Is my new scope faulty? - Page 1
Forum section: electronics / beginners

author: MetalMickey
author_rank: Newbie
timestamp: October 12, 2022, 03:08:52 pm
content: HiReally new to electronics so not sure if it's my inexperience or a faulty scope. I bought this new a couple of weeks ago and other than the test signal, every time I try to use it I get stuck as it just seems to display noise. Today it started to show the trace as attached. The trace doesn't change other than there's more bloom (noise) if I change from 1X to 10X on the probe.I'm in the UK and have tried it at various locations in the house and it's always the same, it's the same regardless of which probe or channel that I use.I'd appreciate any advice on things to try or whether I should return it as faulty.Thanks in advance.Chris

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 12, 2022, 03:18:55 pm
content: Looks like you have turned the sensitivity way up and are picking up the mains through the air. Try it with your finger on the probe tip. The signal should get bigger.The measurements show it is 50Hz and ~130mV. It is set to probe 10x and 50mV/div. Also try to change the setting with the knob under the Vertical text. Turn it towards V to make it less sensitive and then start measuring some signals, but never the mains directly.Search for and look at some videos Dave Jones made about using an oscilloscope.

author: wraper
author_rank: Unknown
timestamp: October 12, 2022, 03:22:52 pm
content: Disconnecting hook attachment should reduce it a lot, disconnecting the probe should eliminate it.

author: radiolistener
author_rank: Super Contributor
timestamp: October 12, 2022, 04:01:39 pm
content: this is electromagnetic interference from your environment. Just decrease sensitivity on your scope.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 12, 2022, 05:20:02 pm
content: Not faulty. The sensitivity seen in that picture is 50mV/division. At such sensitivity the tip of a disconnected probe like you have in the pic it's an antenna capturing mains hum from the surroundings. Doesn't show that signal any more if you disconnect the probe from the oscilloscope completely, isn't it?TL;DR Congrats for your new oscilloscope. It's all OK, read its manual, start learning how to adjust the settings yourself manually, both the sensitivity and the trigger (without using the autoset), then start using that for all the projects to come.

author: Electroplated
author_rank: Regular Contributor
timestamp: October 13, 2022, 07:45:15 pm
content: Welcome to the new scope club !Nowt wrong with your scope, on the settings you show, its working as intended and just picking up local noise that is present in every building that has electric wiring in it, just don't tell any anti wireless freaks you can see the noise in the air that irradiating everyone !If you disconnect the scope probe the noise you see will disappear same as if you set the channel input to GND instead of AC or DC coupling.There are some good guides about using a scope online but I think the best one is in this very forum:https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/It is long but well worth the time to read through it but the best way to learn is by actually using the scope, build a few simple circuits and use the scope to see what is going on.Bear in mind as your a beginner, experiments and poking about should be kept to battery and low voltage stuff, NEVER mains voltages !

author: james_s
author_rank: Super Contributor
timestamp: October 13, 2022, 08:09:47 pm
content: As others have said, you have it set to 50mV/div, at such a sensitive setting it is expected for it to display noise, especially when the probe tip is floating. Find some battery powered (for safety of both you and the scope) device that generates some interesting signals and poke around in it. Proper probing technique is an entire subject in itself.Set the probe to 10X and leave it there. There is almost never a reason to use 1X and it is much more likely to damage your scope if you probe a voltage that is too high. I wish cheap probes didn't almost always have that switch at all, for the rare occasions when a 1X probe is appropriate it makes more sense to have a dedicated 1X probe.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 14, 2022, 01:19:58 am
content: You haven't connected your ground so you're gonna pick up every noise source near you.

author: wraper
author_rank: Unknown
timestamp: October 14, 2022, 05:41:24 am
content: Quote from: JustMeHere on October 14, 2022, 01:19:58 amI don't think so. OP is from UK and sockets lacking earthing is not common there. On other hand, hook attachment of the probe is great at picking up interference.

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2022, 01:47:55 pm
content: Quote from: james_s on October 13, 2022, 08:09:47 pmActually in the OP’s case where the channel input is set to 50mV/div and 10x, the input sensitivity is really at 5mV/div regardless of the division ratio set with the probe switch.

author: MetalMickey
author_rank: Newbie
timestamp: October 14, 2022, 01:56:05 pm
content: HiThanks for all the replies. Good to be reassured that it's me and not the scope that's at fault. As suggested, the noise goes if I disconnect the probe and I have been using the Auto Setup function rather than learning how to do it myself, which probably led to it being set to such a sensitivity.Will definitely look at the guides, it's just good to know that I'm not wasting my time.Thanks againChris

author: james_s
author_rank: Super Contributor
timestamp: October 14, 2022, 06:30:28 pm
content: You can't expect the auto setup to work if you haven't got the scope connected to the thing you want to measure. It can't read your mind, it goes off of the signal that it sees. If you just hit Auto with the probe dangling in the breeze it's going to try to set itself up to measure the background noise because that's all you've given it to work with.

author: rstofer
author_rank: Super Contributor
timestamp: October 14, 2022, 07:46:41 pm
content: Tp see Auto work properly, connect the probe(s) to the compensator signal on the front panel and hit the button.I never remember how I last set the scope so I use Auto as a first step.

author: tautech
author_rank: Super Contributor
timestamp: October 14, 2022, 10:17:27 pm
content: Quote from: rstofer on October 14, 2022, 07:46:41 pmAnd you can't just read the scope settings on the display and adjust them to what is needed ?Respectfully that's not good advice to a new scope user when instead it's best to learn what the information boxes on the display are conveying to the operator for them to make informed operator decisions.Push buttons and hope is no way to use a complex instrument like a scope.......I never ever use Autosetup !

author: rstofer
author_rank: Super Contributor
timestamp: October 14, 2022, 11:31:27 pm
content: Not only do I use Auto, I highly recommend it, especially for newcomers. It gets a well triggered trace on the screen with rational settings for V/div and t/div. It is usually an excellent place to start. We paid extra for that button, might as well use it.It is possible to set the scope to save the setup parameters at shutdown. Goodness only knows what I was doing with the scope 6 months ago but it probably wasn't anything like what I want to do today. One push of the Auto button and everything will be on the screen instead of trying to integrate the waveform over some period (or some other arcane measurement). Of course I could give up storing parameters. That would be the other way.Yes, I can twiddle the knobs. I still have my Tek 485 and it has a lot of knobs. My first scope was a DIY project I built back around '58 from plans in the ARRL Handbook (I believe). In some ways the analog CROs are easier to use. There are a lot of knobs but they're all right in front of you, not buried in a menu system only a mother would praise.I think I'll continue to use and recommend the Auto button.

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2022, 12:16:25 am
content: Quote from: rstofer on October 14, 2022, 11:31:27 pmOr better still set up a custom User Default.Many Siglent DSO's offer this feature where we can set the scope to just as we would prefer every setting to be and then save it in the Save/Recall menu to be recalled with the Default button instead of the factory default.This gives a better known starting point rather than the factory Default or for the occasional user having forgot how they last used the scope and also has the benefit of exercising scope usage skills resulting in better understanding of operational principles rather than press Autosetup and hope it displays something sensible and/or remotely correct.

author: james_s
author_rank: Super Contributor
timestamp: October 15, 2022, 04:56:35 am
content: Quote from: tautech on October 14, 2022, 10:17:27 pmI'm well versed in setting up a scope and I usually start with auto. It isn't always optimal but 9 times out of 10 it gets me pretty close. It's a time saving convenience, not a replacement for knowing how to use the scope. I often don't know exactly what I'm going to find when I set out to measure something.

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2022, 06:40:42 am
content: Quote from: james_s on October 15, 2022, 04:56:35 amExactly and why I never recommend its use to the novice as it's far more valuable to be a competent user of a scope.QuoteHere again you use Autosetup as a crutch instead of the experienced user I know you are, applying a good understanding of what waveform to expect and adjusting the scope even before connecting probes !This ^, nearly 2 decades ago was the best advice from my scope mentor gave to insist the grey matter between the ears was engaged instead of blindly trusting what was on the display of the scope. That advice received in my CRO days has served me well however the modern DSO is a far more powerful device even capable of storing and recalling your personal preference settings with the punch of a button.Still, each to their own and old habits are hard to break yet if the scope has last used settings so unsuitable for the next task Default is my preference and then tune to get the imagined/expected result.