USB Oscilloscope Owon VDS1022 (non "I") - Page 1
Forum section: electronics / testgear

author: Saitama
author_rank: Contributor
timestamp: July 18, 2019, 02:40:15 pm
content: Hello!I have been planning to buy an oscilloscope for an eternity and now, when I have enough money to afford USB based unit, I am doing some research. I looked at different models and found Owon VDS1022 to be the best one that suits my budget (90USD). I searched It's specs and found out that the maximum input voltage is 40V (pk-pk) and the model with "I" has 400V. I am a bit confused by this, I heard that VDSS1022I just has USB isolation and the rest is the same, but how can it measure 360V more than VDS1022?I am a beginner, so don't be too harsh on me if it's a newbie quetion

author: Gyro
author_rank: Super Contributor
timestamp: July 18, 2019, 05:59:44 pm
content: I agree, it is confusing. From my investigation of the VDS1022(I) internals, I believe it goes as follows:- Both the VDS1022 and the VDS1022I share the same input attenuators and circuitry. Both are rated at 40V directly between the BNC centre connection and skirt.- When a x10 scope probe is added, this increases to 400V, probe quality permitting. When measuring voltages significantly above 40V, using a switchable x1 / x10 probe will lead to disaster sooner rather than later.- The VDS1022I has USB isolation. This provides galvanic isolation between the USB interface and the rest of the scope. This uses an AD ADUM3160 USB isolator and a TI DCP02 Isolated DC-DC converter. Both parts are UL recognised and the PCB spacings reasonable, but the purpose of this isolation is NOT to float the scope at high voltages. I think it is this isolation rating that causes the confusion in the spec.- The skirts of both BNC connectors are connected to each other AND the metal sleeve of the scope.The USB isolation of the VDS1022I is extremely useful if the ground clip on one of the probes accidentally contacts a power supply rail - it will protect the USB port of the PC and probably the PC itself. If you are using the scope in a situation where the ground clip could accidentally contact ahazardousvoltage, eg. Mains. The the USB isolation will probably survive BUT there are now other dangers - ie. The scope sleeve would become live, as would the ground clip of the other probe. Clearly something that must be avoided at all costs.It is certainly worth buying the VDS1022I over the VDS1022 for the computer 'insurance' that it buys you though.The main VDS1022(I) thread is here...https://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/In terms of making measurements of 360V or more, there are certainly safety issues involved. The first is that you are a beginner - are you sure that you are safe to be measuring voltages of that level (hint: the default answer should be no!). Granted some high voltages are more dangerous that others. eg. The HT rail of a small valve preamplifier is less dangerous than mains, but it will still be able to put out enough current to hurt or kill you if you are unlucky.The only 'safe' way to measure high voltages is to use a high voltage differential probe - I think the Micsig DP10013 is the cheapest available at the moment and comes with high voltage connections and clips. I say 'safe' because it still depends on your experience and knowledge, not just the probe.Dave has a video called 'How not to blow up your scope'. I recommend watching this, and doing a forum search for other high voltage measurement threads.The best advice I can give is to be safe! If you are not certain and comfortable with something, then back off and ask for further help. I hope this helps.P.S. if you can fill in a bit more detail of what you are trying tolookat (DMMs are better atmeasuringvoltages) then I will try to help further.

author: Saitama
author_rank: Contributor
timestamp: July 18, 2019, 06:23:12 pm
content: I want to see PWM, saw-tooth and low voltage artificial sine waves (not anything above 30V). I can't measure voltages at different spots of the wave with a DMM so that's why I really want an oscilloscope.P.S I recently found this DMM: Sinometer DM88 (https://dac.ge/?en&act=product&prodid=2097)It has good specs, but I don't completely trust chinese brands. It only costs ~28$ so should I buy it?

author: Gyro
author_rank: Super Contributor
timestamp: July 18, 2019, 06:50:49 pm
content: That doesn't sound at all worrying then. Any situation where the scope ground clip will be at ground potential will be fine (as long asdirectcontact with the mains isn't involved). Having a scope certainly opens up a new world to you. Just be careful to check the switch setting on your probes if approaching 40V and stay clear of high voltages until you are more experienced.Check out some more of Dave's videos, most peoplealwayskeep their probes set to x10. It gives 10Minput resistance and low input capacitance instead of 1Mand the full cable capacitance, so it affects the operation of your circuit a lot less, in addition to providing extra input protection to your scope.As I said, the isolated version is worth the few extra dollars, accidentally writing off your PC isn't good economics.Regarding the DMM, it is probably a clone of another low cost DMM, which someone else might be able to identify. It certainly has a good selection of functions (including good sensitivity on the continuity test), it is probably serve you fine for low voltage stuff - battery / mains adaptor / Bench PSU isolated, but don't trust it for high voltages or mains, anything with an exposed transistor test socket (near the knob) certainly won't meet the 1000V rating. There are plenty of threads on low cost DMMs, do a forum search and check a few recent ones and you may find a better value one (I don't know how much 75 GEL is in other currencies... Ah, about £21 then, not bad).Most DMMs are made in China these days but some are certainly better (and better value) than others.EDIT: Image added to aid identification...

author: Saitama
author_rank: Contributor
timestamp: July 19, 2019, 03:15:00 pm
content: Thanks! Now I can go and buy a new Scope and a DMM without any hesitation.

author: tunk
author_rank: Super Contributor
timestamp: July 19, 2019, 03:38:57 pm
content: Is this an alternative: a Hantek 2C42 for around 110us$.

author: Gyro
author_rank: Super Contributor
timestamp: July 19, 2019, 05:52:42 pm
content: I don't know. They're very different beasts and I've never played with a 2C42.It's one small handheld device versus separate scope and DMM, I don't know how much of both functions you can use at the same time? I don't know whether it has a cost advantage or not. It's clearly a better solution for portable use (unless you're carrying a laptop anyway). Display size is an obvious difference (I think I saw somewhere that the 2C42 can display on a PC but very slowly EDIT: Best to check the thread below).There's a forum thread on the 2C42 series here...https://www.eevblog.com/forum/testgear/hantek-2c422c722d422d72/

author: J-R
author_rank: Super Contributor
timestamp: July 20, 2019, 06:48:22 am
content: For anyone curious about the 400Vpp specification Owon has listed, here is some info:The software for the VDS1022(I) will only allow up to 5V/div on the X1 setting, and has 10 divisions on the screen. So 50Vpp is the typical maximum that can be displayed at once in X1 mode. However, you can adjust the zero point by up to 10 divisions. Adjusted down, I was able to reach 104Vpp before the top of the waveform suddenly became severely corrupted. Adjusted up, I reached 141Vpp before the bottom of the waveform started to clip. I momentarily hit 170Vpp as a test without incident. Obviously the scale was very far off at the higher voltages.The probes provided are rated to 200Vpp (70V RMS) on X1 and 600Vpp (212V RMS) on X10.So a likely explanation is that the (USB) isolated version has a maximum normal operating range of 40Vpp with an absolute maximum without damage of 400Vpp. The non-isolated has a maximum normal range of 40Vpp but does not have a safety net beyond that.The scope worked perfectly in all areas at 50Vpp in X1 mode and 500Vpp in X10 mode.With regard to the case being grounded or not, there appears to be at least three different versions of this scope:1. a copper strap goes around the edge of the PCB between the shielded areas on the top and bottom, making contact with the case2. the edge of the PCB is covered with solder and makes contact with the case3. neither of the aboveAny of the three versions could be easily modified to have their metal chassis grounded or floating.

author: Gyro
author_rank: Super Contributor
timestamp: July 20, 2019, 01:15:21 pm
content: Useful info, thank you. It's always nice when someone else willingly undertakes 'stress testing' of that kind!I've never lifted the input stage screening can to trace out the circuit. I'm not surprised that you experienced severe clipping (presumably either clamping diodes or clipping the first opamp) but I'm really surprised that you managed to get to 104 - 141V p-p before it happened!Yes, regarding the case grounding, I too have seen three versions - as you say, the first version (mine) is ungrounded, (actually with whatlooklike reasonable clearances), the second interim step (there's an example in the main thread) used the copper foil and the most recent (seen in a recent a Youtube video), using the tinned PCB side tracks.There doesn't seem to be any significant difference in noise performance between the first version ungrounded case and the others - There were other differences too, the first version used a switching regulator for the analogue negative rail, whereas the later versions used an LM337 linear reg. It is difficult of course to isolate the contributions of both changes, but it's surprising that there doesn't seem to be any visible effect on noise level.Unfortunately, as most units out there have grounded cases, it is necessary to assume this when giving safety advice.

author: J-R
author_rank: Super Contributor
timestamp: July 21, 2019, 01:43:58 am
content: OK, so is the input circuitry the the same on the isolated/non-isolated versions? Owon is VERY proud of the 400Vpp rating on the isolated version as they have it plastered everywhere. So in your opinion would the non-isolated survive the same tests I performed? Or is the 400Vpp maximum rating due exclusively to the isolation feature which is giving them confidence that destruction won't escape the scope up to 400Vpp?Safety advice is good. For these tests and other times I use the scope with inverters/UPSs/etc., I only make/break connections when the equipment is locked out. And hands off while anything is energized. This is especially important for budget-quality equipment.

author: Gyro
author_rank: Super Contributor
timestamp: July 21, 2019, 12:16:52 pm
content: Yes, as far as I am aware, the input stages are identical. I haven't taken the screening shields off to confirm this but I don't see any evidence that they would be different after all, they have the same input impedance and attenuation ratios.I am as sure as I can be that the only difference between the isolated and non-isolated is the inclusion of the ADUM usb isolator and the TI isolated DC-DC. They both use thesame PCB- there are component footprints to bypass the isolation when absent. The software and download FPGA image (there is only one) are also identical.I am pretty certain that the 400V spec is a confusion relating to the rating of the USB isolation components - not that I would want to test that, particularly on a grounded case (ie. to the BNC skirts) version.It does still get you 400V p-p with an appropriately safe x10 probe of course. Personally I would be wanting to use a dedicated x100 probe at that level though.