Upgrade my DSO... or not? - Page 1
Forum section: electronics / testgear

author: IDEngineer
author_rank: Super Contributor
timestamp: May 20, 2019, 08:38:07 pm
content: It's been feeling like time to upgrade my DSO. I have a Rigol DS4024 with all options including 500MHz bandwidth. It's inperfectshape and I figure I can probably sell it to recover some of its value to apply toward something new.I've mentally allowed a budget of up to ~$4K for a new DSO. I've been reading all the threads, watching the teardown videos, comparing spec sheets, etc. And after all of that... I'm questioning whether it's worth changing.Objectively, I'm sitting here with a 500MHz four channel DSO with 4GSa/sec sample rate, an 8 bit front end, deep memory, reasonably sized screen, and so forth. It's not cheap to duplicate that setup. Yes, it's a Rigol and not one of the "bigger brands", but frankly it works remarkably well for my applications. The 4024's biggest negative is the basically useless FFT but a standalone spectrum analyzer would address that and I already have an HP 8921A that goes to 1GHz until I get a formal standalone SA. Other than the FFT, the 4024 works pretty well.On the positive side, the 4000 series is getting a bit older and so it might be nice to freshen my single most important piece of test equipment. I'll openly admit there's an emotional component here, once in a while it's just "nice" to have a new primary scope on the bench.On the negative side: What problem am I really solving? I don't beat the table every day cursing the 4024 because of some fatal flaw. A 10 bit front end might be nice, but I probably don't NEED it. An even larger screen might be useful, but I'm not squinting today. And is it really worth dropping back to 200-350MHz from 500MHz just to get 10 bits or later firmware?Finally... I'm just not sure I can duplicate this performance within a ~$4K budget. Four channels of 500MHz at 4GSa/sec starts pushing the price tag pretty hard. Maybe I should just buy a can of "New Scope Smell" and be happy with that.I know the folks here can relate to this sort of quandry, and I'm wondering what you'd think if you were considering such a decision.

author: maginnovision
author_rank: Super Contributor
timestamp: May 20, 2019, 10:39:33 pm
content: For $4000 I'd probably keep the Rigol and save it for a newer scope later down the road. Might even catch a good deal on something. Unless you would consider buying used then there are a lot of options...

author: tautech
author_rank: Super Contributor
timestamp: May 20, 2019, 11:09:24 pm
content: Yeah well the new 4ch 500 MHz Siglent is $5,689 however its baby 350 MHz brother is a more digestible $3,569 and there's a BW upgrade option for it........no surprises for guessing what I'm thinking.Just unpacked one before it goes to a customer and first impressions are really good.Really really quiet with a smart fan.Still getting to grips with it...................

author: DaJMasta
author_rank: Super Contributor
timestamp: May 21, 2019, 01:37:33 am
content: Got the same scope (sans bandwidth upgrade) and a lesser budget, but I don't think there's any upgrade in my future for a couple of years yet. I think the killer feature I'd want above others is 10 or 12 bit vertical resolution, and I'm not prepared to dish out for a nice current gen scope, so I don't think it's realistic for me until there are some used ones on the market or some are showing up as clearance deals, i.e. a few years down the line.I think there are definitely better scopes than a Rigol DS4000 series if buying new, but right now the price category is sort of a sidegrade rather than an upgrade for responsiveness, analysis features, and maybe a lower noise floor... and I doubt the resell rate for the DS4000 will cover more than half the new scope's cost... so at least for me, not yet worth it.Agreed that the FFT implementation is sort of obtuse and not that useful, but this was sort of before manufacturers really started focusing on it, so any of the newer generation scopes generally treat it better. FWIW, if I were to upgrade now, I'd probably go R&S, the problem is that as nice as their scopes have been since they introduced, the better vertical resolution has only been in the last generation and a half or so. Keysight's got some good options, but they usually command even more of a price premium, Tek's got some but there seem to be complaints with the UI (from some people and not others?) and the price is still up there.... LeCroy has some decent options, but like the other major manufacturers, the pricetag means the value proposition of a Rigol/Siglent/Used scope just doesn't seem the same to me for home use.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 21, 2019, 01:42:24 am
content: Quote from: tautech on May 20, 2019, 11:09:24 pmOK, forgot to mention silence. The Rigol is a bit louder than I'd like though I haven't been tempted to swap for a quieter fan (if that's possible while keeping the CFM).That Siglent sounds tempting.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 21, 2019, 01:52:49 am
content: Quote from: DaJMasta on May 21, 2019, 01:37:33 amAgreed, that's why I mentioned 10 bits specifically.BTW, something I read somewhere (that's real definite, eh?) suggested to me that the DS4000 series might yield >8 bit vertical resolution under certain conditions. Know anything about that? I didn't dig deeper at the time, I'd have to go back and find whatever reference that was. Maybe we already have >8 bit scopes under the correct circumstances.QuoteAgree again. To me a scope is a scope. FFT is a nice bonus but not really a decision maker. If you need a spectrum analyzer, get a spectrum analyzer. I plan to do so at some point, until then the HP 8921A covers me to 1GHz (though it's an older, analog, monochrome device with none of the fancy computational features we expect these days). At least it has an integrated tracking generator, which I used to wind some ham radio antenna traps for an inverted-V a while back.QuoteExactly. There's no clear winner that screams "BUY ME NOW!" and justifies the decision. It's almost like you have to rank the kind of work you plan to do, then favor that aspect of the spec sheets and settle for second-rate in the other departments. There's a thread going right now about serial decoding that makes some brands stand above the others, but the whole time I'm thinking "I can use a logic analyzer for that, why compromise my choice of scope for a digital serial data stream?"Maybe I'm complaining about an embarrassment of riches. We have a LOT of good choices in scopes these days. It's not like back in the days of analog scopes where they all did pretty much the same thing. These days the feature sets themselves differ quite a bit between brands. In many ways that's a GOOD thing, it's nice to have options.Have to admit, though, it would be nice to be driving a solid R&S or LeCroy. I've never had a scope of that caliber on my bench. Probably never be able to afford one either!

author: IDEngineer
author_rank: Super Contributor
timestamp: May 21, 2019, 01:57:50 am
content: Quote from: IDEngineer on May 21, 2019, 01:52:49 amOK, I couldn't stand it so I went looking and found it. Straight off of Rigol's website, the DS4000 User's Guide says this:when ≥5 μs/div @ 4 GSa/s (or ≥10 μs/div @ 2 GSa/s): 12 bit resolutionHere's the link to the spec sheet, it's right on the first page (which is actually chapter 17 of the user's manual):http://beyondmeasure.rigoltech.com/acton/attachment/1579/f-0169/0/-/-/-/-/file.pdfHowever, a couple of pages later it says this:Vertical Resolution Analog channel: 8 bits, two channels sample at the same time

author: 0culus
author_rank: Super Contributor
timestamp: May 21, 2019, 02:42:27 am
content: Honestly, if a higher end DSO that's got better vertical resolution would make you happier, my recommendation is to save up and buy the one you want.

author: DaJMasta
author_rank: Super Contributor
timestamp: May 21, 2019, 03:25:09 am
content: Quote from: IDEngineer on May 21, 2019, 01:42:24 amNever made mine fully silent, but swapped out the original fan for a Scythe (if I remember right) of slightly higher CFM rating, the slapped some VGA memory heatsinks on the ADCs (or was it the acquisition memory management chips.... one has a heatsink, one doesn't in the original design but both get hot), and it's been going great for... 3 years now? You can't really fit a longer fan because there isn't much clearance, and without modifying the shielding you get some noise from the obstruction of the airflow, but it did make an improvement over the stock fan for me.The new gen Siglents aren't full 10 bit but they do seem to have a lower noise floor than most 8 bit options, so eres mode is less noisy and can give you good results, and while I haven't used the Rigol 5000/7000 series scope interfaces, I was partial to the Siglent UI layout and color grading, so it's at least a strong contender. I'm glad vendors are thinking about fan noise now, makes a big difference to me especially with something that's going to be on a lot on the bench.

author: EEVblog
author_rank: Unknown
timestamp: May 21, 2019, 04:19:51 am
content: Quote from: IDEngineer on May 21, 2019, 01:52:49 amYes, you wouldn't upgrade a Rigol 4000 unless you were going higher bits or something else exotic like GHz region BW

author: EEVblog
author_rank: Unknown
timestamp: May 21, 2019, 04:21:33 am
content: Quote from: tautech on May 20, 2019, 11:09:24 pmMine's not "really really quiet". It's ok, but not that good.A few bugs so far...

author: tautech
author_rank: Super Contributor
timestamp: May 21, 2019, 04:25:30 am
content: Quote from: EEVblog on May 21, 2019, 04:21:33 amFW version ?The one I have has 0.8.2R1 installed.

author: tggzzz
author_rank: Super Contributor
timestamp: May 21, 2019, 07:05:02 am
content: Dropping back bandwidth (from 500MHz) feels wrong, unless there is a spec that is more important to you - resolution would be the best case.If you have money and time available, why don't you consider getting a completely differentclassof test equipment, e.g. adecentlogic analyser, or a spectrum analyser?That might enhance your capabilities and be more interesting.

author: 2N3055
author_rank: Super Contributor
timestamp: May 21, 2019, 07:06:54 am
content: Good question.You could upgrade to second gen Rigol/Siglent 500MHz scopes.That would give you color grading, histograms, better decoding and generally better analysis options.They might have some bugs now, but so had (and still does some) R&S..They would be better rounded instruments.On the other hand, as some suggested "save a bit more and go 10 bit", I just love when people throw statements like that.R&S have nice scopes but for 4000USD target you would have to go back to 100MHz. 500MHz RTM3000 with options is more than 10000USD list price + tax.So no, it's not a bit more saving..OTOH, as you say yourself, if you treat a scope simply as scope, and don't use much of analysis stuff (advanced math, FFT, decoding etc), you really won't gain anything.DS4000 has nice big screen, good bandwidth and works just fine as general use scope.If I were you, I would sit down and put down on a piece of paper what I do (or plan to do) and see if there is other instrument I don't have at all that would benefit me more than getting something I already have and that I won't be using to a full potential. Spectrum analyser, multimeter, signal generator (RF or AWG), VNA ?Regards,

author: EEVblog
author_rank: Unknown
timestamp: May 21, 2019, 07:15:42 am
content: Quote from: tautech on May 21, 2019, 04:25:30 amSame

author: maginnovision
author_rank: Super Contributor
timestamp: May 21, 2019, 07:39:50 am
content: Quote from: 2N3055 on May 21, 2019, 07:06:54 amRight now he could get a fully unlocked1Ghz RTM3Kfor 10K, but I agree, a new scope likely isn't worth it for him. Even the RTB2K fully unlocked is 3700 and would require he lose 200Mhz bandwidth.

author: 2N3055
author_rank: Super Contributor
timestamp: May 21, 2019, 09:08:55 am
content: Quote from: maginnovision on May 21, 2019, 07:39:50 amWell, that would be an upgrade, but at the price that is 250% over his budget, a full 6000 USD more.That is what I said, that is not "a bit more saving"...In my country there are many people that work for 500USD a month. 6000USD is somebody's yearly salary.I'm sorry, that is why "a bit more" statement rubs me the wrong way..Any way, rants aside, I agree with you, even if it was much less to "upgrade" it is not an upgrade if you don't gain new measurements and usability enhancements that you will actually use..That is why I shared my experience that most of the time, you get more if you invest money into capabilities that you really miss and not incrementally upgrading what you already have. Unless your existing equipment is obviously limiting to your work, in which case it is obvious that you need to upgrade.As far as scopes, to go further, if you have SA , FFT migh not be really important. If you have LA, you will decode better with that. Etc etc..I have MSOX3000T as fast general purpose scope, supplemented with Pico 3406DMSO for 512 MPoint long mem, and a 16 bit Pico 4262 for low level, low noise, low frequency measurement (less than 8uV noise floor). I also have Zeroplus LAP-C 16128.There is not much I cannot see, measure or decode with that combination in my work.That is my perfect scope. There is no instrument that does all that in one box, at least not at the prices that are not paid by Department of Defense.

author: tv84
author_rank: Super Contributor
timestamp: May 21, 2019, 09:29:01 am
content: Quote from: tautech on May 20, 2019, 11:09:24 pmIf I had $4000 this option would be the one I would take, because inthis price rangeit's the only one worth it. It's the only option available ATM.With more money, you could get R&S, etc.So, my 2 cents: if a SDS5000X is much better that yours, go for it. If not, keep your money for other things.

author: YetAnotherTechie
author_rank: Regular Contributor
timestamp: May 21, 2019, 10:13:56 am
content: 2N3055 Can any of those LAs decode in real time?Thank you

author: ebastler
author_rank: Super Contributor
timestamp: May 21, 2019, 10:29:47 am
content: Quote from: IDEngineer on May 20, 2019, 08:38:07 pmFrankly, I have not seen any reason in your postswhyyou feel it is time to upgrade? The Rigol you have seems to meet your needs just fine. If you have spare money burning a hole into your pocket, I'm sure there are other desirable gadgets?

author: 2N3055
author_rank: Super Contributor
timestamp: May 21, 2019, 10:47:49 am
content: Quote from: YetAnotherTechie on May 21, 2019, 10:13:56 amWhat do you mean? Firstly, only LAP-C is LA, Pico and Keysight are MSO-s.Secondly, what is real time? Faster than you can read? We had discussion about that many times.Any LA and scope must not miss triggers. You capture and you read if you have hundreds of packets, you stop and read next half an hour. User is slowest part of the system. Do you mean connect to live SPI bus and visually look if there is something going on? Yes they can do that, but that has limited use.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 21, 2019, 11:11:21 am
content: Quote from: EEVblog on May 21, 2019, 04:19:51 amand GHz region BW is not anything near $4K unless you (the OP) are willing to buy used unit. DS4024 is already $4K, so trying to spend another $4K i dont call it an upgrade

author: IDEngineer
author_rank: Super Contributor
timestamp: May 21, 2019, 02:25:00 pm
content: Quote from: ebastler on May 21, 2019, 10:29:47 amI agree, which is why I said "What problem am I really solving? I don't beat the table every day cursing the 4024 because of some fatal flaw." Maybe the biggest reason is "The 4000 series is getting a bit older and so it might be nice to freshen my single most important piece of test equipment."About a year ago I purchased a new laptop. Not because my old one had anything wrong with it, but because I refuse to use anything beyond Win7 for as long as I can hold out, and laptops that either ship with Win7 or have Win7 drivers available from their manufacturer's website are becoming increasingly rare. This scope decision is not identical, but you get the parallel... now that test equipment is so heavily software based it's not just about the raw hardware specs like bandwidth and noise floor and resolution. The software environment is a huge part of what you're buying in scopes these days and I'm wondering if maybe it's time to move forward. Like the laptop/Win7, a purchase decision driven by market forces rather than strictly technical issues.QuoteThat might be the MSRP, but mine cost $2600 new straight from Rigol (not clearance, an actual brand new unit) with all decode options. They're $3K right now on TEquipment not counting the EEVBlog discount, and I see them for around my same $2600 purchase price frequently. The value of an object is its replacement cost, not (necessarily) the MSRP. So this isn't a $4K scope. It's a $2600 scope. (Yes, the 500MHz upgrade theoretically adds value but anyone can buy that same $2600 scope and use the free key generators to unlock the max bandwidth, so again - if it can be duplicated for $2600, it's worth $2600.)QuoteThat's kinda the conclusion I'm reaching. It almost feels like the DS4000 series is something of a sweet spot. As I explain above, you can literally buy a brand new 500MHz 4 channel 4GSa/sec DSO with every option enabled for $2600. I cannot find anything in the market to match that price/performance. Looks like that Rigol is going to be on my bench for quite some time.Thanks for everyone's comments, I really do appreciate them.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 21, 2019, 06:28:26 pm
content: Quote from: IDEngineer on May 21, 2019, 02:25:00 pmi dont think "upgrade" is the right term. i think it is "replacement". such as replacing a dying scope. but since its not dead, if its me, i will use it to its last breath and drop of blood. once its dead then buying (replacing to) another scope it will be. my DS1052E that came back to me gave up its monitor, maybe because it was looking at its replacement (upgrade) DS1054Z unit thats currently sitting on my main working bench right now. i have no time yet to repair.Quote from: IDEngineer on May 21, 2019, 02:25:00 pmi feel you, thats why i will hold on to my old pc bought around 10yrs ago as long as it can. when the time comes to its last breath, i hope there is still motherboard that i can install WinXP in it, i'm lucky i still have the original WinXP CD working, i've made several backup for it in case the original CD got damaged. i really hate newer Windows file explorer and search utility, thats why i hesitate to upgrade. not that i havent try them, i did, and i have installation cd/copy for every newer Windows, even bought a Win10 license not so long ago, what a waste, but they are going in the shelf for now. until i have Windows with better or same easeness as WinXP's Explorer and Search, they are backbone to my workflow, young players will not appreciate nor get the chance to experience.

author: cruff
author_rank: Regular Contributor
timestamp: May 22, 2019, 12:34:42 am
content: Quote from: IDEngineer on May 21, 2019, 01:57:50 amThat's because the 12 bits of resolution are produced by the high resolution sampling mode via averaging. Each input channel still only has 8 bits of ADC.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 22, 2019, 03:07:15 am
content: Quote from: Mechatrommer on May 21, 2019, 06:28:26 pmI'm usually that way, but modern DSO's have become mostly computers with an acquisition deck on the front end. So their feature set changes much more rapidly than the analog scopes of yesteryear. BTW, I still have my original Philips PM3214 dual trace delayed timebase 25MHz pure analog scope sitting here on the bench. And I still use it, there are still things where an analog scope is preferable over a DSO. Thus I totally understand keeping equipment for a long (!) time, but DSO's have changed those rules for me a bit for digital-based tools.QuoteYour biggest risk is that a newer motherboard will have peripherals onboard that won't have WinXP compatible drivers available. That's why I got the new laptop when I did. It hasn't been that long since Win7 was native (or at least a "downgrade" option on Win8 laptops) so I could get a bleeding edge (for ~2 years ago) machine with full Win7 support for all of the integrated peripherals. These days new motherboards and laptops are built with peripherals for which nobody bothers to write drivers that are compatible with older versions of Windows (I suspect there may be some strongarming by Microsoft in that) so unless you are careful to get a platform that has drivers for your preferred version of the OS, you're stuck.Like analog electronics, I generally get 10+ years out of a laptop so I figure this one will keep me running until the latter half of the 2020's. By then, hopefully Microsoft will have figured out that folks don't like OS's that snitch on their users back to the mothership, don't like corporate overlords constantly resetting the user's preferences, don't like "upgrades" that happen on a whim, etc. Or else Linux will have become prevalent enough that I won't feel like an unpaid beta tester every time I try it (again). Linux was fun as a playtoy back in the mid-90's, and the 2000's, and the early 2010's, but these days I need tools to be reliable appliances, not their own separate hobby!

author: David Hess
author_rank: Super Contributor
timestamp: May 23, 2019, 01:16:52 am
content: I have used higher resolution DSOs before and the advantage was always qualitative and not quantitative. I was able to detect things which were not present before but not make measurements which were any better because of limitations in linearity and settling time which remained 8-bits. Any improvement in noise was only in comparison to an excessively noisy 8-bit DSO. My analog oscilloscopes and even sampling analog oscilloscopes had the same advantage in qualitative measurements.A better investment might be additional probes (active, low voltage differential, high voltage differential, current, whatever) instead of a similar but marginally better DSO.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 23, 2019, 04:25:53 am
content: Another good investment could be waiting for a deal. If you're happy with what you have, you can afford to wait for lightning to strike.I have been in a position uncannily similar to OP's for the last few years. I had a hacked Rigol DS4014 that met my needs -- it really is a sweet spot for value -- and I had allotted myself a $4000 budget to "take the next step" but wasn't settled on exactly what form that should take. Better FFTs and annotations good enough to break my sticky note habit were my big requirements, but not so pressing that they forced me to jump at something for sticker price. The RTB2000 launch promotion got my attention so I waited for a RTM3000 launch promotion that never quite happened, but then last monthlightning struck. I scored a used 2GHz Rohde & Schwarz beast from Teledyne Lecroy (crazy) that shipped on April 1 (crazier) and was supposed to be half broken but actually wasn't. Best April fools ever. I got my nice FFTs and sticky-note-beating annotations but also considerably more.https://gph.is/g/am6XlXPhttps://photos.app.goo.gl/2cNXcP9UBJ6m39we6You can't win that big every time, of course. Waiting isn't sufficient, but it is necessary, and the fact that my Rigol DS4014 made waiting easy will forever earn it a fond place in my heart, even though it has now moved on to a new owner.

author: tautech
author_rank: Super Contributor
timestamp: May 23, 2019, 04:33:41 am
content: Nice score.

author: Old Printer
author_rank: Frequent Contributor
timestamp: May 23, 2019, 01:54:39 pm
content: Beautiful looking scope, congrats. You obviously have quite a bit of experience, and equipment, but what gave you the courage to plunk down 4K+ with the item description as it was? Did you have a reasonable expectation the problem was either nonexistent or fixable at an affordable cost? Just curious.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 23, 2019, 05:43:44 pm
content: Yes, I did.Previous successin repairing my DS4014 boosted my confidence and drew my attention to the listing's picture showing four active traces with visible nonzero noise-floors. This suggested that everything from the ADCs on back was OK and that the problem was either in the analog front end (I could build a crummy amp/atten and get it limping if needed) or localized to the space between the scope and chair. As it turned out, the problem was not in the analog front end.

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 23, 2019, 06:25:14 pm
content: yeah with some willingness for the risk, and some skills under the belt, we can go the "used equipment" path. i purchased 3 GHz DSOs (3 units, not 3GHz) so far for around that $4K combined, sold the 2nd before buying the 3rd and covered the cost of some GHz active and differential probes. but do mind they are boat anchor type, not slim the latest tech type. ymmv.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 23, 2019, 07:53:01 pm
content: IDEngineer, thanks for this thread. I own a DS4014 fully unlocked, with upgraded heatsinks and fan and for several times I thought about the same thing: should I freshen my main test gear or should I simply run until its encoders fall off? The ensuing discussion here shows some very nice alternatives and made me stay put for this time. The DS4000 series from Rigol is a solid performer.As Mecha mentioned, you may go the used route - a used Keysight DSOX3014A (hackeable), for example, can set you back at around $2200 and a new one can be had for $3400 (fleabay US). However, what you gain in UI responsiveness you lose in memory depth and bandwidth if you don't hack it. YMMV.

author: 2N3055
author_rank: Super Contributor
timestamp: May 23, 2019, 08:04:25 pm
content: Quote from: rsjsouza on May 23, 2019, 07:53:01 pmMake note that DSOX3000A exist in 100/200MHz, 350/500MHz and 1GHz hardware board version.So 100 MHz goes to 200MHz, 350MHz to 500MHz with software unlock.If you want to upgrade 100MHz to 500MHz, you need serious soldering on mainboard...Doable and there are details on EEVBLOG.. But not really just a software hack.

author: Martin72
author_rank: Super Contributor
timestamp: May 23, 2019, 08:29:49 pm
content: Quote from: EEVblog on May 21, 2019, 04:21:33 amWhere´s your review ??

author: IDEngineer
author_rank: Super Contributor
timestamp: May 23, 2019, 10:46:55 pm
content: Quote from: rsjsouza on May 23, 2019, 07:53:01 pmYep, same conclusion I'm reaching. The DS4000 series is hard to beat if 500MHz and 4GSa/sec is enough for your purposes. And honestly, I bet that covers 90% of what most EE's and hobbyists actually work on most of the time. This thread has quenched my curiosity into a new scope, and renewed my faith in the DS4000, to the point that it will be my default recommendation for most people unless they need to stay under $1K or truly need performance over 500MHz and 4GSA/sec. The good news for Rigol is there are a LOT of folks in that middle ground for whom the DS4000 is an absolutely killer deal. Unless I get my hands on something else in the midrange, I'm directing people toward the DS4000 and that will probably make Rigol a lot of money, since I'm sure they've amortized their R&D costs on that line long ago. It's got to be a pure cash cow now.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 23, 2019, 10:54:27 pm
content: Quote from: David Hess on May 23, 2019, 01:16:52 amTrue. In fact I already have a low voltage differential probe (Pintek DP-60HS) that is my second most important piece of test equipment after the scope. So much so that I've been tempted to buy 1-3 more just so I can have more channels of fully differential input. I work on a lot of isolated circuits and the diffprobe has made some impossible measurements possible.One thing that would be nice to have is one or morefully isolatedlow voltage diffprobes. Like seemingly everyone else on here, I have some ideas for a novel architecture, in my case incorporating some of the tricks I've learned designing ultra-high-isolation circuitry. Maybe someday,right?I've also promised myself I'm going to get one of those old Tek DC/AC clip-on current probes with their little TM5xx amplifier. I used one back in the 80's and really liked it. Would be nice to have one again.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 24, 2019, 01:10:18 am
content: Quote from: IDEngineer on May 23, 2019, 10:46:55 pmI usually recommend the DS4000 series if the price is right, given the more modern architectures from them (5000 and 7000 series) seem to bring more to the table at a somewhat lower cost - although they are a new platform still plagued by several bugs. I got mine at a real bargain from their clearance store.It seems Rigol has been somewhat snappier in fixing those when compared to the DS4000 series, which was very frustrating for several users of this forum that intercepted this model at an earlier stage. Mine was a later purchase (2015) and the severe issues were already fixed, that's probably why I still have a good impression of it.

author: David Hess
author_rank: Super Contributor
timestamp: May 24, 2019, 02:33:33 am
content: Quote from: IDEngineer on May 23, 2019, 10:54:27 pmDifferential and isolated operation usually conflict so I am not aware of any probes like that. Most differential probes will not operate correctly with an isolated oscilloscope channel and better ones have a warning to this effect.Isolated single ended probes exist and are very useful. They have better high frequency common mode rejection than a differential probe but require a low impedance common connection to the circuit under test which is usually not a problem.QuoteThey are very nice and there are some modern equivalents. I get by with just a 50 MHz Tektronix AC only current probe.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 24, 2019, 07:43:20 pm
content: Quote from: David Hess on May 24, 2019, 02:33:33 amThat's why I said I have some ideas for the architecture.QuoteAgreed, and if I ever get the chance to pursue this isolated probe idea I'll start with single ended to prove things out, then tackle the differential aspect. Even if the latter isn't successful I'll end up with a useful tool.QuoteYep, AC only makes it easier. But I do enough low frequency stuff that DC is important to me.

author: David Hess
author_rank: Super Contributor
timestamp: May 24, 2019, 11:24:55 pm
content: Quote from: IDEngineer on May 24, 2019, 07:43:20 pmIt is not difficult to fix. The "ground" for the differential probe needs to be connected to "ground" of the circuit under test. The problem is that common high voltage differential probes do not provide this connection point (for good reason, people might use it) although you could use the output "ground".QuoteThese days the isolation for each channel is usually built into the oscilloscope itself but in the past other methods were used.QuoteThe only substitute for an AC/DC probe is to make a different measurement. They are invaluable in applications which demand them.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 25, 2019, 05:54:44 pm
content: Quote from: David Hess on May 24, 2019, 11:24:55 pmYep, a path for the bias current. Can be a problem, unless the measuring circuit is truly isolated from the rest of the world (in which case it can be safely connected to the circuit under test). BTW, I'm not targeting high voltage measurements, my interest is in small signal environments.

author: tggzzz
author_rank: Super Contributor
timestamp: May 25, 2019, 06:42:12 pm
content: Quote from: IDEngineer on May 25, 2019, 05:54:44 pm"Bias current" is incorrect in this context; it isn't an op-amp input! With probes placed incorrectly, high currents can flow, where high implies destruction of electronics, wires (as in they disappear), and potentially people.Note that David Hess puts quote marks around the word "ground". That too is a misleading term; in industrial contexts there can be many volts between points that are all nominally "ground".

author: IDEngineer
author_rank: Super Contributor
timestamp: May 25, 2019, 06:49:01 pm
content: Agreed, I was generalizing my terminology. A bit of laziness showing through. {grin}Your point about different "ground" potentials is spot-on. My point was that, if the portion of the isolated probe that is doing the measuring is truly isolated, its "ground" could be raised to the nonzero potential of the "ground" in the DUT without ill effects as long as common mode limits aren't exceeded. As to the latter, you can provide protection to some degree but ultimately it's the user that must close that loop and make sure limits aren't exceeded. That's all the most true for highly sensitive equipment meant to measure the smallest of signals.

author: David Hess
author_rank: Super Contributor
timestamp: May 25, 2019, 11:08:14 pm
content: Quote from: IDEngineer on May 25, 2019, 05:54:44 pmAs far as I am aware, all low-voltage differential probes provide the "ground" at the probe tips as a third connection in one way or another and there is an expectation that it will be used. This is one thing which distinguishes low-voltage and high-voltage differential probes.Quote from: tggzzz on May 25, 2019, 06:42:12 pmThat cannot happen with a high voltage differential probe, at least between the differential inputs, because the impedance (and voltage rating) between the differential inputs is high.The problem comes about when a high voltage differential probe is connected to an isolated input. Now the common mode voltage cannot be attenuated by the input dividers because they have no connection except to each other. With the common mode voltage unattenuated, the high-voltage differential probe "ground" can charge to the input common mode voltage presenting a safety hazard and eventually causing breakdown at the isolation barrier which should not have been used.So the common mode rating of a high-voltage differential probe, which can be thousands of volts, does not apply if its common terminal is not connected. Typically the common terminal is connected through the oscilloscope input ultimately to earth ground but this does not happen on an oscilloscope with isolated inputs.A similar problem occurs with common x100 passive probes when AC input coupling is used.QuoteI used the quotes because it is more properly called "common". The differential input voltages are referenced to the probe's common terminal which may or may not be attached to actual ground. This is one of those cases where using the correct term can just lead to further confusion.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 26, 2019, 01:04:24 am
content: Quote from: tggzzz on May 25, 2019, 06:42:12 pmWRT this: There are quite a few diffprobe designs floating around that use opamps configured as differential amplifiers. Quite a few on this website, in fact.

author: 2N3055
author_rank: Super Contributor
timestamp: May 26, 2019, 08:15:40 am
content: Quote from: IDEngineer on May 26, 2019, 01:04:24 amTo be more accurate, diff probe is actually nothing more than instrumentation amplifier. A special version that is either really fast or has really robust inputs with large common voltage range.And I guess you could say they have input current that you could call bias, but it is not called so. With probes, it is simply input impedance, both differential (between the inputs) and single ended (towards "ground").And they all have third connection for common reference potential.High speed low voltage probes come with "ground" terminal because of low common mode range and to maximise CMRR and minimise various spurs in signal...Connection to the ground will be short and local to DUT.For a high voltage probe that is not so critical, so their third terminal ("ground", I actually like this quoted term for common reference potential) is directly connected to scope grounding.Any common voltage on inputs gets suppressed by CMRR of the probe. That is why they don't usually have third connection, except some do, and a warning it has to be connected to protective ground or some common reference plane in SUT if your scope input is floating (is isolated from common frame of reference). That would happen if you (not recommended) float your scope, or if you have proper isolated channel scope, in which case you mostly don't need diff probe. Unless you want to use diff probe anyways, because it is more robust, or you want to repeat previous measurement so you want to compare with the same circuit loading (same probe).One not very much discussed point in having a diff probe is mostly overlooked. People speak about reference planes and grounds, dangers and such.To me, best explanation why you need diff probes, and their most useful characteristics is this:With classic grounded (passive or active) probe, you take GND wire from the probe and connect it to GND of your circuit. And then you probe various SINGLE points in circuits. So you are observing a signal at certain net in a circuit. So if you imagine stack of batteries, you can measure voltage on first battery, and then voltage on second battery (that will be in series with first one) etc.If you wanted check a voltage of every individual cell (you want to check if cells are good), you cannot measure voltage ACROSS every cell, like you can with multimeter. Connecting grounded probe across third cell will connect scope ground in such a way that it will short first two cells and kill your scope if there is enough current in them.Diff probes will allow you to do just that. With them you can measure across the components. Between two arbitrary points, not only potential on that net in regards to ground.Like you do with multimeter, and that makes them very useful when trying to understand what is going on in a circuit.Of course, with usual disclaimer that they have input impedance (complex one) that is usually lower that other probes. So they can interfere with high impedance circuits.Like any probe. connecting them to circuit can change circuit behaviour.. So you have to understand both probe spec and circuit you're measuring.Probe is a part of the circuit when connected.* CMRR is common mode rejection ratio, for those that don't know.SUT- system under test

author: Old Printer
author_rank: Frequent Contributor
timestamp: May 30, 2019, 01:08:15 pm
content: Quote from: jjoonathan on May 23, 2019, 05:43:44 pmThe Keysight person between the scope and chair left a lot of money on the table for Keysight to give away. I am happy for you and your good deal, and have to wonder if someone higher up at Keysight might trip across this thread and track down the missing link

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 30, 2019, 01:57:40 pm
content: It would have been a LeCroy person, unless there was a Keysight spy infiltrating a LeCroy facility to sell me a discounted Rohde and Schwarz scope, which is probably one level of silliness too far.In any case, I've seen these sales go down from the other side. If I were in a supervisory position my biggest fear would not be that the person in charge of liquidating the old equipment rack left an extra 20%-50% on the table because they weren't familiar with the quirks of an instrument we were selling 1 of. A 100x larger fear would be that in chasing down the "missed opportunity" and berating the seller I would inadvertently encourage the corporate path of least resistance, which is to let a $200k rack of used equipment sit in a corner and gather dust until it has lost 90% of its value and then sell it to the nearest liquidator for 10% of the remaining 10% -- with employees barred from bidding, because *that* would be a conflict of interest.Recovering 50-80% of the value in an unused asset really isn't bad at all by the corporate standards I've seen.