor
timestamp: November 04, 2016, 01:52:19 am
content: It's a good price for a new 2ch 50Mhz scope, problem with that early model is the very low screen resolution.You seem to be capturing an almost flat line and then expanding it in the Y direction, there's no extra info there, you have to get the waveform a few divisions high before capture.Read the first part of manual and try to get two 1kHz test signals on the screen, it will help to find why the probes don't seem matched.On the cheapest probes, or old well used probes the X1/X10 switch often becomes intermittent.https://www.adafruit.com/datasheets/Users%2520Guide%2520DS1000E.pdf

author: Zero999
author_rank: Super Contributor
timestamp: November 04, 2016, 03:55:31 pm
content: Quote from: NottheDan on November 03, 2016, 10:23:10 pmIt seems like a reasonable price for what you've got but, unless you're strapped for cash, I'd advise spending more and getting something better.

author: tatus1969
author_rank: Super Contributor
timestamp: November 04, 2016, 04:54:22 pm
content: Quote from: StillTrying on November 03, 2016, 03:33:05 amhave you stopped acquisition, and adjusted vertical gain? if yes, the result is not meaningful, as you only stretch the A/D converted memory content. Maybe try and repeat your test with running acquisition.

author: NottheDan
author_rank: Frequent Contributor
timestamp: November 04, 2016, 06:26:50 pm
content: Quote from: tatus1969 on November 04, 2016, 04:54:22 pmDamn if I know. Probably. I'm new to this whole thing.Tried to get some better pictures today and got the problem that it ran at a much lower level. Took me a while to notice that the last time I had it with the hook on while I only had the bare probe connected today. So yeah, hook attached amplifies it, my finger getting anywhere near the tip even more so. Connecting the ground clip to the probe removes it, as does connecting it to the inbuilt signal seems to do.

author: tatus1969
author_rank: Super Contributor
timestamp: November 05, 2016, 06:50:44 am
content: Quote from: NottheDan on November 04, 2016, 06:26:50 pmif it disappears with shorted probe you can assume that your scope is in order. what you experience is normal, you can consider the high impedance probe being an antenna that will pick up everything that is in the air. in fact using the tip needle as a simple E field probe is quite common. try to place it close to the switching node of a dc/dc conveeter for example. when measuring a normal signal everything becomes cleaner because your probe is connected to something low impedance. like the test signal generator.

author: fubar.gr
author_rank: Unknown
timestamp: November 05, 2016, 05:22:19 pm
content: Quote from: Brumby on November 02, 2016, 10:18:19 pm^ThisI've seen people spend $$$ on new equipment in the hopes of making better measurements, only to realize that the problem is still there!

author: beenosam
author_rank: Regular Contributor
timestamp: November 06, 2016, 02:50:18 pm
content: Quote from: fubar.gr on November 05, 2016, 05:22:19 pmThat would be an awful reality check.