Cheap oscilloscope for basic measurements - Page 1
Forum section: electronics / beginners

author: bauto601
author_rank: Contributor
timestamp: December 22, 2018, 04:22:23 pm
content: Hello,This forum has really helped me on choosing which oscilloscope i need and why. Till now, i was just reading without being registered but i want to ask some questions about the use cases for the oscilloscope i'm planning to order and if they fit the capabilities of the oscilloscope.I am looking around for a new USB DSO oscilloscope of around €100's. I found that there are 2 real options in this segment:-Hantek 6022BE-Owon VDS1022(i)The Owon seems to be the better choise of the pair. My use cases for the scope are mainly:- Audio equipment repair (so no high frequency signals)- Power supply ripple/noise measurements (somewhat higher frequency signals)I think that the Hantek isn't really suitable for the second use case, the Owon scope is the only choise then. Altough it's memory of 5k samples is very small, it should be enough for short shots of ripple/noise measurements and somewhat longer shots of audio signals.The 100MSa/s rating should be enough for the use cases, with such small memory you can't really get shots with 100MSa/s precision. I also looked at what JonnyGuru uses as a scope to measure noise/ripple and that is a TDS2012B with just 2.5K memory. When he makes shots of 25ms (from what i can see on his reviews) the amount of samples per second reduces significantly. So the 100MSa/s of this scope in combination with 5k memory should be enough to look at ripple/noise of switching power supplies. Am i right?The second thing is that the bandwidth of the Owon scope is 25mhz. To measure ripple, you officially have to look at the 20Hz-20Mhz range of the output. The bandwidth of the Owon scope should be good enough, but i can't find any information about a 20Mhz filter for this scope. Are there like external 20Mhz filters? Or can i build one myself? Do i actually need it with this scope?And the third thing is that a differential probe is the best option to measure ripple/noise on switching power supplies. But the Owon 1022i already has isolated channels, so then i can just measure with a regular probe right? Since the ground connection is floating on this unit. This would save me the additional costs of needing an expensive differential probe.This is what i understood when i was browsing the internet for like a day or 2. Are my assumptions right? Am i missing some (important) aspects?

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2018, 05:53:10 pm
content: Welcome to the forum.You have summed up your needs very neatly. For the two models you have listed, the main forum threads are (in case you haven't already found them)..https://www.eevblog.com/forum/testgear/hantek-6022be-20mhz-usb-dso/https://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/100msps and 25MHz should be fine for your needs.USB isolation is a great benefit in preventing ground loops which, if nothing else, can protect the scope and more importantly, your PC, from the effects of accidental ground loops. It also helps with floating the scopeto a certain extent.It's important to remember that the isolation should be used with caution - just because the isolation components can handle mains voltage doesn't mean that you should go and strap the ground clip to primary side of an SMPS! The outer case sleeve is connected to the probe ground clips, the two channel grounds are also common (just clarifying your "But the Owon 1022i already has isolated channels")To be clear, the only safe (still dependent on the user!) way to take primary side ripple measurements is a high voltage differential probes. Even the cheap ones will be several times the cost of either scope.Ok, having got the safety stuff out of the way, the VDS1022(i) works way better than the Hantek. It makesfarless demand on PC and USB port performance (something that cripples the Hantek on some ranges), has proper triggering etc. Also, for audio and ripple measurement, the OWON has AC coupling that the Hantek (surprisingly) is missing. There is obviously a price differential but it is much lower than it used to be (just taking ebay prices).Neither scope has a 20MHz filter (the 20MHz on the Hantek is just where the input circuitry and rise time come out). There is no specific filter on the Owon either - I measured the -3bB point at around 32MHz on my unit (31/34MHZ).I doubt the need for a specific external 20MHz filter for most measurements. You can maybe use the FFT function. Neither instrument is a 'calibrated' lab standard limits measurement equipment in any case. The FFT function may be some help here too.

author: bauto601
author_rank: Contributor
timestamp: December 22, 2018, 06:09:21 pm
content: Quote from: Gyro on December 22, 2018, 05:53:10 pmThank you for your reply. I already have readen the 2 main threads on this forum, i saw that the Hantek barely even classifies as an oscilloscope.Also, i phrased my sentence a bit wrong about the isolation. The power and data lines (so effectively the usb port) are isolated. The channels indeed aren't isolated from eachother ground wise. I won't measure high voltages with it. But the ground isolation is something i want to save the extra costs of a differential probe. I will be measuring voltages below 20V, if i ever want to measure high voltages i will probably buy 100x probes and take all the needed precautions. (was also reading about that on this forum) Since i was a 10 year old child i was already poking around with electronics, i know and felt (multiple times) the dangers of mains (high) voltage.The ground obviously isn't going to be connected to a live mains wire or even low voltage positive wires, it's just nice to avoid ground loops and such. For measuring ripple and noise it is also nice to have a floating ground on the oscilloscope.I know i can't expect to have nicely calibrated high voltage rated safe measuring equipment for the price of a regular differential probe, so iwon't expect that from these scopes.

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2018, 06:41:37 pm
content: Glad I could clarify.It sounds as if you have a good match for the job then :-)Just a quick note regard to the audio side, it's worth remembering we're talking 8 bit scopes here... fine for exploring waveforms, tracing faults etc. but if you're after low level FFT distortion measurements then you'll need to add another beast. I'm sure you already realize this.

author: bauto601
author_rank: Contributor
timestamp: December 22, 2018, 07:01:41 pm
content: Quote from: Gyro on December 22, 2018, 06:41:37 pmMy brother is mostly doing the audio repairs. This is just basic stuff, indeed for tracing faults in PA amplifiers. He won't do anything complicated with it since he's mostly a mechanical person. The most intensive task it will see is taking ripple/noise measuring, which is more my area. I'm studying right now at the university for Automotive Technologies, mostly based on Electrical Engineering. So i will probably need something beefier after a couple of years but till then this will suffice. For the real deal we also have oscilloscopes at the university for study related testing, so that's no problem.And if this scope really doesn't cut it in certain situations, i also have an old tektronix 465. But that scope hasn't been calibrated for decades (it really is all over the place calibration wise) and is really worn out. It also got a bad solder joint, so most of the times i have to punch it on the top to get it working again. It does the job, but a modern DSO seems much nicer to use.EDIT:Just bought the VDS1022I for €102 included shipping from Germany. Thanks for your confirmation of my findings.

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2018, 08:09:13 pm
content: Sounds like a good deal, so much nicer than the wait from China.With a 465 too, you're well sorted for pretty much any eventuality. It's worth the hassle of investigating and fixing it. You're quite right, I still like analogue knob twiddling, but there's absolutely no doubting the benefit of single trace capture etc. Both of the above complement each other very nicely.

author: bauto601
author_rank: Contributor
timestamp: December 22, 2018, 08:28:24 pm
content: Quote from: Gyro on December 22, 2018, 08:09:13 pmYeah, the 465 is definately a very nice scope. Analog buttons are also really nice. But it's in a desperate need for a service. Most of the lights at the buttons don't work anymore, calibration, bad solder joint(s), corrosion at the BNC connectors, etc... It probably hasn't been used much but it's just getting old and needs to be serviced. I definately won't sell or scrap it but i also don't have the time and knowledge to service it at the moment.

author: tggzzz
author_rank: Super Contributor
timestamp: December 22, 2018, 08:45:09 pm
content: Don't automatically assume the 465's problems are a bad solder joint: there are other failure mechanisms.There are may internal connectors, one of those may have oxide coatings or be a little dirty. Easy to fix.Many of the controls have strange (by modern standards!) switches consisting of exposed gold contacts that are pressed against the PCB. These can get dirty, and can be easily cleaned - or damagedThe vertical attenuators can become flaky. If it is just the external contact then that can be fixed, but internal contacts are more troublesome.Or, of course, there could be a problem with the electrolytic capacitors.

author: bauto601
author_rank: Contributor
timestamp: December 23, 2018, 12:53:25 pm
content: Quote from: tggzzz on December 22, 2018, 08:45:09 pmAnd there you go, it maybe this, or this, or even that.The problem is that it doesn't react to any input or even any button. It just displays a flat line above the horizontal center line until you hit it on the top. Switching channels also doesn't do anything. After that, everything works fine. Except for the calibration and the other issues.

author: Old Printer
author_rank: Frequent Contributor
timestamp: December 23, 2018, 02:58:55 pm
content: Most if not all of the transistors in that scope, and there are quite a few of them, plug into sockets, like many scopes of that era. At three legs per that is a lot of potential bad connections to cause the type of problem you describe. Usually removing and reinserting the socketed components, with maybe a wipe of Deoxit, is a first step in rehabbing an old scope like that, which in itself would be a great learning experience.

author: bauto601
author_rank: Contributor
timestamp: December 23, 2018, 04:34:18 pm
content: Quote from: Old Printer on December 23, 2018, 02:58:55 pmJust read the story that they plug in sockets so they can be swapped easily because not every transistor met the specifications that were needed for this scope. I will take a look at it some day, i unfortunately don't have the time for it right now.

author: tggzzz
author_rank: Super Contributor
timestamp: December 23, 2018, 06:13:55 pm
content: Quote from: bauto601 on December 23, 2018, 12:53:25 pmAt least you have a non-intermittent problem. I once had a scope with a semi-crap capacitor that, when turned on, failed for 60s twice a day. Turning it on more often made the problem disappear.Think of it as a more interesting and profitable pastime than crosswords or soduku