Professional Scope Purchasing Criteria - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: November 30, 2014, 07:27:42 pm
content: I have been upgrading my bench as my skills grow. Moving from low-end, hobby type gear to instruments intended for professional level work. First major change was getting a really solid power-supply that supports GPIB allowing me to script automate tests etc. Awesome. I have chosen a 6.5 digit DMM, programmable electronic load, thermal wire strippers, pick and place machine, and a number of other pieces that will help me focus on design instead of wrestling the limitations of my tools.Next major decision is a scope. The current scope is a starter model from Rigol DS1102E. I would never complain about this little guy considering the super low price point. It is, however, very basic. Time for more channels, performance, features, etc.It looks like I should be budgeting $3k - $5k to get a mixed signal 4ch scope - although that is only a guess at this point.I would really like to have at least the following:Upgradable speed - starting with 100Mhz is fine as long as I can upgrade to 500Mhz for a cost later.4 analog channels.Logic analyzer built-in with protocol analysis. Triggering on a defined packet would be great.external monitor connection would be nice for better visibility.Some decent way of interfacing with a PC to capture and save waveform data and screen grabs. Rigol sucks in this category.When I purchased my Rigol scope at ~$400 USD, my expectations were low. If it turned out to be totally useless, $400 is not a total financial disaster. In the higher-end, I am hoping to get it right the first time. Day-to-day use-ability is just as important as the electrical specs in my opinion. The hardest thing to get from the data sheets is what my daily experience will be like. Hopefully, some of the forum members have some experiences to offer on various brands and/or product lines that may help.Electronics has become a critical component in my business (I still do mechanical engineering as well). For this reason, I am willing to pay for the tools that minimize design time and provide room to grow. Rigol was a great way to get my feet wet, but it seems that their DNA is in making products to b as low-cost as possible. I would prefer to have a brand with a focus on making the product as good as possible.Thank you all.....

author: tautech
author_rank: Super Contributor
timestamp: November 30, 2014, 07:33:46 pm
content: Could you state where you are or better sill put your country flag in your profile.Will you be considering used?CRO or DSO ?

author: rx8pilot
author_rank: Super Contributor
timestamp: November 30, 2014, 07:45:31 pm
content: Quote from: tautech on November 30, 2014, 07:33:46 pmI am in the USA, California. (updated my profile as well)I will not immediately discount getting a used scope, although the newest models seem to offer a lot more than models even a few years old. I purchased a used power supply after being adamant that only new would work. I quickly found, with the help of this forum, that used power supplies can be a fantastic choice. It seems less likely in the scope category that is rapidly changing relative to power supplies.What is a CRO?

author: tautech
author_rank: Super Contributor
timestamp: November 30, 2014, 08:00:28 pm
content: QuoteCathode Ray Oscilloscope..... uses a CRTMany up to 20 yrs old LCD scopes from the likes of Lecroy, Tek, Agilent etc should meet your requirements, however their bench footprint is usually large along with power requirements.Some have a Windows based UI and also are fitted with a HD that are now getting dated.Boot time also need to be considered and might be frustrating for your use.A modern DSO might be the way to go.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 30, 2014, 08:11:08 pm
content: Quote from: tautech on November 30, 2014, 08:00:28 pmAside from that 20 years ago the only LCD scopes were those with very low resolution black & white displays, not all older scopes are huge and power hogs. And newer scopes aren't necessarily much smaller or use less power.QuoteHard drives are easy to replace on most scopes and cheap like chips these days. Boot time is probably more an issue for a hobbyist who uses his scopes for a few minutes only and not for a professional.And it's not that the boot times of new scopes is necessarily much shorter anyways.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 30, 2014, 08:34:52 pm
content: CRT? nope. I have had a few over the years and the modern DSO is definitely where I need to be.I have taken a website look at Agilent  and Tektronix. Both look pretty great, especially when looking at the modular design. They also offer some interesting ways of analyzing the signals, but it is hard for me to tell the difference between marketing flash features and features that may give me a real edge in tracking down issues or measuring performance. The marketing from both is super slick and polished and I see 'ideal' scenarios to demonstrate various features.While I don't know for sure, it does seem that the size of the scopes with similar features has shrunk. I don't really care about boot time as it would boot up in the morning while I am still working on a cup of coffee and stay on all day. Small physical size is a real feature for me, but I could probably deal with an older/bigger unit.it also seems that integrated mixed signal and/or mixed domain scopes are relatively new. Can't go back too far before you see those as multiple instruments. Being able to trigger on i2c data and see what analog event is happening is pretty great.I have used the basic Tektronix 200Mhz 4ch DSO's and it was really easy to use. The LCD was low-res, but it was easy to use. The newer versions with bigger hi-res displays seems really appealing. One of the things that scares me is that I will find that once I get it on my bench, I find that a frequently used feature is buried 3 levels deep in a menu. The marketing people will always avoid those situations in a demo so I would rely on a real engineer to point those details out.

author: tautech
author_rank: Super Contributor
timestamp: November 30, 2014, 08:39:17 pm
content: Quote from: Wuerstchenhund on November 30, 2014, 08:11:08 pmI said up to 20 yrs..... that covers a shit load of models, B&W and color LCD.Any modern scope that doesn't use less than 100W is a power hog.Who needs an extra thig like a HD to worry about.....any body know of a scope that is fitted with a SSD as standard? That might be more acceptable, power usage, reliability and boot times.With a modest 3-5 K budget you will still have plenty of choice of good SH models.Only a few manufacturers offer BW upgrades, so that might limit your choices.

author: AndyC_772
author_rank: Super Contributor
timestamp: November 30, 2014, 08:55:42 pm
content: You've pretty much described the Agilent 3000X series with the LAN/VGA card.I use mine on a daily basis, and it's become a tool that I use without thinking. That's high praise.

author: nanofrog
author_rank: Super Contributor
timestamp: November 30, 2014, 09:06:44 pm
content: I have two words for you;Trial Program.Seriously, it appears the MSOX3014A is right at the limit of your budget (MSRP of $5,209; 500MHz version is $12,016) and low-end of the specs you listed, but you'd be a fool to just buy one with the expectation it's the perfect scope for your needs.Another alternative might be a DSO + separate Logic Analyzer. A Salae LogicPro16 might be sufficient for your embedded work for now, and would be cheaper than an MSO (8GB version is $499; does require a computer). DSOX3024A + LogicPro16 = $4740 MSRP for example. Not only cheaper, but you get an additional 100MHz of bandwidth. Something to consider at any rate IMHO.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 30, 2014, 09:21:39 pm
content: Quote from: nanofrog on November 30, 2014, 09:06:44 pmThat is good advise. I have seen some rental options as well that can really help get to the right permanent choice. I have a Salae analyzer and love it - for the price. There is no way to trigger on a specific packet so I have to jump through hoops to find what I am looking for. The analog inputs are cool, but obviously not an oscilloscope. My price range is merely a guess - I would be willing to spend more to get the right box on my bench. I learned a long time ago that going cheap on tools is generally a poor way to save money. I may save a few $k on the initial purchase and then work slowly around the limitations of the tool for years to come - missing opportunities along the way. Right now, I am trying to form the real budget. Obviously, I don't want to over-spend either.Quote from: AndyC_772 on November 30, 2014, 08:55:42 pmThat is good info. Real world.If I start with 100Mhz, can I upgrade all the way to 500Mhz or 1Ghz? That process or price was not clear on the website.

author: Someone
author_rank: Super Contributor
timestamp: November 30, 2014, 10:41:44 pm
content: Quote from: rx8pilot on November 30, 2014, 09:21:39 pmThe upgrade prices are a little hard to find, but you pay close to or slightly more than the current price difference between the models. Its an option but you return it to the service location and they replace the acquisition board when you step up to the 350/500MHz or 1GHz bandwidths.The prices for theAgilentKeysight 3000 series haven't dropped since launch which is a sign of their desirability, and they are usually running some sort of deal for discount option packages. If you are certain on the options you will need you will be able to get options for much cheaper if you negotiate buying them up front with the scope, but it does raise the price of purchase.In this price range you should be able to get your local office to lend you a unit for a few days, offer to pick it up and drop it off from their location if you are located close to them. This applies to all the major brands, Keysight, Tektronix, Lecroy, Yokogawa, Rigol, etc.I have an Agilent 3000 that is my daily scope, couldn't be happier with it. I've used scopes of all levels from all the major brands and am happy working with specific scopes from Tektronix, Agilent, and Lecroy models, all those manufacturers have made some bad scopes but they have some great ones in the mix though few of them would meet your desire for a built in logic function.

author: nanofrog
author_rank: Super Contributor
timestamp: November 30, 2014, 11:31:26 pm
content: Quote from: rx8pilot on November 30, 2014, 09:21:39 pmGive the MSOX3xxxA series a try, and see if this will.Past that, you'd be looking at a separate DSO + LA IMHO (better from a technical POV IMHO <see more of what's going on + easier to use w/ second control panel & less cluttered UI of an AIO device>, but also more money for full fledged units).Quote from: rx8pilot on November 30, 2014, 09:21:39 pmI would agree. Hard to figure out though, and the trial programs are a genuine necessity IMHO (technically, you buy it first, with a long-ish return policy, say 30 days, possibly more).Quote from: rx8pilot on November 30, 2014, 09:21:39 pmIIRC, it's a firmware upgrade/s to 350MHz, and hardware change past that for 500MHz and again at 1GHz (not sure if they send you a new unit & you send yours in after <eliminate loss of instrument>, or what). But from a technical POV, they've made it possible to go from the bottom 100MHz BW models to the max of 1 GHz.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 30, 2014, 11:44:01 pm
content: Quote from: tautech on November 30, 2014, 08:39:17 pmJust to remind you what you wrote:Quote from: tautech on November 30, 2014, 08:00:28 pmWhich is nonsense, really, not only because usable LCD screens have been in scopes for a lot less years, but also because it's silly to buy kit that old for professional use, as such old gear is usually closer to the end of its functional life (and often already way beyond its useful life). Anything that is out of support is generally a very bad idea for professional use, which means depending on the support policy of the manufacturer that the scope should not be older than say 5 to 8 years.Quote100W may seem a lot for you, but it really isn't. Of course if you only look at low end stuff like Rigol or Siglent scopes then 100W sounds like a lot, but even if you look at mid-range scopes with fast processing and sample rates 10x as much as your low end lunch boxes then often the acquisition system alone can easily consume 100W or more. A modern high-end scope can easily exceed 600W.Is it a lot of power? Yes. Does it make it a power hog? Not really.QuoteMost of the better scopes run Windows (not just some cut down Embedded variant like Win CE), so some mass storage is needed. A new hard drive is roughly $50. If that amount causes you headache then you've got your priorities seriously wrong.QuoteSome current Windows scopes now come with SSDs instead of hard drives. But many still come with hard drives.QuoteNot really. SSDs have around the same power consumption as 2.5" SATA hard drives (laptop drives), some SSDs even exceed that. Reliability isn't necessarily better with SSDs, as various examples have shown, and hard disks can easily serve for mony years (especially when they're running more constantly and don't have to suffer from lots of on-off cycles). In addition, you need a OS with TRIM support to maintain an SSD's performance, which only became available with Windows 7. Older scopes however run WindowsXP (or even Windows 2000) and for those OSes the standard hard drive is still the better choice. Especially in an application like a scope where drive performance is close to irrelevant.And as I said before, boot time may be an issue for hobbyists, but for a professional who powers the instrument up at the morning and down at night (or even leaves it running 24hrs?day) boot time is simply irrelevant. Especially when boot time also includes checking the hardware which on an advanced scope can easily take much more time than on some el-cheapo low end box.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: November 30, 2014, 11:50:37 pm
content: Quote from: rx8pilot on November 30, 2014, 09:21:39 pmI wouldn't put too much emphasis on the bandwidth upgrade, you're paying through the nose over the years and still end up with a scope with limited capabilities. It's not worth it.Think about how long you want to use the scope, and then about what you want it to do within that time. And then buy a scope now that fulfills these requirements.

author: tautech
author_rank: Super Contributor
timestamp: November 30, 2014, 11:58:09 pm
content: QuoteAt this point we did not know if a LCD or CRT scope was acceptable.WuerstchenhundAll the points discussed are informative and possibly enlightening forrx8pilotas they should be in a thread like this.Knowledge is the key, lets get on and provide it.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 01, 2014, 12:01:44 am
content: Well, I just went the the online configurator on the Tek site with an MDO3024 - 200Mhz/4ch with logic options and logic trigger software. Clearly I need to be prepared to spend $7k+ if going that route. The cost of going from 100Mhz to 200Mhz is $500, so hardly worth doing that later. It's kinda crazy how they break up the software options. $1,100 for the i2c/SPI analysis and another $1,100 if I need to do CAN and another $1,100 if I need to do 422. Starts to get serious. The good news is that I can wait until I have the need and then spend the money which is way better than spending $15k+ up front and hoping I use half the features.It looks like Keysight has a similar configurator as well to get guideline pricing. The only difference I can see from Tek to Keysight is user interface related. They seem very similar in technical respects.Probes could be a killer that I overlooked as well. I like the idea of having an active probe and a differential probe for what I am doing now. Although I knew they were pricey - I did not expect them to exceed the base price of the scope. Welcome to the big time i guess

author: rx8pilot
author_rank: Super Contributor
timestamp: December 01, 2014, 12:18:29 am
content: Quote from: Wuerstchenhund on November 30, 2014, 11:50:37 pmI am on the fence with the concept of "upgradability". If I have an instrument that works well for my relatively simple needs of today, but find that I need a whole new scope to move up to some higher speed project, could be a life saver. All new 1Ghz scope with options may be  $20k, but an upgrade would be $10k.My biggest challenge is guessing what I may be doing during the lifespan of the instrument. At the moment, I am doing 8bit embedded power controllers. I am hoping to get into some FPGA based image processing projects. Clearly, the scope needs are different with those two things. I don't know if those plans will ever happen and would not want to pay for the high-speed today. It's possible that my current product family may be all I do for the next few years.On the other hand, upgrading a 2-3 year old scope may be less desirable than getting the latest tech available and using the older scope for another task. What a challenge to figure it all out.

author: nctnico
author_rank: Super Contributor
timestamp: December 01, 2014, 12:54:42 am
content: Quote from: Wuerstchenhund on November 30, 2014, 11:50:37 pmI agree. Better buy an oscilloscope which fits the purpose now and buy a different one when requirements change. By that time that oscilloscope will have newer bells and whistles. Maybe consider spending less and buy a mid range Rigol or Siglent. The time to buy equipment to last for 20 years is definitely over. Technology is changing too rapidly for that. A good example is serial protocol decoding. All the old scopes don't have this feature which makes them much less attractive than buying a new oscilloscope.It may also be a good idea to buy a specialistic second hand oscilloscope (high bandwidth for example) and a new general purpose oscilloscope.

author: RRobot
author_rank: Regular Contributor
timestamp: December 01, 2014, 12:57:03 am
content: You might also consider getting a used/remanufactured one from Keysight on their ebay store. If they say 'Premium' it usually comes with a three year warranty, note some don't, so look at the description.http://stores.ebay.com/Keysight/PREMIUM-Used-/_i.html?_fsub=874614011&_sid=869664151For example here if a 500MHz MSO for 6K, its possible they might go down to $5500:http://www.ebay.com/itm/Keysight-Premium-Used-MSOX3054A-Oscilloscope-500-MHz-Agilent-MSOX3054A-/181598244400?pt=BI_Oscilloscopes&hash=item2a48194e30Its unfortunate the upgrade to the ultimate scope promotion ended today.They have less expensive models as well.

author: LabSpokane
author_rank: Super Contributor
timestamp: December 01, 2014, 01:37:32 am
content: RX8...Take a hard look at Agilent/Keysight's eBay store. Their "Premium" scopes are 40% off and ship with a full warranty. It doesn't make a 500 GHz scope "cheap" by any means, but it's an awesome deal if you can wait the 3-4 weeks for them to refurb a scope and turn it around to you.I just read that the upgrade deal ended. I'm betting that it will reappear soon. If not, see if they'll do the upgrade before shipping as part of your offer price. Keysight is very responsive.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 01, 2014, 06:31:30 am
content: Quote from: tautech on November 30, 2014, 11:58:09 pmTrue, but honestly, we're in 2014, and CRT scopes have been a dead end for roughly 15 years now. Buying an old boat anchor with a CRT may be fine for a hobbyist (especially if his budget is tight) but for professional use it's simply a no-no.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 01, 2014, 06:38:09 am
content: Quote from: rx8pilot on December 01, 2014, 12:01:44 amHave you considered LeCroy? Their WaveSurfer 3000 might be what you want and should be within your budget:http://teledynelecroy.com/oscilloscope/oscilloscopeseries.aspx?mseries=466It's a pretty new model and from what I know they're working on expanding serial decode support to include more protocols.There's also the new WaveSurfer 10 with 1GHz bandwidth which price-wise should be in the same ballpark as a Keysight DSO/X 3-54, although it's much more powerful than the KeySight:http://teledynelecroy.com/oscilloscope/oscilloscopeseries.aspx?mseries=470Another option would be a second-hand scope. There often are newer LeCroy scopes on ebay that already come with all options enabled (ex demo scopes). For example, another member (TunerSandwich) recently bought a WaveRunner 64MXi (600MHz 4Ch MSO with 10GSa/s and 1.25M wfms/sec), can't remember the price but it was well within your budget. There also was a WaveRunner 6100A (4Ch 1GHz 10GSa/s) with all options which went for around $4k. I bought a WavePro 7300A (4Ch 3GHz 20GSa/s) recently, again with all options enabled, which is a large scope but also would have fit comfortably in your budget. All these scopes are much more advanced than the KeySight DSO-X 3K Series and not only decode RS232 and CAN but also lots of other stuff like USB, Fibre Channel, Ethernet, Firewire, USB and so on.LeCroy also fully supports all of their scopes for 7 years after a series wents out of production which is much longer than what both Tek or KeySight offer, and repairs most of them even way beyond that period (they still do repairs on 9300 Series scopes which went out of production around 1998!). If you buy a scope that is within the 7 year support period you can also buy warranty for it from LeCroy if you send it in for calibration.If I remember right TunerSandwich was in a similar situation as you (looking for a better scope for his business) when he bought his 64MXi. Have a look at the related threads in this forum.

author: EEVblog
author_rank: Unknown
timestamp: December 01, 2014, 06:40:48 am
content: Quote from: rx8pilot on November 30, 2014, 07:45:31 pmGreat value can be had in the US market for refurbished scopes.

author: EEVblog
author_rank: Unknown
timestamp: December 01, 2014, 06:43:41 am
content: Quote from: rx8pilot on November 30, 2014, 09:21:39 pmWith the Agilent's, no. The 300M/500M/1G models uses a different board to the 100M/200M

author: EEVblog
author_rank: Unknown
timestamp: December 01, 2014, 06:47:51 am
content: PM sent to rx8pilot re 3000X scope.

author: coppice
author_rank: Super Contributor
timestamp: December 01, 2014, 07:01:51 am
content: In instrumentation "flexible and "upgradeable" are generally code words for sucking more money out of customers. Some recent products can be upgraded up simple software changes, and these are probably OK in general. Things requiring chunks of hardware be replaced usually ends up costing a lot more, and only a small percentage of units ever get upgraded.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 01, 2014, 08:21:42 am
content: Quote from: RRobot on December 01, 2014, 12:57:03 amYou are right! 200Mhz 4ch+8digital for $2500! At that price I can spend some money on active and differential probes too. When/if I out grow that model, I would not care so much about any upgrades, I would simply replace it and re-purpose or sell the older one.Refurbs may be a great option.

author: LabSpokane
author_rank: Super Contributor
timestamp: December 01, 2014, 11:27:04 am
content: Refurbished is an option you'd really be crazy not to consider in the US. The scope will come from Malaysia likely, but we don't have customs issues like other countries do. My experience was amazingly painless and I got a MSOX2024 for a bit less than $2500 all in with sales tax. It also ships FedEx so there's very little time in transit for something bad to happen to it.

author: Someone
author_rank: Super Contributor
timestamp: December 02, 2014, 12:08:26 am
content: Quote from: rx8pilot on December 01, 2014, 08:21:42 amThe 2000 Series do not support active probes, have fewer options available, and have less memory accessible, you get what you pay for.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 02, 2014, 12:54:01 am
content: Quote from: Someone on December 02, 2014, 12:08:26 amYou saved me from making a poor decision, Than you. I do not want to eliminate active probes right off the bat.Tek MDO3000 or Keysight X3000 seem to be the top choices so far. I can see and touch both of them in the same place close to where I live. The Tek has spectrum, but I don't need that right now and have no plans to need it. Who know what the future holds - RF is pretty far outside of my comfort zone.

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2014, 01:02:01 am
content: For a 200 MHz scope you don't really need an active probe anyway, ordinary probes will be fine.A powered differential probe should have alternative means for power supply.Separate PSU or USB or battery are the usual options.Failing that you can use 2 normal probes and engage the DSO maths.

author: robrenz
author_rank: Super Contributor
timestamp: December 02, 2014, 02:21:23 am
content: Quote from: tautech on December 02, 2014, 01:02:01 amWon't CMRR be vastly worse with that method?

author: coppice
author_rank: Super Contributor
timestamp: December 02, 2014, 04:11:14 am
content: Quote from: robrenz on December 02, 2014, 02:21:23 amBoth CMRR and dynamic range are problems with that method. Sometimes AC coupling removes the dynamic range issue, but if you really need DC coupling to properly see the nature of the differential signal you are stuck. DSO maths as a differential tool is useful, but far less useful than a real differential input.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 02, 2014, 07:11:57 am
content: Quote from: coppice on December 02, 2014, 04:11:14 amJust so it is clear, EE is my second career so I do not have a lot of experience. I come from the ME world and have owned multiple businesses including soup to nuts manufacturing. What I learned is that asking smart people good questions tends to reveal useful answers. Here is an example of what I am trying to measure, maybe you have some insight....Measuring dI/dt across a sense resistor. On the low end, its only a few mV while an inrush spike may be a few hundred mV. My thinking is that the dual probe method would be too crude to make this even remotely accurate. This is what I was planning to use a differential probe for. The good news is that this a low speed event that could easily be captured by a low cost BK PR-60 (at least I hope it would work)http://www.tequipment.net/BKPR60.html?v=0If that is a workable solution, then the auto-ranging self powered probe ports on the higher-end don't really help for that particular scenario. That little guy is self powered. I am still questioning whether this is the right approach to measuring transient current. One note is that the sense resistors are already in the circuit - not as an external measurement fixture.For the single-ended active probes, I don't have a specific need and agree that at 200Mhz they won't do much more than burn a hole in my checkbook. I was only considering those if I developed the need for speed and upgraded the box to a 1Ghz - I would appreciate the having the integration. It seems that most of the active probes I have seen on the market are expecting the integrated interface. I did not understand they could be used with external power. So, single ended active probes are merely a consideration for the future.Side note on my tool purchasing philosophy that has served me well. I have always purchased way more tool than today's job calls for to give me room to grow. For example, when I needed to machine a bunch of simple parts i went out and did some research and came home with a brand new 5 axis CNC mill. It was FAR beyond any skill that I had at the time. In fact, I did not even know how to turn it on. Learning to be a machinist making extremely precise parts advanced my ME skills more than any class could have ever taught. I can now engineer a sophisticated mechanical system that works the first time and has a predictable cost. It's 50% knowledge and 50% dark art. So far EE seems to be a similar experience. I feel that I will be punished if I go low-end on gear and software. My Rigol DS1102E feels like a manual bridgeport mill - good for learning, bad for making money.

author: nctnico
author_rank: Super Contributor
timestamp: December 02, 2014, 11:42:07 am
content: If you want to measure current then you need a current probe. Measuring a few mV across a resistor is not a good idea due to noise.

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2014, 12:00:21 pm
content: Quote from: nctnico on December 02, 2014, 11:42:07 amYep.For the Power electronics the OP is doing a good current probe is invaluable IMOJust make sure the output (mV/A) will match up with the attenuation settings in the new DSO you might buy for accurate readouts on screen.If you must have a sense resistor on the PCB, you can change to a wire link type and attach the current probe there.Otherwise clip over any off PCB cabling for readings.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 02, 2014, 08:22:47 pm
content: So I did some tests measuring current, the hard part is knowing if the results are believable. I also looked at DC current probes at little bit and they seem to be a challenge to get into a small space. They will, however be great for measuring current right at a panel mounted connector with wires.For a test, I used a 1x passive probe [switchable cheap-o, 1x bandwidth limited] and the scope at 2mV/div and a ground spring right at the tip of probe. I isolated the circuit to measure across a 2512 .005ohm resistor with a single probe. The noise did not look crazy at all, relatively flat line with only a tiny offset. I powered the circuit with known external v & i measurements and they matched the scope results at least pretty close.Does this sound like a reasonable way to measure at the sense resistors? I read a Tek paper about probes saying that the active probes will have better noise rejection with low voltage applications. I think that may be splitting hairs though as they go on to say their general purpose passive probe "is also very capable of providing accurate low voltage measurements".

author: robrenz
author_rank: Super Contributor
timestamp: December 02, 2014, 08:35:15 pm
content: You probably already know this but for transients your sense resistor will need to be non inductive.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 02, 2014, 08:42:46 pm
content: Yes, that makes 'sense'I am using these resistorshttp://rohmfs.rohm.com/en/products/databook/datasheet/passive/resistor/chip_resistor/pmr.pdfwhich make no mention of inductance although they are specific to current sensing so maybe that is inferred in such a device?

author: Vgkid
author_rank: Super Contributor
timestamp: December 02, 2014, 09:05:40 pm
content: For those, It doesnt look like inductance will be much of an issue.

author: tautech
author_rank: Super Contributor
timestamp: December 02, 2014, 09:59:50 pm
content: Quote from: rx8pilot on December 02, 2014, 08:22:47 pmThats very easy to check your setup using a DC circuit and a DMM and the scope as well.Convert the turn on waveform "step" to the measured current.Never needed a DC current probe myself, but i'm sure there is good argument for certain applications.Others should chime in with advise on the need for DC current probes.QuoteSure it is for low frequency stuff, the only issue is isolation, forgetting to do it or another person whose skills are lacking.I think for production you should have a differential probe to minimise F*** ups.

author: nctnico
author_rank: Super Contributor
timestamp: December 03, 2014, 03:07:13 am
content: Quote from: rx8pilot on December 02, 2014, 08:22:47 pmThere is an easy solution for that: bring out a wire made of litz wire to make a signal accessible. Litz wire has a very low self inductance and skin effect so the effect on the signal is neglectible. I myself use a current probe in a box which uses banana sockets to feed the signal through the current sensors. The beauty of current is that it flows no matter what.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 03, 2014, 11:34:16 pm
content: In the interest of completely eliminating all options - I took a look as some USB scopes. For a brief moment, the Pico scopes seemed compelling. They have demo software that can be downloaded and played with to get an idea of what can be done. The electrical specs are great in some respects like memory, but hobby level on others like sampling rate - 1GS/s. Not hideous for the modest speed work that I am doing so I continued to look. Obviously screen size is whatever you attach to the computer and that is pretty great. Easy to save data to network without an add-on interface and proprietary software. Serial decoding, waveform generator, spectrum, mask limits, are all included. leveraging the enormous memory, you can zoom in a lot, but it saves the data in windowed segments - you cannot scroll left/right as far as I can tell.The part that I could not deal with is not having buttons and knobs to manipulate the interface. Mousing around and clicking up/down arrows to change timebase or v/div is a show stopper. For professional audio and video, many companies have control surfaces that provide a more intuitive interface for software based recording and editing. The surfaces have LEDs, displays, knobs, buttons, etc that mimic how it was done in the old days. You can map these functions to the keyboard which is helpful, but still too cumbersome.Does anything like that exist for USB scopes? Although they are not perfect, they will likely be contenders in the near future and the human interface seems to be the biggest limitations for me.I am just about to declare the Tek MDO3000 the winner for me. It seems to be a great balance of price, performance, and features for daily use.

author: tautech
author_rank: Super Contributor
timestamp: December 03, 2014, 11:47:51 pm
content: https://www.eevblog.com/forum/testgear/mdo3000-is-have-some-hardware-bug-in-large-signal-test-warning/msg561411/#msg561411

author: rx8pilot
author_rank: Super Contributor
timestamp: December 04, 2014, 12:00:00 am
content: Well, I guess that I should look at those issues during the demo period. I have owned several of the high-end Tek video measurement products and never had any challenges with service and after-sale support. There could be more to the story as well that we do not know about. I will not shift my opinion based on a first post by someone, but will ask the Tek people about the observation.Easy enough to connect it to a square wave right?

author: tautech
author_rank: Super Contributor
timestamp: December 04, 2014, 12:21:01 am
content: Quote from: rx8pilot on December 04, 2014, 12:00:00 amAs you should.It seemed by how I read that post, he was using it in an unusal way, maybe just as he had always done and the latest 3000 HW & FW were giving him a different result.Usage patterns DO vary based on taught procedures or habit or even misunderstandings.But the fact that the other EE's didn't want to use them either should make one wonder.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 04, 2014, 12:39:25 am
content: I have worked with [signed their paycheck] MANY EE's that make snap technical judgments that they are so sure of they fail to look at the problem anymore. I saw this so much that I decided to be an EE myself so that I would know when to call BS.So many simple problems get inflated to the point that the simple solutions are ruled out, including the possibility that there is no problem at all - just a perceived problem.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 04, 2014, 04:32:05 am
content: Quote from: rx8pilot on December 04, 2014, 12:39:25 amThat is most certainly a double edged sword.On one hand you want to make informed decisions, that go beyond the opinion of one individual.On the other hand, you don't want to get so bogged down in discovery, that you wind up becoming a stunt double, for the person's paycheck you are signing.The other issue is that the pace of technology is changing so rapidly, that if you waffle too long in endless marketing and datasheets, you might miss an opportunity to buy something that was "right for the job".I have never found one tool (in any business I have run) that was right for everything. Granted some are more versatile, but I would gladly follow lessons learned, and focus on what you need right now.....if it happens to amortize/depreciate across multiple projects....and outlives it's projected service life....that is gravyI would personally look at Agilent/Keysight direct page on ebay. They have some amazing deals on refub. "high end" scopes there. Shockingly good in some cases. That is if you are sold on Keysight/Agilent.I personally decided on a used LeCroy (recently), as I had much the same needs you do, although I am not sure what your technical requirements are. There simply wasn't a better value than the unit I purchased, and I am quite happy with the tool. Despite being 2009 vintage, it's already replaced my 2 year old Agilent on the bench.Tek represents some of the poorest value (IMO) in "high end" scopes. The offerings in the last year or so are quite interesting, but IMO anything from the prior 4-5 years was WAY behind the curve, as far as processing power vs $ spent. vs competition.I think for MSO under $5-8k Hameg is offering some extremely nice hardware. I always like their UI and the way they drop information onto the screen. they make fantastic use of real estate IMO.If I was looking for another scope right now, for some "serious" work....and I wanted to buy factory direct...I would look at a refurb Agilent MSO9000, a new LeCroy HDO8000 or if my budget was more inline with yours, a top of the range (optioned out) Hameg MSOIMO the Hameg represents the best value in a new scope, in the mid-range category.If you want to run a lot of math/operators and want a ton of flexibility in the way signal is routed, plus want to do some custom UI or app development....I have never touched a tool that does it, quite as good/same way as an upper range LeCroy. I am personally happy enough with my used acquisition, to go further and investigate a brand new HDO8000. Which is saying a lot, considering Agilent filled up my bench space up until very recently.Some more technical insight would be helpful in developing a purchasing criteria.....I.E. how much flexibility do you really want, and what exactly do you envision using the scope for? What is day to day for me, might be considered "minority" for others...

author: cncjerry
author_rank: Unknown
timestamp: December 04, 2014, 08:35:02 am
content: I was in your same position about a year ago wanting to move up from an analog scope into the DSO age. I bought an older used Tektronix TDS744a then a TDS3054b. I don't regret it at all. Yes they don't have all the bells and whistles of the newer scopes but the value for the dollar was exceptional.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 04, 2014, 10:24:53 am
content: Quote from: TunerSandwich on December 04, 2014, 04:32:05 amThey are indeed. The DPO/MDO3k is interesting but that aside they're so much behind the curve it's not even funny, especially on the high end (where they seem to be still stuck at 33GHz anyways).Their sales staff also seems to be really desperate.Tek clearly has passed its zenith. None of the places I know are considering Tek scopes anymore. The majority is now solidly Agilent/Keysight.QuoteLet's say they're definitely some of the better ones, although they could make much better use of their VGA resolution displays.Their MSOs are attractive if you can live with the very limited choice of decode options.QuoteHameg isn't really mid-range (which starts with the R&S RTM), all the Hameg kit is solidly placed in the entry-level sector. Even their top-of-the-range scope (HMO3000) is still a entry-level scope.QuoteIndeed, a bit more information would certainly be helpful.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 04, 2014, 10:51:01 am
content: Quote from: Wuerstchenhund on December 04, 2014, 10:24:53 amI was taking into consideration the context of this forum. I think we have discussed this in the past. Maybe an edit to that statement of mine is due?compared to the commonly discussed product tiers, in this forum, I think Hameg represents the mid-range price point.....feature set follows suit. However I still think they have one of the best UI's and measurement display methodologies on the market...and yes I will agree their screen implementation itself is not fantastic....I would personally like to see them, or another manufacturer, implement the same measurement markers/tags/cursors into a truly "high end" scope....One thing I am finding a bit annoying about the LeCroy is the way it wastes screen space for simple measurements.....I mean at least a floating frequency counter would be nice to have (maybe it's there and I don't know it?).....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 04, 2014, 11:34:43 am
content: Quote from: TunerSandwich on December 04, 2014, 10:51:01 amAH, I see. Yes, I think in the context of that the majority of discussions on this forum is around entry level gear it's probably fair to say that Hameg sits quite well in the mid-range.QuoteIt's not that bad (for a truly horrible use of screen area look no further than to the Siglent SDS2000), but yes they could improve it further.QuoteI doubt we will see that anytime soon, as feature-wise most low end manufacturers seem to more or less copy the same feature sets amongst them. Yes, they get cheaper, and the cheaper ones are built better than before, but they still come with the same limited functionality which I think is a shame.I guess the cheapest new scope with advanced measurement capabilities these days is the LeCroy WaveSurfer 3000 (which starts at roughly $3k) aka the Siglent SDS3000 (which seems to be only sold in China).QuoteNo, there isn't one. Don't forget that the "Frequency Counter" which is available in some cheaper scopes is exactly that, a hardware frequency counter built into the scope. Such stuff is predominantly found in low end scopes only.To save screen area you can disable Statistics display in the Maths section and then select "Frequency" for the appropriate channel.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 04, 2014, 11:59:55 am
content: Quote from: Wuerstchenhund on December 04, 2014, 11:34:43 amYes I have been doing that, as well as removing the somewhat useless "histicons"....I have just been using a cursor to grab a quick view of certain measurements.....I suppose this is where these scopes get good....with all the custom math and measurement tools we can "fake it"I was going to start playing with the XDEV tool-set. I was noticing some ability to write UI changes with VB.One thing I really wish I could do is change that awful purple/blue in the DSO application.....the new black version they have is much better on contrast.....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 04, 2014, 12:09:27 pm
content: Quote from: TunerSandwich on December 04, 2014, 11:59:55 amThe X-Stream scopes are great if you need lots of parameters, but I think the display of only one or two parameters was solved a bit better with their older non-Windows scopes. Oh well, I guess we can't have it all.QuoteYes, you can. In fact, you could write your own scope UI, using all the capabilities that are in the scope. It's really great.QuoteIt's already in the softwar on your scope. What "theme" it uses is decided by the scope model the software installed on.Also, don't forget that newer models run Windows Vista/7 which support Aero effects, and the nice semi-transparent blocks will look dull on Windows XP.The black scheme certainly looks more modern, though.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 04, 2014, 07:20:37 pm
content: Quote from: TunerSandwich on December 04, 2014, 04:32:05 amI can say what I am doing today and what I hope to be doing in the future. At the moment I am designing power related products for industrial/professional imaging systems. This generally means low voltage - medium current from multiple sources being distributed to multiple outputs at various voltages. All of this is managed and monitored with a blend of analog comparators, 16bit A/D, MCU's, i2c, SPI, 1-wire, boost converters, buck converters. I need to see the low mV drop across a resistor compare with an i2c event. Maybe monitor a comparator input to gate timing on routing FETs. Converter design has me looking at shaping the PWM gate pulse while monitoring noise/ripple at various loads. All of these things are normal measurements for most anyone. There are so many things that I am not capable of doing with my limited equipment on my bench right now so I hardly know what to hope for in a new scope. Triggering on digital data would be a great benefit. Right now, trying to temporally tie a Rigol scope with a Saleae logic analyzer is very time consuming. Looking for a specific i2c command and understanding it relationship to an analog event is a pain. Window testing sound really great. As the circuit switches from one power source to another at full load, it can only drop so much before things go bad. That is a simple measurement, but some effort involved in comparing to a previously known good waveform. Some of the advanced math functions I see in the higher-end are outside of my understanding. I would like to learn more about why various math options exist and how they can be used in analysis and understanding of the signals.For the future, I have been studying FPGA dev for the purpose image transformation. This will bring a whole new crop of measuring challenges that I am not even aware of yet. Hopefully the scope I choose today will be enough to get me through the learning curve and at least to the point where I can release my first FPGA device. The cost of developing a new product will involve way more than just a scope and an FPGA dev environment so I am hoping that I don't have to buy a new scope right at the end of development when cash is super tight. If this happens, I will be presented with very fast serial signals at 3gbps+ and I am thinking of renting a scope for that period of development if possible. There is not a long term need to monitor the serial signals beyond knowing that they are properly making their way into the FPGA and back out. After that is worked out, I would be back into the slower parallel world for oscilloscope measurements and the images will be measured on dedicated image monitoring gear - totally separate from an oscilloscope. It's really hard to understand what I may be needing for a project like this.Clearly I am looking for a general purpose scope that will be the least likely to limit my design options in the near-ish future. I would be happy if it was relevant for 3 years but that is a random guess. There is no real way to understand how long it will be before the scope limits my progress. Therefore, I would like to choose something that is significantly more advanced than I need today while not being such a financial burden that it slows down the business. The 'upgradable' scopes seem interesting because I can spread the cost out and choose what I need exactly when I need it. For the moment, I am guessing what the future may bring. I know that I could get everything I would ever need for $30k, but that would mean I would be a slave to the scope for a while. I am also building a small P&P line and spending about $10k+ on other bench gear so I definitely need to balance the budget wisely.Beyond cost, I am certainly worried about the day-to-day experience and ease-of-use. If two scopes are the same purchase price with nearly identical features, but one is a little slow and cumbersome - it may double or triple the cost of that scope over 3 years in labor and missed opportunities. Intuitive is just as critical as bandwidth IMHO. I have learned that lesson in my CNC shop over and over.

author: tautech
author_rank: Super Contributor
timestamp: December 04, 2014, 07:42:07 pm
content: There are a few tricks you can use for the development of high speed stuff.A client had a memory bus running at 800 MHz that they needed to check timing, signal levels, integrity etc.Halved the clock speed and it was visible with a 300 MHz DSO.Answered their questions and they moved on.Sure a DSO that matches or betters the bandwidths in a circuit is nice but not always necessary.Its called measurement techniquesand can save lots of money.Modern DSO's generally have a substantial serial triggering suite and you will have to find one that has the flexibility you need. You may have to option this in for some brands/models.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 04, 2014, 07:48:29 pm
content: That sounds like an absolutely classic example of not understanding the difference between clock rate and edge speed. High speed signal integrity is all about rise and fall times, and they're governed by the design of the silicon and the PCB. The number of transitions per second is largely irrelevant, and it's amazing just how many engineers don't really appreciate and understand the difference.A 300 MHz scope won't show anything useful on a memory bus designed to be able to run at 800 MHz. Very few scopes will; the parasitic effect of the probes dramatically affects the signal shape, regardless of the scope's bandwidth. The only real way to know what signals on a high speed memory interface look like is to simulate them.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 04, 2014, 08:34:10 pm
content: Quote from: tautech on December 04, 2014, 07:42:07 pmI have to agree with AndyC_772 here, signal integrity on these busses very much depends on edges, and the major factor are the vias. Aside that just halfing the clock speed doesn't mean you would get the same results even when measured correctly, the 300MHz scope may have shown something, but certainly nothing that was a relevant denominator of signal integrity.You can properly measure such busses but I'd wouldn't touch it with anything less than a good 2GHz scope and transmission line probes which are designed for such stuff (and even with them the parasitic effects can be noticable impact the measurement).

author: rx8pilot
author_rank: Super Contributor
timestamp: December 04, 2014, 08:39:15 pm
content: Verifying integrity of 800Mhz bus sounds expensive and time consuming in addition to needing to be very knowledgeable in how to measure without killing what you are measuring. Even at much lower levels, that has been a challenge for me - don't kill the signal you are measuring or you will be chasing your tail perpetually.

author: nctnico
author_rank: Super Contributor
timestamp: December 04, 2014, 09:46:32 pm
content: An 800MHz 'bus' is probably a serial link. A simple TDR setup is all you need to check for impedance mismatches and discontinuities.

author: tautech
author_rank: Super Contributor
timestamp: December 05, 2014, 05:14:25 am
content: Quote from: rx8pilot on December 04, 2014, 08:39:15 pmYes of course, however the result was a clear pass in this case.For debugging one would never attempt this, this was more just a test of proof of concept.Should there have been problems there was funds available for hire of appropriate gear.

author: AndyC_772
author_rank: Super Contributor
timestamp: December 05, 2014, 08:00:28 am
content: Well, OK... but what you'd see on a 300 MHz scope screen looksnothinglike the actual shape of signals that exist on a bus capable of 800 MHz. The probe alone will wreck the shape of the signal beyond all recognition, and the low pass filtering effect of the scope ensures you don't even see the wreckage properly.I'm guessing we're talking about DDR2 or DDR3 SDRAM... right?

author: tautech
author_rank: Super Contributor
timestamp: December 05, 2014, 09:11:37 am
content: Quote from: AndyC_772 on December 05, 2014, 08:00:28 amIIRC it was DDR2 but not running @ 800 MHz only about half that.My SDS2304 was on loan to this client at the time for appraisal and this test. Yes there were problems with probe loadings at those frequencies.The probes that were supplied with my pre-release DSO were rated at 300 MHz and were found to inadequate for that job.A BK Precision 500 MHz passive probe was then purchased for this test.We did seriously consider an active probe at the time but chose to to get the BK as intermediate measure as it was only ~ $115.However the probes supplied with the same DSO today are of better quality.How do I know, I delivered a new SDS2204 today.Though we were well past the -3dB point there was enough info available(rf-loops results SDS2000 thread) to project the DSO bandwidth roll off out to the tested frequency for a rough result.Most experienced users are aware that any test connection will affect the DUT or give incorrect results, but its about knowing that and taking steps to minimise errors, maybe that includes shaking the moths out of ones wallet.

author: coppice
author_rank: Super Contributor
timestamp: December 05, 2014, 10:09:44 am
content: Quote from: tautech on December 05, 2014, 09:11:37 amIs that really true? I find a serious lack of skepticism about the information presented by instruments of various types. We all go chasing through smoke and mirrors on the odd occasion, but some people seem to make their entire career out of that.

author: nctnico
author_rank: Super Contributor
timestamp: December 05, 2014, 10:23:21 am
content: Quote from: AndyC_772 on December 05, 2014, 08:00:28 amA standard probe is the wrong tool for these kind of jobs even if they are rated for 300MHz they simply cannot be used at that frequency in any real circuit. An active or low-Z passive divider probe is the only choice and as a rule of thumb you'll need such a probe for measuring signals over 100MHz.

author: coppice
author_rank: Super Contributor
timestamp: December 05, 2014, 10:43:10 am
content: Quote from: nctnico on December 05, 2014, 10:23:21 amEven when you use an active probe you need to take great care about how it is attached to the circuit to get anything close to the true waveform on the screen of a scope. Accurately probing wideband signals is a task for experts, even if they are equiped with the most exotic tools in the world.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 05, 2014, 11:16:08 am
content: Quote from: tautech on December 05, 2014, 09:11:37 amIf it was DDR2 then it was running at 200MHz clock. Still, the problems described before remain an issue even at that lower clock rate.QuoteThe thing is that a normal passive probe is completely inadequate for probing a DDR2-800 memory bus, independent who made it or what the bandwidth is.I'm sure You have seen something on your scope but certainly nothing representative of what's really going on with that line. You really need a low-z passive or active probe for that.QuoteNot in my experience. In fact, I've seen many engineers (even experienced ones) absolutely underestimate the impact the test kit can have on the UUT, and then draw conclusions from bogus measurements.I lost count of how many times I encountered situations as your above example with the memory bus.QuoteThe problem is that many engineers aren't even aware of the basics behind the kit thei're probing, let alone the impact introducing that probe into the circuit. The thing is that you really need to know what you're doing, otherwise you'll never realize that the nice measurements you're just taken are worthless.

author: coppice
author_rank: Super Contributor
timestamp: December 05, 2014, 11:51:20 am
content: Quote from: Wuerstchenhund on December 05, 2014, 11:16:08 amWhen you help someone out in a situation like that they typically say something like "I learned from that. I won't make that mistake again.", yet the next time you see them there's a high chance they are making exactly the same mistake. People are really bad at learning from their mistakes. Look how many divorces are rapidly followed by another marriage.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 05, 2014, 12:27:50 pm
content: Quote from: coppice on December 05, 2014, 11:51:20 amIndeed. Not that institutions (i.e. corporations) are better at that, though. Just have a look at outsourcing.[Company A]"We'll save costs by outsourcing IT/HR/whatever"=> disaster[Company B]"We'll save costs by outsourcing IT/HR/whatever. Company A did it and failed, but we're different and will succeed!"=> disaster[Company C]"We'll save costs by outsourcing IT/HR/whatever. Companies A and B did it and it failed both times, but we're different and will succeed!"=> disaster[Company D]"We'll save costs by outsourcing IT/HR/whatever. Companies A, B and C did it and it failed every time, but we're different and will succeed!"=> disaster[Company E]"We'll save costs by outsourcing IT/HR/whatever. Companies A, B, C and D did it and it failed every time, but we're different and will succeed!"=> disaster... To Be Continued

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 05, 2014, 11:05:54 pm
content: Quote from: rx8pilot on December 04, 2014, 07:20:37 pmThat is VERY similar to the type of work I do. DO NOT underestimate the need for bandwidth. I think a lot of engineers falsely assume that "because my SMPS is below 1MHz, I don't need anything more".Nothing could be further from the truth. You need to consider the ability to analyze feedback loop interactions and external resonant tanks. Do you need to go out into the GHz ranges? chances are no, BUT it really depends on the interaction between your devices, and the PCB (often overlooked).FPGA are very sensitive to step responses, and although most HF artifacts in POL/SMPS are very low in energy, they can cause instability in the sense loops of many POL devices. These problems can lead to inefficiency and can also lead to thermal issues. Especially devices that have large current ripple.The other consideration (often overlooked) is the rise time of highly critical signals. Especially in shared system buss architectures. Remember that bandwidth on the front end also relates to rise time.I think you would be selling yourself VERY short if you didn't look at these very real scenarios. I have been there quite a few times. Everything will seem fine, until you have an UN-explainable problem. Then you are really going to wish you had the ability to properly capture fast, erroneous events.The next MOST critical factor, is your probing solution. In fact I would be willing to say that your probing solution is MORE important than your acquisition device. As with most things, the weakest link in the signal chain will dictate your results.Another consideration is the use of ext Vref. Do you have a meter spec'd that is appropriate for calibrating Vref for a 16 bit A/D? Also do you have a calibration reference for all of these tools?The next question would be about clocking solution. What are your plans for clocking? The MCU's and other devices are going to need to lock to something external.....and using GPIO pins for PWM on a micro is just not going to work out. You will be looking at max PWM of around 500ish HZ. I am assuming you know of that quite well already, and would be using serial i/o for switching, BUT this is generally not a good way of doing this. You will need to be able to respond to external errors (based on sensor f/b) much faster than the MCU can provision for. I have tried many experiments on multiplication of MCU PWM, with mostly unacceptable results.I could go on and on here about WHY more bandwidth is necessary (beyond 100 MHz) but obviously there is a limit. I think a 300-400 MHz front end is MUCH more appropriate, and most tools that you are going to consider and NOT going to offer "upgradeable" bandwidth. Consider this...."upgrading" bandwidth simply means that you ALWAYS had the front end to begin with, and that the manufacturer has simply crippled it, in order to get more $ from you.If I was in your situation I would rent or lease some "high end" tools....and do some comparison. Analyze some of your signals at both 100 MHz and then at 400 MHz or above. You will gain some serious insight into just what you are missing in the lower BW device. Also the probing solution is CRITICAL, I can't stress this enough. If the properties of your probing solution create resonant tanks of their own, you are really flying blind. Also consider the dynamic range of the probing solution and front end. You need a solution that can respond to extremely fast state changes and can resolve the step response of your power devices. FPGAs are tricky that way...P.S.one important thing to note is the usefulness of FFT based operators, in characterizing shifting impedance vs frequency.....you obviously need a front end that can acquire pesky harmonics (or fundamentals) but ALSO need the sample rate to makes sense of it. Since FFT resolution and bandwidth is proportional to half the sample rate of the acquisition device, you aren't going to find many options in large sample rate, low bandwidth scopes.....do you really need to look out to 5GHz+ for oscillation/resonance in your step response? well no i suppose not, BUT you might miss harmonic interactions in your switching devices, that can cause errors in proper voltage regulation.....I could post a screenshot of a budget scope FFT (DS2102A-S) vs the WR64MXi....showing the exact same signal (from a POL). It will clearly show just what you would be missing (in the signal interpolation) between the decreased bandwidth (and crap probing solution) of the Rigol unit, and the increased bandwidth (and proper FET probing solution....).Obviously it's an apples to oranges comparison....and that is the point. The proper way to do that comparison would be with differential probes and a well engineered test, but the differences in captured data are SO SIGNIFICANT, I think the problems will be immediately obvious.Harmonic content in your step response, with complex digitally controlled POL devices, is CRITICAL in properly driving dynamic loads.....I can't think of a more picky dynamic load than a modern FPGA/ASIC/SoCAlso these harmonic interactions and large current oscillations (as a byproduct) can cause massive premature damage to multilayer SMD caps....and if your sensors are sensitive to harmonics and those physical resonances/harmonics are existing on the same PCB/plane...well you know where this is going.....you will get huge instability and oscillation down the line....this can even go as far as LF resonances that will easily destroy the inductor of some POL devices.....not to mention the power lost.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 06, 2014, 07:35:52 pm
content: Excellent info from someone going down a similar path, but further along than I.As I have started the educational process of understanding the finer points of measurement, it has become clear that it is a field of specialty all its own. Just like machine shops have a separate metrology department because it is so challenging to measure properly. Probes have REALLY surprised me in range of capability and difficulty of proper usage just to get the signal to whatever instrument I may have without altering it to the point of chasing my tail. At this point I am putting in a significant number on the probe line of the budget - I want my talent to be the limitation, not the probe. I can always learn how to do it better, but it the probe is the wrong choice in the first place, I am doomed regardless of how well I think through the test.For bandwidth - good points. I realized that the price difference from 100Mhz to 200Mhz is generally pretty small. Makes it easy to get started budgeting for 200Mhz. Stepping up from there starts a steep pricing curve so I need to think pretty hard about where to start. I would certainly prefer to spend the money to get 350Mhz or 500Mhz if I knew that it would save my butt by showing me something that would be invisible on a slower instrument. It is a little hard to guess, however, it is never going to be a problem to have too much bandwidth on the scope from a testing perspective - just a financial one. As others have pointed out, upgrade-ability is not a white knight riding in to save the day.Quote from: TunerSandwich on December 05, 2014, 11:05:54 pmIf you have screenshots, it would be helpful for sure!Thank you to all those that have thrown in various tips, knowledge, experience..... this discussion has been very helpful. The marketing materials and other skin-deep information available from Google searches is not enough to make an informed decision. Actual users making real products offering information is really great.

author: LabSpokane
author_rank: Super Contributor
timestamp: December 07, 2014, 12:35:21 am
content: Quote from: rx8pilot on December 06, 2014, 07:35:52 pmI was in the same boat as well with the sticker shock on the >200 MHz scopes. I went 200 MHz, 4 channel MSO with the thought that as soon as I outgrew the scope I could sell or trade in. I figure by that time I'll have revenue to justify the equipment upgrade, and the scope I have now will still be good to keep or have value to resell.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 12:41:45 am
content: Quote from: rx8pilot on December 06, 2014, 07:35:52 pmThe great thing, is that in the used market, bandwidth doesn't fetch quite the premium it does in the new retail market. The proportional losses of new value, on higher bandwidth front-ends, vs used...greatly benefit the buyer. I can grab a couple hundred "extra" MHz for virtually no additional money. Obviously we are talking about upper mid to high end scopes.ABSOLUTELY measurement of electronics is an art form and diverse skill set of it's own. The other factor in a differential probing solution is safety. A lot of people overlook this. Remember that the negative signal in an active/differential probe is floated from earth ground. In fact thinking of it as ground is wholly wrong. It's a second, isolated signal path. So in a situation where you have floating grounds in your test device, you won't wind up going down the road of disaster. This is especially true with HV, and I have to assume that in imaging equipment, you are dealing with HV at some point.If I was considering a single scope solution for a "professional" development environment....and I needed versatility and viability for a WIDE range of tasks (eventually you will want to deal with wireless stuff....it's the trend in the market)...I would look at a 3GHz front end, a proper isolated HV differential pre-amplifier, a selection of passive differential probe leads for that PA, a selection of current probes with appropriate BW and rise times...a few FET and passive probes...a calibration/de-skew reference and as many math and analysis options as possible. I would also look at a proper user grounding solution and a good clean, dedicate, power source. Also I would look at the devices needed to proper float and decouple various types of grounding scenarios, as well as some isolation chambers to properly characterize field devices.Don't under-estimate the value of a good shielded temperature controlled isolation cabinet....it has been my experience that for every 15 minutes of measurement I do, I spend a good couple hours researching and designing the proper test and fixtures to know that the data/metrics I acquire are actually worth something. The last thing you want to do is go chasing common mode noise or bogus artifacts. It will save you a lot of resources (money,time etc...) in the long run.You can acquire everything I just described, plus a good calibration reference, and a proper DMM (trust me you are going to need this for your ext Vref, and you are going to need 2 units...) and a decent electronic load (another MUST have) for under $30k. You just have to be frugal and look at what you really need/want. You are going to have to buy used to fit your budget vs needs/wants. There is nothing to be scared about, when buying used. Just make sure the devices are still supported, either direct from manufacturer or by a 3rd party support community.Also don't be afraid or get caught up in things like the most possible memory depth or more modern "marketing" ploys. Yeah a lot of the modern bell and whistles are nice, but wholly un-necessary. I am chugging along, happily with my 5 year old, used, LeCroy. Is it the best at everything? NO. Do I wish it had more memory depth? YES. In fact my ds2000A still sits on the bench next to the LC "high end" scope, because it offers that finer resolution in the vertical domain, and slightly more mem depth for long captures. The LeCroy did replace a "only 2 year" old Agilent though. It just does more of what I need and less of what i don't (the Agilent did a lot of the "don't really need" type stuff).I will throw up some pictures of the two scopes, side by side (Agilent is gone already) analyzing the SAME signal, from the same signal test point. The differences are very obvious. Again it's apples to oranges, but that is the point. Let's have a look at the least ideal solution possible, vs the most ideal, with the tools I have available in the home lab. As soon as the LeCroy earns it's wings (in terms of reliability) it will go down to the real lab, and maybe we can shoot it out against some other "exotic" solutions. Perhaps a short video would be more beneficial, that way the entire experiment can be described. The signal chain I can illustrate here, represents well under $20k of total investment, and you will see just how significant the differences are.P.S.THE WORST possible place to install this equipment would be in a "machine shop environment". The stray EMI and dirty power is NOT going to get you anywhere, other than a constant feedback loop of second guessing your measurements. I hope part of your budgetary consideration is a dedicated "clean" room for the lab, and some isolated power. I have seen first hand what PLC controlled devices can inject into a building power system, and it ain't pretty.

author: nctnico
author_rank: Super Contributor
timestamp: December 07, 2014, 01:18:03 am
content: @TunerSandwich: IMHO you are going over the top. A good engineer knows what should be on the screen of the oscilloscope and for 99.9% of the measurements you don't need to get rid of noise and spikes.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 01:31:41 am
content: Quote from: nctnico on December 07, 2014, 01:18:03 amI think you are under-estimating the gentlemans needs......and his very specific applications. I would re-read his specific requirements. Also...how can you go "over the top" in scientific measurement?If this was, "over the top", then these tools wouldn't be made at all....I think you are under-estimating the art of highly reliable field device measurement and development.I suppose I have been going "over the top" for the last few decades ?It seems to earn me a livingAlso where am I mentioning "getting rid of noise" (slapping a 20MHz filter on the inputs of a scope is the method for marketing "low noise"....and isn't a real way to gain insight on potential dynamic load issue). I am saying quite the opposite....that you NEED to look at all aspects of the signal, and be assured that the injected noise form the test jig itself is removed.....A "good engineer" is one who takes into account ALL of the available data, and uses the tools at his/her disposal to understand where things can be improved.A "bad engineer" is one who ignores relevant data and says "well things SHOULD look like XYZ" and I can just ignore anything that doesn't conform to my predictions...The most relevant and truthful answer to the question of "how much bandwidth do I need?"....is "as much as you can afford"...bit puzzled by your blanket statements about "good engineers"Let's have a look at what the manufacturer thinks is "over the top" for their PMA software....which is EXACTLY the type of measurement the OP wants to do.....as you can see in their datasheet, their hardware recommendations mirror mine.....see/read PDF.....is the scope manufacturer "over the top" or wrong in their recommendations to their customers?http://cdn.teledynelecroy.com/files/pdf/lecroy_pma2_datasheet.pdfhttp://literature.cdn.keysight.com/litweb/pdf/5989-7835EN.pdfhttp://www.tek.com/application/power-supply-measurement-and-analysisalso how could you say "99.9% of the measurements you don't need to get rid of noise and spikes"? The step response of a POL is CRITICAL in power distribution systems, especially with dynamic loads.....are you saying that we shouldn't worry about overshoot, ringing/oscillation in Vsense 99.9% of the time? If that were true the computer you are typing on right now simply would NOT work....please qualify your statements with some real world, use case, scenarios...like I have.The gentleman did say he was looking for "professional criteria".....

author: nctnico
author_rank: Super Contributor
timestamp: December 07, 2014, 01:53:08 am
content: Quote from: TunerSandwich on December 07, 2014, 01:31:41 amIf you connect a standard probe to a board with a hefty DC-DC convert to check an SPI interfave you'll likely pickup some noise from the DC-DC converter. As long as that noise isn't in the way of getting the information you want there is no need to spend a lot of time or money on trying to get the signal to look nicer on your oscilloscope. At some point you simply have enough information.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 07, 2014, 03:25:10 am
content: Quote from: nctnico on December 07, 2014, 01:53:08 amAgreed, the question is how much information is enough to make decisions and sleep well at night - at least for me. In other areas of my professional career, I am an 'expert' and able to infer certain results based on experience to determine whether all is good or not while only having partial information. My experience in designing electronics is only a few years deep so it is harder to make a call about whether noise or spikes are ok or not. So far, my more common experience is seeing noise or spikes on the scope and mistakenly chasing down a circuit problem only to find later that the test was creating the problem. I have dedicated some time to understanding the combination of technique and tools needed to really optimize the designs as opposed to 'just getting it to work'. In the end the real world will always prevail - I can't afford a 1Ghz scope with $10k worth of probes added in and isolate my lab in a Faraday cage. I also don't have months to measure and optimize a simple-ish circuit. I need to pick some reasonable starting point that will offer the least amount of limitations for a reasonable time. Obviously, a lot of variables presented there - so I have to take a leap of faith to some extent.Quote from: TunerSandwich on December 07, 2014, 01:31:41 amNice.To add to that.... I take all of the the RELEVANT data and divide by the time allowed, sort problems by order of value to the project and start solving. I have worked with and paid engineers that take all the data available and it simply baffles them to the point of being frozen. Knowing what needs to be solved and in what order is a critical engineering skill that does not come with all engineers. For my business to work, I have to keep a high-altitude view of the project and then swoop into the details to do the actual engineering. Spend too much time in the details and you lose track of what you are trying to accomplish.I am planning to get the Agilent 34461A 6.5 digit DMM and a multi channel electronic load system [probably BK since the prices and performance are reasonable for multi-channel]. This will allow some automation in the testing which will same some time.Why would I need a voltage reference? Do you see that as critical?Also, I am putting the lab in separate building from the CNC shop. Not sure what kind of mayhem they spew into the electrical - never measured or even thought of it. With 30Hp spindles starting and stopping along with huge servos that move an 800 pound table at 1,400 in/minute stop-start, it could be nuts.Looking forward to seeing the screen grabs. Also thinking more and more about renting a 200Mhz and maybe a 500Mhz or 1Ghz together for a month to understand how they will impact the daily challenges. I am lucky enough that a rental company is about 3 miles from my house. Being able to compare with my actual circuits on my bench could reveal a LOT about what is best. It should also teach me a LOT about technique using high-end instruments.

author: LabSpokane
author_rank: Super Contributor
timestamp: December 07, 2014, 04:21:35 am
content: Maybe you should spend less on a scope now and invest some into a separate step down transformer off your mains. Trying to test while fighting crappy power is un-fun. It's a great opportunity to have a few new ground rods pounded in anyway.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 07, 2014, 05:14:12 am
content: No problem - separated from CNC by 12 miles. Should be reasonable HF fall-off at that distance

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 05:56:21 am
content: Quote from: nctnico on December 07, 2014, 01:53:08 amThat is making a HUGE assumption, that the DC POL is in fact stable and doing what it's supposed to....in relation to the dynamic load being presented. You are missing a massive chunk of the OP's equation. You can't assume that the stability of a digitally controlled POL is going to be acceptable, for driving an FPGA/ASIC or similar. The OP's use case scenario is far more complex than you are allowing for. He didn't say he was whacking a beefy DC-DC reg on the front of something. He specifically said he was dealing with a multi-phase architecture.ALSO, by your own admission, you say that the use case scenario I presented isn't relevant 99.9% of the time. Well Murphy will make sure that the 0.1% of the time happens 100% of the timeAgain, i am not sure the nature of multi-phase DC,POL solutions is being understood here. The step response of those devices is absolutely critical in gaining stability....especially for complex multi-phase IBV systems....when the load is dynamic and one would be concerned over dead times and V-sense.We aren't talking about a 5v linear DC regulator here. We are talking about control over a multi=phase architecture, that employs POL changeovers, being controlled by sensor feedback into a MCU or similar. These are the devices I deal with on a daily basis, and I can assure you that these specific topologies are nowhere near as simple as you are making them out to be.I can also assure, that my experience in this VERY specific field, has taught me that 100MHz front ends, with low sample rates is going to turn over and bite you in the ass, when you least expect it. Sure everything will be just fine 90% of the time, and meet your engineering predictions.....but that's not engineering. Any idiot can follow a build example on a datasheet.....when you really earn your pay is when things go the opposite of "plans". If you have to hire out, because of the lack of insight, in your own T&M setup....then the extra $10k you were questioning spending....becomes a VERY VERY valuable investment. Been there many times.One guarantee we all have, is that nothing will ever go 100% according to plans.....you can bank on that. Hence the reason for test and measurement gear, to begin with. If everything stayed perfect 100% of the time, we wouldn't need to check. It's also complacent to think that the laws of physics are fully understood.....or that some joker at the supplier didn't tag a 22uF cap as a 47uF cap.Shit happens

author: tautech
author_rank: Super Contributor
timestamp: December 07, 2014, 06:24:27 am
content: @TunerSandwichAs you seem to have a pretty good handle on the OP's requirements, and the experience to boot, what would be the minimum specs you would see as non-negotiable for his needs ?BW, Sampling rate, Memory, I/O's, Decoding...etc.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 06:32:50 am
content: Quote from: rx8pilot on December 07, 2014, 03:25:10 amYour experience and path, very much mirrors mine. I am not only the lead developer/engineer at my company, but i also own the company....and i have to put on different hats (as you do) when it's necessary.Obviously we NEVER want to get caught up in endless scope crawl. Also, OF COURSE, we only want ot look at relevant data. However, what is relevant isn't always obvious. It's always the most seemingly minor or irrelevant thing that comes back to bite you in the ass. Without fail. It's much better to have over=provisioned and "over engineered" something....than to have to deal with the bad will of a recall. Or discover a week before a product ships that you have some horrific instability or safety issue.Hell even the best engineering firms have bodges on their boards. So we can guarantee that, at some point someone in the production and dev chain will be complacent....or simply make a bad call.There is a very fine line between having all the facts, picking the most efficient and cost effective route and saving a buck. It's not easy. I am sure you know that intimately well.At the same time getting caught up in endless datasheet and equipment marketing is also no solution. As with all things it's specif and has to be balanced (pun on differential pairs there?).However, banking on the experience of others, and using your own educated judgement is a recipe for success. If you can't trust the opinions or work of the people you are hiring, as engineers, and feel you have to play stunt double for them....well then you really have to question why you are keeping them around....? Trust me, i know how difficult it is to walk this line, but at some point you have to be realistic about reality.The worst thing you could wind up doing id buying into a system that doesn't do what you need it to. It would have been far better to lease, or hire out a lab with the correct tools. I get that budgets dictate reality, but so do results. You can't pick one over the other right? If you spend half of what you should have on T&M, AND the product flops because of design problems....well it would have been better to not spend anything at all.I am not here trying to say you have to spend half a million dollars on absolute bleeding edge systems....at the same time, the fact that you are questioning what you really need....kind of says that it's impossible to grasp the reality of a budget. I mean you don't define budgets that way. You don't say I have $xxx to spend, so let me figure out what I need. Instead you say, let me figure out what i really need, and then how to pay for it. Sometimes allowing a pre-conception to dictate a budget is a foundation for disaster (been there many many many many many times).I think it's best to buy this equipment, when you have enough insight to make confident decisions based on your own knowledge. Obviously no-one here can tell you "without doubt this is what you need". I am personally just trying to look at your very specific use-case scenario and use relevant experience to give insight on what has worked for me. Does that mean you MUST have xyz or ABC? Of course not.....and hey you might get really lucky and everything goes off w/o a hitch.....but you must provision for the opposite, so that it doesn't take the entire ship to the depths of the sea.....Glad to hear the lab will be offsite.....the garbage that big boy machinery spews into the building electrical system, and radiates through the "ether" is a hell I wish upon no-one. I have spent more money than I care to mention, trying to band-aid those kind of problems, and it's always a game of compromise. In the end you wind up spending more on mu-metal, isolation transformers and chemical grounds than you would have just building a new structure, from scratch, off-site. YIKES!!!The voltage reference and calibration refs are critical, because you mentioned using a 16 bit external A/D. You will have to lock that to an external V-ref. For example a 12 bit A/D would need a 4.096V A-ref to equal a logical float, in programming. I could get into this more if you don't already know on the traps that crop up there.Now comes the fun part. Lets say you do need to employ this precision V-ref. The V-ref will need to be calibrated, per device. To do that you first have to trust that your calibration meterS (notice the emphasis on plurality) and in fact trustworthy. Also that level of traceability needs to be ongoing. So ONE quality, calibrated 6 1/2 digit MM is simply not enough to bank on. You need a minimum of two, on the same test point....both with identical (as close as possible) test leads etc....BOTH of those units need to be warmed up and verified against a known, traceable reference....I would strongly advise budgeting for that type of situation.The architecture you explained earlier in the thread, is NOT some basic/simple topology. Multi-phase power solutions, driving highly sensitive processing blocks are MUCH more complex and the precision required to keep them working and warrantied is far from "well that's good enough".....I will set-up a test tonight or tomorrow, and show you some differences between a variety of solutions...and will purposely inject a fault into the topology....so you can see the 100MHz DS (Rigol) totally miss it.....hopefully a few simple screenshots will illustrate my points here, but if not then I could possibly make a video.....I have been at this specific engineering discipline for close to 20 years now, and believe me i have made ALL the mistakes....and sometimes they have cost me dearly....I am not trying to present doom and gloom, and say you will fail if blah blah blah....obviously everything is specific and blanket statements are utterly worthless.....but that is the point here....we are getting very specific....

author: rx8pilot
author_rank: Super Contributor
timestamp: December 07, 2014, 07:31:27 am
content: Quote from: TunerSandwich on December 07, 2014, 06:32:50 amSaving a buck is the most expensive thing I have ever endeavored to do.Quote from: TunerSandwich on December 07, 2014, 06:32:50 amPast experience has taught me the very hard and expensive lesson of buying more than you need is cheaper than buying less and failing because of it. It certainly helps that Agilent has 500Mhz MSOX3054A for $6k! Even the options are discounted. That is only $1k above my original thought of spending about $3-5k and I would not likely outgrow that. The Tek MDO3k looks great, but I have not seen one at nearly 50% off either.Quote from: TunerSandwich on December 07, 2014, 06:32:50 amI wish I had this conversation a year ago when I started going down this path. The learning curve has been outrageous and I am just getting up to the starting blocks. It seems like balancing a bowling ball on top of a nail sometimes. Converters aside....the challenge of switching sources is not trivial . This device has three inputs that are prioritized, when one droops or fails it switches to the next one. Challenge #1 is that I do not control the supplied power. It could be a battery of any chemistry, a switching supply of any quality AND it can be supplied from an unknown quality of cable of varying lengths. That all by itself is difficult. It must react VERY fast but cannot tolerate false sensing during a transient load. The loads are also out of my control so I have be prepared for all sorts of scenarios. Some have tons of isolation that makes life easy and others will fall to pieces with the slightest glitch. Also, when one output is shorted or starting a big capacitive load, the rest of the outputs have to remain stable. On top of all that, all inputs have to deal with revers polarity in a way that it will not power a load, but power the logic so the display can inform the user of the condition. I really had no idea what I was getting myself into, but now that I am here, it's great to have the understanding of how much I don't know.The biggest driver of all the upgrade is to improve the performance and reliability of this system. I really appreciate the time you have spent participating in this discussion. The insight from someone doing the same thing, but with far more experience, is extremely valuable. Thank you.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 07:45:33 am
content: Quote from: tautech on December 07, 2014, 06:24:27 amThat really is the million dollar question isn't it?It's a very difficult one to answer, without throwing out blanket statements and generalizations. Last time I checked critical systems didn't work on assumptions and guesses.I think it's near impossible to answer that truthfully, without knowing more specific details, and possibly seeing a schematic.The only honest answer I can come up with is "as much as he can afford"....I know for the systems I am working with (very similar), 300-400 MHz would be a minimum.....a sample rate fast enough to give me FFT results out to what my physical capacitance constraints dictate....a probing solution that doesn't inject error into my measurement, with enough bandwidth to really see resonance faults (especially in the feedback loop of the POL v-sense)...memory depth should be enough so that my scope doesn't go into roll mode at the longest time division I need to measure (that is a bit of a misleading answer) and allows me to zoom in and resolve runt/overshoot errors...I/o's should be a minimum of 4, and the more the better.....logic probes/analyzers are less useful than full BW channels....unless we are talking about massive parallel buss (and we aren't)...so what is MY ideal scope? hell that's a good one....let's dream a bit here....1. 3GHz 8 channel front end (minimum 12 bit vertical resolution)2. Minimum 2-5 GS per channel....more is nice =)3. fast Agilent style waveform update rate...4. better than 14 Mpts (hopefully a lot better)5. runs windows OS, for iScsi and development ability6. has a plethora of math and decoding options7. support for 10 years, and free access to firmware and tech documentation8. the ability to buy service parts direct, for a reasonable cost....9. represents a phenomenal value that amortizes across the entire life of the hardware...10. LOCKS TO EXTERNAL SAMPLE CLOCK!!! and distributes unaltered clock to other devices....yup I know, it doesn't exist =)

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 07, 2014, 09:06:50 am
content: Quote from: rx8pilot on December 07, 2014, 07:31:27 amI work on those EXACT types of systems....but my dynamic loads are resistance wire....with wildly varying tempco....and then the secondary loads are processing systems, that need to process sensor feedback on the primary load...EXTREMELY fast. We need power accuracies in our systems, that really even skirt the usefulness of 6 1/2 dig DMM's. In some cases extremely tight clocks and "over the top" VR is required.The other big problems in these switchers is ringing in the inductor (physical). Especially with a low profile SMT solution. If the thermal constraints are bonded to the PCB...then this ringing can cause havoc to multilayer ceramic caps. As you well know we NEED ceramics for their low ESR (on sense loops especially) and big electrolytic is a no no....for both thermal AND freq vs impedance issues. Also tantalum is a no go in fire rated systems. No way am I sticking a 22uF tantalum on a system with a dynamic or shorting load.....so we are slaves to the ceramics....and the number one cause of instability in DC pol regulation is ringing in the caps/feedback loop...ESPECIALLY if you reference v-sense to the control loop....I can tell you FOR SURE, you are going to encounter this set of problems....especially when your PCB density goes up...and that happens AFTER prototyping. Then shit gets crazy (crazy fun with the right tools)You DO need a device that can resolve these problems. Can you solve them with pencil and paper....YOU BET....and by the time you use that method + trial and error, the market will have abandoned that technology and you will be an old manModern scopes are here to HELP us get things to market. That is the trend is ALL development tools these days. Time to market is everything today. That isn't going to change. This isn't 1950, where a TV repair man comes and plays with some tubes and guesses around about some unknown physics. We understand more about our world today, than at any other point in history. The time to guess is well over.That is what these modern tools are about. It's not enough to see a sine wave at 20 MHz anymore. That is the realm of hobby/maker discussion. If you want to be serious and competitive and move with the times then you need to employ tools that HELP you do that. Looking at some monochrome screen and saying "yeah it's noise, but that must just be the probe" is not going to go very far these days.Even in government contracting it's getting serious (is that even possible?). The public sector is looking to the private sector....for BIG things....hell even space travel is becoming "commoditzed". Gone are the days of bloated 20 year projects. The resources just aren't there anymore. Financial, physical and intellectual.I never understood why so many engineering students get stuck in "teaching"....not until very recently. Traditional tools and programs just don't prepare people for the reality of the industrial machine. About all a traditional engineering degree and toolset is good for these days, is pulling your dick under the podium of some theoretical physics lecture....in the meantime people are actually making things that dramatically CHANGE humanity and our needs/wants.I know that's a bit far off oscilloscope discussion, but let me tie it together.With these modern ideas, systems and economical approaches...it's no longer good enough to get by with "just good enough". Before I am dead I will have 9 billion minds to compete with...for my share of the remaining resources. I sure as hell want every edge possible to get there. If that means i have to look at things a new way....and drop my per-conceptions about "only ever needing xyz bandwidth"....or "eh don't worry about that glitch...it still works"....SO BE IT!!!If you would have asked me what tools I needed 5 years ago, to "make something happen", I surer than shit wouldn't have said what i am saying today. Such is the pace of "progress".If you ask me what I need today, to look out to TOMORROW, well then I have learned some very valuable lessons.....and my answers would be a lot more open minded and challenging than "I need this"....The real answer to your criteria, is get what you need to realize ALL of the potential problems...and potential diversification benefits of doing something "new". If your technology is refined enough and versatile enough you can re-purpose it through endless re-iterations (more like repackagings) and absorb the investment in those "fancier" tools across a more realistic product cycle life. Hell it has worked brilliantly for apple and their little portable phone thingy. Same damn thing, in 6 plus re-packagings...and idiot masses still MUST HAVE IT!!! They invested MORE up front...to do something really cutting edge, so that they could reap the ever increasing margins on re-selling the same thing 10 years later.Sounds like a winning plan to me....seems to have worked for them. That philosophy, coupled with good marketing...has allowed an electronics company (don't forget) to take over the mobile communications AND music industries....If your product is successful....you won't be worried about an extra $10k you spent at the beginning....but if it fails, you will always wonder if/why you didn't buy the right tools to lead to success.Damn that is one annoyingly long winded response....sorry about that

author: tautech
author_rank: Super Contributor
timestamp: December 07, 2014, 11:18:10 am
content: Quote from: TunerSandwich on December 07, 2014, 09:06:50 amMinisterTunerSandwichstands at the pulpit and delivers his sermon.Wonderful to see such passion in this profession. It is a rare thing.Meanwhiletautechgoes looking for the previously spec'ed scope.......................

author: nctnico
author_rank: Super Contributor
timestamp: December 07, 2014, 12:41:35 pm
content: Quote from: rx8pilot on December 07, 2014, 03:25:10 amThe statement above makes me wonder: do you simulate your circuits? Many of my more complex circuits start as a simulation to get a feel on how a circuit will behave, what waveforms to expect and which parameters have the biggest influence (power supply, temperature, etc). Sometimes I try various solutions in a simulation before building a prototype. In a simulated circuit it is also much easier to look at the current through several components. The downside is that simulating a circuit and getting meaningfull information is a bit of an art in itself.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 07, 2014, 08:15:55 pm
content: I have not simulated any of the circuits. Its hard to tell whether its a worthwhile skill/exercise compared to "buildit and study". My ME experiences with simulation did not serve me well. I believe that is mainly because I could physically build a machine and go through a myriad of tests to destruction to build design performance data. the time it would take to build a good simulation and study it was almost always longer and the resulting data (even if perfect) was limited. Building a prototype gave us information that a simulation would never deliver. Now, keep in mind, I do not design or build systems for flight, medical, etc that require far more testing and documentation. Also, just one parameter off and your data looks great, but is trash and you don't find out until you build it for real anyway.My electronics adventures seem to be similar, except that I don't know anything about simulation or the data I could get from it. On paper, it seems fantastic and almost mandatory. in reality, I fear that I would spend a ton of time and get only a handful of useful data. I really don't know - just a guess. It seems that what I struggle with in general is very subtle nuances that a simulation would not help unless I spent a huge amount of time putting it together. I can layout a PCB and have prototype very quickly and I have the equipment to build with even the finest components. My thinking is that if I go through that, I am not only testing the schematic, but also the PCB layout. The layout, in my case, can easily be the difference between a perfect result and a mysterious unstable mess [probably true for a lot of designs]. Do you think this could be a logical fallacy? I am projecting bad experiences from an unrelated discipline here, so I don't really know.Like I said, it seems great to know the 'ideal' result to be looking for. From one end to the other, my current project has a little over 500 components and 180 BOM line items. I would be totally intimidated with creating a simulation of that for sure. I could have simulated smaller sections, but overall it would take the same amount of time I guess. I will read up on the subject to get an overview of what it involves, software available, required skills, etc...

author: nctnico
author_rank: Super Contributor
timestamp: December 08, 2014, 12:19:58 am
content: I think simulation is definitely something which could aid you to help understand what is on the screen of your oscilloscope.During my EE study there was a lot of focus on simulating circuits. In one lab project we had to calculate a circuit 'by hand', simulate the circuit and built it. This was an interesting exercise but I didn't feel I had learned enough about simulating a circuit so I took on a much larger project: designing, simulating and building a pre-regulated 600W linear lab power supply with MOSFETs. The simulation quickly showed some things I overlooked which I fixed in the simulation. When I build the power supply I also discovered that some parts didn't behave as expected. It turned out the simulated circuit behaved the same but that I just didn't test those conditions. Nowadays I often go back and forth between a real circuit and the simulation results to check whether what I'm seeing on my oscilloscope is right or not.Simulating an entire circuit is a good exercise to learn what is useful to simulate and what does not need to be simulated. If you get more grip on simulating a circuit you will be able to create simplified models of the important parts of your circuits. Simulation can also help to find an elusive problem in a circuit: A couple of years ago I had to get a device through an EMC test and I only had 2 days to solve several issues. One problem area was an isolated DC-DC converter. The HF interference caused be the MOSFET was easy to solve by adding some gate resistance and getting the snubber right. But it turned out there was another source of HF ringing as well at the secondary side. The board was quite crowded and I didn't had enough time and boards to try several different methods in a real circuit. I also needed a deeper insight on what was going on in the circuit so I created a simplified model of the DC-DC converter which showed the same ringing as the real circuit. By looking at the current through the components I found out the reverse recovery of the rectifier diode was causing a nasty spike. I simulated several possible solutions and ended up with putting a ferrite bead in series with the diode. Needless to say the board passed the EMC test.

author: coppice
author_rank: Super Contributor
timestamp: December 08, 2014, 01:22:32 am
content: Quote from: nctnico on December 07, 2014, 12:41:35 pmThe beauty of getting information out of a simulation is your probes do not influence the circuit at all. Anything you see on a scope must be treated with suspicion.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 08, 2014, 01:30:56 am
content: Quote from: coppice on December 08, 2014, 01:22:32 amThe truth.Quote from: nctnico on December 08, 2014, 12:19:58 amAny recommendations on where to start? Software? Educational resources? I can see the wisdom and will dedicate some time to the subject. Do you find it a challenge to build the models of specialty silicon or is it SOP for the manufactures to provide simulation models?

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 08, 2014, 01:38:19 am
content: Simulations are only useful for very basic predictions. They mostly represent static ideals. Also the simulations have to be properly characterized for the specific components you are using. It's virtually impossible for a simulator to predict something like a resonant interaction between a PCB and a component, or a thermal condition which isn't yet characterized by the simulator.They are certainly helpful tools, but are no substitute for probing a real production PCB. In some ways they can lend false security. Even the best simulators (dassault) fall short of 100% prediction.Let's look at some simulations vs real world response of a dPOL signal path. This is a simulation of AC response. Freq vs energy/phase.....I can do step response later this week (when I have some time to set-up the experiment).

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 08, 2014, 01:43:34 am
content: In the simulation you can clearly see a predicted response curve.....which is partially represented in the real wold....BUT have a look at the HF energy which the simulation missed.This problem is compounded with a dynamic load (I will simulate that on the next experiment).I purposely use crap power supplies for these tests....to see how input phase/ripple changes the dynamic responses of the POL under test. It's great to have a collection of crap SMPS and linear PSU's. Feeding precise, filtered signal into the POL front end is a terrible way to test these devices. In the real world we have to assume that our hardware is being connected to crap wall-warts or similar. I can also run this experiment using a battery, with both high and low margining. You will see just how far off the predictions are from the real world response

author: rx8pilot
author_rank: Super Contributor
timestamp: December 09, 2014, 09:01:06 pm
content: This is interesting, although I don't feel I am able to understand exactly what is going on. I will look it over one more time and probably have some questions...Thank you for the setup, hoping to be able to interpret what is going on.

author: nctnico
author_rank: Super Contributor
timestamp: December 09, 2014, 09:14:34 pm
content: Quote from: TunerSandwich on December 08, 2014, 01:43:34 amIMHO that is due to the limited model you are using for the simulation. One of the things I like to simulate are worst case conditions which often reveal hidden problems. A 'crappy SMPS' is not very scientific

author: rx8pilot
author_rank: Super Contributor
timestamp: December 09, 2014, 09:47:47 pm
content: While not true in all cases, my experience in ME was that by the time I created a suitable model for a simulation that was to be believable - I could have built and destructive tested it a few times already which gives me the ultimate answer. Even after a good simulation has been built and analyzed, you still have to built and delicately test the circuit to confirm and look for anything unexpected. If there is any truth in that - why/when bother with simulation?I too test with "crappy SMPS" sources to learn how my circuit deals with a variety of non-ideal situations. It seems that simulating and scientific analysis  would not be nearly as good as throwing the real world at it, right? I have not spent much time understanding my own definition of 'crappy' simply because my customers wont or cannot adhere to that - if my device says '12v IN' and their random SMPS says '12V OUT' - they will simply plug it in and expect it to work. I can setup a test with a variety of DC sources and examine the resulting performance impact on my circuit.Is this a logical fallacy, or a reasonable way to go about it? Maybe use a simulation to set a baseline to measure from?

author: nctnico
author_rank: Super Contributor
timestamp: December 09, 2014, 10:18:36 pm
content: Quote from: rx8pilot on December 09, 2014, 09:47:47 pmA simulation can show whether a circuit idea can work. Simulating for worst case conditions can show whether a circuit works in real life. In a simulation you can check the effect of a crappy power supply on the control loop. You can test several control loop methodologies to see which one is best versus the number of components required. Again, it took me quite an investment in time to learn how to simulate circuits and interpret the results but I do feel it was worth it.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 09, 2014, 10:37:17 pm
content: Quote from: nctnico on December 09, 2014, 10:18:36 pmWhat? You need skills for this stuff?Seriously....in ballpark terms, can you say what it took financially and temporally to get a workable simulation skill set. I know there are a million variables in that question, so maybe just a note on your own experience. I am over committed at the moment on education so I have to choose my battles wisely. The sequence in which I learn is nearly as important as what I learn.

author: nctnico
author_rank: Super Contributor
timestamp: December 09, 2014, 11:34:15 pm
content: Though question. I'd start by working through a small (online?) course on how to use Pspice. Perhaps spend two hours per week. That should give you a good grip on 'the tool'. The next step would be to take on a project to see where simulation diverts reality and why. There are also mathematical pitfalls causing the simulator to quit. Sometimes it takes placing some extra resistors to get a circuit to simulate. A bridge rectifier is such an example.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 12:20:40 am
content: Quote from: rx8pilot on December 09, 2014, 09:01:06 pmLet's break it down.First let's understand the signal path. Leading up to the probe test points.The chain starts with with a Korad KA3005D. I chose this supply, because it has two criteria that are fundamentally misleading. Number one it consistently has an overshoot of about 100mA beyond it's current limit set-point. Number two, despite being a "linear" supply it injects about 50mV of "ripple/noise" into the IBV of the circuit under test. The next point is it's less than ideal regulation. It seems to not be able to handle transient events, with much elegance. We could do a separate review of this specific unit, but I believe others have done so already.The PSU is routed to the next item through a "purposely dodgy" set of test leads. They are stranded wire, of unknown origin, and are terminated into the PSU with alligator clips. Certainly not an ideal connection.The other side of the leads are terminated with screw down, banana style terminations. Those are coupled into female banana receptacles of "high quality" (Pomona electric).The female banana couples to a deans connector, using solid core OFC wire (very high quality test lead/adapter, I built in house).The next piece of hardware in the chain is a "hobby grade" power measurement device, from "astro flight" (not sure what pcb is being repackaged inside). That piece of hardware shows me the drop in the leads and shows watt hours used. It draws around 50mA of parasitic current. Again I not trying to build the "best possible" front end power, leading to IBV.From the power meter we again have well made deans to banana pigtail (overkill quality, built in house).That is where the external power ends and merges into the IBV section of the circuit in test.The circuit in test is quite complex, and I won't go into lengthy detail, but it's basically a single phase dPOL and controller (based on an atmel MCU, but with high speed acquisition and switching control topology).The simulation is the programming interface for the dPOL and controller. There is no better simulation available, as it is built specifically for this circuit topology.In the programming interface I have control over an internal feedback loop/filter on the POL itself, as well as the sequencing signal sent (via 56 bit com signal) directly to the POL.The output has been optimized for the "best case scenario". Margining is set up, so is tracking and so is ultra tight VR. Our output voltage on the pol is set to 5.5 volts.The output V sense is coupled back to the digital filter section/feedback loop. So the meters don't load the front end of the pol AT ALL.We can clearly see that two calibrated and verified meters are reading very close to 5.5 V. One is set with fast integration time, the other is not. That is a point that should not be overlooked.The test leads are of high quality and free of faults (the main DMM test lead is shielded and properly terminated into 10Gohm).The scope probes are active FET units and have been fully deskewed, compensated and temperature calibrated. They have also been nulled against a direct ground, to verify that no noise is being injected in the HF ranges. They are 1Mohm 1.8pF with a ratio of 10:1 and a dynamic range of 5v....the dynamic range is matched to scope input rise time quite well.So that is a pretty ideal test right? There is a trap though....I was hoping someone would spot it, but maybe it's a bit too complex to be obvious.Pay careful attention to the voltage min max during the switching pulse. I am triggering off of that event on the scope. Have a look at the readings. We are def overshooting 5.5 V, on both the positive and negative edges of the full switching phase.There is NO bandwidth limiting on the scope front end. If I was to do some sin x/x interpolation, some averaging and employ a 20MHz input filter (AC coupled) we would completely miss this HF overshoot.So let me explain the trap now. The POL output has 2 4.7uF caps to help it out. Obviously those caps are ballasted and properly used. They are ultra low ESR multilayer ceramic.The sense loop has been calibrated to respond out to around 10KHz. OOPS!!!! There should be another set of parallel filters on that control loop!!! I posted the response graph earlier in this thread. So essentially there is a physical ringing external to the POL, but coupled into the control loop. That is why we are overshooting our 5.5 v target, during the POL switching step responseI can go into more detail here, as this is obviously a dramatically over-simplified explanation.....but suffice it to say that we wouldn't have caught these problems on the REAL output of the device, if we hadn't employed this "overkill" methodology of measurement.Is that peak voltage enough to cause an issue in the turn on sequence of a processor? Dunno....that depends on the processor, application and target use. I know that it's an UN-acceptable scenario in my book. We are overshooting 0.05044 V above our target.My point here isn't to explain WHY this is happening or how to solve it....the point is simply to illustrate that the simulation fell short of predicting the real world response and that real world response would have been missed with tools of lower bandwidth

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 12:26:33 am
content: Quote from: nctnico on December 09, 2014, 09:14:34 pmOnce again, you are missing the boat here.Number one, I didn't include screen shots of the entire simulation....only it's predicted output. i would think if you had simulation experience that you would assume the simulation is complete? Do you need screen-shots of the other 5 pages of parametric simulation? Isn't the predicted response enough?Also you are failing to realize that the circuit in test is in fact a VERY high quality (really bleeding edge) DC-DC POL. It's being fed by a less than ideal IBV, to try and gain insight on what happens to a tightly regulated POL, when it's input drive is less than ideal.You are jumping to conclusions again. This is a pattern you are displaying. I am not trying to be rude here, but you are continually making assumptions. That is my entire point here in this thread. You can't make assumptions about your predictions or what "should" happen.....and then limit your tools to only measure your predicted deviations. I hope you see the pattern emerging, on your end, and look at it carefully. It's a very solvable "bad habit".Would you like screen shots of the other components of the simulation? coming up...

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 12:32:26 am
content: Quote from: rx8pilot on December 09, 2014, 09:47:47 pmTrust me, you are doing it right.....simulation is great for early development of VERY complex systems. It is a large waste of resources, on small run, quick to market ideas though. NOTHING beats whacking together a basic prototype and measuring it, against your models and predictions.I personally simulate up to a point, but very quickly abandon the simulations and focus on reality. Simulators are getting better every day, but they aren't a substitute for putting the right tool on a live circuit, with a live load (dynamic).Why spend months building and debugging a simulation, on a circuit I can whack together in 2 hours? I can see the benefit in a system, where you are dealing on macro scales of complexity.....but the stuff you and I are doing (albeit complex in theory) is very easy to assemble and throw some proper test gear on.

author: nctnico
author_rank: Super Contributor
timestamp: December 10, 2014, 12:49:26 am
content: Quote from: TunerSandwich on December 10, 2014, 12:26:33 amYou keep dumping loads of incomplete information without getting your point across. I'm pretty sure you know what you are doing but to me you seem like a professor who is exited about his area of expertise but is just mumbling and writing incomplete equations on the black board. You are writing about a 50mV overshoot; that can be relevant for certain loads but all the equipment in your pictures doesn't show that overshoot hence there is no evidence in your pictures to justify the test setup you are showing. Let's keep the discussion more generic instead of focussing on one niche area of circuit design.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 12:50:48 am
content: Here are some more thorough screen caps of the entire simulation.....I assumed that most folks would only care about the output result....but I can see that is not the case. There is simply NO better simulator available for this specific circuit. This simulation is built by the component level manufacturer, and is literally as good as we can hope to get...for this specific scenario.....This is NOT the actual simulation of the response in the test I showed above. I couldn't be bothered to repeat the entire experiment, but let's assume all of the simulation values were filled in correctly for the prior test (as they were). The predicted step-response and margining in the prior test, simulated to below 5.5V output (in both AC/phase and DC step response). These are random values (defaults).My point here is not to teach how to simulate and measure this specific circuit....rather it is to show that predictions, simulations and assumptions are only as good as the data your test can back them up with

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 12:54:33 am
content: Quote from: nctnico on December 10, 2014, 12:49:26 amYou have got to be kidding?The overshoot is CLEARLY shown on the scope....and it's shown as HF in nature. I am not a professor.Are you being serious here? Or just trolling? I am dumbfounded by your responses.....The completeness of the experiment is FAR above and beyond ANYTHING you have provided. As you have provided NOTHING but inexperienced ramblings, in reply.How can we keep a discussion "generic"....when the OP proposed SPECIFIC criteria?Hoe much more specific do you need this to get? Just because you don't understand the results....doesn't mean the problem is on MY end....like I said you are throwing generalizations out, with NO data to back them up.....on a VERY specific subject....here is your overshootIf YOU don't understand my point....then it's because you either can't interpret the data, or you aren't reading the entire responses.....The point has been, all along (and emphatically overstated) that 100 MHz front end, is going to MISS critical step response event, in multi phase architectures....it's clearly happening in a SINGLE phase architecture.....that my experiment is based on.....Would you like me to post a more complete experiment on a multi-phase system? I am trying to help OP develop his requested criteria here.....not teach a class on how multi-phase DC-DC systems work, and their possible pitfalls....if you would like me to do that make a new thread. I am just here trying to help someone answer their original question, on the basis of experience and insight (that goes beyond most industry ramblings and marketing)I have made NUMEROUS suggestions, in answering the OP's criteria requirements.....SPECIFIC suggestions. Instead of making suggestions about scope criteria, YOU have gone down the path of simulation (which has nothing to do with scope criteria) and then accused me of taking this "off topic". How am I taking it off-topic, by showing real world use case scenarios, for a 400+MHz front end (in relation to DC-DC regulation), while YOU are going down the road of simulations?Can you give OP a reason why (or why not) my suggestions for 400Mhz (or more) of bandwidth are useful to his needs? I am showing why with real world experiments....and you are talking about circuit simulation....In this picture you can clearly see the circled are of the FFT (to the left) which the simulator predicted.....(have a look at the response charts again if you missed it). On the right you can clearly see HF content that was not predicted. In the waveform you can clearly see that the HF content is causing the control loop (vsense coupling) to cause a switching overshoot, that measures ABOVE the predicted range in the simulation...the ripple shown, which is more frequent (brighter part of the trace) is well within the spec of the system......the overshoot event is NOT....and if I didn't loosen up the over provisioning specs in the controller, it would have caused the entire system to turn the POL off....

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 01:37:42 am
content: Let's have a look at the output set points of the POL and controller.....You can see that the load regulation ABOVE 9 amps is set for 1.05mV/A....and that the target out is set for 5.5 V.So then why does our scope pick-up 5.55044 V peak? Despite the POL margining the output above 9 amps?The POL should be outputting 5.5 V - 9.45 mV. It's clearly NOT.This is because the capacitance of the v-Sense (which is controlling the feedback control loop) is incorrect. Despite the simulation and predictions saying it "should be good enough".THAT is why we need these tools. "Good enough" is obviously NOT cutting it here.....and you never would have seen that problem, with lesser tools....Here is a screen-grab of the POL output set-points.....

author: rx8pilot
author_rank: Super Contributor
timestamp: December 10, 2014, 02:26:06 am
content: Of course...I see the story now.the HF spike would never be seen at 100Mhz and you would think all is well with the world. BTW, what timebase was the scope on? Is it 1us/div?It would be such a frustrating scenario when I am experiencing issues on the load, but the scope trace looks perfect at 100Mhz. The cost difference from 100Mhz to 500Mhz is not trivial, but clearly needs some consideration. I am putting financing together for a Pick & Place system, maybe adding a no excuses scope could keep me out of trouble. With all that is going into this effort, it would be criminal to let a glitch sneak by creating some mysterious problem that may never be found.There are Agilent MSOX3000's in 4ch 500Mhz and 1Ghz nearly 50% off list at the Keysight eBay store. At those prices, I would be foolish to not go big.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 05:19:12 am
content: Quote from: rx8pilot on December 10, 2014, 02:26:06 amABSOLUTELY....that is the point. Do we really want perfect looking traces on our scope? hell NO!!! That is the point of having the scope, after all. I WANT to see problems in the trace, and want to KNOW those problems aren't my probing solution. That is not as simple as one would think, without having the experience in the SPECIFIC application intended.Is 100MHz front end good enough to see a 20MHz sine wave, from a pristine generator, in a clinical environment? Sure.....but how is that useful to OUR SPECIFIC needs. We need to see reality, and filters and ideal scope traces do the opposite of allowing you to view that reality.I personally want to make decisions based on the most data possibly available to me. That is how engineering works. It doesn't work on the basis of guesses and simulations. Those predictions and tools are useful, obviously, but don't represent what it takes to ship and warranty a tangible good or service.I think you have an excellent grasp of what it takes to do this, obviously some other folks do not. I also, obviously, have less of a grasp on YOUR specific use case scenario than you do. Even though my scenarios are similar they are not mirror copies....and we also know that mirror copies (in physics and science) are impossible. That's where I think it's beneficial to look at what myself, and others are saying....and learn enough to make your own value judgements.My experiment is pretty useful in determining WHY some extra bandwidth is useful. I think it's proof beyond a reasonable doubt.....BUT the specific spec and manufacturer and model (and budget) are almost impossible to make firm statements on.I personally think the used LeCroy gear is a better value than used Agilent, but that's just some semantics and spin.....as long as the tools do virtually the same thing, then the rest is user preference, and $.I think the Agilent MSO3k is a bit lacking, in comparison to a windows based solution....especially in tool development....but that's just my opinion.There are good deals out there, and like I said the extra couple grand you spend now....won't amount to a hill of beans if the product is successful.If it was me, I would be looking at MSO4k or better, and LeCroy WRXi or better.....I personally went with LeCroy (which replaced the same Agilent hardware we are talking about)Yes the timebase is 1uS/div....it would only get worse from there.....also it was at a sample rate of 10GS....which is what allows the FFT range out to 5GHz. Obviously we have to have a front end that can capture the HF event to begin with though.Like I said I could go on and on about how and whyt this is happening, and how to solve it.....but that doesn't lend much insight into scope criteria....and there would of course be my consultation fee

author: tautech
author_rank: Super Contributor
timestamp: December 10, 2014, 05:37:51 am
content: QuoteYou've earned one with your contribution.There will be many that find this thread and be grateful.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: December 10, 2014, 06:13:34 am
content: reading mr tunersandwich input is very eye opening. and i agree about the extra bandwdth. but for someone going beyond starter scopes, there is just so much to consideri have been looking at ... many used scopes options. but when i fall on lecroy, i saw some that are year 2006 types ... still with 1.44 floppies ... would you (or anyone) care to give some hints about its ... usability? iirc, its also a 10G/sa. for under USD4k. i am guessing just for the bandwidth, there is no way i can get anything at over 1Ghz nearly as new or usable at under USD4k ... but on the other hand ... these are really old units

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 06:15:43 am
content: Oh one VERY important thing to note about FFT results....and I should have mentioned this.The FFT plot is based on a non-truncated window of the waveform timebase.Let's break that down.The timebase of the waveform acquisition window is 1uS/div. The non truncated FFT analysis window spans that ENTIRE timebase. So the FFT result is that of a 10uS timebase, in it's totality.HOWEVER averaging/persistence was turned on, for the FFT. So the results are across a few minutes of total waveform acquisition. This is how we would test our margining on a POL anyhow.We want to see it's behavior, across a wide window of time....in relation to frequency and dynamic load changes. This is very key in finding these problems. Understanding the problems? Well that is a discussion for another day......but before we understand anything we have to quantify/define it.....I think our little test here is the beginnings of understanding. It also mirros the WAY in which we ALL quantify and debug potential "problems". Of course determining if a glitch is a "problem" is wholly dependent on the critical nature of your application, or lack of

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 06:25:36 am
content: Quote from: tautech on December 10, 2014, 05:37:51 amThank you for the accolades.I have always assumed that what i am presenting here is common knowledge. I might be incorrect in that assumption. So if anyone playing along isn't understanding the totality of the experiment....then that is my fault for making assumptions, that everyone doing this has the same level of insight/experience.That obviously doesn't say it's above or beyond anyones scope (pun) of understanding, but it does say that i need to break down my own assumptions on the level of experience of statements/questions posted here.There are no bad students.....only bad teachers

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 06:33:15 am
content: Quote from: 3roomlab on December 10, 2014, 06:13:34 amI wouldn't focus too much on age. If it passes spec....and isn't beat to shit (obviously) then you really only need to look at a few things.Input bandwidth....sample rate/clock....and sample memory depth. Older units will almost always have "less" total sample memory. That isn't always true though.The other important aspect is waveform update rate. Especially when dealing with long time divisions.On a LeCroy having the "wave stream" feature is VERY nice for quick glances at certain problems. It's a very nice persistence tool, available at a button press.Another key aspect is acquisition modes. Sometimes the averaging and sin x/x interpolation is VERY useful.....and on leCroy units there is also a "hires" mode....which reduces the effective input bandwidth (it's really a noise filter), to give greater vertical resolution.....they claim "interpolated 3 bits".I am a bit of a "newbie" on LeCroy scopes, so I might not have the most accurate insights into the brand. However I do believe they represent phenomenal value in the used market. I simply could not get a tool, which stitches together post processing blocks, the way LeCroy x-stream engine does.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: December 10, 2014, 09:09:36 am
content: well i guess i maybe side tracking the issue of high end scopes, but it wouldnt hurt to ... kinda of compare old lecroys ... to say the current problem the rigol is having : jitter issues? ... im not familiar with anything higher than my 20Mhz analogue. but i sure is a fan of high sample rates (or BW). do high end scopes suffer any kind of bugs?1 of the things i noticed about lecroy is, it is actually just a XP PC running very dedicated hardware to grab A to D ... so comparatively ... even if i do get something like say an agilent 2xxx series or anything up to a USD 20k unit ... a lecroy 1.5Ghz 10G/sa is still worth so much more @ USD4k right? (and it is 4 channels) ... that "juice" is in its pristine AD and DSP engine ... if its broken in its knobs or whats nots ... those are ... sort of generally cosmetic? yes?and when you say x stream engine, that would be in their scopes models that are after 2008? (im totally unfamiliar with their tech milestones, but from what im seeing ... it seems they have left the Mhz game a long long long long time ago)edit : see what i mean?http://www.ebay.com/itm/Lecroy-WavePro-960-WP960-4-Channel-2-GHz-Digital-Oscilloscope-/271697521072?pt=BI_Oscilloscopes&hash=item3f426f29b04kUSD i think will only get a agilent 300Mhz .... *expletives* ... this 1 is 2GHZ !!!this seller is near me, 14 year old 584, but what i dont know is, how much functions depend on the floppy, and if that FDD could take the "chingchongchang" FDD to SD converter lolhttp://www.ebay.com/itm/LECROY-LC584AL-1GHZ-4CH-DIGITAL-OSCILLOSCOPE-2-8-GS-s-/321583104404?pt=BI_Oscilloscopes&hash=item4adfd8c194http://www.kustompcs.co.uk/acatalog/5421.jpgedit :: aha ... new knowledge ... so the actual effective sample rate is around 500MS/s ...

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 09:32:25 am
content: Quote from: 3roomlab on December 10, 2014, 09:09:36 amAbsolutely a "high end" DSO can suffer from software/firmware bugs.....it's still a digital system (at heart). I would expect a reputable, high dollar, brand name to do some better testing on their hardware, but that isn't always the case.The lecroy unit you posted is NOT running the x-stream engine. It is lecroys own dedicated OS (I am not fully educated in those older models).Obviously a front end bandwidth is what it is....BUT we also have to consider the processing behind it....and if it's up to the task of fully resolving analogue events on the input a/d.it seems lecroy has invested more in user interface, than most other brands.....their MAUI touch software is truly leagues ahead of others. It even makes touch use on win XP totally workable.it also seems lecroy is focusing efforts on high vertical resolution scopes (which is AWESOME). they do still make some of the absolute highest bandwidth lab scopes in the market.....I believe that lecroy represents the best value in the used market....especially for those looking at post processing operations and interface/tool development.....I could write a few books on the features I have discovered and used, in the wr64MXi, I only recently acquired.I also believe (opinion) LeCroy has the edge (higher end models) in triggering. Hands down the best triggering systems i have ever used in a scope. They simply put to shame even Agilents "ultra high end" models.I am currently considering the HDO8k from LeCroy. That's how impressed I have been with my used WR64MXi acquisition. I personally wouldn't hesitate to buy LeCroy again, despite the new values being a bit "overinflated" (IMO).Used, it's a no brainer.....feature set to feature set the lecroy I have, from 2009....still out classes anything offered from Agilent....The downside is the lower waveform update rate, and memory depth.....neither of which bothers me very much....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 10, 2014, 12:07:26 pm
content: Quote from: 3roomlab on December 10, 2014, 09:09:36 amNot necessarily. Newer scopes (using technology LeCroy calls 'X-Stream') are running Windows (W2k, XP, Vista, 7 depending on the model). X-Stream was introduces with the WaveMaster 8000 IIRC in 2002, followed by the WavePro 7000 and WaveRunner 6000 in 2003 and 2004.The predecessor scopes (WaveRunner LT, WaveRunner2 LT, WavePro 900, mostly made between 1998 and 2003) use a PowerPC processing system and run VxWorks as OS. These are still great scopes, though, and offer many advanced capabilities, although they lack the touchscreen interface (MAUI) of the X-Stream scopes. These scopes were made by Iwatsu (although designed by LeCroy), which means the build quality is excellent.The even older scopes were the 9300 Series (mono CRT, 1994-1997), followed by the LC Series (LC 300/500 with color CRT, LC 600 with TFT, all between 1998-2000). These scopes run some old proprietary OS which is more limited than VxWorks in the later models. The 9300 has a 68k processing system, the LC is PowerPC. The build quality isn't half as good as the later Iwatsu-made scopes, Unless you're into collecting old scopes, I would not invest any money in them.Before the 9300 there were the 9400 and 7200 Series, both roughly from the late 80's to the early 90's. Same here, unless you're into vintage scopes, avoid.All the listed non-Windows scopes (9300, LC, WaveRunner LT, WaveRunner2 LT, WavePro 900) use the same user interface. 9400 and 7200 have a different UI, though, much simpler (obviously).QuoteThere's no "DSP engine". All processing in LeCroy scopes is done by the 68k/PowerPC/x86/x64 "PC". In fact, X-Stream does all calculations in the very fast CPU cache, not in main memory as other scopes do.QuoteSee above.QuoteAbsolutely overpriced! For a WavePro 960 I wouldn't pay more than $2k-$2.5k. For around $4k you can often get a WavePro 7200/7300 (2Ghz/3Ghz) which is a newer X-Stream scope. I didn't pay much more than the asking price in that auction for my WP7300A (made in 2008), and that came with all the software options.QuoteThe asking price for that thing is even more ridiculous than the first one. These scopes regularly go for way below $1k.And btw, it's not 'just' 14 years old, more like 15+ (the sticker on the back says made in 1999). Don't bother with it, really.These scopes were great at their time, but the color CRT is a pain in the arse, and the newer VxWorks scopes are much better anyways.Especially if it's for professional use, I'd either get a X-Stream scope (WaveRunner, WavePro) or a VxWorks-based scope (WaveRunner2 LT or WavePro 900, don't bother with the WaveRunner LT), depending on your budget.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 10, 2014, 12:09:27 pm
content: Quote from: TunerSandwich on December 10, 2014, 09:32:25 amThe (M)Xi Series is spec'd for a max wfm rate of 1.25M waveforms/sec, but I don't know in what configuration this is.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 01:28:27 pm
content: Quote from: Wuerstchenhund on December 10, 2014, 12:09:27 pmIt gets really dodgy under heavy processing and long time bases. I think that is more an issue of the GPU/OS side of things though....not sure how that waveform rate is calculated (since it's dependent on an SoC GPU host)....I have been running my MXi with the outer plastic case off the back.....that dropped temps by orders of magnitude....which lowered the CPU load (goddamn thermal provisioning/stepping). It still needs a better cooling solution. Quite disappointing in that regard.On a side note I scored an un-used LeCroy motherboard/cpu/ram etc assembly (MX855LC)....for $50!!! I might just whack that into a case and do some experimenting with it.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 10, 2014, 02:04:55 pm
content: Quote from: TunerSandwich on December 10, 2014, 01:28:27 pmAs said before I think there's something dodgy with your particular setup. My 64Xi with 1.8Ghz processor gets barely hand warm, and I know that the cooling is perfectly adequate for the 2GHz processor LeCroy offers as an upgrade for these scopes.QuoteNice catch!

author: nctnico
author_rank: Super Contributor
timestamp: December 10, 2014, 03:06:52 pm
content: Quote from: TunerSandwich on December 10, 2014, 12:54:33 amI go with what I see and that is that your multimeters are showing 5.50V like you expected. I also see an oscilloscope image with C3 set to 20mV/div and a relatively clean trace with some spikes but they all stay within 20mVpp. The offset is adjusted to -5.29V in order to see the trace at 20mV/div.QuoteThere is a simple answer to that: If I look up the DC accuracy specs(*) of the 64MXi I see that it has a DC accuracy of 1.5%. At 5.5V that is already an uncertainty of +/-82mV. As a rule of thumb you can't use an oscilloscope for really accurate DC or amplitude measurements. For such measurements a DC or AC voltmeter are much better tools. IMHO Lecroy shows too many meaningless digits in the result.BTW: IMHO the HF content could be GSM interference. It matches some GSM frequency bands perfectly. The same goes for the HF on the left. It matches the frequencies used for FM radio too perfect to be a coincidence.*http://www.testequipmenthq.com/datasheets/LECROY-WAVERUNNER%2064MXI-Datasheet.pdf

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 03:57:48 pm
content: Quote from: nctnico on December 10, 2014, 03:06:52 pmThe DC accuracy is dependent on probing solution, as well as mode dependencies.You also do realize that the accuracy stated on the data sheet is for full scale right? I assume you do understand what "full scale" means?The scope shows accuracy acceptable, for this test....when connected to my 5 V ref.The probes were tested prior....to verify that no HF artifacts were present.You can't see the entirety of the switching pulse peak, at this timebase, or lack of photo resolution.The DMM averaging is on DC....I can guarantee you where the fault is coming from, because I purposely injected it into the test. With the fault removed, the regulation is stable and within spec. The fault is in the control loop (which the DMM's were measuring....you don't seem to get what a V-sense control loop is).I seem to remember you saying earlier in this thread, that the scope probes don't matter....and a differential/active etc probe is unnecessary. Now you are saying that the HF energy is common mode noise....from RF.So which one is it...?DMM's don't show fast transients.I will ask the question again. Can you give anyone here a reason why a recommendation for bandwidth (above 100MHz) is, or is not, necessary to analyze critical step responses in DC-DC (switch-mode) converters?Common knowledge, and this simple experiment says you buy as much bandwidth as you can afford.Do you have a solid grasp on resonant interactions between external capacitance and dc-dc control loops? I ask because I do, and you are missing some very key points about the hows and whys of their operation...and potential problems. As well as the tools used to diagnose and solve such problems.The HF content on the left is exactly predicted by the simulation....I don't think you are reading or observing the simulation screens....or looking at the clearly stated set points for the controller. Which makes arguing with you about this VERY frustrating, because you are trying to explain something away, that is real...and clearly shown in all of the data presented.If you simply want to argue, to try and justify your points (which aren't accurate or based on observation) then please do so with someone else. I am not willing to have a debate, with someone who is ignoring data and trying to nitpick on topics that aren't being understood (by you). It seems when you are confronted with more data and explanation, you try to find an even more esoteric and un-tested theory as to why you simply can't be wrong (about this topic). It's not helping anyone here...First you said my simulation is incomplete (based on assumption). I posted the complete (as you can see VERY complete) simulation parameters. So rather than offering any kind of positive statement or apology you just jump to another point, which is invalid, so you can continue to find fault...that doesn't exist.meh....enough time wasted....the data is there....take it for what it's worth...or don't.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 04:39:33 pm
content: Quote from: Wuerstchenhund on December 10, 2014, 02:04:55 pmHeads up on the hybrid HDD by the way. It looks like the MBR is somehow corrupted. It failed to boot today. I am setting up a recover console to run some dsk utilities. I suppose I am just going to stick a "normal" magnetic (higher RPM) drive in there. Your experience with SSD corruption, and now mine with SHDD makes me lean towards just sticking to the magnetic drives.I am going to get back into that MOBO and have a look at the heatsink. It's entirely possible that something is not right there (can't imagine what).Without a doubt my scopes behavior seems a bit off, since the CPU change.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 07:03:44 pm
content: By the way....just in case anyone wants to know the true accuracy potential of a scope here are some pictures....Let's also clarify what the term "full scale" means....when relating to accuracy criteria.My scope has a claimed DC accuracy of "±1.0% of full scale (typical); ±1.5% of full scale?10 mV/div (warranted)"If my vertical scale is 20mV/div and my full scale is 8 div...my "full scale" = 160mVif my full scale accuracy is 1.5% (+/-)....my accuracy is +/- 2.4mV (full scale)....and chances are those figures are reported using the kit probes. The probe in test (FET) is going to yield even better results...in terms of true accuracy from the load (probe tip) to input (scope input amplifier)That sure as hell doesn't look like a discrepancy of "82mV" to me.....

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 07:21:32 pm
content: annnnnd at 5 volts.....

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 10, 2014, 07:31:52 pm
content: 20 volts? Still looks pretty damn accurate to me.....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 10, 2014, 09:18:26 pm
content: Quote from: nctnico on December 10, 2014, 03:06:52 pmLeCroy scopes have a function where from time to time the acquisition system goes through an auto-calibration cycle to compensate for temperature changes. This function (which can be disabled) increases the precision of voltage measurements, although it sometimes can be a bit annoying if the scope re-calibrates after changes to the vertical settings have been made.Scopes from other manufacturers don't do that. They self calibrate after power up and then that's about it.The specs listed are warranted worst-case limits which are valid even with auto-cal disabled.So no, the digits are not meaningless.

author: nctnico
author_rank: Super Contributor
timestamp: December 10, 2014, 09:56:10 pm
content: Sorry but if the specification says there is a typical error of 1% and worst case 1.5% you can't magically make the measurement more accurate. You have to assume a reading of 10V with a 1% accuracy is somewhere between 9.9 and 10.1V in reality. You could verify your oscilloscope against a reference but that verification is only true for the exact settings per verification. Different attenuation or offset and all bets are off. And that is just DC.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 11, 2014, 03:42:49 am
content: Quote from: nctnico on December 10, 2014, 09:56:10 pm...you obviously aren't reading the posts here...are choosing to ignore fact....or are simply trolling.My guess is you just don't know what "full scale" means. Even though I explained it to you above.....and posted pictures as proof. The scale represented is 160mV.You know those little clicks you here when you are ranging a MM or a scope?By the same token, you claim I am taking things off-topic here....but in fact it YOU that are trying to take things down the road of fiction.Explain to us what "full scale" means....and then explain why the pictures I posted above show accuracy, in accordance with the MM, and certainly within the 2.4mV/160mV claimed by the manufacturer.....

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 11, 2014, 04:48:56 am
content: somehow, even at 20mV.....and through all the noise of the crap Korad PSU (which is greater than 20mV)....the LeCroy acquisition, trigger, cursor, measurement and calibration system....still seems to be able to resolve a pretty outstanding degree of accuracy.....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 11, 2014, 03:18:15 pm
content: Quote from: 3roomlab on December 11, 2014, 01:12:39 pmI've not seen a similar thing on any other scope.

author: nctnico
author_rank: Super Contributor
timestamp: December 11, 2014, 04:19:22 pm
content: Quote from: Wuerstchenhund on December 11, 2014, 03:18:15 pmMy Siglent does a self calibrate every now and then during use. But given their relationship with Lecroy that is not a surprise.Siglent does specify the accuracy very detailed. Not only is the DC accuracy specified for the vertical deflection but also the accuracy of the offset and frequency response flatness in 3 frequency ranges. An oscilloscope may perform better than spefified but you have to do the verification work yourself and be sure to get it right if you want meaningful data beyond the speficied accuracy. Hold on to your helmet if you ever need to take measurements with an oscilloscope which need to hold up in court...

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 11, 2014, 05:12:07 pm
content: Quote from: nctnico on December 11, 2014, 04:19:22 pmIs that a SDS2000?QuoteProbably not.

author: nctnico
author_rank: Super Contributor
timestamp: December 11, 2014, 05:24:15 pm
content: Quote from: Wuerstchenhund on December 11, 2014, 05:12:07 pmIt is indeed.

author: tautech
author_rank: Super Contributor
timestamp: December 11, 2014, 07:49:57 pm
content: Quote from: nctnico on December 11, 2014, 05:24:15 pmAuto Self Cal (actually an auto Quick cal) can be disabled to a manual Self Cal mode in the Siglent SDS2000 series.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 12, 2014, 02:21:37 pm
content: Quote from: tautech on December 11, 2014, 07:49:57 pmOk, so it's a bit different than on LeCroy scopes as they do a full auto calibration, although on newer scopes (i.e. WavePro 7kA manufactured after somewhere late 2008) this can be changed so that the scope does a quick cal instead, with the loss of some accuracy. The recalibration cycles sure can pull on one's nerves sometimes.But it does show the influence LeCroy seems to have on Siglent's developments, and I'd say a quick cal is completely fine for an entry level 2GSa/s scope.Just out of curiosity, it would be interesting to see the same test Tuner Sandwich did with his LeCroy scope done with a SDS2000 scope.

author: nctnico
author_rank: Super Contributor
timestamp: December 12, 2014, 04:10:39 pm
content: I have given the 'auto cal' feature some thought and I'm leaning towards thinking it is a crap solution to hide a poor design. I think we all know component values drift a little bit over temperature. A part of the art of designing electronics is to make sure drifting component values stay within the design limits. The reason you don't see the automatic calibration on Tektronix or Agilent scopes is most probably because they don't have to because their designs are better. Worse, if the auto cal is disabled what kind of accuracy can you expect from a Lecroy scope?Now you could argue Lecroy tries to make their oscilloscopes better than their competitors but then tell me why they specify and accuracy of 1% and not 0.1% or even better? Or 1% with 'auto cal' off and 0.1% with 'auto cal' on? 1% accuracy just puts them in the same league as Tektronix and Agilent.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 12, 2014, 05:12:38 pm
content: Quote from: nctnico on December 12, 2014, 04:10:39 pmThat's utter nonsense, really. I'd say LeCroy has clearly shown that they know quite a bit about proper DSO design, probably more so than Agilent who tends to win customers more by 'optimistic' (sometimes borderline dishonest) marketing than by technical progress. If you look back in the history of DSOs, it was mostly LeCroy who pushed the boundaries (i.e. deep memory scopes, advanced processing, bandwidth pushes for real-time scopes). And while LeCroy came out with a true 12bit scope, Agilent had to resort to some oversampled 8bit scope that needed to be bolstered up by marketing to become competitive. Oh, and Agilent's UI is still as shit as it was in 1998 when they came out with their first Infiniium scope running Windows95.And Tektronix, are you kidding me? I understand some people have some fond memories from the old analog scope days, but frankly in terms of scopes their DSOs are crap. Their low-end designs are buggy, and their high-end designs are ancient (33GHz top). It's shit all around, they can't even compete with Agilent. The only sales they make are probably to people stuck in yesteryear that think the Tek brand still stands for a good product.QuoteSame or better than the specs say. As I said, the specs are worst-case assumptions, and remain valid even if auto-cal is disabled.QuoteSimply because the effectiveness of a temperature-based recalibration very much depends on the environment. The improvement this brings probably also depends on other factors (i.e. vertical setting) as well. I'm sure if they were Agilent they would have made up a best-case scenario and listed the specs for that, but they're not Agilent. So why make up some artificial scenario when the worst-case specs are already as good as for other scopes?BTW: One thing that LeCroy doesn't participate is Tek's and Agilent's 'ours-vs-theirs' comparisons where they stick some moron in front of a camera who then goes to incredible lengths to make the competing product (which is generally a lower model than their own scope model) look as bad as possible, even if this involves lying. You won't see these types of videos from LeCroy, and if any competing products are listed in some of their documents you will find that all test details are clearly specified and repeatable. And they don't try to hide if a competitor's product comes out better from the tests than their own. Such corporate behavior is a really rare thing to find these days.Somehow I have the feeling you haven't really given much thought to it at all.

author: nctnico
author_rank: Super Contributor
timestamp: December 12, 2014, 06:56:50 pm
content: I was hoping you could point me to some specifications which say what the difference is between having an 'auto cal feature' and without. As I wrote before an oscilloscope is just as good as it's specifications say it is. What I've seen in the Lecroy datasheet I pointed to earlier is a very incomplete way to specify an oscilloscope.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2014, 08:07:19 pm
content: I believe you all are not making a distinction between Self Cal & Auto Self CalSelf Cal is a Manually used feature to keep the full range of specifications within the published range.Auto Cal is self calibratimg "on the fly" the range of settings in use at the time.These are very different processes, the FULL Self Cal takes some time while Auto Cal is barely noticeble and incorporated for operator convenience and of course continued ongoing accuracy.Hence we hear relays clicking etc while the scope is in use but not being adjusted if Auto Cal is enabled.

author: tautech
author_rank: Super Contributor
timestamp: December 12, 2014, 08:22:23 pm
content: Quote from: Wuerstchenhund on December 12, 2014, 02:21:37 pmSiglent are about to release the Power Analysis option for their SDS2000 series.They supply an additional USB powered PCB for Skew null adjustment between current and voltage probes.PA is a new field for me but I hope to post some simple analysis in the SDS2000 thread.Back to study in preparation......

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 12, 2014, 08:37:52 pm
content: Quote from: nctnico on December 12, 2014, 04:10:39 pmyou are, once again, bypassing what the term "full scale" means.....LeCroy is stating accuracy over a given range.....which is then temperature compensated. ALL devices change thermally.....just because another manufacturer chooses not to take that into account, doesn't make their design "better".....it looks like I have to provide some more tests......although you won't ever be convinced, because you know it all already

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 12, 2014, 08:50:15 pm
content: Quote from: nctnico on December 12, 2014, 06:56:50 pmIs it? or is it just that you don't know what the specs are for?The automatic recalibration feature offers an improvement in accuracy, nothing more, nothing less. The specs listed in that datasheet are worst-case specifications, that means that the user can expect the scope to be no worse than what's written in that pamphlet. It doesn't mean the specs can't be better, though.Now for some dubious reasons you seem to suggest that a scope from manufacturer X which states 1% accuracy but offers no automatic recalibration is somehow better than a scope which also offers 1% accuracy but also offers a feature (which can be disabled) which improves accuracy further.Either you don't understand the purpose of specs or you don't get what auto recal is for.BTW, in regard to your earlier statement that LeCroy's design is somehow inferior to say Agilents (don't mention Tek, just, don't), I challenge you to highlight some of the (in your opinion) design flaws on the old WaveRunner LT. You'll find the Service Manual including all the schematics and diagrams here:http://168.144.151.127/manuals/82.69.35.198/LeCroy_LTXXX_WaveRunner1_Digital_Storage_Oscilloscope_Service_Manual.pdfI've choosen the WaveRunner because it's one of LeCroy's simpler designs, and the full schematics and diagrams are freely available. I wouldn't expect you to do that for something like my WavePro 7300A (which, laughably as it is, falls under ITAR anyways).So here's your chance to show where exactly LeCroy has failed with their obviously very crappy scope design. Blind me with your expertise

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 12, 2014, 08:59:53 pm
content: Quote from: tautech on December 12, 2014, 08:07:19 pmNone of these terms is standardized, and manufacturers use them as they please (not always in a logical manner). What you say is mostly accurate for older/simpler scopes which don't have a hardware GND setting for the input (i.e. on my old SDS1102CML the GND setting was pure software) and thus all signals had to be removed from the inputs manually.In terms of LeCroy's Auto Re-Calibration, this is a full self calibration which depending on the scope will take somewhere between say 3s (WR2 LT) to over 15s (i.e. WP7kA). This is done by the scope when the environmental temperature has changed by a certain amount after the initial power-up auto self calibration. As these scopes have a software-controlled input switch (1M/50ohms/GND/Cal) there's no need to remove the signals from the input.The thing is that modern scopes do a full self cal after power-up, and as long as the room temperature doesn't change (i.e. aircon'd lab environment) then the scope can be expected to maintain the specs. If the temperature changes, however, it's well possible that the full specifications may no longer maintained. The Auto ReCal feature tries to avoid that. The price the user pays for it is that, depending on how much the temperature changes, the system from time to time stops aquisition to go into calibration, which is a bit of a pain if that happens at the time when you need to find that glitch. That's why the function can be disabled or set to quick calibrations, depending on the scope model.

author: tautech
author_rank: Super Contributor
timestamp: December 13, 2014, 09:13:35 pm
content: Quote from: 3roomlab on December 13, 2014, 08:46:24 pmIn the interest to see this thread remain OT, reply posted:https://www.eevblog.com/forum/testgear/siglent's-new-product-msosds2000-series/msg567800/#msg567800

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 13, 2014, 10:06:05 pm
content: Quote from: 3roomlab on December 13, 2014, 08:46:24 pmNo. If Auto-ReCal is enabled then it will just stop aquisition and display 'Calibration' (on Windows scopes also with a progress bar.If Auto-ReCal is disabled then a manual calibration can be performed when necessary.

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 07:43:58 am
content: I hope I am not hijacking this thread too far,I was reading the thread and learning a lot, and i Have a question regarding the TunerSandwich's 64MXi accuracy:Quote from: TunerSandwich on December 12, 2014, 08:37:52 pmIt seems your scope is in fact very accurate (great!) but regarding the worst case accuracy calculations, why do you ignore the DC offset accuracy specifications ?For they scope, as far as i uderstand, it is: ±(1.5% of offset value + 0.5% of full scale value + 1 mV) (this is from the 64Xi manual, i could not find an english one for 64MXi but from the japanese one I found it seems the same)However, in your case if I understand correctly the offset is internal to the AP020 probe you are using (?), so the accuracy spec is related to the probe and the only number i could find is the 2% attenuation (10:1 transfer) accuracy, which should at least be considered (?) assuming the internal offset generator is prefect, or included in this 2%.Thanks!Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 08:11:04 am
content: Quote from: nightmechanic on December 14, 2014, 07:43:58 amI explained it a few times earlier on....but it must have gotten lost in the muck.The full scale accuracy is based on the scale represented. This is how ALL oscilloscopes and DMM work.Example. The scale is 20mV/div....8 div wide. That is a "full scale" measurement of 160mV.1.5% at >10mV/div is 2.4 mVJust like with a DMM....where the accuracy is stated as "full scale". If the "scale" is 0-10 V the accuracy might be 0.001%. If the scale is 0-100 the stated accuracy usually goes down an order of magnitude....for example, possibly from 0.001% to 0.01%.....However let's say that the circuitry was in the DMM to have a "rescaling" from 90-100V.....then we could re-gain an accuracy of 0.001%, as the "scale" would be the same width....the claims aren't for DC "offset".....as DC offset can be easily nullified etc......so, for example...if I AC couple the input and take a reading....on my specific scope/bench the sDEV in the measurement is the same as it would be when DC coupled....Also LeCroys claims are "warranted"....which is a worst case scenario. Obviously to characterize the accuracy a probe must have been used for the measurement. So if an active probe (PA) wasn't used to make those claims..... then we can only get "better".This is why manufacturer specs are generally only guidelines....what matters is what YOU can measure in YOUR lab environment.P.S.the probe I am using (ap020) has a dynamic range of 5V.....so the maximum scale I can represent with it is 1V/div....8V total....however only 5V of that scale is usable, within the stated accuracy specifications.....

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 14, 2014, 10:00:04 am
content: Quote from: nightmechanic on December 14, 2014, 07:43:58 amIt's onhttp://teledynelecroy.com/under Support -> Tech Library.Look for the WaveRunner Xi-A Manual (the manual for the Xi and Xi-A Series is the same).

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 10:06:58 am
content: As you can see the accuracy of the scope drifts as the vertical scale becomes wider.....That is what the term "full scale" means.....the accuracy has very little to do with total DC offset....The test is a stabilized voltage reference @ 5v (Maxim MAX6350 buried zener) . As you can see it was calibrated using the dm3068.... (0.5ppm/°C, ±0.02% initial accuracy)The DMM's are NOT as accurate as the scope, despite their LONGER integration times. Because they are reading DC, and not all of the signal energy is DC. The AC component can't really be read by the DMM's...even in AC mode, because the max bandwidth of the AC range on the DM3068 is 200Hz.....and it's unknown on the Fluke 289, because they don't state it (and I can't be bothered to actually measure and extrapolate.....that's why i have a scope).The important part of the measurements, on the scope, to pay attention is the MEAN. The mean is as close to the DMM's reading as the scope can get....unless I turn on input filtering and boxcar averaging.....and that would defeat the purpose of the scope....I don't want to see pretty waveforms and filter energetic peaks.....especially if I am using this as a true reference signal, or if this was a critical i/o chain. I want to see the overshooting energy.....that is the point. I want to know if the peak above mean, or the trough below mean is outside of the tolerance for my application.There is a purposeful fault in the output of this voltage reference. I built this circuit specifically to illustrate this problem. The DMM shows it as a nearly perfect V-ref for something like a 16 bit A/D. The scope shows it's clearly problematic and needs some better output filtering.The fault is in the capacitance. I keep showing these capacitance faults, because they illustrate my point about the need for bandwidth in an oscilloscope.The voltage reference is being fed by a linear DC-DC converter (ON semi LM350). I isolated the circuits, so you guys could see what is going on. The DC-DC is on the round disc PCB. (Line Regulation 0.005%/V.....0.3% nominal stability/1000hrs.)The voltage ref has a 4.7k ballast/load....which is a 1% 2watt resistor. I chose this because of it's high stability. It is the v-sense resistor for the DMM's. The scope probe (ap020) is attached to the lowest value output cap (the proper way to measure into the scope).

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: December 14, 2014, 10:25:36 am
content: Quote from: TunerSandwich on December 14, 2014, 08:11:04 amThose specs are pure scope specs and do not consider probes. These are "at port", i.e. a fully parametrized signal is laid to the input (usually via a calibrated direct RF connection, i.e. no probes).If you connect a probe you have to take it's specs into account as well, i.e. if you connect a probe with (just to take some figure) say 2% of warranted accuracy then your warranted accuracy won't be better than that. If however your probe has a warranted accuracy of say 0.5% then the warranted accuracy for that setup will be the 1.5% of the scope.With newer active probes (i.e. AP-033/034, HFP Series) which have their own internal calibration system (which calibrates the probe's amplifier section) the scope basically performs an (almost) end-to-end calibration when it does it ReCal. I'm not sure about your AP-020 probe, though, which is pretty old (it's from the old 9300 Series days, but the fact alone that a pretty modern LeCroy scope still supports their nearly 20 year old probe is just great!), as I don't know if it does have self-cal functionality.Just wondering, for your scope screenshots, why do you use a camera and not just a screen dump? You can reconfigure the printer button in the upper right corner to create a screenshot instead and save it to whatever storage you want to. Quicker and better to read. And you can still use a printer i.e. in LabNotebook.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 10:42:49 am
content: Quote from: Wuerstchenhund on December 14, 2014, 10:25:36 amI assume the specs aren't including a specific retail probe.....but they include a measurement discrepancy either way. Whatever probe/signal path....was used to measure the input amplifier has characteristics of its own.From what I have read the ap020 does self calibrate, as well as auto compensate. It does provide an end to end calibrate solution (have verified this by measuring). I did notice some consistent noise from it's FET though (90-120 ish MHz). Obviously the correct way to read all of this and calibrate the REF is with a differential measurement, into a a pre-amplifier....with some good isolation.My guess is that the input PA/A on the scope is characterized with a broadband signal (weighted noise @ known amplitudes/bins)?. There is still going to be error in the measurement chain. We don't have enough information to know for sure. However the ap020 accuracy (stated) beats the scope input (as far as I can measure/decode/extrapolate)P.S. I could do screen-dumps if you guys prefer. I mainly don't do them, because I have the camera out already to snap the test rig.....also they are extremely small (xVGA I think).

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 11:16:51 am
content: Thanks for the elaborate answer,Using your DMM analogy:Quote from: TunerSandwich on December 14, 2014, 08:11:04 amLets say I did just that (rescaling) using some ”rescaler” module that adds a DC offset to my input, then my overall measurement accuracy would be my, better, DMM accuracy + my rescaler accuracy which , as far as i understand is exactly what happens in a scope when the offset is not 0 - the overallground referencedmeasurement accuracy is the sum of the gain accuracy (usually specified in % of full scale in use as you mentioned) + the DC offset accuracy (either the scope’s or the probe’s as in your case I think).I do not see how the DC offset can be nullified (other than measuring an accurate enough reference at the DC offset setting you are using and subtracting the error).For relative/dual measurements such as peak-peak etc. then, of course, the only thing that counts is the gain accuracy as you mention.Quote from: TunerSandwich on December 14, 2014, 08:11:04 amI agree, however, (short term) sDEV will quantify the noise (source + scope). and I think that scope noise is (should be) only part of the accuracy specifications, other wise there wouldn’t be any margin for any drifts at all (time , temp etc.).Long term sDEV may not be the same due to DC offset drifts.Quote from: TunerSandwich on December 14, 2014, 08:11:04 amI completely agree, I think manufacturer specs are worst case when you are doing nothing wrong, when you are doing everything right you can get better results but you need to verify that somehow (as you have shown for your lab setup).Quote from: TunerSandwich on December 14, 2014, 08:11:04 amAnd the AP020 has a +/-20V offset capability, do you know if there is an accuracy spec for it somewhere? (as I wrote before, the only thing I could find is the 2% attenuation accuracy spec)Thanks again,Ran

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 11:25:35 am
content: Quote from: TunerSandwich on December 14, 2014, 10:06:58 amYour examples clearly show the meaning of ”Full scale” accuracy, however, I would imagine the DC offset error being the same for all the different scales (as it has the same value), so I do not understand how you can rule out any error related to DC offset?Quote from: TunerSandwich on December 14, 2014, 10:06:58 amI am definitely missing something here, DMMs (in DCV mode) are intended to measure the DC component and only the DC component as accurately as possible, if your are looking for something else (ripple etc.) then it is definitely the wrong tool, so why do you think the scope’s MEAN function gives you a more accurate result?Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 11:39:35 am
content: Quote from: nightmechanic on December 14, 2014, 11:16:51 amThe input PA gains accuracy with increasing levels of attenuation. I am not sure the amplifier class in the MXi, but almost every amplifier gains resolution (above noise floor) with less input drive (reduced THD).DC offset is a easy factor to measure, and then reject....through AC coupling....you could easily route an AC coupled line....inject a differential signal (buffered) etc etc etc....lots of methods for removing DC in a measurement...HOWEVER, keep in mind that the specifications aren't for DC offset accuracy. They are simply for "DC full scale". We have to make some assumptions that the DC offset error is going to be a reasonable percentage of the full scale discrepancy.sDEV is the only useful measurement for near 100% DC vs near 100% AC coupled. It's not a perfect benchmark, but it's a ballpark that lets us know the total DC error......it's a well educated guess. If the sDEV was wildly different we could assume that there is an inaccuracy in DC component right?The reason I recommended a traceable collection of references to the OP, was for this very reason. Before we take ANY measurement, that is critical in characterizing a warranted product.....we should verify the signal path with a reference of known traceability. Yup it's a pain in the ass.....but nowhere near as bad as the bad will caused by something avoidable.I have a spec sheet for the ap020 somewhere around here. I do remember choosing them for these specific kind of measurements. They have the bandwidth and accuracy needed, to match (better actually) the scope input. Naturally they should, as they set-up proper tip to end unity gain staging.....(within a reasonable degree....I will try to find that spec sheet).

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 12:00:11 pm
content: Quote from: nightmechanic on December 14, 2014, 11:25:35 amThe DC offset error is not stated by the manufacturer as a DMM would state. It's not wholly relevant to the use of the scope. The purpose of the scope is to resolve "noise" (always AC) above DC. An easy way to tell the DC offset error, would be to feed absolutely pure DC into the scope....with no error from the source.....and a virtually infinite vertical amplifier. Obviously pure DC wouldn't show up on the scope screen at all. So if I ground the inputs, or terminate them into 50ohm, let's say, then I should see the closest possible marker of total DC offset error.I think the context here has been forgotten. This all relates to measuring DC-DC switch-mode POL. Also other reference signals. The AC riding on the DC carrier is always relevant, as it's energy. When you get into precision regulation, this becomes highly critical. Especially inductance and AC coupling from the PCB. If I put my DMM into AC+DC mode (common) it will miss all of the AC component, beyond it's sensitivity.Ripple is a misleading term. It suggest that somehow the deviation in energy is decoupled from the DC component. It never is. The purpose of using a scope to characterize broadband energy is to measure the sDEV from the baseline DC component.here is a screengrab of 50 ohm terminate DC input. You can get a very good idea of what the total inaccuracy of the front end is this way. Obviously the 50 ohm terminator is subject to some inductance etc....but it's a hell of a lot more resolving of total energy than a DC coupled DMM.The MEAN is going to be as close to the DC component as we can get.....obviously removing ALL deviation from the front end is impossible, and there is going to be some DSP/processing error as well.....but you can see just how miniscule it is. Since I can't fully characterize the 50 ohm terminator, and BNC....I can't get a mean of 0V.....which is theoretically impossible anyhow. However look how much loser we get to the pure DC component, with narrower and narrower scales. Do it trust the scope precision down to mV? I sure do....especially when the 50 ohm terminated mean is uV

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 12:02:11 pm
content: Thanks again for taking the time to answer,Quote from: TunerSandwich on December 14, 2014, 11:39:35 amThere is a DC offset accuracy spec:"Offset Accuracy: Fixed gain setting < 2 V/div: ±(1.5% of offset value + 0.5% of full scale value + 1 mV)”(from the Xi users manual in the Lecroy website)Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 12:38:45 pm
content: Quote from: nightmechanic on December 14, 2014, 12:02:11 pmIt's incomplete. We have to go by what we measure in the environment we are calibrating in. Specs are always incomplete and shouldn't be be the benchmark for accuracy....if we can do better than them. If we do worse than them, then we can turn to them as a benchmark for solving a potential problem. I.E. my scope is 'better" than "spec". Awesome, carry on. My scope is "worse" than spec....uh oh better investigate (usually something on the users end....and usually a blindingly stupid error by a human).So if we add up our measurements AND the device functions flawlessly over a reasonable test period.....then we can have 2 markers for successfully meeting or beating "spec". I think a lot of people get buried in "specs" and ignore measurements (with traceability/repeatability) and averages.I am curious to see what LeCroy says it's "best" case scenario specs are. If we had those, and we beat them, then maybe we could look further into the matter and say "something doesn't add up"

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 01:02:58 pm
content: Here is another shot of the same measurement....BUT the pre-processing interpolation is set to 5 averages, sin x/x and leCroys own "ERES" filter. Which is simply a noise filter, that interpolates an effective "dynamic range resolution" of + 3 bits. I left the setup window open so you can see it's effect and configuration.In addition the input now has a 20MHz filter on it. So the ERES + input filter = an effectively "steeper" roll off at the filter point.I also have a zoom window open, so you can actually see the waveform. i wouldn't trust the accuracy of the zoom window that much. It's obviously interpolated and not a representation of the true dynamic range of the scope. The measurements are on the C3 waveform (not the zoom) so I do trust them, to a degree. I don't believe for a second that the scope is uV accurate though. I don't have a reference tight enough to make that determination. If we wanted to verify that, the keithly source meter would have to come out and everything would have to go into an isolation enclosure....and the environment would need better control. I also don't own a signal path I would trust from source meter out to scope input amplifier.Obviously I draw a line at what is "overkill" for my needs. However it's not overkill for something like brain research. Especially neuron or micro tubual mapping/research. Or highly advanced computational r&d.....and who knows, maybe someday we will have a need for that level of precision in DC systems. As we near 99% efficiencies and try to best them, it becomes very relevant.I digress.....here is the screen grabP.S. one critical thing to remember in any measurement, is that there is ALWAYS an AC component in any signal. Sometimes big, sometimes very little. So is a DMM measuring in DCV truly measuring ONLY DC? No. If I have a DC reference that is MORE accurate (remember accuracy and resolution are two different things), and by more accurate I mean LESS total AC inductance than the known DMM inputs/leads....ok then I can also say that the DMM is "less accurate" than the REF. Obviously this traceability then extends to a meter that is KNOWN to be more accurate than the REF (usually the meter the REF was calibrated on). I know that the REF I used in this test is LESS accurate than BOTH the dm3068 AND the MXi, as 5.00000 on the 3068 = 5.003(ish) on the scope. I did this on purpose (like I explained above). Why? Because it highlights a scenario where the scope was used to find a problem, in a DC component (dominant) that the DMM could not resolve. I certainly hope this is as well established as I have considered it to be. This is the protocol for standards and testing. Well at least the way I have been practicing the trade for quite a while. This method has worked well for me. Let's not forget the original post here was asking for criteria, for choosing a "professional" scope...for the very specific kind of work I have demonstrated and applied methodology to. Obviously everything here is specifically applied to that kind of work. I have broken down nearly every stage he will go through in development, and why specific standards and tools are necessary. I like to give thorough answers

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 02:18:30 pm
content: (I hope the OP is still interested in whats going on..)So,You have shown the noise level (sDEV) and the zero offset DC value, both look low and accurate respectively, however, looking at the scopes stated offset accuracy (as incomplete as it may be, thats all I have to go with with regards to theoretical/worst case accuracy limits):"Offset Accuracy: Fixed gain setting < 2 V/div: ±(1.5% of offset value+ 0.5% of full scale value + 1 mV)”There is a (large) error component related to the offset value, so in your example it would be 1.5% of 5V ~75mV, obviously your scope seems much better than that due to the correlation with the DMMs, but if you want to validate how good it really is you need to do so at that operating point, which as you mention is a different and difficult measurement problem.Due to the above, I am still having a hard time accepting that the scopes MEAN value is a more accurate ”DC only” value than a (accurate) DMM, but that is my problemI am not in anyway challenging the fact that large bandwidth is required for such analysis (I am far from being knowledgeable in this field, from my little experience, high frequency artifacts from DCDC converters are a problem and high bandwidth as you mention is required to understand and solve these issues), it is just the DC accuracy that I am struggling with. In the past we have done similar measurements using AC coupling (to minimize scope errors) to see all the non DC energy, and used an accurate DMM to determine the ”MEAN” value, may be a mistake on our part, although I am not yet convinced...but then again, my problemThanks,Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 03:11:01 pm
content: Quote from: nightmechanic on December 14, 2014, 02:18:30 pmI still have to trust what my bench results say...as they are a reference. So let's say I was out by X, and my device under test exhibited acceptable sDEV from "spec". Then I have to accept, that if those results beat a prediction....they offer greater accuracy than the prediction/simulation. I would trade accuracy for resolution any day, as long as the resolution keeps my device at optimal operating specifications. I would trust those results, far above what any manufacturer datasheets tell me. Unless there was some completely wild discrepancy...and if that happened, the chances of a large cross section of production devices working well is seemingly low (yield).Keep in mind, that the DMM may represent DC accuracy, with a steeper filter slope/isolation from AC....BUT the AC is, in reality, there. If the AC is low enough in frequency for the DMM to capture it, and add it to the DC (many DMM have AC+DC measurement for this reason), then you more fully characterize the total power quality of the device under test. That is a quantitative rule in formulating "power quality". It's always the sum of the total components at the point of load.Also, a DMM is a mean value across the integration time, minus the total counts equation. Obviously the higher the total polling rate, the more accuracy you will have. Obviously the higher the total integration time is, you will lose accuracy, but GAIN resolution. This is why I like to have 2 DMM, that can both do trend/min/max/avg readings. I can set each at an offset integration time (one always < other) and try to see a higher degree of accuracy, by margining BOTH results (over time).Here is another screengrab....with the same interpolation pre-processing on the signal. HOWEVER, this time I calibrate the scope against the reference.....so now the scope IS the reference. Do you see my point now about calibrating at least ONE device in the t&m chain to an accurate reference? Remember my REF is the LEAST accurate device in this signal chain. That is often the case with a consumer good that is being tested. So let's make a scenario here...I calibrate ALL devices in the test system against a known stable reference. I then measure the total offset between the entire system....and then use that sDEV as a re-calibration point for the measurement output. It's a vastly more accurate way of obtaining a larger cross section of results, that meet "spec". The other way will have a larger statistical deviation from one point of known reference. This way i maintain traceability across each piece in the test system + each device tested, with a realistic sDEV across the total "yield". Obvious failures will be more obvious. Devices that exceed "spec" can be pulled and analyzed...to gain insight on WHY they are "better" and that can possibly lead to implementing those discoveries....to further yield a higher standard. Traceability is king, above any manufacturers spec book.NOW, if the min max sDEV was supplied for each unique piece of test gear...and all items could be verified on site (of the test) then I would be MUCH more inclined to believe those statements OVER my measurements. Especially if the test gear used to verify the system was provable as "more traceable" than the system. This is why a maintained set of reference standards are important. At the end of the day, you HAVE to have your own internal references, as daily or weekly calibrations against external standards can kill you in downtime and buy in (if one set of gear is always out for cal, you need two sets....).The most accurate reading available...is not the DMMs or the scopes (notice the plurality there). The most accurate reading is the mean of the sDEV average of everything in the test chain....minus/plus the results from the hardware under test.I hope that lends an answer as to why I would say I "trust" the mean result on my scope, more than the mean result on my DMM. The scope is verified as being far more accurate than the datasheet says. The DMM is, however not classified in the same way. I am not sure my point about accuracy is being understood.....or it's quite possible that I have poorly articulated it. The accuracy of my scope is higher, in relation to total power quality, than the DCV reading on my dm3068. The specs for the dm3068 are even more "incomplete" than on the MXi. Is the DC accuracy "better" than the dm3068? That is not provable without some more investigation into the dm3068. However the ref being used says that if I calibrate against my scope reading, I have more real world representation of the total power quality at the point of load.I also hope OP is still around, as these tests all mirror the exact scenario his device will run into.....but I also think some other people might gain some insight from this discussion. It's quite an examination about core fundamentals of oscilloscope usefulness. I think i have also shown some tests, that others can do to see just where their t&m sDEV curve stands. I view that as quite important and a good investment of time/effort.BTW the measurement discrepancy between the scope and the dmm is 0.009276V (DC-5ishMHz. Oddly enough that is virtually identical to the discrepancy between the sDEV of the Fluke 289 and the sDEV of the dm3068. Too close to be coincidence. I think the dm3068 needs to be checked against a standard. I need to send out my 5v lab standard to be checked. If the 3068 has drifted that much since cal something isn't right? I did recently move it and change the environmental control average.

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 05:15:59 pm
content: I am missing something - is this the same MAX6350 reference that you have shown before or a different reference? if it is the same did you move it to match the scope/why doesn’t it match the dm3068 anymore?why do you trust your reference more than your DMM?In any case, as you mentioned, it does seem that the discrepancy between your dm3068 and your reference is too high - one of them is out as far as I understand (the dm3068 error at 5V should be +/-300uV or less if I am reading the specs correctly).I completely agree with the traceability statements:As long as you have a traceable stable (to me it means low noise, low drift, negligible HF contents) reference hopefully with the same voltage as your DUT (e.g. your lab 5V ref), you can figure out your equipments’ offsets (and noise levels) and they will be all traceable to that reference.And you have shown (traced) that your scope is more accurate than your DMM at 5V - great.Quote from: TunerSandwich on December 14, 2014, 03:11:01 pmRegarding ”total power quality”, as you mentioned, it should be the DC value + AC rms value(s), the MEAN function however, tries to mimic the DMM operation in a way by mathematically trying to extract the DC only component and the quality (sDEV) of doing so depends on the number of samples used, noise levels (and as such the used bandwidth) potentially with an ”accurate” scope (with zero gain and offset errors) and lots of memory you could do better than the DMM, but it will just filter the DC component better and reject more AC power, without enough samples you get into the same issues you mentioned for the DMM, its a "DC + some of the AC” measurement, is this what you are looking for?So now I have a(nother) question, when you send your lab reference out for calibration, that (as far as I know) is done using a (very expensive, traceable, lots of digits) DMM - an averaging, limited bandwidth DMM, do you consider that as a calibration reference for your purposes? do you assume that the AC contents of the reference is low enough to be negligible?Thanks for you patience,Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 06:00:14 pm
content: Quote from: nightmechanic on December 14, 2014, 05:15:59 pmI think you missed the paragraph where I described re-calibrating the reference to the scope reading. Again done to show the total discrepancy between the two devices.....and back up the prior measurements.What i was saying is that my dm3068 is reading a tad low compared to the fluke 289. Assuming we can trust the 289. i re-calibrate against it, and the offset between the 2 (3068 vs 289) is consistent high and low.What I have shown is the total sDEV across the entire signal chain. Also that the stability of the vref is very good....as the sDEV avearge has very little drift.MEAN on the scope is not an attempt to null AC. It's the mean above and below the total measured DC offset. The pk-pk is shown as higher frequency, but lower energy.....the applied filter removed most of the AC component.Power quality is a measurement window....in which all of the metrics are time correlated. You will never deduce true power quality with DMM + scope, unless the DMM is somehow sharing the same sample clock.The PMA software in the MXi does exactly this. It also uses a current probe to calculate watts RMS + power spectrum (10MHz) + voltage waveform. The current ripple is part of the equation as well. Memory depth is there, samplerate is there.....far above and beyond the DMM.I assume the returned lab reference is traceable to a larger degree than my equipment....with an accuracy AND resolution BEYOND my needs. I can't assume it is free of noise, so that must be verified. When the ref returns, it will be checked against all available gear in the test system, and a new sDEV will be noted. I will also check is against other known references. For my purposes, it's a prerequisite to usable measurement data.If you go back through all the pictures, and make note of the readings, you will see that the total DC inaccuracy, across all tests (scope) is less than 3mV against the 3086 (which appears to be reading just a tad bit low, in relation to other ref/289).So if lecroy worst case scenario is being calculated (by you) as 75 ish mV DC offset + full scale error.....then Lecroys BEST case must be below 3mV total that i am measuring. If it's that far off between best and worst....then it's hard to trust that the math is being done correctly to calculate the true measurement error stated from the datasheet (I do believe my math is correct, because it's almost exactly what we are actually seeing). My scope is from 2009....so it's aged well (too well) if your math is correct, if my math and measurement is correct it's right around where it should be. Have a look back at the total inaccuracy I predicted, even before posting all the screenshots and engineering the new test. I don't think it's a coincidence that they are within 6uV.Let's assume everything I am saying is totally wrong. Then we are still beating Lecroy datasheet spec by many orders of magnitude. Not matter how we slice it, we are seeing under 3mV total discrepancy across 3 very precise devices, all checked against a highly stable vREF.....DESPITE the vREF resonant tank trap I built in (to illustrate those effects). Also keep in mind that 3mV is a WORST case scenario against ALL of the tests. Some show better (smaller scale dynamic range).P.S.Keep in mind that I didn't JUST show traceability against 5v. I showed it against 20mV, all the way out to 20V, and a bunch in between. I picked 5V to focus on, because it is the dynamic range of the probe....so in case any massive transients showed up, we could have factored them in as "usable". Thankfully we didn't see any 5v swings from nominal offset, so our data is all good.

author: rx8pilot
author_rank: Super Contributor
timestamp: December 14, 2014, 06:42:06 pm
content: I am still here, soaking up a treasure trove of information. We have buried in software deadlines this past week.The discussion is covering so many details I will probably still be referring to a year from now - while continuing to paint a picture of what to consider when deciding on a scope. After I get it, I have tons of learning experiments based on what I learned in this discussion alone.Typing on my tablet is too slow.... To be continued....

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 06:43:55 pm
content: Quote from: TunerSandwich on December 14, 2014, 06:00:14 pmI didn’t miss it, just mis-read itQuote from: TunerSandwich on December 14, 2014, 06:00:14 pmMEAN on the scope is the sum of the sample values divided by the number of samples: it is the average value of the samples, i.e. the DC component in the measurement window, whether you add a DC offset to that does not matter, assuming you were measuring some 5V ideal reference, and you set your DC offset at 5V, it would be your average DC offset + gain errors, i.e. the DC component of your DC errors (within the measurement window of course).sDEV is the RMS level of the signal ”around” the above MEAN (if MEAN is the DC of the measured signal, then sDEV is the RMS AC voltage of the measured signal in the measurement window), this includes the pk-pk energy which in some cases is intermittent / higher frequency and in others (e.g. pure sine-wave ripple) describes all the energy ”collected” by sDEV.There is no argument (only envy) that your lab equipment correlation is amazing and the scope is much much better than the specifications in the manual.(I still believe my math is correct, but it does not really matter, as you said, as you keep saying, what matters most is traceability, although it would be interesting to hear Lecroys view on this)Thanks,Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 14, 2014, 07:28:04 pm
content: Quote from: nightmechanic on December 14, 2014, 06:43:55 pmNegative, mean is a calculated window above and below. I showed the "helper" markers in a few screenshots. I will grab another screen later focusing more on what the mean reading is. It's going to become more complicated, as sample rate (time) is changed. So obviously we both know that the mean is an average, and gains/loses resolution with sample rate.....BUT it isn't a boxcar average. It is not throwing away events, in an attempt to smooth....and gain resolution or sample more quickly and gain accuracy. Hence it isn't like a DMM....integration time correlates to horizontal scale (sort of)....but the total counts (quantization rate) is not the same. If the DMM was capturing the same data, and doing a realtime average....then we could say they are similar.i am not sure if we have a wording discrepancy here or the lecroys use of the term is misleading.I certainly would like to see a lecroy BEST case scenario for the WR64MXi. Come to think of it I would like to see those metrics in EVERY manufacturers specs

author: nightmechanic
author_rank: Contributor
timestamp: December 14, 2014, 10:41:26 pm
content: Thanks again,First of all a correction:when quoting before the DC offset accuracy for the scope (1.5%x DC offset value etc...) and the 75mV figure, I missed the fact that it is not the scope's DC offset mechanism that is used (as far as I understand it is not possible to reach such a high offset at 20mV/div), it is the AP020 (probe) that is internally generating the offset.So, the relevant spec is the offset accuracy of the probe, which I could not find online. (although I assume it is not zero - getting to that later)Regarding the MEAN function, from the scope's manual:It is not a boxcar average in the moving average sense but it is a single value (not a window) "simple" average of the time domain samples.Getting back to accuracy,Lets try another (hopefully viable) theory:Lets take the dm3068 as the "reference" and from this assumption try to figure out (curve fit) the scope's 20mv/Div DC gain error and probe's offset error with the measurements provided in teh history of this thread:DM3068scope MEANoffset (probe)26.3319mV 27.88mV 25.00mV2.99658 3.00037 2.9925.0000 5.00475 5.05.00049 5.0049 5.00420.00656 20.02997 20.0The (Excel) result is that the scope's error (vs the DM3068) is about: 0.11% x DC_offset +40uV, the largest error of this estimation vs the collected data (occurs at the 26mV data point) is 1.5mV.Just showing "my math" perspective, and again, no doubt that the scope + AP020 is a very accurate setup.Ran

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 15, 2014, 04:53:11 am
content: Quote from: nightmechanic on December 14, 2014, 10:41:26 pmHi Ran,Sorry for the late reply (under the weather today...literally).I think now we are getting somewhere, with regard to the usable accuracy of our data.There is one critical missing factor in here. I always take this into account, but obviously the Rigol specs don't (fully). Let's talk about the injected discrepancy of the probes leading to the Rigol. I take most of these readings with the input set to >10Gohm. However, let's characterize the probe/leads from the dm3068. I will work on that in a bit here, as well as show the way in which the MEAN is updated.The MEAN is a calculated vertical window....and can be a truncated, or non-truncated sampling across the horizontal timebase. The best way to do this is enter a narrow enough timebase, in which we can see individual sample points (quantization rate) and then switch to "dots" and remove the vectors applied. The next part of the equation would be to set the integration time of the DMM and scope time base to be the same (which I did for a majority of the tests). The fastest possible integration time (not that simple, but let's call it that) on the dm3068 is 100uS. So lets re-visit that. I showed that earlier on, but let's do it with less noisy signal.I am going to change over from the vREF to the Rigol signal generator. It's DC offset error is stated I believe (can't be bothered to look it up), but regardless of what the claim is, we will clearly see it across all of our "calibrated/traced" devices.....and we can extrapolate the sDEV. Again we are focusing on sDEV and not "hardline" stated specs. I am still a believer in generating our own criteria, and not wholly ignoring the datasheets....but at the same time not taking them as "gospel" (only cross section studies of one potential use case scenario).Also remember that some of the scope data, is best case/worst case. Since the parameters and signal chain have changed, throughout the represented data, we need to focus in on a more standard methodology....that doesn't change. I think we are getting way far away from OP's initial post though. Everything I have shown up to this point was done to illustrate OP's potential use case scenarios. I hardly think DC from a less than stellar sig/gen fits in to his scenario.....but maybe it does. After all this is critera for a verification methodology...which should be done, regardless of the types of systems someone works on (unless those are non critical and the user couldn't be bothered with accuracy). I do recognize that some folks just want to make LEDs blink at unpredicted rates and lumens, and there is nothing wrong with that.I don't reply to a lot of threads here, but this on had really sparked my interest, because OP used the term "professional scope purchasing criteria". I was drawn in, because I recently went through the same situation. So my apologies to the OP if this next series of posts/tests seems off topic.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 15, 2014, 06:35:54 am
content: New test system:Source is the Rigol DS2102A-S. Signal is DC with 2V offset...HighZ impedance.Signal path is Rigol BNC out, via 50ohm coax -->FFM BNC t-fitting --> Pomona BNC to banana (never bothered to measure it's impact, but it's certainly less than the probes leading to the vREF, in the last tests).Scope probe is the same AP020, but with a BNC coupler into the T-fitting.I played with some 0 DCV offset signals, and will show those.....just keep in mind that at those lower levels the impact of the test system will be greater than the discrepancy in both the dm3068 and WR64MXi. I have some fancy impedance matching cables I build, and fittings/adapters/terminators, that can help solve those problems.....but let's focus on the 1 VDC before we go there (keeps it less convoluted for now.....but the other test IS important...and we will get to it).The integration time on the DM3068 is set to 2ms (which loses resolution, but gains accuracy).The MXi timescale is set to 200uS/div. So 10 div = +/- 1mS from center = total 2mS window.I played with triggering the DM3068 from the scope, and the other way around. We can get into that a bit later....obviously the most accurate way to gain a true sample to sample offset, would be through a proper bi-directional triggering sDEV. The DM3068 can output vcomp pulses, which are triggers on the DMM integration (NOT sample) interval. So we can essentially trigger bi-directionally, to gain insight on the trigger/acquisition delay.....but that is getting pretty complicated.here are screen grabs.....also screen grabs showing the "mean" measurement parameter options. I will explain them further if needed.The second to the last picture shows the impact of the DMM BNC to Banana adapter, terminate into 50OHM.Also the last picture is showing the sDEV and statistical analysis (impact) of the DMM probes used in the previous tests, on the vREF. Remember they were the quick clips connected to the ballast/load and was the basis of the vSense loop.The total counts in the statistical study, on the DM3068 are rather low....I only ran the test for a few seconds. So the average is going to be somewhat useless....BUT the SDEV should be good enough. For example I left the terminated BNC/banana adapter on the DMM and left the statistical study running....it's up to around 100k counts now and the AVG = 365 ish nV, and is climbing....but the SDEV is right around 2.28uV, and dropping. This is pretty common as the probes polarize, or the resistor in the 50ohm terminator drifts (i should really replace those with a 2 watt low tempco resistor).

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 15, 2014, 09:01:40 am
content: ...and here is the result of a second test (same signal and signal path), with the MXi locked to the dm3068 vcomp/trigger out....I will include a waveform capture of the vcomp pulse, as it was used into channel 2 of the scope....and then channel 2 was hidden on the main test view, but the waveform was being used as channel 3s trigger. So essentially vcomp out to c2 in...trigger on c2...so that c3 measurement is time correlated to the dm3068 capture (input).I am also including a chart of the results, so you can see the deviations from baseline....the clear winner here is the mean of the mean (MXi). Remember that in 2 samplings the MXi can develop a mean of mean. So we further increase resolution AND accuracy. It beats the DC accuracy of the DM 3068.....Obviously this is using 50ohm coax, so the bandwidth is limited by the cable...VCOMP TRIGGER SIGNAL FROM 3068iF WE WANT TO GET REALLY PRECISE, WE CAN FACTOR IN THE MEASURED ERROR FROM THE BNC TO BANANA ADAPTER ON THE 3068 (i DOCCUMENTED THAT IN THE POST ABOVE THIS ONE)

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 15, 2014, 10:48:49 am
content: Here is a test of the same signal etc....BUT with the absolute tightest lock possible to the VM comp out of the dm3068. After I characterized the signal....I used it into the ext trigger input of the MXi. It does achieve tighter "lock", than the ch. input...Both devices were put on "hold/stop" simultaneously....in which case the dm3068 holds the capture, but keeps the VM comp trig out running....this assures that the MXi is still getting the trigger signal....just in case of a split second delay in the trigger line.It's not sample accurate triggering/timebase.....which is why I was saying earlier that using a separate DMM and Scope to calculate power quality is not productive. It lacks the lock of a sample accurate timebase....

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2014, 05:52:00 am
content: Quote from: robrenz on December 02, 2014, 02:21:23 amThe DC CMRR can be adjusted with the variable controls for the vertical inputs assuming your DSO has them. DSOs which implement the variable gain function after the digitizer (most or all DSOs now?) will perform much worse than an analog oscilloscope or old DSO because of quantization noise when making differential measurements.The AC CMRR can be tweaked with the probe compensation adjustments.The greater problem is the common mode input range which will severely limit sensitivity. Also some DSOs are atrociously slow when doing simple math like invert and add.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2014, 06:16:49 am
content: Quote from: nctnico on December 05, 2014, 10:23:21 amWhen using passive probes, as a sanity check I sometimes attach the probe and then attach a second identical probe to see how the signal changes so I can evaluate the loading effect of the first probe. A suitable capacitor to simulate the tip capacitance can work for this as well.Occasionally when I know it will be a problem, I just design in a little buffer to drive a probe or coaxial line.

author: David Hess
author_rank: Super Contributor
timestamp: December 20, 2014, 06:44:36 am
content: Quote from: rx8pilot on December 03, 2014, 11:34:16 pmI hate GUI implementation which simulate physical interfaces when it detracts from usability which so far has been always. Skeuomorphic interfaces were a blight when the Greeks and Romans did it (triglyphs) and they are a blight now.There might be a good oscilloscope graphical user interface but I have yet to find it. To add to the pain, the ones I have evaluated (at least the Tektronix ones) were full of bugs and the keyboard and mouse take up more workbench space.QuoteI have not seen anything like this. When I do napkin DSO and other instrument designs, I sometimes end up with a separate optional "control head" which controls the base unit though the high speed interface which would otherwise go to the PC and may or may not include a display.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 20, 2014, 09:27:59 am
content: Quote from: David Hess on December 20, 2014, 05:52:00 amThat depends on how the dithering (if any) is applied. Quantization noise can be shifted to orders of magnitude above the measurement range, with proper dither. Sony did this very effectively with DSD.., as the THD can be virtually eliminated from the "usable bandwidth".The holy grail would be to implement an A/D and pre-filter into the probe body and send direct 1 bit digital (at ludicrous sample rate) to the scope input.....a steady state would allow for almost complete reduction of the noise in the step response.....and the signal would be virtually analogous to the analog input.....I do recognize that is wholly impractical though, but a man can dreamP.S. food for thought....it is also plausible that the noise of an analog front end would be greater or equal to a digital signal, depending on the age and spec of the input amplifier.....that is a very interesting potential scenario (I am thinking a test is in order). I should build some filters and test the 2225 against the WRMXi. Not that the 2225 is some fantastically low noise scope, but it's all I have...here are some comparisons.....the 2225 is limited to 5MHz (x10 is pulled), the DS2102A is limited to 100MHz, and the WRMXi is limited to 600MHz....as you can see the rigol is "beating" the "noise" on the 2225.....but it's hard to say if that is actually true, as I am not sure how much of that noise is being eliminated with post A/D filtering/dither.....Rigol seems to be playing around with some trickery in DSP, as I highly doubt the quality/noise of the actual pre-A/D amplifier is better than the LeCroy. However I do wonder if the noise on the 2225 is because of it's inputs being "out of spec.....that is something I will have to investigate...FWIW...IF we can trust the represented waveforms on the display (measurements), I have to say Rigol has done a fantastic job in eliminating noise from the trace....as it's 20 times the bandwidth of the Tek 2225 (as it's setup).....and same from LeCroy as that is 6 times the bandwidth of the Rigol......obviously keeping in mind, that the LeCroy vertical limitation is 2mV/div, and the other two are set to 500uV/div

author: egonotto
author_rank: Super Contributor
timestamp: December 21, 2014, 09:51:31 pm
content: Hello,the Rigol and many other DSO does not show the noise at output from ADC if the input is set to ground. They shows only a useless straight line.Set the input do DC and short the input, then you see the noise.Regardsegonotto

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 22, 2014, 02:18:57 am
content: Quote from: 3roomlab on December 21, 2014, 06:23:50 pmlike I said...I think the Rigol is using some post a/d trickery to put up a false representation.....I don't wholly trust that reading. That line is only a few pixels in height.....seems fishy to me.As I said in the prior post, I highly doubt that the Rigol (below $2k new) pre- a/d amplifier could be anywhere near the noise floor of a $35k (new) WR64MXi......if so, LeCroy has some explaining to doall three units were referenced to ground

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: December 22, 2014, 02:34:56 am
content: Quote from: egonotto on December 21, 2014, 09:51:31 pmI suspected the Rigol was not trustworthy, in this regard. Mentioned it before.....I checked again with the inputs terminated (against 50ohm) and ref to DC.....This time I kept the 2225 in it's standard vertical mag....so it's 5mV/div....with a timebase of 1ms/div.....that SHOULD give us the full 50MHz bandwidthI set the other two scopes accordingly....So here is the result 2225 = 50MHz.........DS2102A-s = 100 MHz.........WR64MXi = 600MHzThe MXi obviously wasn't "nulling" the waveform, when referenced to ground

author: rx8pilot
author_rank: Super Contributor
timestamp: January 08, 2015, 11:39:22 pm
content: I was going through this thread again and appreciating the value of it even more. After TunerSandwich took the time to explain the considerations needed in scope choice, I did some reading. Lots of reading. Lots of learning.The design of SMPS circuits is a delicate symphony of analog signals adjacent to MOSETS and inductors switching huge currents VERY fast. I have been learning the basics with a 100Mhz / 1GS/s scope that simply misses all the important details. The rise time of the signals and the resulting ringing is regularly well beyond 100Mhz for a DC/DC converter operating at 750khz. The high-current switching can and will damage the various control signals and the designer must be able to see what is happening. All the calculations and simulations in the world will not tell you that the PCB layout is killing your otherwise lovely design. I am counting on a tell-all scope to slash my design time and give me much better circuits in the end.I was waiting for the Keysight announcement of the 3000T series before doing anything. In the meantime, I picked up a Tek TDS754 500Mhz/2GS/s off of eBay to get me by for a while. What is abundantly clear is that my original budget for an MSO of $5k-ish is completely ridiculous. I have decided that I need to spend $15k - $20k to get what I want out of a scope. While that is a lot of money, I feel it will pay for itself in a very short period considering that I cannot go any further without some sort of MAJOR upgrade.Although it may be a little overkill for what I do today, I have settled on a minimum of 1Ghz / 5GS/s / 4ch / MSO. I really want a good overall solution - not just what I would need to cover today's design challenges. I can only go by marketing bits and demos I have found on the internet so my view of these models is likely seen through rose colored glasses.Top models being considered:Keysight: MSOX-3000TPROS: fast updates, hardware decode, touch/mouse control, triggering seems great, Arb Gen, lowest cost of the bunchCONS: small memory, small screenKeysight: MSOX-4000PROS: fast updates, huge screen, hardware decode, touch/mouse control, triggering seems great, Arb GenCONS: small memoryLeCroy: HDO4000-MSPROS: GIANT touch screen, 12bits, looong memory, power analysisCONS: 2.5 GS/s (this conflicts with my hope of having 5 GS/s but gives 12 bit vertical resolution)Not sure if trading sample rate for bit depth is worth it on these. 2.5 GS/s seems a little slow for a 1Ghz front end.LeCroy: MXS-BStill trying to add up the benefit of these. They have very fast sampling rates and lots of memory. Trying to figure out if they are near a model change. Does anyone have any opinion on these models.LeCroy: Wavesurfer 10 with MS-500PROS: 10 GS/s, 10Mpts, 10.4" touch screen, compact sizeCONS: Not sure, nothing sticks out as marginal based on the marketing materials.

author: nctnico
author_rank: Super Contributor
timestamp: January 08, 2015, 11:52:11 pm
content: You don't consider getting a second hand high end scope? I did spot a great deal on a Keysight MSO7104A (4ch 1GHz/5Gs/s) the other day. It's already gone but if you have some time to wait I'm sure another great deal will come along.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 09, 2015, 12:03:57 am
content: It's not off the table - the Keysight eBay store has some sweet deals on great stuff. I like the new bells/whistles though.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 09, 2015, 02:47:42 pm
content: Quote from: rx8pilot on January 08, 2015, 11:39:22 pmWell, these are true 12bit scopes (not just 8bit scopes with oversampling that a certain unnamed company which recently changed its name sells as 12bit scopes).QuoteThere's only one MXs-B which is the WaveSurfer MXs-B, which is now quite old (introduced around 2009). It's basically a WaveSurver MXs with faster processing, but it still runs Windowsxp. The successor scopes are the WaveSurfer 3000 for bandwidths from 200MHz to 750MHz and with the new WaveSurfer 10 for 1GHz.The WSMXs-B is not a bad scope per se but unless the price is really good I wouldn't buy one anymore.The new WaveSurfer 10 is a modernized version of the 1GHz WaveSurfer MXs-B, with faster processing and Windows 7 Embedded instead of XP. It starts at $10k which is pretty good for such a scope:http://teledynelecroy.com/oscilloscope/oscilloscopeseries.aspx?mseries=470However, there's also still the WaveRunner 6zi:http://teledynelecroy.com/oscilloscope/oscilloscopeseries.aspx?mseries=352The WaveRunner Series is more flexible than the WaveSurfer or HDO Series, there are much more options available for the WaveRunner, and those options or standard functionality that are also available on the WaveSurfer (i.e. WaveScan, Power Analysis PWA) are more flexible/more capable on the WaveRunner than on the WaveSurfer. As with the WaveSurfer MXs-B, the WaveRunner 6zi was introduced in 2009 but it's specs are pretty much still up to date. And the pivot-able 12.1" 1280x800 WXGA screen is very nice, too.And since the WR6zi is an older model which will probably be replaced in the near future there should be very good deals available for that scope. In terms of analysis capabilities the WaveRunners are top-notch and much better than anything I've seen from Agilent/Keysight in their high-end scopes.But as always, ask the manufacturers to give you a loaner unit for testing. Nothing beats real-life test, especially not when you're about to spend that much money.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 09, 2015, 08:19:51 pm
content: Did you work for LeCroy???The question with the 12bits is this: Does 12bit vertical offer a significant practical advantage? Does sacrificing the sample rate negate the 12bit benefit? To me, it seems like a gain in vertical while significantly sacrificing the horizontal. 2.5 GS/s seems like absolute minimum for a 1Ghz front end.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 09, 2015, 08:31:15 pm
content: Quote from: rx8pilot on January 09, 2015, 08:19:51 pmNo, I'm not affiliated with any T&M manufacturer. I'm just a user of LeCroy high end scopes scopes (sometimes, most of the times I use Agilent high end scopes scopes, though). And I tend to keep myself familiar with the highend scope offerings of the important vendors.QuoteIt depends on what you want to do. 2.5GSa/s isn't that bad for 1GHz bw, and unless your signals are close to the upper bw limit then I#d go out on a limb and say that 2.5GSa/s should be sufficient.But as I said, don't just rely on advice and specs, get some demo scopes and test them for what you need in your own setting.

author: DJ
author_rank: Unknown
timestamp: January 10, 2015, 12:30:08 am
content: What I would really like would be a kickbutt 2channel 2-4GHz scope without all the bells and whistles.Just the front end box, with knobs for coupling, trigger, vert & horiz. Have it drive a tablet or LCD monitor directly.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: January 10, 2015, 05:15:13 am
content: Quote from: rx8pilot on January 08, 2015, 11:39:22 pmI had a feeling you would come around to this conclusion eventually. It's why I posted all the data and scenarios.Since we work on the same systems, let me offer up a suggestion. This is an ideal scenario, with an "unlimited budget". HDO8000 from LeCroy.If that kind of price isn't possible....then have a look at the 104MXi or MXiA.....you can score one used for roughly your projected budget....HOWEVER, let me interject another critically important insight.You NEED some in house standards. I.E. some references that allow you to verify equipment accuracy, before making critical measurements. I personally build all of my standards, and reference them against a known calibrated transfer standard. This is as important, if not more, than any amount of bandwidth or features you may think you need.The other consideration in the scope is going to be memory depth. Remember that a minimum time window, to gather proper spectral results, is going to be greater than 1ms. You are going to need a lot of memory to maintain the proper sample rate across that time division (otherwise it defeats the purpose of the bandwidth and bit depth).I HIGHLY recommend going with LeCroy. Their statistical functionality and interface are head and shoulders above anything I have ever used or owned (i have had some of the fancy agilents you are considering). Also the LeCroy triggering is unparalleled in these top tier models.I hate to sound like a fanboi here, but I have been through this all before...and took a leap of faith (recently) on a LeCroy midrange scope.....I wouldn't even consider going back to anything from agilent or tek....and I am damn picky about this kind of stuff.I wouldn't hold my breath on keysight, or any other company, catching up with the LeCroy philosophy, anytime soon. That isn't saying that LeCroy makes the "best" scopes or that all agilent units are inferior etc.....they simply have different approaches, and cater to different specialties....and LeCroy happens to cater to OUR needs (you and I) above and beyond any other manufacturer....P.S. I sent you a reply to your PM a while back, but am not sure if it went through, as I never heard back from you....let me know (via PM) if you are still needing help, outside of the forum...P.P.S we should really discuss references and standards, as they are going to become a VERY important part of your on-going discovery...and they are an art-form all to themselves. Removing AC coupled line noise from the measurements is going to be HIGHLY critical, and you can do that with some proper stabilized standards. You can then generate a mask (this is why LeCroy leads the way for us) to remove the measured AC/line components from your critical switching measurements. This is really where my experience has taught me that your measurements are key factors in determining potential problems in an SMPS. ESPECIALLY when dealing with DC-DC conversion....P.P.P.Sanother critical factor you need to look at, is the total dynamic range of your front end solutions (probes, i/o amplifiers etc).....this is equally important, as any other factor you might consider....you can't trust measurements that are clipping

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2015, 06:09:37 am
content: Quote from: TunerSandwich on December 22, 2014, 02:34:56 amBeware comparing analog and digital scopes for noise, it's not apples vs apples.

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2015, 06:18:42 am
content: Quote from: rx8pilot on January 08, 2015, 11:39:22 pmDon't forget the refurbished Keysight store:http://stores.ebay.com/keysightYou can get a 2GHz 9000 series on there for $12Khttp://www.ebay.com/itm/Keysight-DSO9204H-High-Definition-Oscilloscope-2-GHz-Agilent-DSO9204H-/181559422822?pt=BI_Oscilloscopes&hash=item2a45c8ef66Or lesser 1GHz one for less than $8Khttp://www.ebay.com/itm/Keysight-DSO9104H-High-Definition-Oscilloscope-1-GHz-Agilent-DSO9104H-/191454554954?pt=BI_Oscilloscopes&hash=item2c9394ab4aUp to 12 bit vertical res and low noise!And 11 bits at 1 GHz is pretty darn good. Sound like exactly want you want for under $8KHow much is competing 12bit Lecroy HDO?Or the 4CH 1GHz MSO3000A series with arb is only $8Khttp://www.ebay.com/itm/Keysight-Premium-Used-MSOX3104A-Oscilloscope-1-GHz-Agilent-MSOX3104A-/181616054054?pt=BI_Oscilloscopes&hash=item2a49290f26

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: January 10, 2015, 06:30:03 am
content: Quote from: EEVblog on January 10, 2015, 06:09:37 amAlthough I wholly agree, it's not apple to apples, it is still a sanity check...in regards to the "trustworthiness" of what we see on a screen. I may have "under-emphasized" the nuances involved in comparing (DSP, aliasing, pre/post filtering etc).I DO find a great deal of validity in making a comparison, on a "simplified" level....because a lot of posts here are mentioning that they "trust" what they see on their oscilloscope screens. I was trying to emphasize that those assumptions should not be made.The biggest problem we are facing (which I mentioned), is that most manufacturers don't state what level or type of dithering is used to remove noise in the quantization step response.However, at the end of the day, I fear that a lot of folks are bypassing these points and trusting manufacturer "specs" as holly gospel....and that if YOUR specific scenario somehow deviates from those specs, that something is "wrong". It's simply not true. A proper measurement should be qualified against a known standard and that should be the basis of your uncertainty (SDEV), NOT some random spec., quoted on XYZ datasheet.I have a sneaking suspicion (always have) that Rigol is removing noise components, post a/d, with dithering....I simply don't trust that Rigol can produce a low noise front end (pre a/d) that can compete with a $30k scopes analog input section. Not for under $2k. So how trustworthy is the Rigol measurement, below 1mV/div.....? Who the hell knows....I haven't taken the time to verify it against a known standard, as we get into some serious probing issues at 500uV/div. Also the offset in the DS2000A is all over the place, when compared against my in-house standards. Although I can't confirm the drift, and therefor can't confirm the accuracy of the SDEV/mean measurements in the Rigol unit I have, I DO trust the LeCroy MXi, as the measurements I did earlier in this thread shows a more linear SDEV across all standards.P.S. I think the point was missed....I was trying to show that the noise on an analog scope input is NOT necessarily lower than that of a DSO/MSO. That was why I included the theoretical bandwidth figures. 2mV pk-pk @ 600MHz (MXi) is damn impressive IMO, and simply outclasses the Tek 2225 @ 50MHz (and likewise the Rigol @ 100 MHz).I did this comparison BECAUSE, someone here claimed that "analog scopes have lower noise"....and by that token I also have to assume "better" linearity....and I was trying to show that is simply not true. I hope the tests I provided reflect this.

author: DJ
author_rank: Unknown
timestamp: January 10, 2015, 06:40:25 am
content: "I personally build all of my standards, and reference them against a known calibrated transfer standard."Can you share some standards you have put together for those who might like to try their hand at it?

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: January 10, 2015, 06:47:58 am
content: Quote from: DJ on January 10, 2015, 06:40:25 amWhat kind of standard? Voltage? AC/DC? Impedance? Null? CC? Theoretical range etc....I can use the "standard" I built for this specific thread (the MAX6350) to emphasize some points. Remember I built it with a specific "error" in it's stability, to illustrate the problem of resonant tanks, and how you need bandwidth to discover these problems...in relation to DC-DC SMPS/POLI have two discreet nodes on that standard. One is a ballasted direct output, and the other is a low pass filtered output. The standard nodes also employ a variety of capacitance scenarios, which illustrate potential issues in stability (remember the MAX6350 excels at driving capacitive loads). Also it's construction is 100% point to point, as I wanted to illustrate these resonant tank issues, without bringing a PCB substrate into the equation. If I wanted to quantify the PCB interactions, I would need to measure past the 1GHz mark, and that is going to bring up a whole other set of issues. Primarily the effects of available probing solutions.P.S. we should start by discussing artifact based standards (PWM) vs your more traditional "linear" standards. One might confuse a "linear" standard with being more "linear"....which is not at all the case. PWM based "artifact" standardizations can be much more linear, free of noise and relevant to calibrating "digital" equipment.....especially DC on a DVMAnother relevant standard for designing multi-phase SMPS would be a +/- voltage standard....which can be very useful for characterizing op-amp performance. In a highly critical, multi phase architecture one might be forced to hand select (bin) precision op-amps. You could consider this a "null" standard, but it's a bit more specific than that. "Nulling" op-amps with the comp pins isn't necessarily useful....if your measurement standards can't resolve the TRUE offset. 2 discreet DVM is hardly a good way of doing this....so we need a null RMS measurement, and to acquire that we need a known "null" reference.....I think the problem of a true "null" standard is often overlooked in production designs.....however if you do some reading into metrology grade devices, you will quickly discover how important null readings can be, in defining baselines.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 10:47:22 am
content: Quote from: EEVblog on January 10, 2015, 06:18:42 amWow. $12k and only 30 days warranty? That's not a lot of trust they're putting in their product, and when spending that much money I'd want my purchase underpinned by a bit more assurance that at least for a while the investment will be a good one.QuoteAgain with just 30 days warranty.QuoteThe 1GHz HDO4k is roughly $17k but then it's a true 12bit scope (not 8bit oversampled like these Agilent's) and it's brand new not used (these are not even remanufactured units) and comes with 3yrs warranty.QuoteNot a bad deal if you primarily need a MSO but as a 1GHz scope I'm not sure if $8k for a refurbished 1GHz MSOX3k (which is rather simple scope) with 2Mpts (4Mpts optional) is that great of a bargain when a brand new WaveSurfer 10 (1GHz 10Mpts, MSO-capable) costs only $2k more (and gives you a much more advanced scope).

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2015, 11:18:21 am
content: Quote from: Wuerstchenhund on January 10, 2015, 10:47:22 amBut what are you paying? something like half the price?Fair compromise I think if you want performance on a budget.QuoteAgain, double the price, your call.But you aren't the OP, he may have an entirely different opinion. Indeed he seems to be constrained by price, and is considering the MDO3000T, so the "almost" 12bit performance of the 9000 is likely good enough.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: January 10, 2015, 11:38:56 am
content: Quote from: Wuerstchenhund on January 10, 2015, 10:47:22 amI was recently offered the same scope, fully loaded (all licenses) for $3500....with all original boxes, documentation, software and accessories.I don't think the 30 day warranty period is worth $4.5kI also think a used MXi (MX, MXiA etc) simply decimates the Agilent, for the same money (used).If the HDO4k is only a few grand more, BNIB with full manufacturer warranty and support....hmmmm.....although the HDO4k might not have the memory depth that OP needs.The Keysight/Agilent refurb stuff is a good price point for used Agilent, however I am not sure that means it's the best value for dollars spent. Agilent/HP/Keysight/etc.. has always been a bit "overvalued" IMO. However nothing like Tek (snickers).....

author: tautech
author_rank: Super Contributor
timestamp: January 10, 2015, 11:54:30 am
content: Quote from: Wuerstchenhund on January 10, 2015, 10:47:22 amI'd be very concerned if that was the best warranty offered and for that reason alone I would give it a wide berth.Hell if I can offer the remaining factory warranty on an 1 year old Siglent demo unit so should Agilent.And chuck in new probes to boot.Piss poor IMO

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 11:58:41 am
content: Quote from: EEVblog on January 10, 2015, 11:18:21 amIs it really? That's alot of money and I'd say in any terms accounts as a serious investment. 30 days means that in the worst case you're out of money and left with non-working kit after a month.If your fine with 30 days lifetime then you could save a whole lot of money by just renting the kit you need.This aside, I can buy some used later-model (i.e. 2004 vintage and later) LeCroy scope from anyone and anywhere (you, me, ebay, the trunk of a car at a lonely car park at night, garage sale, Craig's List, pawn shop, whatever), send it in to LeCroy for calibration, and as long as it passes and the original factory seal is still in place I can buy full manufacturer warranty for that scope for one, two or three years, sometimes (depending on the model) even more. That's how confident they are in the stuff they produce.And Agilent/Keysight can't even provide a simple year of warranty for a pretty young scope they claim has been checked by them and which is sold through their official store? That's ridiculous.30 days is what I usually get when buying 2nd hand kit from private sellers on ebay.QuoteOf course I'm not the OP, and the oversampled 8bit scope may well be good enough, but especially on a tight budget there are other criteria than just technical specs. In regard to these used Agilent scopes, I'm sure the OP wouldn't feel confident to pay for a potentially very expensive repair say 2 months after splashing out $8k or more.And as to list prices, only the lazy ones pay them. I'm pretty sure LeCroy would give him the HDO4104 for a lot less, and even might throw in some of the options ne wants. Keysight does so, too, especially on new scopes (and sometimes even on their CertiPrime remanufactured scopes). Just Tek seems to sit a bit tight on their arses.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 12:15:28 pm
content: Quote from: TunerSandwich on January 10, 2015, 11:38:56 amIf it was from the same seller we got our LeCroy scopes from then it would have come with 30 days as well

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2015, 12:21:30 pm
content: Look at it this way: if you pay less then half the 'new' price you can buy two and still save money.In my experience with used equipment the age is a very important factor. The older a piece of equipment is the bigger the chance of serious problems.

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2015, 12:25:39 pm
content: Quote from: Wuerstchenhund on January 10, 2015, 11:58:41 amOh come on, be reailistic, you know very well the odds of a (proven working "burned in" so the speak demo) Agilent/Keysight scope failing within a few months is not far off zero.And if it's half price of a new one, it's actually not a bad calculated risk. i.e if the used one does fail after the 3 months and before the 3 years you would have got on a new one, then you can buy another one and have not paid any more than a new one.And of course the odds of a 2nd one failing in the same way are lower again.In fact you would be ahead even if it did fail because the failed unit is actually worth something on ebay to someone, or perhaps you could get it repaired for once again a lot less than a new one would have cost.But odds are very high indeed that it will be fine and you are going to save half your money.Fear of lack of warranty often clouds people's opinion of the real economics and statistics of the matter.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 12:42:15 pm
content: Quote from: EEVblog on January 10, 2015, 12:25:39 pmMost of the enivironments I work use Agilent (heck, very few use LeCroy), and while it doesn't happen very often it's not unheard of that young kit gives up. I myself had a 9 months old DSO 90604A dying on me during work. The overall failure rate is still low, but certainly not close to zero.And quite frankly, if the failure quote would be as close to zero as you say, then why doesn't have Agilent/Keysight more confidence in their product and offer more than a measly 30 days of warranty?QuoteSo what if the first one fails after 3 months, and the second after four (I've actually seen that happening)? It means in less than a year you spend roughly 2x 50% of the new price and are still left with non-working kit. That's playing the lottery.This aside, you forgot the whole software option issue. Once you bought options for one scope you can't just transfer them to the 2nd one if the first one fails. That means you'd have to buy a 2nd set of options, which makes the whole thing even less attractive.What you describe can make sense for a hobbyist (although I still can't see why he couldn't just buy the same scope somewhere else for cheaper). But for a professional setting I would want to be able to rely on my kit and the support behind it. Having to deal with broken kit is already a hassle, and because it means I spend the time on dealing with the issue I can't spend that time on making money it's also causing some loss. Warranty and support are there to minimize the impact of such occurrences.But that's just me, and of course I appreciate YMMV.QuoteStatistics is fine unless you're finding yourself inside that low probability figure, which can happen sooner than expected. Don't forget that statistics is a calculation following a standardized mathmatical model and is based on certain defined parameters. It's no way a gurantee that your real-life situation will follow that model.Playing lottery by buying unwarranted/low-warranty kit in the hope it will survive for a certain period is bonkers in a commercial setting. In most cases the more sensible thing is to buy supported/warranted kit and if that fails just get a loaner (either from the manufacturer, which is pretty common for high end scopes, or from a rental provider) and continue working.'Real economics' is taking all subsequent costs into account, which is much more than the initial purchase price (which often turns out to be peanuts anyways).

author: EEVblog
author_rank: Unknown
timestamp: January 10, 2015, 01:15:26 pm
content: Quote from: Wuerstchenhund on January 10, 2015, 12:42:15 pmYep, and I'm not going to bother arguing the point furher. If I want to see people argue the worst case scenario I'll go watch Doomsday Preppers, far more entertaining

author: nctnico
author_rank: Super Contributor
timestamp: January 10, 2015, 01:21:46 pm
content: IMHO there is always a chance an oscilloscope breaks whether it has been bought new or used. And how about sending it away for calibration? As a rule I always have 2 good scopes at minimum just in case.

author: TunerSandwich
author_rank: Frequent Contributor
timestamp: January 10, 2015, 01:30:25 pm
content: The Agilent/Keysight prices that really impressed me...were on the refurb 7000 and 9000 series......those were far better values than the 2000-4000 refurbs....if OP is willing to spend $15-$20k he can really get some huge percentages knocked off "high end" Agilent refurbs (with bargaining on licenses I am sure).Still, if I was even considering that price range, I would have to look at an HDO4000.....and if I was looking to spend brand new 9000 series money I would much rather have the HDO8000....Again the right scope really depends on the specific needs....it's hard to say this one or that one is "better", but you can say that memory depth, sample rate and total bandwidth have some per-requisite values....and if OP is looking in the $15k range, then just about anything is going to meet those minimums, and the rest will be based on Ui, unique features, support etc...

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 02:51:46 pm
content: Quote from: nctnico on January 10, 2015, 01:21:46 pmOf course. The difference is however who pays the bill for getting the scope back to working condition.QuoteThat's a good way as long as the scopes are relatively inexpensive. There's not much wrong with stocking a second low end scope (or a cheap 2nd hand scope) in case the main scope breaks.It's a bit different if the equipment is more expensive, though. If you need a high performance scope (maybe with even some of the software options) then stocking a second scope simply isn't sensible. A cheap scope can't replace your high end scope that's away for calibration, so you'd have to buy another high end scope which means investing a lot of money in what's essentially dead capital, and since your replacement will need calibration, too, it's even costing you money by just sitting there. In such cases it's just more economical to get a loaner for the time the main scope is absent.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 10, 2015, 03:57:47 pm
content: Apart from performance and needs, don't overlook the user interface. Those differ remarkably and you have to be comfortable with it. It's quite personal. I remember one of the first high performance Le Croy's where I had to dig 3 levels down through menus just to change the trigger edge. For general tasks and settings the user interface needs to be quick and intuitive. Some UI designers imho seem to have no idea what the actual use of the thing is.

author: rx8pilot
author_rank: Super Contributor
timestamp: January 10, 2015, 05:52:57 pm
content: Quote from: Wuerstchenhund on January 10, 2015, 11:58:41 amWhile I may feel better with a longer warranty, the 30 days on a refurb does not worry me too much. Of course its possible that it will break, but its not likely and I would have saved enough to justify it. I have spent $millions on industrial equipment over my career and have learned that the top manufacturers get to the top with reliability. Down time is expensive and all the big boys know it. Most of the problems will probably be buttons, connections, etc. that are easy to fix in-house anyway. Not saying that Agilent wins because they have a good eBay store, just saying I would not worry too much if the price outweighed the risk.Quote from: Pjotr on January 10, 2015, 03:57:47 pmThis is a CRITICAL consideration for sure and impossible to really know until a demo period like Wuerstchenhund has pointed out a few times. Little details of the interface can add up to a LOT of time over the life of the instrument. When spending this much, its to save time. I could muddle through with much less - buying used with a separate USB LA etc. The newer instruments are targeted toward solving problems faster and faster which is obviously more than BW and sample rate. To properly focus on my circuit design, the entire test and measurement system has to be second nature and nearly transparent. I have worked in the high-end of the entertainment industry for decades and the top equipment is a great example of how this works. In general, the people pushing buttons in the entertainment world - editors, FOH engineers, colorists.....are all much closer to artists than engineers. With that said, they have to interface and manipulate VERY sophisticted systems intuitively to get a good result. I like science and engineering, but do not want my scope to require those skills since those brain cells should be 99% focused on the new circuit sitting on my bench.In my business, I sell time. The cost of the PCBs is tiny compared to the cost to develop it and all the mechanics that support it. I also split my time between electronics and mechanics so always short on time. Anything that speeds me up, even a little, is worth a lot of money.So far, I have not looked at anything over $20k becuase it seemed like I was getting to the point of diminishing returns. 4Ghz BW won't speed me up. Keep in mind, I am not focused on the price as a limitation. I am trying to put a price range on the purchase to limit how many options I need to evaluate. In the end, I want something I put on the bench that gives me believable answers to as many questions as possible with as little effort as possible. I fully understand and appreciate the cross-check techniques presented by TunerSandwich, but those principles apply to any scope I choose. Ease of daily use is very important to me for sure. TunerSandwich has a finger on the needs I have because he does similar work (albeit a few years ahead of me). It;s about time to start making a move to do demos.

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 10, 2015, 08:04:15 pm
content: Quote from: Pjotr on January 10, 2015, 03:57:47 pmThat must have been a really very long time ago as even the old 9300 Series from 1994 had a "trigger" button (which brings you directly into the trigger menu), as did subsequent scopes. In fact, I'm pretty sure even the old 9400 and 7200 scopes had such buttons, and those were from the 80's.

author: Pjotr
author_rank: Frequent Contributor
timestamp: January 10, 2015, 08:28:21 pm
content: Oh yes, theyhada trigger buttonAs well as they where out for service half the time because of a broken CRT/PSU. B.t.w. I am talking about the early/mid 90's.

author: coppice
author_rank: Super Contributor
timestamp: January 11, 2015, 03:17:19 pm
content: Quote from: Wuerstchenhund on January 10, 2015, 10:47:22 amHalf price with 30 days warranty doesn't sound too bad compared to the full price with 90 days warranty they used to give on brand new equipment, not so many years ago. Warranty is just a part of the price. You can buy warranties, as a risk spreader. A lot of people suppyling refurbished equipment offer the option to pay more for more warranty. If you are a big Agilent user, and do all your own recal and repairs, they used to allow you buy new equipment at a lower price without any warranty, beyond faults found on arrival. I don't know if that's still the case.Can you negotiate a heavy discount on those refurbished prices, as you usually can with the new ones?

author: Wuerstchenhund
author_rank: Super Contributor
timestamp: January 11, 2015, 06:33:57 pm
content: Quote from: coppice on January 11, 2015, 03:17:19 pmMaybe in the US, but in Europe all Agilent equipment bought through regular channels came with at least a year of warranty, if not three.QuoteThat's fine, but the question remains why they don't give more than 30 days in the first place?QuoteYes, but these are individual/special contracts for equipment that's not for re-sale.

author: coppice
author_rank: Super Contributor
timestamp: January 11, 2015, 08:36:14 pm
content: Quote from: Wuerstchenhund on January 11, 2015, 06:33:57 pmActually, that might be true while they were called Agilent. I can't remember when the warranties changed. As Hewlett Packard, through the 70s and 80s, and I think into the 90s, their standard warranty was 90 days in both Europe and America, when you bought directly from them. They also priced their machines in dollars in Europe, which was a huge pain when getting capital purchase approval in some large companies. You could get a quote valid for 90 days, and use that to get approval. However, if the exchange rate adversely changed before approval was given, the approved amount wouldn't buy the kit, and you had more delays going through the process again.

author: nctnico
author_rank: Super Contributor
timestamp: January 16, 2015, 08:39:18 am
content: If the time is limited you could use temporary/trial licenses.

author: EMSpecTrum
author_rank: Newbie
timestamp: March 11, 2015, 03:53:14 pm
content: I only recently came across this topic thread and found it quite informative.I still have some questions concerning parameterizing performance for a reasonable research/development environment. My experience base is a near mirror of the OP albeit more on remote sensing applications and most of my work is done in the conceptual/math domain.TunerSandwich previously posted:Quote from: TunerSandwich on December 07, 2014, 12:41:45 amWhat I was hoping to understand better is the cost breakdown of the $30K for the various components mentioned in the development environment along with the specific performance parameter TunerSandwich associates with the qualitative descriptors chosen to describe the components (e.g., "good", "proper", "decent", etc.). Maybe some make/model examples...I think this would help many of us pro-thusiasts seeking to migrate from hobby to business. Thanks in advance!

author: don
author_rank: Regular Contributor
timestamp: March 11, 2015, 04:41:17 pm
content: Quote from: EMSpecTrum on March 11, 2015, 03:53:14 pmRemember the $30k was for a lab tunersandwich would like. There are many, many, many flavors of labs depending on what your product is - so there are many "correct" answers and all very different. What product are you working on?

author: EMSpecTrum
author_rank: Newbie
timestamp: March 11, 2015, 05:36:45 pm
content: Understand the "it depends" aspect. My application area is best characterized as signal processing of sensor(s). Types of sensors range from seismo-acoustic thru optical (UV)...both active and passive type sensing. Most of it is research related in multi-modal sensing with some communications for cooperative sensing application. While primarily I deal on the physics side (a lot of math modeling), I'm looking to develop the capability to do some proof of concept experimentation...more research, less end product related. From an electronics standpoint, much of what TunerSandwich discussed is applicable. What I was looking for in the answer was more a reference point (based on his application domain) from which to judge where my specific needs may vary. That way I could ask more pointed questions.